全文获取类型
收费全文 | 339381篇 |
免费 | 2700篇 |
国内免费 | 1076篇 |
专业分类
化学 | 168013篇 |
晶体学 | 5173篇 |
力学 | 17375篇 |
综合类 | 5篇 |
数学 | 56736篇 |
物理学 | 95855篇 |
出版年
2018年 | 12920篇 |
2017年 | 12790篇 |
2016年 | 10180篇 |
2015年 | 3451篇 |
2014年 | 4276篇 |
2013年 | 11092篇 |
2012年 | 11464篇 |
2011年 | 19679篇 |
2010年 | 12297篇 |
2009年 | 12553篇 |
2008年 | 14978篇 |
2007年 | 17080篇 |
2006年 | 8554篇 |
2005年 | 8787篇 |
2004年 | 8409篇 |
2003年 | 8146篇 |
2002年 | 7155篇 |
2001年 | 7943篇 |
2000年 | 6060篇 |
1999年 | 4745篇 |
1998年 | 3925篇 |
1997年 | 3821篇 |
1996年 | 3709篇 |
1995年 | 3367篇 |
1994年 | 3196篇 |
1993年 | 3113篇 |
1992年 | 3601篇 |
1991年 | 3541篇 |
1990年 | 3432篇 |
1989年 | 3503篇 |
1988年 | 3382篇 |
1987年 | 3334篇 |
1986年 | 3111篇 |
1985年 | 4095篇 |
1984年 | 4159篇 |
1983年 | 3491篇 |
1982年 | 3699篇 |
1981年 | 3531篇 |
1980年 | 3423篇 |
1979年 | 3615篇 |
1978年 | 3950篇 |
1977年 | 3804篇 |
1976年 | 3627篇 |
1975年 | 3461篇 |
1974年 | 3406篇 |
1973年 | 3426篇 |
1972年 | 2298篇 |
1968年 | 2322篇 |
1967年 | 2488篇 |
1966年 | 2187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
We initiate a program to study certain recent problems in non-compact coset CFT by the BRST approach. We derive a reduction formula for the BRST cohomology by making use of a twisting by highest weight modules. As illustrations, we apply the formula to the bosonic string model and a rank one non-compact coset model [DPL]. Our formula provides a completely new approach to non-compact coset construction.Partially supported by NSF Grant DMS-8703581 相似文献
12.
Equilibrium Problems with Applications to Eigenvalue Problems 总被引:5,自引:0,他引:5
In this paper, we consider equilibrium problems and introduce the concept of (S)+ condition for bifunctions. Existence results for equilibrium problems with the (S)+ condition are derived. As special cases, we obtain several existence results for the generalized nonlinear variational inequality studied by Ding and Tarafdar (Ref. 1) and the generalized variational inequality studied by Cubiotti and Yao (Ref. 2). Finally, applications to a class of eigenvalue problems are given. 相似文献
13.
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
14.
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
15.
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
16.
17.
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
18.
Andrew Barton 《The Journal of the Operational Research Society》1987,38(10):965-974
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area. 相似文献
19.
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
20.