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   157篇
  免费   0篇
电工技术   2篇
化学工业   20篇
金属工艺   4篇
机械仪表   8篇
建筑科学   6篇
能源动力   3篇
轻工业   18篇
水利工程   3篇
无线电   12篇
一般工业技术   19篇
冶金工业   50篇
自动化技术   12篇
  2023年   1篇
  2021年   2篇
  2020年   3篇
  2019年   2篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   4篇
  2012年   5篇
  2011年   10篇
  2010年   6篇
  2009年   4篇
  2008年   7篇
  2007年   5篇
  2006年   7篇
  2005年   4篇
  2004年   2篇
  2003年   7篇
  2002年   5篇
  2001年   4篇
  2000年   2篇
  1999年   7篇
  1998年   17篇
  1997年   10篇
  1996年   8篇
  1995年   5篇
  1994年   7篇
  1989年   2篇
  1987年   1篇
  1986年   2篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1979年   1篇
  1978年   1篇
  1976年   2篇
  1975年   1篇
  1974年   3篇
  1969年   3篇
排序方式: 共有157条查询结果,搜索用时 31 毫秒
41.
We demonstrated the effectiveness of radiation-inducible expression of the TNF-α gene for cancer therapy in vitro. The TNF-α gene under the control of the stress-inducible promoter, gadd 153, was introduced into the human glioma cell line, U251-SP. Without cobalt-60 gamma irradiation, no cytotoxicity against the transfected cells was observed. When the transfected cells were irradiated with 10 or 20 gray (Gy), the gadd 153 promoter was highly induced and the expression level of TNF-α increased. Five days after the irradiation, the TNF-α productions of each cell irradiated with 10 and 20 Gy were 30 and 100 times higher than the basal level, respectively. The cytotoxicities against the transfected cells 5 d after irradiation with 10 and 20 Gy were 79% or 91%, respectively, which are much higher than those against the nontransfected cells that were irradiated at the same dose (43% and 78%, respectively). These results demonstrate that the gadd 153-TNF-α system may be an effective tool for radiosurgery of malignant brain tumors.  相似文献   
42.
Multiple scattering has an important influence on the analysis of microns-thick specimens with MeV electrons. In this paper, we report on effects of multiple scattering of MeV electrons on electron transmission and imaging of tilted and thick amorphous film specimens by experiment and theoretical analysis. Electron transmission for microns-thick epoxy-resin and SiO2 specimens calculated by the multiple elastic-scattering theory is in good agreement with measurements in the ultrahigh voltage electron microscope (ultra-HVEM) at Osaka University. Electron transmission and electron energy are then presented in an approximate power law. The bright-field ultra-HVEM images of gold particles on the top or bottom surfaces of 5 and 15 μm thick specimens further illustrate the effect of multiple scattering on image quality. The observed top‐bottom effect for the very thick specimens appears to be mainly caused by multiple elastic scattering. With increase in the accelerating voltage from 1 to 2 MV, image blurring, contrast, the signal-to-noise ratio, and the top‐bottom effect are improved because of reduction in the influence of multiple scattering. However, the effect of specimen thickness on image blurring is shown to be stronger than that of accelerating voltage. At the 2 MV accelerating voltage, the 100 nm gold particle can be imaged with less blurring of ∼4 nm when located at the bottom surface of a 15 μm thick epoxy-resin specimen.  相似文献   
43.
44.
