全文获取类型
收费全文 | 1723篇 |
免费 | 62篇 |
国内免费 | 11篇 |
专业分类
化学 | 1125篇 |
晶体学 | 3篇 |
力学 | 75篇 |
数学 | 300篇 |
物理学 | 293篇 |
出版年
2023年 | 14篇 |
2022年 | 45篇 |
2021年 | 46篇 |
2020年 | 35篇 |
2019年 | 35篇 |
2018年 | 26篇 |
2017年 | 18篇 |
2016年 | 69篇 |
2015年 | 55篇 |
2014年 | 80篇 |
2013年 | 102篇 |
2012年 | 120篇 |
2011年 | 136篇 |
2010年 | 84篇 |
2009年 | 63篇 |
2008年 | 103篇 |
2007年 | 106篇 |
2006年 | 105篇 |
2005年 | 108篇 |
2004年 | 85篇 |
2003年 | 76篇 |
2002年 | 47篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1921年 | 2篇 |
1868年 | 1篇 |
排序方式: 共有1796条查询结果,搜索用时 15 毫秒
81.
Placido Giannetto Giovanni Sindona Nicola Uccella 《Journal of heterocyclic chemistry》1978,15(1):49-52
The unimolecular processes of some methylenoxazolidinones bombarded in the gas phase by electrons have been investigated by MIKE analysis, precise mass measurements and isotopic labelling studies. The overall delocalisation effect of the substitution on the nitrogen contained has been ascertained through the study of the reaction mechanism and of the possible reacting ionic structures. 相似文献
82.
The performance of 5 and 15 cm long columns packed with shell particles (Halo, AMT) is compared in gradient elution separations of the tryptic digests of myoglobin and bovine serum albumin. The influences of the temperature and the mobile phase flow rate on the column efficiency for two peptides are discussed. The influences of this flow rate, of the temperature, and of the gradient slopes on the peak capacities are also considered. Peak capacities in excess of 400 were achieved in 6h with the longer column. Peak capacities of 200 could be achieved in 30 min with the shorter column. 相似文献
83.
Nicola A. Bailey Darran R. Cairns Gregory P. Crawford James N. Hay 《Liquid crystals》2013,40(12):1761-1765
A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T a, exhibited an endotherm at the transition which developed with extent of ageing time, t a. We attribute this endotherm to the relaxation of the glass towards the equilibrium liquid. The progress of the relaxation process was measured using differential scanning calorimetry. On subsequent reheating, the aged glass showed an apparent shift in the glass transition to higher temperatures. The endotherm was used to define the extent of enthalpic relaxation and the maximum value observed was found to increase initially then decrease, with the extent of undercooling from the glass transition temperature, Δ T, passing through a maximum for a Δ T = 15 K. From the temperature dependence of the relaxation times, an apparent activation enthalpy for the relaxation process of 85 ± 10 kJ mol-1 was determined. The small value of the activation enthalpy compared with that found in the ageing of polymers reflects differences in the molecular species involved in relaxation processes. 相似文献
84.
A one-pot synthesis of poly-substituted tetramic acids and of their six-membered ring analogs have been obtained in one step by reaction of N-Boc dipeptides, activated as their O-succinimidyl esters (Boc-AA-AA-OSu), with the sodium anion of dibenzyl malonate. The adducts spontaneously cyclize to form five or six-member rings. To check whether this class of compounds may be used to promote reverse-turn conformations, one adduct was further derivatized. The formation of a hydrogen bond between the NH–Boc and the carbonyl at C2 of the heterocycle is highlighted, upon analysis of the product by IR, 1H NMR, and MD techniques, thus suggesting that these compounds are good candidates to promote reverse-turn conformations or other secondary structures and may be used for the formation of new foldamers. 相似文献
85.
86.
Nicola Magnani 《International journal of quantum chemistry》2014,114(12):755-759
Magnetic exchange is an essential feature of transition‐metal nanomagnets because it combines the relatively low spin‐only moments of several ions into a “giant spin” ground state, which can make slow magnetic relaxation very favorable in an axially anisotropic environment. In contrast, most of the early research on lanthanide‐based complexes focused on single‐ion magnets, where the required large moment is generated by the unquenched orbital contribution (which is parallel to the spin in heavy rare earths). With their unfilled 5f electronic shell being on the verge between localization and itinerancy, actinides are expected to combine the best of both 3d and 4f metals in terms of exchange and anisotropy, and are therefore under consideration as potential building blocks for the next generation of single‐molecule magnets. In this Perspective, a review of the recent development in this field is given, and some discrepancies between the spectroscopic and magnetic data are discussed. © 2014 European Commission. International Journal of Quantum Chemistry published by Wiley Periodicals, Inc. 相似文献
87.
88.
89.
Nicola Maria Pugno 《Journal of the mechanics and physics of solids》2010,58(9):1397-1410
The study reported in this paper suggests that the influence of the surrounding nanotubes in a bundle is nearly identical to that of a liquid having surface tension equal to the surface energy of the nanotubes. This surprising behaviour is supported by the calculation of the polygonization and especially of the self-collapse diameters, and related dog-bone configurations, of nanotubes in a bundle, in agreement with atomistic simulations and nanoscale experiments. Accordingly, we have evaluated the strength of the nanotube bundle, with or without collapsed nanotubes, assuming a sliding failure: the self-collapse can increase the strength up to a value of about ∼30%, suggesting the design of self-collapsed super-strong nanotube bundles.Other systems, such as peapods and fullerites, can be similarly treated, including the effect of the presence of a liquid, as reported in the appendices. 相似文献
90.
Novel intramolecular TaqMan probes have been evaluated on the W1282X locus of the human ABCC7 gene and shown to be more efficient than traditional TaqMan probes. 相似文献