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   255945篇
  免费   6104篇
  国内免费   4732篇
化学   120314篇
晶体学   3637篇
力学   15322篇
综合类   323篇
数学   42475篇
物理学   84710篇
  2022年   1943篇
  2021年   2696篇
  2020年   3102篇
  2019年   3371篇
  2018年   11934篇
  2017年   12462篇
  2016年   8852篇
  2015年   3899篇
  2014年   4979篇
  2013年   7897篇
  2012年   11534篇
  2011年   19638篇
  2010年   12916篇
  2009年   13088篇
  2008年   16868篇
  2007年   19878篇
  2006年   6457篇
  2005年   11314篇
  2004年   7951篇
  2003年   7754篇
  2002年   6068篇
  2001年   4712篇
  2000年   3776篇
  1999年   2766篇
  1998年   2597篇
  1997年   2273篇
  1996年   2282篇
  1995年   1922篇
  1994年   1971篇
  1993年   1905篇
  1992年   1917篇
  1991年   2030篇
  1990年   1968篇
  1989年   1917篇
  1988年   1751篇
  1987年   1693篇
  1986年   1644篇
  1985年   1796篇
  1984年   1913篇
  1983年   1663篇
  1982年   1678篇
  1981年   1484篇
  1980年   1403篇
  1979年   1609篇
  1978年   1757篇
  1977年   1678篇
  1976年   1739篇
  1975年   1580篇
  1974年   1624篇
  1973年   1639篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
122.
123.
124.
125.
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in...  相似文献   
126.
Physics of Atomic Nuclei - The article presents the concept of a channel-type reactor with a combined cooled moderator. The moderator consists of ceramic beryllium oxide and a liquid...  相似文献   
127.
Submicron CaZrO3 powder is obtained in combustion reactions (solution combustion synthesis—SCS) with glycine. It is found that SCS reduces the sintering temperature of CaZrO3 powders. The dielectric properties of calcium zirconate ceramics are studied by the electrochemical impedance method. It is shown that a ceramics of powders obtained by the SCS method has high dielectric characteristics.  相似文献   
128.
A new asymmetric Salamo‐based ligand H2L was synthesized using 3‐tertbutyl‐salicylaldehyde and 6‐methoxy‐2‐[O‐(1‐ethyloxyamide)]‐oxime‐1‐phenol. By adjusting the ratio of the ligand H2L and Cu (II), Co (II), and Ni (II) ions, mononuclear, dinuclear, and trinuclear transition metal (II) complexes, [Cu(L)], [{Co(L)}2], and [{Ni(L)(CH3COO)(CH3CH2OH)}2Ni] with the ligand H2L possessing completely different coordination modes were obtained, respectively. The optical spectra of ligand H2L and its Cu (II), Co (II) and Ni (II) complexes were investigated. The Cu (II) complex is a mononuclear structure, and the Cu (II) atom is tetracoordinated to form a planar quadrilateral structure. The Co (II) complex is dinuclear, and the two Co (II) atoms are pentacoordinated and have coordination geometries of distorted triangular bipyramid. The Ni (II) complex is a trinuclear structure, and the terminal and central Ni (II) atoms are all hexacoordinated, forming distorted octahedral geometries. Furthermore, optical properties including UV–Vis, IR, and fluorescence of the Cu (II), Co (II), and Ni (II) complexes were investigated. Finally, the antibacterial activities of the Cu (II), Co (II), and Ni (II) complexes were explored. According to the experimental results, the inhibitory effect was found to be enhanced with increasing concentrations of the Cu (II), Co (II), and Ni (II) complexes.  相似文献   
129.
1,3-Azaprotio transfer of propargylic α-ketocarboxylate oximes, a new type of alkynyl oximes featuring an ester tether, has been explored by taking advantage of gold catalysis. The incorporation of an oxygen atom to the chain of alkynyl oximes led to the formation of two different oxa-cyclic nitrones. It was found that internal alkynyl oximes with an E-configuration deliver five-membered nitrones, whereas terminal alkynyl oximes with an E-configuration afford six-membered nitrones. DFT calculations on four possible pathways supported a stepwise formation of C−N and C−H bonds, in which a 1,3-acyloxy-migration competes with the 1,3-azaprotio-transfer, especially in the case of internal alkynyl oximes. The relative nucleophilic properties of oxygen in the carbonyl group and the nitrogen in the oxime, the electronic effects of alkynes, and the influence of the ring system have been investigated computationally.  相似文献   
130.
Physics of Particles and Nuclei Letters - The Silicon Photomultiplier (SiPM) is a novel semiconducting photodetector which can detect single photons. It consists of many microcells (pixels)...  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