全文获取类型
收费全文 | 31299篇 |
免费 | 4257篇 |
国内免费 | 3356篇 |
专业分类
化学 | 16749篇 |
晶体学 | 272篇 |
力学 | 1708篇 |
综合类 | 188篇 |
数学 | 3422篇 |
物理学 | 8435篇 |
无线电 | 8138篇 |
出版年
2024年 | 118篇 |
2023年 | 757篇 |
2022年 | 840篇 |
2021年 | 1170篇 |
2020年 | 1109篇 |
2019年 | 1040篇 |
2018年 | 931篇 |
2017年 | 883篇 |
2016年 | 1335篇 |
2015年 | 1325篇 |
2014年 | 1575篇 |
2013年 | 2238篇 |
2012年 | 2401篇 |
2011年 | 2402篇 |
2010年 | 1857篇 |
2009年 | 1699篇 |
2008年 | 1931篇 |
2007年 | 1753篇 |
2006年 | 1708篇 |
2005年 | 1432篇 |
2004年 | 1145篇 |
2003年 | 1014篇 |
2002年 | 1050篇 |
2001年 | 919篇 |
2000年 | 698篇 |
1999年 | 773篇 |
1998年 | 631篇 |
1997年 | 535篇 |
1996年 | 578篇 |
1995年 | 487篇 |
1994年 | 443篇 |
1993年 | 344篇 |
1992年 | 275篇 |
1991年 | 278篇 |
1990年 | 219篇 |
1989年 | 164篇 |
1988年 | 159篇 |
1987年 | 109篇 |
1986年 | 106篇 |
1985年 | 98篇 |
1984年 | 57篇 |
1983年 | 68篇 |
1982年 | 55篇 |
1981年 | 45篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1977年 | 16篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
Carsey F.D. Argus S.A.D. Collins M.J. Holt B. Livingstone C.E. Tang C.L. 《Geoscience and Remote Sensing, IEEE Transactions on》1989,27(5):468-482
Ice observations, results, and conclusions are summarized for the March 1987 Labrador Ice Margin Experiment (LIMEX'87), an international oceanographic study conducted in the pack ice of the Grand Banks area off the coast of Newfoundland. Included are the ice extent, flow size and thickness, ice kinematics and rheology, ice microwave properties, oceanic properties under the ice, and penetration of swell into the ice 相似文献
13.
Ben J. Morris 《Random Structures and Algorithms》2002,21(2):135-146
We study the problem of sampling contingency tables (nonnegative integer matrices with specified row and column sums) uniformly at random. We give an algorithm which runs in polynomial time provided that the row sums ri and the column sums cj satisfy ri = Ω(n3/2m log m), and cj = Ω(m3/2n log n). This algorithm is based on a reduction to continuous sampling from a convex set. The same approach was taken by Dyer, Kannan, and Mount in previous work. However, the algorithm we present is simpler and has weaker requirements on the row and column sums. © 2002 Wiley Periodicals, Inc. Random Struct. Alg., 21: 135–146, 2002 相似文献
14.
The interactions induced by the nonlinear refractive index in a single-mode optical fiber (Kerr effect) between a modulated wave and a carrier wave have been investigated for amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The theoretical analysis, based on a time-domain solution, exploits the well-known formalism of self-phase modulation to describe the propagation of the input electric field in the fiber. The theoretical results were validated experimentally for amplitude- and phase-modulated waves with heterodyne detection techniques. These experiments mimic a coherent transmission system and allow the measurement of the spectrum of each of the waves that participate in the nonlinear interaction 相似文献
15.
多孔硅发光机制的分析 总被引:4,自引:0,他引:4
从量子力学的基本理论出发讨论了量子限制效应,推导出多孔硅有效禁带宽度增量并用量子限制效应和表面态及其物质在发光中作用的理论解释了PS光致发光的实验现象。 相似文献
16.
17.
For improved mechanical and water‐swelling properties of chitosan films, a series of transparent films were prepared with dialdehyde starch as a crosslinking agent. Fourier transform infrared and X‐ray analysis results demonstrated that the formation of Schiff's base disturbed the crystallization of chitosan. The mechanical properties and water‐swelling properties of the films were significantly improved. The best values of the tensile strength and breaking elongation were 113.1 MPa and 27.0%, respectively, when the dialdehyde starch content was 5%. All the crosslinked films still retained obvious antimicrobial effects toward S. aureus and E. coli, and they showed potential for biomedical applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 993–997, 2003 相似文献
18.
Miniaturized Hexagonal Stepped-Impedance Resonators and Their Applications to Filters 总被引:1,自引:0,他引:1
Rui-Jie Mao Xiao-Hong Tang Ling Wang Guo-Hong Du 《Microwave Theory and Techniques》2008,56(2):440-448
Miniaturized hexagonal stepped-impedance resonators and their applications to bandpass filters are presented. Based on the odd- and even-mode equivalent circuits, the resonance characteristics of these resonators are investigated. A series of circuit configurations, including the third-order Chebyshev, trisection, and fifth-order cascaded trisection filters, are constructed by the proposed resonators. These filters are very compact and have good stopband responses. Measured results validate the analysis and theoretical prediction with good agreement. 相似文献
19.
20.
Yanqing Tian Xiaohe Xu Yingying Zhao Xinyi Tang Fengyu Su Xiaoguang Zhao Enle Zhou 《Liquid crystals》1995,19(3):295-300
The synthesis of three new series of chiral Schiff's bases containing benzilideneaniline and 2-hydroxybenzilideneaniline moieties as mesogenic cores is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements were used to study the phase transition temperatures and behaviour. The results reveal that most of these materials show chiral smectic mesomorphism. 相似文献