OBJECTIVES: This study examined the changes in myocardial energy metabolism during myocardial ischemia after "remote preconditioning" and investigated the involvement of adenosine receptors in the mechanisms of this effect. BACKGROUND: Recent studies have indicated that a brief period of ischemia and reperfusion (ischemic preconditioning, PC) in a remote organ reduces myocardial infarct size (IS) protecting against subsequent sustained myocardial ischemia. However, the mechanisms of "remote PC" remain unclear. We assessed myocardial energy metabolism during sustained myocardial ischemia and reperfusion after renal PC (RPC), in comparison with that after myocardial PC (MPC) in open-chest rabbits. It has been established that adenosine receptors are involved in the mechanisms of MPC. METHODS: Rabbits that had been anesthetized with halothane were divided into six groups. The control (CNT) group underwent 40-min coronary occlusion followed by 120 min reperfusion. Before the procedure, the MPC group underwent an additional protocol of 5 min coronary artery occlusion and 20 min reperfusion, and the RPC group received a 10 min episode of renal artery occlusion and 20 min reperfusion. In additional experimental groups, 8 sulfophenyl-theophylline (SPT, 10 mg/kg), an adenosine receptor inhibitor, was intravenously injected before the 40 min myocardial ischemia (SPT, MPC + SPT and RPC + SPT groups, respectively). Myocardial levels of phosphocreatine (PCr), ATP and intracellular pH (pHi) were measured by 31P-NMR spectroscopy. RESULTS: RPC and MPC delayed the decreases in ATP levels, preserved pHi during 40-min myocardial ischemia and resulted in better recovery of ATP and PCr during 120 min reperfusion compared with the controls. SPT abolished the improvement in myocardial energy metabolism and the reduction in myocardial IS caused by MPC or RPC. Myocardial IS in the CNT (n = 8), MPC (n = 9), RPC (n = 9), SPT (n = 6), MPC + SPT (n = 8) and RPC + SPT (n = 8) groups averaged 42.8+/-3.5%, 18.2+/-1.8%*, 19.6+/-1.3%*, 44.9+/-5.0%, 35.6+/-2.7% and 34.8+/-3.6% of the area at risk (*p < 0.05 vs. CNT), respectively. CONCLUSIONS: PC in a remote organ, similar to MPC, improved myocardial energy metabolism during ischemia and reperfusion and reduced IS in vivo by an adenosine-dependent mechanism in rabbits.  相似文献   
45.
The ultra-HVEM with an accelerating voltage of 3 MV at Osaka University is capable of achieving excellent penetration and resolution for thick specimens. We obtained images of 5-microm-thick slices tilted at angles of up to 70 degrees for biological samples and observed stick-shaped samples of Si devices free from missing zone. These features make the ultra-HVEM an invaluable extension of 3D observation by electron tomography. In this paper, we introduce aspects of ultra-HVEM tomography; specifically, the magnification, the amount of image blurring for thick samples and the electron staining method. Finally, we give some typical applications in the fields of cell biology, pathology and electrical engineering.  相似文献   
46.
Steam dryers are in widespread use for sewage sludge treatment. The effectiveness of the steam dryer could be improved by increasing the drying rate, which is influenced by the movement of the sludge in the dryer. Therefore, it is necessary to understand the movement of sludge and water evaporation in the dryer. In this study, tracers were used to elucidate the behavior of sludge in the dryer. The experiment confirmed that sludge did not simply flow in one direction; instead, part of the sludge flowed in the reverse direction (back-mixing). A tanks-in-series model analysis was performed to analyze the back-mixing phenomenon. This analysis provided insight into the behavior of sludge in the dryer, and the drying rate of each segment was determined.  相似文献   
47.
Broadband CDMA techniques   总被引:4,自引:0,他引:4  
A very high-speed wireless access of 100 Mb/s to 1 Gb/s is required for fourth-generation mobile communications systems. However, for such high-speed data transmissions, the channel is severely frequency-selective due to the presence of many interfering paths with different time delays. A promising wireless access technique that can overcome the channel frequency-selectivity and even take advantage of this selectivity to improve the transmission performance is CDMA. There may be two approaches in CDMA technique: direct sequence CDMA and multicarrier CDMA. A lot of attention is paid to MC-CDMA. However, recently it has been revealed that DS-CDMA can achieve good performance comparable to MC-CDMA if proper frequency domain equalization is adopted. This article discusses their similarities and performances. A major transmission mode in 4G systems is packet-based. Automatic repeat request combined with channel coding is a very important technique. Recent research activity on this technique is also introduced.  相似文献   
48.
