全文获取类型
收费全文 | 1295篇 |
免费 | 19篇 |
专业分类
化学 | 733篇 |
晶体学 | 7篇 |
力学 | 47篇 |
数学 | 121篇 |
物理学 | 406篇 |
出版年
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 19篇 |
2013年 | 68篇 |
2012年 | 51篇 |
2011年 | 59篇 |
2010年 | 34篇 |
2009年 | 21篇 |
2008年 | 45篇 |
2007年 | 48篇 |
2006年 | 68篇 |
2005年 | 56篇 |
2004年 | 49篇 |
2003年 | 40篇 |
2002年 | 34篇 |
2001年 | 35篇 |
2000年 | 31篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 21篇 |
1993年 | 19篇 |
1992年 | 17篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 23篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 28篇 |
1976年 | 15篇 |
1975年 | 20篇 |
1974年 | 20篇 |
1973年 | 24篇 |
1972年 | 13篇 |
1968年 | 11篇 |
1967年 | 10篇 |
排序方式: 共有1314条查询结果,搜索用时 93 毫秒
31.
Gu P Haas P Hogan WP Kim SK Matthews JN Myung SS Schnetzer S Thomson GB Zou Y Arisaka K Roberts D Slater W Spencer MB Weaver M Briere RA Cheu E Harris DA Krolak P McFarland KS Roodman A Schwingenheuer B Somalwar SV Wah YW Winstein B Winston R Barker AR Swallow EC Bock GJ Coleman R Crisler M Enagonio J Ford R Hsiung YB Jensen DA O'Dell VR Ramberg E Tschirhart R Collins EM Gollin GD Nakaya T Yamanaka T 《Physical review letters》1996,76(23):4312-4315
32.
33.
34.
Summary A semi-continuous, counter-current chromatographic refiner (SCCR) was packed with an anion resin in the bisulphite form and used to separate mixtures of sugars from different feedstocks. Products with purities of more than 99% were achieved and solid concentrations of the fructose products of 12% w/v were possible. The deterioration of the anion resin was controlled by simple precautions and thus its useful life was substantially prolonged. 相似文献
35.
S. Pandey K. A. Fletcher W. E. Acree Jr C. Fetzer 《Fresenius' Journal of Analytical Chemistry》1998,360(6):669-674
Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic
aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS)
+ cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate
(SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant
PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant
PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary
to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching
selectivity was restored at concentration ratios of approximately 4 : 1 (anionic:cationic) or less.
Received: 22 May 1997 / Revised: 29 September 1997 / Accepted: 3 October 1997 相似文献
36.
Summary Equipment which has been used or suggested for preparative scale chromatography is reviewed. Particular attention is paid to one form of equipment for continuous counter-current chromatography which employs a moving mechanical seal. The theoretical effects of practical operating conditions and the mode of operation of this equipment are discussed. The influence of these effects on polymer fractionation is also considered. A theoretical model, based on the equilibrium stage concept, is proposed for the simulation of continuous gel permeation chromatography of a binary feed on such an apparatus. Examples of the results obtained from the computer simulation are given. 相似文献
37.
A. N. Fletcher 《Applied physics. B, Lasers and optics》1985,37(1):31-34
Reducing the diameter of the flashlamp was found to increase the percent improvement in output of a solid-state laser caused by using luminescent coolants. However, this change in diameter also reduced the effectiveness of the flashlamp in producing long (150 s) laser pulses so that an overall decrease in laser output was observed. In the formation of short (40 s) laser pulses, on the other hand, larger absolute values were obtained using the smaller diameter flashlamp. 相似文献
38.
L. A. Currie J. D. Kessler R. A. Fletcher J. E. Dibb 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(2):399-411
Summary Results are given from the NIST component of a pilot (“winter-over”) study of seasonal patterns of natural and anthropogenic species in air and snow transported to Summit, Greenland. Central to this research is the quantitative apportionment of fossil and biomass particulate carbon, based on advanced (micromolar) 14C accelerator mass spectrometry (AMS) applied to remote snow samples containing as little as 9 µg C/kg. The measurements were made practicable through stringent attention to the nature and sources of the isotopic-chemical blank, resulting in a blank reduction from »5 µg C to <0.5 µg C. An important result of this work is the first evidence of a seasonal pattern in biomass-C particles in Greenland snow. Although 14C AMS data serve to resolve fossil and biomass carbon quantitatively, a deeper understanding of the aerosol sources and character demands a multidisciplinary approach. This is illustrated with “multi-spectrometric” macro- and micro-analytical data for two cases involving substantial incursions of biomass aerosol to the Summit, Greenland snow. 相似文献
39.
40.
W. Russell Bowman Anthony J. Fletcher Peter J. Lovell Elena Hernández López Graeme B.S. Potts 《Tetrahedron》2007,63(1):191-203
Amides have been successfully used as precursors of imidoyl radicals for radical cyclisation. The amides have been converted to imidoyl selanides via reaction with phosgene to yield imidoyl chlorides followed by reaction with potassium phenylselanide. Imidoyl selanides were reacted with tributyltin hydride (Bu3SnH) as the radical mediator with triethylborane or AIBN as initiators to yield imidoyl radicals for cyclisation reactions. Imidoyl radicals have been cyclised onto alkenes to yield 2,3-substituted-indoles and -quinolines and also onto pyrroles and indoles to give bi- and tricyclic heteroarenes. 相似文献