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   690324篇
  免费   5846篇
  国内免费   1778篇
化学   336209篇
晶体学   9807篇
力学   36839篇
综合类   31篇
数学   104094篇
物理学   210968篇
  2021年   6197篇
  2020年   6732篇
  2019年   7694篇
  2018年   11600篇
  2017年   12043篇
  2016年   15288篇
  2015年   8201篇
  2014年   13726篇
  2013年   29668篇
  2012年   25531篇
  2011年   29017篇
  2010年   21987篇
  2009年   21737篇
  2008年   26189篇
  2007年   26044篇
  2006年   23804篇
  2005年   24656篇
  2004年   22835篇
  2003年   19607篇
  2002年   17950篇
  2001年   18392篇
  2000年   14275篇
  1999年   11101篇
  1998年   9842篇
  1997年   9581篇
  1996年   8930篇
  1995年   7956篇
  1994年   8048篇
  1993年   7820篇
  1992年   8217篇
  1991年   8753篇
  1990年   8453篇
  1989年   8337篇
  1988年   8033篇
  1987年   7864篇
  1986年   7427篇
  1985年   9328篇
  1984年   9847篇
  1983年   8308篇
  1982年   8658篇
  1981年   8095篇
  1980年   7634篇
  1979年   8399篇
  1978年   8599篇
  1977年   8640篇
  1976年   8679篇
  1975年   8252篇
  1974年   8076篇
  1973年   8311篇
  1972年   6378篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Basic principles of the generalized lattice model of multicomponent condensed systems are formulated. Short-range parts of interatomic interactions are taken into account by means of the geometric constraints method. Long-range parts of the interactions are taken into account in mean field approximation. The expression for Helmholtz free energy is obtained. A system of integral equations for the equilibrium distributions of components is derived. The asymptotic properties of its solutions are investigated. Moment expansion of interatomic interactions and localization of integral terms in free energy is obtained. A Ginzburg–Landau-like functional of free energy is derived.  相似文献   
972.
The effect of ethylene glycol (EG) on the formation of whiskers and fibers of complex oxides with the general formula MCo2O4 upon the thermolysis of M1/3Co2/3C2O4 (M = Zn, Mn) oxalates has been studied. New compounds (solvates) are formed when powdered oxalates are heated with EG. In the solvates, EG molecules substitute for water molecules according to the reaction M1/3Co2/3C2O4 · 2H2O + HOCH2CH2OH = M1/3Co2/3C2O4(HOCH2CH2OH) + 2H2O. The solvates have been characterized using X-ray powder diffraction, microscopy, IR spectroscopy, thermogravimetry, and chemical analysis. The shape, structure, and particle size of the thermolysis products of EG-modified oxalates have been determined using scanning electron microscopy.  相似文献   
973.
The restricted Hartree-Fock method was used to determine the cycle size effects on the geometric parameters of several inorganic templates, cyclophosphazenes PnNnX2n (X = H, F, Cl; n = 2, 3, 4). A topological analysis of local electronic properties at the electron density critical points of bonds allowed us to quantitatively characterize the chemical bond in cyclophosphazenes and its dependence on the cycle size and substituents at phosphorus. The calculated distributions of the electron density Laplacian and electron pair localization functions revealed the special features of the electronic structure of the nitrogen and phosphorus atoms. These results explain the nature of noncovalent interactions between the P atoms of one cyclophosphazene molecule and the N atoms of the other.  相似文献   
974.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive projections in Dedekind complete vector lattices and f-algebras. AMS Classification: 47B65, 46A40, 06F25  相似文献   
975.
976.
977.
978.
979.
In this paper the performances of inhomogeneous dielectric slabs as solar light collectors for both illumination and solar energy applications are analysed.  相似文献   
980.
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting.  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