全文获取类型
收费全文 | 266424篇 |
免费 | 3435篇 |
国内免费 | 817篇 |
专业分类
化学 | 136232篇 |
晶体学 | 4163篇 |
力学 | 11505篇 |
综合类 | 2篇 |
数学 | 31555篇 |
物理学 | 87219篇 |
出版年
2020年 | 2237篇 |
2019年 | 2360篇 |
2018年 | 3126篇 |
2017年 | 3049篇 |
2016年 | 4820篇 |
2015年 | 3155篇 |
2014年 | 4855篇 |
2013年 | 11943篇 |
2012年 | 9017篇 |
2011年 | 11164篇 |
2010年 | 7621篇 |
2009年 | 7411篇 |
2008年 | 10389篇 |
2007年 | 10323篇 |
2006年 | 9690篇 |
2005年 | 8778篇 |
2004年 | 7930篇 |
2003年 | 6938篇 |
2002年 | 6831篇 |
2001年 | 7668篇 |
2000年 | 5904篇 |
1999年 | 4624篇 |
1998年 | 3902篇 |
1997年 | 3803篇 |
1996年 | 3750篇 |
1995年 | 3407篇 |
1994年 | 3379篇 |
1993年 | 3544篇 |
1992年 | 3557篇 |
1991年 | 3631篇 |
1990年 | 3403篇 |
1989年 | 3303篇 |
1988年 | 3362篇 |
1987年 | 3234篇 |
1986年 | 3053篇 |
1985年 | 4234篇 |
1984年 | 4404篇 |
1983年 | 3560篇 |
1982年 | 3759篇 |
1981年 | 3702篇 |
1980年 | 3594篇 |
1979年 | 3649篇 |
1978年 | 3768篇 |
1977年 | 3680篇 |
1976年 | 3728篇 |
1975年 | 3413篇 |
1974年 | 3424篇 |
1973年 | 3460篇 |
1972年 | 2362篇 |
1971年 | 1986篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
132.
133.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献
134.
Abstract Under a suitable ellipticity condition, we show that classical SG-pseudodifferential operators of nonnegative order possess
complex powers. We show that the powers are again classical and derive an explicit formula for all homogeneous components.
Keywords: Complex power, Weighted symbols, Noncompact manifolds 相似文献
135.
Zarubitskii O. G. Budnik V. G. Omel'chuk A. A. Melekhin V. T. Opanasyuk V. P. Zakharchenko N. F. 《Russian Journal of Applied Chemistry》2002,75(4):558-561
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry. 相似文献
136.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
137.
The procedure for calculating the dispersion of the refractive and absorption indices and thickness of an optical film, based on measurements of spectral dependence of the transmittance, is described. The film parameters are calculated using a solution of the approximation problem. The effect of the film model on the calculated values of the refractive and absorption indices is analyzed. 相似文献
138.
Rainer Löwen 《Journal of Geometry》1989,36(1-2):110-116
We prove that a spread S over a locally compact nondlscrete field F defines a topological translation plane if and only if the spread is compact. For F=R, this is implicit in Breuning's thesis [Bre], cf. [B 2]. For the proof, we describe the point set of the projective translation plane as a quotient space of some projective space, with identifications taking place in one hyperplane. This is new even for F=R. 相似文献
139.
B. P. Harlamov 《Journal of Mathematical Sciences》2006,133(3):1371-1377
An inverse process with independent positive increments is considered. For such a process, the first hitting time τx of level x as a function of x ≥ 0 is a proper process with independent positive increments. In terms of first hitting times
and their Levy measures, multidemensional distribution densities and Laplace transformations are derived. Stationary distributions
of increments of the process are investigated. Bibliography: 8 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 311, 2004, pp. 286–297. 相似文献
140.
The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies ωmw and ωrf, respectively, is analyzed. The effective time-independent Hamiltonian describing the “dressed” spin states of the “spin + bichromatic field” system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances ω0 = ωmw + rωrf (ω0 is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies. 相似文献