全文获取类型
收费全文 | 701篇 |
免费 | 37篇 |
专业分类
化学 | 478篇 |
晶体学 | 3篇 |
力学 | 16篇 |
数学 | 86篇 |
物理学 | 155篇 |
出版年
2023年 | 4篇 |
2022年 | 21篇 |
2021年 | 33篇 |
2020年 | 27篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 16篇 |
2016年 | 40篇 |
2015年 | 26篇 |
2014年 | 35篇 |
2013年 | 53篇 |
2012年 | 56篇 |
2011年 | 46篇 |
2010年 | 34篇 |
2009年 | 30篇 |
2008年 | 49篇 |
2007年 | 28篇 |
2006年 | 37篇 |
2005年 | 18篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1992年 | 1篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有738条查询结果,搜索用时 93 毫秒
731.
Lucas?T.?Cardoso Jens?MundEmail authorView authors OrcID profile Joseph?C.?Várilly 《Mathematical Physics, Analysis and Geometry》2018,21(1):3
For a renormalizability proof of perturbative models in the Epstein–Glaser scheme with string-localized quantum fields, one needs to know what freedom one has in the definition of time-ordered products of the interaction Lagrangian. This paper provides a first step in that direction. The basic issue is the presence of an open set of n-tuples of strings which cannot be chronologically ordered. We resolve it by showing that almost all such string configurations can be dissected into finitely many pieces which can indeed be chronologically ordered. This fixes the time-ordered products of linear field factors outside a nullset of string configurations. (The extension across the nullset, as well as the definition of time-ordered products of Wick monomials, will be discussed elsewhere). 相似文献
732.
Walid Zeghbib Fares Boudjouan Vitor Vasconcelos Graciliana Lopes 《Molecules (Basel, Switzerland)》2022,27(15)
Within the Cactaceae family, Opuntia comprises the most widespread species, with a recognized importance in human life, including feeding, domestic use as home natural barriers, and as a traditional remedy for diverse diseases and conditions such asthma, edema, and burns. Indeed, scientific reports have stated that these health benefits may be due to various active compounds, particularly polyphenols, which are ubiquitously found in plants and have proven their pharmacological efficiency by displaying antimicrobial, anti-cancer, and anti-inflammatory activities, among others. Opuntia species contain different classes of phenolic compounds that are recognized for their anti-inflammatory potential. Among them, quercetin, isorhamnetin, and kaempferol derivates were reported to greatly contribute to modulate cells’ infiltration and secretion of soluble inflammatory mediators, with key implications in the inflammatory process. In this review, we make a summary of the different classes of phenolic compounds reported in Opuntia species so far and explore their implications in the inflammatory process, reported by in vitro and in vivo bioassays, supporting the use of cactus in folk medicine and valorizing them from the socio-economic point of view. 相似文献
733.
Bassam Felipe Mogharbel Marco Andr Cardoso Ana Carolina Irioda Priscila Elias Ferreira Stricker Robson Camilotti Slompo Julia Maurer Appel Nathalia Barth de Oliveira Maiara Carolina Perussolo Claudia Sayuri Saaki Nadia Nascimento da Rosa Dilcele Silva Moreira Dziedzic Christophe Travelet Sami Halila Redouane Borsali Katherine Athayde Teixeira de Carvalho 《Molecules (Basel, Switzerland)》2022,27(9)
Background: Parkinson’s disease (PD) is the second most common age-related neurodegenerative disorder. Levodopa (L-DOPA) remains the gold-standard drug available for treating PD. Curcumin has many pharmacological activities, including antioxidant, anti-inflammatory, antimicrobial, anti-amyloid, and antitumor properties. Copolymers composed of Poly (ethylene oxide) (PEO) and biodegradable polyesters such as Poly (ε-caprolactone) (PCL) can self-assemble into nanoparticles (NPs). This study describes the development of NH2–PEO–PCL diblock copolymer positively charged and modified by adding glutathione (GSH) on the outer surface, resulting in a synergistic delivery of L-DOPA curcumin that would be able to pass the blood–brain barrier. Methods: The NH2–PEO–PCL NPs suspensions were prepared by using a nanoprecipitation and solvent displacement method and coated with GSH. NPs were submitted to characterization assays. In order to ensure the bioavailability, Vero and PC12 cells were treated with various concentrations of the loaded and unloaded NPs to observe cytotoxicity. Results: NPs have successfully loaded L-DOPA and curcumin and were stable after freeze-drying, indicating advancing into in vitro toxicity testing. Vero and PC12 cells that were treated up to 72 h with various concentrations of L-DOPA and curcumin-loaded NP maintained high viability percentage, indicating that the NPs are biocompatible. Conclusions: NPs consisting of NH2–PEO–PCL were characterized as potential formulations for brain delivery of L-DOPA and curcumin. The results also indicate that the developed biodegradable nanomicelles that were blood compatible presented low cytotoxicity. 相似文献
734.
