全文获取类型
收费全文 | 13747篇 |
免费 | 168篇 |
国内免费 | 51篇 |
专业分类
化学 | 8795篇 |
晶体学 | 162篇 |
力学 | 336篇 |
综合类 | 5篇 |
数学 | 1777篇 |
物理学 | 2891篇 |
出版年
2024年 | 63篇 |
2023年 | 135篇 |
2022年 | 364篇 |
2021年 | 433篇 |
2020年 | 395篇 |
2019年 | 412篇 |
2018年 | 328篇 |
2017年 | 247篇 |
2016年 | 517篇 |
2015年 | 434篇 |
2014年 | 537篇 |
2013年 | 846篇 |
2012年 | 878篇 |
2011年 | 1041篇 |
2010年 | 659篇 |
2009年 | 639篇 |
2008年 | 814篇 |
2007年 | 767篇 |
2006年 | 622篇 |
2005年 | 537篇 |
2004年 | 489篇 |
2003年 | 380篇 |
2002年 | 361篇 |
2001年 | 226篇 |
2000年 | 192篇 |
1999年 | 148篇 |
1998年 | 116篇 |
1997年 | 118篇 |
1996年 | 110篇 |
1995年 | 85篇 |
1994年 | 102篇 |
1993年 | 93篇 |
1992年 | 96篇 |
1991年 | 56篇 |
1990年 | 49篇 |
1989年 | 37篇 |
1988年 | 38篇 |
1987年 | 40篇 |
1986年 | 41篇 |
1985年 | 46篇 |
1984年 | 54篇 |
1983年 | 56篇 |
1982年 | 37篇 |
1981年 | 49篇 |
1980年 | 28篇 |
1979年 | 40篇 |
1978年 | 33篇 |
1977年 | 21篇 |
1974年 | 19篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
861.
Francesco Saracino Joo Brinco Diana Gago Marco Gomes da Silva Ricardo Boavida Ferreira Jorge Ricardo-da-Silva Ricardo Chagas Luísa Maria Ferreira 《Molecules (Basel, Switzerland)》2021,26(20)
Protein haze in white wine is one of the most common non-microbial defects of commercial wines, with bentonite being the main solution utilized by the winemaking industry to tackle this problem. Bentonite presents some serious disadvantages, and several alternatives have been proposed. Here, an alternative based on a new cellulose derivative (dicarboxymethyl cellulose, DCMC) is proposed. To determine the efficiency of DCMC as a bentonite alternative, three monovarietal wines were characterized, and their protein instability and content determined by a heat stability test (HST) and the Bradford method, respectively. The wines were treated with DCMC to achieve stable wines, as shown by the HST, and the efficacy of the treatments was assessed by determining, before and after treatment, the wine content in protein, phenolic compounds, sodium, calcium, and volatile organic compounds (VOCs) as well as the wine pH. DCMC applied at dosages such as those commonly employed for bentonite was able to reduce the protein content in all tested wines and to stabilize all but the Moscatel de Setúbal varietal wine. In general, DCMC was shown to induce lower changes in the wine pH and phenolic content than bentonite, reducing the wine calcium content. Regarding which VOCs are concerned, DCMC produced a general impact similar to that of bentonite, with differences depending on wine variety. The results obtained suggest that DCMC can be a sustainable alternative to bentonite in protein white wine stabilization. 相似文献
862.
