全文获取类型
收费全文 | 1776篇 |
免费 | 130篇 |
国内免费 | 1篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 30篇 |
2020年 | 24篇 |
2019年 | 24篇 |
2018年 | 32篇 |
2017年 | 36篇 |
2016年 | 31篇 |
2015年 | 56篇 |
2014年 | 77篇 |
2013年 | 89篇 |
2012年 | 105篇 |
2011年 | 106篇 |
2010年 | 72篇 |
2009年 | 64篇 |
2008年 | 92篇 |
2007年 | 93篇 |
2006年 | 72篇 |
2005年 | 66篇 |
2004年 | 70篇 |
2003年 | 57篇 |
2002年 | 68篇 |
2001年 | 53篇 |
2000年 | 68篇 |
1999年 | 54篇 |
1998年 | 25篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 29篇 |
1991年 | 33篇 |
1990年 | 32篇 |
1989年 | 32篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 13篇 |
1973年 | 9篇 |
1971年 | 9篇 |
排序方式: 共有1907条查询结果,搜索用时 15 毫秒
1.
A psychological test battery comprising reasoning ability, name and number checking, letter cancellation and associative recall was administered to a group of 70 student nurses at 2-hr intervals from 0800 to 2000 to determine if their performance varied at different times of day. Simultaneously, their oral temperature was recorded. A 7 x 7 latin square design was utilized, and latin square repeated measure analysis of variance was employed. The results indicated variations in oral temperature as the day advanced. While accuracy of performance in cognitive tasks was found to be superior during the early morning, noon or early evening hours, the speed of performance was highest during the period from late-morning to late-evening. 相似文献
2.
Amal Bhattacharya Mrinal Ghosh Amalesh Choudhury 《The Journal of eukaryotic microbiology》1987,34(4):403-405
Acanthamoeba rhysodes has been found to be a predominant intertidal benthic gymnamoeba in the mangrove ecosystem of Sundarbans of lower deltaic Bengal, facing the Bay. The sampling zones under study were the highest high tide regions, with characteristic mangrove litter-soil, inundated twice per month during the highest ebb of spring tide. Population abundance of this species, both in its trophic and cystic forms in the three distinct seasonal periods of pre-monsoon (March to June), monsoon (July to October), and post-monsoon (November to February) has been surveyed for over two years. These seasonal periods affect the physico-chemical parameters of the habitat substrata, including temperature, pH, and salinity. It has been found that the overall number of organisms per gram of soil attains peak value during the monsoon period. This value comes down in post-monsoon samples and is the least in pre-monsoon ones. 相似文献
3.
4.
We present the three-dimensional (3D) solution structure of a calcium-binding protein from Entamoeba histolytica (EhCaBP), an etiologic agent of amoebiasis affecting millions worldwide. EhCaBP is a 14.7 kDa (134 residues) monomeric protein thought to play a role in the pathogenesis of amoebiasis. The 3D structure of Ca(2+)-bound EhCaBP has been derived using multidimensional nuclear magnetic resonance (NMR) spectroscopic techniques. The study reveals the presence of two globular domains connected by a flexible linker region spanning 8 amino acid residues. Each domain consists of a pair of helix-loop-helix motifs similar to the canonical EF-hand motif of calcium-binding proteins. EhCaBP binds to four Ca(2+) with high affinity (two in each domain), and it is structurally related to calmodulin (CaM) and troponin C (TnC) despite its low sequence homology ( approximately 29%) with these proteins. NMR-derived structures of EhCaBP converge within each domain with low RMSDs and angular order-parameters for backbone torsion angles close to 1.0. However, the presence of a highly flexible central linker region results in an ill-defined orientation of the two domains relative to one other. These findings are supported by backbone (15)N relaxation rate measurements and deuterium exchange studies, which reveal low structural order parameters for residues in the central linker region. Earlier, biochemical studies showed that EhCaBP is involved in a novel signal transduction mechanism, distinct from CaM. A possible reason for such a functional diversity is revealed by a detailed comparison of the 3D structure of EhCaBP with that of CaM and TnC. The studies indicate a more open C-terminal domain for EhCaBP with larger water exposed total hydrophobic surface area as compared to CaM and TnC. Further dissimilarities between the structures include the presence of two Gly residues (G63 and G67) in the central linker region of EhCaBP, which seem to impart it a greater flexibility compared to CaM and TnC and also play crucial role in its biological function. Thus, unlike in CaM and TnC, wherein the length and/or composition of the central linker have been found to be crucial for their function, in EhCaBP, both flexibility as well as amino acid composition is required for the function of the protein. 相似文献
5.
6.
7.
8.
9.
Sulphur-containing amino acids including some derivatives have been tested for their effectiveness in suppressing the mutagenic activity of aflatoxin B1 in Salmonella typhimurium strains provided with a rat liver activation system. Cysteine and N-acetylcysteine have been found to be most effective in the 2 strains tested (TA100 and TA98). Glutathione (oxidised and reduced forms) has shown partial activity, while cystine and methionine are found to be partially effective only in strain TA100. Inhibition of mutagenicity may be due to interaction of these substances with microsomal enzymes resulting in interference with the formation of ultimate mutagenic species. 相似文献
10.