全文获取类型
收费全文 | 521篇 |
免费 | 15篇 |
专业分类
化学 | 375篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 49篇 |
物理学 | 100篇 |
出版年
2024年 | 1篇 |
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 5篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 27篇 |
2012年 | 44篇 |
2011年 | 36篇 |
2010年 | 34篇 |
2009年 | 28篇 |
2008年 | 23篇 |
2007年 | 35篇 |
2006年 | 27篇 |
2005年 | 19篇 |
2004年 | 15篇 |
2003年 | 3篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 3篇 |
1966年 | 1篇 |
排序方式: 共有536条查询结果,搜索用时 15 毫秒
81.
A semi-implicit scheme for the numerical solution of the shallow water equations is proposed. An example of successful application is the simulation of the major tidal constituent (M2) on the European Shelf. Good agreement is found both qualitatively and quantitatively. The basic outlines of the method are presented and some practical aspects of computation are discussed. Apart from accuracy, compared to explicit or to existing semi-implicit schemes, this approach has another important feature: its economy and simplicity. 相似文献
82.
A simple, precise and selective procedure for the spectrophotometric determination of carbon disulphide in water is described. The method is based on the quantitative formation of the 1,2,3,4-thiatriazol-5-thiolate ion from carbon disulphide and azide. The specific rate for this reaction at ionic strength 4.0 (NaN3) and 25°C is 8.4·10-3 mol-1 s-1; the kinetic parameters D3H and D3S are 16.7 kcal mol-1 and —14 cal mol-1deg-1, respectively. At the analytical wavelength of 313 nm, the molar absorptivity is 7.27 ·103 l mol-1cm-1. The system obeys Beer's law for 2.3–28.6 g ml-1 of carbon disulphide. The effects of foreign ions are discussed. 相似文献
83.
Techniques for the assessment of internally incorporated radionuclides are essential for monitoring potentially exposed workers to radiation as well as for the preparedness of response in the case of Radiological Emergencies. The Whole Body Counter at Instituto Tecnológico e Nuclear (ITN), Portugal, provides a direct way of measuring the activity of internally incorporated radionuclides in possibly contaminated persons. This equipment is calibrated in energy and efficiency, with a calibration source, and is able to detect and quantify several radionuclides with gamma emissions between 60 and 1900 keV. Also, the Minimum Detectable Activity values for several nuclides of interest were determined, since these values are an indication of the sensitivity of the detection system. Finally, in order to assure reliable measurements, a quality assurance routine has been implemented, consisting of routinely monitoring several parameters of chosen radionuclides with gamma emission energies lying in the energy range of interest, and also for the background. The equipment is now fully operational and a set of routine measurements for the monitoring of exposed personnel, working in different areas of activity, is currently being prepared. 相似文献
84.
85.
Aad G Abbott B Abdallah J Abdelalim AA Abdesselam A Abdinov O Abi B Abolins M Abramowicz H Abreu H Acerbi E Acharya BS Ackers M Adams DL Addy TN Adelman J Aderholz M Adomeit S Adragna P Adye T Aefsky S Aguilar-Saavedra JA Aharrouche M Ahlen SP Ahles F Ahmad A Ahsan M Aielli G Akdogan T Akesson TP Akimoto G Akimov AV Alam MS Alam MA Albrand S Aleksa M Aleksandrov IN Aleppo M Alessandria F Alexa C Alexander G Alexandre G Alexopoulos T Alhroob M Aliev M Alimonti G Alison J Aliyev M Allport PP 《Physical review letters》2010,105(25):252303
By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium. 相似文献
86.
We establish necessary and sufficient conditions for embeddings of Bessel potential spaces H σ X(IR n ) with order of smoothness σ?∈?(0, n), modelled upon rearrangement invariant Banach function spaces X(IR n ), into generalized Hölder spaces (involving k-modulus of smoothness). We apply our results to the case when X(IR n ) is the Lorentz-Karamata space \(L_{p,q;b}({{\rm I\kern-.17em R}}^n)\). In particular, we are able to characterize optimal embeddings of Bessel potential spaces \(H^{\sigma}L_{p,q;b}({{\rm I\kern-.17em R}}^n)\) into generalized Hölder spaces. Applications cover both superlimiting and limiting cases. We also show that our results yield new and sharp embeddings of Sobolev-Orlicz spaces W k?+?1 L n/k(logL) α (IR n ) and W k L n/k(logL) α (IR n ) into generalized Hölder spaces. 相似文献
87.
88.
89.
Transparent SiO2:Li2O:Nb2O5 glass doped with Tm3+ has been prepared by the sol–gel method, and heat-treated in air (HT) at temperatures between 500 and 800 °C. X-ray diffraction (XRD) patterns and Raman spectroscopy show SiO2 and LiNbO3 phases in samples HT above 650 °C, and a NbTmO4 phase for T > 750 °C. The XRD SEM analysis show increasing particle size and number with the increase of HT temperature. Intra-4f12 transitions due to Tm3+ ion dispersed in the matrix are observed in samples with T > 650 °C. The luminescence is dominated by the 1G4 → 3F4 (~650 nm), 1D2 → 3F3 (~780 nm), 3H4 → 3H6 (~800 nm), 3H5 → 3H6 (~1200 nm) and 3H4 → 3F4 (~1500 nm) transitions under resonant excitation to the ion levels. 相似文献
90.
Raiane Aparecida LopesNeves Fausto MoreiraAraujo Felipe SiqueiraPacheco Gustavo ChevitareseAzevedo Maria Auxiliadora CostaMatos Renato CamargoMatos 《Electroanalysis》2019,31(3):496-503
Sunscreen agents and in particular UV filters are compounds added in different cosmetic formulations, that has the function of preventing damage caused by sun exposition. Therefore, this paper proposes the development of a simple, fast and reliable electroanalytical method utilizing square wave voltammetry (SWV) to the determination of Benzophenone‐3 (BZ‐3), camphor 4‐methylbenzylidene (MBC) and 2‐ethylhexyl‐4‐methoxycinnamate (OMC) in cosmetic samples. The electrochemical system consisted of a cell with three electrodes: work – gold electrode modified, reference – Ag/AgCl(sat) and auxiliary – platinum, using as supporting electrolyte 4.0 mL of Britton Robinson Buffer 0.04 mol L?1 (pH=4.0), 1.0 mL of methanol and 5.50×10?4 mol L?1 of cetyltrimethylammonium bromide (CTAB). The method was validated using three commercial sunscreen samples and the results showed recovery values between 83 and 98 %. The average values found for the analysed samples were 3.49 % m/m (728 mg L?1) to BZ‐3, 0.56 % m/m (113 mg L?1) to MBC and 0.99 % m/m (208 mg L?1) to OMC. The detection (DL) and quantification (QL) limits were 0.47 mg L?1 and 1.56 mg L?1 to BZ‐3, 0.77 mg L?1 and 2.58 mg L?1 to MBC and 0.78 mg L?1 and 2.59 mg L?1 to OMC, respectively. The sunscreen protector samples were also evaluated by high‐performance liquid chromatography (HPLC) demonstrating a good correlation between the results and compared the results with allowed concentration. 相似文献