全文获取类型
收费全文 | 5020篇 |
免费 | 496篇 |
国内免费 | 672篇 |
出版年
2024年 | 15篇 |
2023年 | 137篇 |
2022年 | 154篇 |
2021年 | 245篇 |
2020年 | 251篇 |
2019年 | 263篇 |
2018年 | 249篇 |
2017年 | 200篇 |
2016年 | 214篇 |
2015年 | 219篇 |
2014年 | 308篇 |
2013年 | 418篇 |
2012年 | 251篇 |
2011年 | 285篇 |
2010年 | 210篇 |
2009年 | 236篇 |
2008年 | 251篇 |
2007年 | 318篇 |
2006年 | 263篇 |
2005年 | 224篇 |
2004年 | 188篇 |
2003年 | 155篇 |
2002年 | 137篇 |
2001年 | 94篇 |
2000年 | 104篇 |
1999年 | 90篇 |
1998年 | 68篇 |
1997年 | 65篇 |
1996年 | 50篇 |
1995年 | 52篇 |
1994年 | 46篇 |
1993年 | 36篇 |
1992年 | 34篇 |
1991年 | 33篇 |
1990年 | 34篇 |
1989年 | 26篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 27篇 |
1982年 | 30篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1974年 | 5篇 |
排序方式: 共有6188条查询结果,搜索用时 51 毫秒
1.
S. Usha 《Journal of biomolecular structure & dynamics》2013,31(7):1474-1492
We have analyzed the nonbonded interactions of the structurally similar moieties, adenine and guanine forming complexes with proteins. The results comprise (a) the amino acid–ligand atom preferences, (b) solvent accessibility of ligand atoms before and after complex formation with proteins, and (c) preferred amino acid residue atoms involved in the interactions. We have observed that the amino acid preferences involved in the hydrogen bonding interactions vary for adenine and guanine. The structural variation between the purine atoms is clearly reflected by their burial tendency in the solvent environment. Correlation of the mean amino acid preference values show the variation that exists between adenine and guanine preferences of all the amino acid residues. All our observations provide evidence for the discriminating nature of the proteins in recognizing adenine and guanine. 相似文献
2.
Linda Partridge 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2010,365(1537):147-154
Human life expectancy in developed countries has increased steadily for over 150 years, through improvements in public health and lifestyle. More people are hence living long enough to suffer age-related loss of function and disease, and there is a need to improve the health of older people. Ageing is a complex process of damage accumulation, and has been viewed as experimentally and medically intractable. This view has been reinforced by the realization that ageing is a disadvantageous trait that evolves as a side effect of mutation accumulation or a benefit to the young, because of the decline in the force of natural selection at later ages. However, important recent discoveries are that mutations in single genes can extend lifespan of laboratory model organisms and that the mechanisms involved are conserved across large evolutionary distances, including to mammals. These mutations keep the animals functional and pathology-free to later ages, and they can protect against specific ageing-related diseases, including neurodegenerative disease and cancer. Preliminary indications suggest that these new findings from the laboratory may well also apply to humans. Translating these discoveries into medical treatments poses new challenges, including changing clinical thinking towards broad-spectrum, preventative medicine and finding novel routes to drug development. 相似文献
3.
4.
Two new compounds, derriscoumaronochromone (1) and cis-3,4′-dihydroxy- 5,7-dimethoxyflavan (2), as well as trans-4'-O-methylcatechin (3) were isolated from Derris laxiflora, The structures of these compounds were determined by analysis of their spectroscopic data. 相似文献
5.
6.
Nataly Mancette Rijensky Netta R. Blondheim Shraga Eilon Barnea Nir Peled Eli Rosenbaum Aron Popovtzer Solomon M. Stemmer Alejandro Livoff Mark Shlapobersky Neta Moskovits Dafna Perry Eitan Rubin Itzhak Haviv Arie Admon 《Molecular & cellular proteomics : MCP》2020,19(8):1360-1374
- Download : Download high-res image (147KB)
- Download : Download full-size image
- •Sufficient tumor tissues are often unavailable large HLA peptidome discovery.
