全文获取类型
收费全文 | 2823篇 |
免费 | 94篇 |
国内免费 | 8篇 |
专业分类
化学 | 1833篇 |
晶体学 | 17篇 |
力学 | 45篇 |
数学 | 505篇 |
物理学 | 525篇 |
出版年
2023年 | 15篇 |
2022年 | 66篇 |
2021年 | 75篇 |
2020年 | 74篇 |
2019年 | 66篇 |
2018年 | 48篇 |
2017年 | 52篇 |
2016年 | 101篇 |
2015年 | 90篇 |
2014年 | 98篇 |
2013年 | 171篇 |
2012年 | 197篇 |
2011年 | 177篇 |
2010年 | 101篇 |
2009年 | 97篇 |
2008年 | 161篇 |
2007年 | 163篇 |
2006年 | 150篇 |
2005年 | 128篇 |
2004年 | 111篇 |
2003年 | 96篇 |
2002年 | 92篇 |
2001年 | 47篇 |
2000年 | 36篇 |
1999年 | 34篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 29篇 |
1993年 | 27篇 |
1992年 | 28篇 |
1991年 | 19篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1975年 | 15篇 |
1974年 | 16篇 |
1972年 | 6篇 |
排序方式: 共有2925条查询结果,搜索用时 15 毫秒
161.
Lara R. S. Fonseca Gonalo R. Silva ngelo Luís Henrique J. Cardoso Sara Correia Ctia V. Vaz Ana P. Duarte Sílvia Socorro 《Molecules (Basel, Switzerland)》2021,26(10)
Sweet cherries (Prunus avium L.) are among the most appreciated fruits worldwide because of their organoleptic properties and nutritional value. The accurate phytochemical composition and nutritional value of sweet cherries depends on the climatic region, cultivar, and bioaccessibility and bioavailability of specific compounds. Nevertheless, sweet cherry extracts are highly enriched in several phenolic compounds with relevant bioactivity. Over the years, technological advances in chemical analysis and fields as varied as proteomics, genomics and bioinformatics, have allowed the detailed characterization of the sweet cherry bioactive phytonutrients and their biological function. In this context, the effect of sweet cherries on suppressing important events in the carcinogenic process, such as oxidative stress and inflammation, was widely documented. Interestingly, results from our research group and others have widened the action of sweet cherries to many hallmarks of cancer, namely metabolic reprogramming. The present review discusses the anticarcinogenic potential of sweet cherries by addressing their phytochemical composition, the bioaccessibility and bioavailability of specific bioactive compounds, and the existing knowledge concerning the effects against oxidative stress, chronic inflammation, deregulated cell proliferation and apoptosis, invasion and metastization, and metabolic alterations. Globally, this review highlights the prospective use of sweet cherries as a dietary supplement or in cancer treatment. 相似文献
162.
Armando Navarro-Huerta Marcus J. Jellen Jessica Arcudia Simon J. Teat Rubn A. Toscano Gabriel Merino Braulio Rodríguez-Molina 《Chemical science》2021,12(6):2181
This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. The crystal structures of these rotors, determined by synchrotron radiation experiments at different temperatures, show the presence of such C–H⋯F–C contacts between extended carbazole stators featuring fluorinated phenyl rings and the 1,4-diazabicyclo[2.2.2]octane (DABCO) rotator. According to the 2H NMR results, using deuterated samples, and periodic density functional theory computations, the rotators experience fast angular displacements (preferentially 120° jumps) due to their low rotational activation energies (Ea = 0.8–2.0 kcal mol−1). The higher rotational barrier for 1 (2.0 kcal mol−1) is associated with a larger number of weak C–H⋯F–C contacts generated by the stators. This strategy offers the possibility to explore the correlation among weak intermolecular forces, cavity shape, and internal dynamics, which has strong implications in the design of future fine-tuned amphidynamic crystals.This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. 相似文献
163.
