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   6212篇
  免费   4篇
  国内免费   1篇
电工技术   26篇
综合类   1篇
化学工业   124篇
金属工艺   6篇
机械仪表   8篇
建筑科学   28篇
能源动力   8篇
轻工业   28篇
水利工程   1篇
石油天然气   5篇
无线电   102篇
一般工业技术   122篇
冶金工业   5673篇
原子能技术   5篇
自动化技术   80篇
  2016年   12篇
  2014年   15篇
  2013年   32篇
  2012年   25篇
  2011年   22篇
  2010年   17篇
  2009年   11篇
  2008年   28篇
  2007年   14篇
  2006年   21篇
  2005年   18篇
  2004年   24篇
  2003年   32篇
  2002年   20篇
  2001年   14篇
  2000年   14篇
  1999年   176篇
  1998年   1692篇
  1997年   911篇
  1996年   654篇
  1995年   341篇
  1994年   331篇
  1993年   348篇
  1992年   45篇
  1991年   69篇
  1990年   91篇
  1989年   72篇
  1988年   69篇
  1987年   96篇
  1986年   72篇
  1985年   66篇
  1984年   9篇
  1983年   24篇
  1982年   36篇
  1981年   39篇
  1980年   49篇
  1979年   12篇
  1978年   13篇
  1977年   147篇
  1976年   346篇
  1975年   18篇
  1973年   9篇
  1972年   8篇
  1969年   7篇
  1965年   7篇
  1964年   9篇
  1963年   7篇
  1955年   7篇
  1933年   9篇
  1928年   11篇
排序方式: 共有6217条查询结果,搜索用时 15 毫秒
991.
OBJECTIVE: To determine the effect of continuing medical education (CME) with and without a quality assurance component (CME+QA) on physician practices in the prevention of venous thromboembolism. METHODS: A communitywide study was performed in 15 short-stay hospitals in central Massachusetts. The study population included 3158 patients in acute-care hospitals with multiple risk factors for venous thromboembolism. Study hospitals were randomly assigned to one of two educational strategies or to a control group that received no intervention. RESULTS: The proportion of patients at high risk for venous thromboembolism who received effective methods of prophylaxis increased significantly from 29% in 1986 to 52% in 1989 (P < .001). This increase was seen in all study groups: control hospitals, 40% to 51% (P < .001); CME hospitals, 21% to 49% (P < .0001); and CME+QA hospitals, 27% to 55% (P < .0001). The increase in prophylaxis use from 1986 to 1989 was significantly greater among patients cared for in hospitals whose physicians participated in a formal CME program (an increase of 28%) than in control hospitals (an increase of 11%) (P < .001). There was no significant difference in the use of prophylaxis in hospitals whose physicians received CME+QA interventions compared with hospitals whose physicians received CME interventions alone (identical increases of 28%). CONCLUSION: A formal CME program significantly increased the frequency with which physicians prescribed prophylaxis for venous thromboembolism. We believe the key factor in our CME interventions that motivated clinicians to change their practices was the provision of hospital-specific data demonstrating a compelling need for improvement. Despite the substantial investment by hospitals in QA, traditional QA intervention appeared to provide no additional benefit. Even after extensive CME/QA interventions, prophylaxis for venous thromboembolism remained underutilized, suggesting the need to develop new approaches to changing clinical practice.  相似文献   
992.
A cost-effective audit system has been developed that will both detect systematic error in data and procedures and evaluate the quality assurance programme provided by a physics department for radiotherapy. The audit has been developed for external beam radiotherapy and assesses one modality and one treatment machine per year. The audit is carried out on an interdepartmental basis and can be undertaken by two physicists from each department in one working day. The method of assessing the quality assurance programme and the schedule of measurements are described. The process is illustrated using the results of trial audits between the medical physics departments at Coventry and Leicester.  相似文献   
993.
994.
995.
Hospital admission rates and hospital bed utilization rates are presented for all admissions assigned to diabetes mellitus as principal cause in the North Western Region from 1980/81 to 1990/91. Data are derived from Hospital Activity Analysis (1980/81-1986/87) and from the Regional Information System (1988/89-1990/91). Admission rates for all categories of diabetes combined showed little change until 1986/87 after which they rose progressively each year. Hospital bed utilization rates fell progressively from 1986/87 onwards, the number of bed days attributed to diabetes falling from 1.9% to 0.8% of the total for all causes. Most of the rise in admission rates from 1988/89 onwards was attributable to diabetes with ophthalmic complications (ICD 250.4). This was heavily influenced by the enumeration of day cases in the Regional Information System. When these are discounted, admission rates for the more recent years are stable. Diabetes without mention of complications (ICD 250.0) showed the most dramatic decline in its contribution to hospital bed utilization. This may be the result of increasing outpatient support from diabetes specialist nurses whose numbers increased in inverse proportion to the fall in bed utilization attributed to ICD 250.0.  相似文献   
996.