Rafaela Dias Oliveira Snia Pires Celeiro Catarina Barbosa-Matos Ana Sofia Freitas Susana M. Cardoso Marta Viana-Pereira Cristina Almeida-Aguiar Ftima Baltazar 《Molecules (Basel, Switzerland)》2022,27(11)
Melanoma is the most aggressive and life-threatening skin cancer type. The melanoma genome is the most frequently mutated, with the BRAF mutation present in 40–60% of melanoma cases. BRAF-mutated melanomas are characterized by a higher aggressiveness and progression. Adjuvant targeted treatments, such as BRAF and MEK inhibitors, are added to surgical excision in BRAF-mutated metastatic melanomas to maximize treatment effectiveness. However, resistance remains the major therapeutic problem. Interest in natural products, like propolis, for therapeutic applications, has increased in the last years. Propolis healing proprieties offer great potential for the development of novel cancer drugs. As the activity of Portuguese propolis has never been studied in melanoma, we evaluated the antitumoral activity of propolis from Gerês (G18.EE) and its fractions (n-hexane, ethyl acetate (EtOAc), and n-butanol) in A375 and WM9 melanoma cell lines. Results from DPPH•/ABTS• radical scavenging assays indicated that the samples had relevant antioxidant activity, however, this was not confirmed in the cell models. G18.EE and its fractions decreased cell viability (SRB assay) and promoted ROS production (DHE/Mitotracker probes by flow cytometry), leading to activation of apoptotic signaling (expression of apoptosis markers). Our results suggest that the n-BuOH fraction has the potential to be explored in the pharmacological therapy of melanoma. 相似文献
735.
Mirvana Hilal Andreia S. Gaudêncio Pedro G. Vaz Joo Cardoso Anne Humeau-Heurtier 《Entropy (Basel, Switzerland)》2022,24(6)
Texture analysis is a subject of intensive focus in research due to its significant role in the field of image processing. However, few studies focus on colored texture analysis and even fewer use information theory concepts. Entropy measures have been proven competent for gray scale images. However, to the best of our knowledge, there are no well-established entropy methods that deal with colored images yet. Therefore, we propose the recent colored bidimensional fuzzy entropy measure, , and introduce its new multi-channel approaches, and , for the analysis of colored images. We investigate their sensitivity to parameters and ability to identify images with different irregularity degrees, and therefore different textures. Moreover, we study their behavior with colored Brodatz images in different color spaces. After verifying the results with test images, we employ the three methods for analyzing dermoscopic images of malignant melanoma and benign melanocytic nevi. , , and illustrate a good differentiation ability between the two—similar in appearance—pigmented skin lesions. The results outperform those of a well-known texture analysis measure. Our work provides the first entropy measure studying colored images using both single and multi-channel approaches. 相似文献
736.
