全文获取类型
收费全文 | 17396篇 |
免费 | 4190篇 |
国内免费 | 1312篇 |
专业分类
化学 | 4948篇 |
晶体学 | 598篇 |
力学 | 622篇 |
综合类 | 111篇 |
数学 | 266篇 |
物理学 | 16353篇 |
出版年
2024年 | 34篇 |
2023年 | 104篇 |
2022年 | 303篇 |
2021年 | 362篇 |
2020年 | 388篇 |
2019年 | 284篇 |
2018年 | 375篇 |
2017年 | 608篇 |
2016年 | 704篇 |
2015年 | 613篇 |
2014年 | 1117篇 |
2013年 | 1554篇 |
2012年 | 1199篇 |
2011年 | 1216篇 |
2010年 | 897篇 |
2009年 | 1142篇 |
2008年 | 1398篇 |
2007年 | 1219篇 |
2006年 | 1159篇 |
2005年 | 1071篇 |
2004年 | 918篇 |
2003年 | 826篇 |
2002年 | 770篇 |
2001年 | 686篇 |
2000年 | 641篇 |
1999年 | 565篇 |
1998年 | 471篇 |
1997年 | 441篇 |
1996年 | 348篇 |
1995年 | 332篇 |
1994年 | 274篇 |
1993年 | 195篇 |
1992年 | 171篇 |
1991年 | 116篇 |
1990年 | 80篇 |
1989年 | 70篇 |
1988年 | 52篇 |
1987年 | 49篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 28篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
横向放大率法确定复合光学系统的基点 总被引:2,自引:0,他引:2
介绍了应用测量横向放大率确定两薄透镜组成的复合光学系统基点的方法。由于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,提高了测量精度。 相似文献
82.
Linear and nonlinear optical properties of racemic (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals have been comprehensively investigated and compared with those of the enantiomorph (–)2-(α-methylbenzylamino)-5-nitropyridine ((–)MBANP) crystals. (±)MBANP crystal exhibits very high chemical and physical stability, but relatively small nonlinear optical coefficients (d31 = 6.8 pm/V, d32 = 4.7 pm/V, d33 = 0.84 pm/V). A comparison between the nonlinear optical coefficients of (±)MBANP and (–)MBANP demonstrates the validity of the oriented-gas model in molecular crystals that neglects all the contributions from intermolecular interaction. 相似文献
83.
设计一种用归零码及多重相关解调技术的传输方案,并给了所需的几种抗干扰单元电路,最后结合实验说明了此方案可提高不良环境下传输数据的置信率。 相似文献
84.
An optical fiber multi-function device consisting of a single gradient-index-rod lens and a multi-facet blazed reflection
grating is proposed to simultaneously realize functions of wavelength demultiplexing and optical signal distribution in a
multimode optical fiber transmission system. We analyzed the demultiplexing characteristics and the tolerance of optical components
using the ray trace method. This device can realize not only low loss optical signal distribution but also offers improved
demultiplexing characteristics in comparison with the previously proposed demultiplexer-multiposition switch. The following
characteristics are expected from the design using commercially available optical components: a working band of 0.64–0.88
μm, channel separation of 34–36 nm, 3 dB bandwidth of 27–28 nm, channel cross-talk of less than - 40 dB and minimum excess
insertion loss of 0.9–2.1 dB. 相似文献
85.
86.
Xinhuan Feng Lei Sun Yange Liu Lingyun Xiong Shuzhong Yuan Guiyun Kai Xiaoyi Dong 《Optical and Quantum Electronics》2004,36(10):919-926
A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated. 相似文献
87.
B. M. Azizur Rahman A. K. M. Saiful Kabir Muttukrishnan Rajarajan Kenneth T. V. Grattan 《Optical and Quantum Electronics》2005,37(1-3):171-183
Modal solutions of planar photonic crystal waveguides with rectangular air-holes are presented by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations. 相似文献
88.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献
89.
90.