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   18892篇
  免费   1696篇
  国内免费   1427篇
  22015篇
  2023年   242篇
  2022年   532篇
  2021年   895篇
  2020年   605篇
  2019年   687篇
  2018年   726篇
  2017年   541篇
  2016年   703篇
  2015年   1150篇
  2014年   1266篇
  2013年   1365篇
  2012年   1563篇
  2011年   1500篇
  2010年   983篇
  2009年   835篇
  2008年   909篇
  2007年   877篇
  2006年   773篇
  2005年   661篇
  2004年   621篇
  2003年   545篇
  2002年   515篇
  2001年   394篇
  2000年   391篇
  1999年   362篇
  1998年   174篇
  1997年   162篇
  1996年   158篇
  1995年   122篇
  1994年   146篇
  1993年   90篇
  1992年   155篇
  1991年   147篇
  1990年   124篇
  1989年   99篇
  1988年   82篇
  1987年   96篇
  1986年   83篇
  1985年   92篇
  1984年   48篇
  1983年   49篇
  1982年   48篇
  1981年   37篇
  1980年   37篇
  1979年   52篇
  1978年   41篇
  1977年   45篇
  1976年   33篇
  1975年   35篇
  1974年   44篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
Tumour‐derived exosomes have been shown to induce pre‐metastatic niche formation, favoring metastatic colonization of tumour cells, but the underlying molecular mechanism is still not fully understood. In this study, we showed that exosomes derived from the LLC cells could indeed significantly enhance their intrapulmonary colonization. Circulating LLC‐derived exosomes were mainly engulfed by lung fibroblasts and led to the NF‐κB signalling activation. Further studies indicated that the exosomal miR‐3473b was responsible for that by hindering the NFKB inhibitor delta's (NFKBID) function. Blocking miR‐3473b could reverse the exosome‐mediated NF‐κB activation of fibroblasts and decrease intrapulmonary colonization of lung tumour cells. Together, this study demonstrated that the miR‐3473b in exosomes could mediate the interaction of lung tumour cells and local fibroblasts in metastatic sites and, therefore, enhance the metastasis of lung tumour cells.  相似文献   
172.
Serpinb6b is a novel member of Serpinb family and found in germ and somatic cells of mouse gonads, but its physiological function in uterine decidualization remains unclear. The present study revealed that abundant Serpinb6b was noted in decidual cells, and advanced the proliferation and differentiation of stromal cells, indicating a creative role of Serpinb6b in uterine decidualization. Further analysis found that Serpinb6b modulated the expression of Mmp2 and Mmp9. Meanwhile, Serpinb6b was identified as a target of Bmp2 regulation in stromal differentiation. Treatment with rBmp2 resulted in an accumulation of intracellular cAMP level whose function in this differentiation program was mediated by Serpinb6b. Addition of PKA inhibitor H89 impeded the Bmp2 induction of Serpinb6b, whereas 8‐Br‐cAMP rescued the defect of Serpinb6b expression elicited by Bmp2 knock‐down. Attenuation of Serpinb6b greatly reduced the induction of constitutive Wnt4 activation on stromal cell differentiation. By contrast, overexpression of Serpinb6b prevented this inhibition of differentiation process by Wnt4 siRNA. Moreover, blockage of Wnt4 abrogated the up‐regulation of cAMP on Serpinb6b. Collectively, Serpinb6b mediates uterine decidualization via Mmp2/9 in response to Bmp2/cAMP/PKA/Wnt4 pathway.  相似文献   
173.
174.
Sirtuin 5 (SIRT5) is a NAD+‐dependent class III protein deacetylase, and its role in prostate cancer has not yet been reported. Therefore, to explore the diagnosis and treatment of prostate cancer, we investigated the effect of SIRT5 on prostate cancer. Sirtuin 5 was assessed by immunohistochemistry in 57 normal and cancerous prostate tissues. We found that the tissue expression levels of SIRT5 in patients with Gleason scores ≥7 were significantly different from those in patients with Gleason scores <7 (P < .05, R > 0). Further, mass spectrometry and pathway screening experiments showed that SIRT5 regulated the activity of the mitogen‐activated protein kinase (MAPK) pathway, which in turn modulated the expression of MMP9 and cyclin D1. Being a substrate of SIRT5, acetyl‐CoA acetyltransferase 1 (ACAT1) was regulated by SIRT5. SIRT5 also regulated MAPK pathway activity through ACAT1. These results revealed that SIRT5 promoted the activity of the MAPK pathway through ACAT1, increasing the ability of prostate cancer cells to proliferate, migrate and invade. Overall, these results indicate that SIRT5 expression is closely associated with prostate cancer progression. Understanding the underlying mechanism may provide new targets and methods for the diagnosis and treatment of the disease.  相似文献   
175.
