全文获取类型
收费全文 | 4498篇 |
免费 | 119篇 |
国内免费 | 7篇 |
专业分类
化学 | 2894篇 |
晶体学 | 57篇 |
力学 | 65篇 |
数学 | 478篇 |
物理学 | 1130篇 |
出版年
2021年 | 37篇 |
2020年 | 40篇 |
2019年 | 47篇 |
2018年 | 29篇 |
2016年 | 69篇 |
2015年 | 69篇 |
2014年 | 78篇 |
2013年 | 146篇 |
2012年 | 156篇 |
2011年 | 182篇 |
2010年 | 123篇 |
2009年 | 90篇 |
2008年 | 154篇 |
2007年 | 145篇 |
2006年 | 158篇 |
2005年 | 146篇 |
2004年 | 134篇 |
2003年 | 129篇 |
2002年 | 122篇 |
2001年 | 117篇 |
2000年 | 116篇 |
1999年 | 62篇 |
1998年 | 44篇 |
1997年 | 48篇 |
1996年 | 87篇 |
1995年 | 64篇 |
1994年 | 81篇 |
1993年 | 62篇 |
1992年 | 64篇 |
1991年 | 61篇 |
1990年 | 59篇 |
1989年 | 47篇 |
1988年 | 50篇 |
1987年 | 64篇 |
1986年 | 58篇 |
1985年 | 58篇 |
1984年 | 64篇 |
1983年 | 49篇 |
1982年 | 52篇 |
1981年 | 63篇 |
1980年 | 45篇 |
1979年 | 47篇 |
1978年 | 53篇 |
1977年 | 58篇 |
1976年 | 58篇 |
1975年 | 58篇 |
1974年 | 59篇 |
1973年 | 43篇 |
1968年 | 27篇 |
1957年 | 30篇 |
排序方式: 共有4624条查询结果,搜索用时 0 毫秒
151.
152.
153.
Rock porosity determination by combination of X-ray computerized tomography with mercury porosimetry
P. Klobes H. Riesemeier K. Meyer J. Goebbels K.-H. Hellmuth 《Fresenius' Journal of Analytical Chemistry》1997,357(5):543-547
First results are described of coupling of mercury porosimetry with X-ray computerized tomography (CT) as a new combination
technique for rock porosity studies. This technique is suitable for rock samples with a pronounced mercury intrusion-extrusion
hysteresis and includes CT measurements before and after mercury intrusion. The entrapped portion of mercury, when the pressure
after the intrusion into the rock sample is reduced to 0.1 MPa, serves as a contrast agent in the porous network to localize
spatial distribution of rock porosity by CT. The results obtained show that the mercury intrusion and therefore the porosity
were quite different for the separate mineral phases. Therefore the combination of mercury porosimetry and computer tomography
can give 3-D data on mineral-specific porosity distributions with additional pore size information. In contrast to mercury
porosimetry as a single method, results of the combination technique with CT represent a direct visualization of porosity
variation and do not depend on any special pore network model.
Received: 2 July 1996 / Revised: 20 November 1996 / Accepted: 22 November 1996 相似文献
154.
F. Meyer J. Dupré C. Meyer C. Lambeau M. De Vleeschouwer J. -G. Lahaye A. Fayt 《International Journal of Infrared and Millimeter Waves》1982,3(1):83-95
The 5 band of methylacetylene has been studied simultaneously by means of CO2 Laser Stark spectroscopy and high resolution infrared absorption spectroscopy (0.012 cm–1). The primary aim of this work was to assign all the Stark coïncidences. Effective vibration-rotation parameters and the dipole moment of the v5=1 state have been determined. 相似文献
155.
Gerd Meyer 《无机化学与普通化学杂志》1984,515(8):127-132
CsCu2Cl3 and CsCu2Br3 by Synproportionation at the Metallic Substrate CsCu2Cl3 and CsCu2Br3 are obtained as single crystals via a dry route by synproportionation of mixtures of CsX/2 CuX (X = Cl, Br) and CsCuCl3, respectively, with the copper of the surface of a closed copper cylinder as the metallic substrate. Lattice constants of CsCu2Cl3 (CsCu2Br3) are: a = 950.75(9) (987.3(1)), b = 1189.8(2) (1235.5(2)), c = 559.92(6) (581.80(9)) pm, orthorhombic, Cmcm, Z = 4. Details of the Cs? X polyhedra (X = Cl, Br, I) and the double chains of tetrahedra [Cu2X3]? in CsCu2Cl3, CsCu2Br3, and CsCu2I3 are compared. 相似文献
156.
