全文获取类型
收费全文 | 698篇 |
免费 | 24篇 |
专业分类
化学 | 544篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 29篇 |
物理学 | 141篇 |
出版年
2023年 | 3篇 |
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 6篇 |
2013年 | 22篇 |
2012年 | 30篇 |
2011年 | 55篇 |
2010年 | 28篇 |
2009年 | 27篇 |
2008年 | 41篇 |
2007年 | 54篇 |
2006年 | 49篇 |
2005年 | 58篇 |
2004年 | 39篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 5篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 13篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有722条查询结果,搜索用时 31 毫秒
1.
2.
I. P. Kuranova K. M. Polyakov E. A. Smirnova W. E. Höhne V. S. Lamzin R. Meijer 《Crystallography Reports》2003,48(6):953-958
Crystals of Saccharomyces cerevisiae inorganic pyrophosphatase suitable for X-ray diffraction study were grown by cocrystallization of the enzyme with cobalt chloride and imidodiphosphate. Saccharomyces cerevisiae is a metal-dependent enzyme which catalyzes hydrolysis of inorganic pyrophosphate to orthophosphate. The three-dimensional structure of this enzyme was solved by the molecular-replacement method and refined at 1.8 Å resolution to an R factor of 19.5%. Cobalt and phosphate ions were revealed in the active centers of both identical subunits (A and B) of the pyrophosphatase molecule. In subunit B, a water molecule was found between two cobalt ions. It is believed that this water molecule acts as an attacking nucleophile in the enzymatic cleavage of the pyrophosphate bond. It was demonstrated that cobalt ions and a phosphate group occupy only part of the potential binding sites (two chemically identical and crystallographically independent subunits have different binding sites). The arrangement of ligands and the structure of the nucleophile-binding site are discussed in relation to the mechanism of action of the enzyme and the nature of the metal activator. 相似文献
3.
Dehydrogenation of alcohols into aldehydes and ketones by Ru3(CO)12/PPh3 based homogeneous catalysis has been investigated as an alternative for the classical Oppenauer oxidation. Several catalytic systems have been screened in the Oppenauer-like oxidation of alcohols. A systematic study of various combinations of Ru3(CO)12, mono- and bidentate ligands and hydride acceptors was performed to enable dehydrogenation of primary alcohols to stop at the aldehyde stage. Among many H-acceptors screened, diphenylacetylene (tolane) proved the most suitable judged from its smooth reduction. Electron rich and deficient analogues of tolane have been synthesized and, based on competition experiments between these H-acceptors, a tentative catalytic cycle for the Ru3(CO)12/PPh3-catalyzed dehydrogenations has been proposed. 相似文献
4.
Lionel Joucla Florence Popowycz Olivier Lozach Laurent Meijer Benoît Joseph 《Helvetica chimica acta》2007,90(4):753-763
The syntheses of paullone ( 1a ) and three paullone derivatives, including a sulfur analogue ( 2a ), a tricyclic derivative ( 2b ), and a ring‐enlarged variant ( 2c ), are described, Pd‐catalyzed intramolecular Heck reaction being the key step. The kinase‐inhibitory properties of the novel paullone analogues were investigated. 相似文献
5.
It is shown that laser evaporation of a solid target followed by adiabatic expansion can be used to produce cold beams of neutral small open shell molecules. LIF is applied to detect CuH (X
1), CH (X
2), SiH (X
2), CuO (X
2), and FeO (X
5). A production of 109±1 molecules/sr in a single pulse is obtained for SiH. For a copper target, the optical emission of the jet plume is discussed. 相似文献
6.
7.
Abstract— A pre-irradiation of etiolated gherkin seedlings increases the effect of a subsequent irradiation with red light, whereas it does not influence the inhibitive effect of blue light. Blue and far red radiation are more active as a pre-irradiation than red light. It is concluded that at least two photoreactions are involved in the control of the elongation of the gherkin hypocotyl and that the blue, far red sensitive reaction has a synergistic effect on the red sensitive (Phytochrome mediated) reaction. 相似文献
8.
9.
A. Van Baalen C.J. Groenenboom H.J. De Liefde Meijer 《Journal of organometallic chemistry》1974,74(2):245-253
The synthesis and the properties of the complexes Cp2TaCl2, Cp2M(allyl), Cp2M(1-methylallyl) and Cp2M(2-methylallyl) with M Nb, Ta are described. The complex Cp2TaCl2 has one unpaired electron per tantalum atom, while the allyl complexes are diamagnetic. The IR and PMR spectra indicate that the allyl group is π-bonded to the metal. The mass spectra of the complexes are discussed; the thermal stability of the Cp2Nb- and Cp2Ta-(allyl) complexes was investigated by differential thermal analysis. The properties of the niobium and tantalum complexes are compared with those of the corresponding titanium complexes. 相似文献
10.
ten Cate AT Kooijman H Spek AL Sijbesma RP Meijer EW 《Journal of the American Chemical Society》2004,126(12):3801-3808
Bifunctional 2-ureido-4[1H]-pyrimidinone (UPy) derivatives can form small cyclic oligomers as well as long supramolecular polymers in chloroform solutions using the quadruple hydrogen-bonding motif. Ring-chain equilibria of a set of supramolecular monomers containing methyl-substituted alkyl linkers between the hydrogen-bonding UPy moieties were investigated by (1)H NMR spectroscopy and viscometry. The data were characterized in terms of critical concentration (CC, denoting the onset of polymerization) and equilibrium cyclic dimer concentration (EDC, representing preorganization of the monomer toward selective formation of cyclic dimer). Methyl substituents in the monomer were found to promote conformations favorable for cyclic dimerization, leading to an increase in both the EDC and the CC with respect to unsubstituted monomer. Furthermore, we observed an odd-even effect in the CC and EDC with increasing length of the linker between the hydrogen-bonding units. The combined results allow tuning of the critical concentration over a broad range and offer detailed information on the correlation between monomer structure, conformation, and polymerizability which may provide new insights for the study and design of other ring-chain equilibria or helix-random coil transitions. 相似文献