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   2311篇
  免费   20篇
  国内免费   1篇
电工技术   17篇
综合类   1篇
化学工业   118篇
金属工艺   16篇
机械仪表   14篇
建筑科学   35篇
矿业工程   3篇
能源动力   25篇
轻工业   88篇
水利工程   4篇
石油天然气   1篇
无线电   84篇
一般工业技术   127篇
冶金工业   1684篇
原子能技术   13篇
自动化技术   102篇
  2022年   5篇
  2020年   6篇
  2019年   5篇
  2018年   9篇
  2017年   16篇
  2016年   13篇
  2015年   8篇
  2014年   10篇
  2013年   24篇
  2012年   20篇
  2011年   29篇
  2010年   11篇
  2009年   20篇
  2008年   38篇
  2007年   27篇
  2006年   19篇
  2005年   38篇
  2004年   26篇
  2003年   18篇
  2002年   19篇
  2001年   17篇
  2000年   19篇
  1999年   65篇
  1998年   536篇
  1997年   264篇
  1996年   213篇
  1995年   111篇
  1994年   94篇
  1993年   118篇
  1992年   20篇
  1991年   17篇
  1990年   31篇
  1989年   26篇
  1988年   36篇
  1987年   27篇
  1986年   26篇
  1985年   22篇
  1984年   19篇
  1983年   15篇
  1982年   14篇
  1981年   19篇
  1980年   13篇
  1979年   8篇
  1978年   14篇
  1977年   65篇
  1976年   100篇
  1973年   7篇
  1972年   7篇
  1970年   6篇
  1967年   4篇
排序方式: 共有2332条查询结果,搜索用时 0 毫秒
61.
We examined the visceral blood flow distribution during infusion of three vasodilators at doses that produced similar depression of systemic arterial pressure. The studies were performed in pentobarbital-anesthetized dogs using the radioactive microspheres technique. Minoxidil did not alter renal, total visceral, or visceral organ flow distribution with the exception of a modest increase in relative stomach blood flow. Nitroprusside increased the percentage of total visceral flow to the spleen and the hepatic artery. Dopamine increased blood flow to the stomach, intestine, and kidney. After phenoxybenzamine, the augmentation of stomach blood flow by dopamine was greatly increased, while blood flow to the splenic, pancreatic, and hepatic arteriolar vascular beds decreased. The decreases in blood flows may be due to decreased perfusion pressure in the absence of active vasodilation or to myogenic or metabolic autoregulation. Thus, at equivalent hypotensive responses, the vasodilator compounds that we studied produced markedly different patterns of visceral blood flow.  相似文献   
62.
63.
Cryothermia, a new technique for definitive treatment of the pre-excitation syndrome, is described in two patients. The first patient presented with a normal P-R interval with a delta wave and reciprocating tachycardia. Preoperative electrophysiologic study suggested a free-wall atrioventricular connection on the left posterior atrioventricular (A-V) groove. At surgery, epicardial mapping confirmed the site of pre-excitation on the posterior left ventricular (LV) wall. An electrogram arising from the accessory pathway (AP) was recorded at the site of earliest ventricular activation. Interatrial delay combined with an apparently long accessory pathway to the ventricle caused the P-R interval to appear normal. Local pressure abolished pre-excitation. The site of early ventricular activation was cooled to -60 degrees C with a specially designed cryoprobe. All evidence of pre-excitation and arrhythmias disappeared. The second patient presented with a refractory reciprocating tachycardia and was found to have an AP in the septum capable of only retrograde conduction. Retrograde conduction was abolished by applying a temperature of 0 degrees C to the anulus at this site during tachycardia. Conduction over the AP and reciprocating tachycardia returned with rewarming. Ablation of the AP was obtained by applying a temperature of -60 degrees C for 90 seconds on two occasions to the same area. The His bundle was not injured.  相似文献   
64.
Massive medial calcific deposits (M?nckeberg's calcinosis) are described in the peripheral and visceral arteries, and similar but small-sized deposits in the coronary arteries of a 41 year old woman with diabetes mellitus. Although observed by roentgenogram fairly commonly during life in the muscular arteries of the legs in middle-aged men, medial calcinosis infrequently involves the visceral arteries and has never, to our knowledge, been documented in the coronary arteries. Although it may be associated with intimal atherosclerosis, medial calcinosis, per se, does not obstruct the lumens of the arteries and, therefore, does not lead to symptoms or signs of limb or organ ischemia. The cause of medial calcinosis remains a mystery, but it appears to affect people with diabetes more frequently than those without.  相似文献   
65.
