全文获取类型
收费全文 | 140691篇 |
免费 | 1854篇 |
国内免费 | 469篇 |
专业分类
化学 | 77991篇 |
晶体学 | 2082篇 |
力学 | 5221篇 |
综合类 | 5篇 |
数学 | 14337篇 |
物理学 | 43378篇 |
出版年
2016年 | 1651篇 |
2015年 | 1340篇 |
2014年 | 1663篇 |
2013年 | 5428篇 |
2012年 | 4005篇 |
2011年 | 5168篇 |
2010年 | 3086篇 |
2009年 | 2856篇 |
2008年 | 4636篇 |
2007年 | 4691篇 |
2006年 | 4720篇 |
2005年 | 4542篇 |
2004年 | 3911篇 |
2003年 | 3586篇 |
2002年 | 3482篇 |
2001年 | 3891篇 |
2000年 | 2948篇 |
1999年 | 2446篇 |
1998年 | 2088篇 |
1997年 | 2071篇 |
1996年 | 2016篇 |
1995年 | 1988篇 |
1994年 | 1743篇 |
1993年 | 1766篇 |
1992年 | 1971篇 |
1991年 | 1900篇 |
1990年 | 1835篇 |
1989年 | 1856篇 |
1988年 | 1826篇 |
1987年 | 1839篇 |
1986年 | 1750篇 |
1985年 | 2351篇 |
1984年 | 2479篇 |
1983年 | 2080篇 |
1982年 | 2406篇 |
1981年 | 2221篇 |
1980年 | 2271篇 |
1979年 | 2255篇 |
1978年 | 2395篇 |
1977年 | 2292篇 |
1976年 | 2294篇 |
1975年 | 2196篇 |
1974年 | 2033篇 |
1973年 | 2232篇 |
1972年 | 1350篇 |
1971年 | 1043篇 |
1970年 | 976篇 |
1969年 | 979篇 |
1968年 | 1117篇 |
1967年 | 1188篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Fixed-frequency and threshold photoelectron spectra have been recorded for ionization from the S ls shells in SF6, CS2 and COS, the Si 1s shells in SiH4 and SiCl4 and the Cl 1s shell in SiCl4 using synchrotron radiation. Fixed-frequency spectra generally showed a single strong ionization feature with associated weak satellite structure due to excited ionized states. Threshold spectra closely resembled X-ray absorption spectra but with an additional feature due to direct ionization. In cases where resonant process enhanced the NEXAFS spectrum direct ionization was not observed. 相似文献
82.
M. Trunk J. Popp I. Hartmann M. Lankers E. Urlaub W. Kiefer 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):354-356
In situ measurements of gas-liquid surface reactions of single aerosol microdroplets are presented. By means of optical levitation in combination with elastic (Mie) and inelastic (Raman) light scattering it is possible to get information on the chemistry of e.g. acid/base reactions as well as the physical behavior of single microparticles. 相似文献
83.
H. Tietze-Jaensch D. Sieger R. Geick W. Zulehner A. de Geyer 《Applied Physics A: Materials Science & Processing》1992,54(1):19-21
The formation of silicon oxide precipitates from Czochralski grown silicon depends on the time and temperature of the heat treatment as well as on the initial content of interstitially dissolved oxygen. Samples containing between 5×1017 Oi/cm3 and 13×1017 Oi/cm3 have been heated at 750° C for 96 h. SiO2 precipitates of various shape and size have been obtained and investigated by means of small angle neutron scattering (SANS) in the Q-range 0.05 Å–1<Q<0.2 Å–1. The obtained SANS patterns reveal a typical anisotropy of their intensity distribution, which splits into a central peak at Q<0.1 Å–1 due to the shape of the individual particles and a number of weak intensities for large Q-values, originating from a correlation between defects, possibly between the precipitates. While these correlation peaks in the SANS patterns are seen best for rather low values of about (5–7)×1017 Oi/cm3 oxygen content, the central peak anisotropy is most pronounced for higher values of ca 10×1017 Oi/cm3. The integrated intensity of the central peak increases with increasing initial oxygen content. For comparison, untreated samples of the same initial oxygen content do not reveal any anisotropic SAN scattering or a broadened central peak beam. 相似文献
84.
T. B. Anders W. Jachmann A. O. Barut 《Zeitschrift fur Physik C Particles and Fields》1992,56(4):561-563
The polarization asymmetries related to usual polarizations combine at least 4 different helicity amplitudes. The introduction of ±45° inclined transverse polarizations allows us to obtain the complete set of new polarization asymmetries combining only up to 3 helicity amplitudes. There are no further polarization asymmetries depending on a smaller number of helicity amplitudes. These expressions are most economical to determine the helicity amplitudes from observed data. Some of them are suitable to study especially the spin-flip effects. We give a complete Table of all such polarization asymmetries. 相似文献
85.
In this paper we construct a primitive, non-symmetric 3-class association scheme with parameters v = 36, v1 = 7, p111 = 0 and p211 = 4 and show that such a scheme is determined by its parameters. 相似文献
86.
87.
88.
89.
Maria Marques Zhengtian Yu Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2787-2793
4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η5-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc. 相似文献
90.
J.S. Tsay H.W. Chang Y.L. Chiou K.T. Huang W.Y. Chan Y.D. Yao 《Journal of magnetism and magnetic materials》2006
Influences of oxygen exposure on the magnetic properties of Co/Ge(1 1 1) ultrathin films have been investigated by surface magneto-optic Kerr effect technique. As the oxygen exposure increases on Co/Ge(1 1 1) films, their magnetic properties could be modified. As an example for 15 ML Co/Ge(1 1 1) films, the coercivity increases from 730 to 920 Oe and the remanence Kerr intensity is reduced for 500 Langmuir (L) of oxygen exposure. Corresponding compositions analyzed by Auger electron spectroscopy measurement shows that the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. Oxygen distributes on the topmost layers of the film. The adsorbed oxygen influences the electronic density of states of Co and results in the changes of the magnetic properties. Besides, the appearance of O/Co/Ge interface could modify the stress anisotropy, and as a result the coercivity of ultrathin Co/Ge(1 1 1) film is enhanced. 相似文献