全文获取类型
收费全文 | 61653篇 |
免费 | 5174篇 |
国内免费 | 2934篇 |
专业分类
化学 | 42637篇 |
晶体学 | 506篇 |
力学 | 2677篇 |
综合类 | 273篇 |
数学 | 8690篇 |
物理学 | 14978篇 |
出版年
2023年 | 736篇 |
2022年 | 945篇 |
2021年 | 1301篇 |
2020年 | 1604篇 |
2019年 | 1530篇 |
2018年 | 1243篇 |
2017年 | 1140篇 |
2016年 | 2046篇 |
2015年 | 1901篇 |
2014年 | 2281篇 |
2013年 | 3701篇 |
2012年 | 4408篇 |
2011年 | 4986篇 |
2010年 | 2779篇 |
2009年 | 2631篇 |
2008年 | 3736篇 |
2007年 | 3667篇 |
2006年 | 3469篇 |
2005年 | 3077篇 |
2004年 | 2511篇 |
2003年 | 2163篇 |
2002年 | 2024篇 |
2001年 | 963篇 |
2000年 | 944篇 |
1999年 | 1009篇 |
1998年 | 912篇 |
1997年 | 930篇 |
1996年 | 1145篇 |
1995年 | 848篇 |
1994年 | 762篇 |
1993年 | 656篇 |
1992年 | 637篇 |
1991年 | 559篇 |
1990年 | 455篇 |
1989年 | 404篇 |
1988年 | 389篇 |
1987年 | 334篇 |
1986年 | 307篇 |
1985年 | 464篇 |
1984年 | 427篇 |
1983年 | 303篇 |
1982年 | 354篇 |
1981年 | 359篇 |
1980年 | 316篇 |
1979年 | 297篇 |
1978年 | 276篇 |
1977年 | 250篇 |
1976年 | 226篇 |
1975年 | 236篇 |
1974年 | 237篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
92.
A fluorous osmium catalyst was firstly developed. It had been effectively used as recoverable and reusable catalyst in the dihydroxylation of olefins. 相似文献
93.
David S. McGuinness Edward L. Marshall Vernon C. Gibson Jonathan W. Steed 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3798-3803
Hetero‐bimetallic Fe(II) alkoxide/aryloxides were evaluated as initiators for the ring‐opening polymerization of rac‐lactide. [(THF)NaFe(OtBu)3]2 ( 1 ) and [(THF)4Na2Fe(2,6‐diisopropylphenolate)4] ( 2 ) (THF = tetrahydrofuran) both polymerized lactide efficiently at room temperature, with complex 1 affording better control over the molecular weight parameters of the resultant polymer. At conversions below 70%, a linear increase in molecular weight with conversion was observed, indicative of a well‐controlled polymerization process. Complex 2 is the first example of a dianionic Fe(II) alkoxide and has been structurally characterized to reveal a distorted square planar FeO4 array in which both Na counterions bridge two aryloxide ligands and are further complexed by two THF ligands. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3798–3803, 2003 相似文献
94.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
95.
Zhang Xinliang Huang Dexiu Sun Junqiang Liu Deming 《Optical and Quantum Electronics》2004,36(7):627-634
A simple scheme for single to multi-channel wavelength conversion based on cross-gain modulation of amplified spontaneous emission (ASE) spectrum in semiconductor optical amplifier (SOA) is described. Single to 16-channel wavelength conversion at 10 Gb/s is first demonstrated without any additional probe lights, the modulation information carried by input signal could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited. Output performance and pattern effects are investigated experimentally. 相似文献
96.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
97.
Current methodologies used for the inference of thin film stress through curvature measurement are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single layer of thin film deposited on a substrate subjected to the non-uniform misfit strain in the thin film. Such methodologies are further extended to multi-layer thin films deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain. We derive relations between the stresses in each thin film and the change of system curvatures due to the deposition of each thin film. The interface shear stresses between the adjacent films and between the thin film and the substrate are also obtained from the system curvatures. This provides the basis for the experimental determination of thin film stresses in multi-layer thin films on a substrate. 相似文献
98.
We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given. 相似文献
99.
100.