全文获取类型
收费全文 | 44068篇 |
免费 | 3370篇 |
国内免费 | 3029篇 |
专业分类
化学 | 31603篇 |
晶体学 | 526篇 |
力学 | 1665篇 |
综合类 | 265篇 |
数学 | 4304篇 |
物理学 | 12104篇 |
出版年
2023年 | 320篇 |
2022年 | 804篇 |
2021年 | 914篇 |
2020年 | 886篇 |
2019年 | 966篇 |
2018年 | 770篇 |
2017年 | 720篇 |
2016年 | 1396篇 |
2015年 | 1377篇 |
2014年 | 1674篇 |
2013年 | 2726篇 |
2012年 | 3318篇 |
2011年 | 3568篇 |
2010年 | 2389篇 |
2009年 | 2231篇 |
2008年 | 3041篇 |
2007年 | 2848篇 |
2006年 | 2644篇 |
2005年 | 2339篇 |
2004年 | 2129篇 |
2003年 | 1774篇 |
2002年 | 1865篇 |
2001年 | 1391篇 |
2000年 | 1132篇 |
1999年 | 778篇 |
1998年 | 528篇 |
1997年 | 564篇 |
1996年 | 567篇 |
1995年 | 465篇 |
1994年 | 455篇 |
1993年 | 440篇 |
1992年 | 417篇 |
1991年 | 317篇 |
1990年 | 260篇 |
1989年 | 225篇 |
1988年 | 190篇 |
1987年 | 166篇 |
1986年 | 135篇 |
1985年 | 205篇 |
1984年 | 140篇 |
1983年 | 116篇 |
1982年 | 135篇 |
1981年 | 103篇 |
1980年 | 89篇 |
1978年 | 90篇 |
1977年 | 94篇 |
1976年 | 102篇 |
1975年 | 108篇 |
1974年 | 88篇 |
1973年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Inventiones mathematicae - 相似文献
32.
Susan Baker Lisa Kelchner Barbara Weinrich Linda Lee Paul Willging Robin Cotton Karen Zur 《Journal of voice》2006,20(4):631-641
Laryngotracheal stenosis is defined as a congenital or acquired narrowing of the airway. Congenital causes may include subglottic membranous or cartilaginous narrowing. Acquired causes may include trauma due to prolonged endotracheal or tracheal intubation or laryngotracheal injury. Although advances have been made over the past 30 years in reconstructive surgeries to improve airway patency in these patients, long-term laryngeal function for voice production is not well defined in this population. This review examines causes, symptoms and signs, and methods for diagnosing laryngotracheal stenosis. Surgical management procedures are briefly summarized. The current literature on voice outcomes is summarized. The predominant voice characteristics in the population are presented, although results are challenged by the heterogeneity of voice presentation and paucity of data from instrumental measures. Considerations for subjective and instrumental assessment, measures of quality of life, instrumental methods, and treatment options specific to the needs of this population are discussed. Research strategies to identify long-term outcomes of surgical and behavioral treatments in this population are posed. 相似文献
33.
The breakthrough and stoichiometric SO2 adsorption efficiencies of a biomass supported Na2CO3 system (80 wt %Na2CO3/straw) have reached 48.9% and 80.6% respectively at a desulfurization temperature of 80℃. 相似文献
34.
35.
Y.Y. Lee 《Applied Acoustics》2002,63(11):1157-1175
The nonlinear natural frequency of a rectangular box, which consists of one flexible plate and five rigid plates, is studied in this paper. The flexible plate is assumed to vibrate like a simple piston. The behavior of the structural-acoustic coupling between the flexible plate and the air cavity is analyzed by using the proposed finite element modal method. The system finite element equation is reduced and expressed in terms of the modal coordinates with small degrees of freedom by using the proposed reduction method. The system nonlinear stiffness matrix representing the large amplitude vibration can be transformed to be a constant modal matrix. The natural frequencies are determined by using the harmonic balance method to solve the eigenvalue equations of the structural-acoustic system. The effect of the cavity depth on the natural frequencies and convergence studies are discussed in detail. 相似文献
36.
建立了一个四组分一维混合模型,对电子束注入大气产生大尺度等离子体的过程进行了数值模拟.结果表明了能量为140keV、流强为50mA/cm2的注入电子束,可以产生线度为0.5m,密度为1012cm-3量级的大气环境下等离子体.电子束所伴随的空间电荷效应由于等离子体的产生会很快消失,不影响后续的等离子体产生过程.电子束注入流强主要影响产生等离子体的密度,而电子束能量则同时影响其空间线度和密度.
关键词:
电子束
碰撞
电离 相似文献
37.
提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面,用光杠杆技术检测温度在20-40 ℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示:在升温过程中,微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形,这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中,微悬臂梁发生了反方向的弯曲变形,这对应着PNIPAM分子从塌缩小球构象向无规线团构象的构象转变.整个温度变化过程中构象转变是连续进行的,而在低临界溶解温度(约32 ℃)附近转变幅度较大,这与自由水溶液中PNIPAM分子的无规线团-塌缩小球构象转变相对应.实验结果还显示:由于PNIPAM分子在塌缩过程中氢键的形成和链段间可能的缠结效应,整个温度循环过程中微悬臂梁的变形是不可逆的且有明显的迟滞效应. 相似文献
38.
39.
As borders between different entities, lines are an important element of natural images. Indeed, the neurons of the mammalian
visual cortex are tuned to respond best to lines of a given orientation. This preferred orientation varies continuously across
most of the cortex, but also has vortex-like singularities known as pinwheels. In attempting to describe such patterns of
orientation preference, we are led to consider underlying rotation symmetries: Oriented segments in natural images tend to
be collinear; neurons are more likely to be connected if their preferred orientations are aligned to their topographic separation.
These are indications of a reduced symmetry requiring joint rotations of both orientation preference and the underlying topography.
This is verified by direct statistical tests in both natural images and in cortical maps. Using the statistics of natural
scenes we construct filters that are best suited to extracting information from such images, and find qualitative similarities
to mammalian vision.
PACS84.35+i 89.70.+c 87.57.Nk 相似文献
40.
不完全信息群体决策专家权重的集结 总被引:8,自引:5,他引:3
本文对于属性权重信息和属性效用信息都不完全的群体多属性决策问题,通过构造属性值区间和运用系统聚类分析法,对群体决策中的专家进行分类,并确定每位专家的权重. 相似文献