全文获取类型
收费全文 | 439969篇 |
免费 | 3130篇 |
国内免费 | 1106篇 |
专业分类
化学 | 208282篇 |
晶体学 | 7121篇 |
力学 | 21955篇 |
综合类 | 18篇 |
数学 | 63926篇 |
物理学 | 142903篇 |
出版年
2021年 | 2897篇 |
2020年 | 3170篇 |
2019年 | 3639篇 |
2018年 | 11912篇 |
2017年 | 12611篇 |
2016年 | 10558篇 |
2015年 | 4939篇 |
2014年 | 7048篇 |
2013年 | 16828篇 |
2012年 | 16350篇 |
2011年 | 25163篇 |
2010年 | 16935篇 |
2009年 | 16888篇 |
2008年 | 22768篇 |
2007年 | 25463篇 |
2006年 | 13775篇 |
2005年 | 17203篇 |
2004年 | 13522篇 |
2003年 | 12341篇 |
2002年 | 10531篇 |
2001年 | 10832篇 |
2000年 | 8674篇 |
1999年 | 6458篇 |
1998年 | 5438篇 |
1997年 | 5340篇 |
1996年 | 4890篇 |
1995年 | 4504篇 |
1994年 | 4329篇 |
1993年 | 4100篇 |
1992年 | 4661篇 |
1991年 | 4601篇 |
1990年 | 4484篇 |
1989年 | 4236篇 |
1988年 | 4301篇 |
1987年 | 4335篇 |
1986年 | 4035篇 |
1985年 | 5285篇 |
1984年 | 5564篇 |
1983年 | 4740篇 |
1982年 | 4969篇 |
1981年 | 4785篇 |
1980年 | 4653篇 |
1979年 | 4856篇 |
1978年 | 4993篇 |
1977年 | 4859篇 |
1976年 | 5000篇 |
1975年 | 4730篇 |
1974年 | 4671篇 |
1973年 | 4963篇 |
1972年 | 3204篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
We consider the radiation from nonoscillating dipoles traveling with constant velocity directed parallel or antiparallel to
the velocity of a homogeneous transparent moving medium. It is assumed that the medium in its rest frame is isotropic and
has no spatial dispersion. We obtain expressions for the radiative energy losses and estimate the polarization energy losses
of electric and magnetic dipoles of different orientations. In particular, it is shown that the energy loss of a source is
negative if it moves in the direction of the medium motion and the source velocity is less than the medium velocity. Estimates
for the energy losses of dipoles in the cases of an electron beam and a flow of a weakly dispersive medium are given.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 6, pp. 502–512, June 2006. 相似文献
62.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
63.
64.
65.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
66.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
67.
68.
D. A. Tikhomirov O. S. Slyadevskaya A. V. Eremeev 《Chemistry of Heterocyclic Compounds》1991,27(9):966-969
A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1208, September, 1991. 相似文献
69.
I. L. Davies K. E. Markides M. L. Lee M. W. Raynor K. D. Bartle 《Journal of separation science》1989,12(4):193-207
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review. 相似文献
70.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献