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   2009篇
  免费   1篇
化学工业   12篇
轻工业   4篇
一般工业技术   3篇
冶金工业   1977篇
自动化技术   14篇
  2021年   1篇
  2020年   1篇
  2019年   1篇
  2017年   1篇
  2013年   1篇
  2011年   1篇
  2009年   2篇
  2008年   2篇
  2007年   2篇
  2006年   2篇
  2003年   7篇
  1999年   65篇
  1998年   664篇
  1997年   373篇
  1996年   243篇
  1995年   130篇
  1994年   90篇
  1993年   111篇
  1992年   9篇
  1991年   13篇
  1990年   29篇
  1989年   29篇
  1988年   16篇
  1987年   11篇
  1986年   11篇
  1985年   11篇
  1984年   3篇
  1983年   6篇
  1982年   11篇
  1981年   18篇
  1980年   12篇
  1979年   3篇
  1978年   7篇
  1977年   37篇
  1976年   78篇
  1975年   7篇
  1973年   1篇
  1954年   1篇
排序方式: 共有2010条查询结果,搜索用时 0 毫秒
41.
Heuristic construction knowledge generated while contracting is seldom recorded and transferred to other workers. Experiences of past mistakes as well as efficient work practices are crucial means for saving money, time, and improving the safety and quality of construction. With the rising costs of construction and the increased demand of time constraints on contractor schedules, few members of the construction industry can afford to waste time and resources on errors or ineffective work practices. The Constructability Lessons Learned Database (CLLD) prototype described in this paper is a leading edge method of automatically gathering, systematically organizing and efficiently applying vital construction information to a contractor's daily activities. This paper presents a review of previous and current attempts at database constructability programs, uses of constructability feedback systems, challenges to develop and utilize such systems, and an overview of the design and development of the CLLD prototype. The overview describes knowledge elicitation techniques used to gather constructability knowledge, the design of the system (organizing and classifying construction information for efficient retrieval and expansion), and system's implementation, validation, and operation. The conclusion discusses future extensions of the CLLD concept in the construction industry.  相似文献   
42.
The pathophysiology of subarachnoid hemorrhage (SAH) may involve free radical production and lipid peroxidation. We examined plasma levels of cholesteryl ester hydroperoxides (CEOOH) and antioxidants in 25 patients with SAH, and 10 neurologic controls with lacunar stroke. Patients with SAH had significantly increased plasma levels of CEOOH, which peaked on day 5 after the ictus. Concentrations of CEOOH were significantly increased, and ascorbic acid concentrations were significantly decreased in patients who developed vasospasm compared with patients without vasospasm. Increased levels of CEOOH were associated with increased mortality and correlated with clinical outcome scales. These results implicate oxidative stress in the pathogenesis of SAH and suggest that measurements of CEOOH in plasma may be useful both prognostically as well as in monitoring therapeutic interventions.  相似文献   
43.
44.
Responding to demands that nursing leaders conduct business in creative, proactive ways, the authors of this department share the work of The Robert Wood Johnson Foundation's national program. Colleagues in Caring: Regional Collaboratives for Nursing Work Force Development. The purpose of this initiative is to enhance regional and state collaborative planning and implement actions and policies to address the rapid changes occurring in the United States nursing labor market. This department presents the ongoing work of the program, highlighting the work of the 20 individual collaboratives. Regional approaches to the expected program outcomes and specific challenges and opportunities that are unique to each region's environment are included. The Colleagues in Caring program is administered by the American Association of Colleges of Nursing. Current information on the initiative can be found at http:/(/)www.aacn.nche.edu under Special Projects. The staff at the National Program Office can be reached at 202/496-1095 (fax: 202/496-1093).  相似文献   
45.
46.
47.
BACKGROUND/AIMS: Primary carcinoma of the gallbladder is rare and associated with a late diagnosis and poor prognosis. Concurrent acute cholecystitis frequently obscures the presence of carcinoma. The information regarding gallbladder carcinoma with acute cholecystitis is limited. In order to better understand the presentation of gallbladder carcinoma with acute cholecystitis, we retrospectively reviewed the data of patients with primary carcinoma of the gallbladder. METHODOLOGY: The data of 86 patients with primary carcinoma of the gallbladder treated between 1979 and 1994 were compiled and reviewed. The patients were divided into 2 groups: Group 1 (with acute cholecystitis, 21 patients) and Group 2 (without cholecystitis, 65 patients). Clinicopathological comparisons were made and evaluated between these two groups RESULTS: The average age of Group 1 patients was older than that of Group 2 patients (75+/-2 years vs. 63+/-2 years; p<0.05). Three Group 1 patients presented with sepsis. The interval between the onset of symptoms and hospital admission in Group 2 patients was significantly (p<0.05) longer than that in Group 1 patients (243+/-95 days vs. 20+/-11 days). Leukocytosis (>11,000/mm3) was more common in Group 1 patients than in Group 2 patients (47.6% vs. 15.4%). Jaundice was more common in Group 2, and fever was common in Group 1. The majority of Group 2 gallbladder cancers were stage V (75.4%). In contrast, 52.4% of Group 1 gallbladder cancers were stage III and 38.1% were stage V. The 30-day postoperative mortality rate in Group 1 and Group 2 patients was 9.5% and 7.7%, respectively. The cumulative survival of Group 1 patients was not different from that of Group 2 patients (log-rank test, p>0.05). CONCLUSIONS: Age, the interval of symptoms prior to admission, the location of abdominal pain, fever, leukocytosis, and the absence of jaundice suggested the presence of acute cholecystitis in gallbladder carcinoma. A high index of suspicion of the disease, intraoperative examination of gallbladder specimens, and more aggressive surgical treatment may improve patient survival.  相似文献   
48.
49.
Listeria innocua NCTC 11289 was grown aerobically in continuous culture in defined media at 30 degrees C. Both acetate and lactate were produced, the proportion of acetate decreased with increasing dilution rate. Enzymatic analysis showed lactate dehydrogenase was activated 10-fold by fructose-1, 6-bisphosphate. The presence of phosphate acetyltransferase and acetate kinase but not pyruvate oxidase was detected, suggesting the sequential action of phosphate acetyltransferase and acetate kinase to produce acetate from acetyl CoA via acetylphosphate.  相似文献   
50.
BACKGROUND: Liver disease in chronic hepatitis C virus (HCV) infection ranges from minimal lesions to liver cirrhosis, eventually evolving to hepatocellular carcinoma. Whether and how HCV determines the different clinical and histological manifestations of the disease is not fully understood. AIMS: To verify whether the amount of virus in individual patients could be related to the severity of liver injury. PATIENTS AND METHODS: Levels of HCV RNA were measured in serum in 96 consecutive patients with chronic hepatitis type C using a signal amplification assay. The relation between viraemic values and the corresponding viral load in the liver was assessed in a subgroup of 21 patients in whom HCV RNA was measured in serum samples and liver specimens obtained at the same time. RESULTS: A positive correlation was observed between the amount of viral nucleic acid in the two compartments, indicating that levels of viraemia reflect the amount of virus present in the liver. Viral load did not correlate with aminotransferase activities nor with histological diagnosis, and serum and liver levels of HCV RNA were not significantly different in patients infected by the various HCV genotypes. CONCLUSIONS: Measurement of HCV replication in serum is a mirror of viral replication in the liver. The extent of replicative activity of HCV does not seem to play a role in the modulation of the associated hepatic disease.  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