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   3609篇
  免费   56篇
  国内免费   3篇
电工技术   50篇
化学工业   766篇
金属工艺   47篇
机械仪表   61篇
建筑科学   153篇
矿业工程   18篇
能源动力   67篇
轻工业   315篇
水利工程   33篇
石油天然气   8篇
无线电   372篇
一般工业技术   444篇
冶金工业   868篇
原子能技术   34篇
自动化技术   432篇
  2022年   21篇
  2021年   56篇
  2020年   33篇
  2019年   41篇
  2018年   46篇
  2017年   36篇
  2016年   34篇
  2015年   43篇
  2014年   57篇
  2013年   180篇
  2012年   86篇
  2011年   149篇
  2010年   115篇
  2009年   115篇
  2008年   117篇
  2007年   149篇
  2006年   98篇
  2005年   92篇
  2004年   88篇
  2003年   90篇
  2002年   93篇
  2001年   63篇
  2000年   67篇
  1999年   74篇
  1998年   181篇
  1997年   135篇
  1996年   93篇
  1995年   83篇
  1994年   73篇
  1993年   70篇
  1992年   57篇
  1991年   53篇
  1990年   52篇
  1989年   40篇
  1988年   53篇
  1987年   62篇
  1986年   50篇
  1985年   53篇
  1984年   42篇
  1983年   48篇
  1982年   37篇
  1981年   53篇
  1980年   36篇
  1979年   41篇
  1978年   36篇
  1977年   55篇
  1976年   57篇
  1975年   52篇
  1974年   26篇
  1973年   32篇
排序方式: 共有3668条查询结果,搜索用时 0 毫秒
151.
An analytical method based on radioimmunoassay (RIA) has been developed for the determination of the antiarrhythmic agent, MK-0499, in plasma and urine. Owing to the potency of the drug, the specificity of this assay in human plasma could not be adequately determined using conventional RIA procedures. A highly specific procedure, based on LC/MS-MS, was developed to cross-validate the RIA. The lower quantifiable limits of the RIA and LC/MS-MS-based methods were 0.05 and 0.013 ng ml-1, respectively. Cross-validation data, compared using paired student's t-test regression analysis, showed excellent correlation between methods. The mass spectrometric assay was also used to simultaneously measure plasma concentrations of unlabeled and 14C-labeled MK-0499 following administration of the drug at high specific activity to volunteers.  相似文献   
152.
In Alberta, cellulitis condemnations average 0.5% and are among the highest in Canada. Presently, all cellulitis-affected birds are condemned for fear of systemic infections and public health implications. In a slaughterhouse sample of 102 birds condemned with cellulitis, Escherichia coli was isolated from 83.3% of the lesions. All hearts were cultured and from 11.2% E. coli was recovered. Gross lesions of perihepatitis, infected oviducts, and arthritis were found in 11.2%, 6.7%, and 2.9% of the birds, respectively. Serotyping suggested that visceral infection occurs independent of cellulitis in at least half of the cases. There was no correlation between microscopic visceral lesions and positive bacterial cultures. Two E. coli isolates of serogroup 0157 produced no toxin and neither isolate produced CS31A, F107, or F1845 fimbriae. Cellulitis lesions ranged from 0.55 to 218.9 cm2. All lesions under 16 cm2 and 64% of lesions up to 48 cm2 were considered suitable for trimming.  相似文献   
153.
AIM: The study of clinical running of gastric or duodenal ulcer in associated coronary heart disease (CHD). MATERIALS AND METHODS: 209 CHD patients with gastric ulcer (GU) or duodenal ulcer (DU) were examined clinically plus histological examination of gastric or duodenal mucosa biopsies was made. RESULTS: In CHD patients GU occurred more frequently (56%) than DU. The lesions involved more frequently lesser curvature of the stomach and pyloric part of the stomach. Males developed ulcers 3.5 times more frequently than females. Ulcers tended to a painless course without season exacerbations. The disease manifested first with gastric bleeding in 52% of the patients. GU and DU ran with frequent recurrences and long-term exacerbations (76% of patients) which coincided in time with CHD exacerbations. 68% of patients developed exacerbations within 10 days after myocardial infarction or aortocoronary bypass operation. Helicobacter pylori was present as a resolving factor in arising ulcer in 26% of patients. Microcirculatory disorders, reduced blood flow speed in gastric or duodenal mucosa, hypocoagulation syndrome, dyslipidemia provoked exacerbations in 62% of patients. Examinations of biopsies from gastric and duodenal mucosa showed marked dystrophic changes in the mucosa, its connective tissue basis in the vessels in the presence of mild inflammation at ulcer site. CONCLUSION: The onset of ulcers and erosions in the mucosa of the gastrointestinal tract in CHD may be due to circulatory disorders in gastric mucosa. The main factors of aggression are hypoxia, hypoxia-induced trophic defects in gastric and duodenal mucosa, circulatory disorders.  相似文献   
154.