Fry HC Scaltrito DV Karlin KD Meyer GJ 《Journal of the American Chemical Society》2003,125(39):11866-11871
The observation and fast time-scale kinetic determination of a primary dioxygen-copper interaction have been studied. The ability to photorelease carbon monoxide from [Cu(I)(tmpa)(CO)](+) in mixtures of CO and O(2) in tetrahydrofuran (THF) between 188 and 218 K results in the observable formation of a copper-superoxide species, [Cu(II)(tmpa)(O(2)(-))](+) lambda(max) = 425 nm. Via this "flash-and-trap" technique, temperature-dependent kinetic studies on the forward reaction between dioxygen and [Cu(I)(tmpa)(thf)](+) afford activation parameters DeltaH = 7.62 kJ/mol and DeltaS = -45.1 J/mol K. The corresponding reverse reaction proceeds with DeltaH = 58.0 kJ/mol and DeltaS = 105 J/mol K. Overall thermodynamic parameters are DeltaH degrees = -48.5 kJ/mol and DeltaS degrees = -140 J/mol K. The temperature-dependent data allowed us to determine the room-temperature second-order rate constant, k(O2) = 1.3 x 10(9) M(-1) s(-1). Comparisons to copper and heme proteins and synthetic complexes are discussed. 相似文献
157.
The novel versatile cobalt(I) tris-carbene complex [(TIMEN(xyl))Co]Cl (1) (where TIMEN = (tris[2-(3-arylimidazol-2-ylidene)ethyl]amine) reacts with CO, one-electron oxidizers such as CH(2)Cl(2), and O(2) to yield the cobalt complexes [(TIMEN(xyl))Co(CO)]Cl (2), [(TIMEN(xyl))Co(Cl)]Cl (3), and peroxo species [(TIMEN(xyl))Co(O(2))](BPh(4)) (5). All new complexes were fully characterized by (1)H NMR, UV/vis, and IR spectroscopy as well as superconducting quantum interference device (SQUID) magnetization measurements and single-crystal X-ray crystallography. The nucleophilic character of the eta(2)-bound dioxygen ligand in 5 was confirmed by density functional theory (DFT) studies and allows for oxygen-transfer reactions with electron-deficient organic substrates, such as benzoyl chloride. 相似文献
158.
Two New Silicate-Chlorides with Divalent Europium: LiEu3[SiO4]Cl3 and Li7Eu8[SiO4]4Cl7 LiEu3[SiO4]Cl3 was prepared by reaction of LiCl with Eu2SiO4 and Li7Eu8[SiO4]4Cl7 from Li with Eu2O3, SiO2 and LiCl. The crystal structures of LiEu3[SiO4]Cl3 (Pmna, a = 946.95(13); b = 699.52(8); c = 1 368.0(2) pm; Z = 4; R1 = 0.0325, R2w = 0.0642) and Li7Eu8[SiO4]4Cl7 (P21/c; a = 851.85(5); b = 948.62(7); c = 1 679.0(2) pm; β = 96.221(8)°; Z = 2; R1 = 0.0352, R2w = 0.0744) were determined from four-circle diffractometer data. LiEu3[SiO4]Cl3 contains [Li(SiO4)2] units and LiCl6 octahedra while in Li7Eu8[SiO4]4Cl7 larger ?lithosilicate”? groups are found. In both structures, the Eu2+ ions are coordinated mostly eightfold by O2? and Cl? ligands. 相似文献
159.
Amatore C Gamez S Jutand A Meyer G Moreno-Manas M Morral L Pleixats R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(18):3372-3376
The oxidative addition of a cyclic allylic carbonate to the palladium(0) complex generated from a [Pd(dba)2]+2 PPh3 mixture affords a cationic pi-allylpalladium(II) complex with the alkyl carbonate as the counter-anion. This reaction is reversible and proceeds with isomerization of the allylic carbonate at the allylic position. The equilibrium constant has been determined in DMF. The influence of the precursor of the palladium(0) is discussed. 相似文献
160.
Annette C. Niemann Mnica Meyer Thomas Engeloch Oliver Botta Alfons Hdener Peter Strazewski 《Helvetica chimica acta》1995,78(2):421-439
A procedure was developed for the biosynthetic preparation of 15N-labelled guanosine and inosine through the action of a mutant Bacillus subtilis strain. Crude [N2,1,3,7,9-15N]guanosine and [1,3,7,9-15N]inosine were isolated from the culture filtrate by precipitation and anion-exchange chromatography (Scheme 1). No cell lysis and no enzymatic degradation was necessary. The per-isobutyrylated derivatives 1 and 2 were isolated from a complex mixture, purified by virtue of their different lipophilicity, and separated in three steps involving normal-and reversed-phase silica-gel chromatography. One litre of complex nutrient medium yielded 8.44 mmol of guanosine derivative and 2.84 mmol of inosine derivative with high average 15N enrichment (83.5 and 91.9 atom-%, resp.). [N6,1,3,7,9-15N]Adenosine ( 4 ) was obtained from 2′,3′,5′-tri-O-isobutyryl[1,3,7,9-15N]inosine ( 1 ) through the ammonolysis of its 1,2,4-triazolyl derivative with aqueous 15NH3 (Scheme 2). 相似文献