全文获取类型
收费全文 | 4507篇 |
免费 | 122篇 |
国内免费 | 16篇 |
专业分类
化学 | 3307篇 |
晶体学 | 11篇 |
力学 | 66篇 |
数学 | 661篇 |
物理学 | 600篇 |
出版年
2021年 | 39篇 |
2020年 | 36篇 |
2019年 | 45篇 |
2018年 | 25篇 |
2016年 | 76篇 |
2015年 | 78篇 |
2014年 | 90篇 |
2013年 | 173篇 |
2012年 | 145篇 |
2011年 | 173篇 |
2010年 | 103篇 |
2009年 | 92篇 |
2008年 | 132篇 |
2007年 | 150篇 |
2006年 | 181篇 |
2005年 | 165篇 |
2004年 | 145篇 |
2003年 | 136篇 |
2002年 | 136篇 |
2001年 | 88篇 |
2000年 | 68篇 |
1999年 | 70篇 |
1998年 | 71篇 |
1997年 | 60篇 |
1996年 | 81篇 |
1995年 | 62篇 |
1994年 | 71篇 |
1993年 | 72篇 |
1992年 | 82篇 |
1991年 | 85篇 |
1990年 | 59篇 |
1989年 | 88篇 |
1988年 | 77篇 |
1987年 | 84篇 |
1986年 | 72篇 |
1985年 | 98篇 |
1984年 | 103篇 |
1983年 | 63篇 |
1982年 | 94篇 |
1981年 | 82篇 |
1980年 | 80篇 |
1979年 | 93篇 |
1978年 | 70篇 |
1977年 | 84篇 |
1976年 | 72篇 |
1975年 | 61篇 |
1974年 | 74篇 |
1973年 | 48篇 |
1971年 | 44篇 |
1970年 | 24篇 |
排序方式: 共有4645条查询结果,搜索用时 281 毫秒
101.
A new base-labile anchoring group, derived from 9-(hydroxymethyl)fluorene-4-carboxylic acid (HO2CFmoH or HOFmCO2H; 7), for polymer-supported peptide synthesis os described. The synthesis of 7 starting from 2,2′-biphenyldicarboxylic acid ( 1 ) proceeds in an overall yield of 53%. The group HO2CFmo exhibits properties similar to the well known Fmoc protecting group: It is stable to acidic conditions and cleavable by 15% piperidine in DMF. In combination with acid labile Nα-protecting groups (e.g. Boc, Ddz, Bpoc, Nps etc.), it renders more flexibility to the stepwise synthesis using polymer supports. The versatility of the new anchoring group in solid- and liquid-phase peptide synthesis is demonstrated for the synthesis of a model peptide. 相似文献
102.
Synthesis and Crystal Structure of Hydronium-tris-ethylenediamine-cobalt(rhodium)-μ-trichloro-nonachlorotrirhenate(III)-chloride, H3O[MEn3][Re3Cl12]Cl (M=Co, Rh) The chlorides H3O[MEn3][Re3Cl12]CI (M = Co, 1 ; Rh, 2 ) crystallize from hydrochloric acid solutions of ReCl3 and MEn3 · 3H2O as deep red hexagonal columns. They are isotypic and crystallize with the hexagonal system (P6 , Z = 1; 1: a = 1010.87(3); c = 794.30(4) pm, R = 0.023, Rw = 0.016; 2: a = 1018.58(3); c = 794.74(4) pm, R = 0.026, Rw = 0.018). The anions [Re3Cl12]3? are connected via H3O+ cation (C.N. 3). The large channels that run in the [001] direction contain, alternatively, the cations [MEn3]3+ and the lonesome Cl?-anions 相似文献
103.
The synthesis and structure of an acetal protected 10-membered cyclic enediyne-1,2-diol rac-10 is reported. The conformational constrain of the unsaturated macrocycle by the acetal protection group prevents the thermal cyclization reaction of the endiyne during synthesis and purification. 相似文献
104.
The Morita-Baylis-Hillman reaction of cyclohexenone and p-nitro benzaldehyde is catalyzed by carrier proteins such as serum albumins or enzymes such as certain lipases, conversion of up to 35% and enantioselectivities of up to 19% being observed. 相似文献
105.
Stephan Weinbruch Michael Wentzel Manfred Kluckner Peter Hoffmann Hugo M. Ortner 《Mikrochimica acta》1997,125(1-4):137-141
In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
106.
107.
Sagi D Peter-Katalinic J Conradt HS Nimtz M 《Journal of the American Society for Mass Spectrometry》2002,13(9):1138-1148
Application of the negative mode electrospray ionization-quadrupole time-of-flight mass spectrometry (ESI QTOF) tandem MS for determination of substitution patterns by sialic acid and/or fucose and extention by additional LacNAc disaccharide units in single branches of multianternary N-glycans from biological samples is described. Fragmentation patterns which can be obtained by low energy collision-induced dissociation (CID) using the QTOF instrument include cleavage ions, diagnostic for determination of antennarity and for specific structural features of single antennae. Systematic fragmentation studies in the negative ion mode were focussed toward formation of the D diagnostic ion relevant for assignment of 3- and 6-antennae in complex N-glycans carrying three and four antennae in combination with epitope-relevant B- and C-type ions. For validation of this approach ESI QTOF fragmentation of the permethylated analogues was carried out in the positive ion mode. Using this strategy, products of in vitro glycosylation reactions were investigated in order to clarify some general aspects of N-glycan acceptor specificity during biosynthesis. Alpha1-3fucosylation using GDP-fucose along with a soluble form of the recombinant human alpha1-3fucosyltransferase VI was carried out on tri- and tetraantennary precursors to test structural requirements for formation of Le(x) versus sLe(x) motifs. 相似文献
108.
109.
110.