全文获取类型
收费全文 | 4859篇 |
免费 | 1041篇 |
国内免费 | 491篇 |
专业分类
化学 | 1371篇 |
晶体学 | 127篇 |
力学 | 167篇 |
综合类 | 31篇 |
数学 | 166篇 |
物理学 | 1931篇 |
无线电 | 2598篇 |
出版年
2024年 | 17篇 |
2023年 | 88篇 |
2022年 | 103篇 |
2021年 | 168篇 |
2020年 | 189篇 |
2019年 | 168篇 |
2018年 | 152篇 |
2017年 | 229篇 |
2016年 | 258篇 |
2015年 | 293篇 |
2014年 | 345篇 |
2013年 | 480篇 |
2012年 | 370篇 |
2011年 | 358篇 |
2010年 | 279篇 |
2009年 | 318篇 |
2008年 | 296篇 |
2007年 | 345篇 |
2006年 | 278篇 |
2005年 | 238篇 |
2004年 | 165篇 |
2003年 | 175篇 |
2002年 | 185篇 |
2001年 | 142篇 |
2000年 | 138篇 |
1999年 | 77篇 |
1998年 | 73篇 |
1997年 | 60篇 |
1996年 | 64篇 |
1995年 | 59篇 |
1994年 | 47篇 |
1993年 | 40篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 6篇 |
排序方式: 共有6391条查询结果,搜索用时 234 毫秒
141.
142.
E. Pollatos E. Logakis P. Chatzigeorgiou V. Peoglos I. Zuburtikudis M. Gjoka 《Journal of Macromolecular Science: Physics》2013,52(5):1044-1056
In this work, syndiotactic polypropylene/multiwalled carbon nanotubes (MWCNT) nanocomposites, in various concentrations, were produced using melt mixing. The influence of the addition of MWCNT on the morphology, crystalline form, and the thermal and electrical properties of the polymer matrix was studied. To that aim, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, and dielectric relaxation spectroscopy were employed. Significant alterations of both the crystallization behavior and the thermal properties of the matrix were found on addition of the carbon nanotubes: conversion of the disordered crystalline form I to the ordered one, increase of the crystallization temperature and the degree of crystallinity, and decrease of the glass transition temperature and the heat capacity jump. Finally, the electrical percolation threshold was found between 2.5–3.0 wt.% MWCNT. For comparison purposes, the results of the system studied here are also correlated with the findings from a previous work on the isotactic polypropylene/MWCNT system. 相似文献
143.
Ashkan Javaherian Amir Movafeghi Reza Faghihi Effat Yahaghi 《Journal of Visual Communication and Image Representation》2013,24(7):773-785
This study proposes a versatile criterion for estimating quality of images in electrical impedance tomography. The point spread function (PSF) is calculated throughout the domain based on the scattering of energy as responses to a small anomaly spirally moved from the centre to the boundary. The proposed PSF is a measure of weighted spatial variance (WSV) of the conductivity over the whole domain. For each element, the weighting factor is a normalized multiplication of the area of that element by its square intensity. The WSV collectively incorporates all image attributes, i.e., spatial resolution, artifact, amplitude response, positioning error and shape deformation. The location of artifacts, which significantly influences reconstructed images in reality, is taken into account as well. The results illustrate that the proposed measure is more tolerant than existing criteria in evaluating performance of EIT systems in both theory and practice. 相似文献
144.
Hewei Luo Zitong Liu Zhengxu Cai Liusuo Wu Guanxin Zhang Chenyang Liu Deqing Zhang 《中国化学》2012,30(7):1453-1458
A new electroactive polymer 1 with alternating NDI (naphthalene diimide) moieties and fluorinated alkyl chains was prepared and characterized. Gels of polymer 1 were formed in several solvents. Interestingly, gels of polymer 1 exhibited responsiveness toward N2H4, F? and CN?. Absorption and ESR spectroscopic studies revealed that such responsiveness is owing to the reduction of NDI moieties into the respective NDI.?. In addition, thin films of polymer 1 were easily prepared with spin‐coating technique and the electrical conductivity of thin films reached 52.4 S/m after exposure to N2H4 vapor. 相似文献
145.
