全文获取类型
收费全文 | 26691篇 |
免费 | 5957篇 |
国内免费 | 2177篇 |
专业分类
化学 | 6573篇 |
晶体学 | 759篇 |
力学 | 1599篇 |
综合类 | 229篇 |
数学 | 2230篇 |
物理学 | 23435篇 |
出版年
2024年 | 70篇 |
2023年 | 252篇 |
2022年 | 571篇 |
2021年 | 644篇 |
2020年 | 695篇 |
2019年 | 563篇 |
2018年 | 593篇 |
2017年 | 874篇 |
2016年 | 1013篇 |
2015年 | 981篇 |
2014年 | 1511篇 |
2013年 | 2202篇 |
2012年 | 1740篇 |
2011年 | 1826篇 |
2010年 | 1505篇 |
2009年 | 1722篇 |
2008年 | 1906篇 |
2007年 | 1764篇 |
2006年 | 1749篇 |
2005年 | 1550篇 |
2004年 | 1443篇 |
2003年 | 1268篇 |
2002年 | 1163篇 |
2001年 | 1036篇 |
2000年 | 965篇 |
1999年 | 831篇 |
1998年 | 727篇 |
1997年 | 626篇 |
1996年 | 534篇 |
1995年 | 435篇 |
1994年 | 386篇 |
1993年 | 294篇 |
1992年 | 245篇 |
1991年 | 177篇 |
1990年 | 154篇 |
1989年 | 152篇 |
1988年 | 116篇 |
1987年 | 101篇 |
1986年 | 90篇 |
1985年 | 75篇 |
1984年 | 59篇 |
1983年 | 22篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
S. V. Dil’man 《Mathematical Notes》2006,79(5-6):625-631
In 1996, D. Deng established an analog of the Baum—Katz theorem on the convergence rate in the law of large numbers for multi-indexed random variables. The series describing the convergence rate depends, in a natural way, on the parameter characterizing the excess of the normalized sums over some level. In this paper, we find the precise asymptotics of the sum of this series with respect to the above-mentioned parameter. Thus, a generalization of a recent result due to A. Gut and A. Spataru is obtained. 相似文献
82.
The mechanism of X-ray waveguide-resonance propagation or the radiation superstream model, which can become the ground of X-ray nanophotonics, is discussed briefly. Some attention is devoted to features consideration of the simplest devices characterized by the waveguide-resonance transportation of X-ray beams. The experimental data showing the user possibilities of a simplest waveguide-resonators application for diffractometry are presented. We discuss the main reasons to improve the metrological characteristics for total reflection X-ray fluorescence (TXRF) analytical method in case when the target exciting beam is formed by a waveguide-resonator. Some problems appearing during the waveguide-resonator application are formulated. 相似文献
83.
We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array
of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the
components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission
properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the
light by light in all-optical nanoscale devices and circuits. 相似文献
84.
The 57Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?1021 V/m2, 0.97(15) and ?3.95(12)?×?1021 V/m2, 0.00(17). 相似文献
85.
S. C. Tiwari 《Foundations of Physics Letters》2006,19(1):51-62
Advances in gauge theories and unified theories have not thrown light on the meaning of electron. The problem of the origin
of electronic charge is made precise, new insights gained from Weyl space are summarized, and the origin of charge in terms
of fractional spin is suggested. A new perspective on the abelian Chern-Simons theory is presented to explain charge. 相似文献
86.
87.
88.
ZnO naorods on ZnO-coated seed substrates were fabricated by solution chemical method from Zn(NO3)2/NaOH under assisted electrical field. The working mechanism of electrical field was analyzed and the factors affecting the rod growth such as potential, precursor concentration and growth temperature were elucidated. The structural and optical properties are characterized by SEM, TEM, XRD, HRTEM and UV-vis. The results indicated that the nanorods have wurtzite structure without electrical field and are primarily of zincite structure under electrical field; when the electrical field is 1.1-1.3 V, not only the elevation of ion diffusion and adsorption lower the crystallite/solution interfacial energy and then the crystal nucleation barrier by increasing charge intensity, but also the production of H+ through oxidation of OH− increases properly the degree of solution supersaturation near the substrate, and thus lowers the activation energy. Both the two processes do favor to rod growth. With increasing precursor concentration in this system, the average diameter and length of ZnO nanorods increase, leading to decreasing of optical transmittance. The maximum rod growth rate at given concentration of Zn2+ occurs at a specific temperature. 相似文献
89.
横向放大率法测定光具组的基点 总被引:1,自引:1,他引:0
介绍了用横向放大率法确定两薄透镜组成的光具组基点的原理和方法,该方法采用线阵光电耦合器件(CCD)测量物经光学系统成像的横向放大率,进一步提高了测量精度. 相似文献
90.
R. S. Kaler 《Fiber and Integrated Optics》2006,25(1):41-57
In this article, the comparison of large signal theory and small signal theory has been done with dispersive propagation of optical signal with IMDD (Intensity Modulation Direct Detection) systems for semiconductor lasers with higher-order dispersion terms. The expressions for an exact large signal theory and small signal theory including higher-order dispersion terms for propagation of an optical wave with sinusoidal amplitude and frequency modulation in a dispersive fiber have been derived. It is observed that small signal theory is more sensitive compared to large signal theory in terms of intensity modulation/direct detection systems. Also, it is reported that for large signal analysis the higher-order effects of dispersion can be ignored, whereas for small signal theory, the higher-order effects can be ignored for lower modulation frequencies only. The variation in the transfer function for various values of modulation indices are greater for small signal analysis than for large signal analysis. Also, as the intensity modulation index is increased, there is a decrease in the value of transfer function. The large signal model approximates the small signal model for lower values of the intensity modulation index. 相似文献