全文获取类型
收费全文 | 48227篇 |
免费 | 4478篇 |
国内免费 | 4600篇 |
出版年
2024年 | 34篇 |
2023年 | 621篇 |
2022年 | 809篇 |
2021年 | 2474篇 |
2020年 | 1790篇 |
2019年 | 2316篇 |
2018年 | 2147篇 |
2017年 | 1614篇 |
2016年 | 2147篇 |
2015年 | 3093篇 |
2014年 | 3719篇 |
2013年 | 3973篇 |
2012年 | 4567篇 |
2011年 | 4207篇 |
2010年 | 2637篇 |
2009年 | 2337篇 |
2008年 | 2669篇 |
2007年 | 2327篇 |
2006年 | 2007篇 |
2005年 | 1723篇 |
2004年 | 1503篇 |
2003年 | 1328篇 |
2002年 | 1189篇 |
2001年 | 922篇 |
2000年 | 767篇 |
1999年 | 710篇 |
1998年 | 434篇 |
1997年 | 414篇 |
1996年 | 375篇 |
1995年 | 363篇 |
1994年 | 332篇 |
1993年 | 247篇 |
1992年 | 340篇 |
1991年 | 229篇 |
1990年 | 193篇 |
1989年 | 197篇 |
1988年 | 120篇 |
1987年 | 103篇 |
1986年 | 81篇 |
1985年 | 87篇 |
1984年 | 37篇 |
1983年 | 43篇 |
1982年 | 31篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1977年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
1.
Evaluation of diagnostic performance is typically based on the receiver operating characteristic (ROC) curve and the area under the curve (AUC) as its summary index. The partial area under the curve (pAUC) is an alternative index focusing on the range of practical/clinical relevance. One of the problems preventing more frequent use of the pAUC is the perceived loss of efficiency in cases of noncrossing ROC curves. In this paper, we investigated statistical properties of comparisons of two correlated pAUCs. We demonstrated that outside of the classic model there are practically reasonable ROC types for which comparisons of noncrossing concave curves would be more powerful when based on a part of the curve rather than the entire curve. We argue that this phenomenon stems in part from the exclusion of noninformative parts of the ROC curves that resemble straight‐lines. We conducted extensive simulation studies in families of binormal, straight‐line, and bigamma ROC curves. We demonstrated that comparison of pAUCs is statistically more powerful than comparison of full AUCs when ROC curves are close to a “straight line”. For less flat binormal ROC curves an increase in the integration range often leads to a disproportional increase in pAUCs’ difference, thereby contributing to an increase in statistical power. Thus, efficiency of differences in pAUCs of noncrossing ROC curves depends on the shape of the curves, and for families of ROC curves that are nearly straight‐line shaped, such as bigamma ROC curves, there are multiple practical scenarios in which comparisons of pAUCs are preferable. 相似文献
2.
3.
4.
5.
Effect of fertilizers on Cd accumulation and subcellular distribution of two cosmos species (Cosmos sulphureus and Cosmos bipinnata) 总被引:1,自引:0,他引:1
Addition of fertilizer amendments is regarded as an ideal approach to enhancing phytoextraction. However, there is little information available on the influence of common fertilizers on Cd accumulation of two newly reported Cd accumulators, Cosmos sulphureus and Cosmos bipinnata (C. sulphureus and C. bipinnata). The effects of N (CO(NH2)2), NP (CO(NH2)2 + Ca(H2PO4)2), and NPK (CO(NH2)2 + Ca(H2PO4)2 + KCl) fertilizers on Cd accumulation and subcellular distribution of C. sulphureus and C. bipinnata were studied in a 70-d pot experiment. The results showed that Cd uptake of C. sulphureus and C. bipinnata with NPK fertilizer was significantly higher than control, N, and NP fertilizers, especially 3.8- and 4.7-fold higher than control (p < 0.05). Compared with C. bipinnata, C. sulphureus achieved higher biomass and Cd uptake in aboveground parts under fertilizer treatments, especially NPK fertilizer. The Cd subcellular distribution revealed that segregation of Cd to Cd-rich granules (MRG) might play an important role in Cd detoxification in both species. C. sulphureus is more likely than C. bipinnata to separate the Cd in MRG and reduce the partition in the heat-denatured protein fraction, especially with NPK fertilizer. Therefore, C. sulphureus combined with NPK fertilizers could be an effective method to remediate Cd-polluted farmland soils in China. 相似文献
6.
7.
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
8.
9.
10.
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