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   2048篇
  免费   0篇
电工技术   1篇
化学工业   4篇
金属工艺   1篇
建筑科学   1篇
轻工业   2篇
石油天然气   1篇
无线电   3篇
一般工业技术   8篇
冶金工业   2027篇
  2023年   1篇
  2020年   1篇
  2013年   1篇
  2011年   1篇
  2009年   1篇
  2008年   1篇
  2007年   1篇
  2006年   1篇
  2004年   3篇
  2003年   4篇
  2000年   1篇
  1999年   55篇
  1998年   601篇
  1997年   403篇
  1996年   245篇
  1995年   144篇
  1994年   112篇
  1993年   124篇
  1992年   12篇
  1991年   21篇
  1990年   12篇
  1989年   19篇
  1988年   29篇
  1987年   20篇
  1986年   16篇
  1985年   10篇
  1983年   2篇
  1982年   10篇
  1981年   15篇
  1980年   16篇
  1978年   4篇
  1977年   45篇
  1976年   115篇
  1975年   2篇
排序方式: 共有2048条查询结果,搜索用时 875 毫秒
981.
982.
OBJECTIVE: To assess cardiorespiratory, tissue oxygen and hepatic nicotine adenine dinucleotide hydride (NADH) responses to graded hypoxia. DESIGN: Prospective, controlled, randomized study. SETTING: University laboratory. ANIMALS AND INTERVENTIONS: 18 anaesthetised Sprague-Dawley rats spontaneously breathing either 21% (controls), 12.5% or 10% inspired oxygen concentrations (6 rats per group). MEASUREMENTS AND RESULTS: All animals in the 21 and 12.5% O2 groups survived the 3-h study period, compared to only 1 in the 10% O2 group. In this latter group, mean arterial pressure and renal blood flow fell immediately with hypoxaemia, whereas aortic blood flow was maintained until the preterminal stages. Critical cellular hypoxia was suggested by an increasingly severe base deficit, an initial rise then a preterminal fall in hepatic NADH intensity and premature death in all but 1 animal. Hepatic NADH fluorescence intensity was unchanged in control animals but showed a progressive rise in the 12.5% O2 group, accompanied by a small though static increase in arterial base deficit. No significant differences were seen in arterial and tissue partial pressure of oxygen between the 12.5 and 10% O2 groups. CONCLUSIONS: This study demonstrates major differences in cardiorespiratory, hepatic NADH and outcome responses to small variations in the degree of hypoxic hypoxia. The fall in NADH fluorescence intensity presages impending death and is likely to reflect failure of cellular metabolic processes.  相似文献   
983.
Choledochal cysts are prone to complications: cholangitis, biliary cirrhosis, portal hypertension, lithiasis, rupture, pancreatitis, and carcinoma. The coincidence of choledochal cysts and neoplasia ranges from 2.5 to 26 per cent. One hundred six cases of choledochal cysts with neoplasms have been collected from the literature. We have tabulated the results of 68 cases found to have a neoplasm at the initial laparotomy and of 38 patients with pristine choledochal cysts treated electively who subsequently developed a neoplasm. Two original cases are presented. The primary site of neoplasia was not confined only to choledochal cysts. There appears to be a propensity for malignancy to develop anywhere in the biliary tract or gallbladder or pancreas in conjunction with the choledochal cyst. Accompanying choledochal cysts is a high incidence of an anomalous relation at the pancreaticobiliary junction with subsequent malignancy formation. A pathogenetic basis is postulated.  相似文献   
984.
985.
The authors believe this to be the first published case in which a deep hypothermic cardiopulmonary bypass was used to facilitate resection of a large parenchymal arteriovenous fistula. The use of this procedure facilitated resection of the lesion by allowing compression and manipulation of large venous varices that were overlying the deeper arterial feeding vessels. The surgical rationale, technique, and intra- and postoperative management are discussed.  相似文献   
986.
Varicella is a highly communicable infection caused by the varicella-zoster virus. Although generally a benign, self-limited disease, varicella infection may be associated with serious complications, especially in older adults and young infants. Live attenuated varicella vaccine was licensed by the U.S. Food and Drug Administration in March 1995. Assessment of varicella immunity status and vaccination of susceptible persons are desirable in all adolescents and adults. Vaccination guidelines stress a systematic review of several factors: neomycin sensitivity, immunosuppressed status, current health and use of medications (particularly corticosteroids), recent use of immune globulin, risk of pregnancy, lactation status and risk of inadvertent transmission to vulnerable contacts.  相似文献   
987.
声波采油技术处理油层半径范围分析   总被引:10,自引:2,他引:8  
介绍了与声波采油技术有关的基本概念,根据声波的特性,对超声波采油技术,水力振荡解堵技术、低频振动采油技术、井下低频电脉冲采油技术,高能气体压裂技术处理油层半径范围进行比较,并分析了这几种声波采油技术的适用条件,预测了发展前景及研究方向。  相似文献   
988.
Pseudo-aneurysm following diagnostic or interventional procedures is a well-recognized complication. Ultrasound guided compression repair is routinely used to close an uncomplicated pseudo-aneurysm. We describe a patient with a femoral artery pseudo-aneurysm following iliac angioplasty and stenting in which ultrasound guided compression repair failed. Pseudoaneurysm was successfully closed by transcutaneous coil embolization technique.  相似文献   
989.
The modulatory effect of myosin regulatory light chain phosphorylation in mammalian skeletal muscle, first documented as posttetanic potentiation of twitch tension, was subsequently shown to enhance the expression and development of tension at submaximal levels of activating calcium. Structural analyses demonstrated that thick filaments with phosphorylated myosin regulatory light chains appeared disordered: they lost the near-helical, periodic arrangement of myosin head characteristic of the relaxed state. We suggested that disordered heads may be more mobile than ordered heads and are likely to spend more time close to their binding sites on thin filaments. In this study we determined that the physiological effects of phosphorylation could be mimicked by decreasing the lattice spacing between the thick and the thin filaments, either by osmotic compression with dextran or by increasing the sarcomere length of permeabilized rabbit psoas fibers. Phosphorylation of regulatory light chains by incubation of permeabilized fibers with myosin light chain kinase and calmodulin, followed by low levels of activating calcium, potentiated tension development at resting or lower sarcomere lengths in the absence of dextran but had no additional effect on tension potentiation or development in fibers with decreased lattice spacing due to either osmotic compression or increased sarcomere length.  相似文献   
990.
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