We treated 43 acute tears of the calcaneofibular ligament by operation in 43 patients after subtalar arthrography. There were 22 men and 21 women with a mean age of 22.3 years (14 to 61). Anteroposterior (AP), lateral and oblique views were obtained with the foot in 45 degrees of internal rotation and the ankle in the neutral position. Any communication or leakage to the ankle, tendon sheaths, subcutaneous tissue and sinus tarsi was recorded. We examined an oblique view of the microrecess along the interosseous ligament and an AP view of the lateral recess just under the distal end of the fibula. We also studied a control group of 27 patients with isolated injuries of the anterior talofibular ligament without rupture of the calcaneofibular ligament. The findings in the two groups were significantly different when examined for leakage to the ankle (p=0.0002), to the peroneal tendon sheaths (p=0.0347) and to the subcutaneous tissue (p=0.0222), absence of the microrecess (p=0.0055) and presence of the lateral recess (p=0.0012). Many ankle sprains which involve tearing of the calcaneofibular ligament are accompanied by injuries of the subtalar joint. Combined injuries of the anterior talofibular ligament and calcaneofibular ligament, and isolated injury of the anterior talofibular ligament should be differentiated.  相似文献   
49.
To elucidate the role of phosphorylation in regulation of intracellular distribution of myosin II, we have characterized mutant Dictyostelium cells expressing myosin II that could not be regulated by the phosphorylation on the mapped heavy chain sites, the light chain site, or both sites. Immunofluorescence microscopy demonstrated that all three mutant myosin IIs were localized in the furrow region of dividing cells and in the tail region of migrating cells, similar to wild-type cells. Thus, regulation by phosphorylation is not required to direct myosin II toward the furrow region and the tail region in Dictyostelium. However, myosins that were deficient in heavy chain phosphorylation were distributed only in the cortical region of interphase cells, whereas some myosin IIs were present throughout the endoplasm in wild-type cells. Video microscopy showed that the rate of cell migration was significantly lower in cells that were deficient in heavy chain phosphorylation- than in light chain phosphorylation-deficient cells, myosin null cells and wild-type cells. Chemotactic behavior of cells that were deficient in heavy chain phosphorylation was also retarded. These results suggest that loss of regulation by heavy chain phosphorylation results in excessive myosin in the cortex, which leads to retarded motility.  相似文献   
50.
Natural history of scoliosis in spastic cerebral palsy   总被引:1,自引:0,他引:1  
BACKGROUND: Although the frequent occurrence of scoliosis in patients who have spastic cerebral palsy is well known and surgical treatment has often been recommended for these patients, little is known about the natural history of scoliosis in this population. We aimed to clarify the natural history of scoliosis from childhood through to adulthood and provide objective data on proper surgical indications for such patients. METHODS: The participants were 37 institutionalised patients with severe spastic cerebral palsy and scoliosis. All the participants had a series of radiographs taken, starting at a mean age of 7.8 years; they were followed up for an average of 17.3 years. We retrospectively reviewed radiographs and assessed the effect of five factors on progression of scoliosis: sex, degree of spasticity, initial physical capability, pattern of spinal curve, and location of curve. FINDINGS: Scoliosis usually started before the age of 10 years and progressed rapidly during the growth period. In many cases, even after growth had ended, continuous progression was seen. The mean magnitude of the curves at final examination was 55 degrees (Cobb angle). In 11 (85%) of 13 patients who had a spinal curve of more than 40 degrees before age 15 years, the scoliosis progressed to more than 60 degrees by the time of the final examination. Meanwhile, in only three (13%) of 24 patients who had a curve of less than 40 degrees at age 15 years, did the scoliosis progress to more than 60 degrees. Severe scoliosis (> or = 60 degrees) developed predominantly in those who had total body involvement (67%), were bedridden (100%), or had throacolumbar curves (57%). INTERPRETATION: The risk factors for progression of scoliosis in spastic cerebral palsy are: having a spinal curve of 40 degrees before age 15 years; having total body involvement; being bedridden; and having a thoracolumbar curve. Patients with these risk factors might benefit from early surgical intervention to prevent progression to severe scoliosis.  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