全文获取类型
收费全文 | 244729篇 |
免费 | 7073篇 |
国内免费 | 3650篇 |
专业分类
化学 | 134206篇 |
晶体学 | 3478篇 |
力学 | 11852篇 |
综合类 | 287篇 |
数学 | 24833篇 |
物理学 | 80796篇 |
出版年
2022年 | 2085篇 |
2021年 | 2257篇 |
2020年 | 2569篇 |
2019年 | 2545篇 |
2018年 | 2493篇 |
2017年 | 2336篇 |
2016年 | 4259篇 |
2015年 | 3568篇 |
2014年 | 4704篇 |
2013年 | 11664篇 |
2012年 | 10468篇 |
2011年 | 12674篇 |
2010年 | 8043篇 |
2009年 | 8217篇 |
2008年 | 11000篇 |
2007年 | 10809篇 |
2006年 | 10179篇 |
2005年 | 9253篇 |
2004年 | 8174篇 |
2003年 | 7090篇 |
2002年 | 6870篇 |
2001年 | 8794篇 |
2000年 | 6696篇 |
1999年 | 5277篇 |
1998年 | 4028篇 |
1997年 | 3994篇 |
1996年 | 3897篇 |
1995年 | 3372篇 |
1994年 | 3173篇 |
1993年 | 2902篇 |
1992年 | 3489篇 |
1991年 | 3382篇 |
1990年 | 2984篇 |
1989年 | 2831篇 |
1988年 | 2793篇 |
1987年 | 2775篇 |
1986年 | 2565篇 |
1985年 | 3654篇 |
1984年 | 3534篇 |
1983年 | 2745篇 |
1982年 | 2893篇 |
1981年 | 2758篇 |
1980年 | 2641篇 |
1979年 | 2712篇 |
1978年 | 2822篇 |
1977年 | 2802篇 |
1976年 | 2640篇 |
1975年 | 2544篇 |
1974年 | 2468篇 |
1973年 | 2500篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
921.
P. G. Baranov N. G. Romanov A. Hofstaetter A. Scharmann C. Schnorr F. J. Ahlers K. Pierz 《JETP Letters》1996,64(10):754-759
Two types of excitons, localized at opposite interfaces and characterized by different magnitudes of the exchange interactions
at the same radiation energies, are simultaneously in type-II GaAs/AlAs superlattices. It is shown that the additional long-wavelength
luminescence line in superlattices grown with growth interruptions after the GaAs layers is due to the recombination of an
exciton localized at an inverted interface in regions where the quantum-well width is increased by one monolayer.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 701–706 (25 November 1996) 相似文献
922.
C. B?uerle Yu M. Bunkov S. N. Fisher H. Godfrin G. R. Pickett 《Czechoslovak Journal of Physics》1996,46(Z1):5-6
During studies of the impact of single neutrons on superfluid3He at around 100μK we have measured the thermal energy released in the superfluid following the nuclear reaction, n+3He→p+3H+764keV. However, we find that the measured energy deposited in the quasiparticle system shortly after this reaction is substantially
less than what we expect. We believe that this energy deficit represents that energy which has gone into the creation of vortices,
in analogy to the creation of cosmic strings in the early universe via the Kibble mechanism. Furthermore, from the magnitude
of the deficit, we can infer the vortex density which compares favorably with that predicted in Zurek’s scenairo. 相似文献
923.
924.
关于非线性Pochhammer-Chree方程的解 总被引:7,自引:0,他引:7
本文研究了弹性杆纵向形变方程:u_(tt)—u_(ttxx)—u_(xx)—(1/3)(u~3)xx=0的椭圆余弦波解,并用Adomian分解法,求出了其初边值问题解. 相似文献
925.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
926.
L. B. Sjogren H. -X. L. Liu X. -H. Qin C. W. Domier N. C. Luhmann 《International Journal of Infrared and Millimeter Waves》1993,14(6):1201-1216
Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays. 相似文献
927.
Heat transfer in lattice BGK modeled fluid 总被引:1,自引:0,他引:1
The thermal lattice BGK model is a recently suggested numerical tool aiming at solving problems of thermohydrodynamics. The quality of the lattice BGK simulation is checked in this paper by calculating temperature profiles in the Couette flow under different Eckert and Mach numbers. A revised lower order model is proposed to improve the accuracy and the higher order model is proved to be advantageous in this respect, especially in the flow regime with a higher Mach number. 相似文献
928.
A fast electrooptic modulation in a polymer waveguide using a ferroelectric liquid crystal has been proposed. In this device, the surface stabilized ferroelectric liquid crystal and the soft mode ferroelectric liquid crystal are used as an active material on the passive polymer waveguide, and electrooptic switching is realized by controlling the total reflection at the polymer waveguide-liquid crystal interface. The response time is of the order of several microseconds. The analogue electrooptic modulation in the waveguide is realized using the field induced linear molecular tilt of the electroclinic effect in the soft mode ferroelectric liquid crystal. 相似文献
929.
930.
Nonlinear and chaotic oscillations of a constrained cantilevered pipe conveying fluid: A full nonlinear analysis 总被引:2,自引:0,他引:2
In this paper, the planar dynamics of a nonlinearly constrained pipe conveying fluid is examined numerically, by considering the full nonlinear equation of motions and a refined trilinear-spring model for the impact constraints—completing the circle of several studies on the subject. The effect of varying system parameters is investigated for the two-degree-of-freedom (N=2) model of the system, followed by less extensive similar investigations forN=3 and 4. Phase portraits, bifurcation diagrams, power spectra and Lyapunov exponents are presented for a selected set of system parameters, showing some rather interesting, and sometimes unexpected, results. The numerical results are compared with experimental ones obtained previously. It is found that in the parameter space that includesN, there exists a subspace wherein excellent qualitative, and reasonably good (N=2) to excellent (N=4) quantitative agreement with experiment. In the latter case, excellent agreement is not only obtained in the threshold flow velocities (u) for the key bifurcations, but the inclusion of the nonlinear terms improves agreement with experiment in terms of amplitudes of motion and by capturing features of behaviour not hitherto predicted by theory. 相似文献