首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1322篇
  免费   35篇
  国内免费   7篇
化学   1089篇
晶体学   18篇
力学   19篇
数学   46篇
物理学   192篇
  2023年   8篇
  2022年   7篇
  2021年   8篇
  2020年   15篇
  2019年   15篇
  2018年   14篇
  2017年   9篇
  2016年   23篇
  2015年   23篇
  2014年   29篇
  2013年   52篇
  2012年   91篇
  2011年   115篇
  2010年   56篇
  2009年   37篇
  2008年   78篇
  2007年   84篇
  2006年   60篇
  2005年   84篇
  2004年   66篇
  2003年   56篇
  2002年   53篇
  2001年   20篇
  2000年   22篇
  1999年   15篇
  1998年   12篇
  1997年   19篇
  1996年   12篇
  1995年   22篇
  1994年   14篇
  1993年   9篇
  1992年   20篇
  1990年   6篇
  1989年   7篇
  1988年   9篇
  1986年   7篇
  1985年   19篇
  1984年   11篇
  1983年   10篇
  1982年   10篇
  1981年   10篇
  1980年   13篇
  1979年   20篇
  1978年   9篇
  1977年   13篇
  1975年   6篇
  1974年   6篇
  1969年   7篇
  1968年   8篇
  1967年   10篇
排序方式: 共有1364条查询结果,搜索用时 0 毫秒
191.
Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by a syringe pump, providing a laminar flow liquid-liquid interface. The chemiluminescence from the singlet oxygen was emitted in the collapse of the interface due to molecular diffusion under laminar flow conditions. The chemiluminescence intensity was observed continuously and stably for each combination of reagents fed into the micro-channel; while, in the normal batch-type reactor the chemiluminescence peaks from singlet oxygen were observed within ca. 5 s. The features of the chemiluminescence emitted under laminar flow conditions were examined by changing the concentrations of sodium hypochlorite and hydrogen peroxide; the concentrations of 2.5 mM sodium hypochlorite and 7.5 mM hydrogen peroxide provided highest chemiluminescence intensities without bubble formation. Also, the effects of beverages, such as green tea, coffee, white wine, red wine, and sake (rice wine), on the chemiluminescence intensity as well as the concentrations of sodium hypochlorite and hydrogen peroxide were examined. The chemiluminescence intensities observed with addition of the beverages to the reagents decreased in the following orders; green tea > coffee > red wine > rice wine > white wine (being added to sodium hypochlorite); coffee > white wine > green tea > red wine > rice wine (being added to hydrogen peroxide). It was found that coffee decreased the chemiluminescence intensity (ca. 33% chemiluminescence decrease) without altering the concentrations of sodium hypochlorite or hydrogen peroxide. The cause of the decrease in chemiluminescence with coffee is discussed.  相似文献   
192.
Efficient optical phase-conjugate (PC) signals in four kinds of novel polyester films containing cyanoazobenzene units in the side chain are reported. One of them can efficiently generate only the photoinduced anisotropy (PA) component of PC signal, while the other three films can simultaneously generate two types of PC signals, PA and holographic components. These polymers have good potential not only as a phase conjugator but also as a polarization-sensitive hologram-recording material.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994  相似文献   
193.
194.
The effect of electrolyte conductivity on the partial arc discharge development between two electrolyte electrodes on a silicone rubber sheet surface was investigated. Tests were executed by placing the salt-waterlogged glass-filter paper on a silicone rubber sheet to simulate a polluted electrolyte layer, and partial arc discharges with a constant current value of 10 mA were observed. It was found that the formation of an arc channel and a temperature distribution on the sample surface varied with the electrolyte conductivity. In addition, the relation between the electrolyte conductivity and the weight loss due to the heat erosion of specimens was also investigated by a 3D morphological observation and a simulated calculation. The partial arc discharge did significantly not influence on the sample surface erosion under serious polluted conditions. In contrast, the severest erosion appeared under the light pollution with comparatively lower conductivity of the electrolyte electrodes.  相似文献   
195.
Two-phase flow in horizontal pipe was analyzed with simplified models for annular and stratified flow. The velocity profiles for the liquid and gas phase were described with the Prandtl mixing length. From this analysis, the frictional pressure drop was calculated with the modified Baker map for flow pattern transition. The intermediate region, i.e. wavy flow, was interpolated between annular and stratified flow. Comparison of this analysis with existing experimental data of refrigerants showed good agreement.  相似文献   
196.
It is proposed, from an ab initio (4–31G) SCF calculation, that the most stable forms of protonated thioformaldehyde may be the C-protonated complexes H3CS+. The energy-gradient technique was used for geometry optimization, and an energy decomposition analysis was carried out to elucidate the origin of this abnormal behavior of the C=S group.  相似文献   
197.
Optical third-harmonic generation from some high-index glasses was investigated. The highest χ(3) was obtained from As2S3 glass 2.2 × 10−12 esu/ This value was 100 times higher than that of pure SiO2 glass and comparable with that of the polymer with monomer-doping, which are known as organic materials with quite high χ(3). From the relationship between χ(3) and composition, sulfide glasses were found to have higher χ(3) than oxide or semiconductor-doped oxide glasses with similar refractive indices.  相似文献   
198.
We present a fitting method for obtaining a functional form of the refractive index profile of planar microlenses made by ion exchange techniques from total shearing interferometric measurements. Compared to the usual power series expansion fit, this method allows a reduction in the number of coefficients needed to characterize a lens.  相似文献   
199.
A variational formula for the momentum density is derived by using the Hellmann-Feynman theorem and by introducing a reference system whose Hamiltonian differs only in the kinetic energy part from that of the original system. As simple applications of the present results, the reduced mass correction and the relativistic correction for the hydrogen-like atom are discussed.  相似文献   
200.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号