全文获取类型
收费全文 | 406篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 227篇 |
晶体学 | 2篇 |
力学 | 40篇 |
数学 | 21篇 |
物理学 | 131篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 17篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 28篇 |
2012年 | 16篇 |
2011年 | 23篇 |
2010年 | 16篇 |
2009年 | 8篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 21篇 |
2004年 | 10篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1966年 | 2篇 |
1935年 | 2篇 |
1934年 | 2篇 |
排序方式: 共有421条查询结果,搜索用时 15 毫秒
111.
Seltzer SJ Michalak DJ Donaldson MH Balabas MV Barber SK Bernasek SL Bouchiat MA Hexemer A Hibberd AM Kimball DF Jaye C Karaulanov T Narducci FA Rangwala SA Robinson HG Shmakov AK Voronov DL Yashchuk VV Pines A Budker D 《The Journal of chemical physics》2010,133(14):144703
Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10?000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials. 相似文献
112.
Barberá J Cavero E Lehmann M Serrano JL Sierra T Vázquez JT 《Journal of the American Chemical Society》2003,125(15):4527-4533
The present report undertakes a challenge of general interest in supramolecular chemistry: the achievement of helical organizations with controlled structure. To achieve this target we considered the possibility of inducing supramolecular chirality using molecules that were designed to organize into columnar mesophases. The use of oxazoline-derived ligands and metal coordination served as tools to prepare molecules with a phasmidic-like structure, which show columnar organization in the liquid crystalline state. To ensure the formation of chiral mesophases, these complexes bear stereogenic centers in the rigid coordination environment of the metal. X-ray and circular dichroism experiments have revealed that chirality transfer does indeed take place from the chiral molecule to the columnar liquid crystal organization. This chiral columnar organization appears as a helix consisting of stacks of molecules that rotate with respect to one another along the column while maintaining their mean planes parallel to each other. In fact, it has been concluded that packing of these polycatenar molecules must be more efficient upon rotation of a molecule with respect to the adjacent one along the column. Furthermore, the same type of helical supraorganization has been found to be present in the mesophase of the racemic mixture and the mixture of diastereomers prepared from the racemic ligand. In this case, segregation of the optical isomers is proposed to occur to give rise to both types of helix (right-handed and left-handed). 相似文献
113.
Barber J Hooks DE Funk DJ Averitt RD Taylor AJ Babikov D 《The journal of physical chemistry. A》2005,109(15):3501-3505
Survey spectra of single-crystal HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and PETN (pentaerythritol tetranitrate) were acquired in the region from 10 to 80 cm(-1) using terahertz time-domain spectroscopy. The spectra were taken at temperatures ranging from 8.4 to 300 K. Generally, the spectra show multiple absorption peaks in the range 50-80 cm(-1), with PETN (110) showing strong absorption features at room temperature. RDX (210) is the most notable in the region 10-40 cm(-1), showing multiple spectral features, while HMX (010) shows a very broad absorption at 47.8 cm(-1) with a fwhm of 37.3 cm(-1). Future plans include polarization-dependent investigations for multiple crystallographic orientations over an increased spectral range and higher-level theoretical calculations. 相似文献
114.
[3H]-Catecholamine binding to intact cells, isolated cell membranes, and to several isolated macromolecules has been shown by several laboratories to be neither stereospecific nor inhibited by known beta-antagonists. Since additional evidence indicates that this binding is not an artifact (i.e. due neither to the binding of a catecholamine oxidation product nor hormone binding to a catabolic enzyme such as COMT), the question remains as to whether this represents binding to a bona fide membrane receptor. Because all ligands which bind strongly or compete for this binding possess a catechol group, one possible explanation is that the binding affinity is primarily determined by the catechol moiety, whereas the correct stereoisomer of the side chain is necessary to activate the receptor. Thus, although binding is a necessary condition for hormone action, the necessary and sufficient condition for activation of adenyl cyclase is both the catechol group and the correct stereoisomer of the side chain. A theoretical model is developed here to provide a quantitative basis for this hypothesis. This model extends the current concept of distinct subunits in the adenyl cyclase system by separating the receptors from the catalytic sites and placing them at separate locations within the membrane. Utilizing the spare receptor model of Furchgott, and the mobility of macromolecules within a "lipid sea," the appropriate equations to predict both hormone binding and enzyme activation are derived. Using the observed affinity constants from catecholamine binding studies, it is then shown that this model can predict the experimental observation and hence explain the apparent dichotomy arising from binding enzyme activation studies. 相似文献
115.
