全文获取类型
收费全文 | 21014篇 |
免费 | 2048篇 |
国内免费 | 2518篇 |
出版年
2024年 | 17篇 |
2023年 | 324篇 |
2022年 | 499篇 |
2021年 | 1300篇 |
2020年 | 939篇 |
2019年 | 1193篇 |
2018年 | 1083篇 |
2017年 | 767篇 |
2016年 | 1018篇 |
2015年 | 1500篇 |
2014年 | 1785篇 |
2013年 | 1746篇 |
2012年 | 2063篇 |
2011年 | 1930篇 |
2010年 | 1163篇 |
2009年 | 1034篇 |
2008年 | 1147篇 |
2007年 | 968篇 |
2006年 | 801篇 |
2005年 | 693篇 |
2004年 | 644篇 |
2003年 | 612篇 |
2002年 | 509篇 |
2001年 | 340篇 |
2000年 | 284篇 |
1999年 | 258篇 |
1998年 | 168篇 |
1997年 | 129篇 |
1996年 | 114篇 |
1995年 | 99篇 |
1994年 | 72篇 |
1993年 | 65篇 |
1992年 | 63篇 |
1991年 | 38篇 |
1990年 | 40篇 |
1989年 | 56篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 29篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
Siân E. C. Davies Jia Newcombe Stephen R. Williams †W. Ian McDonald John B. Clark 《Journal of neurochemistry》1995,64(2):742-748
Abstract: Tissue from postmortem multiple sclerosis and normal control brains was extracted with perchloric acid and analysed using proton NMR spectroscopy. The content of N -acetyl-derived groups (the sum of N -acetylaspartate, acetate, and N -acetylaspartylglutamate) was decreased in multiple sclerosis plaques compared with normal control white matter (mean, 4.36 vs. 6.64 µmol/g wet weight). In normal appearing white matter adjacent to plaques a corresponding decrease was seen, with no change in white matter distant from plaques. A decrease in the content of total creatine was observed in multiple sclerosis plaques in comparison with normal control white matter (mean, 4.64 vs. 6.56 µmol/g wet weight), which correlated strongly with the decrease in N -acetyl-derived groups. No changes in other metabolites such as total choline or myo -inositol were seen. The decreases in content of N -acetyl-derived groups are in agreement with observations from in vivo proton NMR spectroscopy in multiple sclerosis patients. The decrease in total creatine is in contrast to most of the observations made in vivo where total creatine is assumed to be unchanged and metabolite levels are often expressed as a total creatine ratio. The use of a total creatine ratio in vivo could lead to an underestimation of reductions in N -acetylaspartate and an apparent increase in other metabolites in the multiple sclerosis lesion. 相似文献
4.
5.
6.
Brucella cell surface protein (BCSP31) is potentially useful for diagnosing brucellosis. We aimed to establish a monoclonal antibody
(MAb) against Brucella melitensis BCSP31 and to investigate its distribution in diagnosis. Soluble recombinant BCSP31 was successfully expressed and purified.
Two MAbs (1F1 and 1E5) against B. melitensis BCSP31, effective in detecting both recombinant and cellular proteins, were obtained and characterized. The MAbs did not
react with Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Mycobacterium tuberculosis, or Bacillus aeruginosus, but strongly reacted with BCSP31 and B. melitensis by ELISA and Western blot analysis. We also tested different Brucella species and brucellosis using the prepared anti-BCSP31 MAbs. BCSP31 and anti-BCSP31 MAbs may play important roles in future
research in diagnosing brucellosis. 相似文献
7.
The financing channels, investors and operators of urban rail transit are becoming more and more diversified, and public private partnership pattern has been increasingly suggested in financing and investment field of urban rail transit in China. The diversification of investors of urban rail transit will no doubt lead to the diversification of operators of urban rail transit network. To legitimately distribute the cooperation profits among operators, a model is developed based on passenger’s path choice behavior by considering travel period, travel time, transfer convenience and the comprehensive proportion of different service types provided by operators. In accordance with the features of urban rail transit network and origin-destination (OD) pairs of transferring among lines of different operators, a scheme of improved rail transit network is proposed. On the basis of the algorithm of breadth-first search and depth-first search, an algorithm of searching effective paths based on backtracking and traversing along the shortest path is established by considering the factor of transfer. Taking the example of Shenzhen’s rail transit network, three typical OD pairs are selected to measure and calculate, compare and analyze by six different conditions. The result shows that travel period, travel time, transfer convenience, and service types provided by operators exert great influence on the distribution of cooperation profits. Therefore, it is advisable to comprehensively consider all of these factors to improve the accuracy of cooperation profits distribution. Moreover, the proposed algorithm can search effective paths efficiently. 相似文献
8.
9.
ObjectiveWe investigated whether glutamate, NMDA receptors, and eukaryote elongation factor-2 kinase (eEF-2K)/eEF-2 regulate P-glycoprotein expression, and the effects of the eEF-2K inhibitor NH125 on the expression of P-glycoprotein in rat brain microvessel endothelial cells (RBMECs).MethodsCortex was obtained from newborn Wistar rat brains. After surface vessels and meninges were removed, the pellet containing microvessels was resuspended and incubated at 37°C in culture medium. Cell viability was assessed by the MTT assay. RBMECs were identified by immunohistochemistry with anti-vWF. P-glycoprotein, phospho-eEF-2, and eEF-2 expression were determined by western blot analysis. Mdr1a gene expression was analyzed by RT-PCR.ResultsMdr1a mRNA, P-glycoprotein and phospho-eEF-2 expression increased in L-glutamate stimulated RBMECs. P-glycoprotein and phospho-eEF-2 expression were down-regulated after NH125 treatment in L-glutamate stimulated RBMECs.ConclusionseEF-2K/eEF-2 should have played an important role in the regulation of P-glycoprotein expression in RBMECs. eEF-2K inhibitor NH125 could serve as an efficacious anti-multidrug resistant agent. 相似文献
10.