全文获取类型
收费全文 | 279143篇 |
免费 | 5514篇 |
国内免费 | 957篇 |
专业分类
化学 | 160859篇 |
晶体学 | 3119篇 |
力学 | 10043篇 |
综合类 | 20篇 |
数学 | 33654篇 |
物理学 | 77919篇 |
出版年
2020年 | 2361篇 |
2019年 | 2382篇 |
2018年 | 3017篇 |
2017年 | 2701篇 |
2016年 | 5198篇 |
2015年 | 4230篇 |
2014年 | 4969篇 |
2013年 | 13259篇 |
2012年 | 10930篇 |
2011年 | 12196篇 |
2010年 | 7937篇 |
2009年 | 7373篇 |
2008年 | 10829篇 |
2007年 | 10816篇 |
2006年 | 10078篇 |
2005年 | 9446篇 |
2004年 | 8469篇 |
2003年 | 7251篇 |
2002年 | 6817篇 |
2001年 | 7413篇 |
2000年 | 5900篇 |
1999年 | 4598篇 |
1998年 | 3583篇 |
1997年 | 3500篇 |
1996年 | 3686篇 |
1995年 | 3180篇 |
1994年 | 3176篇 |
1993年 | 3018篇 |
1992年 | 3560篇 |
1991年 | 3299篇 |
1990年 | 3280篇 |
1989年 | 3239篇 |
1988年 | 3127篇 |
1987年 | 3108篇 |
1986年 | 2880篇 |
1985年 | 3912篇 |
1984年 | 3877篇 |
1983年 | 3102篇 |
1982年 | 3373篇 |
1981年 | 3336篇 |
1980年 | 3159篇 |
1979年 | 3301篇 |
1978年 | 3563篇 |
1977年 | 3347篇 |
1976年 | 3349篇 |
1975年 | 3131篇 |
1974年 | 3091篇 |
1973年 | 3115篇 |
1968年 | 2125篇 |
1967年 | 2287篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
991.
The early evolution of gas chromatography in the former German Democratic Republic (GDR) is surveyed and instrument development is outlined, describing the most important models manufactured in the GDR. The organization of the Arbeitsgemeinschaft für Gas-Chromatographie (Working Group for GC) is chronicled and its activities are discussed. Subsequent parts of this article will deal with the six symposia organized by the Arbeitsgemeinschaft between 1958 and 1968. 相似文献
992.
In a previous paper we gave a new formulation and derived the Euler equations and other necessary conditions to solve strong, pathwise, stochastic variational problems with trajectories driven by Brownian motion. Thus, unlike current methods which minimize the control over deterministic functionals (the expected value), we find the control which gives the critical point solution of random functionals of a Brownian path and then, if we choose, find the expected value.This increase in information is balanced by the fact that our methods are anticipative while current methods are not. However, our methods are more directly connected to the theory and meaningful examples of deterministic variational theory and provide better means of solution for free and constrained problems. In addition, examples indicate that there are methods to obtain nonanticipative solutions from our equations although the anticipative optimal cost function has smaller expected value.In this paper we give new, efficient numerical methods to find the solution of these problems in the quadratic case. Of interest is that our numerical solution has a maximal, a priori, pointwise error of O(h3/2) where h is the node size. We believe our results are unique for any theory of stochastic control and that our methods of proof involve new and sophisticated ideas for strong solutions which extend previous deterministic results by the first author where the error was O(h2).We note that, although our solutions are given in terms of stochastic differential equations, we are not using the now standard numerical methods for stochastic differential equations. Instead we find an approximation to the critical point solution of the variational problem using relations derived from setting to zero the directional derivative of the cost functional in the direction of simple test functions.Our results are even more significant than they first appear because we can reformulate stochastic control problems or constrained calculus of variations problems in the unconstrained, stochastic calculus of variations formulation of this paper. This will allow us to find efficient and accurate numerical solutions for general constrained, stochastic optimization problems. This is not yet being done, even in the deterministic case, except by the first author. 相似文献
993.
A. I. Golovashkin G. N. Izmaïlov G. V. Kuleshova T. Q. Khánh A. M. Tskhovrebov L. N. Zherikhina 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):243-249
A scheme of magnetic calorimeter for registration of rare events
characterized by small energy release (cosmic rays, WIMPs, solitary X-ray
quanta) is proposed. The calorimeter is brought to operation by adiabatic
demagnetization, and its magnetic response is measured by a quantum
interferometer (SQUID, A. Barone and G. Paterno, Physics and applications of Josephson Effect). Special consideration is given to the specific
features of calorimeter operation in the ferromagnetic transition region.
The trigger registration of ultrasmall energy release by a ferromagnetic
system in the metastable state is described. 相似文献
994.
Joo J.H. Choi J.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2004,32(6):2263-2264
A new type of microwave amplifier module, consisting of a solid-state amplifier, a predistortion linearizer, and a traveling-wave-tube (TWT), is realized. Measurements show a noise figure of 2.2 dB at 9.5 GHz and the third-order intermodulation distortion ratio of 53 dBc at 10 dB back off from P1 dB point. 相似文献
995.
We prove global existence of solutions to the continuous nonhomogeneous Smoluchowski equation for coagulation rates satisfying a more general structure condition than the Galkin–Tupchiev monotony hypothesis considered in (Ph. Laurençot, S. Mischler, Arch. Rational Mech. Anal. 162 (1) (2002) 45–99). The Smoluchowski coagulation rate fulfils this condition as well as some rates which vanish on the diagonal. Under the condition of positivity of the coagulation rate outside of the diagonal we prove that solutions tend to 0 in the large time asymptotic. These results depend on a new estimate from below for the dissipation rate of the Lp-norm, p>1. To cite this article: S. Mischler, M. Rodriguez Ricard, C. R. Acad. Sci. Paris, Ser. I 336 (2003). 相似文献
996.
997.
We characterize the sequences of orthogonal polynomials on the unit circle whose derivatives are also orthogonal polynomials on the unit circle. Some relations for the sequences of derivatives of orthogonal polynomials are provided. Finally, we pose some problems about orthogonality-preserving maps and differential equations for orthogonal polynomials on the unit circle. 相似文献
998.
M. H. Gehlen M. Van der Auweraer F. C. De Schrwer 《Photochemistry and photobiology》1991,54(4):613-618
The luminescence decay of excited probes in micelles in the presence of a Poisson distribution of quenchers is considered under conditions where both probe and quencher within the lifetime of the excited probe may exchange between the micelles. Analytical and numerical results show that the luminescence decay can be expressed by a generalized self convolution product of a multiexponential decay function. 相似文献
999.
1000.