全文获取类型
收费全文 | 1309篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
化学 | 1042篇 |
晶体学 | 12篇 |
力学 | 17篇 |
数学 | 35篇 |
物理学 | 234篇 |
出版年
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 6篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 25篇 |
2013年 | 52篇 |
2012年 | 56篇 |
2011年 | 81篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 82篇 |
2007年 | 60篇 |
2006年 | 68篇 |
2005年 | 67篇 |
2004年 | 60篇 |
2003年 | 46篇 |
2002年 | 57篇 |
2001年 | 36篇 |
2000年 | 19篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1991年 | 23篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 20篇 |
1987年 | 30篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 17篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 8篇 |
1968年 | 7篇 |
1967年 | 6篇 |
排序方式: 共有1340条查询结果,搜索用时 31 毫秒
31.
Chlorophyll derivatives possessing triethoxysilyl groups have been synthesized for the first time and grafted on mesoporous silica to construct an efficient energy transfer system between the chromophores. 相似文献
32.
Aldehydes are easily converted to 1-bromoolefins or terminal acetylenes by the use of Wittig reaction of bromomethylenetriphenylphosphorane which is prepared from bromomethyltriphenylphosphonium bromide with potassium tert-butoxide. 相似文献
33.
34.
Polysiloxane formation in dimethyldiethoxysilane (DMDES)-ethyl alcohol (EtOH(D))-oxalic acid (OA) (DMDES:EtOH(D):OA=1:2:0.5) and DMDES-dimethylsulfoxide (DMSO)-OA (DMDES:DMSO:OA=1:2:0.5) systems was investigated by gas chromatography-mass spectrometry and 29Si-nuclear magnetic resonance. While the DMDES-EtOH(D)-OA system was homogeneous, the DMDES-DMSO-OA system consisted of two immiscible phases. In both systems, ethoxy-terminated linear oligomers ((EtO)Me2SiO(Me2SiO)nSiMe2(OEt); n=0–4, Et = C2H5, Me = CH3) and cyclic tetramer ((Me2SiO)4) were identified. The reaction mechanism for polysiloxane formation is discussed. 相似文献
35.
36.
P. K. Kuroda L. A. Burchfield I. O. Essien 《Journal of Radioanalytical and Nuclear Chemistry》1989,131(2):369-375
Radiochemical measurements of the concentrations of thorium, uranium and plutonium isotopes were carried out for the samples of Arkansas River collected at six locations in the states of Colorado and Oklahoma. The uranium to thorium ratios in the river samples were found to be highly variable and generally much greater than the ratios found in soils and in rainwater. An attempt has been made to determine the apparent230Th ages (or the times which elapsed since the last major disruption of the radioactive equilibria) from the observed230Th/232Th and234U/232Th ratios in the water samples. 相似文献
37.
Summary The adsorption behaviour of 48 metal ions on DEAE-cellulose layers has been investigated in aqueous hydrobromic and hydriodic acid media. RF values are given as a function of the hydrobromic and hydriodic acid concentration over the ranges 0.01–6 mol dm–3 and 0.01–3 mol dm–3, respectively, and are compared with those obtained with Avicel SF. RF spectra are comparatively simple in both media, reflecting the strong affinity of the bromide and iodide ions to the DEAE-cellulose phase. Pd, Pt, Re, Au and Hg are distributed chromatographically in either system, while most other metal ions exhibit rather extreme RF values of near unity or zero. Therefore, the selectivity of the systems is particularly high for Pd, Pt, Re, Au and Hg, providing the possibility of their excellent selective separations. 相似文献
38.
A flow analysis system involving the on-line configuration of an anion-exchange column has been examined to enrich and determine trace concentrations of zirconium of several ppm to hundred ppm levels in silicate rocks and minerals. About 100 mg of sample is decomposed by fusion with a mixture of boric acid and lithium carbonate and taken up with 1M hydrochloric acid to a total of 100 ml. Depending upon the concentration of zirconium, either a 1- or 4-ml aliquot is introduced into an aqueous carrier stream, merged with sulphuric acid and passed through a small volume anion-exchange column. The enriched zirconium is then back eluted with hydrochloric acid, colour-developed with Arsenazo III, and detected spectrophotometrically at 665 nm. 相似文献
39.
Novel neutral glycosphingolipids isolated from the plerocercoids of a tapeworm, Spirometra erinacei, may be expected to be involved in host-parasite interactions. We have synthesized this glycosphingolipid analogue containing 2-branched fatty alkyl residue in place of ceramide. Glycosylation of nonreducing-end trisaccharide derivative 15 with the reducing-end disaccharide derivative 17 in the presence of trimethylsilyl triflate (TMSOTf) gave the desired oligosaccharide derivative in good yield. The fully per-O-acylated 2-(trimethylsilyl)ethyl glycoside 19 was converted to glycosylimidate 20, which was condensed with 2-(tetradecyl)hexadecanol and subsequently deacylated to give the target glycosphingolipid analogue 22. 相似文献
40.
A total of 13 samples of diamond separates studied so far, all contain excess 244Pu fission xenon. On the other hand, none of the SiC separates contains excess 244Pu fission xenon, while 5 out of 10 samples of graphite separates studied so far contain excess 244Pu fission xenon. 相似文献