During the synthesis of 3-hydroxy-3-ethinylquinuclidine (I), two additional products were isolated and identified as (E)-3-[2-(3-oxoquinuclidine)]quinuclidylidene (III) and (E)-3-[2-(3-hydroxy-3-ethinylquinuclidine)]quinuclidylidene (V). The base-catalyzed autocondensation of 3-quinuclidinone resulted in the alpha,beta-unsaturated ketone dimer (III) as a single isomer. The geometric configuration was deduced by examination of the NMR spectra of the methyl iodide salt. Compound V was thus the result of attack on the carbonyl carbon of III by the acetylide anion. The isolation and identification of these compounds clarified the reported differences in the physical properties of I and its analogs.  相似文献   
66.
A new system of patient protection from bacterial crossinfection called the Bacteria Controlled Nursing Unit (BCNU) is described, based on strict environmental control of a 6 x 10 foot area surrounding the patient's bed rather than the entire patient room or isolation ward, plus the ability to deliver all medical care without entering the protective environment and maintaining all monitoring, life support, and i.v. equipment outside the controlled environment. The clinical effectiveness of this system in the treatment of burn patients has been studied and compared with the effectiveness of single room isolation on a burn isolation ward and conventional isolation techniques on an open burn ward. The studies show that the BCNU is significantly more effective in preventing bacterial cross-contamination than conventional precautions (3.8% vs. 13.1%, P < 0.001; and 8% vs. 22.8%, P < 0.001) over a two and four week period. The studies also indicate that there was a significant increase in the probability of infection occurring following cross-contamination than occurring after auto-contamination (65% vs. 39%, P < 0.005), emphasizing the importance of preventing cross-contamination in reducing the overall infection rate in seriously burned patients. Clinical evaluation of the unit proved it to be compatible with intensive nursing and medical care without increasing the nurse to patient ratio. The unit provided sufficient control of bacterial cross-infection to allow reduction in mortality and improvement in the effectiveness of burn care through routine prompt excision of burn eschar and immediate wound closure to be carried out in severe and massively burned patients without a limiting threat of bacterial burn wound sepsis.  相似文献   
67.
Fistulas between the abdominal aorta and renal vein are exceedingly rare. Diagnostic delays are not unusual. Correction can be extremely difficult because of anatomical distortion and size of the arterialized veins. A young woman with such a fistula following a gunshot wound is presented. Four years following injury, the fistula was repaired successfully during intentional arrest of the circulation for 7 minutes. This was accomplished with deep hypothermia and cardiopulmonary bypass. No serious problems occurred during the operation. The patient tolerated the procedure well and has been relieved of her symptoms completely. Most patients with traumatic or spontaneous arteriovenous fistulas can be managed safely and effectively by conventional operative techniques. In selected situations, the risk of total circulatory arrest and deep hypothermia may be less than the risk of uncontrollable bleeding inherent in conventional techniques. Suggested indications for use of total circulatory arrest in vascular surgery are (1) inability to achieve vascular control by more conventional means, (2) massive distention of regional veins as occurrs in well established fistulas of the trunk, (3) one or more prior corrective attempts with use of conventional techniques, and (4) anticipated anatomical distortion and/or multiple abnormal vascular communications. This technique is a valuable approach to the correction of otherwise inoperable cardiovascular lesions.  相似文献   
68.
Clinical and morphologic observations are described in a 46 year old woman with fatal trichinosis. Attention is called to the occurrence of extensive ventricular endocardial damage with superimposed thrombosis; Evidence is presented to indicate that the most likely cause of the endocardial damage is the associated eosinophilia. The mechanism by which eosinophils damage endocardium, however, remains obscure.  相似文献   
69.
A mixture of sulfacetamide, sulfathiazole, and sulfabenzamide was used to develop a rapid high-pressure liquid chromatographic assay. In addition, this study provided a means to develop concepts relating solvent molar polarization parameters and retention times. A linear correlation between molar polarization and retention time was observed and will permit reasonably rapid predictions about the dependent variable.  相似文献   
70.
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