全文获取类型
收费全文 | 17873篇 |
免费 | 1301篇 |
国内免费 | 1篇 |
出版年
2021年 | 120篇 |
2020年 | 99篇 |
2019年 | 100篇 |
2018年 | 281篇 |
2017年 | 244篇 |
2016年 | 429篇 |
2015年 | 754篇 |
2014年 | 694篇 |
2013年 | 1020篇 |
2012年 | 1237篇 |
2011年 | 1212篇 |
2010年 | 719篇 |
2009年 | 565篇 |
2008年 | 1077篇 |
2007年 | 1070篇 |
2006年 | 1034篇 |
2005年 | 987篇 |
2004年 | 905篇 |
2003年 | 848篇 |
2002年 | 782篇 |
2001年 | 393篇 |
2000年 | 408篇 |
1999年 | 358篇 |
1998年 | 162篇 |
1997年 | 139篇 |
1996年 | 118篇 |
1995年 | 138篇 |
1994年 | 112篇 |
1993年 | 86篇 |
1992年 | 225篇 |
1991年 | 219篇 |
1990年 | 195篇 |
1989年 | 152篇 |
1988年 | 169篇 |
1987年 | 144篇 |
1986年 | 134篇 |
1985年 | 120篇 |
1984年 | 115篇 |
1983年 | 90篇 |
1982年 | 84篇 |
1981年 | 109篇 |
1980年 | 75篇 |
1979年 | 114篇 |
1978年 | 110篇 |
1977年 | 87篇 |
1976年 | 96篇 |
1975年 | 81篇 |
1974年 | 91篇 |
1973年 | 69篇 |
1971年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
31.
Mathieu Lefèvre Daniel J. Felmlee Marie Parnot Thomas F. Baumert Catherine Schuster 《PloS one》2014,9(4)
Hepatitis C virus (HCV) is a major cause of liver disease worldwide and HCV infection represents a major health problem. HCV associates with host lipoproteins forming host/viral hybrid complexes termed lipoviral particles. Apolipoprotein E (apoE) is a lipoprotein component that interacts with heparan sulfate proteoglycans (HSPG) to mediate hepatic lipoprotein uptake, and may likewise mediate HCV entry. We sought to define the functional regions of apoE with an aim to identify critical apoE binding partners involved in HCV infection. Using adenoviral vectors and siRNA to modulate apoE expression we show a direct correlation of apoE expression and HCV infectivity, whereas no correlation exists with viral protein expression. Mutating the HSPG binding domain (HSPG-BD) of apoE revealed key residues that are critical for mediating HCV infection. Furthermore, a novel synthetic peptide that mimics apoE’s HSPG-BD directly and competitively inhibits HCV infection. Genetic knockdown of the HSPG proteins syndecan (SDC) 1 and 4 revealed that SDC4 principally mediates HCV entry. Our data demonstrate that HCV uses apoE-SDC4 interactions to enter hepatoma cells and establish infection. Targeting apoE-SDC interactions could be an alternative strategy for blocking HCV entry, a critical step in maintaining chronic HCV infection. 相似文献
32.
Four main molecular forms of acetylcholinesterase (AChE) can be solubilized from newborn rat superior cervical ganglia (SCG), homogenized in the presence of a high-ionic-strength, detergent-containing medium. These forms, respectively referred to as 16, 10, 6.5, and 4 S, are characterized by their sedimentation coefficients. Their relative proportions in SCG are notably different in vivo during postnatal maturation, and in culture. The 16-S AChE appears to be mainly neuronal in origin, is maintained in culture independently of original presynaptic in vivo elements, and its cellular pool is not depleted in the presence of tetrodotoxin (TTX). 相似文献
33.
Administration of choline chloride i.p. to rats causes a dose-dependent increase in the brain concentration of the neurotransmitter, acetylcholine (ACh). This increase is maximal (22% after a 60-mg/kg dose) 40 minutes after injection. These observations suggest that precursor availability may influence brain ACh synthesis, just as brain tryptophan and tyrosine levels have previously been shown to control the synthesis of brain serotonin and catecholamines. 相似文献
34.
35.
36.
37.
38.
P Navarro-Rosinés C Roux A Bellemère 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》2001,324(5):443-451
An ultrastructural study of Weddellomyces epicallopisma (ascomata wall, asci, ascospores and vegetative hyphae), the first done on the family Dacampiaceae, confirms most of the observations made in light microscopy. Moreover it shows that ascospores are provided with an endospore (not visible in light microscope) and that the structure of the ascospore septum is more complex. The similarity of the wall structure between the ascospore and the hyphoid appendages, developed on the upper part of the ascoma, is emphasized. 相似文献
39.
40.
P. lanceolata andP. major were grown in culture solutions with nitrate or ammonium as the nitrogen source. Dry matter accumulation in the shoot was
faster with nitrate than with ammonium, whilst that of the roots was not affected by the nitrogen source. As a consequence,
the shoot-to-root ratio was lower with ammonium than with nitrate. InP. lanceolata, dry matter percentage of shoot and root tissue was lower with nitrate nutrition, suggesting better elongation growth than
with ammonium. However, in shoot tissue ofP. major the opposite was found. The rate of root respiration declined with time, and this was almost completely due to a declining
activity of the alternative path, which amounted to about 30–60% of total root respiration. Respiration via the cytochrome
path was for a part of time slightly increased by ammonium, whereas the activity of the alternative path was strongly enhanced.
The concentration of ethanol-soluble carbohydrates (SC) in the roots of both species was higher when nitrate was used, but
no difference in the concentration of starch was found. When the plants were transferred from one nitrogen source to the other,
many parameters, including the concentration of nitrate and chloride, and the shoot to root ratio, adjusted to the new situation
in both species.
Grassland Species Research Group, Publication no. 116. 相似文献