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   1670篇
  免费   0篇
  国内免费   1篇
电工技术   1篇
化学工业   14篇
金属工艺   1篇
机械仪表   9篇
建筑科学   3篇
能源动力   2篇
轻工业   40篇
水利工程   1篇
石油天然气   1篇
无线电   40篇
一般工业技术   32篇
冶金工业   1513篇
原子能技术   7篇
自动化技术   7篇
  2019年   2篇
  2014年   2篇
  2013年   26篇
  2012年   6篇
  2011年   5篇
  2010年   5篇
  2009年   8篇
  2008年   5篇
  2007年   4篇
  2005年   3篇
  2004年   3篇
  2003年   6篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   43篇
  1998年   437篇
  1997年   250篇
  1996年   167篇
  1995年   99篇
  1994年   90篇
  1993年   107篇
  1992年   8篇
  1991年   24篇
  1990年   20篇
  1989年   21篇
  1988年   28篇
  1987年   21篇
  1986年   17篇
  1985年   11篇
  1983年   4篇
  1982年   4篇
  1981年   14篇
  1980年   21篇
  1979年   2篇
  1978年   5篇
  1977年   45篇
  1976年   95篇
  1975年   6篇
  1973年   3篇
  1955年   2篇
  1926年   2篇
  1923年   5篇
  1922年   3篇
  1919年   2篇
  1917年   4篇
  1913年   3篇
  1911年   3篇
  1909年   2篇
  1905年   3篇
排序方式: 共有1671条查询结果,搜索用时 15 毫秒
81.
Ohne ZusammenfassungMitteilungen aus dem Chemischen Untersuchungsamte der Stadt Aachen.  相似文献   
82.
83.
84.
85.
Although positron emission tomography (PET) assesses myocardial viability (V) accurately, a rapid, inexpensive substitute is needed. Therefore, the authors developed a low-dose (1 mCi) Iodine-123-Iodophenylpentadecanoic Acid (IPPA) myocardial viability scan requiring analysis of only the first three minutes of data acquired at rest with a standard multicrystal gamma camera. Twenty-one patients > 2 weeks after myocardial infarction (MI) (24 MIs, 10 anterior, 14 inferoposterior, 21 akinetic or dyskinetic) had cardiac catheterization and resting IPPA imaging. V was determined by either transmural myocardial biopsy during coronary bypass surgery (12 patients, 14 MIs) or reinjection tomographic thallium scan (9 patients, 10 MIs), and 50% of MIs were viable. The IPPA variables analyzed were: time to initial left ventricular (LV) uptake in the region of interest (ROI), the ratio of three-minute uptake in the ROI to three-minute LV uptake, three-minute clearing (counts/pixel) in the ROI (decrease in IPPA after initial uptake), and three-minute accumulation (increase in IPPA after initial uptake) in the ROI. Rules for detecting V were generated and applied to 10 healthy volunteers to determine normalcy. While three-minute uptake in nonviable MIs was only 67% of volunteers (P < 0.0001) and 75% of viable MIs, uptake alone identified only 50% of viable MIs and 75% of nonviable MIs. IPPA clearing, however, was > or = 13.5 counts/pixel in 10/12 (83%) of viable MIs, and IPPA accumulation > or = 6.75 counts/pixel identified one more viable MI, for a sensitivity for V of 11/12 (92%), with a specificity of 11/12 (92%), and a 100% normalcy rate. The authors conclude low-dose IPPA (five-minute acquisition with analysis of the first three minutes of data) has potential for providing rapid, inexpensive V data after MI. Since newer multicrystal cameras are mobile, IPPA scans can be done in emergency rooms or coronary care units generating information that might be useful in decisions regarding thrombolysis, angioplasty, or bypass surgery.  相似文献   
86.
PURPOSE: In a recent study we found an increased resistive index immediately after extracorporeal shock wave lithotripsy (ESWL) in patients older than 60 years, which suggests renovascular disturbance. The present 26-month followup study was undertaken to investigate the relevance of elevated resistive index levels and the incidence of new onset hypertension. MATERIALS AND METHODS: Of the initial 76 patients 57, including 20 of the 23 at risk patients 60 or greater years, group 3), were followed for more than 26 +/- 6 months after ESWL. Followup included 2 resistive index measurements by Doppler ultrasound of the treated and the contralateral kidney, at least 2 blood pressure measurements 1 week apart and excretory urography as well as determination of plasma renin activity in 9 patients. RESULTS: With 1 exception, elevated resistive index levels and hypertension were observed exclusively in patients older than 60 years. In these patients the resistive index ranged between 0.65 and 0.86 (mean plus or minus standard deviation 0.74 +/- 0.05, normal less than 0.7). This increase in resistive index was statistically significant (p < 0.0001). Compared to the levels obtained immediately after ESWL, the resistive index continued to increase in all 9 patients older than 60 years who had hypertension (45%), whereas in the normotensive patients the resistive index was either stable or decreased. There was a strong positive correlation (0.903) between pathological resistive index levels and blood pressure. CONCLUSIONS: Patients older than 60 years are at risk for disturbances of renal perfusion as assessed by the resistive index, and 45% of these patients have new onset hypertension within 26 months of treatment.  相似文献   
87.
The authors report a clinical case of the gallbladder carcinoid tumour treated with laparoscopic cholecystectomy. After a short analysis of the classification, the malignant potentiality and the symptoms of gallbladder carcinoids, they conclude that it is possible to treat carcinoids with laparoscopic cholecystectomy, but only in some selected cases, that is to say in the absence of factors indicative of local invasion and that in the other cases it is preferable the classic surgical treatment of laparotomic resection.  相似文献   
88.
Ohne ZusammenfassungMitteilung aus dem Chemischen Untersuchungsamte der Stadt Aachen.  相似文献   
89.
90.
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