176.
Formononetin is a natural isoflavone compound found mainly in Chinese herbal medicines such as astragalus and red clover. It is considered to be a typical phytooestrogen. In our previous experiments, it was found that formononetin has a two‐way regulatory effect on endothelial cells (ECs): low concentrations promote the proliferation of ECs and high concentrations have an inhibitory effect. To find a specific mechanism of action and provide a better clinical effect, we performed a structural transformation of formononetin and selected better medicinal properties for formononetin modifier J1 and J2 from a variety of modified constructs. The MTT assay measured the effects of drugs on human umbilical vein endothelial cell (HUVEC) activity. Scratch and transwell experiments validated the effects of the drugs on HUVEC migration and invasion. An in vivo assessment effect of the drugs on ovariectomized rats. Long‐chain non‐coding RNA for EWSAT1, which is abnormally highly expressed in HUVEC, was screened by gene chip, and the effect of the drug on its expression was detected by PCR after the drug was applied. The downstream factors and their pathways were analysed, and the changes in the protein levels after drug treatment were evaluated by Western blot. In conclusion, the mechanism of action of formononetin, J1 and J2 on ECs may be through EWSAT1‐TRAF6 and its downstream pathways.  相似文献   
177.
Rational design and construction of bifunctional electrocatalysts with excellent activity and durability is imperative for water splitting. Herein, a novel top‐down strategy to realize a hierarchical branched Mo‐doped sulfide/phosphide heterostructure (Mo‐Ni3S2/NixPy hollow nanorods), by partially phosphating Mo‐Ni3S2/NF flower clusters, is proposed. Benefitting from the optimized electronic structure configuration, hierarchical branched hollow nanorod structure, and abundant heterogeneous interfaces, the as‐obtained multisite Mo‐Ni3S2/NixPy/NF electrode has remarkable stability and bifunctional electrocatalytic activity in the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) in 1 m KOH solutions. It possesses an extremely low overpotential of 238 mV at the current density of 50 mA cm?2 for OER. Importantly, when assembled as anode and cathode simultaneously, it merely requires an ultralow cell voltage of 1.46 V to achieve the current density of 10 mA cm?2, with excellent durability for over 72 h, outperforming most of the reported Ni‐based bifunctional materials. Density functional theory results further confirm that the doped heterostructure can synergistically optimize Gibbs free energies of H and O‐containing intermediates (OH*, O*, and OOH*) during HER and OER processes, thus accelerating the catalytic kinetics of electrochemical water splitting. This work demonstrates the importance of the rational combination of metal doping and interface engineering for advanced catalytic materials.  相似文献   
178.
The relatively low capacity and capacity fade of spinel LiMn2O4 (LMO) limit its application as a cathode material for lithium‐ion batteries. Extending the potential window of LMO below 3 V to access double capacity would be fantastic but hard to be realized, as it will lead to fast capacity loss due to the serious Jahn–Teller distortion. Here using experiments combined with extensive ab initio calculations, it is proved that there is a cooperative effect among individual Jahn–Teller distortions of Mn3+O6 octahedrons in LMO, named as cooperative Jahn–Teller distortion (CJTD) in the text, which is the difficulty to access the capacity beyond one lithium intercalation. It is further proposed that the cationic disordering (excess Li at Mn sites and Li/Mn exchange) can intrinsically suppress the CJTD of Mn3+O6 octahedrons. The cationic disordering can break the symmetry of Mn3+ arrangements to disrupt the correlation of distortions arising from individual JT centers and prevent the Mn3+? O bonds distorting along one direction. Interestingly, with the suppressed CJTD, the original octahedral vacancies in spinel LMO are activated and can serve as extra Li‐ion storage sites to access the double capacity with good reversible cycling stability in microsized LMO.  相似文献   
179.
Sleep and Biological Rhythms - To examine the psychometric properties of the Sleep Condition Indicator (SCI) using different psychometric approaches [including classical test theory, Rasch models,...  相似文献   
180.
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