全文获取类型
收费全文 | 852篇 |
免费 | 32篇 |
国内免费 | 2篇 |
专业分类
化学 | 758篇 |
晶体学 | 1篇 |
力学 | 16篇 |
数学 | 34篇 |
物理学 | 77篇 |
出版年
2023年 | 9篇 |
2022年 | 5篇 |
2021年 | 30篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 3篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 20篇 |
2014年 | 21篇 |
2013年 | 45篇 |
2012年 | 65篇 |
2011年 | 62篇 |
2010年 | 42篇 |
2009年 | 28篇 |
2008年 | 59篇 |
2007年 | 70篇 |
2006年 | 62篇 |
2005年 | 61篇 |
2004年 | 59篇 |
2003年 | 56篇 |
2002年 | 39篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 14篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1991年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1904年 | 1篇 |
1899年 | 1篇 |
1892年 | 1篇 |
1890年 | 2篇 |
排序方式: 共有886条查询结果,搜索用时 15 毫秒
101.
Caruso R Gambino GL Scordino M Sabatino L Traulo P Gagliano G 《Natural product communications》2011,6(12):1939-1943
The influence of the wine distillation process on methanol content has been determined by quantitative analysis using gas chromatographic flame ionization (GC-FID) detection. A comparative study between direct injection of diluted wine and injection of distilled wine was performed. The distillation process does not affect methanol quantification in wines in proportions higher than 10%. While quantification performed on distilled samples gives more reliable results, a screening method for wine injection after a 1:5 water dilution could be employed. The proposed technique was found to be a compromise between the time consuming distillation process and direct wine injection. In the studied calibration range, the stability of the volatile compounds in the reference solution is concentration-dependent. The stability is higher in the less concentrated reference solution. To shorten the operation time, a stronger temperature ramp and carrier flow rate was employed. With these conditions, helium consumption and column thermal stress were increased. However, detection limits, calibration limits, and analytical method performances are not affected substantially by changing from normal to forced GC conditions. Statistical data evaluation were made using both ordinary (OLS) and bivariate least squares (BLS) calibration models. Further confirmation was obtained that limit of detection (LOD) values, calculated according to the 3sigma approach, are lower than the respective Hubaux-Vos (H-V) calculation method. H-V LOD depends upon background noise, calibration parameters and the number of reference standard solutions employed in producing the calibration curve. These remarks are confirmed by both calibration models used. 相似文献
102.
Rolando Gonzlez-Pea Rosa María Cibrin-Ortiz de Anda Angel J Pino-Velzquez Yhoama Gonzlez-Jorge Rosario Salvador-Palmer 《Optics and Lasers in Engineering》2003,39(5-6):609-618
Speckle photography (SP) is a powerful tool that is adequate to determine small displacements in micrometer range. This information shows other characteristics of structure deformation under loads and can be determined as stress and strain distribution. In this paper we present the results of the application of the SP technique used to study the behaviour of discontinuities in a shearwall model. These structural elements are very important to the stability of buildings. The displacement whole field around the discontinuities and loading points was determined using the pointwise method. This allows us to determine stress distribution at the point of interest by means of the suitable equations. We also present the stress distribution obtained through the finite element method in order to compare the results obtained by means of these two techniques. Good correspondence was found between the displacements determined by both techniques (r=0.982) and also between the stress values we obtained. 相似文献
103.
Paolo Facchi Rosario Fazio Giuseppe Florio Saverio Pascazio Tetsuya Yoneda 《Foundations of Physics》2006,36(4):500-511
Decoherence is one of the most serious drawback in quantum mechanical applications. We discuss the effects of noise in superconducting devices (Josephson junctions) and suggest a decoherence-control strategy based on the quantum Zeno effect. 相似文献
104.
María del Carmen Barral Rodrigo González-Prieto Santiago Herrero Reyes Jiménez-Aparicio José Luis Priego Elia del Carmen Royer María Rosario Torres Francisco Alejandro Urbanos Felix Zamora 《Journal of Cluster Science》2008,19(1):219-230
Two new complexes, based on the unit Ru2Cl(μ-O2CC4H4N)4 (1) (O2CC4H4N = pyrrole-2-carboxylate), Ru2Cl(μ-O2CC4H4N)4(H2O)·4H2O [1(H
2
O)·4H
2
O], and Ru2Cl(μ-O2CC4H4N)4(Me2CO) [1(Me
2
CO)], are synthesized and structurally characterized. The physical properties of these complexes are studied and compared with
those previously reported for Ru2Cl(μ-O2CC4H4N)4(thf)·thf·H2O [1(thf)·thf·H
2
O]. The nature of the solvent molecule bonded to the axial position of the dimetallic unit determines the supramolecular interactions
leading to different arrangements in the solid state. The presence of NH groups in the pyrrolic rings favours the existence
of hydrogen bond interactions that are present in the three complexes. In addition, complex 1(Me
2
CO) shows π–π stacking interactions through pyrrolic rings of different dimetallic units.
Dedicated to the memory of Prof. F. Albert Cotton. 相似文献
105.
The [Ni(CN)2(CO)2]2? anion (I) reacts with either one or two equivalents of benzyl bromide in either water/acetone or anhydrous acetonitrile to produce mainly 1,3-diphenyl-2-propanone. Excess carbon monoxide inhibits the reaction. These results are interpreted as indicating that I is an intermediate in the reaction of K4[Ni2(CN)6] with CO and PhCH2Br to form 1,3-diphenyl-2-propanone. 相似文献
106.
107.
108.
The synthesis of urethane protected 4- and 5-aminoimidazole nucleoside derivatives 4 and 9 by two different routes is described. These routes are transformation of the carboxylate substituted imidazole nucleoside 1 via a Curtius rearrangement to give 4 and direct ribosylation of the imidazole base 6 to give a mixture of positional isomers 7 and 8 , which by deacetylation afford 4 and 9 , respectively. The convenience of each route depended on the positional isomer to be synthesized. 相似文献
109.
van Zutphen S Pantoja E Soriano R Soro C Tooke DM Spek AL den Dulk H Brouwer J Reedijk J 《Dalton transactions (Cambridge, England : 2003)》2006,(8):1020-1023
New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5'-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes. 相似文献
110.
Perez Gutierrez RM Rosario Vargas S Martinez Martinez F Garcia Baez E Figueroa Torres G 《Natural product research》2006,20(3):305-310
Antispasmodic activity-guided fractionation together with chemical analysis led to the isolation of one novel delta-lactone named oedogonolide from Oedogonium capillare. Identification was based on spectroscopic methods. The oedogonolide produces a significant antispasmodic effect on the contractions of the rat ileum induced by acetylcholine, histamine and barium chloride. 相似文献