全文获取类型
收费全文 | 30212篇 |
免费 | 4069篇 |
国内免费 | 2755篇 |
专业分类
化学 | 20587篇 |
晶体学 | 286篇 |
力学 | 1945篇 |
综合类 | 273篇 |
数学 | 3285篇 |
物理学 | 10660篇 |
出版年
2024年 | 106篇 |
2023年 | 590篇 |
2022年 | 909篇 |
2021年 | 1013篇 |
2020年 | 1115篇 |
2019年 | 1082篇 |
2018年 | 913篇 |
2017年 | 815篇 |
2016年 | 1280篇 |
2015年 | 1273篇 |
2014年 | 1541篇 |
2013年 | 2065篇 |
2012年 | 2637篇 |
2011年 | 2676篇 |
2010年 | 1661篇 |
2009年 | 1642篇 |
2008年 | 1744篇 |
2007年 | 1665篇 |
2006年 | 1493篇 |
2005年 | 1230篇 |
2004年 | 943篇 |
2003年 | 791篇 |
2002年 | 754篇 |
2001年 | 562篇 |
2000年 | 563篇 |
1999年 | 656篇 |
1998年 | 579篇 |
1997年 | 574篇 |
1996年 | 660篇 |
1995年 | 506篇 |
1994年 | 464篇 |
1993年 | 389篇 |
1992年 | 371篇 |
1991年 | 322篇 |
1990年 | 255篇 |
1989年 | 202篇 |
1988年 | 157篇 |
1987年 | 136篇 |
1986年 | 127篇 |
1985年 | 118篇 |
1984年 | 88篇 |
1983年 | 61篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
C. H. Zuo B. T. Zhang Y. B. Liu J. L. He H. T. Huang J. F. Yang J. L. Xu 《Laser Physics》2010,20(8):1717-1720
Using V3+:YAG crystal as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GGG laser operating at 1.3
μm is realized for the first time. The mode-locking modulation depth of nearly 100% has been achieved. The maximum output
power and the single Q-switched pulse energy are 410 mW and 8.3 μJ. The mode-locked pulse inside the Q-switched pulse has
a repetition rate of 349 MHz, and its average pulse width is estimated to be about 750 ps. 相似文献
992.
Chih-Kai Huang Chia-Yin Chen Jin-Lin Han Chii-Chang Chen Meng-Dan Jiang Jen-Sung Hsu Chia-Hua Chan Kuo-Huang Hsieh 《Journal of nanoparticle research》2010,12(1):199-207
The silver nanoparticles (Ag NPs) have been immobilized onto silica microspheres through the adsorption and subsequent reduction
of Ag+ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared
through sol–gel processing; their surfaces were then functionalized using 3-mercaptopropyltrimethoxysilane (MPTMS). The major
aims of this study were to immobilize differently sized Ag particles onto the silica microspheres and to understand the mechanism
of formation of the Ag nano-coatings through the self-assembly/adsorption behavior of Ag NPs/Ag+ ions on the silica spheres. The obtained Ag NP/silica microsphere conglomerates were characterized by field-emission scanning
electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Their electromagnetic
wave shielding effectiveness were also tested and studied. The average particle size of the obtained Ag NPs on the silica
microsphere was found that could be controllable (from 2.9 to 51.5 nm) by adjusting the ratio of MPTMS/TEOS and the amount
of AgNO3. 相似文献
993.
X. H. Deng T. B. Wang J. T. Liu J. H. Huang T. B. Yu Q. H. Liao N. H. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):7-12
We proposed a type of heterostructure by combining two
photonic crystals (PCs) consisting of alternating negative-index materials
and positive-index materials layers. It is demonstrated by transfer matrix
method that the proposed structure has a polarization-independent
omnidirectional band gap (OBG), which is independent of the incident angle
for both TE and TM polarizations. Compared to a single PC, the frequency
range of the OBG in a heterostructure can be notably enlarged. Such a
structure has potential applications in improving planar microcavities,
optical fibers, and Fabry-Pérot resonators, etc. 相似文献
994.
The earth background radiation is a kind of main background interference for satellite borne laser warning system in the space environment, and it is so necessary that the radiation characteristic be studied. In this paper, the mathematic model of the earth background radiation is established, the input parameters of 6S model are analyzed and set, and the simulation of earth background radiation is carried on aiming at the alarm wavelength 1.315 μm and the waveband 0.9-1.7 μm which is the responsive bandwidth of the detector. The results show that: with the increase of zenith angle, the irradiance from ground reflection increases, but the irradiances of atmospheric path radiation and surface-atmosphere interaction at the satellite level decrease; comparing with other two parts, the irradiance from ground reflection weighs most, and the corresponding percentages for 1.315 μm and 0.9-1.7 μm are 75.89% and 73.99%, respectively. The total irradiance at the satellite level from earth background radiation has exceeded the detection sensitivity of the system (about 1 mW/cm2), which may arouse the false alarm. So, the special technique of background suppression must be studied. 相似文献
995.
996.
We proposed a scheme to achieve two-mode CV entanglement with the frequencies of entangled modes in the infrared range in an asymmetric semiconductor double-quantum-wells (DQW), where the required quantum coherence is obtained by inducing the corresponding intersubband transitions (ISBTs) with a classical field. By numerically simulating the dynamics of system, we show that the entanglement period can be prolonged via enhancing the intensity of classical field, and the generation of entanglement doesn't depend intensively on the initial condition of system in our scheme. Moreover, we also show that a bipartite entanglement amplifier can be realized in our scheme. The present research provides an efficient approach to achieve infrared entangled light in the semiconductor nanostructure, which may have significant impact on the progress of solid-state quantum information theory. 相似文献
997.
The thermal infrared imaging system is of greatest importance in modern optics and the image quality closely relies on the accuracy of the optical system. Heat-induced mirror deformation influences the transmission performance of the optical antenna system significantly, which further degrades the accuracy of the whole system. In this work, the simulation on lens deformation circumstances under the thermal environment is carried out using the finite-element analysis software ANSYS. The focus shift property caused by the thermal effect is studied in the cases of reflective and refractive Cassegrain optical antennas, and the athermalizing performance of Cassegrain optical antenna system is also concluded. This work presents a direction to accurate designing of the thermal infrared optical system. 相似文献
998.
Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and La2Ce2O7 (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO3 is formed due to the chemical reaction between LC and Al2O3 which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs. 相似文献
999.
结合衍射理论和矩阵光学方法得出抛物面型X射线组合折射透镜的光学性能指标(包括其焦距的严格表达式、薄透镜近似的判定准则、透过率和有效孔径,以及极限聚焦光斑尺寸等).采用X射线深度光刻技术实际制作了PMMA材料抛物面型X射线组合折射透镜并给出了工艺测试结果.最后在北京同步辐射装置(BSRF)上,实际构建了基于3种不同结构参数的PMMA材料抛物面型X射线组合折射透镜的微束聚焦实验系统.并实际测试了其聚焦性能,均获得了良好的聚焦效果,给出实测结果并对实测结果进行了分析和讨论. 相似文献
1000.
Comparative analysis of phase extraction methods based on phase-stepping and shifting curve in grating interferometry 下载免费PDF全文
Two phase extraction methods which are based separately on
phase-stepping and shifting curve are mainly used in
phase-sensitive imaging in gating interferometry to determine the
x-ray phase shift induced by an object in the beam. In this paper,
the authors perform a full comparative analysis and present the main
virtues and limitations of these two methods according to the
theoretical analysis of the grating interferometry. 相似文献