全文获取类型
收费全文 | 2004篇 |
免费 | 44篇 |
国内免费 | 3篇 |
专业分类
化学 | 1049篇 |
晶体学 | 8篇 |
力学 | 39篇 |
数学 | 200篇 |
物理学 | 755篇 |
出版年
2022年 | 24篇 |
2021年 | 27篇 |
2020年 | 30篇 |
2019年 | 18篇 |
2018年 | 15篇 |
2017年 | 24篇 |
2016年 | 40篇 |
2015年 | 41篇 |
2014年 | 32篇 |
2013年 | 69篇 |
2012年 | 90篇 |
2011年 | 94篇 |
2010年 | 65篇 |
2009年 | 62篇 |
2008年 | 86篇 |
2007年 | 82篇 |
2006年 | 80篇 |
2005年 | 82篇 |
2004年 | 77篇 |
2003年 | 52篇 |
2002年 | 69篇 |
2001年 | 35篇 |
2000年 | 53篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 35篇 |
1995年 | 32篇 |
1994年 | 45篇 |
1993年 | 48篇 |
1992年 | 43篇 |
1991年 | 27篇 |
1990年 | 33篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 47篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 33篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1974年 | 27篇 |
1973年 | 16篇 |
排序方式: 共有2051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.
7.
8.
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
9.
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
10.
A. Subramanian T.-Y. Choi L.X. Dong J. Tharian U. Sennhauser D. Poulikakos B.J. Nelson 《Applied Physics A: Materials Science & Processing》2007,89(1):133-139
We report on a novel method for local control of shell engineering in multiwalled carbon nanotubes (MWNTs) using Joule-heating
induced electric breakdown. By modulating the heat dissipation along a nanotube, we can confine its thinning and shell breakdown
to occur within localized regions of peak temperatures, which are distributed over one-half of the NT length. The modulation
is achieved by using suitably designed nanomachined heat sinks with different degrees of thermal coupling at different parts
of a current-carrying nanotube. The location of electric breakdown occurs precisely at the regions of high temperatures predicted
by the classical finite-element model of Joule heating in the MWNT. The experiments herein provide new insight into the electric
breakdown mechanism and prove unambiguously that shell removal occurs due to thermal stress, underpinning the diffusive nature
of MWNTs. The method demonstrated here has the potential to be a powerful tool in realizing MWNT bearings with complex architectures
for use in integrated nanoelectromechanical systems (NEMS). In addition, the breakdown current and power in the nanotubes
are significantly higher than those observed in nanotubes without heat removal via additional heat sinks. This indicates future
avenues for enhancing the performance of MWNTs in electrical interconnect and nanoelectronic applications.
PACS 73.63.Fg; 65.80.+n 相似文献