全文获取类型
收费全文 | 29593篇 |
免费 | 3631篇 |
国内免费 | 4603篇 |
专业分类
化学 | 9490篇 |
晶体学 | 362篇 |
力学 | 938篇 |
综合类 | 532篇 |
数学 | 1478篇 |
物理学 | 6101篇 |
综合类 | 18926篇 |
出版年
2024年 | 117篇 |
2023年 | 300篇 |
2022年 | 794篇 |
2021年 | 817篇 |
2020年 | 839篇 |
2019年 | 641篇 |
2018年 | 653篇 |
2017年 | 841篇 |
2016年 | 861篇 |
2015年 | 1244篇 |
2014年 | 1670篇 |
2013年 | 1874篇 |
2012年 | 2111篇 |
2011年 | 2296篇 |
2010年 | 2116篇 |
2009年 | 2153篇 |
2008年 | 2411篇 |
2007年 | 2273篇 |
2006年 | 2145篇 |
2005年 | 1930篇 |
2004年 | 1525篇 |
2003年 | 1215篇 |
2002年 | 1344篇 |
2001年 | 1453篇 |
2000年 | 1202篇 |
1999年 | 707篇 |
1998年 | 275篇 |
1997年 | 247篇 |
1996年 | 244篇 |
1995年 | 170篇 |
1994年 | 193篇 |
1993年 | 178篇 |
1992年 | 146篇 |
1991年 | 134篇 |
1990年 | 127篇 |
1989年 | 129篇 |
1988年 | 94篇 |
1987年 | 79篇 |
1986年 | 59篇 |
1985年 | 46篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 34篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1959年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
以“问题”驱动高等数学教学的探究 总被引:1,自引:0,他引:1
郑雪静 《甘肃联合大学学报(自然科学版)》2008,22(6)
问题是数学的心脏,高等数学是理工科的一门重要基础课程,其教学质量对学生来讲至关重要.本文就如何以"问题"趋动高等数学教学提出一些自己的看法供读者商榷. 相似文献
52.
53.
54.
用Quantum Sutton-Chen多体势对Ag6Cu4和CuNi液态金属凝固过程进行了分子动力学模拟研究.在冷却速率2×1012到2×1014K/s范围内,CuNi总是形成fcc晶体结构,而Ag6Cu4总是形成非晶态结构.考虑到CuNi及AgCu中原子半径之比分别为1.025和1.13,那么模拟结果证实了原子的尺寸差别是非晶态合金形成的一个主要影响因素.此外采用键对及原子多面体类型指数法对凝固过程中微观结构组态变化的分析,不但能说明二十面体结构在非晶态合金形成和稳定性中所起的关键作用,又有助于对液态金属的凝固过程、非晶态结构特征的深入理解. 相似文献
55.
56.
郑东升 《长春师范学院学报》2007,26(2):90-93
对语言本质及其实现形式的不同看法构成了当今语言学界的焦点话题之一。主流话语和批评话语在对语言的态度上形成了复杂的关系,澄清其视角之不同是对语言深刻认识的必要前提。 相似文献
57.
58.
Xiao Qi ZHENG Yong Hui WANG Qing Xiang GUO* Li YANG You Cheng LIU Department of Chemistry University of Science Technology of China Hefei National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2003,(8)
As artificial enzymes, the binding constants of cyclodextrins (CDs) and their substrates are expected to be high1. For this purpose, many kinds of bridged cyclodextrin dimers2 whose two cyclodextrins are linked by various spacers have been constructed. It was of interest to make the dimers, whose binding constants would exceed 108dm3/mol3. Up to date, the bridged cyclodextrin dimers have been extensively studied as enzyme models and as molecular receptors4-6. Recently, we synthesized a brid… 相似文献
59.
Peixiang Xing Gilles P. Robertson Michael D. Guiver Serguei D. Mikhailenko Serge Kaliaguine 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):2866-2876
A series of sulfonated poly(aryl ether ketone)s (SPAEKs) were prepared by aromatic nucleophilic polycondensation of 2,6‐dihydroxynaphthalene with 5,5′‐carbonyl‐bis(2‐fluorobenzenesulfonate) and 4,4′‐difluorobenzophenone. The structure and degree of sulfonation (DS) of the SPAEKs were characterized using 1H NMR spectroscopy. The experimentally observed DS values were close to the expected values derived from the starting material ratios. The thermal stabilities of the SPAEKs were characterized by thermogravimetric analysis, which showed that in acid and sodium salt forms they were thermally stable in air up to about 240 and 380 °C, respectively. Transparent membranes cast from the directly polymerized SPAEKs exhibited good mechanical properties in both dry and hydrated states. The dependence of water uptake and of membrane swelling on the DS at different temperatures was studied. SPAEK membranes with a DS from 0.72 to 1.60 maintained adequate mechanical properties after immersion in water at 80 °C for 24 h. The proton conductivity of SPAEK membranes with different degrees of sulfonation was measured as a function of temperature. The proton conductivity of the SPAEK films increased with increased DS, and the highest room temperature conductivity (4.2 × 10?2 S/cm) was recorded for a SPAEK membrane with a DS of 1.60, which further increased to 1.1 × 10?1 S/cm at 80 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2866–2876, 2004 相似文献
60.
Baochun Guo Xing Ouyang Changgeng Cai Demin Jia 《Journal of Polymer Science.Polymer Physics》2004,42(7):1192-1198
Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo‐montmorillonite (O‐MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X‐ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O‐MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O‐MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass‐transition temperatures (Tg's) of the exfoliated nanocomposite were 20 °C higher than that of the neat resin. At higher O‐MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher Tg's as compared with the neat resin. O‐MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O‐MMT loading. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1192–1198, 2004 相似文献