全文获取类型
收费全文 | 1715篇 |
免费 | 168篇 |
国内免费 | 157篇 |
专业分类
化学 | 427篇 |
晶体学 | 2篇 |
力学 | 102篇 |
综合类 | 25篇 |
数学 | 1133篇 |
物理学 | 351篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 44篇 |
2021年 | 35篇 |
2020年 | 54篇 |
2019年 | 50篇 |
2018年 | 55篇 |
2017年 | 65篇 |
2016年 | 46篇 |
2015年 | 46篇 |
2014年 | 58篇 |
2013年 | 238篇 |
2012年 | 48篇 |
2011年 | 77篇 |
2010年 | 68篇 |
2009年 | 80篇 |
2008年 | 101篇 |
2007年 | 97篇 |
2006年 | 93篇 |
2005年 | 86篇 |
2004年 | 72篇 |
2003年 | 66篇 |
2002年 | 66篇 |
2001年 | 53篇 |
2000年 | 60篇 |
1999年 | 52篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 21篇 |
1994年 | 32篇 |
1993年 | 16篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1974年 | 2篇 |
排序方式: 共有2040条查询结果,搜索用时 15 毫秒
51.
Masao Kato Takao Shiraga Tatsumi Kimura Takashi Fukuda Hiro Matsuda Hachiro Nakanishi 《先进技术聚合物》2002,13(2):120-126
We synthesized some novel rigid NLO‐active maleimide copolymers bearing DR‐1 moieties ( PMPD , PHSD and PHND ). All copolymers exhibited high Tg's (190~197 °C), good solubilities for common solvents and excellent film‐forming properties. Dependence of film thickness on the d33 value for the poled copolymer films induced by corona poling was investigated and it was demonstrated that in less than thickness of 0.3 µm decrease of the thickness gives rise to remarkable increase in the d33 value. The poled copolymer films exhibited large d33 values (270 × 10?9 esu (film thickness 0.13 µm) for PMPD , 290 × 10?9 esu (0.12 µm) for PHSD and 350 × 10?9 esu (0.08 µm) for PHND ) as well as large r33 values (51.0 pmV?1 for PMPD and 60.4 pmV?1 for PHND ) which are significantly large compared to the value of LiNbO3 (31 pmV?1) as a typical EO material. The d33 values of the poled copolymers were kept constant even after standing 1000h at 80 °C, although a small decrease was observed at an initial stage. Further, the d33 values did not change up to ca. 123 °C upon heating at the rate of 10 °C/min in all cases. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
52.
Synthesis and properties of novel poly(amide-imide)s containing pendent diphenylamino groups 总被引:1,自引:0,他引:1
A new dicarboxylic acid, 2,4-bis(N-trimellitoyl)triphenylamine, bearing two preformed imide rings was synthesized from the condensation of 2,4-diaminotriphenylamine and trimellitic anhydride at 1:2 molar ratio. A series of poly(amide-imide)s (PAIs) with inherent viscosities of 0.38-0.66 dl/g were prepared by triphenyl phosphite-activated polycondensation from the diimide-dicarboxylic acid with various aromatic diamines. All the resulting PAIs were readily soluble in a variety of organic solvents and formed strong and tough films via solution casting. These PAIs have useful levels of thermal stability associated with moderately high glass-transition temperatures (259-314 °C) and 10% weight loss temperatures in excess of 530 °C in nitrogen or in air. 相似文献
53.
B. Kummer 《Journal of Optimization Theory and Applications》1991,70(3):561-582
The paper shows that Thibault's limit sets allow an iff-characterization of local Lipschitzian invertibility in finite dimension. We consider these sets as directional derivatives and extend the calculus in a way that can be used to clarify whether critical points are strongly stable inC
1,1 optimization problems.Many fruitful discussions with colleagues D. Klatte and K. Tammer as well as with H. Th. Jongen and F. Nozicka have influenced the present investigations in a very constructive manner. For the original papers concerning the sets f(x; u), the author is indebted to Prof. L. Thibault. 相似文献
54.
Hideki Takayasu Misako Takayasu Astero Provata Greg Huber 《Journal of statistical physics》1991,65(3-4):725-745
We study a generalized aggregation process in which charged particles diffuse and coalesce randomly on a lattice. For one-dimensional and mean-field models, we show that there exists a statistically-invariant steady state when randomly charged particles are continuously injected. The steady-state charge distribution obeys a power law with the exponent depending both on the type of the injection and on the spatial dimension. The response of the system to a perturbation (i.e., relaxation) is characterized by either a power law decay (t
–
,1) or a compressed exponential decay [exp(–t
),>1]. 相似文献
55.
56.
57.
细杆在抛物线壁内支承,平衡特性与杆长、倾角和摩擦因子相关.细杆在自身重力作用下可发生焦点下方的顺时针运动,焦点上方的逆时针运动以及两端同时下滑.基于端部支撑力达到摩擦锥边界的条件,可确定细杆状态为不平衡、稳定或不稳定的平衡和摩擦平衡.平衡集为具有宽度的叉式分岔. 相似文献
58.
合成了一种多级孔芳香骨架材料(PAF-70); 使用由氨基修饰过的单体, 应用该合成策略得到了同样具有窄分布介孔的含有氨基活性位点的PAF材料, 并通过硫脲单体与其氨基活性位点的反应, 将硫脲基团引入PAF-70材料中, 获得了含有硫脲催化位点的材料(PAF-70-thiourea). 氮气吸附-脱附测试结果显示, PAF-70存在孔径分布较窄的介孔, 介孔孔径为3.8 nm, 与模拟计算值(约3.7 nm)吻合. 热重分析结果表明, PAF-70具有很高的热稳定性. PAF-70在大多数溶剂中可以稳定存在, 具有良好的化学稳定性. 将PAF-70-thiourea作为催化剂, 应用在N-溴代琥珀酰亚胺(NBS)氧化醇类的反应中, 其表现出较高的催化活性、 较高的稳定性和广泛的底物适用性. 与含有相同硫脲催化位点的金属有机框架(MOF)材料(IRMOF-3-thiourea)作为催化剂对比, 进一步证实PAFs材料非常适合作为催化有机反应的固载平台. 相似文献
59.
60.