全文获取类型
收费全文 | 338458篇 |
免费 | 3133篇 |
国内免费 | 1002篇 |
专业分类
化学 | 185116篇 |
晶体学 | 5305篇 |
力学 | 13889篇 |
综合类 | 9篇 |
数学 | 35789篇 |
物理学 | 102485篇 |
出版年
2021年 | 2617篇 |
2020年 | 2936篇 |
2019年 | 3312篇 |
2018年 | 4440篇 |
2017年 | 4398篇 |
2016年 | 6326篇 |
2015年 | 3712篇 |
2014年 | 5782篇 |
2013年 | 14442篇 |
2012年 | 10969篇 |
2011年 | 13375篇 |
2010年 | 9548篇 |
2009年 | 9488篇 |
2008年 | 12847篇 |
2007年 | 12788篇 |
2006年 | 12116篇 |
2005年 | 11017篇 |
2004年 | 9840篇 |
2003年 | 9044篇 |
2002年 | 8777篇 |
2001年 | 10585篇 |
2000年 | 8035篇 |
1999年 | 6112篇 |
1998年 | 4825篇 |
1997年 | 4920篇 |
1996年 | 4595篇 |
1995年 | 3975篇 |
1994年 | 4066篇 |
1993年 | 3892篇 |
1992年 | 4513篇 |
1991年 | 4616篇 |
1990年 | 4423篇 |
1989年 | 4313篇 |
1988年 | 4233篇 |
1987年 | 4244篇 |
1986年 | 3971篇 |
1985年 | 5096篇 |
1984年 | 5255篇 |
1983年 | 4207篇 |
1982年 | 4446篇 |
1981年 | 4171篇 |
1980年 | 3960篇 |
1979年 | 4410篇 |
1978年 | 4620篇 |
1977年 | 4571篇 |
1976年 | 4529篇 |
1975年 | 4271篇 |
1974年 | 4248篇 |
1973年 | 4381篇 |
1972年 | 2946篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Two families of coherent states (the eigenstates of the annihilation operator and the Klauder–Gazeau temporally stable coherent states) are constructed for the Legendre oscillator defined in this paper. Bibliography: 14 titles. 相似文献
952.
E. Z. Borevich 《Journal of Mathematical Sciences》2004,122(3):3175-3183
We prove that bifurcation solutions to the stationary problem exist and can be extended with respect to parameter. The problem under consideration has a solution with the so-called interior transition layer phenomenon. In the nonstationary case, we establish the existence and uniqueness of a solution for any t > 0. Under certain assumptions, the nonstationary problem determines a dynamical system in some compact set. Bibliography: 9 titles. 相似文献
953.
954.
G. S. Osipenko J. V. Romanovsky N. B. Ampilova E. I. Petrenko 《Journal of Mathematical Sciences》2004,120(2):1155-1166
The Morse spectrum is a limit set of Lyapunov exponents of periodic pseudo-trajectories. This notion is especially important in the case where a dynamical system has infinitely many periodic trajectories of large period. A method for estimating the Morse spectrum was suggested by the first author in J. Math. Anal. Appl., 252 (2000). This method is based on ideas of symbolic dynamics which reduces the study of a dynamical system to the study of a certain graph, called a symbolic image. Within the framework of this method, the computation of the Morse spectrum is connected with searching simple closed paths and extracting contours with suitable characteristics. However, under iterations of the symbolic image, the number of such paths sharply increases, which leads to huge expenses of memory and time. We suggest an algorithm for constructing contours with the maximal and minimal mean values. This algorithm is based on a special version of the simplex method. Numerical tests are also described. Bibliography: 13 titles. Illustrations: 3 figures. 相似文献
955.
956.
What features characterize complex system dynamics? Power laws and scale invariance of fluctuations are often taken as the hallmarks of complexity, drawing on analogies with equilibrium critical phenomena. Here we argue that slow, directed dynamics, during which the system's properties change significantly, is fundamental. The underlying dynamics is related to a slow, decelerating but spasmodic release of an intrinsic strain or tension. Time series of a number of appropriate observables can be analyzed to confirm this effect. The strain arises from local frustration. As the strain is released through “quakes,” some system variable undergoes record statistics with accompanying log‐Poisson statistics for the quake event times. We demonstrate these phenomena via two very different systems: a model of magnetic relaxation in type II superconductors and the Tangled Nature model of evolutionary ecology and show how quantitative indications of aging can be found. © 2004 Wiley Periodicals, Inc. Complexity 10: 49–56, 2004 相似文献
957.
Stefan Richter William T. Ross Carl Sundberg 《Proceedings of the American Mathematical Society》2004,132(8):2361-2365
In this paper, we refine a result of Nagel, Rudin, and Shapiro (1982) concerning the zeros of holomorphic functions on the unit disk with finite Dirichlet integral.
958.
Fix integers m, n such that 1 ≤ m ≤ n ? 3. Let X ? Pn be an integral non-degenerate m-dimensional variety. Assume either char(K) = 0 or char(K) > deg(X). Here we prove that all general 0-dimensional sections of X containing a tangent vector to a smooth point of X are protectively equivalent if and only if n ? m + 1 ≤ deg(X) ≤ n ? m + 2. 相似文献
959.
960.
N.M. Shash F.E. Salman M.G. El-Sharawy M.K. El-Mansy 《Journal of Physics and Chemistry of Solids》2004,65(5):881-889
Vitrification suppression in the (V2O5)1−x (P2O5)x glasses where x=0.10, 0.15, 0.20, and 0.25 was controlled by changing the rate of quenching glasses. The structure variations occurring in the glasses were detected by differential thermal analysis and optical microscope. The results implied the separation and growth of V2O5 orthorhombic microcrystal in the samples with x=0.10 and 0.15 whereas other samples did not illustrate remarkable changes in their microstructure. However, in temperature range between 300 and 473 K a semiconducting behavior for all samples appears during the study of electrical conductivity-temperature dependence. A decrease in conductivity values accompanied with some variations in activation energies by reducing quenching rate was observed. The conductivity results suggested that the conduction occurs by the phonon assisted hopping of a small polaron between V4+ and V5+ states at relatively higher temperature range above θD/2. Whereas at relatively low temperatures the conduction may occur by electron jumping between filled and empty states at Fermi level in the disordered matrix besides polaronic conduction. Reasonable values for the density of localized states, carrier concentration and carrier mobility were estimated and discussed. Also, dielectric constant and dielectric loss were studied as a function of frequency at different temperatures confirming the structure variations in the glass system. 相似文献