全文获取类型
收费全文 | 23687篇 |
免费 | 3733篇 |
国内免费 | 3779篇 |
专业分类
化学 | 17928篇 |
晶体学 | 399篇 |
力学 | 1453篇 |
综合类 | 239篇 |
数学 | 2576篇 |
物理学 | 8604篇 |
出版年
2024年 | 55篇 |
2023年 | 432篇 |
2022年 | 616篇 |
2021年 | 800篇 |
2020年 | 938篇 |
2019年 | 968篇 |
2018年 | 815篇 |
2017年 | 810篇 |
2016年 | 1053篇 |
2015年 | 1056篇 |
2014年 | 1322篇 |
2013年 | 1756篇 |
2012年 | 1907篇 |
2011年 | 2013篇 |
2010年 | 1517篇 |
2009年 | 1487篇 |
2008年 | 1559篇 |
2007年 | 1385篇 |
2006年 | 1354篇 |
2005年 | 1266篇 |
2004年 | 1026篇 |
2003年 | 836篇 |
2002年 | 822篇 |
2001年 | 774篇 |
2000年 | 587篇 |
1999年 | 555篇 |
1998年 | 478篇 |
1997年 | 360篇 |
1996年 | 387篇 |
1995年 | 307篇 |
1994年 | 337篇 |
1993年 | 244篇 |
1992年 | 208篇 |
1991年 | 200篇 |
1990年 | 177篇 |
1989年 | 115篇 |
1988年 | 102篇 |
1987年 | 104篇 |
1986年 | 103篇 |
1985年 | 85篇 |
1984年 | 55篇 |
1983年 | 43篇 |
1982年 | 36篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
121.
两步相移实现投影栅相位测量轮廓术 总被引:9,自引:2,他引:7
提出一种新的投影栅相位测量方法--两步相移法。该方法只需两幅相移条纹图,因此计算量小,速度快。给出了实验及计算结果,并同四步相移法进行了比较,证明了该方法具有较高的精度。 相似文献
122.
123.
T. Ramanathan S. Stankovich D. A. Dikin H. Liu H. Shen S. T. Nguyen L. C. Brinson 《Journal of Polymer Science.Polymer Physics》2007,45(15):2097-2112
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007 相似文献
124.
Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO4) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO4 compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO4 and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO4 compound was mainly due to the crosslinking induced by coordination between CN and Cu2+. The increasing extent of E′ increased with the rise of CuSO4 content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (Ea) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007 相似文献
125.
We analyze an infinite horizon, single product, continuous review model in which pricing and inventory decisions are made simultaneously and ordering cost includes a fixed cost. We show that there exists a stationary (s,S) inventory policy maximizing the expected discounted or expected average profit under general conditions. 相似文献
126.
127.
Protection of iron corrosion by stearic acid and stearic imidazoline self-assembled monolayers 总被引:4,自引:0,他引:4
A type of stearic imidazoline (IM) inhibitor was prepared using stearic acid (SA) and diethylenetriamine (DETA) as raw materials. The monolayers of IM and SA were assembled on the iron surface. The electrochemical characterization of stearic acid (SA) and stearic imidazoline (IM) on an oxide free iron surface had been studied. The monolayers of IM inhibitor were characterized by electrochemical impedance spectroscopy (EIS), electrochemical polarization curves, double layer capacitance, X-ray photoelectron spectroscopy (XPS) and molecular simulation. The results of electrochemical studies had illustrated that the inhibition efficiency of IM was higher than SA. XPS showed that the IM molecules adsorbed on the iron surface. The molecular simulation calculations showed that the IM molecules were tilted at an angle on the iron surface. 相似文献
128.
Xin Tao YE Chong LI 《数学学报(英文版)》2007,23(1):65-76
The BCQ and the Abadie CQ for infinite systems of convex inequalities in Banach spaces are characterized in terms of the upper semi-continuity of the convex cones generated by the subdifferentials of active convex functions. Some relationships with other constraint qualifications such as the CPLV and the Slate condition are also studied. Applications in best approximation theory are provided. 相似文献
129.
外汇储备规模与多元变量弹性系数的实证研究 总被引:5,自引:0,他引:5
中国外汇储备近几年的迅速增长引发了关于中国外汇储备规模是否适度的广泛讨论。本文从需求的角度,运用计量经济学的多元线性回归的方法,建立中国外汇储备与平均进口倾向、进口和国际收支三变量的双对数模型,通过计算并通过相关检验得到外汇储备与相关变量的弹性系数。为预测和制定相关政策提供依据。 相似文献
130.