首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   115974篇
  免费   2204篇
  国内免费   2544篇
  2024年   34篇
  2023年   251篇
  2022年   732篇
  2021年   1275篇
  2020年   884篇
  2019年   1042篇
  2018年   12605篇
  2017年   11181篇
  2016年   8342篇
  2015年   2038篇
  2014年   1992篇
  2013年   2169篇
  2012年   6364篇
  2011年   14532篇
  2010年   13001篇
  2009年   9137篇
  2008年   10866篇
  2007年   12307篇
  2006年   1165篇
  2005年   1300篇
  2004年   1643篇
  2003年   1636篇
  2002年   1315篇
  2001年   734篇
  2000年   575篇
  1999年   426篇
  1998年   262篇
  1997年   290篇
  1996年   265篇
  1995年   242篇
  1994年   226篇
  1993年   165篇
  1992年   225篇
  1991年   182篇
  1990年   137篇
  1989年   116篇
  1988年   90篇
  1987年   107篇
  1986年   56篇
  1985年   56篇
  1984年   50篇
  1983年   47篇
  1982年   32篇
  1981年   19篇
  1972年   246篇
  1971年   274篇
  1965年   13篇
  1962年   24篇
  1944年   12篇
  1940年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.

Background

To examine the characteristics of oxidative stress in patients with acute kidney injury (AKI) and investigate the association between plasma nitrotyrosine levels and 90-day mortality in patients with AKI.

Methodology/Principal Findings

158 patients with hospital-acquired AKI were recruited to this prospective cohort study according to RIFLE (Risk, Injury, Failure, Lost or End Stage Kidney) criteria. Twelve critically ill patients without AKI and 15 age and gender-matched healthy subjects served as control. Plasma 3-nitrotyrosine was analyzed in relation to 90-day all cause mortality of patients with AKI. The patients with AKI were followed up for 90 days and grouped according to median plasma 3-nitrotyrosine concentrations. Highest 3-NT/Tyr was detected in patients with AKI compared with healthy subjects, and critically ill patients without AKI (ANOVA p<0.001). The 90-day survival curves of patients with high 3-NT/Tyr showed significant differences compared with the curves of individuals with low 3-NT/Tyr (p = 0.001 by log rank test). Multivariate analysis (Cox regression) revealed that 3-NT/Tyr (p = 0.025) was independently associated with mortality after adjustment for age, gender, sepsis and Acute Physiology and Chronic Health Evaluation (APACHE) II score.

Conclusions/Significance

There is excess plasma protein oxidation in patients with AKI, as evidenced by increased nitrotyrosine content. 3-NT/Tyr level was associated with mortality of AKI patients independent of the severity of illness.  相似文献   
952.
953.
The genus Amphibacillus was established in 1990, and seven additional species were described in the past two decades. Amphibacillus jilinensis Y1T is a facultatively anaerobic and alkaliphilic bacterium isolated from a soda lake in China. Here we describe the structural and genetic features of the draft genome about the type strain Y1T (3,831,075 bp, with a G+C content of 37.27%). This is the first genome report of the Amphibacillus genus.  相似文献   
954.
955.
956.
DNA sequencing using reversible terminators, as one sequencing by synthesis strategy, has garnered a great deal of interest due to its popular application in the second-generation high-throughput DNA sequencing technology. In this review, we provided its history of development, classification, and working mechanism of this technology. We also outlined the screening strategies for DNA polymerases to accommodate the reversible terminators as substrates during polymerization; particularly, we introduced the "REAP" method developed by us. At the end of this review, we discussed current limitations of this approach and provided potential solutions to extend its application.  相似文献   
957.
958.
The heats of formation (HOFs), energetic properties, and thermal stability of a series of 1,7-diamino-1,7-dinitrimino-2,4,6-trinitro-2,4,6-triazaheptane derivatives with different substituents, different numbers of substituents, and different original chains are found by using the DFT-B3LYP method. The results show that -NO2 or -NH2 is an effective substituent for increasing the gas-phase HOFs of the title compounds, especially -NO2 group. As the numbers of substitutents increase, their HOFs enhance obviously. Increasing the length of original chain is helpful for improving their HOFs. The substitution of -NO2 is useful for enhancing their detonation performances and the effects of the length of original chains on detonation properties are coupled with those of the substituents. An analysis of the BDE of the weakest bonds indicates that the substitution of the -NH2 groups and replacing the -NO2 groups of N-NO2 by the -NH2 groups are favorable for improving their thermal stability, while the substitution of -NO2 and increasing the length of original chain decrease their thermal stability. Considering the detonation performance and thermal stability, seven compounds may be considered as the potential candidates of high energy density compounds.  相似文献   
959.
Insulin-like growth factor-binding proteins (IGFBPs) control bioactivity and distribution of insulin-like growth factors (IGFs) through high-affinity complex of IGFBP and IGF. To get more insight into the binding interaction of IGF system, the site-directed mutagenesis and force-driving desorption methods were employed to study the interaction mechanism of IGFBP4 and IGF-I by molecular dynamics (MD) simulation. In IGF-I, residues Gly7 to Asp12 were found to be the hot spots and they mainly anchored on the N-domain of IGFBP4. The contact area, the shape and size of protein, the surroundings of the binding site, the hydrophobic and electrostatic interaction between the two proteins worked as a complex network to regulate the protein-protein interaction. It was also found that the unfolding of the helix was not inevitable in the mutant, and it could be regulated by careful selection of the substituted amino acid.
Figure
Binding network of IGF-I on the cavity surface of IGFBP4  相似文献   
960.
Experimental neural cell therapies, including donor neural stem/progenitor cells (NPCs) have been reported to offer beneficial effects on the recovery after an injury and to counteract inflammatory and degenerative processes in the central nervous system (CNS). The interplay between donor neural cells and the host CNS still to a large degree remains unclear, in particular in human allogeneic conditions. Here, we focused our studies on the interaction of human NPCs and microglia utilizing a co‐culture model. In co‐cultures, both NPCs and microglia showed increased survival and proliferation compared with mono‐cultures. In the presence of microglia, a larger subpopulation of NPCs expressed the progenitor cell marker nestin, whereas a smaller group of NPCs expressed the neural markers polysialylated neural cell adhesion molecule, A2B5 and glial fibrillary acidic protein compared with NPC mono‐cultures. Microglia thus hindered differentiation of NPCs. The presence of human NPCs increased microglial phagocytosis of latex beads. Furthermore, we observed that the expression of CD200 molecules on NPCs and the CD200 receptor protein on microglia was enhanced in co‐cultures, whereas the release of transforming growth factor‐β was increased suggesting anti‐inflammatory features of the co‐cultures. To conclude, the interplay between human allogeneic NPCs and microglia, significantly affected their respective proliferation and phenotype. Neural cell therapy including human donor NPCs may in addition to offering cell replacement, modulate host microglial phenotypes and functions to benefit neuroprotection and repair.  相似文献   
[首页] « 上一页 [91] [92] [93] [94] [95] 96 [97] [98] [99] [100] 下一页 » 末  页»
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号