全文获取类型
收费全文 | 21042篇 |
免费 | 2229篇 |
国内免费 | 2965篇 |
专业分类
化学 | 10574篇 |
晶体学 | 150篇 |
力学 | 1123篇 |
综合类 | 116篇 |
数学 | 1784篇 |
物理学 | 6325篇 |
无线电 | 6164篇 |
出版年
2024年 | 31篇 |
2023年 | 296篇 |
2022年 | 300篇 |
2021年 | 441篇 |
2020年 | 501篇 |
2019年 | 415篇 |
2018年 | 357篇 |
2017年 | 366篇 |
2016年 | 543篇 |
2015年 | 591篇 |
2014年 | 739篇 |
2013年 | 1012篇 |
2012年 | 1160篇 |
2011年 | 1713篇 |
2010年 | 1119篇 |
2009年 | 1135篇 |
2008年 | 1047篇 |
2007年 | 977篇 |
2006年 | 963篇 |
2005年 | 1021篇 |
2004年 | 1324篇 |
2003年 | 988篇 |
2002年 | 825篇 |
2001年 | 755篇 |
2000年 | 489篇 |
1999年 | 603篇 |
1998年 | 649篇 |
1997年 | 524篇 |
1996年 | 462篇 |
1995年 | 427篇 |
1994年 | 413篇 |
1993年 | 695篇 |
1992年 | 785篇 |
1991年 | 587篇 |
1990年 | 558篇 |
1989年 | 490篇 |
1988年 | 230篇 |
1987年 | 138篇 |
1986年 | 117篇 |
1985年 | 92篇 |
1984年 | 74篇 |
1983年 | 50篇 |
1982年 | 49篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1973年 | 12篇 |
1970年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
Yingyu Hu Guoqiao Lai Yongjia Shen Yongfang Li 《Monatshefte für Chemie / Chemical Monthly》2004,33(2):1167-1172
Zinc(II) and magnesium(II) phthalocyanines bearing four substituted propylenedithiotetrathiafulvalene (PDT-TTF) units were synthesized and characterized by NMR, MS, EA, and UV/VIS spectra. The absorption peaks of two target molecules were hypsochromically shifted compared with the phthalocyanine parent compound. Studies using cyclic voltammetry indicated that introduction of Zn and Mg as central metals enhanced the electronwithdrawing between the phthalocyanine core and the PDT-TTF unit, thus losing one electron to form (PDT-TTF)+ becomes more difficult. 相似文献
133.
Hong-wei Zhang Shao-ying Zhang Bao-gen Shen Helmut Kronmüller 《Journal of magnetism and magnetic materials》2003,260(3):352-360
The magnetization behavior in nanocrystalline permanent magnets has been investigated using mean field Stoner–Wohlfarth model. The model is comparatively simple but allows the numerical treatment of extended nanostructures. The predominant intergrain exchange coupling is expressed by a mean field constant Nm in spite of no explicit relationship between Nm and the microstructure. By this model, the experimental phenomena, such as the remanence enhancement, the shape of demagnetization curve, the irreversible magnetization, the exchange bias field and their respective temperature dependence, can be well explained. The Nm dependence of magnetic properties has been extensively discussed in the present paper. 相似文献
134.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
135.
Spectral and Pseudospectral Approximations Using Hermite Functions: Application to the Dirac Equation 总被引:1,自引:0,他引:1
We consider in this paper spectral and pseudospectral approximations using Hermite functions for PDEs on the whole line. We first develop some basic approximation results associated with the projections and interpolations in the spaces spanned by Hermite functions. These results play important roles in the analysis of the related spectral and pseudospectral methods. We then consider, as an example of applications, spectral and pseudospectral approximations of the Dirac equation using Hermite functions. In particular, these schemes preserve the essential conservation property of the Dirac equation. We also present some numerical results which illustrate the effectiveness of these methods. 相似文献
136.
137.
本文研究非线性算子方程F(x)=y的解,结合最速下降法,Newton-Landweber迭代格式及正则化思想,在F满足适当的条件下,构造出新的双循环迭代格式。本文对格式的收敛性进行了严格论证,并估计出迭代格式的收敛精度。 相似文献
138.
Lin-Ping Shen Wei-Ping Huang Shui-Sheng Jian 《Lightwave Technology, Journal of》2003,21(7):1644-1651
A general procedure for design of photonic crystal fibers (PCFs) with desirable dispersion properties is presented. The design model is based on the combination of a rigorous vector mode solver and a scaling transformation for the dispersion properties of the PCFs. In comparison with the conventional design method, the new design procedure is more efficient and can be readily automated for the purpose of design optimization. Several applications of the design procedure, e.g., the design optimization for dispersion shifted fibers, dispersion flattened fibers, and dispersion compensation fibers, are demonstrated and discussed. 相似文献
139.
光纤接入一直是多年来人们不断追求的梦想和探索的技术方向,但由于成本、技术、需求等方面的障碍,至今还没有得到大规模推广与发展。然而,这种局面最近有了很大的改观,出现可迅速发展的势头。主要是因为一些国家政策的扶持、运营商竞争的需要、对收入的追求,以及设备本身价格的下降,光纤接入技术由于各种原因,至今尚未在全球广泛应用,但在日本、美国、瑞典和意大利等国都获得了较多的应用。在中国,光纤接入也有了良好的开端,将在大城市广泛应用,并逐渐推广到全国。 相似文献
140.