全文获取类型
收费全文 | 25264篇 |
免费 | 4924篇 |
国内免费 | 2276篇 |
专业分类
化学 | 10891篇 |
晶体学 | 780篇 |
力学 | 364篇 |
综合类 | 141篇 |
数学 | 436篇 |
物理学 | 19852篇 |
出版年
2024年 | 57篇 |
2023年 | 166篇 |
2022年 | 534篇 |
2021年 | 556篇 |
2020年 | 652篇 |
2019年 | 510篇 |
2018年 | 549篇 |
2017年 | 773篇 |
2016年 | 865篇 |
2015年 | 770篇 |
2014年 | 1205篇 |
2013年 | 2237篇 |
2012年 | 1539篇 |
2011年 | 1575篇 |
2010年 | 1180篇 |
2009年 | 1547篇 |
2008年 | 1714篇 |
2007年 | 1688篇 |
2006年 | 1632篇 |
2005年 | 1420篇 |
2004年 | 1245篇 |
2003年 | 1154篇 |
2002年 | 1051篇 |
2001年 | 972篇 |
2000年 | 929篇 |
1999年 | 801篇 |
1998年 | 705篇 |
1997年 | 665篇 |
1996年 | 574篇 |
1995年 | 578篇 |
1994年 | 485篇 |
1993年 | 392篇 |
1992年 | 420篇 |
1991年 | 248篇 |
1990年 | 182篇 |
1989年 | 165篇 |
1988年 | 150篇 |
1987年 | 107篇 |
1986年 | 73篇 |
1985年 | 71篇 |
1984年 | 61篇 |
1983年 | 37篇 |
1982年 | 47篇 |
1981年 | 29篇 |
1980年 | 29篇 |
1979年 | 30篇 |
1976年 | 20篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
P.S Erdman M Fajardo K.M Sando W.C Stwalley 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,88(4):447-481
Experimental results are reported for a unique spectroscopic device called the Plasma Spectroscopy Cell. Optical absorption of lithium metal vapor was observed at high density and temperature. Absorption spectra are analyzed using theoretical calculations of absorption cross sections for lithium-helium interactions, and singlet and triplet state transitions of diatomic lithium in the visible spectral range. This is believed to be the most complex example yet calculated in which absolute bound-bound, bound-free, free-bound, and free-free contributions for all possible optically allowed transitions are all included, in quite respectable agreement with experiment. 相似文献
112.
In this paper, we have developed an analytical model to study the temperature distributions in IR optical materials heated by laser pulses. Our model takes into account the two-photon absorption (TPA). The calculations are based on a three-dimensional model of heat diffusion in solids using the integral transform method. We find out the rigorous analytical expression of the thermal field when one considers both one- and two-photon absorption. The model is valid for any laser–solid system whose interaction can be described by the generalized Beer–Lambert law. Specific results are presented for an application of the model to ZnSe sample. We find out that TPA can produce detectable temperature variation. 相似文献
113.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
114.
S. B. Bushuk Yu. A. Kal'vinkovskaya A. N. Rubinov 《Journal of Applied Spectroscopy》2004,71(2):291-294
Capture of an ensemble of polymeric microspheres in a water suspension under the action of optical gradient forces in the field of interfering laser beams has been investigated for the case of two-, three-, and four-beam interference. The self-diffraction and diffraction of radiation on induced ordered spatial distribution of particles have been obtained. 相似文献
115.
116.
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed. 相似文献
117.
聚芳香杂环甲烯的三阶非线性光学效应与时间分辨光克尔效应 总被引:6,自引:4,他引:2
合成了一系列聚芳香杂环甲烯,包括聚吡咯甲烯和聚噻吩甲烯.采用四波混频法研究材料的共振三阶非线性光学效应(λ=532nm),其共振二阶超分子极化率γ三阶非线性光学系数分别达到10-30esu和10-8esu.选择具有良好溶解性、成膜性的聚吡咯对二甲氨基苯甲烯(PPDMAB),采用飞秒时间分辨光克尔效应方法研究材料的非共振三阶非线性光学效应(λ=790nm).实验表明,翠绿亚胺碱溶液的光克尔信号仅表现一超快响应的成分,归功于π电子云扭转产生的非共振激发.PPDMAB的非共振二阶超分子极化率γ三阶非线性光学系数分别达到γ=5.78×10-32esu和χ(3)=1.26×10-10esu. 相似文献
118.
119.
120.
G. Kocher-Oberlehner W. Jantsch L. Palmetshofer A. Ulyashin 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):347
Erbium (Er)- and oxygen (O)-doped Cz–Si was additionally doped with hydrogen, using plasma enhanced chemical vapour deposition. Photoluminescence (PL) spectra show a large enhancement especially for samples treated with solid phase epitaxy before hydrogenation and annealing at 900°C later. Secondary ion mass spectroscopy measurements give evidence for an enhanced diffusion of O and Er at this temperature towards the surface. Etching shows that the PL does not stem from the heavily doped surface layer but from a deeper region with lower Er concentration. This conclusion is supported by the appearance of the so-called “cubic” centre with low solubility. Comparing the PL yield of the hydrogenated samples to that of samples with similar Er volume concentration but without hydrogenation still gives a large enhancement. We thus conclude that hydrogen can enhance the solubility of the cubic centre in Si:Er,O. 相似文献