全文获取类型
收费全文 | 893篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 563篇 |
晶体学 | 6篇 |
力学 | 40篇 |
数学 | 139篇 |
物理学 | 169篇 |
出版年
2023年 | 4篇 |
2022年 | 22篇 |
2021年 | 30篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 14篇 |
2014年 | 26篇 |
2013年 | 71篇 |
2012年 | 65篇 |
2011年 | 64篇 |
2010年 | 30篇 |
2009年 | 39篇 |
2008年 | 53篇 |
2007年 | 62篇 |
2006年 | 36篇 |
2005年 | 40篇 |
2004年 | 32篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 15篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1970年 | 4篇 |
1906年 | 3篇 |
1905年 | 3篇 |
排序方式: 共有917条查询结果,搜索用时 31 毫秒
131.
Villo L Danilas K Metsala A Kreen M Vallikivi I Vija S Pehk T Saso L Parve O 《The Journal of organic chemistry》2007,72(15):5813-5816
A chemoenzymatic synthesis of deoxy sugar esters is described. The synthesis is based on the O-alkylation of carboxylic acid with 2-bromo-5-acetoxypentanal. The method allows treatment of hydroxy carboxylic acids without protection of alcoholic hydroxyl groups. Several stereoisomeric deoxy sugar esters were resolved (up to ee or de > 98%) using a lipase-catalyzed acetylation of hemiacetals that in certain cases afforded deoxy sugar derivatives in the form of aldehydes. The stereochemistry of the reactions was determined by the NMR spectra of mandelic acid derivatives. 相似文献
132.
Barabas B Caglioti L Zucchi C Maioli M Gal E Micskei K Pályi G 《The journal of physical chemistry. B》2007,111(39):11506-11510
Enantiomeric excesses obtained in absolute enantioselective synthesis by chiral autocatalysis (Soai-reaction) were statistically analyzed. Two sets of parallel experiments, which were performed under chemically different conditions, are available. One group contains 37, while the other contains 84 preparative results. The former group shows some interesting tendencies but does not give conclusive statistical results. The sample of 84 parallel experiments, providing 39 R- and 45 S-excesses have shown that these data represent two distinct, non-symmetric sets with different non-Gaussian distributions. Clear S preference was found. 相似文献
133.
Moreno-Villoslada I González F Rivera L Hess S Rivas BL Shibue T Nishide H 《The journal of physical chemistry. B》2007,111(22):6146-6150
Aromatic-aromatic interactions are found between the cationic molecule 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and the molecule poly(sodium 4-styrenesulfonate) (PSS) which makes the overall interaction of TTC with PSS more intense than the interaction with other polyanions containing sulfonate groups and produces a decrease on the redox ability of TTC. Diafiltration was used to compare the binding of TTC to PSS, poly(sodium vinylsulfonate) (PVS), and the more hydrophobic poly(sodium 2-(N-acrylamido)-2-methyl-propanesulfonate) (PAMPS). The UV-vis spectrum of TTC is changed in the presence of the aromatic polyanion. The 1H NMR signals of TTC are broadened and shifted in the presence of PSS, suggesting the occurrence of pi-pi interactions. Moreover, nuclear Overhauser effects (NOE) between the TTC and PSS protons are found. Possible structures for the complex are proposed. 相似文献
134.
135.
Domenico Acierno Luciano Di Maio Pio Iannelli 《Journal of Polymer Science.Polymer Physics》1999,37(14):1601-1607
The molecular structure of the phase—stable at room temperature—for the polymer with formula [ p C6H4 COO p C6H3(R) p C6H3(R) OOC p C6H4 O (CH2)10O ]x, with R = CH2 CHCH2, is reported. The cell is hexagonal (a = b = 13.43 Å, c = 33.3 Å, γ = 120°), space group P63, six chains per unit cell (dcalcd = 1.23 g cm−3). The six chains are packed together to give a bundle with the center of mass set at the origin of the unit cell. The allyl groups are placed inside the bundle, thus explaining the unexpected reactivity of the double bonds to give crosslinking when fiber samples are annealed in the solid state. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1601–1607, 1999 相似文献
136.
Emanuele Pugliese Claudio Castellano Matteo Marsili Luciano Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(3):319-327
We introduce and study a model of an interacting population of agents who collaborate in groups which compete for limited
resources. Groups are formed by random matching agents and their worth is determined by the sum of the efforts deployed by
agents in group formation. Agents, on their side, have to share their effort between contributing to their group’s chances
to outcompete other groups and resource sharing among partners, when the group is successful. A simple implementation of this
strategic interaction gives rise to static and evolutionary properties with a very rich phenomenology. A robust emerging feature
is the separation of the population between agents who invest mainly in the success of their group and agents who concentrate
in getting the largest share of their group’s profits. 相似文献
137.
Carmen Festa Valentina Sepe Paolo Luciano Cecile Débitus Valentina Vellecco 《Tetrahedron》2009,65(50):10424-1496
Two new metabolites, perthamides C and D, have been isolated from the marine sponge Theonella swinhoei. Their structures were determined by interpretation of NMR and ESIMS data. All compounds exhibited in vivo potent anti-inflammatory activity. Biological activity and structural elucidation are reported. 相似文献
138.
139.
The use of explicit methods in the numerical treatment of differential equations of fractional order is an area not yet widely investigated. In this paper stability properties of some multistep methods of explicit type are investigated and new methods with larger intervals of stability are proposed. Some numerical experiments are presented in order to validate theoretical results. 相似文献
140.
Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were performed on wood samples of different essences (fir, chestnut, poplar, linden and oak) before consolidation. A kinetic analysis was applied on the two-steps decomposition processes occurring in all wood samples using either the multiheating rates Kissinger equation and the isoconversional Ozawa-Flynn-Wall method that enables the variation of activation energy to be determined as a function of the degree of reaction. Taking into account both decomposition temperature and activation energy for the first degradation step oak seems to be the less stable sample. The comparison of DSC curves performed in air with those in oxygen enables to consider the role of the partial pressure of oxygen in the mechanisms of both decompositions. 相似文献