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   1246篇
  免费   3篇
  国内免费   7篇
电工技术   1篇
综合类   4篇
化学工业   7篇
金属工艺   1篇
机械仪表   8篇
建筑科学   3篇
能源动力   2篇
轻工业   16篇
水利工程   1篇
石油天然气   1篇
无线电   1篇
一般工业技术   2篇
冶金工业   1188篇
原子能技术   1篇
自动化技术   20篇
  2021年   1篇
  2020年   1篇
  2018年   3篇
  2017年   2篇
  2016年   3篇
  2015年   1篇
  2014年   2篇
  2013年   11篇
  2012年   4篇
  2010年   1篇
  2009年   2篇
  2008年   1篇
  2007年   9篇
  2006年   2篇
  2005年   2篇
  2004年   6篇
  2003年   1篇
  2002年   3篇
  2001年   1篇
  2000年   2篇
  1999年   30篇
  1998年   348篇
  1997年   195篇
  1996年   158篇
  1995年   54篇
  1994年   70篇
  1993年   71篇
  1992年   7篇
  1991年   15篇
  1990年   13篇
  1989年   18篇
  1988年   14篇
  1987年   13篇
  1986年   9篇
  1985年   13篇
  1984年   1篇
  1983年   3篇
  1982年   9篇
  1981年   6篇
  1980年   8篇
  1978年   5篇
  1977年   38篇
  1976年   97篇
  1975年   2篇
  1955年   1篇
排序方式: 共有1256条查询结果,搜索用时 0 毫秒
51.
Using annual bite-wing radiographs, the incidence and progression of approximal caries (4d-7m) were assessed longitudinally in teenagers and adolescents whose treatment had been based on remineralizing rather than restorative strategies. A closed cohort of 536 children initially was followed from 11 to 22 years of age. The scoring system was: 0 = no visible radiolucency; 1-2 = radiolucency in the enamel up to the enamel-dentin border; 3 = radiolucency with a broken enamel-dentin border but with no obvious progression in the dentin; 4 = radiolucency with obvious spread in the outer half of the dentin, and 5 = radiolucency in the inner half of the dentin. Caries rates were estimated as the number of new lesions/100 tooth surface-years, and the Kaplan-Meier estimate was used to calculate the cumulative survival time of each approximal surface. Three events were used: the transitions from states 0 to 2, 2 to 4 and 3 to 4. The results showed a considerable variation between the surfaces in both caries rates and survival time. For all surfaces combined, the median caries rate from state 0 to 2 was 3.9 new lesions/100 tooth surface-years; from state 2 to 4, the rate was 5.4, and from state 3 to 4 it was 20.3. Of the sound surfaces (state 0), 75% survived 6.3 years without reaching state 2. Given state 2, 75% survived 4.8 years without reaching the outer half of the dentin (state 4), while given a lesion at the enamel-dentin border (state 3), 75% survived 1.3 years without doing the same. The median survival time of lesions from state 3 to 4 was 3.1 years. The group with DMFSappr>1 at the age of 11-12 years had a risk of new approximal enamel lesions (state 0-2) that was 2.5 times greater than that of the group with DMFSappr = 0-1.  相似文献   
52.
In a household survey in Guinea-Bissau, 319 episodes of diarrhea in children were followed by interviews every second day with the aim of investigating perceived morbidity and subsequent actions taken. The majority of the mothers had good knowledge of oral rehydration salts (ORS). However, only 58% of the episodes were treated with ORS and the amount given was insufficient. Mothers with no knowledge of ORS did not use it during the observed attack of diarrhea regardless of contact with a health center, which suggests that maternal knowledge is an important determinant of whether health personnel provide ORS. Children with diarrhea considered to be caused by teething were less likely to receive ORS in the acute phase (risk ratio = 0.6, 95% confidence interval [CI] = 0.5-0.9). Univariate analyses showed that the use of ORS was related to number of reported symptoms, the mother being the care taker, consultations, previous use of ORS, good knowledge of ORS, and having ORS sachets at home. Multivariate Cox regression analyses showed that the presence of ORS sachets at home at the onset of diarrhea was the strongest predictor of use (hazard ratio = 3.3, 95% CI = 1.9-3.6). Improved health education should focus more on the quantity of ORS needed, early signs of dehydration, treatment of teething diarrhea, and breast feeding, and address mothers who have no prior knowledge of ORS. Management of diarrhea may be improved by a more liberal distribution of ORS sachets.  相似文献   
53.
