全文获取类型
收费全文 | 24480篇 |
免费 | 295篇 |
国内免费 | 690篇 |
专业分类
电工技术 | 416篇 |
综合类 | 188篇 |
化学工业 | 2391篇 |
金属工艺 | 753篇 |
机械仪表 | 1346篇 |
建筑科学 | 1342篇 |
矿业工程 | 812篇 |
能源动力 | 164篇 |
轻工业 | 4633篇 |
水利工程 | 469篇 |
石油天然气 | 625篇 |
武器工业 | 182篇 |
无线电 | 1575篇 |
一般工业技术 | 8082篇 |
冶金工业 | 536篇 |
原子能技术 | 223篇 |
自动化技术 | 1728篇 |
出版年
2023年 | 46篇 |
2022年 | 87篇 |
2021年 | 89篇 |
2020年 | 73篇 |
2019年 | 57篇 |
2018年 | 99篇 |
2017年 | 35篇 |
2016年 | 69篇 |
2015年 | 99篇 |
2014年 | 185篇 |
2013年 | 175篇 |
2012年 | 2513篇 |
2011年 | 3049篇 |
2010年 | 671篇 |
2009年 | 337篇 |
2008年 | 2066篇 |
2007年 | 1958篇 |
2006年 | 1655篇 |
2005年 | 1438篇 |
2004年 | 1171篇 |
2003年 | 994篇 |
2002年 | 959篇 |
2001年 | 767篇 |
2000年 | 729篇 |
1999年 | 546篇 |
1998年 | 361篇 |
1997年 | 343篇 |
1996年 | 324篇 |
1995年 | 344篇 |
1994年 | 285篇 |
1993年 | 223篇 |
1992年 | 273篇 |
1991年 | 269篇 |
1990年 | 255篇 |
1989年 | 269篇 |
1988年 | 239篇 |
1987年 | 242篇 |
1986年 | 255篇 |
1985年 | 270篇 |
1984年 | 264篇 |
1983年 | 243篇 |
1982年 | 224篇 |
1981年 | 195篇 |
1980年 | 149篇 |
1979年 | 112篇 |
1978年 | 70篇 |
1976年 | 35篇 |
1975年 | 41篇 |
1974年 | 34篇 |
1965年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
Kamlet MJ Doherty RM Carr PW Mackay D Abraham MH Taft RW 《Environmental science & technology》1988,22(5):503-509
94.
Interactions of metals and protons with algae 总被引:2,自引:0,他引:2
Crist RH Oberholser K Schwartz D Marzoff J Ryder D Crist DR 《Environmental science & technology》1988,22(7):755-760
95.
An image-processing method called measurement-dependent filtering has been introduced to improve the SNR (signal-to-noise ratio) of selective images produced by various medical imaging systems. The basic algorithm involves the combination of the low-frequency information of the selective image with the high-frequency information of a nonselective image. A spatially variant control function modulates the amount of high frequency to be added at each point. A least-mean-square (LMS) control function formed from two basis images, namely the high-passed versions of the nonselective image (M(b)) and the selective image (S(b)), is introduced. The original algorithm is now viewed as a two-stage filtering method, including the low-pass filtering noise reduction and least squares filtering for the edge restoration. An appropriate linear transformation is used to convert the original basis images M(b) and S(b) into a new pair with orthogonal noise. This allows the implementation of the LMS and control function with practically obtainable a priori knowledge. 相似文献
96.
A study has been conducted on the microbiology of sheep carcasses processed in a modern abattoir. The data revealed that careful handling at the different stages of processing of sheep reduced the level of microbial contamination of carcasses. Processing steps such as evisceration and washing did not increase the microbial counts on the carcass surface. Sources of microbial contamination in the abattoir were examined. It was observed that skin, floor washings, intestinal contents and gambrels were the major sources of microbial contamination. Seasonality did not have any effect on the microbial contamination of carcasses. The study revealed that total plate counts in 86·6% of the carcasses ranged between 3·0–4·9log/cm2. The counts of coliforms, staphylococci, enterococci and psychrotrophs were low. Pathogens such as Salmonella were not detected. The microbial counts were well within the generally acceptable levels. These findings demonstrated hygienic handling of carcasses. Shoulder and neck are the critical points for microbiological sampling as these sites showed higher microbial counts. Micrococcus and Staphylococcus predominated among microorganisms associated with carcasses. It was noted that differences occurred in microbial types of carcasses processed in tropical and temperate climates. The data generated in a model facility procided useful information for improving meat handling practices. 相似文献
97.
A fundamental analysis of phase aberration correction techniques which use speckle brightness-based image equality factors (QFs) to iteratively reduce phase errors is presented. Phase aberration arises from the spatial inhomogeneity of acoustic velocity in human tissue and degrades the performance of diagnostic ultrasonic imaging systems. A theoretical analysis is presented indicating that the mean speckle brightness decreases with root-mean-square (RMS) phase error. A general definition of QFs is given using the probability of error as a criterion of performance. The QF is optimized through minimization of the probability of error under different conditions. The analysis provides a theoretical framework for the current correction technique using QFs under a variety of conditions, and is a useful tool to evaluate new QFs and correction techniques. 相似文献
98.
99.
In self-paced tracking tasks, such as driving, the speed is related to the lateral tolerance. This lateral tolerance has been varied in two ways in previous studies by changing the track width for constant vehicle width and vice versa. The current study used both an automobile driving task and a computer/mouse task to show that these two ways of varying lateral tolerance did not produce equivalent results. Subjects behaved as if vehicle width were less important than track width. Speeds and errors both increased as vehicle width increased for a constant lateral tolerance. This could have safety consequences when driving in confined spaces. 相似文献
100.
Current applications of electronic performance monitoring based on job design theories that consider worker performance rather than stress issues are likely to generate unsatisfying and stressful jobs (Smith et al, 1986). This study examines critical job design elements that could influence worker stress responses in an electronic monitoring context. A questionnaire survey of employees in telecommunications companies representative of each region in the United States examined job stress in directory assistance, service representative and clerical jobs with specific emphasis on the influence of electronic monitoring of job performance, satisfaction and employee health. Useable surveys were received from 745 employees representing seven operating companies and AT & T; a response rate of about 25%. The results of this survey indicated that employees who had their performance electronically monitored perceived their working conditions as more stressful, and reported higher levels of job boredom, psychological tension, anxiety, depression, anger, health complaints and fatigue. It is postulated that these effects may be related to changes in job design due to electronic performance monitoring. 相似文献