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   1861篇
  免费   25篇
  国内免费   1篇
电工技术   40篇
化学工业   399篇
金属工艺   29篇
机械仪表   32篇
建筑科学   81篇
矿业工程   7篇
能源动力   49篇
轻工业   115篇
水利工程   21篇
石油天然气   4篇
无线电   102篇
一般工业技术   245篇
冶金工业   523篇
原子能技术   14篇
自动化技术   226篇
  2021年   34篇
  2020年   19篇
  2019年   26篇
  2018年   25篇
  2017年   23篇
  2016年   21篇
  2015年   19篇
  2014年   29篇
  2013年   90篇
  2012年   52篇
  2011年   85篇
  2010年   76篇
  2009年   46篇
  2008年   64篇
  2007年   71篇
  2006年   48篇
  2005年   39篇
  2004年   37篇
  2003年   37篇
  2002年   44篇
  2001年   29篇
  2000年   26篇
  1999年   29篇
  1998年   105篇
  1997年   57篇
  1996年   54篇
  1995年   46篇
  1994年   46篇
  1993年   32篇
  1992年   22篇
  1991年   18篇
  1990年   22篇
  1989年   21篇
  1988年   26篇
  1987年   29篇
  1986年   22篇
  1985年   35篇
  1984年   21篇
  1983年   26篇
  1982年   28篇
  1981年   23篇
  1980年   17篇
  1979年   27篇
  1978年   18篇
  1977年   24篇
  1976年   24篇
  1975年   28篇
  1974年   17篇
  1973年   15篇
  1969年   16篇
排序方式: 共有1887条查询结果,搜索用时 328 毫秒
91.
92.
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   
93.
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   
94.
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   
95.

A possible interpretation of the so-called Poley absorption in polar liquids is that it is due to overlapping contributions from liquid- lattice bands together with a contribution from an inertially “rolled-off” Debye absorption. We propose a test involving the inertially similar but electrically very different molecules methyl chloroform and carbon tetrachloride. This test gives results which offer plausible support for the two-component interpretation.

  相似文献   
96.
97.
98.
It is well known that long chain alcohols and phenols cannot react with ethylene oxide in the absence of catalysts, whereas primary fatty amines can take up at least two moles of oxide to form tertiary amines. It has been found that further ethoxylation of this two mole adduct in the absence of added catalyst can proceed only if ethoxylation temperatures are lowered considerably. The present paper demonstrates that this low-temperature ethoxylation is really catalyzed by a previously overlooked highly alkaline compound generated during the course of the reaction. It is shown that this is a long-chain quaternary ammonium compound, and the mechanism of its formation is described. As the addition of ethylene oxide proceeds, this quaternary gradually decomposes and the reaction essentially comes to a halt when it has all disappeared.  相似文献   
99.
Results of a survey of 19 doctoral psychology programs indicate that the majority of faculty in university-affiliated free-standing professional programs are part-time, and their primary income and professional identity are outside the educational program. Questions are raised concerning faculty commitment to student education, financial viability and institutional stability, the history of free-standing schools in other professions, and whether psychology should continue to be based in the university. (4 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
100.
Varied rated noun imagery (I), rated adjective I, and noun-adjective order in a paired-associate (PA) learning task. 98 10th graders learned 2 PA lists, 1 with noun-adjective (N-A) pairs and 1 with adjective-noun (A-N) pairs. Within each list rated I of both nouns and adjectives was varied factorially. Both English- and French-speaking Ss learned the lists in their own languages. Results support the predictions from an hypothesis based on mediating imagery. N-A recall was superior to A-N recall for all combinations of word I, except when nouns were low and adjectives high in I. In the latter case, A-N recall was higher. This pattern was the same for both English- and French-speaking Ss. Results are interpreted as further evidence of the important role played by imagery in verbal learning. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
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