Lewis R. Thomas-Hargreaves Marcus J. Giansiracusa Matthew Gregson Emanuele Zanda Felix O'Donnell Ashley J. Wooles Nicholas F. Chilton Stephen T. Liddle 《Chemical science》2021,12(11):3911
Treatment of the new methanediide–methanide complex [Dy(SCS)(SCSH)(THF)] (1Dy, SCS = {C(PPh2S)2}2−) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)2][Dy(SCS)2(K(DME)2)2] (2Dy), [Dy(SCS)2][Na(DME)3] (3Dy) and [Dy(SCS)2][K(2,2,2-cryptand)] (4Dy). For further comparisons, the bis-methanediide complex [Dy(NCN)2][K(DB18C6)(THF)(toluene)] (5Dy, NCN = {C(PPh2NSiMe3)2}2−, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for 2Dy–5Dy, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s−1). Fitting the alternating current magnetic susceptibility data for 2Dy–5Dy gives energy barriers to magnetic relaxation (Ueff) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus 2Dy–4Dy join a privileged group of SMMs with Ueff values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For 2Dy–4Dy, the Dy-components can be grouped into 2Dy–cation/4Dy and 2Dy–anion/3Dy, where the former have almost linear C Dy C units with short average Dy C distances, and the latter have more bent C Dy C units with longer average Dy C bonds. Both Ueff and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M–L distances produces enhanced SMM properties. Comparison with 5Dy demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between Ueff barrier and axial linearity in structurally comparable systems.Studies on equatorial donor and C Dy C angle variation effects on energy barriers to the slow relaxation of magnetisation are reported. 相似文献
164.
João Miller de Melo Henrique Pablo Cañizares Cristina Saez Elisama Vieira dos Santos Manuel Andrés Rodrigo 《Current Opinion in Electrochemistry》2021
Treatment of polluted soil is one of the priorities in the search of a more sustainable planet. Electrochemically assisted soil remediation has been considered a good option for removing organic contaminants contained in soil, including the removal of volatile organic compounds, associated with gaseous streams produced during the treatment. Also, recently, electrochemical gas treatment technologies have been appointed as promising for the treatment of volatile organic compounds. In this work, we review the current opinion about the most recent studies in both areas. The first section focuses on the production of gaseous compounds during soil remediation by conventional and electrochemical systems. The second section describes the recent progress in the integration of adsorption and absorption with electrochemical processes. Finally, we discuss the holistic application of assisted electrochemical technologies in soil remediation, considering also emerging processes recently published in the literature. 相似文献
165.
Poliana Cristina Spricigo Banny Silva Barbosa Correia Karla Rodrigues Borba Isabela Barroso Taver Guilherme de Oliveira Machado Renan Ziemann Wilhelms Luiz Henrique Keng Queiroz Junior Angelo Pedro Jacomino Luiz Alberto Colnago 《Molecules (Basel, Switzerland)》2021,26(12)
The cambuci is a native Brazilian fruit from the Atlantic Forest biome. A soft and astringent pulp, a green color, and a sweet aroma are its main characteristics. Classical food quality attributes (fresh fruit mass, fruit height, diameters, total soluble solid, titratable acidity, and ratio) and the metabolic profile from ten accessions from three different locations were analyzed herein by analytical methods (refractometry and neutralization titration) and nuclear magnetic resonance spectroscopy. Concerning sugar content, sucrose was the predominant compound, with glucose and fructose alternating in second, depending on the accession. Citric acid was the most relevant acid, followed by shikimic and quinic acids in quite variable amounts. These three main acids vary in amounts for each accession. Ascorbic acid content emerges as an important quality attribute and makes this fruit nutritionally attractive, due to values comparable to those contained in citric fruits. The main amino acids identified in cambuci were glutamic acid individually or in comprising the tripeptide glutathione (glutamic acid, cysteine, glycine). The quality diversity of the evaluated accessions suggests the potentiality of cambuci use in future breeding programs. 相似文献
166.
Giovanny Carvalho dos Santos Lucas Michelão Martins Bruna Andressa Bregadiolli Vitor Fernandes Moreno Luiz Carlos da Silva-Filho Bruno Henrique Sacoman Torquato da Silva 《Journal of heterocyclic chemistry》2021,58(12):2226-2260
A virus outbreak challenges the economic, medical, and public health infrastructure worldwide. More than one virus capable of triggering diseases have been identified per year since 1972, which requires the development of new ways of treatment and prevention, however, such processes are not rapid and easy. With the pandemic scenario experienced since early 2020, several drugs with well-known purposes have gained prominence, due to speculation of their use in the treatment against the new coronavirus. Among the main drugs studied, the vast majority contain a heterocyclic structure. In this review, we presented the traditional and efficient synthesis of 15 drugs that have been studied for the COVID-19 treatment, containing in their structure heterocycles like indole, quinoline, pyrimidone, tetrahydrofuran, pyrrolidine, triazole, pyridazine, pyrazole, pyrrolopyrimidine, azetidine, pyrrolotriazine, pyrazine, tetrahydropyran, benzofuran, spiroketal, and thiazole. Furthermore, we have shown the original applications, as well as their structure–activity relationship and what is their situation as a drug candidate against COVID-19. Thus, the objective was to consolidate the main synthetic and pharmacological aspects involving clinically developed heterocycles that at some point were presented as promising against SARS-CoV-2. 相似文献
167.