- •Using patient derived xenograft (PDX) tumors can overcome this limitation.
- •The large PDX HLA peptidomes expand significantly those of the original biopsies.
- •The HLA peptidomes of the PDX tumors included many tumor antigens.
7.
PurposeThe main objective of this study was to evaluate the efficacy of tungsten carbide as new lead-free radiation shielding material in nuclear medicine by evaluating the attenuation properties.Materials and methodsThe elemental composition of tungsten carbide was analysed using Field-Emission Scanning Electron Microscopy (FESEM) with energy dispersive X-ray (EDX). The purity of tungsten carbide was 99.9%, APS: 40–50 µm. Three discs of tungsten carbide was fabricated with thickness of 0.1 cm, 0.5 cm and 1.0 cm. Three lead discs with similar thickness were used to compare the attenuation properties with tungsten carbide discs. Energy calibration of gamma spectroscopy was performed by using 123I, 133Ba, 152Eu, and 137Cs. Gamma radiation from these sources were irradiated on both materials at energies ranging from 0.160 MeV to 0.779 MeV. The experimental attenuation coefficients of lead and tungsten carbide were compared with theoretical attenuation coefficients of both materials from NIST database. The half value layer and mean free path of both materials were also evaluated in this study.ResultsThis study found that the peaks obtained from gamma spectroscopy have linear relationship with all energies used in this study. The relative differences between the measured and theoretical mass attenuation coefficients are within 0.19–5.11% for both materials. Tungsten carbide has low half value layer and mean free path compared to lead for all thickness at different energies.ConclusionThis study shows that tungsten carbide has high potential to replace lead as new lead-free radiation shielding material in nuclear medicine. 相似文献
8.
Ding-Kwo Chang Shu-Fang Cheng Chi-Hui Lin EricAssen B. Kantchev Cheng-Wei Wu 《生物化学与生物物理学报:生物膜》2005,1712(1):37-51
Two glutamic acid-rich fusion peptide analogs of influenza hemagglutinin were synthesized to study the organization of the charged peptides in the membranous media. Fluorescence and gel electrophoresis experiments suggested a loose association between the monomers in the vesicles. A model was built which showed that a positional difference of 3, 7 and 4, 8 results in the exposure of Glu3 and Glu7 side chains to the apolar lipidic core. Supportive results include: first, pKa values of two pH units higher than reference value in aqueous medium for Glu3 and Glu7 CγH, whereas the deviation of pKa from the reference value for Glu4 and Glu8 CγH is substantially smaller; second, Hill coefficients of titration shift of these protons indicate anti-cooperativity for Glu3 and Glu7 side chain protons but less so for Glu4 and Glu8, implying a strong electrostatic interaction between Glu3 and Glu7 possibly resulting from their localization in an apolar environment; third, positive and larger titration shift for NH of Glu3 is observed compared to that of Glu4, suggesting stronger hydrogen bond between the NH and the carboxylic group of Glu3 than that of Glu4, consistent with higher degree of exposure to hydrophobic medium for the side chain of Glu3. 相似文献
10.
Uichiro Kotera Toru Kodama Yasuji Minoda Koichi Yamada 《Bioscience, biotechnology, and biochemistry》2013,77(8):1315-1325
In the course of study on the mechanism of the tartaric acid formation from 5-ketogluconic acid, a new intermediary substance with mauve color to Abdel-Akhel and Smith’s reagent was isolated from intact cell culture liquid. The chemical structure of this substance was determined as 1,2-dihydroxyethyl hydrogen L(+) tartrate from the results of hydrolysis experiments and from the identifications of the constituents of the molecule, and named “pretaric acid.” Tartaric acid was evidently produced from pretaric acid by intact cell culture. Clearly, then, pretaric acid appears to be an intermediate in the formation of tartaric acid from 5-ketogluconic acid. The authors assumed that in the formation of pretaric acid from 5-ketogluconic acid, a Baeyer-Villiger type oxidation occurred. 相似文献