全文获取类型
收费全文 | 323713篇 |
免费 | 2151篇 |
国内免费 | 881篇 |
专业分类
化学 | 136048篇 |
晶体学 | 4454篇 |
力学 | 18918篇 |
综合类 | 3篇 |
数学 | 69433篇 |
物理学 | 97889篇 |
出版年
2020年 | 1416篇 |
2019年 | 1575篇 |
2018年 | 18583篇 |
2017年 | 19203篇 |
2016年 | 11767篇 |
2015年 | 3413篇 |
2014年 | 3499篇 |
2013年 | 8083篇 |
2012年 | 12551篇 |
2011年 | 26403篇 |
2010年 | 16090篇 |
2009年 | 16518篇 |
2008年 | 21525篇 |
2007年 | 26409篇 |
2006年 | 6459篇 |
2005年 | 12994篇 |
2004年 | 9582篇 |
2003年 | 9474篇 |
2002年 | 6651篇 |
2001年 | 5578篇 |
2000年 | 4420篇 |
1999年 | 3137篇 |
1998年 | 2701篇 |
1997年 | 2532篇 |
1996年 | 2542篇 |
1995年 | 2314篇 |
1994年 | 2242篇 |
1993年 | 2156篇 |
1992年 | 2414篇 |
1991年 | 2369篇 |
1990年 | 2303篇 |
1989年 | 2241篇 |
1988年 | 2254篇 |
1987年 | 2253篇 |
1986年 | 2142篇 |
1985年 | 2757篇 |
1984年 | 2764篇 |
1983年 | 2444篇 |
1982年 | 2569篇 |
1981年 | 2371篇 |
1980年 | 2369篇 |
1979年 | 2533篇 |
1978年 | 2569篇 |
1977年 | 2421篇 |
1976年 | 2502篇 |
1975年 | 2410篇 |
1974年 | 2367篇 |
1973年 | 2585篇 |
1972年 | 1655篇 |
1971年 | 1353篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
151.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
152.
Using an integral theory of grating diffraction we calculate efficiencies greater than 100% if a coating with gain is taken into account. A connection with guided modes is conjectured. The application in optical computing seems to be possible. 相似文献
153.
Chee Sing Yap 《The Journal of the Operational Research Society》1989,40(7):649-658
This paper describes three case studies which investigated issues relating to the implementation and management of advanced information technology. The benefits derived from information technology were found to vary from one organization to another. These studies provide further evidence to support earlier research findings that senior management has an important role to play in the effective exploitation of information technology, and that the investment approach taken by an organization has a significant effect on the development of computer-based information systems. The effectiveness of a system depends not only on applying the appropriate technology, but also on how successfully technical and behavioural issues are resolved. 相似文献
154.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献
155.
156.
Transport as a consequence of state-dependent diffusion 总被引:1,自引:0,他引:1
M. Büttiker 《Zeitschrift für Physik B Condensed Matter》1987,68(2-3):161-167
Overdamped particles subject to a drift in a force field with sinusoidal space dependence and also a sinusoidally modulated space-dependent diffusion, with the same period as the drift, experience a net driving force. The resulting current depends on the amplitude of the modulation of the diffusion and is a periodic function of the phase difference between the sinusoidal drift and the sinusoidal modulation of the diffusion. For small modulation amplitudes a particle subject to state-dependent noise behaves the same way as a particle subject to thermal noise but with a drift which, in addition to the sinusoidal term, contains a net force term.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday 相似文献
157.
Using the method of the tensor Green’s function of the wave equation, the differential and total cross sections for the scattering of surface optical electromagnetic waves (surface plasmon polaritons) by a spherical nanoparticle into surface plasmon polaritons and light have been obtained with the inclusion of the magnetic dipole contribution. Using the example of noble metal systems, it has been shown that the magnetic dipole contribution may significantly affect the angular dependence of the differential cross sections and increase their anisotropy as the plasmon wavelength increases. 相似文献
158.
Space-time directional Lyapunov exponents are introduced. They describe the maximal velocity of propagation to the right or to the left of fronts of perturbations in a frame moving with a given velocity. The continuity of these exponents as function of the velocity and an inequality relating them to the directional entropy is proved. 相似文献
159.
M I Salema A P B Póvoa A Q Novais 《The Journal of the Operational Research Society》2006,57(6):615-629
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis. 相似文献
160.
M. V. Kartikeyan G. Singh E. Borie B. Piosczyk M. Thumm 《International Journal of Infrared and Millimeter Waves》2006,27(5):657-670
The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode
competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic
roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried
out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of
well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector. 相似文献