全文获取类型
收费全文 | 559篇 |
免费 | 12篇 |
国内免费 | 6篇 |
专业分类
化学 | 413篇 |
晶体学 | 8篇 |
力学 | 5篇 |
数学 | 68篇 |
物理学 | 83篇 |
出版年
2020年 | 6篇 |
2019年 | 4篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 27篇 |
2011年 | 34篇 |
2010年 | 17篇 |
2009年 | 11篇 |
2008年 | 31篇 |
2007年 | 31篇 |
2006年 | 31篇 |
2005年 | 39篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 29篇 |
2000年 | 16篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1967年 | 6篇 |
1966年 | 2篇 |
排序方式: 共有577条查询结果,搜索用时 15 毫秒
51.
52.
The electronic properties and formation energy of isolated Cl defects in SiC were investigated by first-principles calculations. Chlorine was studied in a substitutional position, in either a carbon (Cl(C)) or a silicon site (Cl(Si)), and in two interstitial positions (Cl(i)), either tetrahedral or octahedral configurations. Our calculations revealed that Cl(C) is energetically favored and it is a likely candidate to explain the nature of the experimentally observed Cl incorporation reported in SiC epilayers grown by chloride-based chemical vapor deposition. 相似文献
53.
T. Andrew Mobley Eleanor G. Tennyson Grant S. Hisao 《Magnetic resonance in chemistry : MRC》2010,48(10):787-792
Recently reported triple‐resonance Y‐relayed 1H,X correlation experiments have been utilized to characterize 183W and 57Fe chemical shifts using 119Sn as the Y‐relaying nucleus instead of the previously used 31P. Application of an adaptation of Gudat's original INEPT/HMQC sequence results in a significant enhancement of the signal‐to‐noise (S/N) ratio for two‐dimensional 119Sn‐relayed 1H,183W and 1H, 57Fe correlation spectra with efficient detection of the transition metal nucleus in tungsten and iron complexes lacking an observable direct scalar coupling between the transition metal and any hydrogen nuclei. Strengths and shortcomings of the novel sequence and the original sequences reported by Gudat are discussed in the context of 119Sn‐relayed proton detection of very low frequency transition metal nuclei. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
54.
55.
56.
The X-ray crystal structure of the title complex, Co(Cl2bprpi) is described. In this complex the Co(II) center displays a distorted octahedral coordination geometry. The piperazine ring exhibits boat conformation, forming chelate rings and capping the Co atom. The N2-Col-N3 angle is 69.41(15) degrees, extremely smaller than 90 degrees. Because the small angle causes a large steric hindrance, the piperazine ring can be effective as an ion size-recognition site. The molecular structure is stabilized by intramolecular N-H...O hydrogen bonds and Cl...H contacts. 相似文献
57.
Hisao Hayakawa 《Theoretical and Mathematical Physics》1994,99(2):606-610
The author summarize the recent analysis of a two-fluid model which describes fluidized beds of granular particles. It has been found that near the transition point from stable fluidized beds to unstable ones the two-fluid model is reduced to the KdV equation with small dissipation. The amplitude and the propagating velocity of a pulse of the reduced equation is obtained.Department of Physics, Tohoku University, Sendai 980, Japan. E-mail: hisao@cmpt01.phys.tohoku.ac.jp. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 99, No. 2, pp. 309–314, May, 1994. 相似文献
58.
This paper is concerned with the freezing of water in a closed metal tube by regarding the effect of volumetric change of water which is closely related with solidification. The pressure of unfrozen water in the tube increases gradually with increasing frozen layer, consequently the freezing temperature of the water decreases monotonically. It is found from the present results that the freezing limit of water corresponding to the cease of freezing caused by no temperature difference between environmental temperature and freezing point would exist. This remarkable phenomena are mainly attributed to the combined effect of environmental temperature and inner diameter of the tube. 相似文献
59.
Motoyama Y Sakakura T Takemoto T Shimozono K Aoki K Nishiyama H 《Molecules (Basel, Switzerland)》2011,16(7):5387-5401
Bis(oxazolinyl)phenylrhodium(III) aqua complexes, (Phebox)RhX?(H?O) [X = Cl, Br], were found to be efficient Lewis acid catalysts for the enantioselective addition of allyl- and methallyltributyltin reagents to amino aldehydes. The reactions proceed smoothly in the presence of 5-10 mol % of (Phebox)RhX?(H?O) complex at ambient temperature to give the corresponding amino alcohols with modest to good enantioselectivity (up to 94% ee). 相似文献
60.
We developed a useful and preparative method based on high-speed counter-current chromatography with mass spectrometry (HSCCC/MS) to purify gentamicin C1a, C2/2a and C1 from standard powder. The analytes were purified on the HSCCC model CCC-1000 (multi-layer coil planet centrifuge) with a volatile two-phase solvent system composed of n-butanol/10% aqueous ammonia solution (50:50, v/v) and detected on an LCMS-2020EV quadrupole mass spectrometer fitted with an electrospray ionization (ESI) source system in positive ionization following scan mode (m/z 100-500). The HSCCC/ESI-MS peaks indicated that gentamicin C1a (m/z 450: [M+H](+)), C2/2a (m/z 464: [M+H](+)) and C1 (m/z 478: [M+H](+)) have the peak resolution values of 1.3 and 1.7 from 30 mg of loaded gentamicin powder. The HSCCC yielded 3.9 mg of gentamicin C1a, 12.6 mg of gentamicin C2/2a and 12.0 mg of gentamicin C1. These purified substances were analyzed by LC/MS with scan positive-mode. Based on the LC/MS chromatograms and spectra of the fractions, analytes were estimated to be over 95% pure. These gentamicin isomers of C1a, C2/2a and C1 were evaluated for their antibacterial activities. The overall results indicate that this approach of HSCCC/MS is a powerful technique for the purification of gentamicin components. 相似文献