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   33991篇
  免费   3263篇
  国内免费   2392篇
  39646篇
  2024年   202篇
  2023年   423篇
  2022年   822篇
  2021年   1328篇
  2020年   984篇
  2019年   1186篇
  2018年   1158篇
  2017年   806篇
  2016年   1198篇
  2015年   2023篇
  2014年   2247篇
  2013年   2492篇
  2012年   3037篇
  2011年   2832篇
  2010年   1693篇
  2009年   1505篇
  2008年   1833篇
  2007年   1645篇
  2006年   1506篇
  2005年   1239篇
  2004年   1156篇
  2003年   985篇
  2002年   892篇
  2001年   719篇
  2000年   657篇
  1999年   586篇
  1998年   326篇
  1997年   314篇
  1996年   297篇
  1995年   248篇
  1994年   265篇
  1993年   180篇
  1992年   320篇
  1991年   295篇
  1990年   246篇
  1989年   229篇
  1988年   192篇
  1987年   156篇
  1986年   146篇
  1985年   151篇
  1984年   142篇
  1983年   103篇
  1982年   90篇
  1980年   59篇
  1979年   75篇
  1978年   69篇
  1977年   58篇
  1976年   67篇
  1975年   63篇
  1974年   75篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Artificial solid‐electrolyte interphase (SEI) is one of the key approaches in addressing the low reversibility and dendritic growth problems of lithium metal anode, yet its current effect is still insufficient due to insufficient stability. Here, a new principle of “simultaneous high ionic conductivity and homogeneity” is proposed for stabilizing SEI and lithium metal anodes. Fabricated by a facile, environmentally friendly, and low‐cost lithium solid‐sulfur vapor reaction at elevated temperature, a designed lithium sulfide protective layer successfully maintains its protection function during cycling, which is confirmed by both simulations and experiments. Stable dendrite‐free cycling of lithium metal anode is realized even at a high areal capacity of 5 mAh cm?2, and prototype Li–Li4Ti5O12 cell with limited lithium also achieves 900 stable cycles. These findings give new insight into the ideal SEI composition and structure and provide new design strategies for stable lithium metal batteries.  相似文献   
62.
63.
Breast cancer (BC)-related mortality is associated with the potential metastatic properties of the primary breast tumors. The following study was conducted with the main focus on the effect of LINC00518 on the growth and metastasis of BC epithelial cells via the Wnt signaling pathway through regulation of the methylation of CDX2 gene. Initially, differentially expressed long intergenic non-protein coding RNAs (lincRNAs) related to BC were screened out in the Cancer Genome Atlas (TCGA) database, after which we detected the LINC00518 expression and localization in BC tissues and cells. Then the CDX2 positive expression and methylation level were identified. The targeting relationship of LINC00518 and CDX2, and binding methyltransferase in the promoter region were examined. BC epithelial cell proliferation, colony formation ability, invasion, migration and apoptosis were further evaluated. The lincRNA expression data related to BC downloaded from the TCGA database revealed that there was a high expression of LINC00518 in BC, and a negative correlation between LINC00518 and CDX2. In addition, LINC00518 promotes CDX2 methylation by recruiting DNA methyltransferase through activating the Wnt signaling pathway. The down-regulation of LINC00518 inhibited proliferation, invasion, migration, and EMT of BC epithelial cells while enhancing apoptosis. The inhibitory effects of LINC00518 down-regulation was reversed by CDX2 down-regulation. In conclusion, our findings revealed that down-regulation of LINC00518 might have the ability to suppress BC progression by up-regulating CDX2 expression through the reduction of methylation and blockade of the Wnt signaling pathway, resulting in the inhibition of proliferation and promotion of apoptosis of BC epithelial cells.  相似文献   
64.
65.
66.
67.
Photosynthesis Research - The engineering process of C4 photosynthesis into C3 plants requires an increased activity of phosphoenolpyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll...  相似文献   
68.
Antipredator behaviours and the ability to appropriately assess predation risk contribute to increased fitness. Predator avoidance can be costly; however, so we expect prey to most strongly avoid predators that pose the greatest risk (i.e., prey should show threat sensitivity). For invasive species, effectively assessing the relative risk posed by predators in the new environment may help them establish in new environments. We examined the antipredator behaviour of introduced Asian house geckos, Hemidactylus frenatus (Schlegel), by determining if they avoided shelters scented with the chemical cues of native predatory snakes (spotted pythons, Antaresia maculosa [Peters]; brown tree snakes, Boiga irregularis [Merrem]; common tree snakes, Dendrelaphis punctulata [Grey]; and carpet pythons, Morelia spilota [Lacépède]). We also tested if Asian house geckos collected from vegetation vs. anthropogenic substrates (buildings) responded differently to the chemical cues of predatory snakes. Asian house geckos did not show a generalised antipredator response, that is, they did not respond to the chemical cues of all snakes in the same way. Asian house geckos avoided the chemical cues of carpet pythons more strongly than those of other snake species, providing some support for the threat‐sensitivity hypothesis. There was no difference in the antipredator behaviour of Asian house geckos collected from buildings vs. natural vegetation, suggesting that individuals that have invaded natural habitats have not changed their antipredator behaviour compared to urban individuals. Overall, we found some evidence indicating Asian house geckos are threat‐sensitive to some Australian predacious snakes.  相似文献   
69.
70.
The use of natural compounds to potentiate the effect of drugs and lower their adverse effects is an active area of research. The objective is to determine the effect of combined blueberry extracts (BE) and oxaliplatin (OX) in colon cancer cells. The results demonstrated that treatments of BE/OX showed inhibitory effects on HCT-116 cell and nontoxic effect on CCD-18Co normal colon cells. Flow cytometry analysis indicated that treatment with the BE, OX or in combination could induce G0/G1 cell cycle arrest, apoptosis, increase of reactive oxygen species, and induce loss of mitochondrial membrane potential in HCT-116 cells. Furthermore, after treatments, the expression of inflammatory cytokines was decreased, cyclin D1 and CDK4 were decreased; caspases-3 and 9 were activated; the Akt/Bad/Bcl-2 pathway was modulated. Moreover, the combination treatment had a considerably higher growth inhibitory effect on human colon cancer HCT-116 cells than that of BE or oxaliplatin alone. Our results showed that BE increased the anticolon cancer effect of OX making it an attractive strategy as adjuvant therapy to potentially reduce the adverse side effects associated with chemotherapeutic drugs.  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