全文获取类型
收费全文 | 423866篇 |
免费 | 3679篇 |
国内免费 | 864篇 |
专业分类
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 |
出版年
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.
M. U. Belyi N. E. Bartnitskaya I. F. Mel'nik B. A. Okhrimenko S. M. Yablochkov 《Journal of Applied Spectroscopy》1995,62(3):564-567
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.
F. A. Rustamov 《Optical and Quantum Electronics》1995,27(2):117-125
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.
P. C. Morais A. C. Oliveira V. K. Garg M. L. Silva E. F. C. Alcântara F. Q. Soares D. Rabelo 《Hyperfine Interactions》2007,177(1-3):51-56
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