Matthias Ermer Julian Mehler Björn Rosenberger Dr. Marcus Fischer Dr. Peter S. Schulz Prof. Martin Hartmann 《ChemistryOpen》2021,10(2):233-242
Using ionic liquids (ILs) as linker precursors, the well-known metal-organic framework (MOF) UiO-66 (Universitetet i Oslo) and the recently reported MOF hcp UiO-66 (hexagonal closed packed) have been successfully synthesized and characterized. The advantage of the applied novel synthesis approach is an economically and environmentally benign work-up procedure, due to the better solubility of the IL. Additionally, the reactivity of the terephthalate anions is increased compared to terephthalic acid, resulting in faster MOF formation with an increased amount of defects in the MOF structure. In order to explore to the influence of defects on the catalytic performance, the cyclisation of citronellal to isopulegol was employed as test reaction. The activity of hcp UiO-66 and fcc UiO-66 (face centered cubic) is improved compared to other MOF or zeolite based catalysts, while the selectivity is similar. 相似文献
168.
Matthias Krumb Dr. Maximilian Jäger Alice Voss Loreen Immig Dr. Karin Peters Danuta Kowalczyk Prof. Dr. Albrecht Bufe Prof. Dr. Till Opatz Prof. Dr. Otto Holst Prof. Dr. Christian Vogel Dr. Marcus Peters 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):928-933
Arabinogalactan, a microheterogeneous polysaccharide occurring in plants, is known for its allergy-protective activity, which could potentially be used for preventive allergy treatment. New treatment options are highly desirable, especially in a preventive manner, due to the constant rise of atopic diseases worldwide. The structural origin of the allergy-protective activity of arabinogalactan is, however, still unclear and isolation of the polysaccharide is not feasible for pharmaceutical applications due to a variation of the activity of the natural product and contaminations with endotoxins. Therefore, a pentasaccharide partial structure was selected for total synthesis and subsequently coupled to a carrier protein to form a neoglycoconjugate. The allergy-protective activity of arabinogalactan could be reproduced with the partial structure in subsequent in vivo experiments. This is the first example of a successful simplification of arabinogalactan with a single partial structure while retaining its allergy-preventive potential. 相似文献
169.
Caroline K. Williams Amir Lashgari Nilakshi Devi Marcus Ang Ashwin Chaturvedi Pranita Dhungana Prof. Jianbing Jimmy Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(20):6240-6246
In this work, the electrocatalytic reduction of dichloromethane (CH2Cl2) into hydrocarbons involving a main group element-based molecular triazole-porphyrin electrocatalyst H2PorT8 is reported. This catalyst converted CH2Cl2 in acetonitrile to various hydrocarbons (methane, ethane, and ethylene) with a Faradaic efficiency of 70 % and current density of −13 mA cm−2 at a potential of −2.2 V vs. Fc/Fc+ using water as a proton source. The findings of this study and its mechanistic interpretations demonstrated that H2PorT8 was an efficient and stable catalyst for the hydrodechlorination of CH2Cl2 and that main group catalysts could be potentially used for exploring new catalytic reaction mechanisms. 相似文献
170.
Michael S. Gruhne Dr. Maximilian H. H. Wurzenberger Marcus Lommel Dr. Jörg Stierstorfer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(35):9112-9123
Dinitraminic acid (HN(NO2)2, HDN) was prepared by ion exchange chromatography and acid-base reaction with basic copper(II) carbonate allowed the in situ preparation of copper(II) dinitramide, which was reacted with twelve nitrogen-rich ligands, for example, 4-amino-1,2,4-triazole, 1-methyl-5H-tetrazole, di(5H-tetrazolyl)-methane/-ethane/-propane/-butane. Nine of the complexes were investigated by low-temperature X-ray diffraction. In addition, all compounds were investigated by infrared spectroscopy (IR), differential thermal analysis (DTA), elemental analysis (EA) and thermogravimetric analysis (TGA) for selected compounds. Furthermore, investigations of the materials were carried out regarding their sensitivity toward impact (IS), friction (FS), ball drop impact (BDIS) and electrostatic discharge (ESD). In addition, hot plate and hot needle tests were performed. Complex [Cu(AMT)4(H2O)](DN)2, based on 1-amino-5-methyltetrazole (AMT), is most outstanding for its detonative behavior and thus also capable of initiating PETN in classical initiation experiments. Laser ignition experiments at a wavelength of 915 nm were performed for all substances and solid-state UV-Vis spectra were recorded to apprehend the ignition mechanism. 相似文献