全文获取类型
收费全文 | 2931篇 |
免费 | 43篇 |
国内免费 | 7篇 |
专业分类
化学 | 2115篇 |
晶体学 | 10篇 |
力学 | 44篇 |
综合类 | 1篇 |
数学 | 481篇 |
物理学 | 330篇 |
出版年
2016年 | 34篇 |
2015年 | 31篇 |
2014年 | 38篇 |
2013年 | 100篇 |
2012年 | 83篇 |
2011年 | 75篇 |
2010年 | 49篇 |
2009年 | 52篇 |
2008年 | 84篇 |
2007年 | 102篇 |
2006年 | 77篇 |
2005年 | 72篇 |
2004年 | 59篇 |
2003年 | 66篇 |
2002年 | 52篇 |
2001年 | 31篇 |
2000年 | 28篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 38篇 |
1996年 | 35篇 |
1995年 | 38篇 |
1994年 | 51篇 |
1993年 | 31篇 |
1992年 | 29篇 |
1991年 | 35篇 |
1990年 | 30篇 |
1989年 | 40篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 37篇 |
1985年 | 51篇 |
1984年 | 58篇 |
1983年 | 30篇 |
1982年 | 54篇 |
1981年 | 50篇 |
1980年 | 44篇 |
1979年 | 37篇 |
1978年 | 64篇 |
1977年 | 61篇 |
1976年 | 45篇 |
1975年 | 40篇 |
1974年 | 34篇 |
1973年 | 47篇 |
1972年 | 30篇 |
1971年 | 46篇 |
1970年 | 30篇 |
1969年 | 20篇 |
1966年 | 24篇 |
1923年 | 18篇 |
排序方式: 共有2981条查询结果,搜索用时 15 毫秒
121.
Abstract Polystyrene-polyisobutylene-polystyrene triblock copolymer thermoplastic elastomers have been synthesized by living carbocationic sequential copolymerization using the tert-butyl dicumyl chloride/TiCl4/methylcyclohexane:methyl chloride (60:40 v:v)/ ?80°C system in the presence of the proton trap 2,6-di-tert-butylpyridine. Structure-property relationships have been examined by varying the Mn of the PIB middle block (39,000 to 156,000) and that of the PSt end-segment (1,000 to 19,000). The tensile strength is controlled by the molecular weight of the PSt segment and independent of the PIB middle block length in the studied range. Phase separation starts when the Mn of the PSt segment reaches ~ 5,000, and it is complete when the Mn reaches ~ 15,000. These triblocks exhibited 23-25 MPa tensile strength, similar to that of styrenic thermoplastic elastomers obtained by anionic polymerization. 相似文献
122.
Miklós Nagy László Szöllösi Sándor Kéki Rudolf Faust Miklós Zsuga 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):331-338
A series of amphiphilic polyisobutylene-block-poly(vinyl alcohol) (PIB-b-PVA) copolymers of constant PIB and varying PVA block length was synthesized by living carbocationic polymerization and their solution behavior was studied. The synthesis involved the preparation of polyisobutylene-b-poly(tert.-butyl vinyl ether) followed by hydrolysis with hydrogen bromide. The copolymers were characterized by gel permeation chromatography, 1H-NMR, and MALDI-TOF MS methods. The micellization behavior of the copolymers was investigated in aqueous media by direct dissolution and dialysis using static and dynamic light scattering. The critical micelle concentration, micelle size, aggregation number, and micelle shape were determined. The ability of the aggregates as drug carrying nanodevices was also investigated by doping them with indomethacin. UV-Vis measurements showed that the solubility of indomethacine increased significantly. Our findings suggest that the solubility is largely dependent upon the block segment ratios. 相似文献
123.
Julia Grandke Lidia Oberleitner Ute Resch-Genger Leif-Alexander Garbe Rudolf J. Schneider 《Analytical and bioanalytical chemistry》2013,405(5):1601-1611
Enzyme immunoassays with optical detection are amongst the most widely used bioanalytical tools. We defined seven parameters for the quality assessment of immunoassays that were addressed in a systematic study of direct and indirect immunoassays, using the enzymes horseradish peroxidase (HRP) and alkaline phosphatase (AP), the chromogenic substrates 3,3′,5,5′-tetramethylbenzidine (TMB) and para-nitrophenyl phosphate, and the fluorescent substrates 3-(4-hydroxyphenyl)propionic acid and 4-methylumbelliferyl phosphate. The same monoclonal antibody against caffeine was used throughout the study. The four quality parameters regarding the standard curve were the test midpoint (sensitivity), the measurement range, the relative dynamic range of the signal, and the goodness of fit of the adjusted four-parameter logistic function. All HRP immunoassays showed a higher sensitivity compared to the AP assays. On the basis of all four criteria, it was established that the direct assay format is superior to the indirect format, the immunoassay using HRP TMB fulfilling all requirements best. In a second step, caffeine concentrations in 24 beverage and cosmetics samples were determined and three more quality parameters were assessed with this application. The direct HRP TMB assay showed one of the best intra- and inter-plate precisions and the best accuracy, defined by the correlation of results with those from the chosen reference method liquid chromatography tandem mass spectrometry (LC-MS/MS). Considering all criteria, HRP TMB seems to be the enzyme substrate system of choice preferably used in the direct assay format. Figure
Overview on the different enzyme immunoassay formats compared 相似文献
124.
