全文获取类型
收费全文 | 1049篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 709篇 |
晶体学 | 7篇 |
力学 | 58篇 |
数学 | 180篇 |
物理学 | 121篇 |
出版年
2020年 | 6篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 38篇 |
2011年 | 55篇 |
2010年 | 29篇 |
2009年 | 36篇 |
2008年 | 37篇 |
2007年 | 32篇 |
2006年 | 37篇 |
2005年 | 35篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 24篇 |
2000年 | 27篇 |
1999年 | 23篇 |
1998年 | 24篇 |
1997年 | 14篇 |
1996年 | 26篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1992年 | 11篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1972年 | 7篇 |
1970年 | 8篇 |
1969年 | 9篇 |
1968年 | 11篇 |
1966年 | 12篇 |
1930年 | 6篇 |
1929年 | 8篇 |
1928年 | 14篇 |
1927年 | 11篇 |
1893年 | 6篇 |
1883年 | 8篇 |
排序方式: 共有1075条查询结果,搜索用时 250 毫秒
91.
Marian Vîrgolici Corneliu Ponta Mihaela Manea Daniel Neguţ Mihalis Cutrubinis Ioan Moise Rareş Şuvăilă Eugen Teodor Costel Sârbu Andrei Medvedovici 《Journal of chromatography. A》2010,1217(12):1977-1987
Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution & Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis “like” macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers. 相似文献
92.
We construct generalizations of the Kerr black holes by including higher-curvature corrections in the form of the Gauss-Bonnet density coupled to the dilaton. We show that the domain of existence of these Einstein-Gauss-Bonnet-dilaton (EGBD) black holes is bounded by the Kerr black holes, the critical EGBD black holes, and the singular extremal EGBD solutions. The angular momentum of the EGBD black holes can exceed the Kerr bound. The EGBD black holes satisfy a generalized Smarr relation. We also compare their innermost stable circular orbits with those of the Kerr black holes and show the existence of differences which might be observable in astrophysical systems. 相似文献
93.
Alexander Segal 《Geometriae Dedicata》2014,171(1):293-301
In this paper we show that given a \(p\) -convex set \(K \subset \mathbb{R }^n\) , there exist \(5n\) Steiner symmetrizations that transform it into an isomorphic Euclidean ball. That is, if \(|K| = |D_n| = \kappa _n\) , we may symmetrize it, using \(5n\) Steiner symmetrizations, into a set \(K'\) such that \(c_p D_n \subset K' \subset C_p D_n\) , where \(c_p\) and \(C_p\) are constants dependent on \(p\) only. 相似文献
94.
Improved Iterative Version of the Coats-Redfern Method to Evaluate Non-Isothermal Kinetic Parameters 总被引:1,自引:0,他引:1
An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)2 have been processed.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
95.
A general kinetic equation is suggested in order to describe solid state decompositions or, more generally, solid state reactions
and transformations on the basis of some existing general equations. This differential equation can be expressed as: dα/dt=k[(1-α)q]x{[1-(1-α)1−q]/(1-q)}y, where α represents the degree of conversion, k is the rate constant while q, x and y are characteristic parameters for a
given mechanism.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
96.
97.
Ion Grosu Lo?c Toupet Gerard Plé Sorin Mager Eugen Mesaros Andreea Varga Elena Bogdan 《Monatshefte für Chemie / Chemical Monthly》2000,54(5):277-286
The synthesis and stereochemistry of new dibrominated spiro-1,3-dioxane derivatives are reported. Investigations by means
of NMR methods and single crystal X-ray diffraction for two compounds revealed the high regio- and diastereoselectivity of
the bromination reaction of some new spiro-1,3-dioxanes and the asymmetric induction of the chiral carbon atom located in
the spiro skeleton. 相似文献
98.
Journal of Thermal Analysis and Calorimetry - 相似文献
99.
Eugen Borgmann 《Fresenius' Journal of Analytical Chemistry》1883,22(1):58-60
Ohne Zusammenfassung 相似文献
100.
Eugen J. Ionascu 《Journal of Number Theory》2007,126(1):52-67
In this paper, we study the function H(a,b), which associates to every pair of positive integers a and b the number of positive integers c such that the triangle of sides a, b and c is Heron, i.e., it has integral area. In particular, we prove that H(p,q)?5 if p and q are primes, and that H(a,b)=0 for a random choice of positive integers a and b. 相似文献