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   26487篇
  免费   4312篇
  国内免费   2714篇
化学   18892篇
晶体学   336篇
力学   1584篇
综合类   132篇
数学   3041篇
物理学   9528篇
  2024年   42篇
  2023年   540篇
  2022年   644篇
  2021年   876篇
  2020年   1128篇
  2019年   1110篇
  2018年   905篇
  2017年   821篇
  2016年   1285篇
  2015年   1247篇
  2014年   1419篇
  2013年   1910篇
  2012年   2500篇
  2011年   2574篇
  2010年   1697篇
  2009年   1610篇
  2008年   1752篇
  2007年   1586篇
  2006年   1427篇
  2005年   1192篇
  2004年   876篇
  2003年   684篇
  2002年   642篇
  2001年   477篇
  2000年   461篇
  1999年   527篇
  1998年   440篇
  1997年   440篇
  1996年   460篇
  1995年   359篇
  1994年   308篇
  1993年   234篇
  1992年   236篇
  1991年   201篇
  1990年   170篇
  1989年   142篇
  1988年   95篇
  1987年   109篇
  1986年   88篇
  1985年   82篇
  1984年   47篇
  1983年   43篇
  1982年   35篇
  1981年   18篇
  1980年   11篇
  1979年   9篇
  1978年   6篇
  1976年   9篇
  1975年   11篇
  1936年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
984.
Composite catalyst honeycombs without sintering were prepared via kneading, mulling, extrusion molding, and solidifying at room temperature with the magnesite oxychloride gels modified by nano-rice husk ash (RHA) as a solidifying agent. The effects of nano-RHA and composite water-resistant agents on the water resistance of magnesite materials were studied. The solidification of the modified magnesite gels on TiO2 catalyst honeycombs was analyzed. The experiments show that the proportional addition of nano-RHA markedly increases the water resistance of magnesite materials without reducing the bending strength, and the softening coefficient increases from 0.29 to 0.78. With further addiition of the complex water-resistant agents, the softening coefficient increases from 0.78 to 0.97. The optimal mass ratio of MgO in the solidifying agent to TiO2 is 4:1, and the bending strength of unsintered catalyst honeycombs is 11.46 MPa. The desulfurization rate and denitration rate of this composite catalyst honeycomb on simulation smoke was 97 and 65 %, respectively, in 3 h.  相似文献   
985.
A series of novel 1,2,3-benzotriazin-4-one derivatives were designed,synthesized and their inhibitory activities against leulcotriene A_4 hydrolase aminopeptidase in vitro were evaluated.Many compounds showed moderate to good activities at the concentration of 10 μmol/L.Among them,compound Ⅳ-16 exhibited the highest inhibitory activity up to 80.6% with an IC_(50) of 1.30 ± 0.20 μmol/L The compound Ⅳ-16 was also tested the proliferation inhibitory activities in THP1 human AML cell line and its binding model with LTA_4H enzyme by molecular docking was studied.It indicated that 1,2,3-benzotriazin-4-one was a promising scaffold for further study.The relationship between structure and inhibitory activity was also preliminarily discussed.  相似文献   
986.
An interface‐capturing method based on mass fraction is developed to solve the Riemann problem in multi‐component compressible flow. Equations of mass fraction with modified form, which is derived from conservative equations of mass, are employed here to capture the interface. By introducing mass fraction into Euler equations system, as well as other conservative coefficients, a quasi‐conservative numerical model is created. Numerical examples show that the mass fraction model performs well not only in multi‐component fluids modeled by simple stiffened gas equation of state (EOS) but also in that modeled by complex Mie–Grüneisen EOS. Moreover, the mass fraction model is applied to Riemann problem with piecewise EOS; the expression of which depends on density. It is found that the mass fraction model can well adapt to the analytic change in piecewise EOS and produce accuracy solutions with fewer unknown quantities, and the model can be easily extended to m‐component fluid mixture by using only m + 4 equations with no additional conditions. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
987.
Under the influence of thiocyanate anions (SCN?) and cetyltrimethyl ammonium bromide (CTAB), NiS flower-like architectures were successfully synthesized by a one-step hydrothermal method. The synthesized flower-like architectures, with a multilayered and highly ordered texture, have diameters of several micrometers. X-ray powder diffraction (XRD) shows that the NiS flower-like architectures are rhombohedral crystalline. On the basis of condition-dependent experiments, the diffusion-limited aggregation (DLA) model and cage effect were used to explain the growth process of rhombohedral crystalline NiS flower-like architectures. Magnetic measurements showed that the coercivity (Hc) of the as-obtained NiS flower-like architectures was 102.14 Oe.  相似文献   
988.
989.
990.
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