全文获取类型
收费全文 | 5398篇 |
免费 | 471篇 |
国内免费 | 1篇 |
专业分类
5870篇 |
出版年
2023年 | 36篇 |
2022年 | 80篇 |
2021年 | 183篇 |
2020年 | 109篇 |
2019年 | 148篇 |
2018年 | 149篇 |
2017年 | 147篇 |
2016年 | 218篇 |
2015年 | 328篇 |
2014年 | 319篇 |
2013年 | 380篇 |
2012年 | 462篇 |
2011年 | 457篇 |
2010年 | 272篇 |
2009年 | 247篇 |
2008年 | 299篇 |
2007年 | 320篇 |
2006年 | 292篇 |
2005年 | 251篇 |
2004年 | 204篇 |
2003年 | 192篇 |
2002年 | 168篇 |
2001年 | 54篇 |
2000年 | 39篇 |
1999年 | 50篇 |
1998年 | 40篇 |
1997年 | 9篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 33篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1979年 | 9篇 |
1975年 | 7篇 |
1974年 | 15篇 |
1973年 | 15篇 |
1972年 | 8篇 |
1971年 | 10篇 |
1968年 | 7篇 |
排序方式: 共有5870条查询结果,搜索用时 15 毫秒
951.
Mayrim M. Gomes Alexandre Budu Priscilla D.S. Ventura Piero Bagnaresi Simone S. Cotrin Rodrigo L.O.R. Cunha Adriana K. Carmona Luiz Juliano Marcos L. Gazarini 《Analytical biochemistry》2015
In the intraerythrocytic trophozoite stages of Plasmodium falciparum, the calcium-dependent cysteine protease calpain (Pf-calpain) has an important role in the parasite calcium modulation and cell development. We established specific conditions to follow by confocal microscopy and spectrofluorimetry measurements the intracellular activity of Pf-calpain in live cells. The catalytic activity was measured using the fluorogenic Z-Phe-Arg-MCA (where Z is carbobenzoxy and MCA is 4-methylcoumaryl-7-amide). The calmodulin inhibitor calmidazolium and the sarcoplasmic reticulum calcium ATPase inhibitor thapsigargin were used for modifications in the cytosolic calcium concentrations that persisted in the absence of extracellular calcium. The observed calcium-dependent peptidase activity was greatly inhibited by specific cysteine protease inhibitor E-64 and by the selective calpain inhibitor ALLN (N-acetyl-l-leucyl-l-leucyl-l-norleucinal). Taken together, we observed that intracellular Pf-calpain can be selectively detected and is the main calcium-dependent protease in the intraerythrocytic stages of the parasite. The method described here can be helpful in cell metabolism studies and antimalarial drug screening. 相似文献
952.
Carlos E. V. de Moura Ricardo R. Oliveira Alexandre B. Rocha 《Journal of molecular modeling》2013,19(5):2027-2033
Potential energy curves and inner-shell ionization energies of carbon monoxide, oxygen and nitrogen molecules were calculated using several forms of the inner-shell multiconfigurational self-consistent field (IS-MCSCF) method—a recently proposed protocol to obtain specifically converged inner-shell states at this level. The particular forms of the IS-MCSCF method designated IS-GVB-PP, IS-FVBL and IS-CASSCF stand for perfect pairing generalized valence bond, full valence bond-like MCSCF and complete active space self consistent field, respectively. A comparison of these different versions of the IS-MCSCF method was carried out for the first time. The results indicate that inner-shell states are described accurately even for the simplest version of the method (IS-GVB-PP). Dynamic correlation was recovered by multireference configuration interaction or multireference perturbation theory. For molecules not having equivalent atoms, all methods led to comparable and accurate transition energies. For molecules with equivalent atoms, the most accurate results were obtained by multireference perturbation theory. Scalar relativistic effects were accounted for using the Douglas-Kroll-Hess Hamiltonian. 相似文献
953.
Souza NA Andrade-Coelho CA Silva VC Peixoto AA Rangel EF 《Memórias do Instituto Oswaldo Cruz》2005,100(1):39-42
Lutzomyia intermedia (Lutz & Neiva, 1912) and L. whitmani (Antunes & Coutinho, 1939) (Diptera: Psychodidae: Phlebotominae), two important vectors of American cutaneous leishmaniasis in Brazil, occur in sympatry in the locality of Posse county, Petropolis municipality, state of Rio de Janeiro, Brazil. We investigated the influence of the lunar cycle on the frequency of specimens of the two species caught while attempting to bite the collectors and in CDC light traps. Analysis of the numbers of sand flies captured in different lunar phases for two consecutive years in the peridomestic site and forest shows that there is a significant positive correlation between moonlight intensity and the numbers of L. intermedia and L. whitmani females collected while blood-feeding, whereas the opposite was observed for the CDC traps. 相似文献
954.
