全文获取类型
收费全文 | 210717篇 |
免费 | 2264篇 |
国内免费 | 725篇 |
专业分类
化学 | 118758篇 |
晶体学 | 3384篇 |
力学 | 8118篇 |
综合类 | 4篇 |
数学 | 21165篇 |
物理学 | 62277篇 |
出版年
2016年 | 2542篇 |
2015年 | 1976篇 |
2014年 | 2685篇 |
2013年 | 8484篇 |
2012年 | 5925篇 |
2011年 | 7504篇 |
2010年 | 4878篇 |
2009年 | 4758篇 |
2008年 | 6793篇 |
2007年 | 6975篇 |
2006年 | 6743篇 |
2005年 | 6317篇 |
2004年 | 5749篇 |
2003年 | 5097篇 |
2002年 | 4904篇 |
2001年 | 5967篇 |
2000年 | 4577篇 |
1999年 | 3678篇 |
1998年 | 2910篇 |
1997年 | 2979篇 |
1996年 | 2977篇 |
1995年 | 2692篇 |
1994年 | 2557篇 |
1993年 | 2440篇 |
1992年 | 2941篇 |
1991年 | 2811篇 |
1990年 | 2754篇 |
1989年 | 2767篇 |
1988年 | 2714篇 |
1987年 | 2741篇 |
1986年 | 2515篇 |
1985年 | 3519篇 |
1984年 | 3498篇 |
1983年 | 2881篇 |
1982年 | 3149篇 |
1981年 | 3033篇 |
1980年 | 2993篇 |
1979年 | 3098篇 |
1978年 | 3340篇 |
1977年 | 3166篇 |
1976年 | 3076篇 |
1975年 | 2906篇 |
1974年 | 2847篇 |
1973年 | 2863篇 |
1972年 | 1823篇 |
1971年 | 1539篇 |
1968年 | 1961篇 |
1967年 | 2156篇 |
1966年 | 1952篇 |
1965年 | 1520篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Richard Kissling 《Fresenius' Journal of Analytical Chemistry》1885,24(1):64-65
Ohne Zusammenfassung 相似文献
62.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
63.
G.P. Romanelli D. Bennardi D.M. Ruiz G. Baronetti H.J. Thomas 《Tetrahedron letters》2004,45(48):8935-8939
Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H6P2W18O62·24H2O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). 相似文献
64.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
65.
Guido Wauters Jacques Dewaele Carlo Vandecasteele Richard Dams 《Mikrochimica acta》1989,98(4-6):157-162
Proton activation analysis was used for the determination of cadmium and lead in three sediment reference materials. The method is based on the111,112Cd(p, xn)111 In and the206,207,208Pb(p, xn)206Bi reactions.111In and206Bi were chemically separated by anion exchange. The results obtained were taken into account for the certification of the materials and are in the excellent agreement with the certified values. 相似文献
66.
67.
Network survivability analysis 总被引:1,自引:0,他引:1
Richard R. Talbott 《Fiber and Integrated Optics》1989,8(1):13-43
Advances in fiber optic and local area network (LAN) technologies are providing system designers with many new options for interconnecting computer equipment. A recurring problem for military system designers, who are end-users of a LAN standard, is implementing LANs so that the survivability, reliability, maintainability, and availability (SRMA) of a system is maximized. LAN standards working groups are currently making design decisions about topologies, components, and protocols that directly affect the SRMA of the end-user's system. This article focuses on a new analytic technique, called “network survivability analysis,” that provides the mathematical tools needed to compare the survivability of arbitrary network topologies. For background, several network metrics are described and their limitations for LAN standards development identified. Network survivability is defined, and several token-passing ring case examples are analyzed. The primary strength of network survivability analysis is that it can be used to provide a quantitative comparison among LAN topologies without knowledge of the end-user's equipment, systems, or environments. 相似文献
68.
Summary Using a saturated non-boiling hydrocarbon mixture, the influence of two parameters on the results of field ionization mass spectrometry (FI-MS) measurements was studied: (a) the potential difference between the FI emitter and the counterelectrode; (b) the emitter temperature.Variation of the potential difference had only a minor effect on the average molecular mass measured and had no evident effect on the relative ring number distribution in the sample. In contrast, when the emitter temperature was increased, higher average molecular masses were recorded. Moreover, the average molecular masses shifted to higher ring numbers. In order to control the relationship between the described influences during mixture analysis, measuring instructions have been developed that enable the quantitative analysis of unknown saturated samples. However, average molecular mass of the mixture must be known.
Entwicklung einer quantitativen FI-MS-Methode zur Charakterisierung von gesättigten hoch- und nichtsiedenden Kohlenwasserstoffgemischen相似文献
69.
Blood serum samples were irradiated by monochromatic synchrotron radiation (15 keV) and by 2.4-MeV protons to compare their performance for the detection of trace elements by x-ray fluorescence (XRF) spectrometry. Absolute concentration assignment was based on the addition of an internal standard and on a method which uses the incoherent and coherent radiation as a flux monitor of the incoming beam. Preliminary experiments with a synchrotron XRF microprobe are reported. 相似文献
70.