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   18725篇
  免费   3075篇
  国内免费   2467篇
化学   13515篇
晶体学   234篇
力学   1110篇
综合类   165篇
数学   2371篇
物理学   6872篇
  2024年   42篇
  2023年   297篇
  2022年   461篇
  2021年   585篇
  2020年   654篇
  2019年   697篇
  2018年   596篇
  2017年   574篇
  2016年   827篇
  2015年   870篇
  2014年   1050篇
  2013年   1300篇
  2012年   1599篇
  2011年   1826篇
  2010年   1250篇
  2009年   1218篇
  2008年   1386篇
  2007年   1224篇
  2006年   1156篇
  2005年   885篇
  2004年   675篇
  2003年   568篇
  2002年   559篇
  2001年   495篇
  2000年   464篇
  1999年   435篇
  1998年   340篇
  1997年   299篇
  1996年   322篇
  1995年   288篇
  1994年   216篇
  1993年   177篇
  1992年   162篇
  1991年   169篇
  1990年   120篇
  1989年   100篇
  1988年   72篇
  1987年   70篇
  1986年   55篇
  1985年   44篇
  1984年   28篇
  1983年   40篇
  1982年   19篇
  1981年   12篇
  1980年   7篇
  1979年   4篇
  1974年   4篇
  1972年   4篇
  1971年   4篇
  1957年   3篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
We consider a useful modification of the inexact implicit method with a variable parameter in Wang et al. J Optim Theory 111: 431–443 (2001) for generalized mixed monotone variational inequalities. One of the contributions of the proposed method in this paper is that the restrictions imposed on the variable parameter are weaker than the ones in Wang et al. J Optim Theory 111: 431–443 (2001). Another contribution is that we establish a sufficient and necessary condition for the convergence of the proposed method to a solution of the general mixed monotone variational inequality.  相似文献   
32.
This paper undertakes a systematic treatment of the low regularity local wellposedness and ill-posedness theory in Hs andHs for semilinear wave equations with polynomial nonlinearity in u and (e)u. This ill-posed result concerns the focusing type equations with nonlinearity on u and (e)tu.  相似文献   
33.
本文对线性约束优化问题提出了一个新的广义梯度投影法,该算法采用了非精确线性搜索,并在每次迭代运算中结合了广义投影矩阵和变尺度方法的思想确定其搜索方向.在通常的假设条件下,证明了该算法的整体收敛性和超线性收敛速度.  相似文献   
34.
Neodymium doped bismuth layer structure ferroelectrics (BLSFs) ceramics CaBi4−xNdxTi4O15 (x=0, 0.25, 0.50, 0.75) were prepared by solid-state reaction method. X-ray diffraction pattern showed that single phase was formed when x=0-0.75. The refined lattice parameters showed that a (b) axes decrease at x=0.25 and increase with more Nd3+ dopant. The effects of Nd3+ doping on the dielectric and ferroelectric properties of CaBi4Ti4O15 ceramics are studied. Nd3+ dopant decreased the Curie temperature linearly, and the dielectric loss, tan δ, as well. The remnant polarization of Nd3+ doped CaBi4Ti4O15 ceramics was increased by 80% at x=0.25, while more Nd3+ dopant decreased the remnant polarization. CaBi3.75Nd0.25Ti4O15 ceramics had the largest piezoelectric constant d33. The structure and properties of CaBi4−xNdxTi4O15 ceramics showed that Nd3+ may occupy different crystal locations when Nd3+ content x is less than 0.25 and more than 0.50.  相似文献   
35.
HL-2A is the first divertor tokamak in China. The vacuum system is one of the important parts of the HL-2A tokamak, which has to be work well during the physics campaign in 2004. As the tokamak machine is separated from the operation staff during discharges, to guarantee the safe and reliable operation of the vacuum system, it is necessary to watch the vacuum system outside the machine hall with an automatic monitoring system. The paper describes the design and manufacture of the monitoring system.  相似文献   
36.
The vacuum system of today's tokamak devices is designed to meet the operational requirements of the experiments. The operation can be divided into five modes, (1) pumping down and leak detecting of the vacuum vessel, (2) baking, (3) plasma-facing component (PFC) conditioning, (4)evacuating and controlling of the particles at plasma edge, (5) plasma discharge experiments.  相似文献   
37.
Foratwo-particle(spin1/2)systemthespinstateisdescribedusingavectorinafour-dimensionalHilbertspace.Inangularmomentumcouplingtheory[1],theangularmomentumuncouplingandcouplingrepresentationsareusuallyadopted.WhilethesimultaneouseigenstatesoftheCSCO(s1z,s2z),12,12,12and12,arechosenasthebasisofangularmomentumuncouplingscheme,thesimultaneouseigenstatesoftheCSCO(2,zSS),,SM(12=+Sss),arechosenasthebasisofangularmomentumcouplingscheme,1212100,2轾=-臌1212110,2轾=+臌121211,1,1.=-=Thefo…  相似文献   
38.
We develop the three-step explicit and implicit schemes of exponential fitting methods. We use the three- step explicit exponential fitting scheme to predict an approximation, then use the three-step implicit exponential fitting scheme to correct this prediction. This combination is called the three-step predictor-corrector of exponential fitting method. The three-step predictor-corrector of exponential fitting method is applied to numerically compute the coupled nonlinear Schroedinger equation and the nonlinear Schroedinger equation with varying coefficients. The numerical results show that the scheme is highly accurate.  相似文献   
39.
The purpose of this paper is to investigate the problem of approximating fixed points of non-Lipschitizian asymptotically pseudocontractive mappings in an arbitrary real Banach space by the modified Ishikawa iterative sequences with errors.  相似文献   
40.
A series of pyrimidoquinoline derivatives were synthesized through one‐pot condensation of 2,6‐diaminopyrimidin‐4‐one, aldehyde and cyclic a 1,3‐dicarbonyl compound in glycol under microwave irradiation without catalyst. The protocol in the absence of catalyst has the advantage of good yield (87‐95%), short reaction time (4‐7 min) and an environmentally friendly technique.  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