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   61954篇
  免费   7629篇
  国内免费   6280篇
化学   12835篇
晶体学   969篇
力学   10962篇
综合类   1067篇
数学   31306篇
物理学   18724篇
  2024年   70篇
  2023年   614篇
  2022年   926篇
  2021年   1241篇
  2020年   1614篇
  2019年   1495篇
  2018年   1520篇
  2017年   2028篇
  2016年   2320篇
  2015年   1795篇
  2014年   3179篇
  2013年   4532篇
  2012年   3653篇
  2011年   4228篇
  2010年   3618篇
  2009年   4234篇
  2008年   4150篇
  2007年   4194篇
  2006年   3783篇
  2005年   3516篇
  2004年   2968篇
  2003年   2729篇
  2002年   2365篇
  2001年   1985篇
  2000年   1789篇
  1999年   1574篇
  1998年   1448篇
  1997年   1300篇
  1996年   1041篇
  1995年   901篇
  1994年   805篇
  1993年   631篇
  1992年   609篇
  1991年   478篇
  1990年   410篇
  1989年   299篇
  1988年   264篇
  1987年   202篇
  1986年   155篇
  1985年   209篇
  1984年   177篇
  1983年   101篇
  1982年   137篇
  1981年   116篇
  1980年   79篇
  1979年   79篇
  1978年   66篇
  1977年   65篇
  1976年   44篇
  1973年   28篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
51.
This article proposes a global, chaos-based procedure for the discretization of functionals of Brownian motion into functionals of a Poisson process with intensity λ>0. Under this discretization we study the weak convergence, as the intensity of the underlying Poisson process goes to infinity, of Poisson functionals and their corresponding Malliavin-type derivatives to their Wiener counterparts. In addition, we derive a convergence rate of O(λ?14) for the Poisson discretization of Wiener functionals by combining the multivariate Chen–Stein method with the Malliavin calculus. Our proposed sufficient condition for establishing the mentioned convergence rate involves the kernel functions in the Wiener chaos, yet we provide examples, especially the discretization of some common path dependent Wiener functionals, to which our results apply without committing the explicit computations of such kernels. To the best our knowledge, these are the first results in the literature on the universal convergence rate of a global discretization of general Wiener functionals.  相似文献   
52.
In this paper, we define the generalised relative operator entropy and investigate some of its properties such as subadditivity and homogeneity. As application of our result, we obtain the information inequality. In continuation, we establish some reverses of the operator entropy inequalities under certain conditions by using the Mond–Pe?ari? method.  相似文献   
53.
In this paper, we derive the non-singular Green’s functions for the unbounded Poisson equation in one, two and three dimensions using a spectral cut-off function approach to impose a minimum length scale in the homogeneous solution. The resulting non-singular Green’s functions are relevant to applications which are restricted to a minimum resolved length scale (e.g. a mesh size h) and thus cannot handle the singular Green’s function of the continuous Poisson equation. We furthermore derive the gradient vector of the non-singular Green’s function, as this is useful in applications where the Poisson equation represents potential functions of a vector field.  相似文献   
54.
55.
Under some assumptions we find a general solution of the factorization problem for a family of second order difference equations.  相似文献   
56.
57.
In this work, low‐moisture glycidyl azide polymer (GAP) was successfully prepared using a modified two‐step method. The modified method resembles the structure of the classical two‐step method, which is widely used to prepare the GAP. Firstly, epichlorohydrin (ECH) is polymerized into polyepicholorohydrin (PECH), which is subjected afterward to azidation step using sodium azide (NaN3). Interestingly, minimizing the water content in the final GAP product, which is a challenging when dealing with GAP as a rocket propellant binder, was effectively achieved by utilizing low boiling point solvents instead of the relatively high boiling point Dimethyl formamide (DMF), monitoring the volatility of ECH and controlling the exothermicity of the reaction. Prepared GAP samples were investigated using Fourier transformer infra‐red (FT‐IR), gel‐permeation chromatography (GPC) and elemental analysis apparatus (CHNS) were used to characterize the product. The moisture % in the final product was examined using the Karl‐Fisher Technique. Results showed the successful preparation of GAP with low water content (<0.01 %), high average molecular weight (> 2000 g · mol–1), 42.82 % nitrogen, a viscosity of 3484 cP at 20 °C, yield ranges between 95–98 % and a polydispersity index of 1.2. The prepared GAP is promising for replacement of the classical GAPs in the energetic materials applications.  相似文献   
58.
建立了一种细胞趋硬性迁移的理论模型和有限元分析框架,为连续变刚度人工基质的试验设计提供理论依据。考虑了细胞体的黏弹性属性,以及细胞与基质间的配受体动态反应过程,并以配受体合成时间为时间步长,将细胞运动方程化为静力学形式进行求解。对有限元过程提出一种动约束,便于消除其结构矩阵的奇异性。结果表明,模型能够模拟黏着斑内部力的快速波动现象,细胞的运动速度与观测数据一致,可有效模拟20,h以上的长时程问题。  相似文献   
59.
现有考核评价方式侧重期末考试而忽略过程考核,结合材料力学课程,探索一套注重过程考核的评价体系,综合评价学生对本课程的掌握程度,即将期末考试成绩在总评中的占比由70%降低至50%,平时作业、随堂测验、模块测验、实验考核和案例分析成绩各占比10%。新评价方式更加注重对学生学习过程的考核,使学生在整个课程学习过程中保持高度紧张感,提高学习的时效性和目的性,进而提高学生学习材料力学的热情和材料力学课堂教学效果。  相似文献   
60.
The current paper presents a thorough study on the pull-in instability of nanoelectromechanical rectangular plates under intermolecular, hydrostatic, and thermal actuations. Based on the Kirchhoff theory along with Eringen's nonlocal elasticity theory, a nonclassical model is developed. Using the Galerkin method(GM), the governing equation which is a nonlinear partial differential equation(NLPDE) of the fourth order is converted to a nonlinear ordinary differential equation(NLODE) in the time domain. Then, the reduced NLODE is solved analytically by means of the homotopy analysis method. At the end, the effects of model parameters as well as the nonlocal parameter on the deflection, nonlinear frequency, and dynamic pull-in voltage are explored.  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