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   1547篇
  免费   2篇
  国内免费   2篇
电工技术   3篇
化学工业   4篇
金属工艺   1篇
机械仪表   1篇
建筑科学   3篇
轻工业   2篇
无线电   37篇
一般工业技术   5篇
冶金工业   1476篇
自动化技术   19篇
  2021年   1篇
  2020年   1篇
  2019年   3篇
  2018年   2篇
  2017年   2篇
  2016年   3篇
  2015年   4篇
  2014年   2篇
  2013年   3篇
  2012年   1篇
  2008年   1篇
  2007年   2篇
  2006年   1篇
  2005年   4篇
  2004年   3篇
  2003年   4篇
  2002年   1篇
  2001年   1篇
  2000年   5篇
  1999年   47篇
  1998年   423篇
  1997年   275篇
  1996年   184篇
  1995年   95篇
  1994年   81篇
  1993年   98篇
  1992年   10篇
  1991年   22篇
  1990年   23篇
  1989年   13篇
  1988年   16篇
  1987年   11篇
  1986年   15篇
  1985年   20篇
  1983年   2篇
  1982年   7篇
  1981年   8篇
  1980年   14篇
  1979年   2篇
  1978年   3篇
  1977年   53篇
  1976年   82篇
  1975年   3篇
排序方式: 共有1551条查询结果,搜索用时 15 毫秒
51.
A 67 yr old female with mitral stenosis presented with an acute haemoptysis caused by the rupture of pulmonary varices. Chest radiography and bronchoscopy showed nonspecific abnormalities. The diagnosis of this rare but potentially lethal complication was made using computed tomographic angiography with three-dimensional volume rendering.  相似文献   
52.
53.
Small cell tumors of the ovary are uncommon but represent an important group to recognize in the differential diagnosis of primary and metastatic ovarian neoplasms. In some cases the correct diagnosis cannot be confidently made on the basis of clinical setting, routine light microscopy, and immunohistochemistry, and electron microscopy may be supportive or definitive in establishing cell type. The cell type is often important in choosing optimal therapy and in predicting prognosis. The authors performed electron microscopy on a moderate number of ovarian small cell tumors and here describe and illustrate the diagnostic features of representative examples of various types. The ultrastructural features of the metastatic tumors, such as embryonal rhabdomyosarcoma, neuroblastoma, and melanoma, are identical to those of their respective primary tumors, are well known, and usually pose no problem in diagnosis. On the other hand, the ultrastructural features of some primary ovarian small cell tumors may present a more difficult differential diagnosis, because they have features that are subtle and/or in common. Exemplary of tumors in this category are diffuse adult granulosa cell tumor, endometrial stromal sarcoma, and small cell carcinomas of the hypercalcemic and pulmonary (oat cell) types. Distinguishing among them may be difficult but is possible, and electron microscopy may be a valuable supplement to the diagnostic information obtained from the clinical presentation, light microscopy, immunohistochemistry and, in some tumors, cytometric analysis of these neoplasms.  相似文献   
54.
55.
We have conducted a retrospective review of 134 cases of neurogenic tumors of the thorax, including 66 in infants and children and 68 in adults. Nerve cell tumors were the majority in infants and children (84.8%) and were mostly malignant (67.2%). Nerve sheath tumors were more frequent in adults (73.5%). Nerve cell tumors were the most frequent tumors in males and nerve sheath tumors in females. Nineteen tumors were associated with von Recklinghausen's disease. The tumors were symptomatic in 76.4% of children and 36.7% of adults. Spinal cord compression was observed in 8 infants and children and in 2 adults. Neo-adjuvant treatment was administrated to 3 patients. Resection was complete for 80 benign tumors out of 86 (93%) and for 26 malignant tumors out of 48 (54%). Postoperative chemo- or radiotherapy (or both) was administrated to 17 children and 8 adults. The mean followup periods were 11 years for the infants and children and 8 years, 6 months for the adults. There was one postoperative death. There were no late deaths related to benign tumor. The prognosis of spinal cord compression depended on the malignancy and staging of the tumors. At 5 years postoperatively, 21 children out of 28 with neuroblastomas and 8 out of 9 with ganglioneuroblastomas were alive. The possibility of maturation of neuroblastomas and survival with hepatic metastases was confirmed. The prognosis in cases of chemodectoma depended on the extension. Patients with malignant schwannomas had very poor prognoses, especially when associated with von Recklinghausen's disease.  相似文献   
56.
57.
58.
A large body of literature indicates that the serotonergic system is involved in behavioral regulation, as evidenced by the inverse relationship between impulsive aggression and serotonergic function found in adult alcoholics and nonalcoholics. However, studies of this relationship among child and adolescent offspring of alcoholics (COAs) have not previously been done. This study examines the potentially parallel relationship between behavioral dysregulation and low serotonergic function in young COAs. The relationship is of potential interest as a phenotypic marker of biological vulnerability to aggressiveness, which itself has been hypothesized to be a risk factor for later antisocial alcoholism. The present work is part of an ongoing prospective study of the development of risk for alcohol abuse/dependence and other problematic outcomes in a sample of families subtyped by the fathers' alcoholism classification. We examined the relationship between overt behavior problems in middle childhood (mean age = 10.5 +/- 1.7 years) and whole blood serotonin (5-HT) in a subsample of the offspring (N = 32 boys and 12 girls). Using a Child Behavior Checklist (CBCL) index of behavioral undercontrol, we obtained results indicating that high total behavior problem (TBP) children had lower levels of whole blood 5-HT than did low-TBP children (p < 0.01). These results support the hypothesis that there is an inverse relationship between whole blood serotonin levels and behavior problems in young male and female COAs. A father's alcoholism status was not significantly related to his child's 5-HT level, i.e., the child's phenotypic expression of behavioral dysregulation was more reliably connected to serotonergic function than was paternal alcoholism.  相似文献   
59.
Bronchiolar lesions continue to be increasingly recognized as a cause of airflow obstruction. Thus, it is important to have a current update of the current clinical, radiographic, and immunologic perspective of these disorders. Diffuse panbronchiolitis has been reported to occur in the United States and Europe, and the anti-inflammatory action of erythromycin appears to be effective in management. Idiopathic bronchiolitis obliterans, post-fume or post-infectious, or connective tissue disorder bronchiolitis obliterans continues to be rare and often has a poor prognosis. Lung transplantation bronchiolitis obliterans continues to be the major complication and cause of mortality in transplant recipients. Risk factors of this form of chronic rejection include more frequent and more severe acute rejection and the coexistence of organizing pneumonia. The recognition of the distinctive differences among the bronchiolar airflow disorders continues to be essential for improved patient care, greater understanding of the pathogenesis, and development of therapeutic advances.  相似文献   
60.
A trajectory defined by three time-ordered events was offered as a useful adjunct to building a development theory about antisocial behaviors. A sequence was defined with significant linkages between antisocial childhood behavior and early arrest and between early arrest and chronic offending. The majority of chronic offenders traveled through all three events in the sequence. Each event in the sequence shared a common process of disrupted family process plus frequent family transitions and marked social disadvantage. The findings support the hypothesis that the process that leads to antisocial behaviors at grade four may also maintain the entire sequence. The level of disrupted process at initiation and a time-based measure of involvement with deviant peers predicted which individuals moved forward in the sequence and which did not. The findings are consistent with the idea that the majority of chronic offending juveniles follow a trajectory that can be explained by a single theory.  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