全文获取类型
收费全文 | 27357篇 |
免费 | 5284篇 |
国内免费 | 3123篇 |
专业分类
化学 | 19533篇 |
晶体学 | 621篇 |
力学 | 1560篇 |
综合类 | 195篇 |
数学 | 946篇 |
物理学 | 12909篇 |
出版年
2024年 | 31篇 |
2023年 | 251篇 |
2022年 | 503篇 |
2021年 | 809篇 |
2020年 | 974篇 |
2019年 | 777篇 |
2018年 | 702篇 |
2017年 | 833篇 |
2016年 | 1111篇 |
2015年 | 1212篇 |
2014年 | 1517篇 |
2013年 | 2422篇 |
2012年 | 1678篇 |
2011年 | 1991篇 |
2010年 | 1650篇 |
2009年 | 1827篇 |
2008年 | 1881篇 |
2007年 | 1970篇 |
2006年 | 1915篇 |
2005年 | 1545篇 |
2004年 | 1427篇 |
2003年 | 1229篇 |
2002年 | 1129篇 |
2001年 | 883篇 |
2000年 | 803篇 |
1999年 | 671篇 |
1998年 | 586篇 |
1997年 | 546篇 |
1996年 | 431篇 |
1995年 | 415篇 |
1994年 | 345篇 |
1993年 | 297篇 |
1992年 | 243篇 |
1991年 | 200篇 |
1990年 | 165篇 |
1989年 | 117篇 |
1988年 | 115篇 |
1987年 | 92篇 |
1986年 | 80篇 |
1985年 | 67篇 |
1984年 | 71篇 |
1983年 | 24篇 |
1982年 | 53篇 |
1981年 | 39篇 |
1980年 | 37篇 |
1979年 | 21篇 |
1978年 | 21篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 569 毫秒
991.
SrO—Al2O3—SiO2:Eu^3+,Bi^3+发光体的溶胶—凝胶法合成 总被引:2,自引:1,他引:2
制备无机固体材料大都采用高温固相反应,1971年Dislich报导了用溶胶-凝胶法制备多组份固体材料。近年来,有报导利用此法研制玻璃、玻璃陶瓷和陶瓷。我们在过去工作的基础上,合成了SrO-Al_2O_3-SiO_2:Eu~(3 ),Bi~(3 )发光体,研究了从凝胶至发光晶体的转变过程、Eu~(3 )和Bi~(3 )在SrO-Al_2O_3-SiO_2基质中的发光性质以及Bi~(3 )对 EU~(3 )的能量传递。 相似文献
992.
ZHAO Xue CHEN De-Zhan WANG Zhen HAO Zhao-Ling 《结构化学》2007,26(8):980-987
5,8-Hihydroxyl-1,4-naphthazarin was taken as a model compound to explore the effect of halogen substitution on intramolecular proton transfer process. Calculations indicate that the substitution in the R2- and R4-positions far away from the active region has much weaker influence on the IPT process than that in the R1-and R3-positions. IPT barriers for substitution in the R1-position are higher than that of parent molecule. However, it is quite reverse for substitution in the R3-position. The IPT process is a proton transfer process coupled with charge separation and coulombic interaction would be dominant during this process. As for naphthazarin, halogen substitution would decrease the quantum yields of O2 but increase those of 1O2. 相似文献
993.
994.
天线若丹明染料分子内能量与电荷传递的研究 总被引:2,自引:0,他引:2
染料三重态在染料激光的应用中起着重要作用,尤其是三重态一Z重态(T-T)吸收常常会造成谐振腔损耗*.为了减少由基态吸收而造成的话振腔损耗,带有紫外吸收天线分子的三发色团染料已在研究问,2,5·二苯基螨喳(PP0)在紫外区(如308删)有很强的吸收,PPO-rhod.系列染料(见图1)在紫外区的吸收就很强,由PPO到若丹明母体的单线态一单线态(S功能量传递使这类三发色团染料具有较大的荧光量子效率,较小的基态重复吸收耗能卜,司.然而,在610N640nm区域中这些天线若丹明染料的激光输出效率远远小于若丹明Rh630*,其原因正是… 相似文献
995.
Robert S. Pomeroy Jeffrey D. Kolczynski Jonathan V. Sweedler M. Bonner Denton 《Mikrochimica acta》1989,99(3-6):347-353
A unique simultaneous emission spectrograph is utilized to perform qualitative and quantitative analysis on trace quantities of solid particulates. The atomic emission spectroscopic system consists of a direct current plasma source and an echelle spectrograph with a charge injection device detector, enabling the system to simultaneously measure the wavelength range from 220 nm to 520 nm with 0.02 nm resolution at 300 nm. Monitoring all wavelengths simultaneously allows the qualitative and quantitative determination of most major and minor constituent in a trace quantity of sample with little prior knowledge about the sample. The ability to perform qualitative and quantitative analysis on particulates is demonstrated by evaluating NBS certified coal fly ash, as well as a sample taken from the respirator air filter at an acute care unit in a hospital.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria 相似文献
996.
Matthew T. AllinghamAndrew Howard-Jones Patrick J. MurphyPeter W.R. Caulkett 《Tetrahedron letters》2003,44(48):8677-8680
The preparation of the tetracyclic C2-symmetric guanidinium salts 5 and 11-13 is reported together with their application to enantioselective transformations. 相似文献
997.
998.
S. M. Matthews A. J. Boegel J. A. Loftis R. A. Caufield B. J. Mincher D. H. Meikrantz R. J. Murphy 《Radiation Physics and Chemistry》1993,42(4-6):689-693
Radiolytic decomposition of chlorinated hydrocarbons and other toxic compounds has been experimentally measured using ionizing radiation produced by electron accelerator and nuclear isotope sources. Decomposition products have been identified. A portable, commercially available electron accelerator was set up at a Superfund site where vapor extraction wells were removing trichloroethylene (TCE) from a spill into the unsaturated soil. The extraction vapor was passed through the accelerator beam to decompose the TCE. On site radiolytic decomposition of TCE vapor using an accelerator is shown to be significantly less expensive than filtration of TCE vapor using activated charcoal. 相似文献
999.
A coalesced high-intensity dc discharge is maintained between three cathodes and a single anode, stabilized by using resistors on each cathode leg. Jets of plasma gas are produced from either the cathode area or the anode area of the device. Cathode jets are generated by the self-induced pumping at the cathode tips and augmented by central gas injection. Arc voltage-current characteristics show classical convection-stabilized arc behavior. Anode heat transfer rates may be substantially increased by central gas injection toward the anode. Temperature fields in the coalesced, axially symmetric portion of the arc are determined spectrometrically and compared to those of a classical single-cathode free-burning arc. 相似文献
1000.
A design of a combined ozone/electron beam irradiation process for treating a 50 m3/h waste water stream from a molasses processing is discussed. Moreover, a cost evaluation of such a process in comparison to a conventional ozonation/biology treatment process has been performed to assess the potential of the irradiation process for technical use. Although the result of this comparison is not bad for the irradiation process an implementation into a full scale plant would not seem to be the thing to do in the present case. 相似文献