全文获取类型
收费全文 | 447375篇 |
免费 | 6087篇 |
国内免费 | 1770篇 |
专业分类
化学 | 232891篇 |
晶体学 | 6071篇 |
力学 | 18389篇 |
综合类 | 14篇 |
数学 | 50384篇 |
物理学 | 127587篇 |
综合类 | 19896篇 |
出版年
2020年 | 2827篇 |
2019年 | 2815篇 |
2018年 | 2831篇 |
2016年 | 5608篇 |
2015年 | 4662篇 |
2014年 | 6268篇 |
2013年 | 19468篇 |
2012年 | 15377篇 |
2011年 | 19212篇 |
2010年 | 11764篇 |
2009年 | 11778篇 |
2008年 | 17635篇 |
2007年 | 18027篇 |
2006年 | 17430篇 |
2005年 | 16004篇 |
2004年 | 14409篇 |
2003年 | 12728篇 |
2002年 | 12506篇 |
2001年 | 14618篇 |
2000年 | 11353篇 |
1999年 | 8761篇 |
1998年 | 6618篇 |
1997年 | 6459篇 |
1996年 | 6475篇 |
1995年 | 5910篇 |
1994年 | 5541篇 |
1993年 | 5279篇 |
1992年 | 6328篇 |
1991年 | 6163篇 |
1990年 | 5749篇 |
1989年 | 5567篇 |
1988年 | 5837篇 |
1987年 | 5489篇 |
1986年 | 5252篇 |
1985年 | 7517篇 |
1984年 | 7449篇 |
1983年 | 6094篇 |
1982年 | 6464篇 |
1981年 | 6371篇 |
1980年 | 6200篇 |
1979年 | 6524篇 |
1978年 | 6533篇 |
1977年 | 6431篇 |
1976年 | 6290篇 |
1975年 | 6213篇 |
1974年 | 6180篇 |
1973年 | 6152篇 |
1972年 | 3649篇 |
1971年 | 2938篇 |
1970年 | 2871篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
991.
Héctor J. Sussmann 《Set-Valued Analysis》2002,10(2-3):233-285
It is shown that the construction of needle variations can be carried out for almost lower semicontinuous differential inclusions rather than for the case of ordinary single-valued continuously differentiable vector fields usually considered in the literature. The construction leads to needle variations whose flows are in general set-valued but still have good differentiability properties. The variations are constructed by using single-valued selections that are not necessarily continuous with respect to the state variable, but have instead a much weaker 'integral continuity' property, somewhat more general that the 'directional continuity' considered in previous work by A. Cambini and S. Querci, A. Pucci, and A. Bressan. The existence of many such selections is proved by slightly adapting an argument due to Bressan, extending it from the lower semicontinuous to the almost lower semicontinuous case, and strengthening it to yield not only directional continuity at all points but also full continuity at a specified point. 相似文献
992.
A datalogger was developed to identify vocalizing dolphins within socially interacting captive groups. Every 50 ms the logger stores data on the level and frequency of detected sound. Dataloggers are temporarily attached to dolphins by suction cups for data collection sessions lasting up to 45 min. Later, computer analysis of data from the dataloggers reveals which dolphin produced each vocalization recorded during the session. Results from use of dataloggers with two captive bottlenose dolphins (Tursiops truncatus) at the New England Aquarium in Boston, MA are presented. The possible use of dataloggers with wild dolphins is discussed. 相似文献
993.
The classical (first integral) methods of studying restrictions on the possible motion of gravitationally interacting bodies are reviewed. The simple and flexible inequality method is extended to a similar approach to the relationship between possible forbidden motion and (asymptotic) symmetries in the relativistic few-body problem. This extended method is used to reproduce the standard results of bounded motion for a test particle in a Schwarzschild geometry. The existence of bounded motion is shown for the general relativistic few-body problem and the difficulties in determining such bounded motion is analysed. The use of this approach to obtaining a relativistic alternative to the classical Roche lobe analysis in contact binaries is discussed. 相似文献
994.
J. W. Barrett 《International Journal of Theoretical Physics》1991,30(9):1171-1215
This article is about a different representation of the geometry of the gravitational field, one in which the paths of test bodies play a crucial role. The primary concept is the geometry of the motion of a test body, and the relation between different such possible motions. Space-time as a Lorentzian manifold is regarded as a secondary construct, and it is shown how to construct it from the primary data. Some technical problems remain. Yang-Mills fields are defined by their holonomy in an analogous construction. I detail the development of this idea in the literature, and give a new version of the construction of a bundle and connection from holonomy data. The field equations of general relativity are discussed briefly in this context. 相似文献
995.
Robert J. Rubin 《Journal of statistical physics》1991,65(5-6):1207-1216
A one-dimensional lattice random walk in the presence ofm equally spaced traps is considered. The step length distribution is a symmetric exponential. An explicit analytic expression is obtained for the probability that the random walk will be trapped at thejth trapping site. 相似文献
996.
997.
Lerner E.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(2):259-263
A cosmological model is presented that produces He, C, O, D, Li, Be, and B in their observed abundances without a Big Bang. The elements are produced during the 1.5-Gy formation period of a galaxy, with C, O, and other heavy elements produced by stars of M >12 M3 , He by stars of 6 Ms<M <12 Ms, and D, Li, Be, and B by cosmic-ray reactions in a nearly pure H plasma halo. Thus, the model shows that the major elements used in astrophysical studies can be produced during galactic formation by exactly the same processes known to function today at much lower rates 相似文献
998.
Myron B. Allen Mark C. Curran 《Numerical Methods for Partial Differential Equations》1989,5(2):121-132
An adaptive grid refinement procedure allows accurate solutions to advection-dominated, time-dependent flows using finite-element collocation. The technique relies on a data structure that is readily amenable to parallel computing. The paper discusses computational aspects of the method. 相似文献
999.
S. J. Montgomery-Smith 《Israel Journal of Mathematics》1989,67(1):123-128
We show that the canonical embeddingC(K) →L
Φ(μ) has Gaussian cotypep, where μ is a Radon probability measure onK, and Φ is an Orlicz function equivalent tot
p(logt)
p/2 for larget. 相似文献
1000.
Applying tight-binding approximation and spin pairing of like charge carriers in a pair of excitons created in a lattice, the possibility of forming a bound exciton-exciton state is studied. It is found that, provided there exists strong exciton-lattice interaction, such a bound state may be formed and its energy may lie within the valence band deforming the material into a crystalline solid with no energy gap. Lowering of the energy is calculated in naphthalene and anthracene crystals where some experimental results are known. The excess energy released after the formation of such bound state can be adequate, depending on the material, to desorb neutral atoms or eject of electrons from surfaces. 相似文献