全文获取类型
收费全文 | 654316篇 |
免费 | 7345篇 |
国内免费 | 2271篇 |
专业分类
化学 | 327593篇 |
晶体学 | 9481篇 |
力学 | 32345篇 |
综合类 | 14篇 |
数学 | 100375篇 |
物理学 | 194124篇 |
出版年
2021年 | 4514篇 |
2020年 | 4955篇 |
2019年 | 5400篇 |
2018年 | 16383篇 |
2017年 | 16320篇 |
2016年 | 16028篇 |
2015年 | 7540篇 |
2014年 | 10745篇 |
2013年 | 27479篇 |
2012年 | 24051篇 |
2011年 | 34502篇 |
2010年 | 22455篇 |
2009年 | 22675篇 |
2008年 | 28619篇 |
2007年 | 30801篇 |
2006年 | 21804篇 |
2005年 | 20315篇 |
2004年 | 19069篇 |
2003年 | 17434篇 |
2002年 | 16395篇 |
2001年 | 17832篇 |
2000年 | 13638篇 |
1999年 | 10798篇 |
1998年 | 8958篇 |
1997年 | 8687篇 |
1996年 | 8549篇 |
1995年 | 7557篇 |
1994年 | 7265篇 |
1993年 | 7077篇 |
1992年 | 7761篇 |
1991年 | 7874篇 |
1990年 | 7457篇 |
1989年 | 7261篇 |
1988年 | 7290篇 |
1987年 | 7109篇 |
1986年 | 6813篇 |
1985年 | 9211篇 |
1984年 | 9339篇 |
1983年 | 7674篇 |
1982年 | 8086篇 |
1981年 | 7875篇 |
1980年 | 7637篇 |
1979年 | 7978篇 |
1978年 | 8054篇 |
1977年 | 7963篇 |
1976年 | 7931篇 |
1975年 | 7653篇 |
1974年 | 7400篇 |
1973年 | 7637篇 |
1972年 | 4940篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Calculations of the effects of amplified spontaneous emission (ASE) in laser amplifiers designed to amplify sub-picosecond pulses are presented. A one-dimensional code is used with some simple approximations to account for aspect ratio variation in cases of cylindrical symmetry. Gain depletion due to ASE is compared for various multi-pass geometries. Optimisation for short pulse amplification of a telescopic, beam-expanding, 4-pass amplifier is considered.On leave from Electrotechnical Laboratory, Tsukuba, Ibaraki, Japan 相似文献
992.
993.
Flux jumps have been observed in a large (138 mg) single crystal of La1.86Sr0.14CuO4. Both complete and incomplete flux jumps are observed with the energy dissipated by complete flux jumps consistent with temperature rises to nearly Tc. The systematics of these flux jumps with respect to field history, temperature and the time duration of the hysteresis measurements are reported. The field at which flux jumps first occur and their subsequent spacing are not consistent with a simple adiabatic theory of flux jumps for our experimental conditions. Instead, the crystal is observed to be stabilized against flux jumps by flux creep which occurs during the time interval over which field steps are accomplished as well as during imposed time intervals between field steps. 相似文献
994.
Christian Prins 《The Journal of the Operational Research Society》1994,45(6):611-623
Satellite communications, like batches of work in a job shop, need to be scheduled in order to use their resources as efficiently as possible. The most common satellite communications system in use today is known as Time Division Multiple Access (TDMA), in which data from earth stations is buffered before being transmitted to the appropriate receiver on a satellite. Cycles of transmission are fixed for all stations. Since the same satellite will be used for routeing data in several different ways, a schedule must be devised to use the receivers, repeaters and transmitters on board to minimize the time needed for completion of a batch of work. This paper is a survey of current scheduling algorithms used for optimizing satellite communications resources. Apart from telecommunications, the methods presented here could be applied to more general scheduling problems with renewable resources but without precedence constraints. 相似文献
995.
996.
997.
Cheriyan and Hagerup developed a randomized algorithm to compute the maximum flow in a graph with n nodes and m edges in O(mn + n2 log2n) expected time. The randomization is used to efficiently play a certain combinatorial game that arises during the computation. We give a version of their algorithm where a general version of their game arises. Then we give a strategy for the game that yields a deterministic algorithm for computing the maximum flow in a directed graph with n nodes and m edges that runs in time O(mn(logm/n log nn)). Our algorithm gives an O(mn) deterministic algorithm for all m/n = Ω(nε) for any positive constant ε, and is currently the fastest deterministic algorithm for computing maximum flow as long as m/n = ω(log n). 相似文献
998.
The authors study a one-dimensional model for optical tunnellingwith a refractive index in the shape of a square well. The relevanceof the model and its limiting cases are discussed. The mainresult is the leading behaviour of the exponentially small imaginarypart of the eigenvalue which determines the radiation loss.The leading behaviour of the imaginary part is calculated usingBerry's formula which controls the asymptotic expansion of theAiry function Bi(z) to better-than-exponential accuracy. 相似文献
999.
1000.
A. R. Kuznetsov S. G. Lunter S. I. Nikitina A. G. Plyukhin Yu. K. Fedorov 《Journal of Applied Spectroscopy》1992,56(1):68-72
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 56, No. 1, pp. 90–95, January, 1992. 相似文献