997.
STUDY OBJECTIVE: To evaluate the usefulness of routine radiographs and arterial blood gases in children with blunt trauma. DESIGN: Retrospective chart review. TYPE OF PARTICIPANTS: Ninety patients who met triage criteria for our trauma team evaluation and who were less than 15 years old were evaluated. Patients with a Glasgow Coma Scale score (GCS) of 15 (lie, mild to moderately injured children) were the focus of this study. METHODS: Children seen from May 1991 through August 1992 had charts reviewed systematically and within 24 hours of emergency department evaluation. Standard radiologic evaluation, including cervical-spine, chest, and pelvic radiographs, as well as arterial blood gas analysis, were obtained. The severity of injury was graded according to the Modified Injury Severity Scale. RESULTS: The mean age of patients was 6.4 years, and the injuries observed were exclusively extremity fractures. The correlation between physical examination findings and radiologic evaluation was assessed. Forty-three patients had an abnormal physical examination (ie, gross deformity, limitation of motion, or pain), and 26 had a fracture identified on radiograph. Forty-seven patients had a normal physical examination and none had a fracture identified on radiograph (P < .001; sensitivity of positive signs and symptoms, 100%; false-negative findings, 0%). Four patients with abnormal blood gases are described. No patient had any vascular or solid organ injury identified. CONCLUSION: In children with a GCS score of 15, selected radiologic and laboratory tests based on clinical findings are recommended. Careful observation and repeat examinations by trained clinicians can select a group of children at low risk for occult injury.  相似文献   
998.
The type I inositol 1,4,5-trisphosphate (InsP3) receptor can be rapidly depleted from cells during stimulation of phosphoinositide hydrolysis because its degradation is accelerated (Wojcikiewicz, R. J. H., Furuichi, T., Nakade, S., Mikoshiba, K., and Nahorski, S. R. (1994) J. Biol. Chem. 269, 7963-7969). The present study examines the regulatory properties of type II and III InsP3 receptors. Initially, the relative abundance of InsP3 receptors was defined in a range of cell types by quantitative immunoblotting. These studies showed that the proportions in which type I, II, and III InsP3 receptors are expressed differs greatly and that some cells (for example, AR4-2J rat pancreatoma cells) express all three receptors. Analysis of the effects of cholecystokinin and bombesin on AR4-2J cells showed that each of the InsP3 receptors could be down-regulated during activation of phosphoinositide hydrolysis, but that depletion of the type II receptor was limited. Such a discrepancy was also seen in rat cerebellar granule cells and was found to result from the type II receptor being relatively resistant to degradation. In conclusion, type I, II, and III receptors can all be down-regulated, but with different characteristics. As the relative abundance of InsP3 receptors is extremely variable, the extent to which activation of the down-regulatory process alters intracellular signaling will vary depending on which InsP3 receptors are expressed.  相似文献   
999.
In Saccharomyces cerevisiae, transient accumulation of G1 cyclin/p34CDC28 (Cdc28p) complexes induces cells to traverse the cell cycle Start checkpoint and commit to a round of cell division. To investigate posttranslational controls that modulate Cdc28p activity during the G1 phase, we have reconstituted cyclin-dependent activation of Cdc28p in a cyclin-depleted G1 extract. A glutathione S-transferase-G1 cyclin chimera (GST-Cln2p) efficiently binds to and activates Cdc28p as a histone H1 kinase. Activation of Cdc28p by GST-Cln2p requires ATP, crude yeast cytosol, and the conserved Thr-169 residue that serves in other organisms as a substrate for phosphorylation by cyclin-dependent protein kinase-activating kinase. This assay may be useful for distinguishing genes that promote directly the posttranslational assembly of active Cln2p/Cdc28p kinase complexes from those that stimulate the accumulation of active complexes via a positive-feedback loop that governs synthesis of G1 cyclins.  相似文献   
1000.
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