全文获取类型
收费全文 | 11740篇 |
免费 | 547篇 |
国内免费 | 79篇 |
专业分类
化学 | 8332篇 |
晶体学 | 117篇 |
力学 | 279篇 |
数学 | 1070篇 |
物理学 | 2568篇 |
出版年
2023年 | 63篇 |
2022年 | 191篇 |
2021年 | 252篇 |
2020年 | 189篇 |
2019年 | 197篇 |
2018年 | 177篇 |
2017年 | 173篇 |
2016年 | 343篇 |
2015年 | 338篇 |
2014年 | 411篇 |
2013年 | 730篇 |
2012年 | 823篇 |
2011年 | 914篇 |
2010年 | 589篇 |
2009年 | 470篇 |
2008年 | 800篇 |
2007年 | 704篇 |
2006年 | 712篇 |
2005年 | 599篇 |
2004年 | 570篇 |
2003年 | 470篇 |
2002年 | 445篇 |
2001年 | 279篇 |
2000年 | 215篇 |
1999年 | 171篇 |
1998年 | 110篇 |
1997年 | 86篇 |
1996年 | 109篇 |
1995年 | 114篇 |
1994年 | 92篇 |
1993年 | 77篇 |
1992年 | 69篇 |
1991年 | 44篇 |
1990年 | 73篇 |
1989年 | 74篇 |
1988年 | 43篇 |
1987年 | 37篇 |
1986年 | 21篇 |
1985年 | 63篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 39篇 |
1981年 | 43篇 |
1980年 | 33篇 |
1979年 | 33篇 |
1978年 | 23篇 |
1977年 | 29篇 |
1976年 | 23篇 |
1975年 | 21篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
An analytical method has been developed for determination of dextromethorphan (DMP) and dextrorphan (DRP) in human hair by gas chromatography–mass spectrometry (GC–MS). Hair samples (30 mg) were washed with distilled water and acetone and cut into small fragments (<1 mm) before extraction with methanol. The extracts were evaporated to dryness and then derivatized by use of BSTFA containing 1% TMCS, for preparation of the trimethylsilyl (TMS) derivative of DRP. The extract (1 μL) was then injected into the GC–MS. Recoveries of DMP and DRP at 7.0 and 22.5 ng mg?1 were in the range 90.6–97.2% with intra-assay and inter-assay precision of less than 5.7% and 4.7%, respectively. LOD and LOQ were, respectively, 0.67 and 2.13 ng mg?1 for DMP and 0.14 and 0.47 ng mg?1 for DRP. The responses were linear with correlation coefficients (r > 0.9995) for the drugs studied. The applicability of the method was proven by analysis of authentic hair samples. 相似文献
102.
Here we report the first example of catalytic metallogels, which are formed irreversibly in dimethylsulfoxide via the creation of cross-linked, three-dimensional coordination polymer networks by using transition-metal ions with multiple sites available for coordination and multidentate ligands. Conformational flexibility of the ligands and slow formation of the coordination polymers apparently favor the gelation. These metallogels are stable in water and most organic solvents and can catalyze the oxidation of benzyl alcohol to benzaldehyde by using their PdII moieties as the catalytic centers. The best catalytic turnover of the metallogel is twice that of [Pd(OAc)2] under similar reaction conditions. 相似文献
103.
Blends of ABS (acrylonitrile–butadiene–styrene) with phenoxy(poly(hydroxyether bisphenol A)) were prepared using a Branender single screw extruder. Scanning and transmission electron micrographs (SEM, TEM) showed a typical two-phase morphology; particle-in-matrix (90/10) (ABS/phenoxy by weight), 70/30, 10/90), island/sea (30/70) and co-continuous (50/50) morphologies. The glass transition temperature (Tg) of SAN was almost unchanged in the blends, while the Tg of phenoxy increased by about 5 °C in the blends. The synergistic effect of tensile modulus and strength was noted in ABS-rich blends, where a drastic drop of ductility was seen, and the results were interpreted in terms of rubber particle migration form SAN to phenoxy phase, which was visualized by TEM. Melt viscosity showed yield in ABS-rich blends, and generally followed the log additivity. 相似文献
104.
Heung-Jin Choi Dong-Hee Lee Yeon Sil Park In-Kyu Lee Young-Chul Kim 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):15-18
Octahedrally converging hexadentate macrocyclic receptors 1 and 2, based on L-tartaric acid and furanmoieties, were synthesized andtheir complexation properties studied. In this paper,magnesium ion selectivitiesdetermined by ISE experiments, chiroptical changes observedby circular dichroism(CD) on complexation, and association constants measuredby NMR titration arediscussed. 相似文献
105.
Viorica Lopez-Avila Richard Young Werner F. Beckert 《Journal of separation science》1997,20(9):487-492
This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber. 相似文献
106.
The second-order rate constants for the nucleophilic replacement of fluorine by isopropoxide in 5,6,7,8-tetrafluoro- and 6,7,-difluoro-1,2,3,4-tetrahydro-9-alkenyl-1,4-methanonaphthalenes and related 9-alkyl systems have been measured. A factor of 6 - 7 separates the most reactive compounds [the 9- (4′-trifluoromethylbenzylidene) derivatives] from the least reactive compounds [the syn-9-isopropyl derivatives] in both the tetrafluoro- and difluoro-series. It is concluded for these small reactivity differences. 相似文献
107.
108.
Ovshinsky SR Young RT Allred DD DeMaggio G Van der Leeden GA 《Physical review letters》1987,58(24):2579-2581
109.
110.