全文获取类型
收费全文 | 11783篇 |
免费 | 1396篇 |
国内免费 | 745篇 |
专业分类
化学 | 5569篇 |
晶体学 | 180篇 |
力学 | 1223篇 |
综合类 | 52篇 |
数学 | 285篇 |
物理学 | 4806篇 |
无线电 | 1809篇 |
出版年
2024年 | 10篇 |
2023年 | 112篇 |
2022年 | 205篇 |
2021年 | 302篇 |
2020年 | 384篇 |
2019年 | 290篇 |
2018年 | 289篇 |
2017年 | 373篇 |
2016年 | 514篇 |
2015年 | 528篇 |
2014年 | 601篇 |
2013年 | 802篇 |
2012年 | 557篇 |
2011年 | 759篇 |
2010年 | 623篇 |
2009年 | 810篇 |
2008年 | 726篇 |
2007年 | 919篇 |
2006年 | 811篇 |
2005年 | 606篇 |
2004年 | 616篇 |
2003年 | 519篇 |
2002年 | 408篇 |
2001年 | 353篇 |
2000年 | 283篇 |
1999年 | 276篇 |
1998年 | 216篇 |
1997年 | 205篇 |
1996年 | 161篇 |
1995年 | 128篇 |
1994年 | 108篇 |
1993年 | 82篇 |
1992年 | 45篇 |
1991年 | 56篇 |
1990年 | 37篇 |
1989年 | 22篇 |
1988年 | 34篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1975年 | 3篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
本文描述用离子束透过钽金属膜进行混合和快速热处理方法来形成钽的硅化物.用溅射方法在P型硅衬底上淀积一层金属钽,然后用砷离子束透过钽金属模进行混合,采用快速热处理后形成了平整的硅化钽薄层.使用厚度为500埃的钽金属膜,得到钽的硅化物薄层电阻为5.5Ω/□.研究了砷离子能量、剂量及钽膜厚度对钽的硅化物薄层电阻的影响.用透射电镜和台阶仪对所形成的硅化钽进行了分析和厚度测量. 相似文献
92.
氟碳铈矿/直氟碳钙铈矿混层结构中新规则混层矿物的超微结构研究 总被引:4,自引:0,他引:4
用电子衍射和晶格像技术研究了钙稀土氟碳酸盐矿物中的氟碳铈矿(B)/直氟碳钙铈矿(S)混层结构,发现并确定了B_4S_4、B_8S_6、B_1S_6、B_7S_4和B_2S_15种新规则混层矿物的对称性、晶胞参数及理论晶体化学式。根据所获得的高分辨晶格像真实而直观地揭示出该类B_mS_n(m>n)型新规则混层矿物的长周期有序堆垛结构特征及变化规律。 相似文献
93.
Alberto Gambi 《Journal of Molecular Spectroscopy》2002,216(2):508-514
The anharmonic force field of difluoromethanimine, F2C NH, has been reinvestigated theoretically using a coupled-cluster singles and doubles approach, augmented for structural optimization and harmonic force field by a contribution of connected triple excitations, CCSD(T). The cubic and quartic force constants have been obtained by numerical derivatives computed from analytical quadratic force constants calculated by second-order Møller-Plesset perturbation theory, MP2. The quadratic force constants and the equilibrium structure of F2C NH have then been scaled by a global least-squares fitting procedure to the spectroscopic data and parameters experimentally determined for this molecule. This force field, obtained in the internal coordinates space and therefore valid for all isotopomers of difluoromethanimine, yields a complete set of spectroscopic molecular constants providing a critical assessment of the experimental rotational and centrifugal distortion constants, fundamentals, overtones, and combination bands determined so far for F2C NH. In addition, the final force field can be used to make predictions of all important vibrational and rotational parameters which should be accurate and useful for new spectroscopic investigations. 相似文献
94.
The growth of Ge and SiGe alloy films on Si substrates has attracted considerable interest in the last years because of their importance for optoelectronic devices as well as Si-based high speed transistors. Here we give a short overview on our recent real time stress measurements of Ge and SiGe alloy films on Si(0 0 1) performed with a sensitive cantilever beam technique and accompanied by structural investigations with atomic force microscopy. Characteristic features in the stress curves provide detailed insight into the development and relief of the misfit strain. For the Stranski–Krastanow system Ge/Si(0 0 1) as well as for SiGe films with Si contents below 20%, the strain relaxation proceeds mainly into two steps: (i) by the formation of 3D islands on top of the Ge wetting layer; (ii) via misfit dislocations in larger 3D islands and upon their percolation. 相似文献
95.
96.
We report here the identification of a new precipitate phase in thin-film Al-4wt.%Cu metallization used for interconnects
on integrated circuits. The phase is based on a trigonal distortion of a face centered cubic lattice. Computer simulation
of electron diffraction intensities suggests that the basis structure is isomorphous with Al2Ca but with a large and ordered population of vacancies on Cu sites. The reason for the formation of the new phase and its
implications for electromigration reliability are discussed. 相似文献
97.
Near-field thermoelastic imaging is a simple way to investigate the thermal and coupled thermoelastic properties of materials. A few microscopes, deriving from the atomic force microscope, have been used to observe and to quantify the samples observed. But the main problem is the absolute measurement of the temperature, because surface topography and thermal expansion contributions are not easily discernible. In the proposed SThEM (scanning thermoelastic microscope), the tip is excited at the resonance frequency of the cantilever and the sample is periodically heated by the Joule effect. Thus the static contributions (drift, topography) are reduced. Moreover, a radiometric sensor, operating in the far field, has been added in order to quantify the temperature. This multi-acquisition microscope enables one to investigate small objects at the nanoscale with complementary information at the micrometric scale. 相似文献
98.
H. Kuramochi J. Okabayashi F. Takano M. Mizuguchi T. Manago H. Akinaga 《Surface science》2004,550(1-3):192-198
Strong magnetic poles at characteristic rectangular defects have been observed using a magnetic force microscope on a MnAs(
1 0 0) thin film with the thickness of 30 nm. The MnAs thin film was epitaxially grown on a GaAs(0 0 1) substrate. The magnetic poles were in one-arranging direction, being independent of the magnetization direction of the film. The poles were pinned at the edges of the rectangular defects until just below the Curie temperature, and formed a stable magnetic-field loop on the MnAs surface. The stability of the magnetic pole pinning shows the distinctive feature of the magnetic domain structure on the surface with a strong anisotropy, which was built in the heterostructure of MnAs and GaAs. 相似文献
99.
100.
A numerical model is presented to calculate V(z) and V(x, z) curves for a line focus acoustic microscope and a specimen containing a subsurface crack. In this model, a Gaussian beam which is tracked through the lens into the coupling fluid and into the specimen, interacts with the crack. The numerical approach is based on the solution of singular integral equations by the boundary element method. The system of singular integral equations follows from the conditions at the interface of the coupling fluid and the specimen and on the faces of the crack. An electromechanical reciprocity relation is used to express the voltage at the terminals of the microscope's transducer in terms of the calculated incident and back-scattered fields. V(z) and V(x, z) curves are presented for various locations and orientations of the crack. The characteristic features of the V(z) and particularly the V(x, z) curves, as they relate to crack configuration, are discussed in some detail. 相似文献