全文获取类型
收费全文 | 2784篇 |
免费 | 64篇 |
国内免费 | 96篇 |
专业分类
化学 | 1173篇 |
晶体学 | 9篇 |
力学 | 115篇 |
综合类 | 15篇 |
数学 | 646篇 |
物理学 | 986篇 |
出版年
2024年 | 2篇 |
2023年 | 56篇 |
2022年 | 38篇 |
2021年 | 30篇 |
2020年 | 35篇 |
2019年 | 33篇 |
2018年 | 35篇 |
2017年 | 48篇 |
2016年 | 63篇 |
2015年 | 53篇 |
2014年 | 108篇 |
2013年 | 270篇 |
2012年 | 244篇 |
2011年 | 163篇 |
2010年 | 106篇 |
2009年 | 169篇 |
2008年 | 117篇 |
2007年 | 144篇 |
2006年 | 144篇 |
2005年 | 125篇 |
2004年 | 97篇 |
2003年 | 74篇 |
2002年 | 67篇 |
2001年 | 54篇 |
2000年 | 55篇 |
1999年 | 52篇 |
1998年 | 55篇 |
1997年 | 64篇 |
1996年 | 63篇 |
1995年 | 65篇 |
1994年 | 42篇 |
1993年 | 37篇 |
1992年 | 28篇 |
1991年 | 29篇 |
1990年 | 17篇 |
1989年 | 21篇 |
1988年 | 13篇 |
1987年 | 23篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有2944条查询结果,搜索用时 134 毫秒
21.
Dr Martin Seah, NPL, was the initiator, founder, and first chairman of the Surface Analysis Working Group (SAWG) at the Consultative Committee for Amount of Substance, Metrology in Chemistry and Biology (CCQM) at the Bureau International des Poids et Mesures (BIPM), the international organization established by the Metre Convention. This tribute letter summarizes his achievements during his chairmanship and his long-running impact on the successful work of the group after his retirement. 相似文献
22.
23.
24.
25.
26.
An ESR study has been made on the course of grafting of tetrafluoroethylene onto polyethylene. Alkyl and allyl radicals trapped in the polymers were measured under various grafting conditions. It was observed that alkyl radicals decay very rapidly when monomers are in contact with the irradiated polymer, while allyl radicals decay very slowly even in the presence of monomers as in the decay of radicals in irradiated polymers without monomers. The effect of pre-irradiation temperature on grafting was also studied, and the rate of grafting was found to be much faster for lower pre-irradiation temperatures. From these experimental results it was concluded that alkyl radicals play an important Tole in the initiation reaction of grafting. 相似文献
27.
Blast is one of the most devastating fungal diseases of rice caused by Magnaporthe oryzae. Plant essential oil (EO) can function as antifungal agents and are regarded as a safe and acceptable method for plant disease control. However, EOs are unstable and hydrophobic, which limits its use. In the present study, we aimed for the preparation and characterization of a nanoemulsion (NE) from green tea essential oil (GTO) by ultrasonication method and determined the antifungal activity of NE on M. oryzae. The particle size and zeta potential of the NE were 86.98 nm and −15.1 mV, respectively. The chemical composition and functional groups of GTO and NE were studied by using GC–MS analysis, portable Raman spectroscopy, and FTIR coupled with chemometric analysis. GC–MS analysis showed the major components in GTO and NE were n-Hexyl cinnamaldehyde and L-α-Terpineol. Both GTO and NE showed good antioxidant activity and total phenol content. Moreover, the NE showed good antifungal activity against M. oryzae which was further confirmed by scanning electron microscopy (SEM) examination. Also, confocal Raman micro-spectroscopy (CRM) revealed the antifungal mechanism of GTO and NE on M. oryzae which proves the cell damage. To the best of our knowledge, this is the first study on the antifungal activity of GTO and NE against M. oryzae and also the use of CRM for the evaluation of the chemical changes in single fungal hyphae in a holistic approach. This study suggests that the prepared NE could be a potential candidate for use as a substitute for synthetic fungicides. 相似文献
28.
Thibaut Vidal Teodor Gabriel Crainic Michel Gendreau Christian Prins 《European Journal of Operational Research》2013
The attributes of vehicle routing problems are additional characteristics or constraints that aim to better take into account the specificities of real applications. The variants thus formed are supported by a well-developed literature, including a large variety of heuristics. This article first reviews the main classes of attributes, providing a survey of heuristics and meta-heuristics for Multi-Attribute Vehicle Routing Problems (MAVRP). It then takes a closer look at the concepts of 64 remarkable meta-heuristics, selected objectively for their outstanding performance on 15 classic MAVRP with different attributes. This cross-analysis leads to the identification of “winning strategies” in designing effective heuristics for MAVRP. This is an important step in the development of general and efficient solution methods for dealing with the large range of vehicle routing variants. 相似文献
29.
Affine semigroups are convex sets on which there exists an associative binary operation which is affine separately in either variable. They were introduced by Cohen and Collins in 1959. We look at examples of affine semigroups which are of interest to matrix and operator theory and we prove some new results on the extreme points and the absorbing elements of certain types of affine semigroups. Most notably we improve a result of Wendel that every invertible element in a compact affine semigroup is extreme by extending this result to linearly bounded affine semigroups. 相似文献
30.
Javier Alcaraz Nuria RamónJosé L. Ruiz Inmaculada Sirvent 《European Journal of Operational Research》2013
The existence of alternate optima for the DEA weights may reduce the usefulness of the cross-efficiency evaluation, since the ranking provided depends on the choice of weights that the different DMUs make. In this paper, we develop a procedure to carry out the cross-efficiency evaluation without the need to make any specific choice of DEA weights. The proposed procedure takes into consideration all the possible choices of weights that all the DMUs can make, and yields for each unit a range for its possible rankings instead of a single ranking. This range is determined by the best and the worst rankings that would result in the best and the worst scenarios of each unit across all the DEA weights of all the DMUs. This approach might identify good/bad performers, as those that rank at the top/bottom irrespective of the weights that are chosen, or units that outperform others in all the scenarios. In addition, it may be used to analyze the stability of the ranking provided by the standard cross-efficiency evaluation. 相似文献