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   2273篇
  免费   4篇
  国内免费   1篇
电工技术   1篇
化学工业   9篇
金属工艺   3篇
机械仪表   4篇
建筑科学   1篇
轻工业   10篇
水利工程   1篇
石油天然气   2篇
无线电   4篇
一般工业技术   10篇
冶金工业   2219篇
原子能技术   1篇
自动化技术   13篇
  2021年   2篇
  2020年   1篇
  2018年   2篇
  2017年   3篇
  2016年   1篇
  2013年   1篇
  2011年   1篇
  2010年   3篇
  2009年   2篇
  2008年   2篇
  2007年   1篇
  2006年   5篇
  2005年   3篇
  2004年   5篇
  2003年   3篇
  2002年   3篇
  2001年   1篇
  1999年   57篇
  1998年   623篇
  1997年   376篇
  1996年   221篇
  1995年   112篇
  1994年   113篇
  1993年   141篇
  1992年   20篇
  1991年   25篇
  1990年   22篇
  1989年   37篇
  1988年   32篇
  1987年   38篇
  1986年   29篇
  1985年   23篇
  1984年   2篇
  1983年   6篇
  1982年   17篇
  1981年   17篇
  1980年   26篇
  1978年   5篇
  1977年   87篇
  1976年   191篇
  1975年   4篇
  1972年   2篇
  1968年   2篇
  1967年   1篇
  1965年   1篇
  1963年   1篇
  1962年   1篇
  1960年   1篇
  1957年   1篇
  1955年   5篇
排序方式: 共有2278条查询结果,搜索用时 328 毫秒
71.
Between 1974 and 1989 we prospectively observed 530 patients with brucellosis. The findings for 62 patients (42 males and 20 females; mean age, 34.7 years) with 63 episodes in which the sacroiliac joint was involved (the most frequent osteoarticular location [11.7%]) were analyzed. Ten of the older patients (mean age, 55.3 years) had concomitant spondylitis. Systemic symptoms were usually important, and characteristic pain and findings of sacroiliitis were observed in approximately 75% of cases. Blood cultures were positive for Brucella melitensis for 44 patients. The most frequent radiographic findings were blurring of articular margins (42 cases) and widening of the sacroiliac space (20 cases). No radiographic anomalies were detected in 13 cases. Results of 99mTc and gallium-67 bone scans were abnormal in approximately 90% of cases (abnormalities were often mild). Overall, clinical, radiographic, and isotopic bone scan findings were sensitive and useful, although they were occasionally minimal or difficult to evaluate, making diagnostic findings confusing or misleading. Brucellar sacroiliitis is a mild disease associated with a good outcome similar to that observed for patients with uncomplicated brucellosis.  相似文献   
72.
This article covers the fine needle aspiration biopsy cytomorphology of papillary carcinomas of different organs, differential diagnoses, and clinical correlation. Diagnostic problems and helpful cytologic features are emphasized. The purpose is to have a concise source of information that helps the pathologist to evaluate these neoplasms.  相似文献   
73.
Recurrent respiratory papillomatosis is a disease characterized by the growth of wart-like neoplasms anywhere along the aerodigestive tract. The etiologic agent is the human papillomavirus, of which 90 subtypes have been described. The age distribution of those affected appears to be a bimodal curve, with the first peak around 5 years of age and the second occurring in adults in the third decade of life. The mainstay of treatment is surgical resection to maintain an adequate airway; patients often require multiple surgeries. The epidemiology, pathogenesis, clinical features, and treatment options are discussed. Current evidence regarding prognosis and the multifactorial nature of pathogenesis are also reviewed.  相似文献   
74.
Oxytocin (OT) is present in the mammalian testis and has been shown to play a role in the modulation of seminiferous tubule contractility and steroidogenesis. However, stage-specific effects of the peptide have not been previously investigated. In this study, computer-assisted analysis and time-lapse videomicrography were used to investigate basal contractility and the response to OT of seminiferous tubules at specific stages of the spermatogenic cycle. Adult rat testes were placed in fresh oxygenated DMEM F12 medium, decapsulated, and the tubules gently teased apart. Stages were identified by transillumination and a 10 mm section of tubule at each of stages IV-V, VII-VIII and XIII-I was placed in a microslide chamber and perifused with medium. After a control period of 3 h, OT (2 nM) was given for 1 h, followed by another control period of 1 h. The experiment was repeated using tubules from different rats and data were analysed to give arbitrary units of tubule contractility. Contractility was observed in all the tubules studied and the contractile activity was shown to vary depending on the stage of the spermatogenic cycle. Mean basal contractility at stages VII-VIII, the time when sperm are shed from the epithelium, was significantly lower than that at stages IV-V and XIII-I. The response of the tubules to OT was also stage-dependent, with the peptide producing the largest increases in contractile activity at stages VII-VIII and having no effect at stages IV-V. We postulate that these stage-specific differences in basal and OT-stimulated contractility may be important in co-ordinating the movement of developing germ cells towards the lumen of the seminiferous epithelium and in the process of spermiation.  相似文献   
75.
