全文获取类型
收费全文 | 43799篇 |
免费 | 10926篇 |
国内免费 | 2812篇 |
专业分类
化学 | 47401篇 |
晶体学 | 451篇 |
力学 | 982篇 |
综合类 | 133篇 |
数学 | 3189篇 |
物理学 | 5381篇 |
出版年
2024年 | 21篇 |
2023年 | 229篇 |
2022年 | 300篇 |
2021年 | 520篇 |
2020年 | 1681篇 |
2019年 | 2981篇 |
2018年 | 1368篇 |
2017年 | 1003篇 |
2016年 | 3782篇 |
2015年 | 3972篇 |
2014年 | 3963篇 |
2013年 | 4801篇 |
2012年 | 3714篇 |
2011年 | 2930篇 |
2010年 | 3437篇 |
2009年 | 3401篇 |
2008年 | 2975篇 |
2007年 | 2229篇 |
2006年 | 1906篇 |
2005年 | 1964篇 |
2004年 | 1707篇 |
2003年 | 1499篇 |
2002年 | 2204篇 |
2001年 | 1530篇 |
2000年 | 1447篇 |
1999年 | 546篇 |
1998年 | 191篇 |
1997年 | 168篇 |
1996年 | 138篇 |
1995年 | 93篇 |
1994年 | 112篇 |
1993年 | 86篇 |
1992年 | 66篇 |
1991年 | 52篇 |
1990年 | 71篇 |
1989年 | 53篇 |
1988年 | 49篇 |
1987年 | 41篇 |
1986年 | 32篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 25篇 |
1979年 | 14篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Feng-Ling Qing Min JiRonghua Lu Kelu YanZhiping Mao 《Journal of fluorine chemistry》2002,113(1):139-141
A new kind of perfluoroalkyl-containing multifunctional groups compound was designed. Treatment of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (4) with allylmagnesium bromide provided key intermediate 1H,1H,2H,2H-perfluorooctyltriallylsilane (2). Hydroboration followed by oxidation, epoxidation and dihydroxylation of 2 gave perfluoroalkyl-containing multifunctional groups compound 1a, 1b and 1c, respectively. 相似文献
962.
Houda Marouani Mohamed Rzaigui Muriel Bagieu‐Beucher 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):356-357
In hexakis(m‐toluidinium) cyclohexaphosphate, 6C7H10N+·P6O186?, the atomic arrangement is typical of a layer structure. Layers including the centrosymmetric P6O18 ring anions develop around the (100) planes at x = . The hydrogen‐bond distribution is described. 相似文献
963.
964.
965.
966.
The isolation and identification of eighteen components from the leaves of Schefflera taiwaniana are presented. Their structures were determined on the basis of spectral data as well as direct comparison with authentic samples. These compounds include two polyacetylenes, one carotenoid‐like, three sesquiterpenes, one diterpene, four triterpenes, two tocopherols, and five alkyl 4‐hydroxycinnamate mixtures. Among these, 4‐hydroxy‐trans‐cinnamic acid docosyl ester and 4‐hydroxy‐cis‐cinnamic acid tetracosyl ester are new compounds. Some of these components exhibit cytotoxic activity. 相似文献
967.
Han Nim Choi Jee Hoon Han Ji Ae Park Joong Min Lee Won‐Yong Lee 《Electroanalysis》2007,19(17):1757-1763
A highly sensitive and selective glucose biosensor has been developed based on immobilization of glucose oxidase within mesoporous carbon nanotube–titania–Nafion composite film coated on a platinized glassy carbon electrode. Synergistic electrocatalytic activity of carbon nanotubes and electrodeposited platinum nanoparticles on electrode surface resulted in an efficient reduction of hydrogen peroxide, allowing the sensitive and selective quantitation of glucose by the direct reduction of enzymatically‐liberated hydrogen peroxide at ?0.1 V versus Ag/AgCl (3 M NaCl) without a mediator. The present biosensor responded linearly to glucose in the wide concentration range from 5.0×10?5 to 5.0×10?3 M with a good sensitivity of 154 mA M?1cm?2. Due to the mesoporous nature of CNT–titania–Nafion composite film, the present biosensor exhibited very fast response time within 2 s. In addition, the present biosensor did not show any interference from large excess of ascorbic acid and uric acid. 相似文献
968.
969.
Matthieu Baudelet Myriam Boueri Jin Yu Samuel S. Mao Vincent Piscitelli Xianglei Mao Richard E. Russo 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(12):1329-1334
Ultraviolet pulses (266 nm) delivered by a quadrupled Nd:YAG laser were used to analyze organic samples with laser-induced breakdown spectroscopy (LIBS). We present characteristics of the spectra obtained from organic samples with special attentions on the emissions of organic elements, O and N, and molecular bonds CN. The choice of these atomic or molecular species is justified on one hand, by the importance of these species to specify organic or biological materials; and on the other hand by the possible interferences with ambient air when laser ablation takes place in the atmosphere. Time-resolved LIBS was used to determine the time-evolution of line intensity emitted from these species. We demonstrate different kinetic behaviors corresponding to different origins of emitters: native atomic or molecular species directly vaporized from the sample or those generated through dissociation or recombination due to interaction between laser-induced plasma and air molecules. Our results show the ability of time-resolved UV-LIBS for detection and identification of native atomic or molecular species from an organic sample. 相似文献
970.
A series of new 2‐substituted 3‐(4‐chlorophenyl)‐5,8,9‐trimethylthieno[3′,2′: 5,6]pyrido[4,3‐d]pyrimidin‐4(3H)‐ones 8 were synthesized via an aza‐Wittig reaction. Phosphoranylideneamino derivatives 6a or 6b reacted with 4‐chlorophenyl isocyanate to give carbodiimide derivatives 7a or 7b , respectively, which were further treated with amines or phenols to give compounds 8 in the presence of a catalytic amount of EtONa or K2CO3. The structure of 2‐(4‐chlorophenoxy)‐3‐(4‐chlorophenyl)‐5,8,9‐trimethylthieno[3′,2′: 5,6]pyrido[4,3‐d]pyrimidin‐4(3H)‐one ( 8j ) was comfirmed by X‐ray analysis. 相似文献