全文获取类型
收费全文 | 2393篇 |
免费 | 88篇 |
国内免费 | 8篇 |
专业分类
化学 | 1629篇 |
晶体学 | 13篇 |
力学 | 103篇 |
数学 | 344篇 |
物理学 | 400篇 |
出版年
2023年 | 28篇 |
2022年 | 33篇 |
2021年 | 54篇 |
2020年 | 59篇 |
2019年 | 58篇 |
2018年 | 41篇 |
2017年 | 29篇 |
2016年 | 71篇 |
2015年 | 63篇 |
2014年 | 59篇 |
2013年 | 102篇 |
2012年 | 147篇 |
2011年 | 169篇 |
2010年 | 84篇 |
2009年 | 70篇 |
2008年 | 152篇 |
2007年 | 137篇 |
2006年 | 147篇 |
2005年 | 126篇 |
2004年 | 67篇 |
2003年 | 74篇 |
2002年 | 47篇 |
2001年 | 39篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 32篇 |
1997年 | 21篇 |
1996年 | 23篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 20篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 19篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 29篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 21篇 |
1975年 | 16篇 |
1974年 | 11篇 |
1972年 | 11篇 |
排序方式: 共有2489条查询结果,搜索用时 15 毫秒
61.
62.
63.
The optical and ESR spectra of electrochemically reduced phosphotungstate and polyphosphotungstate anions in phosphoric acid were examined as quantitative functions of W5+ concentration. The optical spectra obey Beer-Lambert laws and are similar to the spectra of reduced silicotungstate anions, indicating the secondary nature of the central cluster in the keggin structure with regard to interactions with the reduction electron. ESR spectra indicate an equivalent correspondence for the W5+ concentration and unpaired spins for the reduced polyphosphotungstate anion but for the reduced phosphotungstate anion monomer the unpaired spin concentration estimated by ESR was much lower than the W5+ concentration. Reacting reduced phosphotungstate anions with oxygen showed a I-electron reduction of the oxygen molecule with concomitant oxidation of W5+ to W6+ and possibly production of high-molecular-weight, polyanion clusters. 相似文献
64.
Jacob J. Habeeb Farouq F. Said Dennis G. Tuck 《Journal of organometallic chemistry》1980,190(4):325-334
The electrochemical oxidation of indium metal in cells of the type
leads to the formation of RInX2 compounds; if 2,2′-bipyridine is also present, the products are the adducts RInX2·bipy (R = CH3, C2H5, C6H5, C6H5CH2, C6F5; X = Cl, Br, I (not all combinations)). When R′4NX is present instead of bipy, the products are the salts R′4N[RInX3]. The electrochemical oxidation apparently proceeds via the general mechanism discussed previously. Anomalous results with CH3I or C2H5I are discussed in the light of the known solution chemistry of organoindium(III) compounds. 相似文献
65.
Additivity schemes for estimating heats of formation and heats of atomization of alkanes and halo- alkanes are scrutinized. A least squares analysis of the heats of atomization of alkanes leads to a revision of the values of the parameters. The improvement in the estimated heats of atomization over the values obtained with parameters previously suggested amounts to at least 100%. The reasons for the deviations from the experimental values are discussed. These parameters can be transfered to haloalkanes. Additional parameters necessary for estimating heats of atomization of haloalkanes are also obtained through least squares analyses. 相似文献
66.
Inside Cover: Solvent‐Driven Reductive Activation of CO2 by Bismuth: Switching from Metalloformate Complexes to Oxalate Products (Angew. Chem. Int. Ed. 48/2016) 下载免费PDF全文
67.
