全文获取类型
收费全文 | 624篇 |
免费 | 28篇 |
专业分类
化学 | 527篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 51篇 |
物理学 | 58篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 48篇 |
2021年 | 40篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 23篇 |
2015年 | 26篇 |
2014年 | 20篇 |
2013年 | 42篇 |
2012年 | 36篇 |
2011年 | 56篇 |
2010年 | 37篇 |
2009年 | 23篇 |
2008年 | 25篇 |
2007年 | 28篇 |
2006年 | 26篇 |
2005年 | 25篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有652条查询结果,搜索用时 15 毫秒
1.
Normal human dermal fibroblasts: proteomic analysis of cell layer and culture medium. 总被引:7,自引:0,他引:7
Federica Boraldi Luca Bini Sabrina Liberatori Alessandro Armini Vitaliano Pallini Roberta Tiozzo Ivonne Pasquali Ronchetti Daniela Quaglino 《Electrophoresis》2003,24(7-8):1292-1310
Proteins present within the cell layer and those released in the cell medium from in vitro cultured normal human dermal fibroblasts were separated and characterized in terms of their isoelectric point and molecular weight, by two-dimensional (2-D) gel electrophoresis. All spots in the synthetic gel were firstly analyzed by the Melanie 3 software and compared with those of breast cancer cells, colorectal epithelial cells, HL60, lymphoma cells, and platelets, already available on-line. From the identification of 144 spots from both the cell layer and the medium, we were able to recognize 89 different proteins, since a certain number of spots represented different isoforms of the same molecule. Identifications were performed by matching with on-line 2-D databases, and by matrix assisted laser-desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), in order to confirm the identification by matching, or to identify new proteins. The procedure we used allows (i) to design a highly reproducible reference map of the proteome of adult human normal fibroblasts in culture, (ii) to evaluate protein species produced in the cell layer as well as those released in the culture medium, and (iii) to compare data from gel matching with those obtained by MS. This work represents an essential step for a better knowledge of mesenchymal cells, given the widespread use of this cell type in both clinical and experimental investigations. 相似文献
2.
Standardization and certification in the area of environmentally degradable plastics 总被引:1,自引:0,他引:1
Andrej Krzan Sarunya Hemjinda Stanislav Miertus Emo Chiellini 《Polymer Degradation and Stability》2006,91(12):2819-2833
Environmentally degradable polymers and plastics (EDPs) are a group of polymeric materials experiencing a rapid growth in number as well as in their applications and quantities used. The assessment of their key characteristic - degradability, including eventually biodegradability as the ultimate stage, is scientifically and technically a challenging issue and has led to differing interpretations in the past. In order to standardize techniques and criteria a number of standards were established by different standardization bodies which are also used as a basis for certification schemes. An up-to-date inventory of the rapidly growing standardization body is presented with basic interpretation to help guide the non-expert. A basic introduction to EDPs and polymer degradation is added for clarity. 相似文献
3.
Carlo Carlini Emo Chiellini Roberto Solaro 《Journal of polymer science. Part A, Polymer chemistry》1980,18(7):2129-2142
Homogeneous catalytic systems based on optically active low-molecular-weight and macromolecular titanium alcoholates and tri-isobutyl aluminum were used in the isomerization and hydrogenation of chiral and prochiral olefins. The reactions performed in a nitrogen and hydrogen atmosphere show a different behavior in regard to reaction rate, composition of reaction mixture, and stereochemical control. The catalyst based on macromolecular titanium alcoholate displays lower activity and a varying influence on the stereochemical pathway with respect to the catalysts based on low- molecular-weight alcoholates. The data obtained in both cases strongly support the absence of a stereocontrol by the growing chain in the stereoelective polymerization of racemic α-olefins by Ziegler-Natta catalysts based on optically active precursors. Finally evidence is provided in favor of the intermediate step responsible for asymmetric isomerization which does not occur via η-allyl complex. 相似文献
4.
Tondi D Morandi F Bonnet R Costi MP Shoichet BK 《Journal of the American Chemical Society》2005,127(13):4632-4639
Bacterial expression of beta-lactamases is the most widespread resistance mechanism to beta-lactam antibiotics, such as penicillins and cephalosporins. There is a pressing need for novel, non-beta-lactam inhibitors of these enzymes. One previously discovered novel inhibitor of the beta-lactamase AmpC, compound 1, has several favorable properties: it is chemically dissimilar to beta-lactams and is a noncovalent, competitive inhibitor of the enzyme. However, at 26 microM its activity is modest. Using the X-ray structure of the AmpC/1 complex as a template, 14 analogues were designed and synthesized. The most active of these, compound 10, had a K(i) of 1 microM, 26-fold better than the lead. To understand the origins of this improved activity, the structures of AmpC in complex with compound 10 and an analogue, compound 11, were determined by X-ray crystallography to 1.97 and 1.96 A, respectively. Compound 10 was active in cell culture, reversing resistance to the third generation cephalosporin ceftazidime in bacterial pathogens expressing AmpC. In contrast to beta-lactam-based inhibitors clavulanate and cefoxitin, compound 10 did not up-regulate beta-lactamase expression in cell culture but simply inhibited the enzyme expressed by the resistant bacteria. Its escape from this resistance mechanism derives from its dissimilarity to beta-lactam antibiotics. 相似文献
5.
