全文获取类型
收费全文 | 2971篇 |
免费 | 55篇 |
国内免费 | 9篇 |
专业分类
化学 | 1922篇 |
晶体学 | 18篇 |
力学 | 82篇 |
数学 | 305篇 |
物理学 | 708篇 |
出版年
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 27篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 38篇 |
2015年 | 35篇 |
2014年 | 34篇 |
2013年 | 92篇 |
2012年 | 129篇 |
2011年 | 159篇 |
2010年 | 76篇 |
2009年 | 46篇 |
2008年 | 128篇 |
2007年 | 132篇 |
2006年 | 158篇 |
2005年 | 139篇 |
2004年 | 135篇 |
2003年 | 94篇 |
2002年 | 110篇 |
2001年 | 76篇 |
2000年 | 85篇 |
1999年 | 44篇 |
1998年 | 45篇 |
1997年 | 31篇 |
1996年 | 68篇 |
1995年 | 39篇 |
1994年 | 56篇 |
1993年 | 77篇 |
1992年 | 57篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 30篇 |
1987年 | 43篇 |
1986年 | 28篇 |
1985年 | 48篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 49篇 |
1981年 | 31篇 |
1980年 | 45篇 |
1979年 | 29篇 |
1978年 | 44篇 |
1977年 | 36篇 |
1976年 | 27篇 |
1975年 | 43篇 |
1974年 | 29篇 |
1973年 | 35篇 |
1972年 | 19篇 |
排序方式: 共有3035条查询结果,搜索用时 15 毫秒
101.
A family of homochiral metal carboxylate coordination polymers have been synthesized by treating 2,2'-dihydroxy-1,1'-binaphthalene-6,6'-dicarboxylic acid (H(2)BDA) with metal salts at elevated temperatures. BDA ligands link adjacent metal centers to form 1D coordination polymeric chains using the carboxylate functionality, while the hydroxyl groups of BDA ligands form H-bonds with carboxylate oxygen atoms to link 1D coordination polymeric chains into open frameworks of higher dimensionality. We also present evidence for the important role played by H-bonds in the stabilization of open framework structures which allows for the hierarchical assembly of chiral porous solids. 相似文献
102.
The regioselectivity of the intramolecular [2+2] photocycloaddition of certain 6-allylcyclohexenones appears to be largely independent of the substituent (H,OR) on the dital terminus of the isolated double bond. 相似文献
103.
Michael I. Bruce Jennifer K. Walton Michael L. Williams Brian W. Skelton Allan H. White 《Journal of organometallic chemistry》1981,212(3):C35-C38
Contrary to some previously depicted structures, the proton in HC5(CO2Me)5 is bonded to two oxygens rather than to carbon; the lithium ion in Li[C5(CO2Me)5] (H2O) is tetrahedrally coordinated by two carbonyl oxygens from one C5 anion, one from a second anion, and a water molecule. 相似文献
104.
D. White 《International Journal of Theoretical Physics》1985,24(2):201-216
Based upon a recently published work in which a model for hadron pair production via virtual synchrotron radiation in uniform magnetic fields was introduced, an ansatz for calculating
s
is presented. The resulting function is unique within the above-mentioned context. Along with a scheme introduced in which vector mesons arise by virtue of quark spin-flip with accompanying gluon emission, the
s
function is used to successfully explain the observed hadronic widths of the ,, andJ mesons. In addition the hadronic and leptonic widths of the upsilon meson are calculated. Based upon gathered upsilon data, a charge on theb quark of (2e/3) is found to be consistent with the above model. Finally, the derived
s
function is compared with results of gauge-theoretical calculations. 相似文献
105.
Bintinger D Kees KH Masek GE Miller ES Thompson JR Vernon W White JT Eisner AM Palmer DA Sullivan MK Armitage JC Buijs A Van Driel MA Erné FC Langeveld WG Paar HP Sens JC Timmer J Van Uitert B Cain MP Ko W Lander RL Maeshima K McNeil RR Pellett DE Smith JR Williams MC Caldwell DO Joshi UP Lu A Schwitkis KA Yellin SJ 《Physical review letters》1985,54(8):763-766
106.
