全文获取类型
收费全文 | 482611篇 |
免费 | 3423篇 |
国内免费 | 1097篇 |
专业分类
化学 | 236666篇 |
晶体学 | 7607篇 |
力学 | 24043篇 |
综合类 | 12篇 |
数学 | 68610篇 |
物理学 | 150193篇 |
出版年
2020年 | 3206篇 |
2019年 | 3576篇 |
2018年 | 11860篇 |
2017年 | 12585篇 |
2016年 | 10436篇 |
2015年 | 4880篇 |
2014年 | 6927篇 |
2013年 | 17201篇 |
2012年 | 16212篇 |
2011年 | 25367篇 |
2010年 | 16899篇 |
2009年 | 16742篇 |
2008年 | 22918篇 |
2007年 | 25832篇 |
2006年 | 13863篇 |
2005年 | 17485篇 |
2004年 | 14083篇 |
2003年 | 13154篇 |
2002年 | 11304篇 |
2001年 | 11499篇 |
2000年 | 8983篇 |
1999年 | 6760篇 |
1998年 | 5838篇 |
1997年 | 5722篇 |
1996年 | 5526篇 |
1995年 | 5142篇 |
1994年 | 5220篇 |
1993年 | 4887篇 |
1992年 | 5533篇 |
1991年 | 5512篇 |
1990年 | 5387篇 |
1989年 | 5230篇 |
1988年 | 5285篇 |
1987年 | 5171篇 |
1986年 | 4938篇 |
1985年 | 6493篇 |
1984年 | 6793篇 |
1983年 | 5864篇 |
1982年 | 6007篇 |
1981年 | 5817篇 |
1980年 | 5750篇 |
1979年 | 5864篇 |
1978年 | 6205篇 |
1977年 | 6012篇 |
1976年 | 6144篇 |
1975年 | 5752篇 |
1974年 | 5776篇 |
1973年 | 6073篇 |
1972年 | 4198篇 |
1971年 | 3452篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
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
22.
23.
G. L. Booth 《Acta Mathematica Hungarica》1989,54(3-4):201-208
24.
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
25.
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
26.
Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献
27.
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
28.
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
29.
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
30.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques. 相似文献