1,3-Dipolar cycloaddition of acrylamide with the cyclic nitrone derived from proline tert-butyl ester has been employed in the synthesis of bicyclic Gly-(s-cis)Pro isosteres suitably protected for the Fmoc-based solid phase peptide synthesis. (R)-1-Phenylethylamine was introduced as chiral auxiliary to resolve racemic intermediates and obtain enantiopure compounds. Using methacrylamide as dipolarophile, the analogous Ala-Pro mimetics have been prepared in racemic form, whereas the same strategy applied to methyl itaconate failed to give the corresponding Asp-Pro mimetic. 相似文献
6.
Mario Giuffrida Pietro Maravigna Giorgio Montaudo Emo Chiellini 《Journal of polymer science. Part A, Polymer chemistry》1986,24(7):1643-1656
Some bipolyesters consisting of 1,2-propene glycol residue (P) and symmetric aromatic diacid residue constituted by two p-oxybenzoyl groups coupled by a terephthaloyl (HTH), phthaloyl (HOH) and isophthaloyl (HIH) group, and a nonsymmetric diacid residue constituted by a p-oxybenzoyl and a terephthaloyl group (HT), have been investigated by direct pyrolysis–mass spectrometry. The results show that intramolecular exchange reactions occurring at the pyrolysis stage cause a reorganization of the copolymer sequences. Sequential bipolyesters I–IV are ideal materials for the investigation of the extent of thermal reorganization induced in the bipolymer sequences by the pyrolytic process. 相似文献
7.
Results obtained by using "Analyst", a long-term diffusive sampler, in some monitoring campaigns, performed for the determination of benzene and the volatile aromatic pollutants, in five cities of the Italian Umbria Region and at the city of Forlì, are presented and discussed. First results of an inter comparison between the "Analyst" and "radial-type" diffusive samplers, carried out by the Regional Agency for the Ambient Protection (ARPA) of Forlì, point out substantial advantages with the long-time sampling devices. 相似文献
8.
Chevelkov V van Rossum BJ Castellani F Rehbein K Diehl A Hohwy M Steuernagel S Engelke F Oschkinat H Reif B 《Journal of the American Chemical Society》2003,125(26):7788-7789
In this communication, we demonstrate the feasibility of 1H detection in MAS solid-state NMR for a microcrystalline, uniformly 2H,15N-labeled sample of a SH3 domain of chicken alpha-spectrin, using pulsed field gradients for suppression of water magnetization. Today, B0 gradients are employed routinely in solution-state NMR for coherence order selection and solvent suppression. We suggest to use gradients to purge water magnetization which cannot be suppressed using conventional water suppression schemes. The achievable gain in sensitivity for 1H detection is in the order of 5 compared to the 15N detected version of the experiment (at a MAS rotation frequency of 13.5 kHz). We expect that this labeling concept which achieves high sensitivity due to 1H detection, in combination with the possibility to measure long range 1H-1H distances as we have shown previously, to be a useful tool for the determination of protein structures in the solid state. 相似文献
9.
[reaction: see text] The palladium-catalyzed reaction of aryl iodides with acetic anhydride provides a straightforward and experimentally simple carbon monoxide-free route to acetophenones. The reaction tolerates a wide range of functionalized aryl iodides. Acetophenones are isolated in excellent yield with a variety of neutral, slightly electron-rich, and slightly electron-poor aryl iodides, whereas moderate yields are obtained with aryl iodides containing strongly electron-withdrawing substituents. 相似文献
10.
Castagnola M Zuppi C Rossetti DV Vincenzoni F Lupi A Vitali A Meucci E Messana I 《Electrophoresis》2002,23(12):1769-1778
The general properties of dendrimers and in particular their electrolytic characteristics that are relevant in electrokinetic separations, are described. In order to confirm theoretical considerations on commercial dendrimer charge and hydrodynamic radius, several capillary zone electrophoresis (CZE) experiments were performed. Electrophoretic mobilities measured at different pH values indicated a sensible increase of dendrimer hydrodynamic radius at pH values lower than 2.5. This was probably due to the Coulombic repulsion of charged amine groups of the inner dendrimer shells. The principal reasons that should address the use of dendrimers as pseudostationary phases in micellar electrokinetic chromatography (MEKC) are discussed. Moreover, a survey of different separations performed utilizing dendrimers in MEKC as well as of several future plausible uses of various classes of dendrimers is presented. 相似文献