全文获取类型
收费全文 | 8355篇 |
免费 | 1587篇 |
国内免费 | 553篇 |
专业分类
化学 | 2003篇 |
晶体学 | 56篇 |
力学 | 571篇 |
综合类 | 63篇 |
数学 | 171篇 |
物理学 | 7631篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 114篇 |
2021年 | 126篇 |
2020年 | 159篇 |
2019年 | 101篇 |
2018年 | 152篇 |
2017年 | 294篇 |
2016年 | 335篇 |
2015年 | 266篇 |
2014年 | 594篇 |
2013年 | 637篇 |
2012年 | 488篇 |
2011年 | 582篇 |
2010年 | 413篇 |
2009年 | 539篇 |
2008年 | 667篇 |
2007年 | 594篇 |
2006年 | 524篇 |
2005年 | 515篇 |
2004年 | 494篇 |
2003年 | 431篇 |
2002年 | 369篇 |
2001年 | 329篇 |
2000年 | 318篇 |
1999年 | 257篇 |
1998年 | 229篇 |
1997年 | 190篇 |
1996年 | 158篇 |
1995年 | 137篇 |
1994年 | 102篇 |
1993年 | 67篇 |
1992年 | 71篇 |
1991年 | 64篇 |
1990年 | 51篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 1篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
41.
用紫外光直接在光纤内写入布拉格反射光栅的实验研究 总被引:2,自引:0,他引:2
用紫外光直接在光纤内写入布拉格反射光栅的实验研究杜卫冲谭华耀*刘颂豪华南师范大学,激光生命科学研究所,广州510631*香港理工大学,电机系自1989年Meltaz[1]首次提出采用两束波长位于掺Ge-石英光纤吸收带内的相干紫外激光相干涉,从侧面照射... 相似文献
42.
用反向调制照明法分析光栅成像效应 总被引:2,自引:1,他引:1
提出了用反向调制照法明分析光栅成像效应的观点,研究了光栅系统的反向衍射干涉效应,成功地揭示了泰伯效应与劳效应的内在联系,并在白光双光栅衍射干涉的“消色效应”的基础上获得了白光扩展光源照明下白光光栅成像效应和具有实用意义的四光栅干涉系统。 相似文献
43.
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
44.
I.IntroductionThepcrformanccsofAcousto-optic(AO)dcviccareoftenlimitcdbythepropertiesofAOmcdiawhenitisusedinAOsigna1processingsystems.Thespectrumanalyzersandcorre1ationreceivers,forinstancc,areexpcctcdtoimprovcthereso1utionanddynamicrangcwhilereducingtheproccssorvolume.Rccent1y,ancwclassofmateria1s,themercurousha1ides,promiscstocontributeimportantsolutionstosuchnccdsandisrefincdtopractica1uti1izations.Themecurousha1ideweconsidcrinthispapcrismecurouschloride(Hg,C1,).Thesing1ecrystalofHg,Cl… 相似文献
45.
The impact of fabrication errors on a planar waveguide demultiplexer is analyzed based on an analytical method. The explicit
expression of the transfer function taking into account phase and amplitude errors is presented in order to analyze the loss
and crosstalk of the demultiplexer caused by fabrication errors. A basic requirement for the demultiplexer with a certain
crosstalk criterion can be easily obtained. Using an etched diffraction grating demultiplexer as an example, it is shown that
the analytical results have a good agreement with results from a numerical method. 相似文献
46.
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
47.
A. Di Maio A. Rocco P. Ferraro M. De Rosa P. De Natale S. De Nicola A. Finizio G. Pierattini G. Coppola M. Iodice V. Striano 《Optics and Lasers in Engineering》2007,45(3):385
In view of the growing interest for non-destructive tests of materials, geodynamical monitoring and in general remote sensing, there is a great effort to bring practical optical sensors from research labs to industrial and environmental applications. In this paper, we employ digital holographic technique as an efficient tool for evaluating the strain measurement capability of fiber Bragg gratings (FBG). A cantilever beam has been employed as a test structure under loading test. The strain measurements results obtained by fiber-based sensors have been compared to those obtained by using full-field digital holographic technique and point-wise strain gauge sensors glued on the same cantilever beam. A simple theoretical model is also presented to interpret and compare the experimental results coming from different techniques. 相似文献
48.
49.
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
50.