Joo A. Baptista Mrio T. S. Rosado Ricardo A. E. Castro Antnio O. L. vora Teresa M. R. Maria Manuela Ramos Silva Joo Canotilho M. Ermelinda S. Eusbio 《Molecules (Basel, Switzerland)》2021,26(21)
In this work, co-crystal screening was carried out for two important dihydrofolate reductase (DHFR) inhibitors, trimethoprim (TMP) and pyrimethamine (PMA), and for 2,4-diaminopyrimidine (DAP), which is the pharmacophore of these active pharmaceutical ingredients (API). The isomeric pyridinecarboxamides and two xanthines, theophylline (THEO) and caffeine (CAF), were used as co-formers in the same experimental conditions, in order to evaluate the potential for the pharmacophore to be used as a guide in the screening process. In silico co-crystal screening was carried out using BIOVIA COSMOquick and experimental screening was performed by mechanochemistry and supported by (solid + liquid) binary phase diagrams, infrared spectroscopy (FTIR) and X-ray powder diffraction (XRPD). The in silico prediction of low propensities for DAP, TMP and PMA to co-crystallize with pyridinecarboxamides was confirmed: a successful outcome was only observed for DAP + nicotinamide. Successful synthesis of multicomponent solid forms was achieved for all three target molecules with theophylline, with DAP co-crystals revealing a greater variety of stoichiometries. The crystalline structures of a (1:2) TMP:THEO co-crystal and of a (1:2:1) DAP:THEO:ethyl acetate solvate were solved. This work demonstrated the possible use of the pharmacophore of DHFR inhibitors as a guide for co-crystal screening, recognizing some similar trends in the outcome of association in the solid state and in the molecular aggregation in the co-crystals, characterized by the same supramolecular synthons. 相似文献
863.
Viet Hung Dao Isabelle Ourliac-Garnier Cdric Log Florence O. McCarthy Stphane Bach Teresinha Gonalves da Silva Caroline Denevault-Sabourin Jrme Thifaine Blandine Baratte Thomas Robert Fabrice Gouilleux Marie Brachet-Botineau Marc-Antoine Bazin Pascal Marchand 《Molecules (Basel, Switzerland)》2021,26(21)
Pim kinases (proviral integration site for Moloney murine leukemia virus kinases) are overexpressed in various types of hematological malignancies and solid carcinomas, and promote cell proliferation and survival. Thus, Pim kinases are validated as targets for antitumor therapy. In this context, our combined efforts in natural product-inspired library generation and screening furnished very promising dibenzo[b,d]furan derivatives derived from cercosporamide. Among them, lead compound 44 was highlighted as a potent Pim-1/2 kinases inhibitor with an additional nanomolar IC50 value against CLK1 (cdc2-like kinases 1) and displayed a low micromolar anticancer potency towards the MV4-11 (AML) cell line, expressing high endogenous levels of Pim-1/2 kinases. The design, synthesis, structure–activity relationship, and docking studies are reported herein and supported by enzyme, cellular assays, and Galleria mellonella larvae testing for acute toxicity. 相似文献
864.
Ariadna Berenice Trejo-Raya Víctor Manuel Rodríguez-Romero Silvia Bautista-Baos Francisco Roberto Quiroz-Figueroa Ramn Villanueva-Arce Enrique Durn-Pramo 《Molecules (Basel, Switzerland)》2021,26(21)
A biofungicide is a natural product that can be derived from various sources such as, among others, microorganisms, higher plants, animal products, phytochemicals, semiochemicals, and antagonist microorganisms. One of the most important approaches for the production of biofungicides is the combination of biocontrol agents. This study showed the inhibition growth of Alternaria alternata and Fusarium solani treated with cell-free extracts of P. fluorescens. Using thin-layer chromatography and plate assays it was also demonstrated that the cell-free extracts of P. fluorescens contained siderophores and derivates of 4-diacetylphloroglucinol and phenazine. Moreover, the combination of cell-free extracts of P. fluorescens and chitosan [50–1.5% (v/v)] had a synergistic effect since they notably inhibited the mycelial growth of A. altenata and F. solani. Various morphological alterations to the mycelia and conidia of the treated fungi as a result of this combination were also observed. The present study could be a starting point to control other fungal phytopathogens using different cell-free extracts and chitosan as biocontrol agents. 相似文献
865.
