全文获取类型
收费全文 | 9154篇 |
免费 | 1886篇 |
国内免费 | 3362篇 |
专业分类
化学 | 6707篇 |
晶体学 | 384篇 |
力学 | 593篇 |
综合类 | 457篇 |
数学 | 1480篇 |
物理学 | 4781篇 |
出版年
2024年 | 14篇 |
2023年 | 76篇 |
2022年 | 312篇 |
2021年 | 316篇 |
2020年 | 267篇 |
2019年 | 294篇 |
2018年 | 299篇 |
2017年 | 444篇 |
2016年 | 299篇 |
2015年 | 473篇 |
2014年 | 535篇 |
2013年 | 730篇 |
2012年 | 696篇 |
2011年 | 745篇 |
2010年 | 779篇 |
2009年 | 786篇 |
2008年 | 946篇 |
2007年 | 854篇 |
2006年 | 853篇 |
2005年 | 626篇 |
2004年 | 535篇 |
2003年 | 433篇 |
2002年 | 437篇 |
2001年 | 459篇 |
2000年 | 496篇 |
1999年 | 278篇 |
1998年 | 144篇 |
1997年 | 117篇 |
1996年 | 109篇 |
1995年 | 78篇 |
1994年 | 104篇 |
1993年 | 122篇 |
1992年 | 93篇 |
1991年 | 72篇 |
1990年 | 74篇 |
1989年 | 62篇 |
1988年 | 52篇 |
1987年 | 61篇 |
1986年 | 52篇 |
1985年 | 41篇 |
1984年 | 37篇 |
1983年 | 33篇 |
1982年 | 27篇 |
1981年 | 21篇 |
1980年 | 22篇 |
1979年 | 27篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1975年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
Felipe Avalos‐Belmontes Ivan Zapata‐Gonzalez Luis F. Ramos‐De Valle Roberto Zitzumbo‐Guzman Sergio Alonso‐Romero 《Journal of Polymer Science.Polymer Physics》2009,47(19):1906-1915
The composition, the thermal properties, and the kinetics of the thermo‐oxidative degradation of high‐density polyethylene (HDPE) were studied as a function of the increasing crystalline fraction, which resulted from the selective extraction of the amorphous part, through digestion by immersion in fuming nitric acid (HNO3) for different periods of time. The chemical and thermodynamic changes in HDPE, brought about by digestion in nitric acid for different periods of time, are discussed. Changes in the chemistry and microstructure of the HDPE, as a function of acid treatment for different periods of time, were studied using infra‐red spectroscopy (FTIR), gel permeation chromatography (GPC), and thermal analysis (DSC and TGA), as well as scanning electron microscopy (SEM). These studies were carried out as a function of the extracted amorphous fraction of HDPE samples via digestion in HNO3. These studies showed that in the first stages of the acid chemical attack, the amorphous part first undergoes a chemical modification and then dissolves into the strong acid medium. The total crystalline fraction apparently decreases during the first stages of the chemical attack and then increases as the amorphous part is extracted. TGA results show that as the selective extraction of the amorphous part occurs, there is a displacement of the thermo‐oxidative degradation toward higher temperatures. The kinetics of the thermo‐oxidative degradation as a function of the extraction of the amorphous part was followed according to the Horowitz‐Metzger method, and it was found that as the concentration of the crystalline fraction increases, the activation energy for the thermo‐oxidative degradation increases. SEM studies show that the extraction of the amorphous part does not affect the size of the crystalline lamellar thickness of HDPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1906–1915, 2009 相似文献
974.
本文提出采用两片尖峰简并型共振反射器作为磷玻璃振荡器的耦合输出镜,利用其反射调制包络特性,实现了带宽100(?)的激光输出方案,并获得了成功,实验分析了宽带输出特性. 相似文献
975.
976.
977.
给出了拓扑线性空间中的一个Drop定理.利用此Drop定理,证明了拓扑线性空间中的每个序列紧凸集具有Drop性质;每个可数紧闭凸集具有拟Drop性质.而且结出了拓扑线性空间中Drop性质和拟Drop性质的序列流特征.也讨论了Drop性质和拟Drop性质与泛函取极值之间的联系. 相似文献
978.
本文证明了在正规locale范畴中,Banaschewski-Mulvey形式的紧正则反射与Johnstone形式的Wallman紧化一致,从而推广了Johnstone在文献[4]中的主要结果. 相似文献
979.
In this paper,we first introduce a new class of generalized accretive operators named(H,η)-accretive in Banach space.By studying the properties of(H,η)-accretive,we extend the concept of resolvent operators associated with m-accretive operators to the new (H,η)-accretive operators.In terms of the new resolvent operator technique,we prove the existence and uniqueness of solutions for this new system of variational inclusions.We also construct a new algorithm for approximating the solution of this system a... 相似文献
980.
This paper presents an infeasible-interior-point algorithm for a class of nonmonotone complementarity problems, and analyses
its convergence and computational complexity. The results indicate that the proposed algorithm is a polynomial-time one. 相似文献