全文获取类型
收费全文 | 37681篇 |
免费 | 2606篇 |
国内免费 | 4931篇 |
专业分类
化学 | 20408篇 |
晶体学 | 1079篇 |
力学 | 1131篇 |
综合类 | 509篇 |
数学 | 14843篇 |
物理学 | 7248篇 |
出版年
2024年 | 37篇 |
2023年 | 336篇 |
2022年 | 1015篇 |
2021年 | 976篇 |
2020年 | 799篇 |
2019年 | 856篇 |
2018年 | 721篇 |
2017年 | 923篇 |
2016年 | 992篇 |
2015年 | 859篇 |
2014年 | 1450篇 |
2013年 | 2680篇 |
2012年 | 1823篇 |
2011年 | 2286篇 |
2010年 | 2224篇 |
2009年 | 2590篇 |
2008年 | 2635篇 |
2007年 | 2743篇 |
2006年 | 2435篇 |
2005年 | 2139篇 |
2004年 | 1968篇 |
2003年 | 1813篇 |
2002年 | 1531篇 |
2001年 | 1176篇 |
2000年 | 1218篇 |
1999年 | 1002篇 |
1998年 | 943篇 |
1997年 | 779篇 |
1996年 | 618篇 |
1995年 | 531篇 |
1994年 | 480篇 |
1993年 | 405篇 |
1992年 | 371篇 |
1991年 | 290篇 |
1990年 | 178篇 |
1989年 | 196篇 |
1988年 | 186篇 |
1987年 | 124篇 |
1986年 | 83篇 |
1985年 | 126篇 |
1984年 | 134篇 |
1983年 | 46篇 |
1982年 | 79篇 |
1981年 | 85篇 |
1980年 | 78篇 |
1979年 | 65篇 |
1978年 | 44篇 |
1977年 | 40篇 |
1976年 | 24篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
本文给出了超球上加权Bergman空间上Hankel算子属于Schattenp-类(2≤p<+∞)的一个充要条件,推广了文[10]中的主要结果。 相似文献
162.
Spin-lattice relaxation mechanisms in kaolinite have been reinvestigated by magic-angle spinning (MAS) of the sample. MAS is useful to distinguish between relaxation mechanisms: the direct relaxation rate caused by the dipole-dipole interaction with electron spins is not affected by spinning while the spin diffusion-assisted relaxation rate is. Spin diffusion plays a dominant role in 1H relaxation. MAS causes only a slight change in the relaxation behavior, because the dipolar coupling between 1H spins is strong. 29Si relaxes directly through the dipole-dipole interaction with electron spins under spinning conditions higher than 2 kHz. A spin diffusion effect has been clearly observed in the 29Si relaxation of relatively pure samples under static and slow-spinning conditions. 27Al relaxes through three mechanisms: phonon-coupled quadrupole interaction, spin diffusion and dipole-dipole interaction with electron spins. The first mechanism is dominant, while the last is negligibly small. Spin diffusion between 27Al spins is suppressed completely at a spinning rate of 2.5 kHz. We have analyzed the relaxation behavior theoretically and discussed quantitatively. Concentrations of paramagnetic impurities, electron spin-lattice relaxation times and spin diffusion rates have been estimated. 相似文献
163.
The application and the performance of the neighboring optimal feedback scheme presented in Part 1 of this paper is demonstrated for the heating-constrained cross-range maximization problem of a space-shuttle-orbiter-type vehicle. This problem contains five state variables, two control variables, and a state variable inequality constraint of order zero.This research was supported in part by the Deutsche Forschungsgemeinschaft under the Schwerpunktprogramm Anwendungsbezogene Optimierung und Steuerung.The authors wish to express their sincere and grateful appreciation to Professor Roland Bulirsch who encouraged this work. 相似文献
164.
In his celebrated paper, Polya has considered the random walk in the three-dimensional (cubic) lattice and showed that the probability of return to the origin is less than 1. Subsequent authors have shown that the probability is %34.053.... Here we consider the same random walk, with the restriction that the drunkard is only allowed to stay inxyz. It is shown that his probability of returning to the originand staying in the allowed region is %6.4844.... 相似文献
165.
The Fermi and Coulomb holes of the 21
S state of the helium isoelectronic sequence are investigated. Several interesting differences between the results obtained and those which might be expected on the basis of the corresponding 23
S state are pointed out and discussed. 相似文献
166.
Stationary phase properties of the organic molten salt ethylpyridinium bromide in gas chromatography
Summary The organic molten salt, 1-ethylpyridinium bromide, is suitable for use as a stationary phase in gas chromatography. It has a usable liquid temperature range of 110 to 160°C. It undergoes a single phase transition at 110°C which corresponds to the bulk melting point. Below the melting point the phase may be used as a selective adsorbent, although column efficiency and peak symmetry deteriorate as the temperature is lowered from the melting point. Above the melting point, ethylpyridinium bromide can be used to separate a wide variety of organic compounds retaining strongly those compounds possessing large dipole or hydrogen bonding functional groups. 相似文献
167.
This is a sequel to Part I of A Subjective Bayesian Approach to the Theory of Queues. The focus here is on inference and a use of Shannon's measure of information for assessing the amount of information conveyed by the various types of data from queues. The notation and terminology used here is established in Part I. 相似文献
168.
Let A(X) be the space defined by Waldhausen whose homotopy groups define the algebraic K-groups of the space X and let
. Here (X) denotes the free loop space of X and Q denotes the functor . For X = Y, the suspension of a connected space Y, we shall prove that the homotopy fibers Ã(X), B(X) of the maps A(X) A (point), B(X) B (point) are equivalent as infinite loop spaces. 相似文献
169.
The lattice model for equilibrium polymerization in a solvent proposed by Wheeler and Pfeuty is solved exactly on a Bethe lattice (core of a Caylay tree) with general coordination numberq. Earlier mean-field results are reobtained in the limitq, but the phase diagrams show deviations from them for finiteq. Whenq=2, our results turn into the solution of the one-dimensional problem. Although the model is solved directly, without the use of the correspondence between the equilibrium polymerization model and the diluten0 model, we verified that the latter model may also be solved on the Bethe lattice, its solution being identical to the direct solution in all parameter space. As observed in earlier studies of the puren0 vector model, the free energy is not always convex. We obtain the region of negative susceptibility for our solution and compare this result with mean field and renormalization group (-expansion) calculations. 相似文献
170.