Joo Victor Batista da Silva Carlos Augusto Fernandes de Oliveira Leandra Nira Zambelli Ramalho 《Molecules (Basel, Switzerland)》2021,26(23)
Aflatoxins are mycotoxins produced as secondary fungal metabolites. Among them, aflatoxin B1 (AFB1) stands out due to its genotoxic and mutagenic potential, being a potent initiator of carcinogenesis. In this review, the outcomes from the published literature in the past 10 years on the effects of AFB1 pathophysiological mechanisms on embryological and fetal development are discussed. In several animal species, including humans, AFB1 has a teratogenic effect, resulting in bone malformations, visceral anomalies, lesions in several organs, and behavioral and reproductive changes, in addition to low birth weight. The mutagenic capacity of AFB1 in prenatal life is greater than in adults, indicating that when exposure occurs in the womb, the risk of the development of neoplasms is higher. Studies conducted in humans indicate that the exposure to this mycotoxin during pregnancy is associated with low birth weight, decreased head circumference, and DNA hypermethylation. However, as the actual impacts on humans are still unclear, the importance of this issue cannot be overemphasized and studies on the matter are essential. 相似文献
866.
Jos B. de Araújo-Neto Maria M. C. da Silva Cícera D. de M. Oliveira-Tintino Iêda M. Begnini Ricardo A. Rebelo Luiz E. da Silva Sandro L. Mireski Michele C. Nasato Maria I. L. Krautler Jaime Ribeiro-Filho Abolghasem Siyadatpanah Polrat Wilairatana Henrique D. M. Coutinho Saulo R. Tintino 《Molecules (Basel, Switzerland)》2021,26(23)
The search for new antibacterial agents has become urgent due to the exponential growth of bacterial resistance to antibiotics. Nitrogen-containing heterocycles such as 1,8-naphthyridine derivatives have been shown to have excellent antimicrobial properties. Therefore, the purpose of this study was to evaluate the antibacterial and antibiotic-modulating activities of 1,8-naphthyridine derivatives against multi-resistant bacterial strains. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of the following compounds: 7-acetamido-1,8-naphthyridin-4(1H)-one and 3-trifluoromethyl-N-(5-chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide. The antibiotic-modulating activity was analyzed using subinhibitory concentrations (MIC/8) of these compounds in combination with norfloxacin, ofloxacin, and lomefloxacin. Multi-resistant strains of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were used in both tests. Although the compounds had no direct antibacterial activity (MIC ≥ 1.024 µg/mL), they could decrease the MIC of these fluoroquinolones, indicating synergism was obtained from the association of the compounds. These results suggest the existence of a structure–activity relationship in this group of compounds with regard to the modulation of antibiotic activity. Therefore, we conclude that 1,8-naphthyridine derivatives potentiate the activity of fluoroquinolone antibiotics against multi-resistant bacterial strains, and thereby interesting candidates for the development of drugs against bacterial infections caused by multidrug resistant strains. 相似文献
867.
Machining is very common in industry, e.g. automotive industry and aerospace industry, which is a nonlinear dynamic problem including large deformations, large strain, large strain rates and high temperatures, that implies some difficulties for numerical methods such as Finite element method. One way to simulate such kind of problems is the Particle Finite Element Method (PFEM) which combines the advantages of continuum mechanics and discrete modeling techniques. In this work we introduce an improved PFEM called the Adaptive Particle Finite Element Method (A‐PFEM). The A‐PFEM introduces particles and removes wrong elements along the numerical simulation to improve accuracy, precision, decrease computing time and resolve the phenomena that take place in machining in multiple scales. At the end of this paper, some examples are present to show the performance of the A‐PFEM. 相似文献
868.
