全文获取类型
收费全文 | 736847篇 |
免费 | 6741篇 |
国内免费 | 2210篇 |
专业分类
化学 | 337754篇 |
晶体学 | 9373篇 |
力学 | 32100篇 |
综合类 | 24篇 |
数学 | 83542篇 |
物理学 | 198780篇 |
无线电 | 84225篇 |
出版年
2021年 | 6369篇 |
2020年 | 7036篇 |
2019年 | 7906篇 |
2018年 | 10092篇 |
2017年 | 10171篇 |
2016年 | 14475篇 |
2015年 | 8155篇 |
2014年 | 13489篇 |
2013年 | 31249篇 |
2012年 | 24324篇 |
2011年 | 29239篇 |
2010年 | 21763篇 |
2009年 | 22631篇 |
2008年 | 29087篇 |
2007年 | 29622篇 |
2006年 | 27507篇 |
2005年 | 25068篇 |
2004年 | 23234篇 |
2003年 | 21053篇 |
2002年 | 20626篇 |
2001年 | 21715篇 |
2000年 | 17431篇 |
1999年 | 13959篇 |
1998年 | 12253篇 |
1997年 | 11918篇 |
1996年 | 11127篇 |
1995年 | 10102篇 |
1994年 | 10101篇 |
1993年 | 9769篇 |
1992年 | 10161篇 |
1991年 | 10588篇 |
1990年 | 9976篇 |
1989年 | 9696篇 |
1988年 | 9276篇 |
1987年 | 8426篇 |
1986年 | 8071篇 |
1985年 | 10307篇 |
1984年 | 10549篇 |
1983年 | 8875篇 |
1982年 | 9186篇 |
1981年 | 8606篇 |
1980年 | 8303篇 |
1979年 | 8615篇 |
1978年 | 8923篇 |
1977年 | 8750篇 |
1976年 | 8669篇 |
1975年 | 8312篇 |
1974年 | 8096篇 |
1973年 | 8462篇 |
1972年 | 5980篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Compensated SC integrator stages are analysed and compared with respect to their sensitivities to finite amplifier gain effects. Simple single-stage amplifiers may be used in such circuits even in highly selective filtering applications. This may allow an extension of the present frequency range of SC circuits. 相似文献
62.
63.
A. Sebbar 《Mathematische Zeitschrift》1989,201(4):561-581
Sans résumé 相似文献
64.
L. A. Khalfin 《Journal of Mathematical Sciences》1987,36(5):616-626
The article surveys the main results of the statistical approach to the solution of ill-posed problems of mathematical physics, in application to specific ill-posed inverse problems in geophysics.Invited paper presented at the International Seminar on Mathematical Foundations of the Interpretation of Geophysical Fields, Moscow, May–June 1972.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 79, pp. 67–81, 1978. 相似文献
65.
66.
A. I. Nazarov 《Journal of Mathematical Sciences》2006,133(3):1314-1327
We find logarithmic small ball asymptotics for the L2-norm with respect to self-similar measures for a certain class of Gaussian processes including Brownian motion, Ornstein-Uhlenbeck
process, and their integrated counterparts. Bibliography: 46 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 311, 2004, pp. 190–213. 相似文献
67.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
68.
An examination is presented of three techniques used for the efficient computation of fields diffracted by a subreflector that has been shaped by geometrical optics synthesis. It is found that these techniques, which are based on the geometrical theory of diffraction (GTD), produce errors in the computed fields that are specific to shaped reflectors. These errors are examined for a reflector system shaped to produce maximum gain from a tapered feed illumination. The discrepancies are directly related to the caustic being located near an observation point of the GTD calculations. The errors found are localized, and they increase in magnitude as the caustic approaches the main reflector. In a general offset geometry, the location of the caustic may be located arbitrarily close to the main reflector given a prescribed output aperture distribution. For the specific case considered here-the common situation of shaping to produce maximum gain-the caustic is located near the edge of the main reflector and on the reflection shadow boundary. A local correction is derived which creates a uniform solution through the caustic and across the reflection shadow boundary. Away from this point the calculation recedes to the standard GTD solution 相似文献
69.
Shamansky H.T. Dominek A.K. Peters L. Jr. 《Antennas and Propagation, IEEE Transactions on》1989,37(8):1019-1025
The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth 相似文献
70.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献