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   41883篇
  免费   3490篇
  国内免费   2394篇
  47767篇
  2024年   192篇
  2023年   497篇
  2022年   1166篇
  2021年   1969篇
  2020年   1252篇
  2019年   1509篇
  2018年   1412篇
  2017年   1095篇
  2016年   1624篇
  2015年   2428篇
  2014年   2851篇
  2013年   3091篇
  2012年   3586篇
  2011年   3398篇
  2010年   1944篇
  2009年   1794篇
  2008年   2087篇
  2007年   1867篇
  2006年   1604篇
  2005年   1420篇
  2004年   1199篇
  2003年   1053篇
  2002年   905篇
  2001年   851篇
  2000年   740篇
  1999年   716篇
  1998年   435篇
  1997年   464篇
  1996年   441篇
  1995年   390篇
  1994年   378篇
  1993年   308篇
  1992年   441篇
  1991年   383篇
  1990年   331篇
  1989年   246篇
  1988年   236篇
  1987年   198篇
  1986年   141篇
  1985年   184篇
  1984年   121篇
  1983年   104篇
  1982年   80篇
  1981年   60篇
  1980年   55篇
  1979年   72篇
  1978年   66篇
  1977年   46篇
  1976年   48篇
  1973年   48篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Brucella melitensis infection causes acute necrotizing inflammation in pregnant animals; however, the pathophysiological mechanisms leading to placentitis are unknown. Here, we demonstrate that high‐mobility group box 1 (HMGB1) acts as a mediator of placenta inflammation in Bmelitensis‐infected pregnant mice model. HMGB1 levels were increased in trophoblasts or placental explant during B. melitensis infection. Inhibition of HMGB1 activity with neutralising antibody significantly reduced the secretion of inflammatory cytokines in B. melitensis‐infected trophoblasts or placenta, whereas administration of recombinant HMGB1 (rHMGB1) increased the inflammatory response. Mechanistically, this decreased inflammatory response results from inhibition of HMGB1 activity, which cause the suppression of both mitogen‐activated protein kinases and nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) activation. Moreover, neutralising antibody to HMGB1 prevented B. melitensis infection‐induced activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in trophoblasts. In contrast, in vitro stimulation of trophoblasts with rHMGB1 caused activation of NADPH oxidase and increased the production of ROS, which contributes to high bacterial burden within trophoblasts or placenta. In vivo, treatment with anti‐HMGB1 antibody increases the number of Brucella survival within placenta in B. melitensis‐infected pregnant mice but successfully reduced the severity of placentitis and abortion.  相似文献   
63.
64.
Construction of well‐defined metal–organic framework precursor is vital to derive highly efficient transition metal–carbon‐based electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting. Herein, a novel strategy involving an in situ transformation of ultrathin cobalt layered double hydroxide into 2D cobalt zeolitic imidazolate framework (ZIF‐67) nanosheets grafted with 3D ZIF‐67 polyhedra supported on the surface of carbon cloth (2D/3D ZIF‐67@CC) precursor is proposed. After a low‐temperature pyrolysis, this precursor can be further converted into hybrid composites composed of ultrafine cobalt nanoparticles embedded within 2D N‐doped carbon nanosheets and 3D N‐doped hollow carbon polyhedra (Co@N‐CS/N‐HCP@CC). Experimental and density functional theory calculations results indicate that such composites have the advantages of a large number of accessible active sites, accelerated charge/mass transfer ability, the synergistic effect of components as well as an optimal water adsorption energy change. As a result, the obtained Co@N‐CS/N‐HCP@CC catalyst requires overpotentials of only 66 and 248 mV to reach a current density of 10 mA cm?2 for HER and OER in 1.0 m KOH, respectively. Remarkably, it enables an alkali‐electrolyzer with a current density of 10 mA cm?2 at a low cell voltage of 1.545 V, superior to that of the IrO2@CC||Pt/C@CC couple (1.592 V).  相似文献   
65.
66.
Alternative chemicals to diverse fossil-fuel-based products is urgently needed to mitigate the adverse impacts of fossil fuel depletion on human development. To this end, researchers have focused on the production of biochemical from readily available and affordable waste biomass. This is consistent with current guidelines for sustainable development and provides great advantages related to economy and environment. The search for suitable biochemical products is in progress worldwide. Therefore, this review recommends a biochemical (i.e., medium chain carboxylic acids (MCCAs)) utilizing an emerging biotechnological production platform called the chain elongation (CE) process. This work covers comprehensive introduction of the CE mechanism, functional microbes, available feedstock types and corresponding utilization strategies, major methods to enhance the performance of MCCAs production, and the challenges that need to be addressed for practical application. This work is expected to provide a thorough understanding of the CE technology, to guide and inspire researchers to solve existing problems in depth, and motivate large-scale MCCAs production.  相似文献   
67.
Molecular dynamics simulations (MDS) are employed to investigate the effects of interatomic interaction and nanostructure on wettability of water on a copper plate. In the nano scale, these simulation results showed that the contact angle gradually increases with the decreasing of the reaction parameters, which results in the decreasing of free energy on the solid-liquid interface. Therefore, it leads to that the hydrophilic material is turned into hydrophobic, which fits the results that the wettability is changed by low surface energy materials in macro scale. Furthermore, the contact angles on smooth and rough surfaces are 87° and 71.6°, respectively. That is to say that the hydrophilic will increase for hydrophilic material due to the existence of one-layer structure; it agrees with the experimental results in macro scale.  相似文献   
68.
69.
Chromatin conformation,localization,and dynamics are crucial regulators of cellular behaviors. Although fluorescence in situ hybridization-based techniques have been widely utilized for investigating chromatin architectures in healthy and diseased states,the requirement for cell fix-ation precludes the comprehensive dynamic analysis necessary to fully understand chromatin activ-ities. This has spurred the development and application of a variety of imaging methodologies for visualizing single chromosomal loci in the native cellular context. In this review,we describe currently-available approaches for imaging single genomic loci in cells,with special focus on clus-tered regularly interspaced short palindromic repeats (CRISPR)-based imaging approaches. In addition,we discuss some of the challenges that limit the application of CRISPR-based genomic imaging approaches,and potential solutions to address these challenges. We anticipate that,with continued refinement of CRISPR-based imaging techniques,significant understanding can be gained to help decipher chromatin activities and their relevance to cellular physiology and pathogenesis.  相似文献   
70.
Chen  Qian  Xu  Lixia  Du  Tianjiao  Hou  Yongxin  Fan  Weijia  Wu  Qiaoli  Yan  Hua 《Neurochemical research》2019,44(11):2470-2481
Neurochemical Research - Neuroinflammation and brain edema are major complications in the pathophysiology of surgical brain injury (SBI). Programmed death-ligand 1 (PD-L1), an immune inhibitory...  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