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   90805篇
  免费   2282篇
  国内免费   3151篇
化学   35199篇
晶体学   1030篇
力学   7223篇
综合类   210篇
数学   33171篇
物理学   19405篇
  2024年   42篇
  2023年   212篇
  2022年   451篇
  2021年   499篇
  2020年   507篇
  2019年   545篇
  2018年   10801篇
  2017年   10678篇
  2016年   6638篇
  2015年   1524篇
  2014年   1148篇
  2013年   1453篇
  2012年   4954篇
  2011年   11704篇
  2010年   6578篇
  2009年   6912篇
  2008年   7607篇
  2007年   9674篇
  2006年   1064篇
  2005年   1985篇
  2004年   2103篇
  2003年   2436篇
  2002年   1463篇
  2001年   660篇
  2000年   619篇
  1999年   416篇
  1998年   381篇
  1997年   274篇
  1996年   325篇
  1995年   234篇
  1994年   182篇
  1993年   173篇
  1992年   112篇
  1991年   122篇
  1990年   113篇
  1989年   84篇
  1988年   96篇
  1987年   75篇
  1986年   85篇
  1985年   70篇
  1984年   62篇
  1983年   52篇
  1982年   48篇
  1981年   44篇
  1980年   51篇
  1979年   49篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
We investigate the face-to-face collision between multisolitons in spin-1/2 quantum plasma. It is studied in the framework of the model proposed by Marklund et al in Phys. Rev. E 76, 067401 (2007). This study is done with the help of the extended Poincare–Lighthill–Kno (PLK) method. The extended PLK method is also used to obtain two Korteweg–de Vries (KdV) equations and the phase shifts and trajectories during the head-on collision of multisolitons. The collision-induced phase shifts (trajectory changes) are also obtained. The effects of the Zeeman energy, total mass density of the charged plasma particles, speed of the wave and the ratio of the sound speed to Alfvén speed on the phase shifts are studied. It is observed that the phase shifts are significantly affected by all these parameters.  相似文献   
995.
We study the junction condition relating the pressure to heat flux at the boundary of an accelerating and expanding spherically symmetric radiating star. We transform the junction condition to an ordinary differential equation by making a separability assumption on the metric functions in the space–time variables. The condition of separability on the metric functions yields several new exact solutions. A class of shear-free models is found which contains a linear equation of state and generalizes a previously obtained model. Four new shearing models are obtained; all the gravitational potentials can be written explicitly. A brief physical analysis indicates that the matter variables are well behaved.  相似文献   
996.
In this paper we report a time-delayed chameleon-like chaotic system which can belong to different families of chaotic attractors depending on the choices of parameters. Such a characteristic of self-excited and hidden chaotic flows in a simple 3D system with time delay has not been reported earlier. Dynamic analysis of the proposed time-delayed systems are analysed in time-delay space and parameter space. A novel adaptive modified functional projective lag synchronization algorithm is derived for synchronizing identical time-delayed chameleon systems with uncertain parameters. The proposed time-delayed systems and the synchronization algorithm with controllers and parameter estimates are then implemented in FPGA using hardware–software co-simulation and the results are presented.  相似文献   
997.
Although LiFePO4/C has been successfully put into practical use in lithium-ion batteries equipped on new energy vehicles, its unsatisfactory low temperature results in poor low performance of lithium-ion batteries, leading to a much smaller continue voyage course at extreme environments with low temperature for electric vehicles. In this paper, the electrochemical performance of the LiFePO4/C prepared by polyol route was investigated at a temperature range from 25 to ?20 °C. Compared to commercial ones, as-prepared LiFePO4/C shows a much better low-temperature performance with a reversible capacity of 30 mA h g?1 even at 5 C under ?20 °C and a capacity retention of 91.1 % after 100 cycles at 0.1 C under 0 °C. Moreover, high-resolution transmission electron microscopy (HRTEM) revealed that this outstanding performance at low temperatures could be assigned to uniform carbon coating and the nano-sized particles with a highly crystalline structure.  相似文献   
998.
In this paper, we discuss the existence and uniqueness of solutions for a new class of multi-point boundary value problems of multi-term fractional differential equations by using standard fixed point theorems. We also demonstrate the application of the obtained results with the aid of examples. The paper concludes with the study of multi-term fractional integro-differential equations supplemented with multi-point boundary conditions. Our results are new and contribute significantly to the existing literature on the topic.  相似文献   
999.
1000.
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