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   390735篇
  免费   2277篇
  国内免费   555篇
化学   182456篇
晶体学   5843篇
力学   22387篇
综合类   9篇
数学   56068篇
物理学   126804篇
  2020年   4162篇
  2019年   5055篇
  2018年   7448篇
  2017年   7610篇
  2016年   9529篇
  2015年   4427篇
  2014年   8436篇
  2013年   15849篇
  2012年   12898篇
  2011年   15126篇
  2010年   12612篇
  2009年   12806篇
  2008年   14587篇
  2007年   14379篇
  2006年   12883篇
  2005年   11205篇
  2004年   10842篇
  2003年   10027篇
  2002年   10335篇
  2001年   10476篇
  2000年   8117篇
  1999年   6190篇
  1998年   5689篇
  1997年   5480篇
  1996年   5012篇
  1995年   4464篇
  1994年   4505篇
  1993年   4507篇
  1992年   4586篇
  1991年   5074篇
  1990年   4999篇
  1989年   5048篇
  1988年   4695篇
  1987年   4773篇
  1986年   4461篇
  1985年   5353篇
  1984年   5548篇
  1983年   4724篇
  1982年   4972篇
  1981年   4633篇
  1980年   4286篇
  1979年   4924篇
  1978年   5103篇
  1977年   5296篇
  1976年   5450篇
  1975年   5057篇
  1974年   4887篇
  1973年   5132篇
  1972年   4303篇
  1971年   3944篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T 1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the doubly magic 68Ni and its neighbor 69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed. Received: 1 May 2001 / Accepted: 4 December 2001  相似文献   
912.
Experimental proofs of asymmetric trapping of atoms at the growth step in vapor-phase epitaxy of gallium arsenide in the GaAs–AsCl3–H2 system are given. The data obtained confirm the important role of the surface diffusion mass transfer in the growth of epitaxial GaAs layers on vicinals in the neighborhood of (111)A. The effective diffusion length is estimated.  相似文献   
913.
We present an extension of the Tomonaga-Luttinger model in which left and right-moving particles have different Fermi velocities. We derive expressions for one-particle Green's functions, momentum-distributions, density of states, charge compressibility and conductivity as functions of both the velocity difference ε and the strength of the interaction β. This allows us to identify a novel restricted region in the parameter space in which the system keeps the main features of a Luttinger liquid but with an unusual behavior of the density of states and the static charge compressibility κ. In particular κ diverges on the boundary of the restricted region, indicating the occurrence of a phase transition. Received 20 May 2002 / Received in final form 23 August 2002 Published online 19 November 2002  相似文献   
914.
The energy characteristics of an XeCl exciplex lamp with planar construction pumped by a low-pressure gas discharge are investigated experimentally. When a discharge gap of width 2 cm and a Xe-Cl2 mixture were used, average radiation powers up to 20 mW were obtained in the wavelength interval 200–380 nm at efficiencies of ∼0.4%. In this case the total efficiency of radiation into an angle of 4π exceeded 4%. It is shown that increasing the working pressure and using low discharge currents can lead to “point” radiation sources. Zh. Tekh. Fiz. 67, 43–46 (December 1997)  相似文献   
915.
We propose a way of modifying the mathematical model of the nondestructive theoretical-experimental method of determining the residual stresses for a specific collection of technological conditions for welding two cylindrical glass shells. The method is based on the general theory of boundary-value problems for ordinary differential equations.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 33, 1991, pp. 69–73.  相似文献   
916.
New radiative transfer theory is developed for stochastically inhomogeneous scattering media. The three-dimensional shapes and large scale (compared to the mean free path) structures of the media are modeled by stochastic interfaces separating regions of different scattering properties. The small scale fluctuations are characterized by a pair-correlation function. The radiative transfer equation is extended to include individual scattering and propagation probabilities of a ray for each subregion as well as the probability for a ray to cross the interface between two subregions. The propagation probability is found to depend on the entire preceding path of the ray; the present formulation accounts for the two previous scatterings. A new adding/doubling algorithm is developed to solve this problem numerically. Transmission through a cloud layer and backward scattering seem to be particularly sensitive to inhomogeneities.  相似文献   
917.
This paper analyzes the requirements that CASE tools should meet for effective database reverse engineering (DBRE), and proposes a general architecture for data-centered applications reverse engineering CASE environments. First, the paper describes a generic DBMS-independent DBRE methodology, then it analyzes the main characteristics of DBRE activities in order to collect a set of desirable requirements. Finally, it describes DB-MAIN, an operational CASE tool developed according to these requirements. The main features of this tool that are described in this paper are its unique generic specification model, its repository, its transformation toolkit, its user interface, the text processors, the assistants, the methodological control and its functional extensibility. Finally, the paper describes five real-world projects in which the methodology and the CASE tool were applied. This is a heavily revised and extended version of “Requirements for Information System Reverse Engineering Support” by J.-L. Hainaut, V. Englebert, J. Henrard, J.-M. Hick, D. Roland, which first appeared in the Proceedings of the Second Working Conference on Reverse Engineering, IEEE Computer Society Press, pp. 136–145, July 1995. This paper presents some results of the DB-MAIN project. This project is partially supported by the Région Wallonne, the European Union, and by a consortium comprising ACEC-OSI (Be), ARIANE-II (Be), Banque UCL (Lux), BBL (Be), Centre de recherche public H. Tudor (Lux), CGER (Be), Cockerill-Sambre (Be), CONCIS (Fr), D'Ieteren (Be), DIGITAL, EDF (Fr), EPFL (CH), Groupe S (Be), IBM, OBLOG Software (Port), ORIGIN (Be), Ville de Namur (Be), Winterthur (Be), 3 Suisses (Be). The DB-Process subproject is supported by the Communauté Fran?aise de Belgique.  相似文献   
918.
919.
920.
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