全文获取类型
收费全文 | 74588篇 |
免费 | 6434篇 |
国内免费 | 3289篇 |
专业分类
电工技术 | 4236篇 |
技术理论 | 10篇 |
综合类 | 4890篇 |
化学工业 | 12668篇 |
金属工艺 | 3946篇 |
机械仪表 | 4213篇 |
建筑科学 | 5775篇 |
矿业工程 | 1971篇 |
能源动力 | 2073篇 |
轻工业 | 6164篇 |
水利工程 | 1440篇 |
石油天然气 | 4029篇 |
武器工业 | 569篇 |
无线电 | 8826篇 |
一般工业技术 | 9246篇 |
冶金工业 | 3606篇 |
原子能技术 | 831篇 |
自动化技术 | 9818篇 |
出版年
2024年 | 370篇 |
2023年 | 1343篇 |
2022年 | 2485篇 |
2021年 | 3289篇 |
2020年 | 2501篇 |
2019年 | 2036篇 |
2018年 | 2322篇 |
2017年 | 2424篇 |
2016年 | 2310篇 |
2015年 | 3047篇 |
2014年 | 3700篇 |
2013年 | 4322篇 |
2012年 | 4776篇 |
2011年 | 5212篇 |
2010年 | 4292篇 |
2009年 | 4104篇 |
2008年 | 4043篇 |
2007年 | 3723篇 |
2006年 | 3514篇 |
2005年 | 3037篇 |
2004年 | 2251篇 |
2003年 | 1981篇 |
2002年 | 1798篇 |
2001年 | 1589篇 |
2000年 | 1756篇 |
1999年 | 2064篇 |
1998年 | 1737篇 |
1997年 | 1440篇 |
1996年 | 1409篇 |
1995年 | 1171篇 |
1994年 | 1021篇 |
1993年 | 711篇 |
1992年 | 557篇 |
1991年 | 404篇 |
1990年 | 345篇 |
1989年 | 315篇 |
1988年 | 226篇 |
1987年 | 156篇 |
1986年 | 114篇 |
1985年 | 81篇 |
1984年 | 62篇 |
1983年 | 41篇 |
1982年 | 53篇 |
1981年 | 35篇 |
1980年 | 36篇 |
1979年 | 14篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Y. Lu 《Journal of Materials Science》2003,38(5):1081-1085
A Golden Section approach combined with relational grade analysis is proposed as an experimental design tool helpful in the development of new automotive friction materials. Golden Section was used to design the volume fraction of the components systematically. The changes in friction performance (friction coefficient and wear) measured using Friction Assessment and Screening Test (FAST) can be correlated with component variations by use of relational grade analysis. This approach was utilized to optimize a non-metallic friction material containing seven ingredients including two fibers (aramid and slag fiber), four fillers (Al2O3, BaSO4, graphite and nitrile rubber) and one binder (benzoxazine). The volume fraction of seven components was varied simultaneously in order to optimize the parameters of friction coefficient and wear with a minimum number of tests. Three phases were performed to find the optimal proportion of the components. The optimized friction performance was obtained after doing 19 formulation experiments. 相似文献
62.
63.
A jet-printed digital-lithographic method, in place of conventional photolithography, was used to fabricate 64 /spl times/ 64 pixel (300 /spl mu/m pitch) matrix addressing thin-film transistor (TFT) arrays. The average hydrogenated amorphous silicon TFT device within an array had a threshold voltage of /spl sim/3.5 V, carrier mobility of 0.7 cm/sup 2//V/spl middot/s, subthreshold slope of 0.76 V/decade, and an on/off ratio of 10/sup 8/. 相似文献
64.
4G mobile communications: toward open wireless architecture 总被引:2,自引:0,他引:2
65.
66.
Zhen-Qiu Lu Yan-Yun Zhang 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(2):296-302
Reconstruction algorithms and their numerical examples of acoustical tomography based on the second-order Born transform perturbation approximation are presented. The reconstruction algorithms in the second-order Born approximation are similar in form to those in the first-order Born approximation. Replacing the angular spectrum of the scattered wave in the first-order case by the result of applying a first-order operator to the angular spectrum of the scattered wave or applying a second-order operator to the angular spectrum of the incident wave leads to the second-order reconstruction algorithms. Also, comparisons of reconstruction algorithms of the first- and second-order Born approximations are given, and they show that the second-order Born approximation algorithms have a distinct advantage over the first-order approximations in many cases 相似文献
67.
68.
含H_2S井完井液对井下金属管串具有腐蚀性。采用锌基或铁基螯合物除硫剂及咪唑啉缓蚀剂可有效地防止这种腐蚀的发生。本文对H_2S的腐蚀、除硫剂和缓蚀剂产品及其对产层的损害作了介绍与探讨。 相似文献
69.
The aim of this study was to determine the actual prevalence of diabetes mellitus and to investigate the contribution of various risk factors to the diabetes mellitus among the population in a methyl mercury polluted area. The study was a population based cross sectional mass screening survey. A case-control study was designed to estimate the role of various risk factors including methyl mercury exposure for diabetes mellitus. The study was confined to a small rural town 10 km north of Minamata City; 1,087 persons older than 40 years were examined. Measurement of glucose metabolism was made on the basis of urine and haematological examinations. Data on risk factors were collected by questionnaire, and by measurement of body height and weight (obesity). The prevalence rate of the diabetes mellitus was 8.4% in males and 5.3% in females. The odds ratio of family history was significantly higher, 4.63. The odds ratio of residential history in a methyl mercury high polluted area was 0.58. The prevalence of the diabetes mellitus in this methyl mercury polluted area was not increased, contrary to what was expected based on the pathological findings. 相似文献
70.
Robot Pose Estimation in Unknown Environments by Matching 2D Range Scans 总被引:14,自引:0,他引:14
A mobile robot exploring an unknown environment has no absolute frame of reference for its position, other than features it detects through its sensors. Using distinguishable landmarks is one possible approach, but it requires solving the object recognition problem. In particular, when the robot uses two-dimensional laser range scans for localization, it is difficult to accurately detect and localize landmarks in the environment (such as corners and occlusions) from the range scans.In this paper, we develop two new iterative algorithms to register a range scan to a previous scan so as to compute relative robot positions in an unknown environment, that avoid the above problems. The first algorithm is based on matching data points with tangent directions in two scans and minimizing a distance function in order to solve the displacement between the scans. The second algorithm establishes correspondences between points in the two scans and then solves the point-to-point least-squares problem to compute the relative pose of the two scans. Our methods work in curved environments and can handle partial occlusions by rejecting outliers. 相似文献