全文获取类型
收费全文 | 60100篇 |
免费 | 6127篇 |
国内免费 | 3130篇 |
专业分类
电工技术 | 3258篇 |
技术理论 | 1篇 |
综合类 | 3909篇 |
化学工业 | 10357篇 |
金属工艺 | 3224篇 |
机械仪表 | 3761篇 |
建筑科学 | 3736篇 |
矿业工程 | 1291篇 |
能源动力 | 1529篇 |
轻工业 | 6447篇 |
水利工程 | 1163篇 |
石油天然气 | 2001篇 |
武器工业 | 464篇 |
无线电 | 7236篇 |
一般工业技术 | 7789篇 |
冶金工业 | 3364篇 |
原子能技术 | 718篇 |
自动化技术 | 9109篇 |
出版年
2024年 | 210篇 |
2023年 | 831篇 |
2022年 | 1591篇 |
2021年 | 2271篇 |
2020年 | 1695篇 |
2019年 | 1549篇 |
2018年 | 1773篇 |
2017年 | 1868篇 |
2016年 | 1868篇 |
2015年 | 2438篇 |
2014年 | 3130篇 |
2013年 | 3997篇 |
2012年 | 4375篇 |
2011年 | 4982篇 |
2010年 | 4385篇 |
2009年 | 4289篇 |
2008年 | 4142篇 |
2007年 | 3797篇 |
2006年 | 3431篇 |
2005年 | 2880篇 |
2004年 | 2167篇 |
2003年 | 1730篇 |
2002年 | 1609篇 |
2001年 | 1339篇 |
2000年 | 1074篇 |
1999年 | 877篇 |
1998年 | 902篇 |
1997年 | 683篇 |
1996年 | 509篇 |
1995年 | 393篇 |
1994年 | 356篇 |
1993年 | 329篇 |
1992年 | 226篇 |
1991年 | 191篇 |
1990年 | 161篇 |
1989年 | 146篇 |
1988年 | 105篇 |
1987年 | 88篇 |
1986年 | 86篇 |
1985年 | 88篇 |
1984年 | 85篇 |
1983年 | 55篇 |
1982年 | 65篇 |
1981年 | 49篇 |
1980年 | 48篇 |
1979年 | 51篇 |
1978年 | 46篇 |
1977年 | 71篇 |
1976年 | 97篇 |
1975年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
63.
While digital signals tend to be more immune to noise as measured in analog systems, other noise related phenomena such as bit errors can cause problems which are equally as undesirable. This paper addresses one such noise artifact which is jitter in a digital bit stream. While the typical method of measuring jitter is with a sampling oscilloscope, a new technique using modulation domain analyzers was used. This method allows direct measurement of the spectral content of jitter. This technique has been used in the telecommunications industry and examples of their specifications are provided 相似文献
64.
65.
BACKGROUND: The enterococci have become important nosocomial pathogens. They can cause multiple site infections and enterococcal bacteremia becomes more frequently associated with a high mortality rate. Previous studies of enterococcal bacteremia showed a variety of results. To establish the significance and importance of enterococci as nosocomial pathogens in this hospital, to characterize their clinical pictures and to search for the risk factors for mortality, this retrospective study was performed. METHODS: There were 208 cases of enterococcal bacteremia which occurred from 1988 to 1992. Twenty-seven cases had no medical charts, dismissing possibility of evaluation. Finally, 181 cases of enterococcal bacteremia were analysed. RESULTS: One hundred and eighteen episodes were nosocomial infections. Polymicrobial bacteremia occurred in 68.5% of the patients and the most common co-isolate was Pseudomonas aeruginosa. Those patients (78.5%) with underlying diseases and malignancies were the most common underlying problems. The portal of entry could be found in 69.6 percent of patients, with the gastrointestinal tract the most common sources. Antimicrobial susceptibility testing showed high gentamicin resistance rate (89.5%), and ampicillin still had about 80 percent sensitivity rate. The group who received specific antibiotic therapy for enterococcus showed lower mortality (36.4% versus 47.6%). Only one case had infective endocarditis. Forty-nine patients suffered from septic shock, the cause of 30 deaths. Totally 75 patients died during hospitalization. Besides sepsis, another major cause of death was their underlying diseases itself. CONCLUSIONS: Enterococci have no doubt become important nosocomial pathogens and enterococcal bacteremia were associated with high mortality, especially in elderly patients with underlying diseases such as malignancy or diabetes. When clinically dealing with sepsis from the gastrointestinal or biliary tract, especially when previous cephalosporins therapy showed no response, the possibility of enterococcal bacteremia should always be considered. 相似文献
66.
无线局域网安全问题研究 总被引:10,自引:0,他引:10
为了提供相当于有线局域网的数据安全,IEEE802.11定义了有线等价保密(WEP)协议。然而,最近的研究发现WEP存在严重的缺陷。介绍了无线局域网存在的安全隐患,分析了WEP的结构以及WEP协议的缺陷以及可能遭受的攻击,并探讨了改进方案。 相似文献
67.
An endocrine testing center (ETC) is a universal requirement for the practice of endocrinology. Modifications of the Mayo Clinic model for an ETC should be applicable to most endocrine practices. Key components of an ETC include a centralized testing area, registered nurse-physician team, detailed testing protocols, and patient education programs. 相似文献
68.
JW Rhee 《The Journal of communication》1997,47(3):26-48
This study examines how news frames in campaign coverage affect individuals' interpretation of campaigns. Framing effects are conceptualized in terms of the process by which textual features in news stories set limits on knowledge use in the construction of a discourse model - a mental model constructed through the interaction between news frames and the interpreter's social knowledge. Examining message structures in campaign news stories led to identifying two major frames in campaign coverage: strategy and issue. Narrative data collected from two field experiments were analyzed. The findings suggest that both strategy-framed and issue-framed print news stories are effective in influencing campaign interpretation. 相似文献
69.
70.
深亚微米MOSFET衬底电流的模拟与分析 总被引:1,自引:0,他引:1
利用器件模拟手段对深亚微米MOSFET的衬底电流进行了研究和分析,给出了有效的道长度,栅氧厚度,源漏结深,衬底掺杂浓度以及电源电压对深亚微米MOSFET衬底电流的影响,发现电源电压对深亚微米MOSFET的衬底电流有着强烈的影响,热载流子效应随电源电压的降低而迅速减小,当电源电压降低到一定程度时,热载流子效应不再成为影响深亚微米MOS电路可靠性的主要问题。 相似文献