Use of Lanthanide‐Containing Polyoxometalates to Sensitise the Emission of Fluorescent Labelled Serum Albumin 下载免费PDF全文
Dr. A. Sheila Holmes‐Smith Jacob Crisp Dr. Firasat Hussain Prof. Dr. Greta R. Patzke Dr. Graham Hungerford 《Chemphyschem》2016,17(3):418-424
Monitoring the interaction of biomolecules is important, and the use of energy transfer is a principal technique in elucidating nanoscale interactions. Lanthanide compounds are promising luminescent probes for biological samples as their emission is longer‐lived than any native autofluorescence. Polyoxometalates (POMs) are interesting structural motifs to incorporate lanthanides, offering low toxicity and a size pertinent for biological applications. Here, we employ iso‐structured POMs containing either terbium or europium and assess their interaction with serum albumin by sensitisation of a fluorescent tag on the protein via LRET (luminescence resonance energy transfer) by exciting the lanthanide. Time‐resolved measurements showed energy transfer with an efficiency of over 90 % for the POM–protein systems. The Tb–POM results were relatively straightforward, while those with the iso‐structured Eu–POM were complicated by the effect of protein shielding from the aqueous environment. 相似文献
68.
Yu. A. Ryndin Yu. N. Nogin V. I. Zaikovskii K. Jacob K. -H. Thiele Yu. I. Yermakov 《Reaction Kinetics and Catalysis Letters》1985,29(2):395-402
(Pd+Ce)/SiO2 catalysts prepared by decomposition of organometallic complexes of Ce and Pd have higher activity, dispersity and selectivity in methanol synthesis than Pd/SiO2 catalysts.
, (Pd+Ce)/SiO2 , Ce Pd, Pd/SiO2.相似文献
69.
The synthesis and characterization of water-soluble dispersions of Ag nanoparticles by the reduction of AgNO(3) using tryptophan under alkaline synthesis conditions are reported. The Ag nanoparticle formation was very slow at low concentration and rapid at extremes. For surface modification and redox reactions, manipulating the interparticles interaction controlled the size of Ag nanoparticles aggregates. Our results suggest that the replacement of the BH(4)(-) ions adsorbed on the nanoparticle surface by tryptophan destabilizes the particles and further caused aggregation. A mechanism is proposed for the formation of silver nanoparticles by tryptophan. The experimental results are supported by theoretical calculations. The Ag nanoparticles were characterized by UV-vis absorption, dynamic light scattering and transmission electron microscopy techniques. 相似文献
70.
W. K. Warburton Wolfgang Hennig Jacob A. Bertrand Steven M. George Steven Biegalski 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(1):541-549
Well designed scintillator detectors, including such examples as ARSA, SAUNA, and XIA’s “PhosWatch”, can readily achieve the state of the art radioxenon detection limits required for nuclear explosion monitoring. They are also reliable, robust detectors that do not require cryogenic cooling for operation. All three employ the principle of beta-gamma coincidence detection to reduce background counting rates, using a BC-404 plastic scintillator to detect the betas and a CsI or NaI scintillator to detect the gamma-rays. As a consequence of this commonality of design, all three also display a “memory effect” arising from the diffusion of Xe into BC-404. Thus, when one sample is pumped out of the detector, a fraction remains behind, embedded in the BC-404, where it artificially raises the signal counting rate for the next sample. While this is not a fatal flaw in scintillator detectors, developing a method to eliminate the memory effect would significantly enhance their utility. This paper reports efforts to develop thin, amorphous Al2O3 films, deposited by atomic layer deposition (ALD) to act as diffusion barriers on the BC-404 surfaces exposed to radioxenon. Using radon as a convenient substitute for Xe, film thicknesses between 2 and 10 nm were originally investigated and found to show a memory effect to varying degrees. A second set of 20 and 30 nm films was then produced, which appeared to completely eliminate the radon memory effect, but, when consequentially tested with radioxenon, were found to exhibit xenon memory effects that were approximately half of the effect found on uncoated BC-404. We draw two conclusions from this result. The first is that it will be necessary to develop an improved method for depositing thicker ALD Al2O3 films at lower temperatures while still retaining high film quality. The second is that, since xenon is required to test for the xenon memory effect, we need a test method that does not require xenon radio-isotopes in order to facilitate screening large numbers of samples. 相似文献