全文获取类型
收费全文 | 20911篇 |
免费 | 792篇 |
国内免费 | 354篇 |
专业分类
化学 | 13772篇 |
晶体学 | 120篇 |
力学 | 582篇 |
综合类 | 30篇 |
数学 | 2893篇 |
物理学 | 4660篇 |
出版年
2023年 | 129篇 |
2022年 | 220篇 |
2021年 | 458篇 |
2020年 | 373篇 |
2019年 | 372篇 |
2018年 | 293篇 |
2017年 | 236篇 |
2016年 | 604篇 |
2015年 | 568篇 |
2014年 | 623篇 |
2013年 | 1170篇 |
2012年 | 1142篇 |
2011年 | 1285篇 |
2010年 | 845篇 |
2009年 | 757篇 |
2008年 | 1110篇 |
2007年 | 1084篇 |
2006年 | 944篇 |
2005年 | 889篇 |
2004年 | 851篇 |
2003年 | 806篇 |
2002年 | 813篇 |
2001年 | 493篇 |
2000年 | 454篇 |
1999年 | 356篇 |
1998年 | 253篇 |
1997年 | 246篇 |
1996年 | 262篇 |
1995年 | 269篇 |
1994年 | 255篇 |
1993年 | 191篇 |
1992年 | 172篇 |
1991年 | 182篇 |
1990年 | 204篇 |
1989年 | 169篇 |
1988年 | 143篇 |
1987年 | 143篇 |
1986年 | 136篇 |
1985年 | 240篇 |
1984年 | 256篇 |
1983年 | 179篇 |
1982年 | 197篇 |
1981年 | 168篇 |
1980年 | 165篇 |
1979年 | 149篇 |
1978年 | 124篇 |
1977年 | 176篇 |
1976年 | 149篇 |
1975年 | 125篇 |
1973年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
This paper studies the problem of how changes in the design of the genetic algorithm (GA) have an effect on the results obtained in real-life applications. In this study, focused on the application of a GA to the tuning of technical trading rules in the context of financial markets, our tentative thesis is that the GA is robust with respect to design changes. The optimization of technical trading systems is a suitable area for the application of the GA metaheuristic, as the complexity of the problem grows exponentially as new technical rules are added to the system and as the answer time is crucial when applying the system to real-time data. Up to now, most of GAs applications to this subject obviated the question of possible “design dependence” in their results. The data we report, based on our experiments, do not allow us to refute the hypothesis of robustness of the GA to design implementation, when applying to technical trading systems tuning. 相似文献
72.
Laura Bader Nicola Durante Maska Law Guglielmo Lunardon Tim Penttila 《Designs, Codes and Cryptography》2003,29(1-3):41-50
We do the tentative beginnings of a study of BLT-sets of generalised quadrangles via their symmetries. In particular, the study of whorls about a line leads us to hyperbolic reflections preserving a BLT-set of Q(4, q). 相似文献
73.
复Finsler流形上的Koppelman-Leray-Norguet公式 总被引:1,自引:1,他引:0
利用不变积分核(Berndtsson核),复Finsler度量和联系于Chern-Finsler联络的非线性联络,研究复Finsler流形上具有逐块光滑C~((1))边界的有界域上(p,q)型微分形式的积分表示,得到了(p,q)型微分形式的Koppelman-Leray-Norguet公式和■-方程的解.作为应用,利用复Finsler度量和联系于Chern-Finsler联络的非线性联络,给出了Stein流形上具有逐块光滑C~((1))边界的有界域上(p,q)型微分形式的Koppelman- Leray-Norguet公式以及■-方程的解,并且得到了Stein流形上实非退化强拟凸多面体上(p,q)型微分形式的积分表示式和■-方程的解. 相似文献
74.
75.
P. Schuurmans J. Wouters P. De Moor N. Severijns W. Vanderpoorten J. Vanhaverbeke L. Vanneste 《Hyperfine Interactions》1992,75(1-4):423-430
Anisotropic α-emission from nuclei in the decay chain from223Ra to207Tl has been observed using low temperature nuclear orientation in combination with high resolution α-detection at 4.2 K. Information
on partial wave amplitudes as well as hyperfine interactions has been extracted. 相似文献
76.
77.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
78.
D. Kast A. Jungclaus K.P. Lieb M. Górska G. de Angelis P.G. Bizzeti A. Dewald C. Fahlander H. Grawe R. Peusquens M. De Poli H. Tiesler 《The European Physical Journal A - Hadrons and Nuclei》1998,3(2):115-128
In the neutron deficient isotopes 104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler
shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the
problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model
calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and
still fair agreement for most measured B(M1) and B(E2) values.
Received: 30 June 1998 相似文献
79.
80.
Carlos E. Alciaturi Thais Montero Carlos De La Cruz Marcos E. Escobar 《Analytica chimica acta》1997,340(1-3):233-240
Reduction of the representation of infrared spectra from coal samples by osculating polynomials of degree nine is discussed. The reduced representation contains polynomial coefficients of order zero to four. Mathematical models of the original spectra are obtained by linear combination of the coefficients. These compressed models are statistically correlated to coal properties, namely, volatile matter, fixed carbon, ash content, heating value, hydrogen, carbon, sulphur, nitrogen, and maximum vitrinite reflectance, and the results are compared with those previously obtained from second derivatives of the same spectra. The use of compressed data, while giving slightly better correlations for some of the properties, has the advantage of requiring less computational time. 相似文献