全文获取类型
收费全文 | 2171篇 |
免费 | 52篇 |
国内免费 | 3篇 |
专业分类
化学 | 1199篇 |
晶体学 | 12篇 |
力学 | 40篇 |
数学 | 206篇 |
物理学 | 769篇 |
出版年
2022年 | 27篇 |
2021年 | 31篇 |
2020年 | 31篇 |
2019年 | 21篇 |
2018年 | 17篇 |
2017年 | 25篇 |
2016年 | 47篇 |
2015年 | 43篇 |
2014年 | 33篇 |
2013年 | 75篇 |
2012年 | 97篇 |
2011年 | 107篇 |
2010年 | 71篇 |
2009年 | 61篇 |
2008年 | 97篇 |
2007年 | 95篇 |
2006年 | 93篇 |
2005年 | 95篇 |
2004年 | 87篇 |
2003年 | 65篇 |
2002年 | 74篇 |
2001年 | 35篇 |
2000年 | 58篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 38篇 |
1995年 | 34篇 |
1994年 | 45篇 |
1993年 | 51篇 |
1992年 | 49篇 |
1991年 | 28篇 |
1990年 | 33篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 35篇 |
1986年 | 23篇 |
1985年 | 49篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 34篇 |
1978年 | 25篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 27篇 |
1973年 | 16篇 |
排序方式: 共有2226条查询结果,搜索用时 15 毫秒
1.
2.
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
3.
Using lower-cost lasers, 30% savings are possible for 10-Gb/s uncompensated metro transmission over NZDF, compared to G.652 fiber. We present WDM transmission results for a mixed plant of NZDF rings interconnected to G.652.C-fiber access laterals. 相似文献
4.
We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems. 相似文献
5.
6.
Belting, a vocal technique typically cultivated in musical theatre singing, differs timbrally from operatic singing in many interesting respects. The underlying phonatory differences have not been previously investigated in detail. Yet, belting is frequently associated with disturbances of voice function. Articulatory and phonatory characteristics are investigated in a female subject who is a professional singer (co-author JL) trained in both the operatic and belting styles and in an intermediate vocal technique (“mixed”). This article presents data obtained from this subject by video-fiberoptic observation of the pharynx, inverse filtering of airflow, and measurement of subglottal pressure. The results reveal that belting was characterized by very high subglottal pressures and sound levels, and apparently also by a comparatively high degree of glottal adduction. Comparisons with other investigations of related aspects of belting and operatic singing support the assumption that the data obtained from our subject are representative for these vocal techniques. 相似文献
7.
8.
9.
We present a new mathematical programming formulation for the Steiner minimal tree problem. We relax the integrality constraints on this formulation and transform the resulting problem (which is convex, but not everywhere differentiable) into a standard convex programming problem in conic form. We consider an efficient computation of an ε-optimal solution for this latter problem using an interior-point algorithm. 相似文献
10.
In [1, 2] we established and dicussed the algebra of observables for 2+1 gravity at both the classical and quantum level. Here our treatment broadens and extends previous results to any genusg with a systematic discussion of the centre of the algebra. The reduction of the number of independent observables to 6g-6(g>1) is treated in detail with a precise classification forg=1 andg=2. 相似文献