全文获取类型
收费全文 | 506篇 |
免费 | 21篇 |
国内免费 | 5篇 |
专业分类
化学 | 345篇 |
晶体学 | 2篇 |
力学 | 9篇 |
数学 | 64篇 |
物理学 | 112篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 22篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 35篇 |
2012年 | 41篇 |
2011年 | 31篇 |
2010年 | 19篇 |
2009年 | 22篇 |
2008年 | 29篇 |
2007年 | 23篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 21篇 |
2003年 | 12篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 12篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有532条查询结果,搜索用时 15 毫秒
1.
Herraiz A. Gutierrez M. Ortega-Mier M. 《Central European Journal of Operations Research》2022,30(4):1427-1450
Central European Journal of Operations Research - We define a geometric transformation of Euclidean Travelling Salesman Problem (TSP) tours that leads to a new formulation of the TSP. For every... 相似文献
2.
We show that, contrary to earlier reports, application of the one-parameter variational technique to the classical (image) model for H in front of an Al surface leads to energy shifts for the ground state which are very close to those obtained numerically with a more sophisticated model of the system. 相似文献
3.
4.
Estrada E Patlewicz G Gutierrez Y 《Journal of chemical information and computer sciences》2004,44(2):688-698
A general strategy for knowledge flow concerning skin sensitization based on the combined use of TOPS-MODE and DEREK expert system is proposed. TOPS-MODE is used as a knowledge generator, while DEREK represents the knowledge archive. A TOPS-MODE classification model allows the identification of structural fragments and groups responsible for strong/moderate skin sensitization. These structural contributions are sorted, analyzed, and graphically displayed in an appropriate way allowing the identification of several structural alerts for skin sensitization. Nine structural alerts already implemented in DEREK are identified using this strategy. They comprise, among others, alkyl halides, aldehydes, alpha,beta-unsaturated compounds, aromatic amines, phenols, hydroquinone, isothiazolinone, and alkyl sulfonates. Four new hypotheses are generated using TOPS-MODE structural contributions to skin sensitization, which are not recognized as structural alerts by DEREK. They include the reduction of aromatic nitro groups and epoxidation reaction of double bonds as metabolic activation steps that can lead to reactive haptens which can trigger the skin sensitization mechanism. Another new alert is based on 1,2,5-thiadiazole-1,1-dioxide for which we have identified a possible mechanism explaining its strong skin sensitization profile. It is based on the existence of a tautomeric equilibrium and further reaction with nucleophiles, which are both supported by experimental evidence. Finally, we have identified a possible new mechanism for the skin sensitization of nonreactive compounds, which involves the formation of noncovalent complexes with proteins in a processing- and metabolism-independent way. 相似文献
5.
1,3-Dialkylimidazolium-2-carboxylate compounds have recently been fully characterised. Here we describe the utilisation of 1,3-dimethyl (1a) and 1-butyl-3-methyl-imidazolium-2-carboxylate (1b) in a carboxylation reaction with transfer of the CO2 moiety to benzoylacetone and methanol for the synthesis, in high yield, of benzoylacetate and monoalkylcarbonate anions, respectively. Conversely, when compounds 1a and b are reacted with carbonylic substrates lacking C-H active bonds, a product resulting from nucleophilic attack of the 1,3-dialkylimidazol-2-ylidene species on the carbonyl moiety is obtained. The reported reactions can find applications in organic synthesis and in the synthesis of halogen-free ionic liquids. 相似文献
6.
Farré M Fernandez J Paez M Granada L Barba L Gutierrez HM Pulgarin C Barceló D 《Analytical and bioanalytical chemistry》2002,373(8):704-709
The controlled biodegradation of ametryn and methomyl has been performed, in accordance with the OECD Zahn-Wellens/EMPA procedure, by use of an enriched mixture of activated sludge collected from three domestic waste-water-treatment plants (WWTP). During the process concentrations of ametryn and methomyl in the water samples were isolated by solid-phase extraction (SPE); recovery rates were 98.9 and 93.2 for methomyl and ametryn, respectively. Liquid chromatography-mass spectrometry (LC-MS) was used to determine final pesticide concentrations and for metabolite identification.The efficiency of aerobic biodegradation of ametryn and methomyl was evaluated by measuring both the decrease in the concentration of the pesticides and global properties such as the chemical oxygen demand (COD). The acute toxicity of ametryn and methomyl was evaluated by use of the ToxAlert100 biological test, which is based on inhibition of the bioluminescence of Vibrio fischeri. There was significant correlation between results from primary and ultimate biodegradation and those from determination of toxicity. Pesticide concentrations were always reduced to below the limit of detection in less than 17 days. High COD removal (90-96%) was achieved in 28 and 18 days for methomyl and ametryn, respectively. 相似文献
7.
Carlos Gutierrez Marco-Antonio Teixeira 《Bulletin of the Brazilian Mathematical Society》1995,26(1):57-66
Let >0 andX be aC
1 vector field on the plane such that: (i) for allq2, Det(DX(q))>0; and (ii) for allp2, with p, Trace(D(X(p))<0. IfX has a singularity and
2 Trace(DX)dxdy is less than 0 (resp. greater or equal than 0), then the point at infinity of the Riemann sphere 2{} is a repellor (resp. an attractor) ofX. 相似文献
8.
9.
Alverson G Baker WF Ballocchi G Benson R Berg D Blusk S Bromberg C Brown D Carey D Chand T Chandlee C Choudhary BC Chung WH de Barbaro L DeSoi W Dlugosz W Dunlea J Easo S Engels E Faissler W Fanourakis G Ferbel T Garelick D Ginther G Glass G Glaubman M Gutierrez P Hartman K Huston J Johnstone C Kapoor V Kourbanis L Lanaro A Lirakis C Lobkowicz F Lukens P Mani S Maul A Mansour J Miller R Nelson CA Oh BY Orris D Pothier E Prebys E Rajaram BM Roser R Ruddick K Shepard P Shivpuri RK Sinanidis A 《Physical review D: Particles and fields》1993,48(1):5-28
10.
Katiuska Araujo Marinela Colina Román Mazurek José Delgado Hilda Ledo Elizabeth Gutierrez Lenín Herrera 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):319-320
The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110° C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 ± 0.75 gl–1 have been found at the entrance of the system and 0.74 ± 0.0 gl–1 at the exit, while in sludge the results were between 0.29 ± 0.12 gkg–1 in the facultative pond and 0.04 ± 0.02 gkg–1 in the second maturation pond (exit). 相似文献