全文获取类型
收费全文 | 411篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 322篇 |
晶体学 | 6篇 |
力学 | 3篇 |
数学 | 32篇 |
物理学 | 63篇 |
出版年
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 16篇 |
2011年 | 32篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 22篇 |
2007年 | 20篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 18篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 15篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1984年 | 9篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有426条查询结果,搜索用时 62 毫秒
101.
ABSTRACT Three sucrose monoalcohols with free hydroxyl groups at C-1', C-6, and C-6' (1, 4, and 6) were prepared selectively and in good yield from 2,3,3',4,4'-penta-O-benzylsucrose. These compounds were oxidized to aldehydes and reacted with stabilized ylide, Ph3P=CHCO2Me to afford appropriate α,β-unsaturated esters 10, 11, and 12. Each olefin was cis-hydroxylated with OsO4/NMO to stereoisomeric diols 13/14, 15/16, and 17/18, configurations of which were assigned by chemical correlation and CD evaluation. Stereoselectivity of the osmylation reaction was surprisingly low (ca 3:2), especially as compared to a similar process performed on simple derivatives of 6,7-unsaturated methyl glycosides for which the ratio of isomeric diols was assigned as 10:1. The osmylation of 11 (derivative homologated by a C2-unit at the glucose part) did not obey Kishi's rule. Horner-Emmons reaction of sucrose aldehyde 7 with a sugar-derived phosphonate 22 afforded α,β-unsaturated derivative 24, homologated by a C7-unit at the glucose end. 相似文献
102.
Anna Klepacz-Smółka Jadwiga Sójka-Ledakowicz Katarzyna Paździor Stanisław Ledakowicz 《Chemical Papers》2010,64(2):230-236
An anoxic fixed film bioreactor (FFB) with biomass immobilized on activated carbon and an aerobic continuous stirred tank
bioreactor with overflow were applied to degrade concentrate from nanofiltration of real textile effluents containing Reactive
Red 120 (RR-120). The efficiency of color removal was 99 % irrespective of the fraction of nanofiltration concentrate in the
feed. An approximate dye balance based on the assessed adsorption capacity of RR-120 by activated carbon indicated that the
dye was removed by means of adsorption as well as of biological processes. Aromatic amine released from a dye molecule was
fully adsorbed by activated carbon. COD level in the outflow of the system was above that imposed by legislation. Despite
an adjustment of the feed pH to 7 this was constantly increasing up to the value above 9 in both reactors. Neither the nanofiltration
concentrate nor the effluents from the bioreactors affected the growth of Pseudomonas putida used as toxicity indicator. 相似文献
103.
104.
In this article, using the generalized Newton transformation, we define higher order mean curvatures of distributions of arbitrary codimension and we show that they agree with the ones from Brito and Naveira [F. Brito, A.M. Naveira, Total extrinsic curvature of certain distributions on closed spaces of constant curvature, Ann. Global Anal. Geom., 18 (2000) 371–383]. We also introduce higher order mean curvature vector fields and we compute their divergence for certain distributions and using this we obtain total extrinsic mean curvatures. 相似文献
105.
Jadwiga Skubiszewska-Zi?ba 《Applied Surface Science》2010,256(17):5520-5527
VPO catalysts were prepared on oxidized and unoxidized activated carbons differing in initial porous structure. Carbons were oxidized under relatively soft (30% H2O2, 200 °C) and hard (50% H2O2, 350 °C) conditions. Carbon modification was carried out hydrothermally in a traditional autoclave (HTT) or a microwave reactor (MWT). The synthesis was also carried out under hydrothermal (HTS or MWS) conditions. V2O5 and NH4VO3 were used as precursors. The samples are characterized by diversified porous structure at SBET = 732-1617 m2/g and Vpor = 0.44-0.90 cm3/g, as well as various degree of VPO crystallinity. Possibility of preparation of the VPO catalysts under ecologically appropriate conditions, i.e. in aqueous solutions, was shown. 相似文献
106.
Kuta J Patchkovskii S Zgierski MZ Kozlowski PM 《Journal of computational chemistry》2006,27(12):1429-1437
Computational modeling of the enzymatic activity of B12-dependent enzymes requires a detailed understanding of the factors that influence the strength of the Co--C bond and the limits associated with a particular level of theory. To address this issue, a systematic analysis of the electronic and structural properties of coenzyme B12 models has been performed to establish the performance of three different functionals including B3LYP, BP86, and revPBE. In particular the cobalt-carbon bond dissociation energies, axial bond lengths, and selected stretching frequencies have been analyzed in detail. Current analysis shows that widely used B3LYP functional significantly underestimates the strength of the Co--C bond while the nonhybrid BP86 functional produces very consistent results in comparison to experimental data. To explain such different performance of these functionals molecular orbital analysis associated with axial bonds has been performed to show differences in axial bonding provided by hybrid and nonhybrid functionals. 相似文献
107.
Walczak RM Cowart JS Abboud KA Reynolds JR 《Chemical communications (Cambridge, England)》2006,(15):1604-1606
We report a tethered poly(3,4-propylenedioxythiophene) derivative with a built-in polymer conformation restriction which locks the conjugated chain at a specific dihedral angle, thus providing a handle in which to tune the optical and electronic properties of the material. 相似文献
108.
A sensitive and specific liquid chromatography tandem mass spectrometry method with electrospray ionization for the determination of endothelin-1 in rat plasma and lung effluents has been developed and validated. Detection was achieved by an Applied Biosystems MDS Sciex API 2000 triple quadrupole mass spectrometer coupled to an Agilent 1100 LC system. The limit of detection and the limit of the quantification of ET-1 in matrix buffer was estimated at 40 pM and 1 nM, respectively. The precision and accuracy for both intra- and inter-day determination of the analyte ranged from 2.5% to 14.7% and from 104.2% to 113.3%, respectively. No significant relative matrix effect was observed. Stability of ET-1 established in a bench-top, autosampler, long-term storage stability as well as freeze/thaw cycles shown no significant degradation products in the samples. The results of the method validation indicated that this method is applicable for the determination of the ET-1 concentration in an effluent from the isolated lung preparation as well as in vivo in plasma samples to evaluate ET-1 as a potential biomarker of the progression of pulmonary endothelial dysfunction and pulmonary hypertension in rats induced by a monocrotaline injection. 相似文献
109.
110.
Photodegradation of two dihydropyridine compounds has been studied in accordance with the recommendations of the first version of the ICH guidelines. Photodecomposition was monitored by UV–visible spectroscopy, LC, and LC–MS. Quantum yields and kinetic data were obtained for the photochemical reactions. The new dihydropyridine derivatives were found to decompose into different numbers of photoproducts with different rate constants. The derivative with two chlorine atoms in the phenyl ring proved to be more stable than the nitro derivative. 相似文献