全文获取类型
收费全文 | 15259篇 |
免费 | 3820篇 |
国内免费 | 1410篇 |
专业分类
化学 | 9801篇 |
晶体学 | 205篇 |
力学 | 147篇 |
综合类 | 76篇 |
数学 | 105篇 |
物理学 | 10155篇 |
出版年
2024年 | 23篇 |
2023年 | 129篇 |
2022年 | 412篇 |
2021年 | 576篇 |
2020年 | 706篇 |
2019年 | 576篇 |
2018年 | 522篇 |
2017年 | 590篇 |
2016年 | 807篇 |
2015年 | 807篇 |
2014年 | 1146篇 |
2013年 | 1474篇 |
2012年 | 1066篇 |
2011年 | 1105篇 |
2010年 | 884篇 |
2009年 | 983篇 |
2008年 | 977篇 |
2007年 | 1097篇 |
2006年 | 959篇 |
2005年 | 739篇 |
2004年 | 626篇 |
2003年 | 601篇 |
2002年 | 497篇 |
2001年 | 448篇 |
2000年 | 420篇 |
1999年 | 347篇 |
1998年 | 310篇 |
1997年 | 290篇 |
1996年 | 226篇 |
1995年 | 188篇 |
1994年 | 170篇 |
1993年 | 138篇 |
1992年 | 105篇 |
1991年 | 78篇 |
1990年 | 87篇 |
1989年 | 56篇 |
1988年 | 56篇 |
1987年 | 51篇 |
1986年 | 43篇 |
1985年 | 35篇 |
1984年 | 42篇 |
1983年 | 7篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1970年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
By using the methods of the matrix decomposition and expansion of the hard-edged aperture function into a finite sum of complex Gaussian functions, the recurrence propagation expressions for a flattened Gaussian beam (FGB) through multi-apertured optical imaging systems of B = 0 are derived and illustrated with numerical examples. Comparisons with the straightforward numerical integration of the Collins formula and with the previous work are made. It is shown that the main advantages of our methods and results are the more accuracy and great reduction of computer time. 相似文献
83.
84.
Nongelatin dichromated holographic film(NGD) is a new holographic recordingmaterial.Holograms recorded on this material have better environmental stability, higherdiffraction efficiency and stronger real time effect, etc..An experimental study to ascertainthe influence of two electron donors, namely,N,N-dimethylformamide(DMF) and dimethyl-sulfoxide(DMSO),on the real time diffraction efficiency(RTDE) of NGD holograms is car-ried out.The pressence of electron donors not only improves the sensitivity,but also enhancesthe real time effect greatly.RTDE of above 60% at±1 orders of NGD plane transimissiongrating is achieved by introducing electron donors. 相似文献
85.
本文对轴对称场二极管区电子运动所遵循的近似轨迹方程进行数值求解,以此做为设计相对论二极管电子枪的依据,与实验结果相比较,符合较好。 相似文献
86.
N. Nishi J. Nishijo K. Judai C. Okabe O. Oishi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):287-290
UV photoexcitation of (t-butylethynyl copper)24
cluster films induces segregation of the crystals into metallic and organic
phases and leads to evolve the metallic sheets sandwiched by organic
polymers. The growth of the metallic crystals in the plane of the
photo-electromagnetic field is attributed due to plasmon-plasmon interaction
among nanoparticles embedded in dielectric polymer matrices. The surface
enhanced photochemical reaction of residual cluster molecules on the photon
incident direction is expected to take an important role for joining the
metal particles to produce a metallic sheet. We can apply this phenomenon
for photolithographic copper pattern generation on a flexible base plate. 相似文献
87.
Endoscopic Observation of Tissue by Narrowband Illumination 总被引:6,自引:0,他引:6
Kazuhiro Gono Kenji Yamazaki Nobuyuki Doguchi Tetsuo Nonami Takashi Obi Masahiro Yamaguchi Nagaaki Ohyama Hirohisa Machida Yasushi Sano Shigeaki Yoshida Yasuo Hamamoto Takao Endo 《Optical Review》2003,10(4):211-215
We propose a new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed. To confirm how the spectral specifications of the filtered light influence a reproduced image, an experiment was conducted observing the endoscopic images of the back mucosa of a human tongue. In addition, the effect of NBI on endoscopic images was investigated through preliminary clinical tests in colonoscopy and upper gastrointestinal endoscopy. It has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa. These patterns are useful features for diagnosing an early cancer. 相似文献
88.
The first-principle was employed to study the six possible models for the Fe3O4(110) surface, namely the AB-terminated surface (AB model), the AB-terminated with FeA vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic
properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than
other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models
exhibit metallic properties. At the same time, the AB, AB-FeA vac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.
相似文献
89.
自由电子激光振荡器的二维数值模拟 总被引:2,自引:2,他引:0
在柱二维坐标系中,用数值计算方法求解了摇摆器内电子模拟方程组、光场方程组和无源区(不含摇摆器区)经非自适应方法变换后的无源旁轴波动方程并设计了相应的程序R_2D。用该程序计算的数值结果表明,在有源条件下二维数值模拟结果与高斯光束近似下的数值模拟结果符合较好;取完全相同的计算条件R-2D程序与洛斯阿拉莫斯实验室(LANL)的FELEX程序的计算结果符合较好;初步认为LANL实验数据的物理图象合理,数值结果基本可信;最后给出北京自由电子激光器(BFEL)的一些物理数据。 相似文献
90.
V. L. Bratman G. G. Denisov A. V. Savilov 《International Journal of Infrared and Millimeter Waves》1995,16(3):459-471
A relatively high level of the minimal electron energy at the gyrotron output even at very large spread in pitch factor is explained. An estimation of the recuperation efficiency, which can be obtained due to this effect, is given. 相似文献