全文获取类型
收费全文 | 60434篇 |
免费 | 10191篇 |
国内免费 | 8471篇 |
专业分类
化学 | 42788篇 |
晶体学 | 932篇 |
力学 | 3577篇 |
综合类 | 778篇 |
数学 | 6876篇 |
物理学 | 24145篇 |
出版年
2024年 | 204篇 |
2023年 | 1179篇 |
2022年 | 2352篇 |
2021年 | 2469篇 |
2020年 | 2528篇 |
2019年 | 2353篇 |
2018年 | 2052篇 |
2017年 | 2116篇 |
2016年 | 2830篇 |
2015年 | 3015篇 |
2014年 | 3545篇 |
2013年 | 4525篇 |
2012年 | 5416篇 |
2011年 | 5420篇 |
2010年 | 3952篇 |
2009年 | 3725篇 |
2008年 | 4089篇 |
2007年 | 3613篇 |
2006年 | 3330篇 |
2005年 | 2910篇 |
2004年 | 2202篇 |
2003年 | 1724篇 |
2002年 | 1589篇 |
2001年 | 1402篇 |
2000年 | 1305篇 |
1999年 | 1286篇 |
1998年 | 964篇 |
1997年 | 914篇 |
1996年 | 879篇 |
1995年 | 796篇 |
1994年 | 697篇 |
1993年 | 602篇 |
1992年 | 509篇 |
1991年 | 448篇 |
1990年 | 389篇 |
1989年 | 320篇 |
1988年 | 231篇 |
1987年 | 205篇 |
1986年 | 193篇 |
1985年 | 171篇 |
1984年 | 113篇 |
1983年 | 114篇 |
1982年 | 78篇 |
1981年 | 71篇 |
1980年 | 41篇 |
1979年 | 28篇 |
1977年 | 23篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
本文以fp 同伦方法为工具,借助于一些适当的变换,研究有序的(B)空间中的集值映象方程的多正解问题;在文中的有关工作中,还使用了集值映象的拟导数的某些性质. 相似文献
43.
数字散斑干涉技术在振动分析中的应用 总被引:2,自引:0,他引:2
首次将相移技术应用于频闪数字散斑干涉计量中,对物体的振动进行了定量分析.实验证明,这种方法有广泛的实用价值.另外,介绍了一套自动分析系统,讨论了各参数对测量结果的影响. 相似文献
44.
In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of TChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation. 相似文献
45.
Chii-Wann Lin Kuo-Ping Chen Ming-Chii Su Chih-Kung Lee Chih-Chung Yang 《Optical and Quantum Electronics》2005,37(13-15):1423-1437
We have reported a novel design of surface plasmon resonance (SPR) device, which uses alternating dielectric layers to enhance the SPR signal quality and modulate its resonant position. Admittance loci method of thin film design has been used in the design of such a device. The use of biomolecular thin film, such as DNAs or Porteins, in this design can result in resonant condition of wavelength changes as well. Bio-plasmonics is proposed for the research and development of novel devices, which use biomolecules as a part of the plasmon oscillation system to actively interact with nano/micro structure. 相似文献
46.
Yang Zuosheng 《国际流体数值方法杂志》2005,47(12):1423-1430
A complete boundary integral formulation for compressible Navier–Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for wall pressure and wall skin friction of two‐dimensional compressible laminar viscous flow around airfoils are in good agreement with field numerical methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
47.
关于多线性振荡奇异积分在加权Hardy-型空间上的一致估计 总被引:1,自引:0,他引:1
本文对一类具有光滑位相函数的多线性振荡奇异积分算子建立了一致的加权(H^1(R^n),L^1(R^n))估计及一致的加权(HKp(R^n),Kp(R^n)估计。 相似文献
48.
Effects of Substrate Temperature on Helium Content and Microstructure of Nanocrystalline Titanium Films 下载免费PDF全文
Helium-charged nanocrystalline titanium films have been deposited by HeAr magnetron co-sputtering. The effects of substrate temperature on the helium content and microstructure of the nanocrystalline titanium films have been studied. The results indicate that helium atoms with a high concentration are evenly incorporated in the deposited titanium films. When the substrate temperature increases from 60℃ to 350℃ while the other deposition'parameters are fixed, the helium content decreases gradually from 38.6 at.% to 9.2at.%, which proves that nanocrystalline Ti films have a great helium storage capacity. The 20 angle of the Bragg peak of (002) crystal planes of the He-charged Ti film shifts to a lower angle and that of (100) crystal plane is unchanged as compared with that of the pure Ti film, which indicates that the lattice parameter c increases and a keeps at the primitive value. The grain refining and helium damage result in the diffraction peak broadening. 相似文献
49.
Yu You George W. Kattawar Ping Yang Yong X. Hu Bryan A. Baum 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):470-482
Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer. 相似文献
50.
In this paper, nonconvex multiobjective optimization problems are studied. New characterizations of a properly efficient solution in the sense of Geoffrion's are established in terms of the stability of one scalar optimization problem and the existence of an exact penalty function of a scalar constrained program, respectively. One of the characterizations is applied to derive necessary conditions for a properly efficient control-parameter pair of a nonconvex multiobjective discrete optimal control problem with linear constraints. 相似文献