全文获取类型
收费全文 | 6621篇 |
免费 | 850篇 |
国内免费 | 563篇 |
专业分类
化学 | 2650篇 |
晶体学 | 71篇 |
力学 | 1759篇 |
综合类 | 82篇 |
数学 | 346篇 |
物理学 | 3126篇 |
出版年
2024年 | 11篇 |
2023年 | 48篇 |
2022年 | 108篇 |
2021年 | 145篇 |
2020年 | 215篇 |
2019年 | 150篇 |
2018年 | 176篇 |
2017年 | 196篇 |
2016年 | 257篇 |
2015年 | 217篇 |
2014年 | 357篇 |
2013年 | 412篇 |
2012年 | 345篇 |
2011年 | 451篇 |
2010年 | 366篇 |
2009年 | 457篇 |
2008年 | 390篇 |
2007年 | 472篇 |
2006年 | 407篇 |
2005年 | 374篇 |
2004年 | 375篇 |
2003年 | 313篇 |
2002年 | 264篇 |
2001年 | 224篇 |
2000年 | 218篇 |
1999年 | 198篇 |
1998年 | 141篇 |
1997年 | 117篇 |
1996年 | 102篇 |
1995年 | 77篇 |
1994年 | 63篇 |
1993年 | 55篇 |
1992年 | 48篇 |
1991年 | 58篇 |
1990年 | 37篇 |
1989年 | 21篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1977年 | 3篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1957年 | 4篇 |
排序方式: 共有8034条查询结果,搜索用时 31 毫秒
51.
The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining
explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant
changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution
from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for
a number of dilute alloys based on Mo, Nb, W, Ta and V. 相似文献
52.
We investigate the change in the calculated value of asymptotic normalization constant (ANC) by the hyperspherical harmonics
expansion method with the inclusion of three nucleon force (3BF) in addition to two nucleon force. We see that ANC does not
change very much with the inclusion of 3BF indicating that the 3BF does not alter the asymptotic behaviours of HHE wavefunction
significantly. 相似文献
53.
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
54.
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
55.
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
56.
We introduce a dynamic force spectroscopy technique enabling the quantitative measurement of conservative and dissipative tip-sample forces in ambient conditions. In difference to the commonly detected force-vs-distance curves dynamic force microscopy allows to measure the full range of tip-sample forces without hysteresis effects caused by a jump-to-contact. The approach is based on the specific behavior of a self-driven cantilever (frequency-modulation technique). Experimental applications on different samples (Fischer-sample, silicon wafer) are presented. 相似文献
57.
提出了一种新结构的X波段五腔渡越管振荡器,进行了理论和实验研究。根据场分布进行了一维非线性分析,结果表明该结构可以产生高功率微波,并判断了工作模式,为TM01模的3π/5模。采用粒子模拟验证了一维非线性分析的结论,并优化设计出五腔渡越管振荡器,优化结果为:输出功率约1 GW, 工作频率9.3 GHz,束波转换效率约22%。实验中,通过参数调节,得到频率约9.25 GHz,峰值功率约780 MW,脉宽(半高宽)21 ns的输出微波,束波转换效率约为16%。实验结果与模拟结果基本符合。 相似文献
58.
共轴均匀带电薄圆盘间的相互作用力 总被引:3,自引:0,他引:3
本文利用静电场的高斯定律和环路定律巧妙地求出了均匀带电圆盘在空间任一点所产生的电场 ,进而计算出了共轴均匀带电薄圆盘之间的相互作用力 相似文献
59.
For the purpose of testing the spherical uniformity based on i.i.d. directional data (unit vectors) zi, i=1,…,n, Anderson and Stephens (Biometrika 59 (1972) 613–621) proposed testing procedures based on the statistics Smax=maxu S(u) and Smin=minu S(u), where u is a unit vector and nS(u) is the sum of squares of u′zi's. In this paper, we also consider another test statistic Srange=Smax−Smin. We provide formulas for the P-values of Smax, Smin, Srange by approximating tail probabilities of the limiting null distributions by means of the tube method, an integral-geometric approach for evaluating tail probability of the maximum of a Gaussian random field. Monte Carlo simulations for examining the accuracy of the approximation and for the power comparison of the statistics are given. 相似文献
60.