全文获取类型
收费全文 | 204篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 102篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 42篇 |
物理学 | 63篇 |
出版年
2020年 | 4篇 |
2016年 | 2篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 7篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1998年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1968年 | 4篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1962年 | 2篇 |
1912年 | 1篇 |
1907年 | 2篇 |
1905年 | 2篇 |
1898年 | 1篇 |
排序方式: 共有210条查询结果,搜索用时 0 毫秒
161.
162.
Brand MA Malinowski A Karimov OZ Marsden PA Harley RT Shields AJ Sanvitto D Ritchie DA Simmons MY 《Physical review letters》2002,89(23):236601
Optical spin-dynamic measurements in a high-mobility n-doped GaAs/AlGaAs quantum well show oscillatory evolution at 1.8 K consistent with a quasi-collision-free D'yakonov-Perel'-Kachorovskii regime. Above 5 K evolution becomes exponential as expected for collision-dominated spin dynamics. Momentum scattering times extracted from Hall mobility and Monte Carlo simulation of spin polarization agree at 1.8 K but diverge at higher temperatures, indicating the importance of electron-electron scattering and an intrinsic upper limit for the spin-relaxation rate. 相似文献
163.
164.
The GAUSSIAN 2, GAUSSIAN 3, complete basis set-QB3, and complete basis set-APNO methods have been used to calculate DeltaH( composite function) and DeltaG( composite function) values for ionic clusters of hydronium and hydroxide ions complexed with water. Results for the clusters H3O+(H2O)n and OH-(H2O)n, where n=1-4 are reported in this paper, and compared against experimental values contained in the National Institutes of Standards and Technology (NIST) database. Agreement with experiment is excellent for the three ab initio methods for formation of these clusters. The high accuracy of these methods makes them reliable for calculating energetics for the formation of ionic clusters containing water. In addition this allows them to serve as a valuable check on the accuracy of experimental data reported in the NIST database, and makes them useful tools for addressing unresolved issues in atmospheric chemistry. 相似文献
165.
G. C. Shields P. A. Steiner P. R. Nelson M. C. Trauner T. F. Moran 《Journal of mass spectrometry : JMS》1987,22(2):64-69
Cross sections for charge transfer reactions of organic ions containing oxygen have been obtained using time-of-flight techniques. Charge transfer cross sections have been determined for reactions of 2.0 to 3.4 keV ions produced by electron impact ionization of oxygen containing molecules such as methanol, ethanal and ethanol. Experimental cross section magnitudes have been correlated with reaction energy defects computed from ion recombination energies and target ionization energies. Large cross sections are observed for reacting systems with small energy defects. 相似文献
166.
The Gaussian-2, Gaussian-3, complete basis set- (CBS-) QB3, and CBS-APNO methods have been used to calculate Delta H degrees and Delta G degrees values for neutral clusters of water, (H(2)O)(n), where n = 2-6. The structures are similar to those determined from experiment and from previous high-level calculations. The thermodynamic calculations by the G2, G3, and CBS-APNO methods compare well against the estimated MP2(CBS) limit. The cyclic pentamer and hexamer structures release the most heat per hydrogen bond formed of any of the clusters. While the cage and prism forms of the hexamer are the lowest energy structures at very low temperatures, as temperature is increased the cyclic structure is favored. The free energies of cluster formation at different temperatures reveal interesting insights, the most striking being that the cyclic trimer, cyclic tetramer, and cyclic pentamer, like the dimer, should be detectable in the lower troposphere. We predict water dimer concentrations of 9 x 10(14) molecules/cm(3), water trimer concentrations of 2.6 x 10(12) molecules/cm(3), tetramer concentrations of approximately 5.8 x 10(11) molecules/cm(3), and pentamer concentrations of approximately 3.5 x 10(10) molecules/cm(3) in saturated air at 298 K. These results have important implications for understanding the gas-phase chemistry of the lower troposphere. 相似文献
167.
