全文获取类型
收费全文 | 179195篇 |
免费 | 2340篇 |
国内免费 | 601篇 |
专业分类
化学 | 99966篇 |
晶体学 | 2147篇 |
力学 | 7295篇 |
综合类 | 8篇 |
数学 | 20556篇 |
物理学 | 52164篇 |
出版年
2020年 | 1425篇 |
2019年 | 1474篇 |
2018年 | 1744篇 |
2017年 | 1732篇 |
2016年 | 3040篇 |
2015年 | 2146篇 |
2014年 | 3058篇 |
2013年 | 7659篇 |
2012年 | 6265篇 |
2011年 | 7857篇 |
2010年 | 5186篇 |
2009年 | 5075篇 |
2008年 | 7086篇 |
2007年 | 7150篇 |
2006年 | 6855篇 |
2005年 | 6287篇 |
2004年 | 5656篇 |
2003年 | 4898篇 |
2002年 | 4864篇 |
2001年 | 4766篇 |
2000年 | 3704篇 |
1999年 | 2953篇 |
1998年 | 2608篇 |
1997年 | 2595篇 |
1996年 | 2362篇 |
1995年 | 2245篇 |
1994年 | 2262篇 |
1993年 | 2061篇 |
1992年 | 2305篇 |
1991年 | 2423篇 |
1990年 | 2190篇 |
1989年 | 2188篇 |
1988年 | 2103篇 |
1987年 | 1959篇 |
1986年 | 1931篇 |
1985年 | 2531篇 |
1984年 | 2679篇 |
1983年 | 2197篇 |
1982年 | 2406篇 |
1981年 | 2259篇 |
1980年 | 2208篇 |
1979年 | 2286篇 |
1978年 | 2481篇 |
1977年 | 2337篇 |
1976年 | 2325篇 |
1975年 | 2203篇 |
1974年 | 2249篇 |
1973年 | 2220篇 |
1972年 | 1462篇 |
1971年 | 1302篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
81.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron... 相似文献
82.
Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity.
PACS 47.80.Jk, 47.40.Ki, 47.60.+i 相似文献
83.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased. 相似文献
84.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
85.
P. Seelig A. Dax S. Faber M. Gerlach G. Huber T. Kühl D. Marx P. Merz W. Quint F. Schmitt H. Winter M. Würtz 《Hyperfine Interactions》1998,114(1-4):135-139
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric
and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique
using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics
from an ion beam at relativistic velocities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
86.
Peter Imkeller 《Probability Theory and Related Fields》1996,106(1):105-135
Summary. The analytic treatment of problems related to the asymptotic behaviour of random dynamical systems generated by stochastic
differential equations suffers from the presence of non-adapted random invariant measures. Semimartingale theory becomes accessible
if the underlying Wiener filtration is enlarged by the information carried by the orthogonal projectors on the Oseledets spaces
of the (linearized) system.
We study the corresponding problem of preservation of the semimartingale property and the validity of a priori inequalities
between the norms of stochastic integrals in the enlarged filtration and norms of their quadratic variations in case the random
element F enlarging the filtration is real valued and possesses an absolutely continuous law. Applying the tools of Malliavin’s calculus,
we give smoothness conditions on F under which the semimartingale property is preserved and a priori martingale inequalities are valid.
Received: 12 April 1995 / In revised form: 7 March 1996 相似文献
87.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
88.
Peter J. Grabner 《Random Structures and Algorithms》1993,4(1):99-110
We investigate the following process: N people select b losers by flipping coins. The 0-party continues until there are less than b losers; then the 1-party has to find the other losers by the same process. The average time for this process is about long2 N, but this result requires rather advanced methods. Furthermore, the average size of a binary tree associated to this process and the average number of coin flippings are computed. The method used in this article can be used to give asympotical solutions of a special type of bivariate recurrences. © 1993 John Wiley & Sons, Inc. 相似文献
89.
Peter A. McCoy 《Journal of Mathematical Analysis and Applications》2002,275(2):761-770
An integral transform based method is given for determining information about the locating and properties of singularities of electromagnetic fields associated with axially symmetric radiating sources. 相似文献
90.