全文获取类型
收费全文 | 173585篇 |
免费 | 2741篇 |
国内免费 | 1521篇 |
专业分类
化学 | 72341篇 |
晶体学 | 2425篇 |
力学 | 11628篇 |
综合类 | 81篇 |
数学 | 40207篇 |
物理学 | 51165篇 |
出版年
2022年 | 937篇 |
2021年 | 1030篇 |
2020年 | 1089篇 |
2019年 | 1047篇 |
2018年 | 11556篇 |
2017年 | 11226篇 |
2016年 | 7837篇 |
2015年 | 2184篇 |
2014年 | 2334篇 |
2013年 | 4705篇 |
2012年 | 7735篇 |
2011年 | 15339篇 |
2010年 | 9085篇 |
2009年 | 9448篇 |
2008年 | 10867篇 |
2007年 | 12763篇 |
2006年 | 4109篇 |
2005年 | 4669篇 |
2004年 | 4585篇 |
2003年 | 4664篇 |
2002年 | 3566篇 |
2001年 | 4411篇 |
2000年 | 3328篇 |
1999年 | 2461篇 |
1998年 | 1890篇 |
1997年 | 1793篇 |
1996年 | 1655篇 |
1995年 | 1422篇 |
1994年 | 1274篇 |
1993年 | 1156篇 |
1992年 | 1484篇 |
1991年 | 1492篇 |
1990年 | 1372篇 |
1989年 | 1236篇 |
1988年 | 1251篇 |
1987年 | 1282篇 |
1986年 | 1104篇 |
1985年 | 1373篇 |
1984年 | 1344篇 |
1983年 | 947篇 |
1982年 | 998篇 |
1981年 | 948篇 |
1980年 | 863篇 |
1979年 | 1068篇 |
1978年 | 1059篇 |
1977年 | 1062篇 |
1976年 | 969篇 |
1975年 | 837篇 |
1974年 | 850篇 |
1973年 | 807篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
Z. Slanina 《Journal of Radioanalytical and Nuclear Chemistry》1987,111(1):43-49
A search for conditions leading to the highest possible difference between equilibrium association (clustering) degree in the H and D steam has been carried out and related optimal steam pressures evaluated. The difference decreases with increasing temperature but still is a few per cent at moderate temperatures. 相似文献
84.
Supposa that f(x) is a quasidifferentiable function, defined on S(?)R~n where S is an open set, with a -equivalent bounded quasidifferential subfam ily. Lenma I 相似文献
85.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
86.
M I Salema A P B Póvoa A Q Novais 《The Journal of the Operational Research Society》2006,57(6):615-629
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis. 相似文献
87.
Data Envelopment Analysis (DEA) offers a piece-wise linear approximation of the production frontier. The approximation tends to be poor if the true frontier is not concave, eg in case of economies of scale or of specialisation. To improve the flexibility of the DEA frontier and to gain in empirical fit, we propose to extend DEA towards a more general piece-wise quadratic approximation, called Quadratic Data Envelopment Analysis (QDEA). We show that QDEA gives statistically consistent estimates for all production frontiers with bounded Hessian eigenvalues. Our Monte-Carlo simulations suggest that QDEA can substantially improve efficiency estimation in finite samples relative to standard DEA models. 相似文献
88.
In the study of the behaviors of barriers in an enclosed field, one should take into account such phenomena as sound energy reflection, absorption, scattering and diffraction. Therefore, the study is much more difficult than that in free field. In this paper, sound barriers are classified into four kinds according to their size, number and shape. Each kind of barriers is modelled by a corresponding method based on a computer program—SOFIS. The program combines the ray-tracing technique and statistical method. The impulse response and some acoustical parameters such as sound pressure level at different positions can be calculated by the program, no matter there are a certain kind of barriers in the field or the field is empty. The ray-tracing program and the algorithms for various barriers are validated by the comparison between measurement and prediction of the reverberation room and the anechoic room of the Northwestern Polytechnic University. 相似文献
89.
Zygmunt Bak 《Czechoslovak Journal of Physics》2002,52(1):A25-A28
We consider RKKY interaction in a quasi 2D system with nonparabolic dispersion. In our paper we calculate the RKKY range function assuming the in-layer confinement via effective dimensionality approach. We show, that indirect magnetic exchange in our system can be modelled by the effective spectral dimension which equals one. 相似文献
90.
K Kawasaki T Tsuji K Hirase M Miyano Y Imoto M Iwamoto 《Chemical & pharmaceutical bulletin》1991,39(3):584-589
N-Terminal tripeptide analogs of fibrin alpha-chain were synthesized and their inhibitory effect on fibrinogen/thrombin clotting was examined. A new water-soluble active ester, 3-pyridinium ester, was used for the synthesis. Among the synthetic peptides, H-Gly-Pro-Arg-hexamethyleneimine exhibited the highest inhibitory effect on fibrinogen-thrombin clotting. 相似文献