Reaction of 5S RNA with chlorocetaldehyde leads to the conversion of unpaired adenines to the fluorescent 1,N6-etheno-adenine derivatives. Up to 16 of the 23 adenines in free 5S RNA can be modified, the fastest reacting are A29, A34, A57-59. Partial modification of adenines in this area results in a 20% reduction in the efficiency of 5S RNA incorporation into 50S subunits during reconstitution and a 15% reduction in the activity of these subunits in peptide synthesis. Fluorescence from 1,N6-etheno-adenine is quenched in free 5S RNA and is not detectably further influenced by the binding of proteins E-L5, E-L18 and E-L25, nor by the first stage of the two step E. coli 50S subunit reconstitution procedure. However, the fluorescence is further reduced to near zero after the second step of the reconstitution. Thus, 5S RNS free in solution contains 16 unpaired adenines, those in the region between A29 and A59 particularly accessible to modification by chlorocetaldehyde. This portion of the 5S RNA molecule appears to undergo either a conformational change or interacts with other ribosomal components in the last stage of subunit reassembly. 相似文献
955.
The katA catalase gene is regulated by OxyR in both free-living and symbiotic Sinorhizobium meliloti 下载免费PDF全文
The characterization of an oxyR insertion mutant provides evidences that katA, which encodes the unique H2O2-inducible HPII catalase, is regulated by OxyR not only in free-living Sinorhizobium meliloti but also in symbiotic S. meliloti. Moreover, oxyR is expressed independently of exogenous H2O2 and downregulates its own expression in S. meliloti. 相似文献
956.
François-René Alexandre Eric Badaroux John P. Bilello Stéphanie Bot Tony Bouisset Guillaume Brandt Sylvie Cappelle Christopher Chapron Dominique Chaves Thierry Convard Clément Counor Daniel Da Costa David Dukhan Marion Gay Gilles Gosselin Jean-François Griffon Kusum Gupta Brenda Hernandez-Santiago Cyril B. Dousson 《Bioorganic & medicinal chemistry letters》2017,27(18):4323-4330
Herein we describe the discovery of IDX21437 35b, a novel RP d-aminoacid-based phosphoramidate prodrug of 2′-α-chloro-2′-β-C-methyluridine monophosphate. Its corresponding triphosphate 6 is a potent inhibitor of the HCV NS5B RNA-dependent RNA polymerase (RdRp). Despite showing very weak activity in the in vitro Huh-7 cell based HCV replicon assay, 35b demonstrated high levels of active triphosphate 6 in mouse liver and human hepatocytes. A biochemical study revealed that the metabolism of 35b was mainly attributed to carboxyesterase 1 (CES1), an enzyme which is underexpressed in HCV Huh-7-derived replicon cells. Furthermore, due to its metabolic activation, 35b was efficiently processed in liver cells compared to other cell types, including human cardiomyocytes. The selected RP diastereoisomeric configuration of 35b was assigned by X-ray structural determination. 35b is currently in Phase II clinical trials for the treatment of HCV infection. 相似文献
957.
Association Between Aerobic Exercise and Rosiglitazone Avoided the NAFLD and Liver Inflammation Exacerbated in PPAR‐α Knockout Mice 下载免费PDF全文
958.
959.
Liliane Viana Pires Adriana Aparecida Siviero-Miachon Angela Maria Spinola-Castro José Alexandre Coelho Pimentel Luciana Sigueta Nishimura Carla Soraya Costa Maia Silvia Maria Franciscato Cozzolino 《Biological trace element research》2017,176(2):217-224
Studies about selenium status in patients with Turner syndrome (TS) are non-existent in the literature. The aim of this study was to evaluate selenium status in patients with TS, while considering the different ages of the studied population and the relation with body composition. In total, 33 patients with TS were evaluated and grouped according to their developmental stages (children, adolescents, and adults). Selenium concentrations in their plasma, erythrocytes, urine, and nails were determined by using hydride generation atomic absorption spectrometry and erythrocyte glutathione peroxidase activity were measured by using Randox commercial kits. Additionally, height, weight, body fat percentage, waist circumference, and waist-height ratio were measured to characterize the patients. No differences in the selenium concentrations in the plasma, erythrocyte, urine, and nails or in the glutathione peroxidase activity were observed among the age groups (p > 0.05). The evaluated selenium levels were less than the established normal ones. The patients with larger waist circumference, body fat percentage, body mass index, and waist-height ratio showed lower glutathione peroxidase enzyme activity (p = 0.023). The present study shows that most patients with TS are deficient in selenium and that those with a greater accumulation of body fat have a lower GPx activity. 相似文献
960.
Eugênia Barbosa Varella Costa Pedro Henrique de Faria Peres Francisco Grotta-Neto Alexandre Vogliotti Ubiratan Piovezan 《Studies on Neotropical Fauna and Environment》2017,52(1):37-42
Morphometric feces data are used to identify ungulates, but their effectiveness is questioned by numerous authors. Herein, we evaluated the efficiency of this tool in discriminating scat samples from Neotropical deer with sympatric distributions. We performed discriminant analysis of previously identified scat samples (n = 204). The accuracy of discriminant analysis (56–92%) was lower than the confidence limit established in this study in all sympatric combinations expected in these biomes. These results demonstrate serious limitations regarding the use of scat morphometry for species identification of Neotropical deer and reinforce the need to use non-invasive genetic techniques. 相似文献