全文获取类型
收费全文 | 7625篇 |
免费 | 419篇 |
国内免费 | 53篇 |
专业分类
化学 | 5750篇 |
晶体学 | 62篇 |
力学 | 153篇 |
数学 | 698篇 |
物理学 | 1434篇 |
出版年
2023年 | 34篇 |
2022年 | 38篇 |
2021年 | 149篇 |
2020年 | 131篇 |
2019年 | 159篇 |
2018年 | 121篇 |
2017年 | 115篇 |
2016年 | 250篇 |
2015年 | 234篇 |
2014年 | 307篇 |
2013年 | 488篇 |
2012年 | 572篇 |
2011年 | 658篇 |
2010年 | 388篇 |
2009年 | 313篇 |
2008年 | 524篇 |
2007年 | 462篇 |
2006年 | 462篇 |
2005年 | 386篇 |
2004年 | 361篇 |
2003年 | 301篇 |
2002年 | 279篇 |
2001年 | 126篇 |
2000年 | 120篇 |
1999年 | 84篇 |
1998年 | 60篇 |
1997年 | 57篇 |
1996年 | 67篇 |
1995年 | 60篇 |
1994年 | 55篇 |
1993年 | 36篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 33篇 |
1989年 | 38篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 22篇 |
1985年 | 47篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 30篇 |
1978年 | 18篇 |
1977年 | 24篇 |
1976年 | 22篇 |
1975年 | 18篇 |
1973年 | 27篇 |
排序方式: 共有8097条查询结果,搜索用时 31 毫秒
71.
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
72.
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
73.
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
74.
The surface-enhanced Raman scatterings of dimethyl sulfide, diethyl sulfide and dimethyl disulfide have been investigated in silver sol. The dimethyl disulfide molecule decomposes on silver to the corresponding mercaptide implying facile cleavage of its S---S bond. The C---S bond in dialkyl monosulfide appears not to cleave on silver. For diethyl sulfide, the C2 conformation seems to be favorable on silver than other conformations. 相似文献
75.
76.
Ovshinsky SR Young RT Allred DD DeMaggio G Van der Leeden GA 《Physical review letters》1987,58(24):2579-2581
77.
78.
Summary Real hypersurfaces of an almost Hermitian manifold naturally admit an almost contact metric structure and the (f, g, u, v, w, , , )-structure is defined on submanifolds of codimension 3 of an almost Hermitian manifold. We study the so-called semi-invariant submanifolds of a complex space form with almost contact metric compound structure which is a general notion of (f, g, u, v, w, , , )-structure.Dedicated to professor Eulyong Pak on his 60th birthdayThis research was partially supported by Korean Science and Engineering Foundation Grant. 相似文献
79.
80.
Photodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue was investigated using a homebuilt tandem time-of-flight mass spectrometer equipped with a matrix-assisted laser desorption/ionization source. Efficient photodissociation of the protonated peptides was demonstrated. Most of the intense peaks in the laser-induced tandem mass spectra were sequence ions. Furthermore, sequence ions due to cleavages at all the peptide bonds were observed; this is a feature of the technique that is particularly useful for peptide sequencing. Fragmentations at both ends of the tryptophanyl residue were especially prevalent, which can be useful for location of the tryptophanyl chromophore in a peptide. 相似文献