全文获取类型
收费全文 | 7921篇 |
免费 | 1352篇 |
国内免费 | 918篇 |
专业分类
化学 | 5577篇 |
晶体学 | 90篇 |
力学 | 109篇 |
综合类 | 45篇 |
数学 | 57篇 |
物理学 | 4313篇 |
出版年
2024年 | 14篇 |
2023年 | 71篇 |
2022年 | 169篇 |
2021年 | 223篇 |
2020年 | 313篇 |
2019年 | 272篇 |
2018年 | 250篇 |
2017年 | 329篇 |
2016年 | 384篇 |
2015年 | 354篇 |
2014年 | 483篇 |
2013年 | 658篇 |
2012年 | 552篇 |
2011年 | 474篇 |
2010年 | 409篇 |
2009年 | 439篇 |
2008年 | 536篇 |
2007年 | 515篇 |
2006年 | 456篇 |
2005年 | 382篇 |
2004年 | 380篇 |
2003年 | 342篇 |
2002年 | 306篇 |
2001年 | 249篇 |
2000年 | 197篇 |
1999年 | 196篇 |
1998年 | 161篇 |
1997年 | 152篇 |
1996年 | 155篇 |
1995年 | 132篇 |
1994年 | 116篇 |
1993年 | 68篇 |
1992年 | 74篇 |
1991年 | 52篇 |
1990年 | 46篇 |
1989年 | 42篇 |
1988年 | 43篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 33篇 |
1984年 | 23篇 |
1983年 | 8篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
《Journal of separation science》2003,26(5):402-408
When nitrated polynuclear aromatic hydrocarbons (NPAH) were recognised as long‐term toxic compounds and were also identified in several anthropogenic emissions and among the by‐products of photochemical smog they became objects of investigation in ambient air in both polluted and clean environments. In Italy the first investigations focussing on atmospheric NPAH were performed in the early eighties and encompassed both the canyon streets and dwelling areas of Rome. Because NPAH were indicated as markers of vehicle emission, new investigations were performed in other cities and also in rural and (nominally) unpolluted locations. In general, the first measurements of NPAH were episodic and could not be assumed to be strictly representative of the sites investigated. In contrast, nowadays consistent data bases on NPAH have been built up and are discussed in the technical literature, so that both neat concentrations and the yearly timed variation of the most important NPAH congeners have been measured in Italian air. Although concentrations of NPAH in air are usually much lower than those of PAH, owing to their very high potency in inducing mutations and tumours NPAH are regarded as having an important health impact on populations living in Italian urban areas. In this regard the genotoxicity of atmospheric aerosols is partly associated with nitrofluoranthenes and nitropyrenes whereas nitronaphthalenes and methylnitronaphthalenes seem to contribute to that of the gaseous organic fraction. Several civic and regional administrations are introducing control of atmospheric NPAH among ways of improving air quality in cities. 相似文献
72.
73.
74.
Implementation and experimental study on fast object modeling based on multiple structured stripes 总被引:6,自引:0,他引:6
In this paper, a practical structured light-based system for fast object modeling and reconstruction is reported. The system consists of an off-the-shelf digital projector, a video camera and a turntable. The system calibration is implemented accurately and automatically by taking a single image of an illuminated calibration template. The multiple color light stripes emitted by the projector adopt only three colors and the color can be modified easily according to the surface texture of the object. This makes the system widely applicable in many situations, and the assumption about color neutrality, which is a limitation to other similar systems, can be largely relaxed. The registration and merging algorithm is greatly simplified by employing a turntable. The validity and high accuracy of the method are demonstrated by extensive real experiments. 相似文献
75.
电磁诱导透明和导致极慢光速的机制 总被引:2,自引:0,他引:2
根据有关文献 ,描述了电磁诱导透明和导致光速极慢的物理机制 ,并对实验结果也做了介绍 相似文献
76.
77.
78.
79.
关于杨氏干涉条纹的讨论 总被引:1,自引:0,他引:1
阐述了杨氏干涉实验中,理论上应该看到明暗相间双曲线条纹,而实际上,在实验室中看到的是明暗相间直线条纹。 相似文献
80.