全文获取类型
收费全文 | 990篇 |
免费 | 18篇 |
国内免费 | 8篇 |
专业分类
化学 | 675篇 |
晶体学 | 14篇 |
力学 | 33篇 |
数学 | 157篇 |
物理学 | 137篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 54篇 |
2012年 | 45篇 |
2011年 | 38篇 |
2010年 | 32篇 |
2009年 | 23篇 |
2008年 | 52篇 |
2007年 | 48篇 |
2006年 | 61篇 |
2005年 | 42篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 45篇 |
2001年 | 18篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1976年 | 12篇 |
1974年 | 8篇 |
1973年 | 13篇 |
1972年 | 10篇 |
1971年 | 6篇 |
排序方式: 共有1016条查询结果,搜索用时 15 毫秒
1.
Leslie S. Ettre 《Journal of separation science》1993,16(4):258-261
The background of the new Unified Nomenclature for Chromatography just accepted by the International Union of Pure and Applied Chemistry (IUPAC) is explained and selected highlights of the new rules are elaborated. 相似文献
2.
The rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate-determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley & Sons, Inc. 相似文献
3.
After describing simplified equations exspressing the temparature dependency of the viscosity of carrier gases (helium, nitrogen and hydrogen ) relative to a base value, absolute relationships based on the kinetic theory of gases are discussed. Comparative data obtained using various calculation methods are given and are compared to measured values. Based on the kinetic relationshipsm, of viscosity. Finally, the influence of pressure on the viscosity is also briefly discussed. As a supplement, Viscosity data are tabulated for the three gases in the range of 0°C to 400°C in increments of 2 K, calculated using the kinetic relationships. 相似文献
4.
以硅溶胶和氧氯化锆为硅源和锆源,采用水热合成的方法制得具有ZSM-5结构的Zr-Si分子筛;用0.5mol/L的硫酸处理该分子筛,并在550℃焙烧,制得具有ZSM-5结构的SO4^2-/ZrO2-SiO2分子筛型的固体超强酸。采用XRD、SEM、TG、IR、NH3-PHD和指示剂法对其结构和酸性进行表征。结果表明,该SO4^2-/ZrO2-SiO2具有ZSM-5结构和超强酸性,其酸强度大于-13.75,且具有良好的热稳定性。 相似文献
5.
Christopher J. Chandler Leslie W. Deady James A. Reiss Vasilios Tzimos 《Journal of heterocyclic chemistry》1982,19(5):1017-1019
The preparation of a series of macrocycles, formed by reaction of HO-(-CH2-CH2-O-)nH with 1,10-phenanthroline-2,9-dicarbonyl chloride (n = 2,3,4) and 1,8-naphthyridine-2,7-dicarbonyl chloride (n = 3,4), is described. An improved synthetic route to 2,7-dimethyl-1,8-naphthyridine 9 is also reported. 相似文献
6.
7.
Born—Oppenheimer potential surfaces for a bridged three-site electron-transfer system are calculated. The adiabatic potentials depend upon both the vibrational sum and difference coordinates. Along the vibrational difference coordinate, the ground-state surface has single-minimun form when the through-bridge electronic coupling is strong, and double-minimum form for weak through-bridge coupling. The results are compared to those previously reported for two-site models. 相似文献
8.
Garner P Anderson JT Cox PB Klippenstein SJ Leslie R Scardovi N 《The Journal of organic chemistry》2002,67(17):6195-6209
The development of an effective chiral auxiliary for hydroxyalkyl radicals is delineated. Both the 2-tetrahydropyranyl (THP) and tri-O-benzyl-2-deoxy-alpha-D-glucopyranosyl (GLU) auxiliaries resulted in diastereoselective radical additions to methyl acrylate at -78 degrees C (ds = 6/1 and 11/1, respectively). The developing stereochemistry at the radical center was completely under auxiliary control. Correlation experiments showed that the D-GLU auxiliary led to attack on the radical Si-face. The selectivity of these radical additions dropped-off considerably when the more reactive 2-nitropropene trap was employed. Computational studies suggested that the observed facial selectivity was due primarily to entropic factors in the transition state but that a smaller temperature-dependent enthalpic contribution was also involved. It was hypothesized that incorporation of a quaternary center at C-6 (THP numbering) would restore the facial selectivity with more reactive radical traps by restricting the orientations available to the incoming alkene. In the event, the trans-6-tert-butyltetrahydropyranyl (tBu-THP) auxiliary resulted in very good diastereoselection with 2-nitropropene (ds = 35/1 at -78 degrees C, 15/1 at 0 degrees C, and 8/1 at RT) as did the tri-O-benzyl-6,6-dimethyl-2-alpha-D-deoxyglucopyranosyl (diMe-GLU) auxiliary during additions to ethyl alpha-trifluoroacetoxyacrylate (ds = 10/1 at 0 degrees C). A protocol for recovery of the sugar-derived chiral auxiliaries was also established. This work sets the stage for the development of a novel approach to 1, 3, 5.(2n + 1) polyols based on iterative radical homologation as well as the application of these pyranosidic auxiliaries to other synthetically important reactions. 相似文献
9.
Leslie D. Field Adrian V. George Trevor W. Hambley Peter Turner Brian J. Wallace 《Journal of organometallic chemistry》1997,540(1-2):95-99
Reaction of cis-[FeH2(dmpe)2](1) with diphenylbutadiyne results in an insertion into both of the iron-hydride bonds to form an iron metallocycle. Spectroscopic and crystallographic data of [Fe(PhHCC2CHPh)(dmpe)2] (3) show 1,4-diphenylbutatriene is symmetrically bound to the metal via the central double bond. The reaction to form the metallocyclic complex is greatly accelerated by application of external pressure. A 41% yield of (3) is isolated after two days at atmospheric pressure or after approximately 75 min at 800MPa. 相似文献
10.
Hydroboration of 1,2-dimethylcyclopentene with BH3·THF affords a product in which boron migrates at low temperature into the cyclopentane ring. At higher temperatures subsequent (non-stereospecific) isomerisation occurs via a competing reaction mechanism. 相似文献