全文获取类型
收费全文 | 586383篇 |
免费 | 6313篇 |
国内免费 | 2672篇 |
专业分类
化学 | 275370篇 |
晶体学 | 7919篇 |
力学 | 23229篇 |
综合类 | 66篇 |
数学 | 60391篇 |
物理学 | 159394篇 |
无线电 | 68999篇 |
出版年
2020年 | 4507篇 |
2019年 | 4937篇 |
2018年 | 6328篇 |
2017年 | 6263篇 |
2016年 | 9417篇 |
2015年 | 5935篇 |
2014年 | 9407篇 |
2013年 | 23538篇 |
2012年 | 18190篇 |
2011年 | 22419篇 |
2010年 | 16163篇 |
2009年 | 16876篇 |
2008年 | 22196篇 |
2007年 | 22932篇 |
2006年 | 21769篇 |
2005年 | 19957篇 |
2004年 | 18275篇 |
2003年 | 16206篇 |
2002年 | 16061篇 |
2001年 | 17550篇 |
2000年 | 14035篇 |
1999年 | 11148篇 |
1998年 | 9843篇 |
1997年 | 9689篇 |
1996年 | 9147篇 |
1995年 | 8426篇 |
1994年 | 8392篇 |
1993年 | 8217篇 |
1992年 | 8540篇 |
1991年 | 8698篇 |
1990年 | 8248篇 |
1989年 | 7966篇 |
1988年 | 7711篇 |
1987年 | 6916篇 |
1986年 | 6718篇 |
1985年 | 8773篇 |
1984年 | 9020篇 |
1983年 | 7574篇 |
1982年 | 7896篇 |
1981年 | 7603篇 |
1980年 | 7181篇 |
1979年 | 7462篇 |
1978年 | 7869篇 |
1977年 | 7686篇 |
1976年 | 7790篇 |
1975年 | 7226篇 |
1974年 | 7362篇 |
1973年 | 7427篇 |
1972年 | 5448篇 |
1971年 | 4502篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
51.
Dr. H. Schmieg Prof. Dr. P. Vielsack 《Archive of Applied Mechanics (Ingenieur Archiv)》1987,57(6):446-458
Übersicht Betrachtet wird ein zwangserregtes Zweikörpersystem mit wechselnden Bindungen infolge trockener Reibung. Stationäre Bewegungen werden als Grenzfall instationärer Einschwingvorgänge berechnet. Abhängig von den Systemparametern ergeben sich drei typische Bewegungsformen. Ihnen entsprechen dauernde Haftzustände, wechselnde Haft-Gleitzustände oder dauernde Gleitzustände an der Berührfläche beider Körper.
Intermittant constraints in a two-body-system with dry friction
Summary An externally excited two-body-system with intermittant constraints due to dry friction is considered. Stationary motions are calculated as limit cases of instationary transients. Depending on the parameters of the system, three typical modes are of interest. These correspond to permanent sticking, slipstick behaviour, or to permanent slipping in the contact surface of the bodies, respectively.相似文献
52.
A. L. Chistov 《Journal of Mathematical Sciences》2006,138(3):5733-5752
Consider a projective algebraic variety W which is an irreducible component of the set of all common zeros of a family of
homogeneous polynomials of degrees less than d in n + 1 variables over a field of zero characteristic. Consider a dominant
rational morphism from W to W′ given by homogeneous polynomials of degree d′. We suggest algorithms for constructing objects
in general position related to this morphism. They generalize some algorithms from the first part of the paper to the case
dim W > dim W′. These algorithms are deterministic and polynomial in (dd′)n and the size of the input. Bibliography: 12 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 325, 2005, pp. 181–224. 相似文献
53.
54.
A minimal integrated filter containing four MOS transistors as the only circuit elements is presented. Voltage tuning is used to set the cutoff frequency and band-edge peaking. A filter test chip occupies an active area of 0006mm2, has acutoff frequency of 40 MHz and dissipates 580W. 相似文献
55.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
56.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating 相似文献
57.
58.
Jeroen J. L. M. Cornelissen W. Sander Graswinckel Alan E. Rowan Nico A. J. M. Sommerdijk Roeland J. M. Nolte 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1725-1736
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003 相似文献
59.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed. 相似文献
60.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献