Ana Sofia Freitas Marta Costa Olívia Pontes Veronique Seidel Fernanda Proena Susana M. Cardoso Rui Oliveira Ftima Baltazar Cristina Almeida-Aguiar 《Molecules (Basel, Switzerland)》2022,27(13)
Renal cell carcinoma is the most lethal cancer of the urological system due to late diagnosis and treatment resistance. Propolis, a beehive product, is a valuable natural source of compounds with bioactivities and may be a beneficial addition to current anticancer treatments. A Portuguese propolis sample, its fractions (n-hexane, ethyl acetate, n-butanol and water) and three subfractions (P1–P3), were tested for their toxicity on A498, 786-O and Caki-2 renal cell carcinoma cell lines and the non-neoplastic HK2 kidney cells. The ethyl acetate fraction showed the strongest toxicity against A498 (IC50 = 0.162 µg mL−1) and 786-O (IC50 = 0.271 µg mL−1) cells. With similar toxicity against 786-O, P1 (IC50 = 3.8 µg mL−1) and P3 (IC50 = 3.1 µg mL−1) exhibited greater effect when combined (IC50 = 2.5 µg mL−1). Results support the potential of propolis and its constituents as promising coadjuvants in renal cell carcinoma treatment. 相似文献
737.
Deyber Arley Vargas Medina Alessandra Timoteo Cardoso João Victor Basolli Borsatto Fernando Mauro Lanças 《Journal of separation science》2023,46(18):2300373
Nano-liquid chromatography (nanoLC) is gaining significant attention as a primary analytical technique across various scientific domains. Unlike conventional high-performance LC, nanoLC utilizes columns with inner diameters (i.ds.) usually ranging from 10 to 150 μm and operates at mobile phase flow rates between 10 and 1000 nl/min, offering improved chromatographic performance and detectability. Currently, most exploration of nanoLC has focused on particle-packed columns. Although open tubular LC (OTLC) can provide superior performance, optimized OTLC columns require very narrow i.ds. (< 10 μm) and demand challenging instrumentation. At the moment, these challenges have limited the success of OTLC. Nevertheless, remarkable progress has been made in developing and utilizing OTLC systems featuring narrow columns (< 2 μm). Additionally, significant efforts have been made to explore larger columns (10–75 μm i.d), demonstrating practical applicability in many situations. Due to their perceived advantages, interest in OTLC has resurged in the last two decades. This review provides an updated outlook on the latest developments in OTLC, focusing on instrumental challenges, achievements, and advancements in column technology. Moreover, it outlines selected applications that illustrate the potential of OTLC for performing targeted and untargeted studies. 相似文献
738.
Letícia S. Contieri Leonardo M de Souza Mesquita Vitor L. Sanches Juliane Viganó Renan Canute Kamikawachi Wagner Vilegas Mauricio A. Rostagno 《Journal of separation science》2023,46(3):2200440
Propolis is a bee product with a complex chemical composition formed by several species from different geographical origins. The complex propolis composition requires an accurate and reproducible characterization of samples to standardize the quality of the material sold to consumers. This work developed an ultra-high-performance liquid chromatography with a photodiode array detector method to analyze propolis phenolic compounds based on the two key propolis biomarkers, Artepillin C and p-Coumaric acid. This choice was made due to the complexity of the sample with the presence of several compounds. The optimized method was hyphenated with mass spectrometry detection allowing the detection of 23 different compounds. A step-by-step strategy was used to optimize temperature, flow rate, mobile phase composition, and re-equilibration time. Reverse-phase separation was achieved with a C18 fused-core column packed with the commercially available smallest particles (1.3 nm). Using a fused-core column with ultra-high-performance liquid chromatography allows highly efficient, sensitive, accurate, and reproducible determination of compounds extracted from propolis with an outstanding sample throughput and resolution. Optimized conditions permitted the separation of the compounds in 5.50 min with a total analysis time (sample-to-sample) of 6.50 min. 相似文献