全文获取类型
收费全文 | 40580篇 |
免费 | 4501篇 |
国内免费 | 6362篇 |
专业分类
化学 | 28979篇 |
晶体学 | 1312篇 |
力学 | 767篇 |
综合类 | 232篇 |
数学 | 2079篇 |
物理学 | 9060篇 |
无线电 | 9014篇 |
出版年
2024年 | 82篇 |
2023年 | 614篇 |
2022年 | 860篇 |
2021年 | 1150篇 |
2020年 | 1364篇 |
2019年 | 1329篇 |
2018年 | 1048篇 |
2017年 | 1488篇 |
2016年 | 1535篇 |
2015年 | 1481篇 |
2014年 | 2003篇 |
2013年 | 3218篇 |
2012年 | 2435篇 |
2011年 | 2983篇 |
2010年 | 2548篇 |
2009年 | 2865篇 |
2008年 | 2812篇 |
2007年 | 2803篇 |
2006年 | 2665篇 |
2005年 | 2449篇 |
2004年 | 2067篇 |
2003年 | 1752篇 |
2002年 | 1456篇 |
2001年 | 1246篇 |
2000年 | 1155篇 |
1999年 | 888篇 |
1998年 | 764篇 |
1997年 | 659篇 |
1996年 | 575篇 |
1995年 | 575篇 |
1994年 | 510篇 |
1993年 | 442篇 |
1992年 | 347篇 |
1991年 | 250篇 |
1990年 | 153篇 |
1989年 | 142篇 |
1988年 | 120篇 |
1987年 | 75篇 |
1986年 | 77篇 |
1985年 | 67篇 |
1984年 | 53篇 |
1983年 | 37篇 |
1982年 | 45篇 |
1981年 | 48篇 |
1980年 | 50篇 |
1979年 | 44篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
111.
Dimitrios Tzovaras Nikos Grammalidis Michael G. Strintzis 《Signal Processing: Image Communication》1998,11(3):205-230
In the present paper techniques are examined for the coding of the depth map and disparity fields for stereo or multiview image communication applications. It is assumed that both the left and right channels of the multiview image sequence are coded using block- or object-based methods. A dynamic programming algorithm is used to estimate a disparity field between each stereo image pair. Depth is then estimated and occlusions are optionally detected, based on the estimated disparity fields. Spatial interpolation techniques are examined based on the disparity/depth information and the detection of occluded regions using either stereoscopic or trinocular camera configurations. It is seen that the presence of a third camera at the transmitter site improves the estimation of disparities, the detection of occlusions and the accuracy of the resulting spatial interpolation at the receiver. Various disparity field and depth map coding techniques are then proposed and evaluated, with emphasis given to the quality of the resulting intermediate images at the receiver site. Block-based and wireframe modeling techniques are examined for the coding of isolated depth or disparity map information. Further, 2D and 3D motion compensation techniques are evaluated for the coding of sequences of depth or disparity maps. The motion fields needed may be available as a byproduct of block-based or object-based coding of the intensity images. Experimental results are given for the evaluation of the performance of the proposed coding and spatial interpolation methods. 相似文献
112.
Several α-ketoalcohols of synthetic value were resolved using lipase as a catalyst. Lipoprotein lipase (LPL) provided the best rate of hydrolysis and kinetic differentiation. One of these optically pure α-ketoalcohol was converted to (5)-ibuprofen in good optical purity. The stereospecific inversion of (R)-alcohol to (S)-alcohol is described. 相似文献
113.
114.
115.
Semi-empirical molecular orbital calculations were carried out for the compounds (C2H5)3As, (C2H5)3Ga and RAsH2 (R = C2H5, i-C3H7, i-C4H9, and t-C4H9) by using the CNDO/2-U program, and their capability of β-elimination reaction is compared on the basis of the torsion energy to the transition state, electrostatic interactions and orbital overlapping between the central atom and the β-hydrogen, and bond order of the metal-carbon, and carbon-hydrogen bond. In the comparison of (C2H5)3As with (C2H5)3Ga, we found that the β-elimination of (C2H5)3As could hardly be expected to take place in the thermal decomposition. The capability of β-elimination would be smaller in C2H5AsH2 than that in (C2H5)3As. Moreover when the ethyl group is replaced by a t-butyl group in RAsH2, the β-elimination reaction appears to become more difficult and a large possibility for a radical process is suggested. 相似文献
116.
117.
The response to Hg(II) of a thin all-solid-state Te-doped silver chalcogenide membrane, described by the general formula Ag2 + δSe1 − xTex, which has been electrochemically prepared following a previously proposed approach, has been investigated. The kinetics of formation of the membrane's secondary dynamic response to Hg(II) has been successfully combined with the precise timing and transient signal, typical for flow-injection (FI) measurements, in developing a sensitive and reliable mercury FI detector. Under optimized stream conditions it exhibits a linear Nernstian response, with a double slope of the calibration graph of 59 mV dec−1, over the mercury(II) concentration range 10−6 − 10−3 M, the typical sample throughput amounting to about 70 samples per hour. The observed chemical amplification of the signal is due to the specificity of the processes dominating the initial step in formation of the steady-state signal of the membrane to mercury. The analytical performance of the Hg(II) FI detector, as regards sensitivity, reproducibility, selectivity and long-term stability has been thoroughly investigated. The exact procedure for membrane electrodeposition is given and the potential of the proposed approach as a cost-effective way for preparing chalcogenides of unique structure and properties has been outlined in the above context. 相似文献
118.
热处理WO3电变色膜稳定性研究 总被引:1,自引:0,他引:1
采用电子束蒸发淀积WO3薄膜。根据已有的WO3薄膜脱水过程结论而选择适当温度对薄膜进行退火处理。在大量含水的和不含水的两类Li^+电解质中进行比较性着色和消色循环实验,表明在290℃以下热退火处理能明显增加WO3薄膜在含水 电解质中的循环寿命。 相似文献
119.
钛酸铅系薄膜的热释电性能及其应用 总被引:10,自引:1,他引:9
叙述了钛酸铅系薄膜的热释电原理,介绍了国际上近几年钛酸铅系薄膜材料、制备工艺及热释电性能,并与块状陶瓷材料进行了比较,分析表明钛酸铅系薄膜具有优良的热释电性能及可观的应用前景。 相似文献
120.
微波介电陶瓷与微波磁介电陶瓷 总被引:6,自引:0,他引:6
微波陶瓷的应用越来越受到人们的重视。文章概括介绍了二元系微波介电陶瓷BaO-TiO2和微波磁性陶瓷BaO—Fe2O3,以及三元系微波磁介电陶瓷BaO—Fe2O3—TiO2的研究情况,并对预期进展作了展望。 相似文献