首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   765122篇
  免费   22513篇
  国内免费   10454篇
电工技术   22603篇
技术理论   13篇
综合类   12171篇
化学工业   116725篇
金属工艺   34162篇
机械仪表   29771篇
建筑科学   27061篇
矿业工程   7980篇
能源动力   21237篇
轻工业   60012篇
水利工程   8801篇
石油天然气   19603篇
武器工业   1423篇
无线电   92526篇
一般工业技术   136152篇
冶金工业   122031篇
原子能技术   13823篇
自动化技术   71995篇
  2023年   4525篇
  2022年   9460篇
  2021年   13449篇
  2020年   10088篇
  2019年   9844篇
  2018年   13787篇
  2017年   14440篇
  2016年   14305篇
  2015年   13232篇
  2014年   18659篇
  2013年   39168篇
  2012年   27282篇
  2011年   33342篇
  2010年   27375篇
  2009年   28789篇
  2008年   29061篇
  2007年   28112篇
  2006年   26507篇
  2005年   23574篇
  2004年   20094篇
  2003年   19234篇
  2002年   18321篇
  2001年   17815篇
  2000年   16748篇
  1999年   18283篇
  1998年   39538篇
  1997年   28072篇
  1996年   22217篇
  1995年   16691篇
  1994年   14591篇
  1993年   14033篇
  1992年   10226篇
  1991年   9605篇
  1990年   9039篇
  1989年   8568篇
  1988年   8166篇
  1987年   7083篇
  1986年   6896篇
  1985年   7758篇
  1984年   7071篇
  1983年   6366篇
  1982年   5930篇
  1981年   6017篇
  1980年   5616篇
  1979年   5341篇
  1978年   5294篇
  1977年   6252篇
  1976年   8577篇
  1975年   4532篇
  1973年   4311篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Simultaneous determination of six ephedrines in urine sample has been achieved by high performance liquid chromatography on a Lichrospher RP-18 column, using methylamphetamine as internal standard. The 6 ephedrines are well separated in 25 minutes with resolution better than 1.8. This method has high recovery, selectivity and reproducibility, and the linearity is satisfactory from 1.5 micrograms/ml to 25 micrograms/ml with correlation coefficients better than 0.999.  相似文献   
72.
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis.  相似文献   
73.
One month following the Great Hanshin Earthquake of January 17, 1995, we conducted a survey of 173 hospitals in Aichi Prefecture to pinpoint problems related to their actual disaster-readiness and the medical backup systems in place to deal with such disasters. This study revealed that staff at 50% of the surveyed hospitals could reach the hospital within an hour, but that communication is almost entirely dependent on phone lines, suggesting that cordless/portable/mobile phones, radio systems, Internet, communications satellites and the like should be studied in the days to come for possible use as effective communication alternatives in times of disaster. Whereas 92% of the surveyed hospitals had manuals dealing with fire outbreaks, other areas were less well represented. For example, only 36.9% of surveyed hospitals had manuals for earthquakes, 31.7% had manuals for power outages and 14.2% had manuals to deal with flooding and water disasters. New manuals must be developed incorporating the key points garnered from experience (especially Hanshin) and be ready for use immediately. It is the time for each hospital to seriously rethink the measures it should take to deal with disasters.  相似文献   
74.
75.
The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels  相似文献   
76.
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   
77.
78.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
79.
In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature.  相似文献   
80.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号