Complete Basis Set and Gaussian-n methods were combined with CPCM continuum solvation methods to calculate pK(a) values for six carboxylic acids. An experimental value of -264.61 kcal/mol for the free energy of solvation of H(+), DeltaG(s)(H(+)), was combined with a value for G(gas)(H(+)) of -6.28 kcal/mol to calculate pK(a) values with Cycle 1. The Complete Basis Set gas-phase methods used to calculate gas-phase free energies are very accurate, with mean unsigned errors of 0.3 kcal/mol and standard deviations of 0.4 kcal/mol. The CPCM solvation calculations used to calculate condensed-phase free energies are slightly less accurate than the gas-phase models, and the best method has a mean unsigned error and standard deviation of 0.4 and 0.5 kcal/mol, respectively. The use of Cycle 1 and the Complete Basis Set models combined with the CPCM solvation methods yielded pK(a) values accurate to less than half a pK(a) unit. 相似文献
168.
G. C. Shields L. Wennberg J. B. Wilcox T. F. Moran 《Journal of mass spectrometry : JMS》1986,21(3):137-149
Charge transfer reactivities of hydrocarbon ions have been measured with time-of-flight techniques, and results correlated with theoretical structures computed by self-consistent field molecular orbital methods. Recombination energies, ion structures, heats of formation, reaction energetics and relative charge transfer cross-sections are presented for molecular and fragment ions produced by electron bombardment ionization of CH4, C2H4, C2H6, C3H8 and C4H10 molecules. Even-electron bridged cations have low ion recombination energies and relatively low charge transfer cross-sections as compared with odd-electron hydrocarbon cations. 相似文献
169.
Dowling P Shields W Rani S Meleady P Henry M Jeppesen P O'Driscoll L Clynes M 《Electrophoresis》2008,29(20):4141-4149
Media conditioned by dysfunctioning pancreatic beta cells offer an excellent source of potential protein markers associated with this phenotype. Proteins identified from cell culture model systems are often found to be of importance clinically. Previous work by us and others have shown that low-passage MIN-6 cells (MIN-6(L)) respond to changes in glucose concentrations, producing an approximately 5.5-fold glucose-stimulated insulin secretion (GSIS) in response to 26.7 mmol/L, compared with 3.3 mmol/L, glucose. After continuous culture or high-passage (MIN-(H)), this GSIS was no longer present and thus represents an excellent model system for investigating beta cell dysfunction. Employing 2-D difference gel electrophoresis and mass spectrometry a panel of protein markers were identified in conditioned media (CM) from MIN-6(L) and MIN-6(H) beta cells. These proteins, including secretogranin II, secretogranin III and transthyretin, are associated with secretory granule biogenesis and were found to have substantially increased levels in the CM from the non-responsive high-passage MIN-6 beta cells. A panel of protein markers found to have increased abundance levels in CM from MIN-6(H) compared with MIN-6(L) beta cells may have the potential to be used clinically for assessing beta cell function and to monitor the effects of specific therapeutics. 相似文献
170.
Lunkenheimer ES Hollenstein T Wang J Shields AM 《Nonlinear dynamics, psychology, and life sciences》2012,16(3):269-291
Familial emotion socialization practices relate to children's emotion regulation (ER) skills in late childhood, however, we have more to learn about how the context and structure of these interactions relates to individual differences in children's ER. The present study examined flexibility and attractors in family emotion socialization patterns in three different conversational contexts and their relation to ER in 8-12 year olds. Flexibility was defined as dispersion across the repertoire of discrete emotion words and emotion socialization functions (emotion coaching, dismissing, and elaboration) in family conversation, whereas attractors were defined as the average duration per visit to each of these three emotion socialization functions using state space grid analysis. It was hypothesized that higher levels of flexibility in emotion socialization would buffer children's ER from the presence of maladaptive attractors, or the absence of adaptive attractors, in family emotion conversation. Flexibility was generally adaptive, related to children's higher ER across all contexts, and also buffered children from maladaptive attractors in select situations. Findings suggest that the study of dynamic interaction patterns in context may reveal adaptive versus maladaptive socialization processes in the family that can inform basic and applied research on children's regulatory problems. 相似文献