全文获取类型
收费全文 | 290461篇 |
免费 | 2096篇 |
国内免费 | 999篇 |
专业分类
化学 | 140779篇 |
晶体学 | 4016篇 |
力学 | 14953篇 |
综合类 | 6篇 |
数学 | 54508篇 |
物理学 | 79294篇 |
出版年
2020年 | 1970篇 |
2019年 | 2263篇 |
2018年 | 13388篇 |
2017年 | 13158篇 |
2016年 | 10185篇 |
2015年 | 3181篇 |
2014年 | 4084篇 |
2013年 | 9529篇 |
2012年 | 10522篇 |
2011年 | 18603篇 |
2010年 | 11530篇 |
2009年 | 11787篇 |
2008年 | 14499篇 |
2007年 | 16663篇 |
2006年 | 7805篇 |
2005年 | 8159篇 |
2004年 | 7624篇 |
2003年 | 7535篇 |
2002年 | 6466篇 |
2001年 | 6165篇 |
2000年 | 4947篇 |
1999年 | 3595篇 |
1998年 | 3178篇 |
1997年 | 3168篇 |
1996年 | 3004篇 |
1995年 | 2432篇 |
1994年 | 2492篇 |
1993年 | 2541篇 |
1992年 | 2644篇 |
1991年 | 2718篇 |
1990年 | 2608篇 |
1989年 | 2591篇 |
1988年 | 2519篇 |
1987年 | 2490篇 |
1986年 | 2413篇 |
1985年 | 3082篇 |
1984年 | 3236篇 |
1983年 | 2595篇 |
1982年 | 2866篇 |
1981年 | 2740篇 |
1980年 | 2547篇 |
1979年 | 2761篇 |
1978年 | 2866篇 |
1977年 | 2874篇 |
1976年 | 2847篇 |
1975年 | 2703篇 |
1974年 | 2676篇 |
1973年 | 2835篇 |
1972年 | 1892篇 |
1967年 | 1840篇 |
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
191.
Palle E. T. Jorgensen 《Mathematische Zeitschrift》1989,201(4):455-476
Work supported in part by the NSF 相似文献
192.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献
193.
Summary In 1980 Dahmen-DeVore-Scherer introduced a modulus of continuity which turns out to reflect invariance properties of compound cubature rules effectively. Accordingly, sharp error bounds are derived, the existence of relevant counterexamples being a consequence of a quantitative resonance principle, established previously. 相似文献
194.
José E. Valdés 《Operations Research Letters》2006,34(1):49-52
Components C1 and C2 form a series system. Suppose we can allocate the spare R1 in parallel with C1 and the spare R2 in parallel with C2, or otherwise, allocate R1 with C2 and R2 with C1. In this paper, we compare these two options using hazard rate ordering. 相似文献
195.
We establish soliton-like asymptotics for finite energy solutions to the Schrödinger equation coupled to a nonrelativistic classical particle. Any solution with initial state close to the solitary manifold converges to a sum of a travelling wave and an outgoing free wave. The convergence holds in global energy norm. The proof uses spectral theory and the symplectic projection onto the solitary manifold in the Hilbert phase space. 相似文献
196.
K.R. Allakhverdiev T. Baykara E. Günay A. Kulibekov E.Yu. Salaev 《Optics Communications》2006,261(1):60-64
The Bridgman method is used to grow single crystals of ε-GaSe. The two-photon absorption (TPA) coefficient β was measured for especially un-doped crystals at room temperature for the ordinary o-ray (β⊥) and extraordinary e-ray (β∥) using single-wavelength excitation by a Nd:YVO4 laser at 1.064 μm with a pulse duration of 10 ps and a repetition rate of 81 MHz. No large anisotropy was observed for the TPA coefficients between the two geometries. The TPA coefficients were found to be β⊥ = 1.07 × 10−9 cm/W and β∥ = 1.88 × 10−9 cm/W. It was found that doping slightly increases the TPA coefficient. The value of the TPA for crystals doped with 0.5 at.% of Tl is β⊥ = 7.56 × 10−9 cm/W. 相似文献
197.
198.
The spatial structure of Bragg angles and the transfer functions of an acousto-optic cell are calculated for the cases of isotropic and anisotropic light diffraction in a uniaxial crystal. Their change with ultrasound frequency is traced. The possibility of image processing by acousto-optic filtration of the spatial spectrum of an image is considered. The results of experimental visualization of the transfer functions of a calcium molybdate crystal cell are presented. 相似文献
199.
J Ashenfelter 《Pramana》2002,59(5):713-717
The ESTU began operation in 1988 and achieved the design voltage of 20 MV in 1990. Since that time, improvements to the gas
handling system, negative ion injector, accelerator terminal and control system have greatly increased its capability and
reliability. Today, the ESTU can efficiently produce an extensive assortment of stable ions at wide-ranging energies in support
of low-energy nuclear physics. 相似文献
200.
D. De Salvador A. Coati E. Napolitani M. Berti A.V. Drigo M.S. Carroll J.C. Sturm J. Stangl G. Bauer L. Lazzarini 《Applied Physics A: Materials Science & Processing》2002,75(6):667-672
In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC
layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N2) or oxidizing (O2) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under
oxidation enhances the C diffusion with respect to the N2-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the
layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration.
This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act
as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion
is discussed.
Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002 相似文献