全文获取类型
收费全文 | 340878篇 |
免费 | 5925篇 |
国内免费 | 1351篇 |
专业分类
化学 | 174256篇 |
晶体学 | 3713篇 |
力学 | 16314篇 |
综合类 | 14篇 |
数学 | 66056篇 |
物理学 | 87801篇 |
出版年
2022年 | 1489篇 |
2021年 | 2336篇 |
2020年 | 2575篇 |
2019年 | 2635篇 |
2018年 | 12864篇 |
2017年 | 12328篇 |
2016年 | 11049篇 |
2015年 | 5371篇 |
2014年 | 5605篇 |
2013年 | 14031篇 |
2012年 | 15741篇 |
2011年 | 23462篇 |
2010年 | 13903篇 |
2009年 | 13952篇 |
2008年 | 18570篇 |
2007年 | 20393篇 |
2006年 | 12068篇 |
2005年 | 12209篇 |
2004年 | 11181篇 |
2003年 | 10119篇 |
2002年 | 8748篇 |
2001年 | 8046篇 |
2000年 | 6525篇 |
1999年 | 4876篇 |
1998年 | 3816篇 |
1997年 | 3727篇 |
1996年 | 3973篇 |
1995年 | 3245篇 |
1994年 | 3256篇 |
1993年 | 3060篇 |
1992年 | 3353篇 |
1991年 | 3168篇 |
1990年 | 2919篇 |
1989年 | 2814篇 |
1988年 | 2789篇 |
1987年 | 2681篇 |
1986年 | 2547篇 |
1985年 | 3670篇 |
1984年 | 3631篇 |
1983年 | 2871篇 |
1982年 | 3141篇 |
1981年 | 3015篇 |
1980年 | 2936篇 |
1979年 | 2802篇 |
1978年 | 2866篇 |
1977年 | 2743篇 |
1976年 | 2743篇 |
1975年 | 2646篇 |
1974年 | 2533篇 |
1973年 | 2657篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
771.
Djamel Meraghni Abdelhakim Necir 《Methodology and Computing in Applied Probability》2007,9(4):557-572
The characteristic exponent α of a Lévy-stable law S
α
(σ, β, μ) was thoroughly studied as the extreme value index of a heavy tailed distribution. For 1 < α < 2, Peng (Statist. Probab. Lett. 52: 255–264, 2001) has proposed, via the extreme value approach, an asymptotically normal estimator for the location parameter μ. In this paper, we derive by the same approach, an estimator for the scale parameter σ and we discuss its limiting behavior.
相似文献
772.
Seismic data is modeled in the high‐frequency approximation, using the techniques of microlocal analysis. We consider general, anisotropic elastic media. Our methods are designed to allow for the formation of caustics. The data is modeled in two ways. First, we give a microlocal treatment of the Kirchhoff approximation, where the medium is assumed to be piecewise smooth, and reflection and transmission occur at interfaces. Second, we give a refined view on the Born approximation based upon a linearization of the scattering process in the medium parameters around a smooth background medium. The joint formulation of Born and Kirchhoff scattering allows us to take into account general scatterers as well as the nonlinear dependence of reflection coefficients on the medium parameters. The latter allows the treatment of scattering up to grazing angles. The outcome of the analysis is a characterization of the singular part of seismic data. We obtain a set of pseudodifferential operators that annihilate the data. In the process we construct a Fourier integral operator and a reflectivity function such that the data can be represented by this operator acting on the reflectivity function. In our construction this Fourier integral operator becomes invertible. We give the conditions for invertibility for general acquisition geometry. The result is also of interest for inverse scattering in acoustic media. © 2002 John Wiley & Sons, Inc. 相似文献
773.
We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599. 相似文献
774.
775.
776.
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
777.
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
778.
Pál Sohár Gábor Bernáth Géza Stájer Angela E. Szabo 《Magnetic resonance in chemistry : MRC》1989,27(9):872-876
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments. 相似文献
779.
780.
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