全文获取类型
收费全文 | 103343篇 |
免费 | 1495篇 |
国内免费 | 1227篇 |
专业分类
电工技术 | 1957篇 |
综合类 | 139篇 |
化学工业 | 10616篇 |
金属工艺 | 5463篇 |
机械仪表 | 3198篇 |
建筑科学 | 2036篇 |
矿业工程 | 159篇 |
能源动力 | 2976篇 |
轻工业 | 6111篇 |
水利工程 | 705篇 |
石油天然气 | 668篇 |
武器工业 | 15篇 |
无线电 | 15994篇 |
一般工业技术 | 21824篇 |
冶金工业 | 25404篇 |
原子能技术 | 1399篇 |
自动化技术 | 7401篇 |
出版年
2022年 | 458篇 |
2021年 | 707篇 |
2020年 | 522篇 |
2019年 | 682篇 |
2018年 | 1140篇 |
2017年 | 1098篇 |
2016年 | 1179篇 |
2015年 | 928篇 |
2014年 | 1499篇 |
2013年 | 4688篇 |
2012年 | 2586篇 |
2011年 | 3865篇 |
2010年 | 3110篇 |
2009年 | 3745篇 |
2008年 | 3917篇 |
2007年 | 4094篇 |
2006年 | 3707篇 |
2005年 | 3341篇 |
2004年 | 3192篇 |
2003年 | 3040篇 |
2002年 | 2687篇 |
2001年 | 2986篇 |
2000年 | 2735篇 |
1999年 | 3092篇 |
1998年 | 9500篇 |
1997年 | 6189篇 |
1996年 | 4785篇 |
1995年 | 3186篇 |
1994年 | 2801篇 |
1993年 | 2734篇 |
1992年 | 1638篇 |
1991年 | 1597篇 |
1990年 | 1521篇 |
1989年 | 1329篇 |
1988年 | 1174篇 |
1987年 | 870篇 |
1986年 | 893篇 |
1985年 | 918篇 |
1984年 | 805篇 |
1983年 | 702篇 |
1982年 | 700篇 |
1981年 | 682篇 |
1980年 | 576篇 |
1979年 | 479篇 |
1978年 | 417篇 |
1977年 | 539篇 |
1976年 | 968篇 |
1975年 | 301篇 |
1974年 | 277篇 |
1973年 | 257篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
22.
D. Kherifi H. Belhouchet S. Ramesh K.Y. Sara Lee A. Kenzour S. Djoualah M.K.G. Abbas Y.H. Wong S. Ramesh 《Ceramics International》2021,47(12):16483-16490
In this work, the sintering behaviour of fluorapatite (FAp)–silicate composites prepared by mixing variable amounts of natural quartz (2.5 wt% to 20 wt%) and FAp was studied. The composites were pressureless sintered in air at temperatures from 1000 °C to 1350 °C. The effects of temperatures on the densification, phase formation, chemical bonding and Vickers hardness of the composites were evaluated. All the samples exhibited mixed phase, comprising FAp and francolite as the major constituents along with some minor phases of cristobalite, wollastonite, dicalcium silicate and/or whitlockite dependent on the quartz content and sintering temperature. The composite containing 2.5 wt% quartz exhibited the best sintering properties. The highest bulk density of 3 g/cm3 and a Vickers hardness of >4.2 GPa were obtained for the 2.5 wt% quartz–FAp composite when sintered at 1100 °C. The addition of quartz was found to alter the microstructure of the composites, where it exhibited a rod-like morphology when sintered at 1000 °C and a regular rounded grain structure when sintered at 1350 °C. A wetted grain surface was observed for composites containing high quartz content and was believed to be associated with a transient liquid phase sintering. 相似文献
23.
Evangelopoulos Xenophon Brockmeier Austin J. Mu Tingting Goulermas John Y. 《Machine Learning》2019,108(4):595-626
Machine Learning - We propose a set of highly scalable algorithms for the combinatorial data analysis problem of seriating similarity matrices. Seriation consists of finding a permutation of data... 相似文献
24.
25.
Scientometrics - The purpose of this study is to ascertain the suitability of GS’s url-based method as a valid approximation of universities’ academic output measures, taking into... 相似文献
26.
The performance of surface ionic conduction single chamber fuel cell (SIC‐SCFC) prepared by the sol gel method was studied on electric characteristics due to the differences of the operating temperature and humidity, the electrode distance and electrolyte film depth, and multiple cells with the series and parallel connections. The SIC–SCFC was arranged the both anode of Pt and cathode of Au on the boehmite electrolyte. The open circuit voltage (OCV) of single cell achieved a maximum of 530mV in the dry gas mixtures of O2/H2=50% in room temperature operation, and but it became decrease as over 60%. The OCV was maintained the constant value between operating temperatures of 30°C to 80°C, and but it was decreased sharply at over 90°C because a humidity on the cell became lower as increasing operating temperature. Then, the cell property was improved to 120°C by adding to the humidity of 70% using a humidifier. The electrode distance and the electrolyte film depth of SIC‐SCFC found to be contributed to the reductions of the cell resistance and the surface roughness on the electrode, respectively. Moreover, the power property of SIC‐SCFC was significantly improved by cell stacks comprised of the series or parallel connection of a cell. 相似文献
27.
28.
29.
P.Y. Raval P.R. Pansara A.R. Makadiya N.H. Vasoya S.N. Dolia K.B. Modi 《Ceramics International》2018,44(15):17667-17674
The consequences of high energy mechanical milling, microwave-assisted heating and rapid thermal cooling on magnetic ordering in polycrystalline CaCu3Ti4O12 cubic perovskite have been investigated by means of X-ray powder diffractometry (300?K), dc magnetization in field – cooled and zero – field cooled modes (H = 100?Oe and 1000?Oe, T?=?5–300?K) (M – T curves) and M – H loop characteristics (T?=?5?K and 300?K, Hmax = 70?kOe). The M – T curves of unmilled and 16?h milled samples show pure antiferromagnetic and weak ferromagnetic ordering, respectively, 1?h and 6?h milled samples demonstrate the coexistence of both the phases while microwave-assisted and quenched samples exhibit classic antiferromagnetic transition and a low temperature paramagnetic–like contribution with different weights, well supported by the M – H loop characteristics. The observed transformations in the magnetic ordering are attributed to the ball-milling induced stress which curtails hybridization of empty Ti-3d orbitals with Cu-3d and O-2p orbitals and secondary phase formation. Oxygen vacancies associated with bound magnetic polarons originate ferromagnetism in the milled samples while unpaired electrons inhabited at the empty sites are the cause of paramagnetic centers. The low-temperature Curie – tail in M – T curve for quenched and microwave assisted samples is attributed to Ti3+ cations. 相似文献
30.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance
下载免费PDF全文
![点击此处可从《Journal of Computer Assisted Learning》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance. 相似文献