全文获取类型
收费全文 | 218434篇 |
免费 | 2385篇 |
国内免费 | 765篇 |
专业分类
化学 | 123350篇 |
晶体学 | 3490篇 |
力学 | 8406篇 |
综合类 | 5篇 |
数学 | 22556篇 |
物理学 | 63777篇 |
出版年
2016年 | 2681篇 |
2015年 | 2003篇 |
2014年 | 2807篇 |
2013年 | 9052篇 |
2012年 | 6316篇 |
2011年 | 7964篇 |
2010年 | 5115篇 |
2009年 | 4935篇 |
2008年 | 7227篇 |
2007年 | 7441篇 |
2006年 | 7162篇 |
2005年 | 6657篇 |
2004年 | 6057篇 |
2003年 | 5364篇 |
2002年 | 5205篇 |
2001年 | 6104篇 |
2000年 | 4665篇 |
1999年 | 3734篇 |
1998年 | 3002篇 |
1997年 | 3066篇 |
1996年 | 3069篇 |
1995年 | 2776篇 |
1994年 | 2647篇 |
1993年 | 2551篇 |
1992年 | 3024篇 |
1991年 | 2885篇 |
1990年 | 2817篇 |
1989年 | 2847篇 |
1988年 | 2818篇 |
1987年 | 2815篇 |
1986年 | 2617篇 |
1985年 | 3617篇 |
1984年 | 3680篇 |
1983年 | 3013篇 |
1982年 | 3291篇 |
1981年 | 3207篇 |
1980年 | 3065篇 |
1979年 | 3190篇 |
1978年 | 3449篇 |
1977年 | 3249篇 |
1976年 | 3144篇 |
1975年 | 2995篇 |
1974年 | 2937篇 |
1973年 | 2930篇 |
1972年 | 1883篇 |
1971年 | 1574篇 |
1969年 | 1526篇 |
1968年 | 2001篇 |
1967年 | 2183篇 |
1966年 | 1967篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
本文给出了在Re=50—400范围内二维圆柱后涡脱落的有序和混沌现象的一些初步实验结果。涡脱落由有序到混沌的转捩发生在Re=184.6—193.5之间,但是它不是通过准周期途径。在涡脱落频率与Re数的关系曲线上有两个间断。在Re=70处的间断可能对应于倾斜涡脱落模式的变化,在Re≈193.5处的第二间断对应于由有序到混沌状态的转捩。 相似文献
3.
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
4.
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
5.
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
6.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
7.
H. Moers H. Klewe-Nebenius G. Pfennig und H. J. Ache 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):361-366
Summary The adsorption of gaseous molecular iodine on clean silver surfaces proceeds in the first stage by dissociative chemisorption. After the formation of half a monolayer of chemisorbed iodine atoms the formation of silver iodide begins, which forms a very regular overlayer on top of the substrate. Both iodine species can be distinguished due to a difference in chemical shift of the M4N4, 5N4, 5-Auger transitions. After completion of this overlayer further iodine uptake is slowed down significantly. Above an overlayer thickness of about 10 nm a further progress of the reaction cannot be followed anymore due to the limited information depth of XPS. 相似文献
8.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 相似文献
9.
D. Amutha Rani Y. Yamamoto S. Mohri M. Sivakumar Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2003,41(3):269-273
In this study, a novel stepwise extraction method has been examined. The guest molecules housed between the helices of the clathrate δ form of syndiotactic polystyrene can be removed completely with this method. A systematic study of the preparation of a solvent‐free mesophase (emptied clathrate) membrane, its helical and residual solvent contents, and its structural transformations has been performed. In this first attempt, an enhancement in the TTGG helical content has been observed in the extracted membrane, and a conceptual mechanism is proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 269–273, 2003 相似文献
10.
R. Hefelmann P. Mann A. Aignan F. Filsinger und H. Amsel 《Fresenius' Journal of Analytical Chemistry》1902,41(1):66-68
Ohne Zusammenfassung 相似文献