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   434158篇
  免费   4382篇
  国内免费   1078篇
化学   234115篇
晶体学   7194篇
力学   18916篇
综合类   19篇
数学   46995篇
物理学   132379篇
  2019年   3906篇
  2018年   4959篇
  2017年   5020篇
  2016年   7406篇
  2015年   4523篇
  2014年   7245篇
  2013年   18456篇
  2012年   13496篇
  2011年   16540篇
  2010年   11767篇
  2009年   11601篇
  2008年   15199篇
  2007年   15280篇
  2006年   14263篇
  2005年   12903篇
  2004年   11866篇
  2003年   10881篇
  2002年   10569篇
  2001年   12289篇
  2000年   9447篇
  1999年   7267篇
  1998年   6091篇
  1997年   6068篇
  1996年   5716篇
  1995年   5363篇
  1994年   5406篇
  1993年   4992篇
  1992年   6000篇
  1991年   5917篇
  1990年   5806篇
  1989年   5680篇
  1988年   5844篇
  1987年   5710篇
  1986年   5407篇
  1985年   7109篇
  1984年   7350篇
  1983年   6033篇
  1982年   6188篇
  1981年   6177篇
  1980年   5991篇
  1979年   6241篇
  1978年   6542篇
  1977年   6522篇
  1976年   6431篇
  1975年   5917篇
  1974年   5931篇
  1973年   6037篇
  1972年   4238篇
  1968年   3573篇
  1967年   3555篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The statistical characteristics of conditional time before ruin of an insurance company, including the distribution function of conditional time and its moments are examined.  相似文献   
992.
The bivalent chromium impurity centers in CdF2 and CaF2 crystals are investigated using electron paramagnetic resonance (EPR) in the frequency range 9.3–300 GHz. It is found that Cr2+ ions in the lattices of these crystals occupy cation positions and form [CrF4F4]6? clusters whose magnetic properties at low temperatures are characterized by orthorhombic symmetry. The parameters of the electron Zeeman and ligand interactions of the Cr2+ ion with four fluorine ions in the nearest environment are determined. The initial splittings in the system of spin energy levels of the cluster are measured.  相似文献   
993.
We investigate the simple quantum relativistic Toda chain. The ultralocal simple Weyl algebra pair is associated with each site of the chain. Weyl’s q is considered to be inside a unit circle. Both independent Baxter operators Q are constructed explicitly as series in local Weyl generators. The operator-valued Wronskian of Q-s is also calculated.  相似文献   
994.
The results of investigations into the high-resolution Fourier spectrum of the AsH3 molecule first registered in the range 9720–9900 cm–1 with a resolution of 0.015 cm–1 are given in the present paper. Lines of (500; A 1) and (500; E) bands are interpreted by the method of combination differences. The spectroscopic constants of the examined arsine bands are determined by solving the inverse problem. They have allowed 98 rotational energy levels (with J max = 6) to be reproduced with errors close to the experimental ones.  相似文献   
995.
Efficient quenching of eosin phosphorescence by amino-acid derivatives of fullerene (AADFs) such as C60-alanine and C60-glycine in aqueous solutions indicates the possibility of transferring electrons from eosin to fullerene upon collisions or in the exciplex state. To investigate electron transfer in the protein structure, we studied the process of incorporation of C60-alanine and C60-glycine into the heme pocket of myoglobin by controlling Förster quenching. The dissociation constant for the protein-AADF complex was estimated.  相似文献   
996.
A model of silane decomposition in a radio-frequency argon plasma is constructed. The concentrations of SiH4 decomposition products, as well as products of synthesis (higher silanes), are calculated. The role of metastable argon atoms in the formation of SiH3 radicals and the higher silanes is analyzed.  相似文献   
997.
998.
We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass resonance suggests that it is a parametric instability of a Mathieu type equation of motion. Received 11 July 2001 and Received in final form 12 November 2001  相似文献   
999.
The thermal decomposition of lead and manganese salts of mono(hydroxyethyl) phthalate was studied by thermogravimetry and differential scanning calorimetry. The kinetic parameters for the various stages of decomposition of these salts were calculated by different methods and mechanisms are proposed to explain the results.  相似文献   
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