全文获取类型
收费全文 | 51120篇 |
免费 | 2193篇 |
国内免费 | 2982篇 |
专业分类
化学 | 38179篇 |
晶体学 | 294篇 |
力学 | 541篇 |
综合类 | 633篇 |
数学 | 7040篇 |
物理学 | 9608篇 |
出版年
2023年 | 646篇 |
2022年 | 1837篇 |
2021年 | 1600篇 |
2020年 | 966篇 |
2019年 | 1209篇 |
2018年 | 856篇 |
2017年 | 1107篇 |
2016年 | 1029篇 |
2015年 | 1145篇 |
2014年 | 1541篇 |
2013年 | 2725篇 |
2012年 | 2527篇 |
2011年 | 2318篇 |
2010年 | 2020篇 |
2009年 | 2553篇 |
2008年 | 2785篇 |
2007年 | 3103篇 |
2006年 | 2354篇 |
2005年 | 1786篇 |
2004年 | 1698篇 |
2003年 | 1507篇 |
2002年 | 4728篇 |
2001年 | 1564篇 |
2000年 | 1074篇 |
1999年 | 941篇 |
1998年 | 901篇 |
1997年 | 665篇 |
1996年 | 735篇 |
1995年 | 641篇 |
1994年 | 607篇 |
1993年 | 627篇 |
1992年 | 632篇 |
1991年 | 436篇 |
1990年 | 368篇 |
1989年 | 311篇 |
1988年 | 308篇 |
1987年 | 215篇 |
1986年 | 227篇 |
1985年 | 338篇 |
1984年 | 256篇 |
1983年 | 159篇 |
1982年 | 302篇 |
1981年 | 475篇 |
1980年 | 433篇 |
1979年 | 476篇 |
1978年 | 386篇 |
1977年 | 287篇 |
1976年 | 242篇 |
1974年 | 109篇 |
1973年 | 192篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献
82.
The main results of the paper are as follows: covering characterizations of wQN-spaces, covering characterizations of QN-spaces and a theorem saying that Cp(X) has the Arkhangel'ski?ˇ property (α1) provided that X is a QN-space. The latter statement solves a problem posed by M. Scheepers [M. Scheepers, Cp(X) and Arhangel'ski?ˇ's αi-spaces, Topology Appl. 89 (1998) 265-275] and for Tychonoff spaces was independently proved by M. Sakai [M. Sakai, The sequence selection properties of Cp(X), Preprint, April 25, 2006]. As the most interesting result we consider the equivalence that a normal topological space X is a wQN-space if and only if X has the property S1(Γshr,Γ). Moreover we show that X is a QN-space if and only if Cp(X) has the property (α0), and for perfectly normal spaces, if and only if X has the covering property (β3). 相似文献
83.
This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel.
From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission
electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the
block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant
in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different
values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly
oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical
particle model with a locked aspect ratio. 相似文献
84.
Bahattin Gümgüm Nermin Biricik Feyyaz Durap Ismail Özdemir Nevin Gürbüz Wee Han Ang Paul J. Dyson 《应用有机金属化学》2007,21(8):711-715
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
85.
86.
E. V. Ermanyuk 《Experiments in fluids》2002,32(2):242-251
This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly
stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating
in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional
similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by
vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids
having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients
is based on Fourier analysis of the time-history of damped oscillation tests.
Received: 25 September 2000 / Accepted: 6 July 2001 Published online: 29 November 2001 相似文献
87.
Robert J. Rubin 《Journal of statistical physics》1991,65(5-6):1207-1216
A one-dimensional lattice random walk in the presence ofm equally spaced traps is considered. The step length distribution is a symmetric exponential. An explicit analytic expression is obtained for the probability that the random walk will be trapped at thejth trapping site. 相似文献
88.
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
89.
90.
Igor Chueshov 《Journal of Differential Equations》2007,233(1):42-86
We study von Karman evolution equations with non-linear dissipation and with partially clamped and partially free boundary conditions. Two distinctive mechanisms of dissipation are considered: (i) internal dissipation generated by non-linear operator, and (ii) boundary dissipation generated by shear forces friction acting on a free part of the boundary. The main emphasis is given to the effects of boundary dissipation. Under suitable hypotheses we prove existence of a compact global attractor and finiteness of its fractal dimension. We also show that any solution is stabilized to an equilibrium and estimate the rate of the convergence which, in turn, depends on the behaviour at the origin of the functions describing the dissipation. 相似文献