Total synthesis of polycavernoside A, a lethal toxin of the red alga Polycavernosa tsudai 总被引:1,自引:0,他引:1
Blakemore PR Browder CC Hong J Lincoln CM Nagornyy PA Robarge LA Wardrop DJ White JD 《The Journal of organic chemistry》2005,70(14):5449-5460
[structure: see text] Two approaches to the synthesis of the aglycon 120 of polycavernoside A (1) were developed, only one of which was completed. The successful "second-generation" route assembled the aglycon seco acids 102 and 106 via Nozaki-Hiyama-Kishi coupling of aldehyde 70, prepared from methyl (S)-3-hydroxy-2-methylpropionate (72) and (S)-pantolactone (73), with vinyl bromide 71. The latter was obtained from a sequence which commenced from the silyl ether 24 of 3-hydroxypropionaldehyde and entailed cyclization of (Z)-zeta-hydroxy-alpha,beta-unsaturated ester 82. Regioselective Yamaguchi lactonization of trihydroxycarboxylic acids 102 and 106 and subsequent functional-group adjustments led to macrolactone 120, to which the fucopyranosylxylopyranoside moiety was attached. Stille coupling of the glycosidated aglycon 128 with dienylstannane 129 furnished polycavernoside A in a synthesis for which the longest linear sequence was 25 steps. The overall yield to lactone 120 was 4.7%. 相似文献
107.
This report describes the synthesis and characterization of a series of octaethylporphyrin derivatives in which the porphyrin pi-network is connected to phenyl, 3-fluoranthenyl, or 1-pyrenyl aromatic systems through a meso amino or amido nitrogen. Metal-free bases and zinc(II) and iron(III) complexes have been obtained. These compounds represent the first examples of linkages between porphyrins and extended pi-networks through a nitrogen atom directly attached to a porphyrin meso position. 1H NMR studies of the metal-free bases and zinc complexes showed that in the amido-linked adducts, the plane containing the aryl substituent was oriented perpendicular to the plane of the porphyrin. Linkage through the secondary amino nitrogen, however, allowed the aryl plane to rotate toward coplanarity with the porphyrin plane, resulting in conjugation of the highest occupied aryl and porphyrin molecular orbitals through the nitrogen lone pair. In developing routes to the amino-linked compounds, the facile formation of fused azaaryl chlorins via an oxidative intramolecular cycloaddition was observed. An aryl carbon ortho to the meso linkage attacked the beta-carbon of an adjacent pyrrole ring, accompanied by 1,2-migration of a pyrrole beta-ethyl substituent and a two-electron oxidation of the initially formed macrocycle. The resulting structures are analogous to benzochlorins. The electronic spectra of the metal-free bases are characterized by intense, long-wavelength bands in the visible region. Molecular structures of the chloroferric complexes of the azabenzofluorantheno- and azabenzpyrenoporphyrin macrocycles (derived from fusion of the fluoranthenyl and pyrenyl substituents, respectively) were obtained by X-ray diffraction. The porphyrin moiety in the azabenzofluoranthenoporphyrin adopted a gable structure, with a 22 degrees fold along a diagonal including the pyrrole-ring C4 and C16 alpha-carbons. By contrast, the azabenzpyrenoporphyrin was virtually planar. 相似文献
108.
Ottenberg CM McDonald FC O'Donnell ET Skrabal SA White DP 《Inorganic chemistry》2002,41(26):7151-7158
Increased preorganization can be achieved by immobilizing ligands on solid supports. Photoluminescent porous silicon, which can undergo facile hydrosilylation, was used as a support for open chain neutral N- and O-donor ligands. The abilities of these ligands to bind the divalent metal ions Ni(2+), Cu(2+), Zn(2+), and Pb(2+) are examined. Immobilized ligands selectively complexed Cu(II) over the other metal ions studied. Ligands immobilized on photoluminescent porous silicon also removed a significant amount, up to 98%, of Cu(II) from copper(II)-spiked, organic-rich, seawater samples. 相似文献
109.
Among several products isolated in the reaction between Ru3(μ3-PhC2C≡CPh)(μ-dppm)(CO)8 and Me3SiCэCCэCSiMe3 was the Ru3{μ3-CPhCC(O)C(SiMe3)C(C≡CSiMe3)CCPh)(μ-ddpm)(CO)7 complex formally obtained by coupling of the two diynes and a CO molecule on the Ru3 framework. Other products were Ru4(μ4-PhC2C≡CPh)(μ≡dppm)(CO)10 and the already known complex Ru3{μ3-PhCCHCC(C6H4}(μ-dppm)(CO)8.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1012–1016, May, 1998. 相似文献
110.
Ring-opening/ring-closing metathesis on cyclobutene-containing substrates with angular oxygen functionality provides a stereospecific introduction of 1,5-bis-dienes required for an anion-accelerated oxy-Cope rearrangement. The reaction sequence offers generally a stereocontrolled preparation of a variety of medium ring-containing bicyclic ring systems, while rearrangement to the bicyclo[7,3,0]dodecane (9-5) system leads to a mixture of olefin isomers. 相似文献