全文获取类型
收费全文 | 73513篇 |
免费 | 14795篇 |
国内免费 | 6508篇 |
专业分类
化学 | 66615篇 |
晶体学 | 792篇 |
力学 | 2815篇 |
综合类 | 301篇 |
数学 | 5962篇 |
物理学 | 18331篇 |
出版年
2024年 | 155篇 |
2023年 | 810篇 |
2022年 | 1456篇 |
2021年 | 1794篇 |
2020年 | 2807篇 |
2019年 | 4014篇 |
2018年 | 2372篇 |
2017年 | 1920篇 |
2016年 | 5159篇 |
2015年 | 5252篇 |
2014年 | 5656篇 |
2013年 | 6822篇 |
2012年 | 6331篇 |
2011年 | 5670篇 |
2010年 | 5144篇 |
2009年 | 5023篇 |
2008年 | 4868篇 |
2007年 | 3960篇 |
2006年 | 3541篇 |
2005年 | 3223篇 |
2004年 | 2724篇 |
2003年 | 2339篇 |
2002年 | 3205篇 |
2001年 | 2321篇 |
2000年 | 2058篇 |
1999年 | 1176篇 |
1998年 | 710篇 |
1997年 | 642篇 |
1996年 | 619篇 |
1995年 | 531篇 |
1994年 | 436篇 |
1993年 | 378篇 |
1992年 | 330篇 |
1991年 | 283篇 |
1990年 | 231篇 |
1989年 | 173篇 |
1988年 | 118篇 |
1987年 | 99篇 |
1986年 | 119篇 |
1985年 | 89篇 |
1984年 | 49篇 |
1983年 | 56篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1969年 | 5篇 |
1968年 | 7篇 |
1966年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
Vibrational circular dichroism (VCD) in the past two decades has developed into a powerful new structural tool. A concise review of the applications of VCD to determine the structures of various biological molecules, namely peptides and proteins, nucleic acids and carbohydrates, is provided. 相似文献
192.
193.
194.
Bisfunctionalized m-phenylene ethynylene imine oligomers were polymerized in the polar solvent acetonitrile, resulting in high-molecular weight poly(m-phenylene ethynylene imine)s. It is hypothesized that this polymerization, which proceeds through the reversible metathesis of imine bonds, is driven by the folding of the long m-phenylene ethynylene imine chains. Upon conducting the polymerization in a series of solvents in which the m-phenylene ethynylene oligomers exhibit different folding stabilities, it was possible to correlate the molecular weight of the resulting poly(m-phenylene ethynylene imine)s with the helical stability of the corresponding oligomers. The polymerization was also demonstrated to be reversible and responsive to solvent and temperature changes. 相似文献
195.
Ju-Chun Huang Chien Hong Cheng Shyang Roeng Sheen Zhi Ling Lee Chien Ming Lei Maw Kuen Wu 《中国化学会会志》1996,43(2):139-143
The synthesis of bulk Y2Ba4Cu7O15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y2Ba4Cu7O15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y2Ba4Cu7O15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described. 相似文献
196.
Core/shell nanocomposite based on the local polarization and its electrorheological behavior 总被引:2,自引:0,他引:2
Aimed at the increase of electrorheological effect, a novel core/shell material was prepared by the combination of mechanochemical activity and sol-gel technique. The structure analyses X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy, and energy-dispersive spectrometry showed that a modified kaolinite/titanium oxide nanocomposite consisted of the mechanochemically activated kaolinite/NaCl complex coated by titanium oxide. A distinct enhancement of the electrorheological activity was found by using such particles dispersed in silicone oil than those of kaolinite or titanium oxide alone under a direct current electric field. Modified kaolinite/titanium oxide electrorheological fluid has a larger dielectric constant enhancement deltaepsilon', and a strong interfacial polarization occurs with a clear dielectric loss peak around 2 kHz. Doping NaCl into the core (kaolinite) by the mechanochemical activation and limiting the transferring of the ions by the shell (titanium oxide) may increase the interfacial polarizability of particles and induce a high electrorheological effect. 相似文献
197.
Liu H Hu Y Yang S Guo W Lu X Zhao L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(21):6392-6406
We report herein a comprehensive study of photoinduced reactions in complexes of Mg+ with primary (n-propyl- and isopropylamine) and secondary amines (dipropyl- and diisopropylamine) in the spectral range of 230-440 nm. Similar to the methyl- and ethylamine complexes studied previously, N-H bond activation of these complexes is very unfavorable. Instead, the C(alpha)-C, C-N, and C(alpha)-H bond-cleavage photoproducts are observed after photoexcitation of the Mg+ complexes (3(2)P<--3(2)S). For Mg+(primary amine) complexes, for example, Mg+-NH2CH2CH2CH3, and Mg+-NH2CH(CH3)2, the photoproducts resulting from C(alpha)--C rupture prevail after P(z) and charge-transfer excitations, whereas the Mg+ photofragment is predominant upon P(x,y) excitation. However, with further N-alkyl substitution, as in Mg+(secondary amine) complexes, for example, Mg+-NH(CH2CH2CH3)2 and Mg+-NH[CH(CH3)2]2, a novel intracomplex C-C coupling photoreaction dominates on P(x,y) excitation of Mg+, which is believed to arise from Mg+* insertion into the C-N bond. With P(z) and charge-transfer excitation, the Mg-R elimination photoproducts, arising from C(alpha)-C bond cleavage, predominate. The energetics and possible mechanisms of the intracomplex photoreactions are analyzed in detail with the help of extensive quantum mechanics calculations. 相似文献
198.
Shen YH Li SH Li RT Han QB Zhao QS Liang L Sun HD Lu Y Cao P Zheng QT 《Organic letters》2004,6(10):1593-1595
Both coriatone (1). a novel highly oxygenated picrotoxane-type sesquiterpene, and corianlactone (2). with an unprecedented sesquiterpene basic skeleton, named coriane, were isolated from Coriaria nepalensis Wall. The structures of 1 and 2 were determined by analysis of their two-dimensional NMR data, and the structure of 2 was confirmed by X-ray analysis. Compounds 1 and 2 showed no remarkable inhibitory activity toward K(562) cells. They are cytotoxic with IC(50) > 50 microg/mL (cis-platinim: IC(50) = 0.49 microg/mL). 相似文献
199.
A novel route for waste water treatment: photo-assisted Fenton degradation of dye pollutants accumulated in natural polyelectrolyte microshells 总被引:2,自引:0,他引:2
The efficient accumulation of dyes in constructed natural polyelectrolyte microshells under moderate conditions, combined with the photo-assisted Fenton reagent, opens a new route for the effective elimination of dye pollutants from waste water. 相似文献
200.