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   174784篇
  免费   16948篇
  国内免费   12107篇
化学   93975篇
晶体学   1852篇
力学   11949篇
综合类   666篇
数学   43470篇
物理学   51927篇
  2024年   247篇
  2023年   2000篇
  2022年   3585篇
  2021年   3575篇
  2020年   4116篇
  2019年   3878篇
  2018年   13092篇
  2017年   12643篇
  2016年   10389篇
  2015年   5455篇
  2014年   6066篇
  2013年   7838篇
  2012年   12664篇
  2011年   19330篇
  2010年   11927篇
  2009年   11966篇
  2008年   12906篇
  2007年   14260篇
  2006年   5773篇
  2005年   5888篇
  2004年   5095篇
  2003年   4821篇
  2002年   3624篇
  2001年   2455篇
  2000年   2226篇
  1999年   2199篇
  1998年   1922篇
  1997年   1701篇
  1996年   1745篇
  1995年   1480篇
  1994年   1313篇
  1993年   1094篇
  1992年   953篇
  1991年   838篇
  1990年   700篇
  1989年   560篇
  1988年   434篇
  1987年   395篇
  1986年   393篇
  1985年   308篇
  1984年   230篇
  1983年   189篇
  1982年   166篇
  1981年   116篇
  1980年   105篇
  1979年   68篇
  1978年   56篇
  1973年   42篇
  1914年   45篇
  1909年   41篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
In this paper, we study an existence theorem of systems of generalized quasivariational inclusions problem. By this result, we establish the existence theorems of solutions of systems of generalized equations, systems of generalized vector quasiequilibrium problem, collective variational fixed point, systems of generalized quasiloose saddle point, systems of minimax theorem, mathematical program with systems of variational inclusions constraints, mathematical program with systems of equilibrium constraints and systems of bilevel problem and semi-infinite problem with systems of equilibrium problem constraints. This research was supported by the National Science Council of the Republic of China.  相似文献   
932.
In this paper, continuous wave Yb3+-doped double-clad fiber lasers (DCFLs) with linear-cavity are investigated theoretically and numerically using the rate equations. Under the steady state conditions, the simplified analytic solutions of Yb3+-doped DCFLs under considering the scattering loss are deduced in the strongly pump condition. Compared with the known analytic solutions in published literatures, our analytic solutions are more accurate, especially, at higher reflectivity of output mirror. In addition, a fast and stable algorithm based on the Newton-Raphson method is proposed to simulate numerically Yb3+-doped DCFLs. The results by simplified analytic solutions are in good agreement with those by the numerical simulation. Moreover, we have performed the optimization of an Yb3+-doped DCFL using the simplified analytic solutions and the numerical simulations, respectively.  相似文献   
933.
In this paper we prove the validity of the Maximum Principle for some class of elliptic and parabolic equations of diffusion type in infinite dimension. The main tools are Asplund’s theorem and Preiss’ theorem on differentiability of Lipschitz functions in Banach space.   相似文献   
934.
935.
We prove some basic properties of Donaldson’s flow of surfaces in a hyperkähler 4-manifold. When the initial submanifold is symplectic with respect to one Kähler form and Lagrangian with respect to another, we show that certain kinds of singularities cannot form, and we prove a convergence result under a condition related to one considered by M.-T. Wang for the mean curvature flow.  相似文献   
936.
Consider a semigroup generated by matrices associated with an edge-coloring of a strongly connected, aperiodic digraph. We call the semigroup Lie-solvable if the Lie algebra generated by its elements is solvable. We show that if the semigroup is Lie-solvable then its kernel is a right group. Next, we study the Lie algebra generated by the kernel. Lie algebras generated by two idempotents are analyzed in detail. We find that these have homomorphic images that are generalized quaternion algebras. We show that if the kernel is not a direct product, then the Lie algebra generated by the kernel is not solvable by describing the structure of these algebras. Finally, we discuss an infinite class of examples that are shown to always produce strongly connected aperiodic digraphs having kernels that are not right groups.  相似文献   
937.
938.
Gap length (GL) of reading head is one of the most critical parameters for high-density magnetic recording systems. A novel method is proposed for quantitative evaluation of the GL fluctuation among a batch of magneto-resistive/giant magneto-resistive heads with same structure design. The method works at head-gimbal assembly level and the evaluation can be done with any read/write analysis equipment. The testing process is based on harmonic analysis of the readback signal. The testing system consists of a selected reference head and sample heads for evaluation. A GL variation function is introduced for the evaluation of GL deviation between the reference head and sample head. This method proved to be easy for implementation and results suggest that variation of GL is considerable and has obvious effect on recording performance in high recording density systems.  相似文献   
939.
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated.  相似文献   
940.
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