Daniel Xu Andreas Tairych Iain A. Anderson 《Journal of Polymer Science.Polymer Physics》2016,54(4):465-472
Practice makes perfect to some extent. Research has shown that musicians who practice the piano for long periods of time can suffer a range of hand problems from loss of control to diminished speed. Now imagine a rubber keyboard that is springy, soft, and elastic. This is the new type of input device that dielectric elastomers (DE) can create. However their usage in large sensing systems is limited by a scalability challenge. Each DE sensor is married to a pair of connection cables and electronics, adding to the complexity of the background overheads. A new efficient multi‐frequency method is presented that is capable of detecting internal pressure changes from a difference in the DE's capacitance without the need for any additional wires or connections. This effectively segments the DE into smaller sections, achieving information from a single sensor equivalent to multiple sensors. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 465–472 相似文献
146.
Dongho Park Nak‐Kyoung Choi Sang‐Gu Lee Jungho Hwang 《Particle & Particle Systems Characterization》2009,26(4):179-186
For this study, a 4 stage electrical low pressure impactor was designed to measure the real‐time size distribution of diesel particulate matter (DPM). For the performance evaluation, sodium chloride (NaCl) particles and dioctyl sebacate (DOS) particles were used. After evaluating the collection efficiency of each stage of the impactor, the size distributions of test particles were estimated using electrical current data and their inversion algorithm, and this was found to agree with the results obtained by a scanning mobility particle sizer (SMPS). For measurement of DPM, a common‐rail direct injection (CRDI) diesel engine, for engine speeds of 1,200 rpm and 1,500 rpm at 2.7 kgf·m, was used. Therefore, it was found that the size distribution of the DPM could be easily obtained, with the currents measured by the impactor and the data inversion algorithm, in less than 5 seconds. Furthermore, the effective density of the DPM could be obtained using the calculated results and the SMPS data. 相似文献
147.
This paper deals with ultrasound medical image processing, particularly to filter the noise while preserving the edges and
structures of information. The mathematical processing consists in solving by a numerical way a nonlinear evolutive boundary
value problem. Several numerical semi-implicit time marching schemes are considered and analyzed. At each time step, parallel
synchronous or asynchronous Schwarz alternating methods are used to solve the linear system and its convergence is studied.
Lastly, the results of sequential and parallel simulations are presented.
相似文献
148.
149.
寄生电容参数提取是集成电路领域的关键课题,也是典型的静电场问题之一。通过研究电磁场对偶离散几何法, 探讨在二维非结构化网格离散空间上相应的寄生电容提取算法, 其中重点考察其对偶特性以及能量互补特性。基于该特性,同时采用对偶的两种方法能够有效地消除网格离散带来的误差,比采用单一方法更快地逼近真实解,从而可发展出静电场能量快速算法。并从理论与实例两方面将其与对偶有限元法实施分析对比。离散几何法采用对偶两套网格上的标量电势作为未知量,具有简单的形式与良好的精度,有望成为相关领域的一种主流方法。 相似文献
150.
The crystallization kinetics of Sn40Se60 thin films has been successfully investigated using sheet resistance versus temperature measurements. Thermal evaporation was used to deposit the films on ordinary glass substrates. The crystallization temperature for Sn40Se60 thin film was found to be 156.6 ± 0.3 ℃. In the as-deposited state, the sheet resistance was found to be 195 MΩ, this value declined to 1560 Ω/口 upon annealing. The value of activation energy obtained from the Kissinger plot was 0.62 ± 0.07 eV. From the results obtained, Sn40Se60 is a promising alloy for PCM application because of its high electrical contrast, high crystallization temperature, and relatively high activation energy. 相似文献