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   423866篇
  免费   3679篇
  国内免费   864篇
化学   212136篇
晶体学   6640篇
力学   20343篇
综合类   17篇
数学   56310篇
物理学   132963篇
  2020年   2705篇
  2019年   2951篇
  2018年   11449篇
  2017年   12242篇
  2016年   9337篇
  2015年   4343篇
  2014年   5817篇
  2013年   14871篇
  2012年   14730篇
  2011年   24621篇
  2010年   15830篇
  2009年   15968篇
  2008年   21617篇
  2007年   24811篇
  2006年   11571篇
  2005年   16573篇
  2004年   12432篇
  2003年   11502篇
  2002年   9506篇
  2001年   9948篇
  2000年   7763篇
  1999年   5806篇
  1998年   4789篇
  1997年   4652篇
  1996年   4514篇
  1995年   4214篇
  1994年   4077篇
  1993年   3764篇
  1992年   4613篇
  1991年   4631篇
  1990年   4412篇
  1989年   4458篇
  1988年   4430篇
  1987年   4329篇
  1986年   4110篇
  1985年   5309篇
  1984年   5472篇
  1983年   4376篇
  1982年   4621篇
  1981年   4542篇
  1980年   4274篇
  1979年   4725篇
  1978年   4906篇
  1977年   4819篇
  1976年   4719篇
  1975年   4408篇
  1974年   4407篇
  1973年   4389篇
  1972年   2977篇
  1968年   2751篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A short-term load-forecasting system has been developed to predictload demand for the Irish Electricity Supply Board from 1 to10 days in advance. Model output is acceptably accurate at mosttimes, but special days such as public holidays and the Easterweekend etc. require individual treatment. The basic model usedin everyday load forecasting is presented first, and specialdays when this model fails in accuracy are then examined andtreated separately using rule-based procedures. These proceduresare based on identified relationships between weather conditionsand prevailing daily load shapes. Comparisons are made betweenthe forecasts for these special days as given by the standardmodel and the ruled-based procedures.  相似文献   
992.
T. Shevchenko Kiev University, 252022 Kiev, Pr. Akad. Glushakova, 6, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 192–196, May–June, 1995.  相似文献   
993.
994.
As a leading defence equipment company, the Dynamics Divisionof British Aerospace Defence Company (BAeDef(DD)) has experiencedthe worst effects of post-Coldwar defence cuts, a global recession,and a determination by the U.K. Government to achieve greatervalue for money in defence procurement. The major tenet of thisnew approach to defence prwurement was 'eyes on, hands off',promoting a shift of the management of project risks from theMinistry of Defence (MOD) to industry. Initial industry reactionwas sceptical but bxame increasingly compliant as tenderingrequirements included visibility of contractors' risk assessment.This paper describes the risk-assessment methodology createdby BAeDef(DD) to meet these changed conditions. The human and organizational aspects of these developments onrisk have helped create a pro-active risk-management cultureat BAeDef(DD). Continuous assessment of project risks providesthe impetus for wider thinking beyond risk-taking or risk-aversionpreferences, leading to greater realism in planning. Decisionsto implement risk resolution measures require competence incost-benefit analysis. The conditions to foster this new behaviourare better-informed senior management, with the rejection ofbad news eliminated at all levels, and the laying of a pathto becoming a learning company.  相似文献   
995.
996.
Methods are proposed for determining the diffusion coefficients of adsorbed molecules and the adsorption isotherms from given concentrations of the solutes in the external solution. The methods are based on a comparison of experimental data with the numerical results produced by a mathematical model of internal-diffusion kinetics of adsorption from a constant bounded volume.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 66, pp. 41–46, 1988.  相似文献   
997.
Identification of nonlinear elliptic equations   总被引:1,自引:0,他引:1  
An optimization theoretic approach and algorithm for the estimation of state-dependent coefficients in nonlinear elliptic equation is presented. It is based on a splitting method combined with convex analysis techniques. Convergence of the algorithm is established and numerical examples are included.The research of K. Kunisch was supported in part by a grant from the Bundesministerium für Wissenschaft und Forschung, Austria.  相似文献   
998.
999.
Based on a previously developed two-level model of four-wave interaction in photorefractive crystals, expressions for the amplitude and phase of a transmission holographic grating have been obtained. The analysis of these expressions points to the dependence of both the amplitude and the phase of the grating on the intensity of the readout beam.  相似文献   
1000.
We have used time-differential perturbed angular correlation (PAC) spectroscopy with 181Ta-probes to study the electric field gradient at Zr-sites in synthetic zircon and hafnon between room temperature and 1,200°C. PAC spectra are similar to those obtained from naturally occurring zircons. In particular, a change in slope of the quadrupole coupling vs. temperature is observed in the synthetic zircon at the same temperature as seen in natural zircons from the Mud Tank carbonatite (Australia). The synthetic hafnon data also shows this feature but at somewhat higher temperature. Low-temperature PAC spectra of both synthetic zircon and hafnon have a clearly reduced anisotropy. We believe that the cause for this is a electronic defect, possibly created during the β-decay of the probe parent nucleus.  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