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   882篇
  免费   2篇
  国内免费   3篇
化学工业   10篇
金属工艺   10篇
机械仪表   1篇
建筑科学   7篇
能源动力   1篇
轻工业   6篇
水利工程   1篇
无线电   7篇
一般工业技术   16篇
冶金工业   820篇
原子能技术   3篇
自动化技术   5篇
  2021年   1篇
  2019年   1篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   3篇
  2012年   2篇
  2011年   9篇
  2010年   6篇
  2009年   6篇
  2008年   6篇
  2007年   2篇
  2006年   2篇
  2005年   2篇
  2003年   4篇
  2002年   1篇
  2001年   3篇
  2000年   2篇
  1999年   21篇
  1998年   242篇
  1997年   154篇
  1996年   112篇
  1995年   49篇
  1994年   43篇
  1993年   36篇
  1992年   7篇
  1991年   12篇
  1990年   8篇
  1989年   12篇
  1988年   4篇
  1987年   7篇
  1986年   10篇
  1985年   9篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1981年   1篇
  1980年   11篇
  1979年   1篇
  1978年   3篇
  1977年   21篇
  1976年   55篇
  1975年   1篇
  1972年   1篇
  1969年   1篇
  1955年   1篇
排序方式: 共有887条查询结果,搜索用时 15 毫秒
121.
122.
123.
124.
125.
A 27 month old child presented with left hemiplegia and was found to have deep cerebral venous thrombosis. The deep cerebral venous thrombosis resolved on warfarin. Elevated and fluctuating anticardiolipin antibodies as well as protein S deficiency were detected.  相似文献   
126.
Partial liquid ventilation using conventional ventilatory schemes improves lung function in animal models of respiratory failure. We examined the feasibility of high-frequency partial liquid ventilation in the preterm lamb with respiratory distress syndrome and evaluated its effect on pulmonary and systemic hemodynamics. Seventeen lambs were studied in three groups: high-frequency gas ventilation (Gas group), high-frequency partial liquid ventilation (Liquid group), and high-frequency partial liquid ventilation with hypoxia-hypercarbia (Liquid-Hypoxia group). High-frequency partial liquid ventilation increased oxygenation compared with high-frequency gas ventilation over 5 h (arterial oxygen tension 253 +/- 21.3 vs. 17 +/- 1.8 Torr; P < 0.001). Pulmonary vascular resistance decreased 78% (P < 0.001), pulmonary blood flow increased fivefold (P < 0.001), and aortic pressure was maintained (P < 0.01) in the Liquid group, in contrast to progressive hypoxemia, hypercarbia, and shock in the Gas group. Central venous pressure did not change. The Liquid-Hypoxia group was similar to the Gas group. We conclude that high-frequency partial liquid ventilation improves gas exchange and stabilizes pulmonary and systemic hemodynamics compared with high-frequency gas ventilation. The stabilization appears to be due in large part to improvement in gas exchange.  相似文献   
127.
BACKGROUND: Destruction of uterine vasculature is a common phenomenon in gestational trophoblastic tumors. The authors categorized such uterine vasculature by color Doppler ultrasound and studied its clinical significance. METHODS: Color Doppler ultrasound was performed in 28 patients with gestational trophoblastic tumors. The vascular morphologic manifestations were recorded, and the peak systolic velocity and resistance index of uterine artery were calculated. Serum beta-human chorionic gonadotropin (hCG) levels were measured periodically to monitor chemotherapy response. Seventeen uneventful postmole uteri were used as controls. Two-tailed Student's t-test and Fisher's exact test were used for statistical analysis. RESULTS: The gestational trophoblastic tumors were categorized as diffuse type (N = 7), lacunar type (N = 16), and compact type (n = 5) according to their vascular patterns. The mean serum beta-hCG level at diagnosis in diffuse type lesions (6608 +/- 6320 mIU/mL) was significantly lower than in the lacunar type (40462 +/- 39735 mIU/mL; P = 0.04) and compact type (212114 +/- 205126 mIU/mL; P = 0.02), whereas the level in compact type lesions was significantly higher than in the lacunar type (P = 0.003). Lacunar type lesions exhibited a significantly lower uterine artery resistance index (0.51 +/- 0.13) than diffuse type (0.66 +/- 0.10; P = 0.03) or compact type lesions (0.70 +/- 0.06; P = 0.02). All lesions exhibited significantly higher peak systolic velocity than control subjects (P < 0.001); however, no significant difference was observed among them. Brief courses (< 5 cycles) of chemotherapy cured more diffuse type (6 of 7) than lacunar type (3 of 15, P = 0.006) or compact type lesions (0 of 5, P = 0.008). Histopathologic diagnosis was available for 11 lesions. They were invasive mole in seven lacunar type lesions and choriocarcinoma in four compact type lesions. CONCLUSION: Vascular morphologic patterns of gestational trophoblastic tumors by color Doppler ultrasound correlated well with beta-hCG levels, uterine hemodynamics, chemotherapy response, and possibly the histopathologic diagnosis.  相似文献   
128.
The increasing use of mice in renal and cardiovascular studies has necessitated adapting physiological methods used for rats to mice, which are far smaller in size. We have adapted measurements of continuous renal blood flow, pressure natriuresis and diuresis, and laser-Doppler cortical and medullary flow to 40 g mice with DOCA-salt hypertension. We demonstrated a rightward shift in the pressure-natriuresis-diuresis curve. We conclude that with current, commercially-available equipment, sophisticated renal physiology can be conducted in the mouse. These methods will be important to investigations of gene-targeted mice.  相似文献   
129.
We have previously documented that transgenic mice expressing SV40 Tag regulated by the rat prostatic steroid-binding protein C3(1) 5'-flanking region display multistage mammary tumorigenesis. To delineate genetic changes associated with mammary tumor progression, comparative genomic hybridization (CGH) was performed. CGH revealed a consistent gain of the telomeric region of chromosome 6. This region contains the Ki-ras proto-oncogene. Analyses of genomic DNA by Southern blot demonstrated up to 40-fold amplification of the Ki-ras gene. Ki-ras amplification was detected in 12, 46 and 68% of tumors from 4, 5 and 6 month old mice, respectively, whereas no amplifications were found in any preneoplastic mammary tissues. Tumors bearing Ki-ras gene amplification exhibited high levels of Ki-ras RNA and protein. The over-expressed Ki-Ras protein in these tumors appeared functionally active as indicated by the elevated MAP kinase activity. These data demonstrate that while Ki-ras amplification might not be an early event, there is a strong association between Ki-ras amplification and over-expression and mammary tumor progression in this model. This study also shows that CGH is a powerful and useful technique for identifying chromosomal copy number changes during tumor progression, and that this model may provide a predictable in vivo system for studying gene amplification.  相似文献   
130.
Structural equation modeling was used to examine relationships among prewar factors, dimensions of war-zone stress, and current posttraumatic stress disorder (PTSD) symptomatology using data from 1,632 female and male participants in the National Vietnam Veterans Readjustment Study (R. A. Kulka et al; 1990). For men, previous trauma history (accidents, assaults, and natural disasters) directly predicted PTSD and also interacted with war-zone stressor level to exacerbate PTSD symptoms for high combat-exposed veterans. Male veterans who entered the war at a younger age displayed more symptoms. Family instability, childhood antisocial behavior and age had indirect effects on PTSD for men. For women, indirect prewar effects emanated from family instability. More attention should be given to critical developmental conditions, especially family instability and earlier trauma exposure, in conceptualizing PTSD in adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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