全文获取类型
收费全文 | 8474篇 |
免费 | 224篇 |
国内免费 | 57篇 |
专业分类
化学 | 4928篇 |
晶体学 | 86篇 |
力学 | 212篇 |
数学 | 1417篇 |
物理学 | 2112篇 |
出版年
2022年 | 107篇 |
2021年 | 198篇 |
2020年 | 150篇 |
2019年 | 207篇 |
2018年 | 238篇 |
2017年 | 207篇 |
2016年 | 303篇 |
2015年 | 230篇 |
2014年 | 271篇 |
2013年 | 533篇 |
2012年 | 497篇 |
2011年 | 627篇 |
2010年 | 438篇 |
2009年 | 381篇 |
2008年 | 498篇 |
2007年 | 459篇 |
2006年 | 417篇 |
2005年 | 398篇 |
2004年 | 332篇 |
2003年 | 281篇 |
2002年 | 255篇 |
2001年 | 129篇 |
2000年 | 124篇 |
1999年 | 117篇 |
1998年 | 108篇 |
1997年 | 74篇 |
1996年 | 109篇 |
1995年 | 65篇 |
1994年 | 62篇 |
1993年 | 73篇 |
1992年 | 56篇 |
1991年 | 47篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 30篇 |
1979年 | 28篇 |
1978年 | 25篇 |
1977年 | 35篇 |
1975年 | 32篇 |
1972年 | 28篇 |
1971年 | 25篇 |
1970年 | 30篇 |
1969年 | 27篇 |
排序方式: 共有8755条查询结果,搜索用时 640 毫秒
121.
Mono- or 1,1′-bis-acylation of ferrocene, its mono and 1,1′-dimethyl and phenyl derivatives and of [3]ferrocenophane with o-chlorobenzoyl chloride/AlCl3 affords the corresponding (isomeric) chlorobenzoyl ferrocenes in high yields which can be separated by column, layer or high pressure liquid chromatography and in the case of the monomethylferrocene monoketones also by crystallization. The cleavage of the (o-chlorobenzoyl)ferrocenes by potassium-t-butoxide (and traces of water) yields the corresponding ferrocene carboxylic acids except for the α-phenyl derivatives in almost quantitative yields, thus offering a very convenient access to these acids. In all cases the isomer distribution and thereby the relative site reactivities were determined. 相似文献
122.
Nataliya A. Mayorova Olga A. Khazova Vladimir S. Bagotzky 《Journal of Solid State Electrochemistry》1998,2(4):262-265
Methanol electrooxidation on smooth platinum electrodes bonded to solid polymer electrolytes was studied in water and acid
solution by voltammetric measurements with different scanning rates. An enhancement of the oxidation rates was observed in
these systems as compared to identical platinum electrodes in contact with liquid electrolytes. This electrocatalytic effect
strongly depends on the measuring conditions and on the electrode potential. The reasons for the catalytic effects at different
potentials are discussed.
Received: 8 January 1997 / Accepted: 1 December 1997 相似文献
123.
Alexander D. Dilman Dmitry E. Arkhipov Valentine P. Ananikov Vladimir A. Tartakovsky 《Journal of organometallic chemistry》2005,690(16):3680-3689
A general method for the synthesis of carbon-centered tris(pentafluorophenyl)silyl derivatives (RSi(C6F5)3) by reaction of trichlorosilanes (RSiCl3) with pentafluorophenylmagnesium bromide was described. The crystal structures of obtained compounds were studied by X-ray diffraction analysis (7 structures). The peculiarities of crystal packing were analyzed by means of DFT calculations. 相似文献
124.
Hiroshi Ito Vladimir Marousek Conrad Schuerch 《Journal of polymer science. Part A, Polymer chemistry》1979,17(5):1299-1307
1,6-Anhydro-2,3,4-tri-O-(p-methylbenzyl)-ß-D -galactopyranose (TXGal,M1) has been copolymerized with 1,6-anhydro-2,3,4-tri-O-benzyl-ß-D -mannopyranose (TBMan,M2), the products characterized by NMR, specific rotation, and viscosity, and the reactivity ratios calculated. The reactivity ratios r1 = 0.37 ± 0.15 and r2 = 38 ± 4 indicate that the anhydromannose derivative is about 100 times as reactive as that of anhydrogalactose. A comparison of glucose, mannose, and galactose copolymerizations suggests that the reactivity differences of the three propagating cations are comparatively small and the reactivity differences of the monomers large. This result is consistent with a mechanism proposed earlier. Methyl substitution on the aromatic rings of the p-xylyl groups inhibits the initiation process significantly relative to benzyl, but propagation only slightly. 相似文献
125.