155.
PURPOSE: Present radiobiological studies for different cell lines in vitro demonstrate the equivalence and efficacy of continuous low-dose-rate brachytherapy (LDR-BT) and pulsed dose rate brachytherapy (PDR-BT) when using small and frequent dose pulses. The aim of this study was to examine monolayer fibroblast cultures in vitro to examine the biological effects of different pulse doses and dose rates under clinically conditions. MATERIAL AND METHODS: B14 cells, Hy B14 FAF 28, peritoneal fibroblasts, were cultured in multi-well plates and exposed to a PDR radiation source at a distance of 9 mm. The following PDR-schemes were compared: dose per pulse: 1 Gy, 2.5 Gy and 5 Gy to a total dose of 5 Gy/5 h (overall time), 10 Gy/10 h, 20 Gy/20 h and 30 Gy/30 h. The pulse duration for the examination of dose rate effects was 20 min, 30 min or 52 min corresponding by dye pulse dose rate of 300 cGy/h, 200 cGy/h or 115 cGy/h. Treatment endpoints were cell measured by dye exclusion test and clonogenic cell survival. RESULTS: Cell survival decreased for pulse doses of 5 Gy compared to 2.5 Gy or 1 Gy per pulse (mean dose rate 200 to 300 cGy/h). No differences were observed with dose rates during irradiation of 300 cGy/h, 200 cGy/h or 115 cGy/h (20 Gy/1 Gy). CONCLUSION: Radiobiological effects of PDR-RT are dependent on the dose per pulse, with differences in biological effects only with a dose per pulse of more than 2.5 Gy, considering the described in-vitro conditions. More examinations with a more pronounced difference in dose rate will be continued for evaluation of dose rate effects.  相似文献   
156.
OBJECTIVES: This study was performed to determine the efficacy of new encircling overlapping multipulse, multipathway waveforms for transthoracic defibrillation. BACKGROUND: Alternative waveforms for transthoracic defibrillation may improve shock success. METHODS: First, we determined the shock success achieved by three different waveforms at varying energies (18-150 J) in 21 mongrel dogs after short-duration ventricular fibrillation. The waveforms tested included the traditional damped sinusoidal waveform, a single pathway biphasic waveform, and a new encircling overlapping multipulse waveform delivered from six electrode pads oriented circumferentially. Second, in 11 swine we compared the efficacy of encircling overlapping multipulse shocks given from six electrode pads and three capacitors versus encircling overlapping shocks given from a device utilizing three electrodes and one capacitor. RESULTS: In the first experiment, the encircling overlapping waveform performed significantly better than biphasic and damped sinusoidal waveforms at lower energies. The shock success rate of the overlapping waveform (six pads) ranged from 67+/-4% (at 18-49 J energy) to 99+/-3% at > or = 150 J; at comparable energies biphasic waveform shock success ranged from 26+/-5% (p < 0.01 vs. encircling overlapping waveforms) to 99+/-5% (p = NS). Damped sinusoidal waveform shock success ranged from 4+/-1% (p < 0.01 vs. encircling overlapping waveform) to 73+/-9% (p = NS). In the second experiment the three electrode pads, one capacitor encircling waveform achieved shock success rates comparable with the six-pad, three-capacitor waveform; at 18-49 J, success rates were 45+/-15% versus 57+/-12%, respectively (p = NS). At 100 J, success rates for both were 100%. CONCLUSIONS: We conclude that encircling overlapping multipulse multipathway waveforms facilitate transthoracic defibrillation at low energies. These waveforms can be generated from a device that requires only three electrodes and one capacitor.  相似文献   
157.
This paper describes the development of a zero base budgeting process as part of an integral planning-budgeting-control system relating client needs with service programs. Particular attention is focused on designing, gaining acceptance for and implementing a new budgeting system for the human services agencies of a rural county government. The relationship of the zero base budgeting process to the client case management and evaluation system are explored. Problems encountered in implementing the system and an evaluation of the results are discussed.  相似文献   
158.
During the past five years we have evaluated argon laser photocoagulation in various canine models of upper gastrointestinal hemorrhage. In gastric erosions, the eight-watt argon laser was uniformly effective in stopping bleeding. In our standard acute ulcer model the seven-watt argon laser was effective in stopping bleeding from most ulcers and only occasionally produced deep injury. With the addition of a jet of CO2 exiting the laser catheter coaxial to the laser beam, the argon laser was 100% effective and no deep injury resulted. The application of the argon laser in a more physiologic canine bleeding model using a single bleeding vessel in an ulcer base is currently under study. The development of improved animal models of gastrointestinal bleeding should contribute to the identification of effective and safe endoscopic hemostatic methods.  相似文献   
159.
160.
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