全文获取类型
收费全文 | 3160篇 |
免费 | 88篇 |
国内免费 | 11篇 |
专业分类
化学 | 1937篇 |
晶体学 | 23篇 |
力学 | 121篇 |
数学 | 381篇 |
物理学 | 797篇 |
出版年
2022年 | 42篇 |
2021年 | 62篇 |
2020年 | 50篇 |
2019年 | 43篇 |
2018年 | 35篇 |
2017年 | 40篇 |
2016年 | 82篇 |
2015年 | 80篇 |
2014年 | 82篇 |
2013年 | 146篇 |
2012年 | 161篇 |
2011年 | 173篇 |
2010年 | 137篇 |
2009年 | 130篇 |
2008年 | 172篇 |
2007年 | 142篇 |
2006年 | 135篇 |
2005年 | 121篇 |
2004年 | 108篇 |
2003年 | 101篇 |
2002年 | 99篇 |
2001年 | 79篇 |
2000年 | 64篇 |
1999年 | 44篇 |
1998年 | 42篇 |
1997年 | 38篇 |
1996年 | 42篇 |
1995年 | 35篇 |
1994年 | 35篇 |
1993年 | 49篇 |
1992年 | 41篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1979年 | 16篇 |
1978年 | 27篇 |
1977年 | 21篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 23篇 |
1973年 | 17篇 |
1972年 | 18篇 |
排序方式: 共有3259条查询结果,搜索用时 46 毫秒
1.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
2.
3.
João Marcos G. Barbosa Milenna K. Fernandes Rodrigues Lurian C. David Taynara C. e Silva Danielly A. Fortuna Lima Naiara Z. Pereira Emmanuel B. D'Alessandro Anselmo E. de Oliveira Paulo H. Jorge da Cunha Maria Clorinda S. Fioravanti Nelson R. Antoniosi Filho 《Biomedical chromatography : BMC》2020,34(11):e4935
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication. 相似文献
4.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
5.
Paulo D. Cordaro 《Advances in Mathematics》2004,184(1):89-118
Taking as a start point the recent article of Meziani [7], we present several results concerning the normalization of a class of complex vector fields in the plane which degenerate along a real curve. We mainly deal with operators with finite regularity and analyze both the local situation as well as the case of normalization near a circle. Some related questions (e.g., on semi-global solvability and on the normalization of a class of generalized Mizohata operators) are also discussed. 相似文献
6.
A magic labelling of a set system is a labelling of its points by distinct positive integers so that every set of the system has the same sum,
the magic sum. Examples are magic squares (the sets are the rows, columns, and diagonals) and semimagic squares (the same, but without
the diagonals). A magilatin labelling is like a magic labelling but the values need be distinct only within each set. We show that the number of n × n magic or magilatin labellings is a quasipolynomial function of the magic sum, and also of an upper bound on the entries in
the square. Our results differ from previous ones because we require that the entries in the square all be different from
each other, and because we derive our results not by ad hoc reasoning but from a general theory of counting lattice points in rational inside-out polytopes. We also generalize from
set systems to rational linear forms.
Dedicated to the memory of Claudia Zaslavsky, 1917–2006
Received August 10, 2005 相似文献
7.
4-Amino-3-arylisothiazole-5-carboxylate esters are converted to the corresponding desamino, chloro, bromo, and iodo esters by processes involving nonaqueous diazotization. These related procedures open up the possibility for the conversion of readily available heterocyclic ortho-amino esters and nitriles to related heterocyclic derivatives, which are not easily obtained by alternate routes. 相似文献
8.
9.
10.
D. H. Beck 《Progress in Particle and Nuclear Physics》2003,50(2):248-449
A brief review of the structure of the nucleon as determined through parity-violating electron scattering is presented. The relationship between the electromagnetic and neutral weak currents is developed in a pedagogical introduction. Recent results and present measurements are discussed. 相似文献