Elena V Chubarova Denis G. Samsonenko Maxim N. Sokolov Olga A. Gerasko Vladimir P. Fedin Javier G. Platas 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(1-2):31-35
A new inclusion compound which is a supramolecular adduct of cucurbit[8]uril with two guest molecules of phenylphosphonic acid, PhP(O)(OH)2, included into the cavity as ``two guests in host'' is reported. The guests match both size and hydrophilicity/hydrophobicity requirements. Two phenyl groups of molecules of PhP(O)(OH)2 are directed toward the center of the large hydrophobic cavity whereas the PO(OH)2 groups are outward-looking and bound with each hydrophilic portal of cucurbit[8]uril by a short hydrogen bond. 相似文献
126.
E. A. Chernyshev O. V. Kuz'min A. V. Lebedev V. G. Zaikin A. I. Mikaya 《Russian Chemical Bulletin》1986,35(4):821-824
Conclusions The main products of the pyrolysis of 8,8-dimethyl-8-sila-2,3,4,5-tetrathiabicycIo-[4.3.0]nonane at 400 are 1,1-dimethylsilacyclopent-3-ene and 1,1-dimethyl-1-sila-2-thiacyclo-hexa-3, 5-diene, and at 600 carbon disulfide and thiophene; silacyclopentene is the sole reaction product, characteristic for the mass-spectrometric decomposition of the initial tetrasulfide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No, 4, pp. 902–905, April, 1986. 相似文献
127.
The temperature dependences of the heat capacities of crystalline tetraphenyltetrahydroxycyclotetrasiloxane, octaphenyltetrahydroxytricyclooctasiloxane, and octaphenylpentacyclosilsesquioxane and of glassy polyphenylsilsesquioxane were measured in the range 6-300 K with an adiabatic vacuum calorimeter, with an accuracy of 0.3%. From these data, the thermodynamic functions C
0
p
(T), H
0(T) - H
0(0), S
0(T) - S
0(0), and G
0(T) - H
0(0) of these substances were calculated for the range 0-300 K. The standard entropies of their formation from elements at 298.15 K,
f
S
0, and the entropies of mutual transformations of these substances in the range 0-298.15 K were calculated. 相似文献
128.
VladimirS.Arutyunov 《天然气化学杂志》2004,13(1):10-22
Recent experimental results and kinetic modeling of fast flow gas-phase oxidation of methane and other lower alkanes to methanol and other oxygenates are discussed,alongside with prospects and possible areas for applications of the processes. 相似文献
129.
The irradiation of 2-diazo-1(2H)-naphthalenone (1), the common component of positive photoresists, with 800 nm pulses of ultrafast laser results in Wolff rearrangement via nonresonant two-photon absorbance of light. The 10% conversion of starting material resulting in the formation of methyl 1H-indene-3-carboxylate (2) was achieved after 11 min of irradiation of the methanol solution of 1 with an unfocused beam of a Ti:Sapphire laser operating at 1 kHz. The two-photon cross-section of the diazonaphthoquinone 1 at 800 nm was calculated to be sigma = 2.2 x 10-51 cm4 s photon-1 (0.2 GM). 相似文献
130.
Retsek JL Drain CM Kirmaier C Nurco DJ Medforth CJ Smith KM Sazanovich IV Chirvony VS Fajer J Holten D 《Journal of the American Chemical Society》2003,125(32):9787-9800
The ground- and excited-state metal-ligand dynamics of nonplanar nickel(II) 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (NiDPP) and two fluorinated analogues (NiF(20)DPP and NiF(28)DPP) have been investigated using static and time-resolved absorption spectroscopy in toluene and in ligating media that differ in basicity, aromaticity, and steric encumbrance. Because of the electronic and steric consequences of nonplanarity, NiDPP does not bind axial ligands in the ground state, but metal coordination does occur after photoexcitation with multistep dynamics that depend on the properties of the ligand. Following the structural relaxations that occur in all nickel porphyrins within approximately 10 ps, ligand binding to photoexcited NiDPP is progressively longer in pyridine, piperidine, and 3,5-lutidine (25-100 ps) but does not occur at all in 2,6-lutidine in which the ligating nitrogen is sterically encumbered. The transient intermediate that is formed, which nominally could be either a five- or six-coordinate species, also has a ligand-dependent lifetime (200-550 ps). Decay of this intermediate occurs partially via ligand release to re-form the uncoordinated species, in competition with binding of the second axial ligand and/or conformational/electronic relaxations (of a six-coordinate intermediate) to give the ground state of the bis-ligated photoproduct. The finding that the photoproduct channel principally depends on ligand characteristics along with the time-evolving spectra suggests that the transient intermediate may involve a five-coordinate species. In contrast to NiDPP, the fluorinated analogues NiF(20)DPP and NiF(28)DPP do coordinate axial ligands in the ground state but eject them after photoexcitation. Collectively, these results demonstrate the sensitivity with which the electronic and structural characteristics of the macrocycle, substituents, and solvent (ligands) can govern the photophysical and photochemical properties of nonplanar porphyrins and open new avenues for exploring photoinduced ligand association and dissociation behavior. 相似文献