全文获取类型
收费全文 | 70387篇 |
免费 | 5648篇 |
国内免费 | 2972篇 |
专业分类
电工技术 | 3890篇 |
技术理论 | 10篇 |
综合类 | 4535篇 |
化学工业 | 11517篇 |
金属工艺 | 3583篇 |
机械仪表 | 3885篇 |
建筑科学 | 5375篇 |
矿业工程 | 1823篇 |
能源动力 | 1915篇 |
轻工业 | 5305篇 |
水利工程 | 1288篇 |
石油天然气 | 3663篇 |
武器工业 | 526篇 |
无线电 | 8235篇 |
一般工业技术 | 8504篇 |
冶金工业 | 5168篇 |
原子能技术 | 715篇 |
自动化技术 | 9070篇 |
出版年
2024年 | 310篇 |
2023年 | 1175篇 |
2022年 | 2085篇 |
2021年 | 2872篇 |
2020年 | 2243篇 |
2019年 | 1782篇 |
2018年 | 2045篇 |
2017年 | 2132篇 |
2016年 | 2084篇 |
2015年 | 2675篇 |
2014年 | 3337篇 |
2013年 | 3890篇 |
2012年 | 4298篇 |
2011年 | 4704篇 |
2010年 | 3881篇 |
2009年 | 3705篇 |
2008年 | 3679篇 |
2007年 | 3440篇 |
2006年 | 3277篇 |
2005年 | 2856篇 |
2004年 | 2134篇 |
2003年 | 1889篇 |
2002年 | 1729篇 |
2001年 | 1546篇 |
2000年 | 1687篇 |
1999年 | 2059篇 |
1998年 | 2243篇 |
1997年 | 1710篇 |
1996年 | 1592篇 |
1995年 | 1250篇 |
1994年 | 1105篇 |
1993年 | 797篇 |
1992年 | 554篇 |
1991年 | 418篇 |
1990年 | 357篇 |
1989年 | 335篇 |
1988年 | 243篇 |
1987年 | 176篇 |
1986年 | 127篇 |
1985年 | 106篇 |
1984年 | 61篇 |
1983年 | 42篇 |
1982年 | 59篇 |
1981年 | 41篇 |
1980年 | 43篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 41篇 |
1976年 | 102篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Wang Tian-kui Lu Fang Fan Xiao-bing Shi Xiao-jun China Ship Scientific Research Center Wuxi China 《水动力学研究与进展(B辑)》2003,15(4)
1 . INTRODUCTIONIntherecentdecades ,itisrealizedthatitisquitenecessarytocarryouttestsathighReynoldsnumberwithalowbackgroundnoiselevelinordertomeetmoreandmoreurgentneedsofmodernnavyandmaritimeindustry .Anewlargecavita tionchannelisdevelopedinCSSRCfortestingcompletehull/ propulsor/appendagesarrange ments[1] .Itrepresentsoneofthelatestintechno logicallyadvancedlargecavitationtestfacilities.Inthefollowingsections ,thefeaturesandthefirsttestresultsofthechannelwillbedescribed .2 . DICRIP… 相似文献
92.
4G mobile communications: toward open wireless architecture 总被引:2,自引:0,他引:2
93.
Researchers have carried out a variety of investigations to determine the properties of available dentin bonding systems. The test methods and variables used in 50 published investigations of bond strength were analyzed. Among the studies analyzed, shear tests predominated, being used in 80% of the studies; dentin from human molar teeth was used most often (in 88% of investigations); and the most prevalent time of testing was 24 hours postcuring. However, a number of potential variables were not recorded in a high proportion of articles, among these the film thickness, the type of dentin tested, and the surface condition (moist or dry). The mode of failure was recorded in only 42% of the investigations assessed. It was found that there is little standardization of test methods in studies of dentin bond strength and that a number of variables are often either not recorded or reported. 相似文献
94.
95.
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
96.
本文利用OMA-Ⅲ系统测量了脉冲TEA CO_2激光诱发的SiH_4等离子体发光谱内H巴耳末系的H_α、H_β和H_γ线的线型及线宽。通过理论及实验分析,认为这些谱线的主要加宽机制为Stark加宽。由实验线型和理论线型的拟合得到等离子体的电子温度T≈40000K和电子密度N≈10~(17)cm~(-3)。 相似文献
97.
98.
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
99.
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
100.
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