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   31993篇
  免费   2418篇
  国内免费   2240篇
  2024年   67篇
  2023年   437篇
  2022年   1077篇
  2021年   1770篇
  2020年   1167篇
  2019年   1558篇
  2018年   1427篇
  2017年   999篇
  2016年   1443篇
  2015年   2019篇
  2014年   2415篇
  2013年   2645篇
  2012年   2897篇
  2011年   2602篇
  2010年   1524篇
  2009年   1407篇
  2008年   1665篇
  2007年   1472篇
  2006年   1214篇
  2005年   951篇
  2004年   790篇
  2003年   749篇
  2002年   573篇
  2001年   494篇
  2000年   464篇
  1999年   440篇
  1998年   275篇
  1997年   259篇
  1996年   259篇
  1995年   235篇
  1994年   220篇
  1993年   153篇
  1992年   207篇
  1991年   180篇
  1990年   130篇
  1989年   99篇
  1988年   82篇
  1987年   70篇
  1986年   43篇
  1985年   47篇
  1984年   26篇
  1983年   31篇
  1982年   24篇
  1981年   22篇
  1980年   8篇
  1979年   6篇
  1978年   2篇
  1976年   2篇
  1969年   1篇
  1965年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Evolutionary analysis of Prodiamesinae has long been impeded by lack of information, and its phylogenetic relationship with Orthocladiinae remains questionable. Here, ten complete mitochondrial genomes (mitogenomes) of Orthocladiinae sensu lato were newly sequenced, including three Prodiamesinae species and seven Orthocladiinae species. Coupled with published mitogenomes, a total of 12 mitogenomes of Orthocladiinae sensu lato were selected for a comparative mitogenomic analysis and phylogenetic reconstruction. Mitogenomes of Orthocladiinae sensu lato are conserved in structure, and all genes arrange the same gene order as the ancestral insect mitogenome. Nucleotide composition is highly biased, and the control region displayed the highest A + T content. All protein-coding genes are under purifying selection, and the ATP8 evolves at the fastest rate. In addition, the mitogenomes of Orthocladiinae sensu lato are highly conserved, and they are practically useful for phylogenetic inference, suggesting a re-classification of Orthocladiinae by sinking Prodiamesinae as a subgroup of Orthocladiinae.  相似文献   
32.
In this article, we designed and synthesized two series of matrine analogs with ring-opening in the lactam portion of the molecule. Our in vitro cytotoxicity study showed that analog N-(3-bromophenyl)-4-[(1R,3aS,10aR,10bS)-decahydro-1H,4H-pyrido[3,2,1-ij][1,6]naphthyridin-1-yl]butanamide ( B11 ) with a meta-bromide on the phenyl ring displayed the best antiproliferative activity. Moreover, B11 induced cell cycle arrest in G1 phase and cell apoptosis in a dose-dependent manner in A549 cells. Molecular modeling revealed that B11 achieved a higher docking score compared to its precursor tert-butyl (1R,3aS,10aR,10bS)-1-[4-(3-bromoanilino)-4-oxobutyl]octahydro-1H,4H-pyrido[3,2,1-ij][1,6]naphthyridine-2(3H)-carboxylate ( A11 , an analog of B11 with a Boc group) and parent compound matrine, possibly because B11 formed a hydrogen bond with SER91 and a halogen bond with GLN320 on the binding site of annexin A2. Overall, we discovered the potential anticancer lead compound B11 , which can be used for further study both in vitro and in vivo.  相似文献   
33.
Dendritic cells (DCs) play an important role in the generation of anti-cancer immune responses, however there is evidence that DCs in cancer patients are dysfunctional. Lipid accumulation driven by tumor-derived factors has recently been shown to contribute to DC dysfunction in several human cancers, but has not yet been examined in mesothelioma. This study investigated if mesothelioma tumor cells and/or their secreted factors promote increases in DC lipid content and modulate DC function. Human monocyte-derived DCs (MoDCs) were exposed to human mesothelioma tumor cells and tumor-derived factors in the presence or absence of lipoproteins. The data showed that immature MoDCs exposed to mesothelioma cells or factors contained increased lipid levels relative to control DCs. Lipid accumulation was associated with reduced antigen processing ability (measured using a DQ OVA assay), upregulation of the co-stimulatory molecule, CD86, and production of the tolerogenic cytokine, IL-10. Increases in DC lipid content were further enhanced by co-exposure to mesothelioma-derived factors and triglyceride-rich lipoproteins, but not low-density lipoproteins. In vivo studies using a murine mesothelioma model showed that the lipid content of tumor-infiltrating CD4+CD8α- DCs, CD4-CD8α- DCs DCs and plasmacytoid DCs increased with tumor progression. Moreover, increasing tumor burden was associated with reduced proliferation of tumor-antigen-specific CD8+ T cells in tumor-draining lymph nodes. This study shows that mesothelioma promotes DC lipid acquisition, which is associated with altered activation status and reduced capacity to process and present antigens, which may impair the ability of DCs to generate effective anti mesothelioma T cell responses.  相似文献   
34.
Two mutants that grew faster than the wild-type (WT) strain under high light conditions were isolated from Synechocystis sp. strain PCC 6803 transformed with a transposon-bearing library. Both mutants had a tag in ssl1690 encoding NdhO. Deletion of ndhO increased the activity of NADPH dehydrogenase (NDH-1)-dependent cyclic electron transport around photosystem I (NDH-CET), while overexpression decreased the activity. Although deletion and overexpression of ndhO did not have significant effects on the amount of other subunits such as NdhH, NdhI, NdhK, and NdhM in the cells, the amount of these subunits in the medium size NDH-1 (NDH-1M) complex was higher in the ndhO-deletion mutant and much lower in the overexpression strain than in the WT. NdhO strongly interacts with NdhI and NdhK but not with other subunits. NdhI interacts with NdhK and the interaction was blocked by NdhO. The blocking may destabilize the NDH-1M complex and repress the NDH-CET activity. When cells were transferred from growth light to high light, the amounts of NdhI and NdhK increased without significant change in the amount of NdhO, thus decreasing the relative amount of NdhO. This might have decreased the blocking, thereby stabilizing the NDH-1M complex and increasing the NDH-CET activity under high light conditions.  相似文献   
35.
Journal of Plant Growth Regulation - With the increasing popularity of urban landscaping, there is a greater need to address iron deficiency and chlorosis in Cinnamomum camphora. Beneficial...  相似文献   
36.
37.
38.
39.
40.
Lin  Xiang  Lin  Shuang  Liu  Yuanlan  Zhao  Haiyan  Wang  Li  Hasi  Wuliji 《Plasmonics (Norwell, Mass.)》2018,13(5):1749-1758
Plasmonics - Large-scale ordered two-dimensional (2D) superlattices at oil/water interface were fabricated using single-crystal Au nanospheres (NSs) with different diameters as building blocks. A...  相似文献   
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