Estefania Estalayo Julene Aramendia Ludovic Bellot-Gurlet Laura Garcia Iñaki Garcia-Camino Juan Manuel Madariaga 《Journal of Raman spectroscopy : JRS》2021,52(1):230-240
Cultural heritage often brings to mind elements like sculptures, paintings, monuments, and buildings as well as archeological objects. Today, underwater heritage and its surrounding environment are also considered part of cultural heritage because communities identify themselves with the natural landscape. This study is focused on a shipwreck belonging to the second half of the 15th century that was discovered in 1998 by chance in the sediments of the Urdaibai estuary, in Urbieta (Gernika, Basque Country), at 4 m underground. A scientific study presented in this work was performed, as this archeological site was absolutely out of context and in need of a preservation and conservation procedure. Therefore, our aim was to shed light on the origin of the shipwreck and to assess the conservation state to develop a precise conservation plan. Pursuing this objective, a first analysis on three selected groups of iron nails was performed, looking at the raw materials and degradation patterns through the knowledge of the alteration compounds. By means of nondestructive analytical techniques such as Raman spectroscopy and X-ray fluorescence, the presence of iron, zinc, and silicon was detected in the outer layer of the iron samples. The analysis of the nails and wood of the shipwreck confirmed that the presence of zinc in the pieces indicates an important impact of the contaminated sediments deposited in the last 80 years on the upper part of the burial in which the shipwreck was located. 相似文献
869.
Camila Mortari Alexandre Nobre Pais Lurdes Esteves Alexandra Gago da Câmara Maria Luísa Carvalho Marta Manso 《Journal of Raman spectroscopy : JRS》2021,52(1):59-70
A set of decorative contemporary tile panels, created by the Portuguese artist Maria Keil (1914–2012) for the Lisbon metro stations, was studied under a noninvasive analytical methodology. This methodology combines X-ray fluorescence spectrometry (μ-XRF) and Raman spectroscopy in microscopic (μ-Raman) mode for an elemental and structural composition characterisation of the glaze (glass matrix and network modifiers such as fluxes, opacifiers and colouring agents). μ-XRF quantitative evaluation of the glassy matrix shows that all glazes have a lead silicate glass base. Results obtained by the combined use of μ-XRF and μ-Raman show that a zirconium-based opacifier was used. Naples yellow (Pb2Sb2O7), lead–tin yellow type II (Pb(Sn,Si)O3), Pb–Sn–Sb triple oxide, cobalt blue (CoAl2O4), chromium oxide (Cr2O3) and malayite sphene (CaO·SnO2·SiO2) have been identified by μ-Raman as some of the colouring agents, either used by themselves or in mixtures for obtaining the desirable colours intended by the artist. 相似文献
870.
Nagore Prieto-Taboada Silvia Fdez-Ortiz de Vallejuelo Anne Santos Marco Veneranda Kepa Castro Maite Maguregui Héctor Morillas Gorka Arana Alberta Martellone Bruno de Nigris Massimo Osanna Juan Manuel Madariaga 《Journal of Raman spectroscopy : JRS》2021,52(1):85-94
Ariadne's house is in the Regio VII of the Archaeological Park of Pompeii (Italy). As it is exposed to external alteration agents (rainfall, water infiltration and atmospheric pollution), the mural paintings located in this important residence clearly show the effects of ongoing degradation processes. This is especially the case of Room 22 (also called the blue room), where the original blue decorations varied towards greyish green hues. In situ and laboratory spectroscopic analyses by means of non-destructive X-ray fluorescence, infrared and Raman spectroscopies identified the original pigments and the materials used in the conservation works. Looking in detail at the stratigraphic distribution of the original pigments, using Raman spectroscopy, an inner layer of Egyptian blue mixed with celadonite was detected under a layer of pure Egyptian blue. This discovery proves the presence of a more ancient painting below the one that can be observed today. Considering that celadonite was an inexpensive pigment (thus, probably used to reduce the costs of the paintings), this information strengthens the hypothesis that based on archaeological evidences, there is evidence of an evolution of the socio-economic status of the ancient owners of the residence. In addition to that, Raman data also proved the occurrence of salt efflorescences; they provided insights about the compromised conservation state of the wall paintings, and they highlighted the action of atmospheric acid gases as an important factor. 相似文献