Victor I. Boev Alexei Soloviev Carlos J. R. Silva Maria J. M. Gomes David J. Barber 《Journal of Sol-Gel Science and Technology》2007,41(3):223-229
Optically clear and elastic organic-inorganic hybrid materials were synthesized by hydrolysis and condensation of ureasilicate
precursors. Ammonia or citric acid was used as a catalyst for hydrolysis and condensation reactions. The influence of the
catalyst nature and the precursor content on the optical, mechanical and thermal properties of samples was investigated. It
was shown that it is possible to significantly change the elastic properties of the ureasilicates keeping their good optical
transparency in the visible range. The preparation conditions assuring long-term optical and mechanical stability of the samples
were determined. 相似文献
116.
María del Mar Cordero-Rando Manuel Barea-Zamora Juan M. Barberá-Salvador Ignacio Naranjo-Rodríguez Juan A. Muñoz-Leyva José L. Hidalgo-Hidalgo de Cisneros 《Mikrochimica acta》1999,132(1):7-11
A zeolite-modified carbon paste electrode (CPE) has been used for the determination of 4-nitrophenol by differential pulse
voltammetry (DPV). The electrochemical reduction of 4-nitrophenol at −1.0 V is carried out in a Britton-Robinson medium at
pH 3.5. The cyclic voltammetric (CV) behaviour has been investigated to study the nature of the process. Studies on the effect
of pH were carried out over the pH range 2–9 with the Britton-Robinson buffer solution, and the influence of pH on peak height
and peak potential was analyzed. A linear relationship between peak intensity and concentration is obtained in the range 0.2–10 mg L−1, with a detection limit of 0.04 mg L−1; a relative standard deviation of 1.5% for a 5 mg L−1 4-nitrophenol concentration and a relative error of 2.6% were also obtained (n=11).
Received March 3, 1998. Revision December 10, 1998. 相似文献
117.
Peter Williams R. C. Barber K. S. Sharma H. E. Duckworth 《Journal of the American Society for Mass Spectrometry》1995,6(12):1243-1246
A critical discussion is given of the suggestion by Dougherty et al. (J. Am. Soc. Mass Spectrom.1994, 5, 120) that the 12C60 molecule replace the 12C atom as the primary standard of atomic mass. Adoption of the proposed standard would require that the unified atomic weight/mass scale, finally achieved with much difficulty in 1960, be abandoned without demonstrable benefit. Furthermore, the proposed standard has a molecular mass that is inherently ambiguous at a level that makes it unacceptable for that purpose. 相似文献
118.
Jon Kadish J.R. Barber P.D. Washabaugh D.J. Scheeres 《International Journal of Solids and Structures》2008,45(2):540-550
An explicit analytical solution is obtained for the stress field in an accreted triaxial ellipsoid under the influence of self-gravitation and rotation. Material is assumed to attach to the surface of the accreting body in a stress-free state, after which it behaves elastically. The results differ significantly from the classical elasticity solutions that are based on the assumption that the body is fully formed before the loading is applied. These results are relevant to the strengths of accreted planetary bodies such as comets and asteroids.The solution allows both the magnitude and direction of the angular velocity to be a general function of the time-like parameter defining the progress of accretion. Simple closed-form expressions are given for two special cases—the ellipsoid accreting at constant angular velocity and the sphere accreting with an angular velocity vector that precesses through 90° during the accretion process. A Mathematica notebook permitting the solution of other problems can be downloaded from the website http://www-personal.umich.edu/jbarber/ellipsoid.nb. 相似文献
119.
D. Dini J.R. Barber C.M. Churchman A. Sackfield D.A. Hills 《European Journal of Mechanics - A/Solids》2008,27(5):847-858
We give the contact pressure distribution near a contacting wedge having a slightly rounded form adjacent to a discontinuity in surface profile. It is shown that, well away from the rounding the pressure is logarithmic in form, just as it is near the apex of a sharp wedge. This pair of solutions may then be used to ‘patch in’ a roundness correction relevant to any punch having a discontinuous gradient. Further, it is noted that the multiplier on the logarithm term is pre-determined by the change in gradient. This process is applied to a finite, slightly blunt wedge, where the exact answer is known, and to a wheel having a worn flat. The agreement with the exact solution in the former case is seen to be very good. 相似文献
120.
Michael N. Barber 《Physics Reports》1980,59(4):375-409
Recent developments - both theoretical and experimental - in the understanding of phase transitions in two-dimensional systems are reviewed. Topics discussed include the classification and characterization of order/disorder transitions in adsorbed monolayers, the breakdown of universality, superfluidity in helium films and the critical behaviour of the two-dimensional XY model, Abelian and non-Abelian symmetry and the analogies between the theory of phase transitions in two dimensions and quantum field theory, especially quark confinement, in four-dimensional space time. 相似文献