全文获取类型
收费全文 | 870篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 457篇 |
晶体学 | 7篇 |
力学 | 30篇 |
数学 | 88篇 |
物理学 | 306篇 |
出版年
2021年 | 7篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 13篇 |
2013年 | 44篇 |
2012年 | 38篇 |
2011年 | 45篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 42篇 |
2007年 | 33篇 |
2006年 | 37篇 |
2005年 | 42篇 |
2004年 | 32篇 |
2003年 | 32篇 |
2002年 | 31篇 |
2001年 | 24篇 |
2000年 | 16篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 24篇 |
1993年 | 19篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1973年 | 13篇 |
1972年 | 6篇 |
1970年 | 8篇 |
1969年 | 6篇 |
排序方式: 共有888条查询结果,搜索用时 46 毫秒
51.
Grace B. Panetti Patrick J. Carroll Michael R. Gau Brian C. Manor Eric J. Schelter Patrick J. Walsh 《Chemical science》2021,12(12):4405
The super electron donor (SED) ability of 2-azaallyl anions has recently been discovered and applied to diverse reactivity, including transition metal-free cross-coupling and dehydrogenative cross-coupling processes. Surprisingly, the redox properties of 2-azaallyl anions and radicals have been rarely studied. Understanding the chemistry of elusive species is the key to further development. Electrochemical analysis of phenyl substituted 2-azaallyl anions revealed an oxidation wave at E1/2 or Epa = −1.6 V versus Fc/Fc+, which is ∼800 mV less than the reduction potential predicted (Epa = −2.4 V vs. Fc/Fc+) based on reactivity studies. Investigation of the kinetics of electron transfer revealed reorganization energies an order of magnitude lower than commonly employed SEDs. The electrochemical study enabled the synthetic design of the first stable, acyclic 2-azaallyl radical. These results indicate that the reorganization energy should be an important design consideration for the development of more potent organic reductants.The super electron donor (SED) capabilities of 2-azaallyl anions has recently been discovered and applied to diverse reactivity; their structures and electron transfer characteristics are reported herein. 相似文献
52.
Joseph A. Rard Kirk J. Staggs S. Dan Day Susan A. Carroll 《Journal of solution chemistry》2006,35(8):1187-1215
Boiling temperature measurements have been made at ambient pressure for saturated ternary solutions of NaCl + KNO3 + H2O, NaNO3 + KNO3 + H2O, and NaCl + Ca(NO3)2 + H2O over the full composition range, along with those of the single salt systems. Boiling temperatures were also measured for the four component NaCl + NaNO3 + KNO3 + H2O and five component NaCl + NaNO3 + KNO3 + Ca(NO3)2 + H2O mixtures, where the solute mole fraction of Ca(NO3)2, x{Ca(NO3)2}, was varied between 0 and 0.25. The maximum boiling temperature found for the NaCl + KNO3 + H2O system is ≈134.9 ∘C; for the NaNO3 + KNO3 + H2O system is ≈165.1 ∘C at x(NaNO3) ≈ 0.46 and x(KNO3) ≈ 0.54; and for the NaCl + Ca(NO3)2 + H2O system is 164.7 ± 0.6 ∘C at x{NaCl} ≈ 0.25 and x{Ca(NO3)2} ≈ 0.75. The NaCl + NaNO3 + KNO3 + Ca(NO3)2 + H2O system forms molten salts below their maximum boiling temperatures and the temperatures corresponding to the cessation of boiling (dry-out temperatures) of these liquid mixtures were determined. These dry-out temperatures range from ≈300 ∘C when x{Ca(NO3)2} = 0 to ≥ 400 ∘C when x{Ca(NO3)2} = 0.20 and 0.25. Mutual deliquescence/efflorescence relative humidity (MDRH/MERH) measurements were also made for the NaNO3 + KNO3 and NaCl + NaNO3 + KNO3 salt mixture from 120 to 180 ∘C at ambient pressure. The NaNO3 + KNO3 salt mixture has a MDRH of 26.4% at 120 ∘C and 20.0% at 150 ∘C. This salt mixture also absorbs water at 180 ∘C, which is higher than expected from the boiling temperature experiments. The NaCl + NaNO3 + KNO3 salt mixture was found to have a MDRH of 25.9% at 120 ∘C and 10.5% at 180 ∘C. The investigated mixture compositions correspond to some of the major mineral assemblages that are predicted to control brine composition due to the deliquescence of salts formed in dust deposited on waste canisters in the proposed nuclear repository at Yucca Mountain, Nevada. 相似文献
53.
54.
