全文获取类型
收费全文 | 10925篇 |
免费 | 1309篇 |
国内免费 | 624篇 |
专业分类
化学 | 7034篇 |
晶体学 | 58篇 |
力学 | 305篇 |
综合类 | 189篇 |
数学 | 814篇 |
物理学 | 4458篇 |
出版年
2024年 | 21篇 |
2023年 | 151篇 |
2022年 | 352篇 |
2021年 | 516篇 |
2020年 | 409篇 |
2019年 | 357篇 |
2018年 | 289篇 |
2017年 | 500篇 |
2016年 | 529篇 |
2015年 | 503篇 |
2014年 | 733篇 |
2013年 | 708篇 |
2012年 | 739篇 |
2011年 | 652篇 |
2010年 | 544篇 |
2009年 | 680篇 |
2008年 | 636篇 |
2007年 | 621篇 |
2006年 | 538篇 |
2005年 | 544篇 |
2004年 | 487篇 |
2003年 | 331篇 |
2002年 | 253篇 |
2001年 | 192篇 |
2000年 | 175篇 |
1999年 | 186篇 |
1998年 | 142篇 |
1997年 | 136篇 |
1996年 | 141篇 |
1995年 | 127篇 |
1994年 | 74篇 |
1993年 | 81篇 |
1992年 | 71篇 |
1991年 | 43篇 |
1990年 | 63篇 |
1989年 | 53篇 |
1988年 | 56篇 |
1987年 | 52篇 |
1986年 | 28篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
911.
A novel quasi-physical edge detection model is presented. The model, referred to as the effusion-evaporation model (EEM), is inspired by the natural phenomenon that the water effusing from the ground evaporates in the sunshine and leaves a wire like water stain on the ground surface, which reflects the physiognomy of the terrain. Based on the simulation of water effusing and evaporating, an EEM regards the complement of gradient magnitude image as a three-dimensional terrain, and the concave regions, which contain the residual water in the evolution final state, are used to determine the edges. Subjective and objective comparisons are performed on the proposed algorithm and two conventional edge detectors, namely Canny and LoG. The comparison results show that the proposed method outperforms Canny and LoG detectors for the real images and the standard test images with Gaussian noise. 相似文献
912.
Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction (θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1] and [2]. 相似文献
913.
Xia Liu Hang Song Guoqing MiaoHong Jiang Lianzhen Cao Dabing LiXiaojuan Sun Yiren Chen 《Applied Surface Science》2011,257(6):1996-1999
In0.82Ga0.18As epilayers were grown on InP substrates using a two-step growth technique by LP-MOCVD. A homogeneous low-temperature (450 °C) In0.82Ga0.18As buffer layer was introduced to improve the crystalline quality of epilayers. The influence of low-temperature buffer layer deposition condition, such as thermal annealing duration, on the crystalline quality of the In0.82Ga0.18As epilayer was investigated. Double-crystal X-ray diffraction measurement, Hall measurement, and Raman scattering spectrum were used to evaluate the In0.82Ga0.18As epilayers. Atomic force microscope was used to study the surface morphology. It is found that the In0.82Ga0.18As epilayer, with buffer layer thermal annealing for 5 min, exhibits the best crystalline quality. The change of the surface morphology of the buffer layer after thermal annealing treatment was suggested to explain the phenomenon. 相似文献
914.
In this paper, porous WO3 films were prepared by anodic oxidation of metallic tungsten (W) films deposited on alumina substrates. The structural and morphological properties of the porous WO3 films were investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). A large number of cracks appeared on the surface of films after anodization, which makes the films porous. The porous WO3 sensors achieved their maximum response values to NO2 at a low operating temperature of 150 °C. The porous WO3 sensors showed high response values, great stability and fast response-recovery characteristics to different concentration of NO2 gas due to the high specific surface area and special structural and morphological properties. 相似文献
915.
916.
基于自再现原理,利用菲涅耳-基尔霍夫衍射积分方程,引入腔镜失调、激光介质上的增益分布以及光阑口径,采用本征矢量法分析了大口径平凹腔薄片激光器的本征模式,并计算了相应的光束质量因子M2.建立了千瓦级薄片激光系统和光纤扫描光斑诊断装置,开展了高功率激光输出特性研究.结果表明,在大口径高功率平凹腔中多个本征模式可同时起振,获... 相似文献
917.
918.
919.
螺旋管内高压汽水两相流动沸腾干涸点的研究 总被引:1,自引:0,他引:1
在较宽的实验参数范围内(系统压力P=8~15 MPa,质量流速G=800~1800 kg·m~(-2)·s~(-1),壁面热流密度q_w=200~950 kW·m~(-2))对一立式螺旋管内(管内径为10 mm,螺旋直径为300 mm,节距为50 mm)汽水两相流动沸腾干涸特性进行了实验研究。通过研究,获得了干涸发生时螺旋管圈壁温的分布特征以及压力、质量流速和壁面热流密度这三个参数对临界干度的影响规律。同时在实验数据的基础上,提出了一个适用于计算螺旋管内高压高含汽率工况下汽水两相流临界干度的经验关系式。 相似文献
920.
Two-dimensional photon counting imaging detector based on a Vernier position sensitive anode readout 总被引:1,自引:0,他引:1
A two-dimensional photon counting imaging detector based on a Vernier position sensitive anode is reported. The decode principle and design of a two-dimensional Vernier anode are introduced in detail. A photon counting imaging system was built based on a Vernier anode. The image of very weak optical radiation can be reconstructed by image processing in a period of integration time. The resolution is superior to 100 μm according to the resolution test. The detector may realize the imaging of very weak particle flow of high-energy photons, electrons and ions, so it can be used for high-energy physics, deep space exploration, spectral measurement and bio-luminescence detection. 相似文献