There has been little empirical study of risk factors for the development of late-life late-onset drinking problems. In the current prospective study, we compare two groups of older adults who, at a baseline assessment, were nonproblem drinkers: individuals who developed drinking problems over the course of the next 7 years (n = 77) and those who did not (n = 197). Late-onset problem drinkers reported mild to moderate drinking problems and spontaneous remission rates were high. Compared with stable nonproblem drinkers, late-onset problem drinkers at baseline were more likely to report incipient problems, heavier alcohol consumption, greater friend approval of drinking, more reliance on avoidance coping strategies, were more likely to smoke, and were less likely to have acute medical conditions that could potentially be complicated by alcohol consumption. Contrary to expectation, life stressors did not predict drinking problem onset. However, compared with stable nonproblem drinkers, late-onset problem drinkers were more likely to have a history of responding to stressors and negative affect with increased alcohol consumption.  相似文献   
76.
77.
78.
BACKGROUND: Organ transplant recipients who are seropositive for cytomegalovirus (CMV) and who are treated with antilymphocyte antibody (ALA) therapy have a high rate of symptomatic CMV disease. The intravenous administration of ganciclovir therapy once daily during ALA therapy decreased the incidence from 24% to 10% in patients receiving ALA as an induction therapy and from 64% to 22% in those treated for rejection. The present study was undertaken to determine whether a more intensive and sustained antiviral regimen could be more effective. METHODS: From April 1995 to December 1997, all CMV seropositive renal and liver transplant recipients who received ALA therapy were treated with intravenously administered ganciclovir (5 mg/kg/day with dose adjusted for renal dysfunction) for the length of ALA therapy and then with orally administered acyclovir (400 mg three times/day) or ganciclovir (1 gm twice/day) for 3 to 4 months. The incidence of CMV viremia and of CMV disease was determined during the 6 months after completion of ALA therapy. RESULTS: Forty-one patients (35 renal and 6 liver transplant recipients) were studied. CMV disease occurred in 2 patients (4.9%), both of whom were treated for rejection; it occurred in 1 of 21 patients (4.8%) treated with orally administered acyclovir, and in 1 of 20 patients (5%) treated with orally administered ganciclovir. The only patient who developed CMV disease in the ganciclovir group had received only 26 days of oral antiviral therapy. No CMV disease was documented in the group of patients receiving ALA therapy as induction therapy. CMV viremia occurred in three patients in the acyclovir group (14.3%) and in one patient in the ganciclovir group (5%). Among renal transplant recipients only, 1 of 35 patients developed CMV disease (2.9%) and no case of CMV disease was documented in patients treated with orally administered ganciclovir. All six patients receiving two courses of ALA therapy each were free of CMV disease. Toxicity of the regimen was minimal, and antiviral resistance did not develop. CONCLUSIONS: Preemptive antiviral therapy with intravenously administered ganciclovir during ALA therapy and then orally administered ganciclovir for 3 to 4 months provides virtually complete protection against the excessive rate of CMV disease that occurs in CMV seropositive allograft recipients receiving ALA therapy.  相似文献   
79.
80.
BACKGROUND AND PURPOSE: The Bone Stiffness Measurement Device-Swing is capable of measuring the propagation velocity of flexural waves in human tibial bone, which relates to bending stiffness. If the interrater and intrarater reliability of measurements obtained with the device are established, it can be used with confidence in assessing changes in bone. The purposes of this study were to detect potential sources of measurement error and to establish the interrater and intrarater reliability of measurements taken with the device. SUBJECTS AND METHODS: In the first part of the study, a random-effects design was used to obtain phase-velocity measurements in subjects without known orthopedic or neurological impairments. The second part of the study consisted of possible applications of the device with mixed designs on subjects with spinal cord injuries. By means of generalizability theory, multiple sources of error (eg, occasion, clinician, repetition) were estimated. For the clinical trial, 17 persons with spinal cord injuries not older than 5 weeks were tested. RESULTS: The standard error of measurement (SEM) for intrarater reliability measurements ranged from 7.3 to 9.8 m x s(-1) . The SEMs for interrater reliability measurements ranged from 5.7 to 9.5 m x s(-1). The SEMs for measurements obtained by a single clinician in a clinical population ranged from 11.9 to 39.7 m x s(-1). CONCLUSION AND DISCUSSION: The reproducibility of measurements obtained with the device is suitably high for the device to be used for evaluation in clinical and research settings.  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