全文获取类型
收费全文 | 1671篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
化学 | 1122篇 |
晶体学 | 15篇 |
力学 | 75篇 |
数学 | 299篇 |
物理学 | 199篇 |
出版年
2023年 | 12篇 |
2022年 | 10篇 |
2021年 | 24篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 47篇 |
2015年 | 29篇 |
2014年 | 34篇 |
2013年 | 76篇 |
2012年 | 68篇 |
2011年 | 104篇 |
2010年 | 61篇 |
2009年 | 48篇 |
2008年 | 79篇 |
2007年 | 92篇 |
2006年 | 80篇 |
2005年 | 84篇 |
2004年 | 75篇 |
2003年 | 67篇 |
2002年 | 57篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1974年 | 15篇 |
排序方式: 共有1710条查询结果,搜索用时 31 毫秒
991.
Giorgio Montaudo Maurizio S. Montaudo Concetto Puglisi Filippo Samperi 《Journal of polymer science. Part A, Polymer chemistry》1996,34(3):439-447
Four samples of Ny6, each terminated by different end groups, i.e., diamino terminated, monoamino terminated (monocapped), dicarboxyl terminated, and amino-carboxyl terminated, were synthesized and analyzed by MALDI-TOF Mass Spectrometry, in order to accurately characterize their structure by direct identification of mass resolved chains. A self-calibrating method for the MALDI-TOF mass spectra of polymeric samples was used in order to distinguish the end groups existing in the four samples of Ny6. The MALDI-TOF spectra showed the presence of protonated, sodiated, and potassiated ions that were assigned to Ny6 chains containing the expecteted end groups. Furthermore, the MALDI-TOF spectra made possible the simultaneous detection of the cyclic oligomers of Ny6 present in these samples, thus achieving the full structural characterization of the molecular species present in these polyamides. © 1996 John Wiley & Sons, Inc. 相似文献
992.
Giorgio Montaudo 《Macromolecular Symposia》1995,98(1):899-909
Mass Spectrometry, being able to look at the mass of individual molecules in a mixture of homologues, is particularly suitable for the detection of a series of oligomers. However, mass spectra had not been exploited to estimate oligomers distributions, due to the diffuse notion that a lack of correlation existed between peak intensities and concentration of the oligomers in the mixture. The introduction of soft-ionization techniques has largely eliminated this problem. A novel method for the determination of the microstructure of copolymers is presented here. We have recently found that opportune decoding of the information contained in the mass spectral intensities leads to the determination of composition and microstructure in copolymers, and this represents a significant progress. Statistical modeling of the mass spectral intensities of copolymers has been used to derive information on the distribution of monomers along the copolymer chain, and an automated procedure to find the composition and the sequence of the copolymers analyzed has been developed. The statistical analysis of copolymers makes use of Bernoullian and Markovian models in order to characterize the microstructure of copolymer samples, and assuming a theoretical distribution and then fitting the calculated oligomer abundances with the experimental MS peak intensities, the copolymer composition can be determined. A method is also reported to obtain the copolymer conposition by direct analysis of the mass spectra. These theories have been applied to determine the composition and the microstructure of several copolymers whose mass spectra have been reported in the most recent literature. 相似文献
993.
Domenico Osella Carlo Nervi Francesco Galeotti Giorgio Cavigiolio Anne Vessires Grard Jaouen 《Helvetica chimica acta》2001,84(11):3289-3298
We prepared the organometallic complex 17α‐(ferrocenylethynyl)estradiol (=[(3,17β‐dihydroxyestra‐1,3,5(10)‐trien‐17α‐yl)ethynyl]ferrocene; FcEE; 1 ) by a novel synthetic method. This metallocene possesses sufficient stability in aqueous media to permit the study of its biological properties. Thus, we were able to show that, despite the addition of a bulky substituent at the 17α position of the steroid, the metallocene is still well‐ recognized by an antibody specific to estradiol (CR=40%) and by both subtypes (ERα, ERβ) of the estrogen receptor (at 0°, RBA=28 and 37%, resp.). A DCI‐MS study of the stability of the carbocation [FcEE−OH]+ showed moderate stabilization of the carbocation, in agreement with the pK value of −0.72 found for the metallocene by means of Deno's method. The presence of the ferrocene allows the electrochemical detection of FcEE ( 1 ) by HPLC‐ED, with a detection limit of ca. 1 nM , suitable for quantitative pharmacological analysis. 相似文献
994.
995.
996.
997.
998.
Interfacial stress analysis and prediction of debonding for a thin plate bonded to a curved substrate 总被引:2,自引:0,他引:2
This paper focuses on the analytical and numerical modeling of the interface between a rigid substrate with simple constant curvature and a thin bonded plate. The interfacial behavior is modeled by independent cohesive laws in the normal and tangential directions, coupled with a mixed-mode fracture criterion. The newly developed analytical model determines the interfacial shear and normal stress distributions as functions of the substrate curvature, during the various behavioral stages of the interface prior to the initiation of debonding. The model is also able to predict the debonding load and the effective bond length. In the numerical model the interface is modeled by zero-thickness node-to-segment contact elements, in which both the geometrical relationships between the nodes of the discretized problem and the interface constitutive laws are suitably defined. Numerical results and comparisons between the predictions of the two models are presented. 相似文献
999.
Stefania Villa Giorgio Cignarella Michela M. Curzu Grard A. Pinna Elena Pini Lucio Toma 《Journal of heterocyclic chemistry》1999,36(5):1253-1257
The isomeric compounds 5,6-dihydrothieno[2,3-h]cinnolin-3(2H)-one ( 7a ) and 5,6-dihydrothieno-[3,2-h]cinnolin-3(2H)-one ( 7b ) rapidly tautomerise to the corresponding 1,4-dihydrothienocinnolinones 8a,b when kept in refluxing hydrazine hydrate. With longer reaction times the initially formed 8a,b dehydrogenate to the thienocinnolinones 9a,b which eventually are aminated to 4-aminothienocinnolinones 10a,b . This behaviour recalls that reported for the related 5,6-dihydrobenzocinnolin-3(2H)-one ( 1 ) which under the same conditions undergoes dehydrogenation to benzo[h]cinnolin-3(2H)-one ( 2 ) followed by 4-amination to 3 , but differs for the stability of the intermediates, for the mechanism of the final amination, and for the higher reaction rate. All these differences can be rationalised in terms of the heats of formation of the intermediates and products of the two series of transformations. 相似文献
1000.