全文获取类型
收费全文 | 451篇 |
免费 | 0篇 |
国内免费 | 4篇 |
专业分类
化学 | 284篇 |
力学 | 18篇 |
数学 | 92篇 |
物理学 | 61篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 23篇 |
2011年 | 26篇 |
2010年 | 19篇 |
2009年 | 16篇 |
2008年 | 35篇 |
2007年 | 31篇 |
2006年 | 25篇 |
2005年 | 14篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 26篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有455条查询结果,搜索用时 31 毫秒
141.
Genetic algorithms for the traveling salesman problem 总被引:2,自引:0,他引:2
Jean-Yves Potvin 《Annals of Operations Research》1996,63(3):337-370
This paper is a survey of genetic algorithms for the traveling salesman problem. Genetic algorithms are randomized search techniques that simulate some of the processes observed in natural evolution. In this paper, a simple genetic algorithm is introduced, and various extensions are presented to solve the traveling salesman problem. Computational results are also reported for both random and classical problems taken from the operations research literature. 相似文献
142.
J. -Y. Chemin 《Inventiones Mathematicae》1991,103(1):599-629
Sans résuméOblatum 9-I-1990 & 25-VI-1990 相似文献
143.
144.
Jean-Yves Hée 《Geometriae Dedicata》1991,37(1):65-102
A theory of root systems over a totally ordered commutative ring is developed. This theory includes, in particular, the usual
finite root systems and the Kac-Moody real root systems. It is adapted to the construction of twisted Kac-Moody groups.
Dédié à Jacques Tits à l'occasion de son soixantième anniversaire 相似文献
Dédié à Jacques Tits à l'occasion de son soixantième anniversaire 相似文献
145.
Chen's lemma on iterated integrals implies that certain identities involving multiple integrals, such as the de Bruijn and Wick formulas, amount to combinatorial identities for Pfaffians and Hafnians in shuffle algebras. We provide direct algebraic proofs of such shuffle identities, and obtain various generalizations. We also discuss some Pfaffian identities due to Sundquist and Ishikawa–Wakayama, and a Cauchy formula for anticommutative symmetric functions. Finally, we extend some of the previous considerations to hyper-Pfaffians and hyper-Hafnians. 相似文献
146.
J.F. Chemin S. Andriamonje J. Roturier B. Saboya J.P. Thibaud S. Joly S. Plattard J. Uzureau H. Laurent J.M. Maison J.P. Shapira 《Nuclear Physics A》1979,331(2):407-428
A new method for measuring compound-nucleus lifetimes in the range of 10?18–10?16 s is presented. The method is based on the comparison between the known lifetime of an atomic excited state used as a reference and the nuclear delay time to be measured. On-line coincidences performed between the nuclear reaction products and the emitted X-rays enable the selection of the atomic vacancies decaying during the compound stage of the nuclear interaction. The main characteristics of this technique are illustrated by measurements of lifetimes of the 107In compound nucleus excited at 13.6 and 15.6 MeV in the 106Cd(p, p')106Cd reaction. They are found in agreement with statistical model calculations. The spurious effect associated with decay by internal conversion of final states populated by the competitive (p, n) reaction is emphasized. 相似文献
147.
A unique extraction procedure leading to the separation of 2 different pharmaceutical classes molecules has been developed and optimised by chemometric tools. From only one sampling, this analytical method allows the determination of 21 pharmaceuticals from corticosteroids and β-blockers classes. Performing the SPE on Oasis MCX (mixed-mode cation exchange), the sequential elution of each pharmaceutical class is achievable, allowing a high purity level of extracts as well as high recovery rates. Performing a unique sample preparation results in an important save of time. The extracts were then analysed by LC/MS/MS, using a Hibar Purospher Star column for β-blockers and an X-Bridge column for corticosteroids with formate buffer (pH 3.8)/AcN and water/AcN mobile phases, respectively. This work also includes a study of the chromatographic and mass spectrometric parameters in order to increase the analyte signal. The optimised SPE-LC/MS/MS method was then applied to environmental samples from sewage treatment plant (STP). β-Blockers and corticosteroids were detected, respectively, in concentrations up to 318 ng L−1 (sotalol) and 174 ng L−1 (cortisone), in STP influents. Moreover, both pharmaceutical classes have also been detected in STP effluents. As far as we know, this is the first paper reporting the detection of corticosteroids in environmental waters. The developed analytical method can be used in further studies to investigate the environmental contamination by these drugs. 相似文献
148.
