全文获取类型
收费全文 | 1474篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 1362篇 |
力学 | 2篇 |
数学 | 67篇 |
物理学 | 67篇 |
出版年
2020年 | 6篇 |
2018年 | 8篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 27篇 |
2012年 | 27篇 |
2011年 | 34篇 |
2010年 | 16篇 |
2009年 | 22篇 |
2008年 | 19篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 24篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 15篇 |
1988年 | 8篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1966年 | 76篇 |
1965年 | 129篇 |
1964年 | 143篇 |
1963年 | 123篇 |
1962年 | 125篇 |
1961年 | 146篇 |
1960年 | 124篇 |
1959年 | 62篇 |
排序方式: 共有1498条查询结果,搜索用时 234 毫秒
61.
Optimization of effective atom centered potentials for london dispersion forces in density functional theory 总被引:1,自引:0,他引:1
von Lilienfeld OA Tavernelli I Rothlisberger U Sebastiani D 《Physical review letters》2004,93(15):153004
We add an effective atom-centered nonlocal term to the exchange-correlation potential in order to cure the lack of London dispersion forces in standard density functional theory. Calibration of this long-range correction is performed using density functional perturbation theory and an arbitrary reference. Without any prior assignment of types and structures of molecular fragments, our corrected generalized gradient approximation density functional theory calculations yield correct equilibrium geometries and dissociation energies of argon-argon, benzene-benzene, graphite-graphite, and argon-benzene complexes. 相似文献
62.
We show that attosecond pulse trains have a natural application in the control of strong field processes. In combination with an intense infrared laser field, the pulse train can be used to microscopically select a single quantum path contribution to a process that would otherwise consist of several interfering components. We present calculations that demonstrate this by manipulating the time-frequency properties of high order harmonics at the single atom level. This quantum path selection can also be used to define a high resolution attosecond clock. 相似文献
63.
Loss S Magistrato A Cataldo L Hoffmann S Geoffroy M Röthlisberger U Grützmacher H 《Angewandte Chemie (International ed. in English)》2001,40(7):1143
The cover picture shows the metalloporphyrin heterodimer [(tpp)Mo$\rm{\mathop{-}^{4}}$Re(oep)](+) with the novel [Mo$\rm{\mathop{-}^{4}}$Re](5+) core. The core represents the first example of a quadruple bond between elements of different triads, thus proving that heterometallic quadruple bonds are not limited to the Group 6 metals. From the space-filling model it is clear that there is no interaction between the stabilizing porphyrin ligands. The ORTEP plot in a projection along the Re-Mo axis emphasizes the perfectly eclipsed geometry of the porphyrins, which is unambiguous proof of the existence of the quadruple bond in the solid state. The diamagnetism and large magnetic anisotropy of the cation, as determined by (1)H NMR spectroscopy, indicate that the quadruple bond is retained in solution. A logical and well-defined synthetic route was used to synthesize the dimer, and can be extended to other metalloporphyrins to generate further novel quadruple bonds (the picture was generated by Marina Boulan, St. Petersburg, Russia), full details are reported by J. P. Collman et al. on p. 1271 ff. 相似文献
64.
65.
66.
67.
68.
Product line selection and pricing decisions are critical to the profitability of many firms, particularly in today’s competitive business environment in which providers of goods and services are offering a broad array of products to satisfy customer needs.We address the problem of selecting a set of products to offer and their prices when customers select among the offered products according to a share-of-surplus choice model. A customer’s surplus is defined as the difference between his utility (willingness to pay) and the price of the product. Under the share-of-surplus model, the fraction of a customer segment that selects a product is defined as the ratio of the segment’s surplus from this particular product to the segment’s total surplus across all offered products with positive surplus for that segment.We develop a heuristic procedure for this non-concave, mixed-integer optimization problem. The procedure utilizes simulated annealing to handle the binary product selection variables, and a steepest-ascent-style procedure that relies on certain structural properties of the objective function to handle the non-concave, continuous portion of the problem involving the prices. We also develop a variant of our procedure to handle uncertainty in customer utilities. In computational studies, our basic procedures perform extremely well, producing solutions whose objective values are within about 5% of those obtained via enumerative methods. Our procedure to handle uncertain utilities also performs well, producing solutions with expected profit values that are roughly 10% higher than the corresponding expected profits from solutions obtained under the assumption of deterministic utilities. 相似文献
69.
The enolic form of cyclic compounds like 4-hydroxycoumarin,-2-pyronones,-2-pyridones and cyclohexane-1,3-diones yields malonyl heterocycles by heating withMeldrum acid.Enolisierbare Ringverbindungen vom Typ des 4-Hydroxycumarins,-2-pyronons und-2-pyridons sowie des 1,3-Cyclohexandions schließen beim Erhitzen mitMeldrumsäure Ringe zu Malonyl-heterocyclen.
Herrn Prof. Dr.H. Nowotny gewidment. 相似文献
Herrn Prof. Dr.H. Nowotny gewidment. 相似文献
70.
Lorien J. Parker Louis C. Italiano Craig J. Morton Nancy C. Hancock David B. Ascher Jade B. Aitken Hugh H. Harris Pablo Campomanes Ursula Rothlisberger Anastasia De Luca Mario Lo Bello Wee Han Ang Paul J. Dyson Michael W. Parker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(28):7705-7705