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   103389篇
  免费   10043篇
  国内免费   6701篇
化学   27952篇
晶体学   1894篇
力学   8037篇
综合类   790篇
数学   27372篇
物理学   54088篇
  2023年   397篇
  2022年   682篇
  2021年   984篇
  2020年   1451篇
  2019年   1632篇
  2018年   1557篇
  2017年   1538篇
  2016年   1568篇
  2015年   1223篇
  2014年   2428篇
  2013年   3638篇
  2012年   2591篇
  2011年   3404篇
  2010年   3765篇
  2009年   8515篇
  2008年   9426篇
  2007年   7878篇
  2006年   7069篇
  2005年   5072篇
  2004年   4850篇
  2003年   4863篇
  2002年   5526篇
  2001年   4317篇
  2000年   4031篇
  1999年   3800篇
  1998年   3177篇
  1997年   2243篇
  1996年   1996篇
  1995年   2492篇
  1994年   2412篇
  1993年   1829篇
  1992年   1323篇
  1991年   1000篇
  1990年   824篇
  1989年   712篇
  1988年   677篇
  1987年   524篇
  1985年   1068篇
  1984年   744篇
  1983年   558篇
  1982年   730篇
  1981年   851篇
  1980年   747篇
  1979年   595篇
  1978年   609篇
  1977年   565篇
  1976年   555篇
  1975年   324篇
  1974年   361篇
  1973年   484篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
21.
22.
23.
Multistrain diseases, which are infected through individual contacts, pose severe public health threat nowadays. In this paper, we build competitive and mutative two‐strain edge‐based compartmental models using probability generation function (PGF) and pair approximation (PA). Both of them are ordinary differential equations. Their basic reproduction numbers and final size formulas are explicitly derived. We show that the formula gives a unique positive final epidemic size when the reproduction number is larger than unity. We further consider competitive and mutative multistrain diseases spreading models and compute their basic reproduction numbers. We perform numerical simulations that show some dynamical properties of the competitive and mutative two‐strain models.  相似文献   
24.
This paper develops a framework to deal with the unconditional superclose analysis of nonlinear parabolic equation. Taking the finite element pair $Q_{11}/Q_{01} × Q_{10}$ as an example, a new mixed finite element method (FEM) is established and the $τ$ -independent superclose results of the original variable $u$ in $H^1$-norm and the flux variable $\mathop{q} \limits ^{\rightarrow}= −a(u)∇u$ in $L^2$-norm are deduced ($τ$ is the temporal partition parameter). A key to our analysis is an error splitting technique, with which the time-discrete and the spatial-discrete systems are constructed, respectively. For the first system, the boundedness of the temporal errors is obtained. For the second system, the spatial superclose results are presented unconditionally, while the previous literature always only obtain the convergent estimates or require certain time step conditions. Finally, some numerical results are provided to confirm the theoretical analysis, and show the efficiency of the proposed method.  相似文献   
25.
We consider the Griffith fracture model in two spatial dimensions, and prove existence of strong minimizers, with closed jump set and continuously differentiable deformation fields. One key ingredient, which is the object of the present paper, is a generalization to the vectorial situation of the decay estimate by De Giorgi, Carriero, and Leaci. This is based on replacing the coarea formula by a method to approximate SBDp functions with small jump set by Sobolev functions, and is restricted to two dimensions. The other two ingredients will appear in companion papers and consist respectively in regularity results for vectorial elliptic problems of the elasticity type and in a method to approximate in energy GSBDp functions by SBVp ones.  相似文献   
26.
27.
28.
29.
30.
Diabetes mellitus (DM) is the fastest growing metabolic disorder in the world. Recently, more attention is paid to the study of natural products due to side effects of synthetic drugs. Stevia rebaudiana (Bertoni) is considered an encouraging starting point for the antidiabetic lead development. In the present study, the in vitro α-amylase inhibitory activity of the extracts of S. rebaudiana is investigated. In order to understand the molecular mechanism and future pharmacophore development, in silico study of secondary metabolites isolated from S. rebaudiana was carried out. Results indicated that water extract shows highest α-amylase inhibitory activity as compared to other extracts. Moreover, compound 20 (rebaudioside A) which has been previously reported and isolated from water extract showed the impressive binding profile with α-amylase. Therefore, our study suggests that S. rebaudiana could be used in the development of therapeutic drugs for the treatment of diabetes.  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