全文获取类型
收费全文 | 1250篇 |
免费 | 53篇 |
国内免费 | 71篇 |
专业分类
化学 | 529篇 |
晶体学 | 12篇 |
力学 | 22篇 |
综合类 | 2篇 |
数学 | 254篇 |
物理学 | 196篇 |
综合类 | 359篇 |
出版年
2023年 | 16篇 |
2022年 | 37篇 |
2021年 | 32篇 |
2020年 | 36篇 |
2019年 | 41篇 |
2018年 | 41篇 |
2017年 | 44篇 |
2016年 | 44篇 |
2015年 | 38篇 |
2014年 | 60篇 |
2013年 | 86篇 |
2012年 | 77篇 |
2011年 | 79篇 |
2010年 | 62篇 |
2009年 | 55篇 |
2008年 | 81篇 |
2007年 | 59篇 |
2006年 | 68篇 |
2005年 | 44篇 |
2004年 | 45篇 |
2003年 | 33篇 |
2002年 | 22篇 |
2001年 | 28篇 |
2000年 | 27篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1985年 | 6篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1374条查询结果,搜索用时 531 毫秒
1.
2.
Andr Luciani Christopher J. G. Plummer Tuan Nguyen Lszl Garamszegi Jan‐Anders E. Mnson 《Journal of Polymer Science.Polymer Physics》2004,42(7):1218-1225
The effects of the size (pseudo‐generation number) and nature of end groups on physical and rheological properties were investigated for a series of hyperbranched polyesters based on an ethoxylated pentaerythritol core and 2,2‐bis‐(hydroxymethyl)propionic acid repeat units. The observed linear dependence of the melt viscosity on the molar mass in the high pseudo‐generation‐number limit indicated that entanglement effects were substantially absent. Moreover, the marked influence of end capping of the end groups on the physical and rheological properties suggested that intermolecular interactions were dominated by contacts between the outer shells of the molecules, in which the end groups were assumed to be concentrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1218–1225, 2004 相似文献
3.
The conductivity of Polypyrrole-viscose conducting fiber prepared with author's method can be shown up to as high as 2.106x10~(-2) S/cm. The main factors influencing the conductivity are the concentration of FeCl_3 used as dopant and initiator, the treatment time of viscose fiber as base material in FeCl_3 solution, temperature and polymerization time. It is found that the orientation and crystallization degree of viscose fiber keep constant before and after conducting treatment and the mechanical properties of conducting fiber is the same as that of base material. In addition, the distribution of polypyrrole in viscose fiber, and its effect on the conductivity were investigated in details by TEM. 相似文献
4.
N.D. Tho N. Chau S.C. Yu H.B. Lee N.D. The L.A. Tuan 《Journal of magnetism and magnetic materials》2006
Effect of annealing on the soft magnetic properties of Fe73.5Si13.5B9Nb3Au1 amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing. 相似文献
6.
太行山长城岭南山东北坡植被的研究 总被引:4,自引:1,他引:3
本文研究了太行山长城岭南山东北坡的植被分布及其特征。结果表明,从山麓至山顶,由于气候条件随海拨的逐渐升高而产生了明显的垂直变化,从而导致了植被分布的垂直变化。从山麓至山顶依次分布有落叶阔叶林、针阔混交林、针叶林和落叶阔叶灌丛等四个植被型、并因人为干扰落叶阔叶林正向针阔叶混交林和针叶林方向演替。 相似文献
7.
The problem of finding the number of intersections between two geometric figures in the plane has been studied extensively in literature. In this paper, the geometric figure comprising a continuous rectilinear path (called rectangular path) is considered, and a tight (least) upper bound onI(P, Q), the number of intersections between two rectangular pathsP andQ, is given.Editors' Note: One of our referees has reported that the main result of this paper has recently been given independently by a Chinese researcher at the University of Science and Technology, Hefei, P. R. of China. His paper is under publication in the Chinese Science Bulletin. However, since this journal may not be easily accessible to our readers, and further the two papers are obviously independent of each other, theBIT Editors have decided to accept the present paper. 相似文献
8.
用化学液相沉积方法,在高强度灰铸铁活塞环表面实现了Nbc覆层,盘销磨擦磨损试验表明,无论在无润滑的情况时,Nbc镀层表面要比镀Cr表面或铸铁原始表面具有更高的耐磨性,可以延长活塞环使用寿命,而Nbc镀层与铸铁之间低的磨擦系数可使S195柴油机磨擦损失降低0.35kW,降低比油耗9-5g/(kW.h)。 相似文献
9.
We interpret the recently observedU(3.1) mesons with the \(\Lambda \bar p\) + pions decays as the bound state of \(\Lambda ,\bar p\) andX 0(1480). TheX 0(1480) is a mesonium with \(Q^2 \bar Q^2 \) structures observed in γγ reactions and \(\bar pn\) annihilations. With this interpretation, we can understand its decay modes. Furthermore, we predict the ratio of \(\sigma (\Lambda \bar p\pi ^ + \pi ^ - )/\sigma (\Lambda \bar p\pi ^ + \pi ^ + )\) to be ?3.1 for centrally produced events and that the width of \(U^ - (\Lambda \bar p\pi ^ + \pi ^ - )\) to be greater than that of \(U^ + (\Lambda \bar p\pi ^ + \pi ^ + )\) . Both predictions seem to be in reasonable accord with the available data. We call for the detection of the \(\Lambda \bar p\pi ^ - \pi ^ - \) mode to verify the present interpretation. 相似文献
10.