全文获取类型
收费全文 | 12436篇 |
免费 | 786篇 |
国内免费 | 1592篇 |
专业分类
化学 | 2417篇 |
晶体学 | 43篇 |
力学 | 658篇 |
综合类 | 84篇 |
数学 | 489篇 |
物理学 | 1937篇 |
综合类 | 9186篇 |
出版年
2024年 | 10篇 |
2023年 | 64篇 |
2022年 | 42篇 |
2021年 | 85篇 |
2020年 | 37篇 |
2019年 | 64篇 |
2018年 | 45篇 |
2017年 | 30篇 |
2016年 | 39篇 |
2015年 | 33篇 |
2014年 | 626篇 |
2013年 | 166篇 |
2012年 | 82篇 |
2011年 | 79篇 |
2010年 | 78篇 |
2009年 | 117篇 |
2008年 | 122篇 |
2007年 | 153篇 |
2006年 | 78篇 |
2005年 | 51篇 |
2004年 | 67篇 |
2003年 | 844篇 |
2002年 | 3328篇 |
2001年 | 4210篇 |
2000年 | 1048篇 |
1999年 | 542篇 |
1998年 | 460篇 |
1997年 | 228篇 |
1996年 | 229篇 |
1995年 | 327篇 |
1994年 | 227篇 |
1993年 | 368篇 |
1992年 | 337篇 |
1991年 | 188篇 |
1990年 | 203篇 |
1989年 | 157篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1961年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
91.
Sound Field Calculations of Elliptical Pistons by the Superposition of Two—Dimensional Gaussian Beams 下载免费PDF全文
We present an alternative approach to calculate the sound field of ultrasonic transducers.The distribution function of sources is expanded into the superposition of a series of two-dimensional Gaussian functions.The corresponding radiated sound field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions.This treatment does not require the condition that the shape of the source is of circular axial symmetry.A numerical example is presented for the uniform elliptical piston transducer and this is in good agreement with the results given by complicated computation. 相似文献
92.
We have experimentally studied the characteristics of fifth-order harmonic radiation produced by two coherent femtosecond laser pulses with a changeable relative phase.The intensities of harmonic generation are found to increase with the coherent degree.In one optical Period,the temporal variation of harmonics exhibits an asymmetric characteristic,which is interpreted in terms of ionization theory and the deformation of the wave packets of fundamental field contribution to harmonic generation. 相似文献
93.
We show theoretically that it is possible to modify absorption of a bulk absorbing material by inserting another non-absorbing dielectric slab periodically to form one-dimensional photonic crystals.It is found that,for frequencies within photonic bandgaps,absorption is always suppressed.For frequencies located at photonic bands,absorption can be suppressed or enhanced,which depends on the relative values of the real refractive index of the absorbing and non-absorbing dielectric layers. 相似文献
94.
95.
The experimental conditions for photoactivated intermittent fluorescence from nanoscale silver oxide were studied with fluorescence microscopy.Strong fluorescence was observed from the Ag2O particles with size of 10-20nm excited with both blue and green light .We observed the saturation of Photoexcitation with blue light and explained the experimental results using the model of agglomeration of silver atoms to form small clusters and the fluorescence of Ag2 and Ag3 clusters. 相似文献
96.
一类广义维里拉普拉斯,把在白噪声分析构架中通常定义的维里拉普拉斯作为特殊情形而包含。 相似文献
97.
DAPI(4-6=脒基-2-苯基吲哚)是检测微量DNA的专一性荧光染料,其最高灵敏度为0.1ng/ml,DNA浓度由微微克向毫微克增大时,峰位红移10-20nm。DNA浓度在1-100ug/ml时,DAPI的适宜浓度范围为30-100ng/ml。 相似文献
98.
The reactivity ratios of vinyl acetate(VAc) and divinyl benzene (DVB) were calculated from the Q and e values.The possibility of the copolymerization of these two monomers was predicted and the copolymerization was carried out by suspension polymerization technique in the presence of pore producing agent (toluene and gasoine).The relative ratio of acetoxy group and benzene ring in the copolymer were monitored by IR measurement during the polymerization.The variation of pore properties,such as spectific surface area,porosity and average pore diameter,with polymerization time were determined.The copolymers at various polymerization time were alcoholyzed and thus the variation of the hydroxyl group content with polymerization time was studied. 相似文献
100.