In the cranio-facial region the giant-cell reparative granuloma (GCRG) is a typical lesion of the maxillary bones. Because giant-cell reparative granuloma is not strictly a granuloma, clinically and histologically, many authors prefer call it giant-cell lesion (GCL). A review of the literature have along with our experiences is reported. Authors present 17 patients with giant-cell lesion and their results, treated at the Maxillo-Facial Department of Parma. Clinical, radiographic and pathologic features were evaluated and differential diagnosis was considered, showing the real great difficulty in differential diagnosis also and especially for surgical treatment.  相似文献   
54.
55.
56.
The type and distribution of keratins (K) in malignant tumors of eyelids were examined immunohistochemically to understand the pathomechanism of intercellular interactions. All of the tumor cells in the basal cell carcinoma were positive for K14, which is specific for basal cells, whereas all of them were negative for K10, which is specific for suprabasal layers in stratified squamous epithelia. These findings suggest that basal cell carcinoma may consist of uniform, basal cell-like tumor cells. On the other hand, the squamous cell carcinoma and sebaceous carcinoma, which were positive for either K14 or K10 to varying extent, may consist of various tumor cells with different types and degrees of differentiation. In these tumors, K14 was frequently detected throughout the border cells of the tumor mass. Apoptotic bodies were detected at the region where this continuous distribution of K14 was interrupted. These findings may help to clarify the pathomechanism of the interactions between the tumor cells and stromal cells.  相似文献   
57.
58.
Genetics, cell biology, and whole-genome sequencing of pathogens have changed dramatically the opportunities to investigate the epidemiology, pathogenesis, diagnosis, and control of microbial diseases. For example, recombinant DNA and PCR are powerful tools used to isolate genes whose role in pathogenicity can be investigated in biologically relevant virulence assays. Vaccines that target one or more of these genes can then be developed. Complete genome sequences of microbes provide an inventory of the genes encoding every virulence factor and potential immunogen. Candidate vaccines can be selected and developed using various approaches, including the recent innovation of immunisation with nucleic acids. Although many successful vaccines have been and will continue to be developed through empirical approaches, molecular microbiology provides a rational basis for discovery, development, and implementation of safer, more effective and, potentially cheaper vaccines.  相似文献   
59.
For the study of the relationship of the pelviureteric system of one kidney to that of the contralateral one, bilateral cutaneous ureterostomy was performed in 14 dogs. The renal pelvis (RP) and ureter (U) of one side were distended separately with a balloon filled with saline in increments of 1 and 0.25 ml, respectively, and the pressure response of the contralateral RP and U was recorded. The test was repeated after anesthetization of the RP and U. RP distension with 1 ml of saline effected a pressure rise (P < 0.05) in the ipsilateral RP but no pressure response in the ipsilateral U or the contralateral RP or U (P > 0.05). RP distension with 2, 3, and 4 ml of saline induced a significant pressure rise in the ipsi- and contralateral RP but not in the ureters. Ureteric distension produced a pressure elevation (P < 0.05) on the ipsilateral U but had no effect on the contralateral U (P > 0.05) or on either of the renal pelves (P > 0.05). Distension of the anesthetized RP or U effected no pressure response in any of the ipsi- or contralateral RPs or Us. In conclusion, distension of the RP with large volumes led to an increase in pressure in the contralateral RP but not in the U. A reflex relationship is postulated to exist between the two renal pelves and to be mediated through a reflex we call the reno-renal pelvic reflex. It seems that this reflex acts to allow either of the kidneys to share an extra load of the other one by increasing the contractile activity of the RP, thus assumedly assisting the regulation of urine flow.  相似文献   
60.
BACKGROUND: Exercise testing is useful in the assessment of symptomatic patients for diagnosis of significant or extensive coronary disease and to predict their future risk of cardiac events. The Duke treadmill score (DTS) is a composite index that was designed to provide survival estimates based on results from the exercise test, including ST-segment depression, chest pain, and exercise duration. However, its usefulness for providing diagnostic estimates has yet to be determined. METHODS AND RESULTS: A logistic regression model was used to predict significant (>/=75% stenosis) and severe (3-vessel or left main) coronary artery disease, and a Cox regression analysis was used to predict cardiac survival. After adjustment for baseline clinical risk, the DTS was effectively diagnostic for significant (P<0.0001) and severe (P<0.0001) coronary artery disease. For low-risk patients (score >/=+5), 60% had no coronary stenosis >/=75% and 16% had single-vessel >/=75% stenosis. By comparison, 74% of high-risk patients (score <-11) had 3-vessel or left main coronary disease. Five-year mortality was 3%, 10%, and 35% for low-, moderate-, and high-risk DTS groups (P<0.0001). CONCLUSIONS: The composite DTS provides accurate diagnostic and prognostic information for the evaluation of symptomatic patients evaluated for clinically suspected ischemic heart 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