Levard C Rose J Masion A Doelsch E Borschneck D Olivi L Dominici C Grauby O Woicik JC Bottero JY 《Journal of the American Chemical Society》2008,130(18):5862-5863
A simple aqueous synthesis yielded about 100 times more structurally well-organized single-walled aluminogermanate nanotubes than previously reported "standard" procedures. The structure analyses using XRD, IRTF, TEM, and XAS were greatly facilitated by the high concentrations available, and they ascertained the imogolite-like structure of the nanotubes. Simplicity and yield of the synthesis protocol are likely to favor commercial applications of theses materials as well as simplified syntheses of other nanophases. 相似文献
149.
Lamsabhi AM Mó O Yáñez M Guillemin JC Haldys V Tortajada J Salpin JY 《Journal of mass spectrometry : JMS》2008,43(3):317-326
The gas-phase reactions between Ni(+) ((2)D(5/2)) and aminoacetonitrile, a molecule of prebiological interest as possible precursor of glycine, have been investigated by means of mass spectrometry techniques. The mass-analyzed ion kinetic energy (MIKE) spectrum reveals that the adduct ions [NC--CH(2)--NH(2), Ni(+)] spontaneously decompose by loosing HCN, H(2), and H(2)CNH, the loss of hydrogen cyanide being clearly dominant. The structures and bonding characteristics of the aminoacetonitrile-Ni(+) complexes as well as the different stationary points of the corresponding potential energy surface (PES) have been theoretically studied by density functional theory (DFT) calculations carried out at B3LYP/6-311G(d,p) level. A cyclic intermediate, in which Ni(+) is bisligated to the cyano and the amino group, plays an important role in the unimolecular reactivity of these ions, because it is the precursor for the observed losses of HCN and H(2)CNH. In all mechanisms associated with the loss of H(2), the metal acts as hydrogen carrier favoring the formation of the H(2) molecule. The estimated bond dissociation energy of aminoacetonitrile-Ni(+) complexes (291 kJ mol(-1)) is larger than those measured for other nitrogen bases such as pyridine or pyrimidine and only slightly smaller than that of adenine. 相似文献
150.
Bourderioux A Bénéteau V Mérour JY Baldeyrou B Ballot C Lansiaux A Bailly C Le Guével R Guillouzo C Routier S 《Organic & biomolecular chemistry》2008,6(12):2108-2117
We report the synthesis and biological evaluation of new oxophenylarcyriaflavins designed as potential anticancer agents. An efficient synthesis involving palladium-catalyzed Suzuki and Stille reactions is presented, without any indolic protective group. The central ring closure of the scaffold was performed through an electrophilic reaction on the position C-2 of the indole ring. The use of indole and 5-benzyloxyindole, along with substituted phenyl rings, generated three different scaffolds, which were successively exploited to modulate the structure. The cytotoxicity of the newly designed compounds on four cancer cell lines and activities against three kinases (CDK1, CDK5 and GSK3) were evaluated. Several compounds showed a marked cytotoxicity with IC(50) values in the sub-micromolar range, and induced important cell cycle perturbations, with a G2/M arrest. Some compounds revealed DNA binding properties and were found to inhibit topoisomerase-mediated DNA relaxation of supercoiled DNA, but these properties are not mandatory for a cytotoxic action. A novel lead compound () has been identified and warrants further investigations. 相似文献