全文获取类型
收费全文 | 69504篇 |
免费 | 3360篇 |
国内免费 | 2843篇 |
专业分类
化学 | 38606篇 |
晶体学 | 721篇 |
力学 | 3113篇 |
综合类 | 248篇 |
数学 | 13208篇 |
物理学 | 19811篇 |
出版年
2023年 | 310篇 |
2022年 | 523篇 |
2021年 | 878篇 |
2020年 | 893篇 |
2019年 | 955篇 |
2018年 | 1954篇 |
2017年 | 2196篇 |
2016年 | 2042篇 |
2015年 | 1853篇 |
2014年 | 2144篇 |
2013年 | 3203篇 |
2012年 | 6199篇 |
2011年 | 5729篇 |
2010年 | 4113篇 |
2009年 | 3735篇 |
2008年 | 3428篇 |
2007年 | 3281篇 |
2006年 | 3148篇 |
2005年 | 6690篇 |
2004年 | 5831篇 |
2003年 | 3822篇 |
2002年 | 2141篇 |
2001年 | 1474篇 |
2000年 | 1089篇 |
1999年 | 801篇 |
1998年 | 564篇 |
1997年 | 496篇 |
1996年 | 500篇 |
1995年 | 390篇 |
1994年 | 392篇 |
1993年 | 360篇 |
1992年 | 491篇 |
1991年 | 406篇 |
1990年 | 327篇 |
1989年 | 288篇 |
1988年 | 272篇 |
1987年 | 200篇 |
1986年 | 156篇 |
1985年 | 225篇 |
1984年 | 148篇 |
1983年 | 137篇 |
1982年 | 147篇 |
1981年 | 112篇 |
1979年 | 101篇 |
1978年 | 121篇 |
1977年 | 108篇 |
1976年 | 180篇 |
1975年 | 141篇 |
1974年 | 124篇 |
1973年 | 156篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
181.
The Cahn-Hilliard equation is modeled to describe the dynamics of phase separation in glass and polymer systems. A priori error estimates for the Cahn-Hilliard equation have been studied by the authors. In order to control accuracy of approximate solutions, a posteriori error estimation of the Cahn-Hilliard equation is obtained by discontinuous Galerkin method. 相似文献
182.
183.
We study the stationary measure for the two-dimensional Boussinesq equation with random forcing. We prove the ergodicity for the two-dimensional stochastically forced Boussinesq equation. We also study the Galerkin truncations of the three-dimensional Boussinesq equations under degenerate stochastic forcing. We follow closely the previous results on the stochastically forced Navier–Stokes equations. 相似文献
184.
The Kα to Lα and Kβ to Lβ intensity ratios of seven elements have been measured following photoionization at 59.5 keV by using a Si (Li) detector
(FWHM=155 eV at 5.96 keV). The intensity ratios were determined by measuring K and L x-rays emitted from a standard target of a given element. The theoretical values of the Kα to Lα and Kβ to Lβ intensity ratios were calculated using theoretically tabulated values of shell/subshell photoionization cross sections,
fluorescence yields, Coster-Kronig transition probabilities, and radiative decay rates for ηKLi≠ and ηKLi=0. The measured values are in good agreement with theoretical results.
From Optika i Spektroskopiya, Vol. 97, No. 2, 2004, pp. 186–189.
Original English Text Copyright ? 2004 by A. Kü?ük?nder, S?ğüt, E. Kü?ük?nder, Büyükkasap.
This article was submitted by the authors in English. 相似文献
185.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis. 相似文献
186.
187.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献
188.
Hyun Chul Choi Min Kyu Lee Hyun Joon Shin Seung Bin Kim 《Journal of Electron Spectroscopy and Related Phenomena》2003,130(1-3):85-96
To investigate the formation of a solid electrolyte interface (SEI) on the Li1+xV3O8 electrode surface in the thermodynamic stability range of the organic electrolyte, we applied scanning photoelectron microscopy (SPEM) to a pristine electrode and to an electrode after ten cycles. The F K-edge absorption spectrum of the cycled electrode showed that LiF forms on the electrode surface during the lithium insertion–extraction process in the Li1+xV3O8/Li cell. The photoelectron spectrum for the cycled electrode showed intense spectral features corresponding to Li 1s, F 2s, F 2p, and P 2p electron signals, whereas these spectral features were of negligible intensity for the pristine electrode. The above results give strong support for the formation of an SEI that consists of LiF and compounds containing phosphorus during operation of the battery. The SPEM images also revealed that the fluorine distribution on the surface of the cycled electrode was inhomogeneous. 相似文献
189.
Yong Lee Kazuhiko Hosomi Hiroyuki Uchiyama Toshio Katsuyama Shinya Kominami Tomoyoshi Mishima 《Optical Review》2003,10(1):38-42
An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode. 相似文献
190.
J. H. Lu Y. Y. Yang C. C. Chen C. H. Kuan H. T. Chen S. C. Lee 《Infrared Physics & Technology》2003,44(5-6):399-409
Superlattices have been demonstrated previously by our group in the design of the multicolor infrared photodetector. In general, the period number of the superlattice may be up to several dozens. In this paper, we have investigated the performance of the infrared photodetectors especially with 3, 5 and 15 periods. The detector structure contains a thick blocking barrier embedded between two superlattices with different period numbers but with the same well and barrier widths. This double-superlattice structure shows switchable spectral responses between two spectral regions by the voltage polarities. The photoresponse in each spectral region is also tunable by the magnitude of the applied voltage. The voltage-dependent behavior reveals the photoelectron relaxation and transport mechanism in the superlattice miniband. Superlattice with few periods has high electron group velocity, less relaxation effect and less collection efficiency. Therefore the superlattice with few periods may have better responsivity and narrower photoresponse range than the one with many periods. Based on the experimental results of our devices, it is observed that the superlattice with fewer periods has better detectivity, responsivity, wider range of the operational temperature, and more flexible miniband engineering than the conventional multiple quantum well infrared photodetector. 相似文献