全文获取类型
收费全文 | 13884篇 |
免费 | 4470篇 |
国内免费 | 856篇 |
专业分类
化学 | 4843篇 |
晶体学 | 432篇 |
力学 | 422篇 |
综合类 | 63篇 |
数学 | 128篇 |
物理学 | 13322篇 |
出版年
2024年 | 13篇 |
2023年 | 51篇 |
2022年 | 180篇 |
2021年 | 203篇 |
2020年 | 202篇 |
2019年 | 225篇 |
2018年 | 294篇 |
2017年 | 445篇 |
2016年 | 500篇 |
2015年 | 631篇 |
2014年 | 916篇 |
2013年 | 1005篇 |
2012年 | 1048篇 |
2011年 | 1233篇 |
2010年 | 873篇 |
2009年 | 997篇 |
2008年 | 1073篇 |
2007年 | 1131篇 |
2006年 | 984篇 |
2005年 | 806篇 |
2004年 | 813篇 |
2003年 | 754篇 |
2002年 | 678篇 |
2001年 | 580篇 |
2000年 | 590篇 |
1999年 | 533篇 |
1998年 | 408篇 |
1997年 | 354篇 |
1996年 | 309篇 |
1995年 | 249篇 |
1994年 | 206篇 |
1993年 | 175篇 |
1992年 | 170篇 |
1991年 | 130篇 |
1990年 | 105篇 |
1989年 | 80篇 |
1988年 | 56篇 |
1987年 | 57篇 |
1986年 | 31篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 18篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This paper presents a method of measuring a light field of a light source with high directional resolution using a mirrored
ball and a pinhole camera. The light field describes a spatial and directional distribution of radiances from the light source.
The directional distribution is expanded by a reflection on the mirrored ball, and the radiances are measured by a charge-coupled
device (CCD) camera with a pinhole lens. The light source is laterally moved by a robot arm to measure the directionally expanded
light field, and each pixel on a CCD can obtain the radiances from the light source through the pinhole lens with high directional
resolution. The light field is estimated from the pixel value and the position of each pixel using a ray tracing technique.
The light field of a krypton lamp was experimentally measured by the proposed method, and the accuracy of the measurement
was evaluated against the irradiances measured by a spectro-radiometer at sample points. 相似文献
102.
Optical trapping forces of polystyrene microspheres are analyzed both theoretically and experimentally, and comparisons are
made between the two. Discrepancies are mainly caused by straight-ray approximation for axial trapping, and by trapping-position
vertical displacement due to gravity for transverse trapping. 相似文献
103.
104.
Zhong‐Zhen Yu Mingshu Yang Qingxin Zhang Chungui Zhao Yiu‐Wing Mai 《Journal of Polymer Science.Polymer Physics》2003,41(11):1234-1243
Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with an alkyl ammonium surfactant pretreated montmorillonite (MMT). The thermal stability of the organic MMT powders was measured by thermogravimetric analysis. The decomposition of the surfactant on the MMT occurred from 200 to 500 °C. The low onset decomposition temperature of the organic MMT is one shortcoming when it is used to prepare polymer nanocomposites at high melt‐compounding temperatures. To provide greater property enhancement and better thermal stability of the polymer/MMT nanocomposites, it is necessary to develop MMT modified with more thermally stable surfactants. The dispersion and spatial distribution of the organic MMT layers in the nylon‐66 matrix were characterized by X‐ray diffraction. The organic MMT layers were exfoliated but not randomly dispersed in the nylon‐66 matrix. A model was proposed to describe the spatial distribution of the organic MMT layers in an injection‐molded rectangular bar of nylon‐66/organic MMT nanocomposites. Most organic MMT layers were oriented in the injection‐molding direction. Layers near the four surfaces of the bar were parallel to their corresponding surfaces; whereas those in the bulk differed from the near‐surface layers and rotated themselves about the injection‐molding direction. The influence of the spatial distribution of the organic MMT on crystallization of nylon‐66 was also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1234–1243, 2003 相似文献
105.
Hongrui Zhang Mingju Chao Mingyi Gao Liwen Zhang Jianquan Yao 《Optics & Laser Technology》2003,35(6):573-449
A fiber-coupled diode-single-end-pumped Nd:YVO4 laser with an Nd:YVO4 crystal of 0.3 at% doping concentration and 3×3×10 mm3 dimensions was reported. 14.850 W of continuous-wave output power in an M2 factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%. 相似文献
106.
S. Schrader A. Penzkofer W. Holzer R. Velagapudi B. Grimm 《Journal of luminescence》2004,110(4):303-308
Optical, structural and morphological properties of thin films of polyparaphenylenevinylene (PPV) formed by an alkyl sulfinyl precursor route have been studied. Thin films were fabricated on an optical glass and on quartz glass either by spin-coating of the precursor solution or by layer-by-layer deposition using Langmuir–Blodgett technique. PPV precursor films were also spin-coated on gold-coated glass in order to study thin-film optical parameters by surface plasmon spectroscopy. We have been successful in forming about 40 precursor mono layers on quartz glass by Langmuir–Blodgett technique using optimized surface pressure and dipping conditions. After thermal conversion of the precursor layers good quality fluorescent PPV films of yellow colour have been obtained. Optical characterization of the films was carried out by linear absorption and emission spectroscopy, ellipsometry, and surface plasmon spectroscopy. Structural and morphological studies on the thin films were carried out by using X-ray scattering and atomic force microscopy. Wave-guided travelling-wave laser action has been achieved in a PPV film on quartz glass. The sample was transversally pumped with picosecond laser pulses (wavelength 347.15 nm, duration 35 ps). Laser emission occurred at 550 nm for pump pulse energy densities above . 相似文献
107.
Low-loss and rugged distal tips for CO2 laser have been proposed and fabricated based on a commercially available stainless steel (St) pipe. A method of smoothening the inner surface of the St pipe with a rough inner surface is put forward. Fabrication parameters, transmission properties, and mechanical strength of the cyclic olefin polymer-coated silver hollow St distal tip are experimentally discussed. 相似文献
108.
109.
激光水下扫描成像系统的图像修正机理 总被引:2,自引:0,他引:2
同步扫描系统可以克服后向散射,但同时也产生了两种非线性,一是扫描线速度的非线性,一是由于距离对光能衰减造成的非线性,两种非线性都需要修正,本文从原理上讨论水下激光成像时能量衰减的修正原理与修正方法,并给出仿真结果。 相似文献
110.