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   784篇
  免费   81篇
  国内免费   52篇
化学   359篇
晶体学   18篇
力学   67篇
综合类   14篇
数学   239篇
物理学   220篇
  2023年   9篇
  2022年   32篇
  2021年   24篇
  2020年   17篇
  2019年   17篇
  2018年   26篇
  2017年   26篇
  2016年   29篇
  2015年   18篇
  2014年   48篇
  2013年   70篇
  2012年   34篇
  2011年   27篇
  2010年   20篇
  2009年   34篇
  2008年   37篇
  2007年   52篇
  2006年   34篇
  2005年   27篇
  2004年   24篇
  2003年   43篇
  2002年   39篇
  2001年   26篇
  2000年   26篇
  1999年   24篇
  1998年   17篇
  1997年   17篇
  1996年   9篇
  1995年   8篇
  1994年   11篇
  1993年   12篇
  1992年   14篇
  1991年   6篇
  1990年   5篇
  1989年   5篇
  1988年   3篇
  1987年   4篇
  1986年   7篇
  1985年   1篇
  1984年   3篇
  1983年   5篇
  1982年   10篇
  1981年   1篇
  1980年   4篇
  1979年   6篇
  1978年   1篇
  1976年   2篇
  1972年   2篇
  1971年   1篇
排序方式: 共有917条查询结果,搜索用时 15 毫秒
881.
杨庆秀 《数学进展》1994,23(5):411-418
本文利用Dirichlet型中有产在容度的结论,从几何的观点刻画了反射扩散过程的极集。  相似文献   
882.
Summary Principles are proposed to select solvents for the coating of glass capillary columns with medium-polar and polar stationary phases applying the free-release static-coating technique, practical examples are given, demonstrating that this technique is suitable to coat stationary phases like OV-1701 and Carbowaxes.  相似文献   
883.
In the crystal structure of N,N′-dimethylurea, there is one molecule in the asymmetric unit, but with two halves related by an axis of pseudosymmetry. All nonhydrogen atoms of each molecule lie on a plane. In the crystal the molecules are held together by hydrogen bonds in the direction of the “a” axis. They form parallel rows with the same sense orientation, so that the crystal has a polar structure.  相似文献   
884.
For a collection C of convex bodies let h(C) be the minimum number m with the property that every element K of C can be covered by m or fewer smaller homothetic copies of K. Denote by C d * the collection of all duals of cyclic d-polytopes, d 2. We show that h(C 2k * )=(k +1)2 for any k 2. We also prove the inequalities (d+1) (d+3)/4 h(C d * ) (d+1) 2/2$ for any d 2.  相似文献   
885.
In bose&burton, Bose and Burton determined the smallest point sets of PG(d, q) that meet every subspace of PG(d, q) of a given dimension c. In this paper an equivalent result for quadrics of elliptic type is obtained. It states the folloing. For 0 c n - 1 the smallest point set of the elliptic quadric Q -(2n + 1, q) that meets every singular subspace of dimension c of Q -(2n + 1, q) has cardinality (q n+1 + q c )(q n-c - 1)/(q - 1). Furthermore, the point sets of the smallest cardinality are classified.  相似文献   
886.
A submillisecond response, wide view and single-cell-gap transflective (TR) display employing a blue-phase liquid crystal is proposed. The device employs polar opposite in-plane switching (IPS) electrodes. To balance the optical phase retardation between transmissive (T) and reflective (R) regions, the IPS electrodes are formed with unequal gaps in the two regions. This display exhibits reasonably high optical efficiency and well-matched voltage-dependent transmittance and reflectance curves.  相似文献   
887.
The paper presents a study of 5-MeV energy Au+ ion implantation in polar c-plane (0001), nonpolar a-plane (11-20) and m-plane (10–10) ZnO crystallographic cuts using fluences of 5 × 1014 and 1 × 1015 cm−2. The implanted samples were subsequently annealed in O2 atmosphere at 600°C. It was shown that a-plane ZnO exhibited a lowest level of Zn sublattice disorder evidenced by Rutherford backscattering spectroscopy in channelling mode (RBS-C); in contrast, m-plane ZnO showed the highest disorder. The disorder in the Zn sublattice grew progressively in the subsurface as well as in the implanted layer in c-plane and m-plane ZnO, while a-plane has shown slight increase of disorder just in the implanted layer. Angular scans provided using RBS-C have shown the preservation of channelling effect in the subsurface layer in a-plane ZnO. On the contrary, the narrowed and shallow angular scan dips were seen in m-plane ZnO. Raman spectroscopy has shown significant O-sublattice disorder and O rearrangement mainly in a-plane and m-plane ZnO compared to c-plane. After ion implantation, the exciton-related luminescence band at 375 nm vanished almost completely, and the defect-related band ‘shifted’ to shorter wavelengths. Annealing has beneficial influence on near-band-edge (NBE) luminescence recovery, whereas deep-level-emission (DLE) luminesce has been shifted to lower wavelengths than appeared after implantation.  相似文献   
888.
李平  赵润昌  王伟  耿远超  蒲昱东  粟敬钦 《物理学报》2014,63(8):85206-085206
梳理了两极驱动的研究思路和神光-Ⅲ原型装置两极驱动的研究内容;提出了针对靶丸表面均匀照明设计的光束近似原则,基于该原则建立了"逐次递进"的方法,优化设计了不同条件下靶丸表面均匀照明的激光条件,并对设计方法进行了数值模拟分析,设计内容在神光一III原型装置上进行了初步的实验验证,结果进一步支持了靶丸表面均匀照明设计的合理性,研究结果为后续的实验设计和理论研究提供了指导方向。  相似文献   
889.
890.
ReaxFF molecular dynamics (MD) simulations are performed to study high-temperature pyrolysis of toluene under microwave heating. It is observed that the temperature of the reaction system under microwave heating has a rapidly rising stage, which is similar to the phenomenon of thermal runaway often appeared in reactions under microwave heating. Simulations indicate that the consumption rate of toluene and generating rates of H2 and CH4 obtained under microwave heating are always lower than those obtained under conventional heating at the early stage. Analyses of the pyrolysis of toluene show that ReaxFF MD simulations can provide an efficient way to study chemical reactions under microwave heating.  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