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   14974篇
  免费   2611篇
  国内免费   1725篇
化学   11008篇
晶体学   143篇
力学   847篇
综合类   125篇
数学   1777篇
物理学   5410篇
  2024年   26篇
  2023年   260篇
  2022年   427篇
  2021年   488篇
  2020年   528篇
  2019年   574篇
  2018年   457篇
  2017年   445篇
  2016年   719篇
  2015年   714篇
  2014年   805篇
  2013年   1079篇
  2012年   1266篇
  2011年   1371篇
  2010年   918篇
  2009年   993篇
  2008年   1014篇
  2007年   869篇
  2006年   839篇
  2005年   708篇
  2004年   594篇
  2003年   530篇
  2002年   604篇
  2001年   479篇
  2000年   353篇
  1999年   298篇
  1998年   274篇
  1997年   239篇
  1996年   183篇
  1995年   220篇
  1994年   191篇
  1993年   141篇
  1992年   117篇
  1991年   105篇
  1990年   107篇
  1989年   71篇
  1988年   51篇
  1987年   39篇
  1986年   44篇
  1985年   31篇
  1984年   26篇
  1983年   27篇
  1982年   17篇
  1981年   10篇
  1980年   14篇
  1979年   6篇
  1978年   7篇
  1976年   7篇
  1975年   4篇
  1971年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
邱春晖 《数学学报》2003,46(3):591-600
本文得到复流形局部q-凸楔形上(r,s)型微分形式的带权的同伦公式和(r,s)型的方程的带权的连续解,并给出(r,s)型微分形式的不含边界积分的新的带权的同伦公式和(r,s)型的方程的新的带权的连续解.这些新的带权公式尤其适用于具有非光滑边界的局部q-凸楔形,这时不但可以避免边界积分的复杂估计,而且积分密度也不必在边界有定义,只要在区域上有定义就行.其次,引进权因子,带权的积分公式在应用上(比如在函数的插值方面)具有更大的灵活性.  相似文献   
112.
A polymerized quaternary ammonium salt polydiallyldimethylammonium chloride, exhibiting high stability to heat and base, was prepared and applied as phase-transfer catalyst (PTC) in halogen-exchange (Halex) fluorination of chloronitrobenzenes to give excellent yields of corresponding fluoronitrobenzenes. Dimethyl sulfoxide was found to be the best solvent when microwave was applied as heating resource.  相似文献   
113.
强激光远场焦斑重构算法研究   总被引:6,自引:1,他引:5       下载免费PDF全文
 通过CCD图像采集单元结合传统的列阵相机测量高功率固体激光器的远场焦斑分布,采用图像处理技术的边缘算子提取焦斑的几何中心,提出通过几何中心对心的焦斑嵌套重构算法,解决了光斑饱和时的对心难题,实现了快捷准确测量激光焦斑,为激光器的实时控制提供参考数据。  相似文献   
114.
This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.  相似文献   
115.
Based on the basic theory of molecular vibration relaxation and semi-classical density matrix theory, operating parameters optimization of buffer gas in the process of miniature pulsed optically pumped submillimeter wave laser was systemically studied and the theoretical calculated result was tested by experiments. The result would do favor to develop and study high-power and wide-range tunable miniature and high-efficient pulsed optically pumped submillimeter wave laser and also had some instruction to its application.  相似文献   
116.
Sufficient conditions for asymptotic behavior of the solutions of nonlinear forced neutral delay differential equations with impulses are found. The results given in [2,4,6,7] are generalized and improved.  相似文献   
117.
基于累积损伤过程研究旧系统的不完全预防维护策略,冲击服从非时齐Poisson过程,并产生随机的损伤量,损伤量是加法累加的.系统在累积损伤量达到k或系统运行年龄达到T时进行计划内预防维护.在两次计划内预防维护之间,当累积损伤量达到预定水平K (k K)时,对系统进行计划外维护,其费用高于计划内预防维护,利用再生过程理论得到单位时间维护成本,讨论在时齐Poisson过程下的时间预防维护策略与水平预防维护策略,同时给出算例.  相似文献   
118.
Condition monitoring and life prediction of the vehicle engine is an important and urgent problem during the vehicle development process. The vibration signals that are closely associated with the engine running condition and its development trend are complex and nonlinear. The chaos theory is used to treat the nonlinear dynamical system recently. A novel chaos method in conjunction with SVD (singular value decomposition)denoising skill are used to predict the vibration time series. Two types of time series and their prediction errors are provided to illustrate the practical utility of the method.  相似文献   
119.
We have investigated the magnetic and magneto-transport properties of a systematic sequence of five InAs/Mn digital alloys grown by a combination of molecular beam epitaxy and atomic layer epitaxy. The samples consist of 30 periods of Mn fractional monolayers (ML) (0.17–0.5 ML) separated by 14 ML thick InAs spacer layers in a superlattice configuration. Four samples show n-type electrical conduction while the fifth (0.25 ML Mn) is p-type. Squid magnetization measurements performed on these samples show remnant magnetization above room temperature, which is apparently related to a second phase.  相似文献   
120.
Retractable structures which alter their geometries according to practical requirements are widely used in roof structures of stadiums for their versatility. A retractable structure based on threefold-symmetric Bricard linkages and rotating rings of tetrahedra is proposed and developed in this paper. By replacing each link of a threefold-symmetric Bricard linkage with a tetrahedron, a retractable structure is obtained which can repeatedly open and close by rotating the tetrahedra. The geometric relationship between the retractable structure and the threefold-symmetric Bricard linkage is derived and ranges of main geometric parameters are determined to ensure a continuous and smooth movement in the deployment of the structure. Then the relative displacement of the support and the open rate of the structure, two main parameters concerned in practical applications, are investigated. Preferred ranges of main geometric parameters are proposed and a physical model is manufactured to verify them. A discussion on some possible improvements and modifications of the structure is also presented.  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