In order to detect histamine receptors on the surface of human peripheral blood mononuclear cells, the cells were incubated in the presence of radiolabelled histamine and then the bifunctional crosslinker disuccimidyl suberate was added in various concentrations. They were then solubilized with sodium dodecyl sulphate, boiled, reduced and the lysate separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both 3H and 125I-radiolabelled ligands bound to a 16 kDa band, to be defined although a much clearer and obviously unequivocal signal was obtained with 3H-labelled histamine. This molecule migrated with the same mass on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 16 kDa subunit which had been purified on a histamine affinity column from Triton X-100 solubilized mononuclear cells, indicating it to be the ligand-binding subunit for the histamine receptor on these cells. For 3H, fluorography with Entensify was required to obtain an autoradiographic signal. Although 3H took much longer to give a signal than 125I, the considerable background, artefacts and heavy lane trailing seen with [125I] histamine were completely abrogated when [3H]histamine was used. In addition, the distinction between specific and nonspecific binding was more clearly seen using [3H]histamine. The modifications reported here which improve signal detection for 3H should encourage the use of tritiated ligands in radioreceptor crosslinking, particularly those of low molecular weight which might otherwise undergo steric modification due to iodination, this having the potential for interfering with receptor ligand binding. 相似文献
55.
Samir B. Hanna Rita Hessley William H. Webb William R. Carroll 《Fresenius' Journal of Analytical Chemistry》1971,255(1):30-32
Summary The rates of oxidation of four chelating agents, NTA, EDTA, CDTA, and DTPA with Ce(IV), in sulfuric acid media, were determined spectrophotometrically by a stopped-flow technique. The reductive ability is in the order CDTA > EDTA > DTPA > NTA. The influence of varying the acidity of the medium was studied, and in each case a maximum in the rate constant vs. [H+] plot was observed. A possible interpretation of the reactivities and the influence of acidity is advanced.
Part I: Z. Anal. Chem. 246, 231 (1969). 相似文献
Oxydative Decarboxylierung von PolyaminocarbonsäurenII. Vergleichende kinetische Untersuchung der Oxydation von NTA, ÄDTA, CDTA und DTPA mit Ce(IV) in saurer Lösung
Zusammenfassung Die Oxydationsgeschwindigkeiten von 4 Chelaten (NTA, ÄDTA, CDTA und DTPA) mit Ce(IV) in saurer Lösung wurden spektrophotometrisch mit Hilfe der stopped-flow-Technik bestimmt. Die Reduzierfähigkeit nimmt in der Reihenfolge CDTA > ÄDTA > DTPA > NTA ab. Der Einfluß verschiedener Säuregehalte in der Lösung wurde untersucht, und in jedem Fall wurde ein Maximum in der graphischen Darstellung der Geschwindigkeitskonstante gegen [H+] beobachtet. Eine mögliche Erklärung des Reaktionsvermögens und des Säureeinflusses wird gegeben.
Part I: Z. Anal. Chem. 246, 231 (1969). 相似文献
56.
Palumbo A. V. Strong-Gunderson J. M. Carroll S. 《Applied biochemistry and biotechnology》1997,(1):789-796
To determine if compounds added during trichloroethylene (TCE) degradation could reduce the loss of enzyme activity or increase
enzyme recovery, different compounds serving as energy and carbon sources, pH buffers, or free radical scavengers were tested.
Formate and formic acid (reducing power and a carbon source), as well as ascorbic acid and citric acid (free radical scavengers)
were added during TCE degradation at a concentration of 2 mM. A saturated solution of calcium carbonate was also tested to
address pH concerns. In the presence of formate and methane, only calcium carbonate and formic acid had a beneficial effect
on enzyme recovery. The calcium carbonate and formic acid both reduced the loss of enzyme activity and resulted in the highest
levels of enzyme activity after recovery. 相似文献
57.
58.
Gerald A. Miller Anthony W. Thomas Jonathan D. Carroll Johann Rafelski 《Few-Body Systems》2012,52(3-4):357-366
The existence and importance of the proton radius puzzle, observed via a Lamb shift measurement in muonic atoms, is discussed. Possible resolutions of the puzzle are discussed. Then the broader question of the meaning of the proton radius is addressed and examples of correctly defined charge densities are presented. 相似文献
59.
Abstract Atmospheric pressure ionization (API) mass spectrometry is a novel form of mass spectrometry in which the ionization process is carried out in a reaction chamber external to the mass analyzer region. The mass analyzer serves as a device to detect positive or negative ions present in the reaction chamber, which is maintained at atmospheric pressure. 相似文献
60.