全文获取类型
收费全文 | 109686篇 |
免费 | 6514篇 |
国内免费 | 5518篇 |
专业分类
化学 | 47348篇 |
晶体学 | 1271篇 |
力学 | 8695篇 |
综合类 | 452篇 |
数学 | 35445篇 |
物理学 | 28507篇 |
出版年
2024年 | 101篇 |
2023年 | 614篇 |
2022年 | 1165篇 |
2021年 | 1253篇 |
2020年 | 1458篇 |
2019年 | 1413篇 |
2018年 | 11417篇 |
2017年 | 11224篇 |
2016年 | 7570篇 |
2015年 | 2547篇 |
2014年 | 2352篇 |
2013年 | 2860篇 |
2012年 | 6830篇 |
2011年 | 13494篇 |
2010年 | 7869篇 |
2009年 | 8254篇 |
2008年 | 8988篇 |
2007年 | 10768篇 |
2006年 | 2159篇 |
2005年 | 2899篇 |
2004年 | 2834篇 |
2003年 | 2969篇 |
2002年 | 2028篇 |
2001年 | 1122篇 |
2000年 | 993篇 |
1999年 | 772篇 |
1998年 | 656篇 |
1997年 | 582篇 |
1996年 | 591篇 |
1995年 | 439篇 |
1994年 | 390篇 |
1993年 | 316篇 |
1992年 | 231篇 |
1991年 | 248篇 |
1990年 | 214篇 |
1989年 | 172篇 |
1988年 | 163篇 |
1987年 | 138篇 |
1986年 | 124篇 |
1985年 | 103篇 |
1984年 | 91篇 |
1983年 | 79篇 |
1982年 | 79篇 |
1981年 | 64篇 |
1980年 | 63篇 |
1979年 | 52篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Cun Feng Fan David A. Waldman Shaw Ling Hsu 《Journal of Polymer Science.Polymer Physics》1991,29(2):235-246
Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface. 相似文献
52.
53.
CLIFFORDMARTINGALESΦ-EQUIVALENCEBETWEENS(f)ANDf¥LONGRULIN;QIANTAO(InstituteofMathematics,AcademiaSinica,Beijing100080,China.)... 相似文献
54.
A well-known problem of prediction in linear regression models is to find a confidence interval for the random value of the dependent variable when the values of the independent variables are given. Such a situation may arise in economic quality control models when the independent variables are costly inputs and the dependent variable is some measure of quality or production. In such a circumstance, an important control objective may be to find values for the inputs that will maximize the lower limit of the prediction confidence interval for a fixed budget, or alternatively, to minimize the cost of the inputs for a fixed lower limit of the confidence interval. In this paper, we shall show that global optima can be found using known algorithms. The special case of simple linear regression is discussed and an illustrative example is provided. 相似文献
55.
Yasunari Nagai 《manuscripta mathematica》2003,110(3):273-282
We give a characterization of irreducible symplectic fourfolds which are given as Hilbert scheme of points on a K3 surface.
Received: 26 June 2002 / Revised version: 9 September 2002 Published online: 14 February 2003
Mathematics Subject Classification (2000): Primary 14J32, Secondary 32Q20 相似文献
56.
57.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
58.
59.
60.
A group of machines for processing a set of jobs in a manufacturing system is often located in a serial line. An efficient strategy for locating these machines such that the total travel distance or the cost of transporting the jobs is minimized is desired. In this research, the assumption of a linear line with equally spaced machine location is relaxed. This research addressed problems of locating unique machines. It is found that the machine distances possess unique properties in this type of a problem. Utilizing these properties, heuristic strategies are proposed to obtain efficient solution where optimal methods are expected to be computationally prohibitive. A lower bound for the optimum solution is also proposed. Results are encouraging. 相似文献