全文获取类型
收费全文 | 705篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 401篇 |
晶体学 | 1篇 |
力学 | 10篇 |
数学 | 52篇 |
物理学 | 250篇 |
出版年
2020年 | 5篇 |
2019年 | 5篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 21篇 |
2011年 | 25篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 12篇 |
2002年 | 22篇 |
2001年 | 21篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 15篇 |
1972年 | 6篇 |
1969年 | 5篇 |
1968年 | 5篇 |
1894年 | 5篇 |
排序方式: 共有714条查询结果,搜索用时 15 毫秒
31.
A. Hinz J. S. Wells A. G. Maki 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,5(4):351-358
Heterodyne frequency measurements are reported for absorption transitions of N2O in the frequency range from 1257 to 1335 cm?1. The measurements use a CO laser as a transfer oscillator whose frequency is measured directly against combinations of frequencies of two stabilized CO2 lasers whose frequencies are well known. A tunable diode laser is locked to the N2O absorption feature and the frequency difference is measured between the diode laser and the CO laser. Thev 3 fundamental bands of the15N14N16O and14N15N16O isotopes are reported. Measurements are also given for the 0002–0001, 0201–0200, and 0221–0220 vibrational transitions of N2O. A table of frequencies is given for the 0002–0000 band near 2560 cm?1 based on these and earlier measurements. 相似文献
32.
Claude Delseth Luhata Tolela Carl Djerassi Paul J. Scheuer Robert J. Wells 《Helvetica chimica acta》1979,62(1):101-109
The steroidal components of 2 marine sponges, Terpios zeteki (from Hawaii) and Dysidea herbacea (from Australia) were fractionated through a combination of chromatographic methods, including reversed phase HPLC., and were analyzed by a combination of physical methods, including high resolution GC.-MS. and 360 MHz 1H-NMR. T. zeteki contains 6 conventional 5α-stanols which comprise 91% of the sterol mixture, and traces (0.5%) of a new C26 sterol, 5α-24-norcholestan-3β-ol. Minor amounts of conventional Δ5-sterols (6.5%) and of a single Δ4-3-ketosteroid (1.5%) were also present. In contrast, the Australian sponge (D. herbacea) contains 3 Δ5,7-sterols which comprise 1.5% of the sterol mixture, and one new C29 sterol, (24 Z)-stigmasta-5,7,24(28)-trien-3β-ol, as the major component (75%). In addition, minor amounts of conventional 5α-stanols (0.5%), Δ5-sterols (5%) and 5α-Δ7-sterols (18%) were present in this complex sterol mixture. The possible dietary or endosymbiotic origins of these sterols are discussed. 相似文献
33.
Chevreux G Potier N Van Dorsselaer A Bahloul A Houdusse A Wells A Sweeney HL 《Journal of the American Society for Mass Spectrometry》2005,16(8):1367-1376
Among the myosin superfamily, myosin VI differs from all others by a reverse directionality and a particular motility. Little structural information is available for myosin VI. It is known that it binds one calmodulin (CaM) by means of a single "IQ motif" and that myosin VI contains a specific insert located at the junction between the motor domain (MD) and the lever arm, likely to play a critical role for the unusual motility previously observed. Electrospray ionization mass spectrometry (MS) was used to determine the CaM and Ca2+ stoichiometries in several myosin VI constructs. In particular, the experimental conditions required for the observation of multiprotein/Ca2+ noncovalent assemblies are detailed for two truncated MD constructs (less than 20 kDa) and for three full MD constructs (more than 90 KDa). The specificity of the detected stoichiometries is discussed for each construct and the resolving power of Time of Flight mass spectrometry is stressed, in particular for the detection of metal ions binding to high molecular weight complexes. MS reveals a new CaM binding site for myosin VI and highlights a different behavior for the five myosin VI constructs versus Ca2+ binding. In addition to these stoichiometry based experiments, gas-phase dissociation analyses on intact complexes are described. They reveal that Ca2+ transfer between protein partners occurs during the dissociation process for one construct with a full MD. Charge-transfer and dissociation behavior has allowed to draw structural assumptions for the interaction of the MD with the CaM N-terminal lobe. 相似文献
34.
Teixeira-Neto É Leite CA Cardoso AH Medeiros da Silva MC Braga M Galembeck F 《Journal of colloid and interface science》2000,231(1):182-189
Poly(styrene-co-acrylamide) (PS-AAM) latex was prepared, fractionated by sedimentation under gravity, and characterized by PCS, infrared spectra, secondary and backscattered electron imaging in the scanning electron microscope, and electron spectroscopy imaging in an analytical transmission electron microscope. Three latex fractions were obtained. The lower fraction was opalescent and its particles were the more uniform, concerning size, chemical composition, and topochemical features. This lower fraction was still further fractionated by zonal centrifugation in a density gradient, yielding two fractions with similar macrocrystal-forming abilities but different sizes and chemical compositions. These results confirm those previously obtained for the PS-HEMA latex. Copyright 2000 Academic Press. 相似文献
35.
Hexamethylditin in methanol solution reacts rapidly with mercuric chloride to yield mercury and trimethyltin chloride. With alkylmercuric salts the reaction is complex, yielding tetraalkyltin and/or dialkylmercury, depending upon the reactivity of the alkylmercuric salt. An electrophilic substitution mechanism involving trimethylstannyl mercurials as transient intermediates is suggested. The reaction of hexaalkylditin with diarylmercury is suggested to follow a homolyric pathway. 相似文献
36.
37.
38.
39.
40.