Ondřej Rudolf Michal Rouchal Antonín Lyčka Antonín Klásek 《Helvetica chimica acta》2013,96(10):1905-1917
3‐Alkyl/aryl‐3‐hydroxyquinoline‐2,4‐diones were reduced with NaBH4 to give cis‐3‐alkyl/aryl‐3,4‐dihydro‐3,4‐dihydroxyquinolin‐2(1H)‐ones. These compounds were subjected to pinacol rearrangement by treatment with concentrated H2SO4, resulting in 4‐alkyl/aryl‐3‐hydroxyquinolin‐2(1H)‐ones. When a benzyl (Bn) group was present in position 3 of the starting compound, its elimination occurred during the rearrangement, and the corresponding 3‐hydroxyquinolin‐2(1H)‐one was formed. The reaction mechanisms are discussed for all transformations. All compounds were characterized by IR, 1H‐ and 13C‐NMR spectroscopy, as well as mass spectrometry. 相似文献
125.
Ondřej Rudolf Vladimír Mrkvička Antonín Lyčka Michal Rouchal Antonín Klásek 《Journal of heterocyclic chemistry》2013,50(Z1):E100-E110
3‐Chloroquinoline‐2,4‐diones do not react with phosphoryl chloride, however, 2,4‐dichloroquinolines and/or 4‐chloroquinolin‐2‐ones are formed in the presence of N,N‐dimethylaniline. Along with these compounds, small quantities of novel dihydrogen phosphates of 4‐hydroxyquinolin‐2‐ones were isolated. We outline a simple procedure that allows for the preparation of these compounds in moderate to good yields. All compounds were characterized by 1H and 13C NMR, IR, EI‐MS, and ESI‐MS spectroscopy, and in select cases by 31P NMR spectroscopy. 相似文献
126.
Hans Peter Wessel Rudolf Minder Gerhard Englert 《Journal of carbohydrate chemistry》2013,32(8):1101-1115
Abstract α,β-(1→4)-Glucans were devised as models for heparan sulfate with the simplifying assumptions that carboxyl-reduction and sulfation of heparan sulfate does not decrease the SMC antiproliferative activity and that N-sulfates in glucosamines can be replaced by O-sulfates. The target oligo-saccharides were synthesized using maltosyl building blocks. Glycosylation of methyl 2,3,6,2′,3′,6′-hexa-O-benzyl-β-maltoside (1) with hepta-O-acetyl-α-maltosyl bromide (2) furnished tetrasaccharide 3 which was deprotected to α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc-(1→4)-β-D-Glc-(1→OCH3) (5) or, alternatively, converted to the tetrasaccharide glycosyl acceptor (8) with one free hydroxyl function (4?′-OH). Further glycosylation with glucosyl or maltosyl bromide followed by deblocking gave the pentasaccharide [β-D-Glc-(1→4)-α-D-Glc-(1→4)]2-β-D-Glc-(1→OCH3) (11) and hexasaccharide [α-D-Glc-(1→4)-β-D-Glc-(1→4)2-α-D-Glc-(1→4)-β-D-Glc-(1→OCH3) (14). The protected tetrasaccharide 3 and hexasaccharide 12 were fully characterized by 1H and 13C NMR spectroscopy. Assignments were possible using 1D TOCSY, T-ROESY, 1H,1H 2D COSY supplemented by 1H-detected one-bond and multiple-bond 1H,13C 2D COSY experiments. 相似文献
127.
128.
129.
Journal of Solid State Electrochemistry - 相似文献
130.
Wu Y Toccoli T Koch N Iacob E Pallaoro A Rudolf P Iannotta S 《Physical review letters》2007,98(7):076601
The key role of the pentacene kinetic energy (Ek) in the early stages of growth on SiOx/Si is demonstrated: islands with smooth borders and increased coalescence differ remarkably from fractal-like thermal growth. Increasing Ek to 6.4 eV, the morphology evolves towards higher density of smaller islands. At higher coverage, coalescence grows with Ek up to a much more uniform, less defected monolayer. The growth, interpreted by the diffusion mediated model, shows the critical nucleus changing from 3 to 2 pentacene for Ek>5-6 eV. Optimal conditions to produce single crystalline films are envisaged. 相似文献