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   783篇
  免费   21篇
  国内免费   6篇
电工技术   98篇
综合类   2篇
化学工业   131篇
金属工艺   37篇
机械仪表   8篇
建筑科学   14篇
能源动力   18篇
轻工业   52篇
水利工程   3篇
石油天然气   3篇
无线电   69篇
一般工业技术   133篇
冶金工业   154篇
原子能技术   17篇
自动化技术   71篇
  2023年   2篇
  2022年   21篇
  2021年   17篇
  2020年   3篇
  2019年   12篇
  2018年   17篇
  2017年   11篇
  2016年   17篇
  2015年   8篇
  2014年   30篇
  2013年   25篇
  2012年   25篇
  2011年   41篇
  2010年   31篇
  2009年   29篇
  2008年   32篇
  2007年   30篇
  2006年   30篇
  2005年   24篇
  2004年   13篇
  2003年   23篇
  2002年   24篇
  2001年   9篇
  2000年   10篇
  1999年   19篇
  1998年   62篇
  1997年   31篇
  1996年   29篇
  1995年   27篇
  1994年   16篇
  1993年   18篇
  1992年   9篇
  1991年   12篇
  1990年   7篇
  1989年   8篇
  1988年   6篇
  1987年   8篇
  1986年   7篇
  1985年   8篇
  1984年   6篇
  1983年   9篇
  1982年   8篇
  1981年   4篇
  1980年   6篇
  1979年   2篇
  1978年   6篇
  1977年   6篇
  1976年   8篇
  1975年   2篇
  1973年   1篇
排序方式: 共有810条查询结果,搜索用时 31 毫秒
1.
The arc welding has been used in various welding methods because it is inexpensive and high in strength after welding. However, it is a problem that accidents such as collapse of the bridge occur because of the welding defects. The welding of low cost and high productivity is required without the welding defects. The pulsed TIG welding is inexpensive and capable of high‐quality welding. The electromagnetic force contributing to penetration changes because the transient response of arc temperature and iron vapor generated from anode occurs. However, the analysis of pulsed TIG welding with metal vapor has been elucidated only metal vapor concentration near anode with transient phenomenon and heat flux. Thus, the theoretical elucidation of penetration depth with control factor has not been researched. In this paper, the contribution of metal vapor mass at the periphery part of pulsed arc to the electromagnetic force in the weld pool is elucidated. As a result, the iron vapor mass at periphery part decreased with increasing the frequency. The iron vapor was stagnated at axial center within one cycle. The electromagnetic force to the penetration depth direction in weld pool increased at axial center. Therefore, the metal vapor mass at periphery part plays an important role for the electromagnetic force increment at axial center.  相似文献   
2.
Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00?l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor.  相似文献   
3.
A worksite study was conducted to examine whether a 15-min nap during a post-lunch rest period would affect subsequent alertness, performance, and nocturnal sleep in eight factory workers under a 3-week protocol. Subjects were asked to take the nap at 12:30 h on a reclining chair during the nap week, and to remain awake during the no-nap week. The order of these 2 weeks was counterbalanced between the subjects. During the third, follow-up week, each subject determined whether or not she/he would nap. Alertness on the job and nocturnal sleep were assessed using a sleep diary. Wrist activity was also recorded during sleep at night. Choice reaction time task (RT) was performed at 10:00 and 15:00 h every day of the nap week and every other day of the no-nap and follow-up weeks. Perceived alertness was significantly higher in the afternoon after nap than after no nap at the end of the week. Similar effects were observed during the follow-up week where almost half of the subjects napped. No significant differences between the three weeks were found for RT performance or nocturnal sleep. Workers' attitudes toward the nap were favourable. Although further intervention research is required, our results suggest that post-lunch napping may have the potential to promote daytime alertness at work.  相似文献   
4.
To detect cytomegalovirus-associated interstitial pneumonia (CMV-IP) in recipients of BMT in its earliest stage, five CMV methods were assessed for their usefulness using bronchoalveolar lavage fluid as the test specimen. Of the 43 cases enrolled in the study, PCR was positive in 12 cases, shell vial in eight, culture in eight and cytology in three. There were no positive cases in in situ hybridization. Based on this result, the 43 cases were classified into four groups: Group 1, three cases: positive in PCR, shell vial and cytology; Group 2, five cases: positive in PCR and shell vial; Group 3, four cases: positive only in PCR; and Group 4, 31 cases: negative in all CMV tests. Cases in Group 1 were judged as having the highest risk of overt CMV-IP. They were successfully treated with a combination of ganciclovir and immunoglobulin. Group 2 was diagnosed as having active CMV infection and ganciclovir monotherapy was effective for these patients. Groups 3 and 4 were not given anti-CMV therapy, but they were free from CMV-related manifestations throughout the study. The sensitivity and specificity of each survey method for the detection of Groups 1 and 2 were 1.0 and 0.89 in PCR, 1.0 and 1.0 in shell vial, 0.88 and 1.0 in culture, and 0.38 and 1.0 in cytology. Similarly, the positive and negative predictive values were 0.67 and 1.0 in PCR, 1.0 and 1.0 in shell vial, 1.0 and 0.97 in culture, and 1.0 and 0.88 in cytology. Thus, CMV survey on bronchoalveolar fluid was thought to be useful in detecting post BMT CMV-IP in its earliest stage.  相似文献   
5.
The purpose of this study was to evaluate the clinical usefulness of three-dimensional (3D) images of the bronchi obtained using helical CT. Thirteen patients with lung cancer, one with tracheal diverticulum, and one with bronchial amyloidosis were examined. The CT scanner employed was the Toshiba Xforce. The helical CT scan cycle consisted of 20 continuous rotations, each requiring 1.5 sec, for a total scanning time of 30 sec. Scans were obtained using a 5-mm X-ray beam width, a 5-mm/1.5 sec couchtop sliding speed, and a 2-mm reconstruction interval. 3D images were reconstructed using a CEMAX VIPstation. The optimal lower and upper threshold CT values for 3D images of the bronchi were -650 and -100 HU, respectively, and 3D images clearly depicted endobronchial lesions. Cartilage crescents were also demonstrated, but longitudinal and circular mucosal folds could not be visualized. In conclusion, 3D images of the bronchi acquired using helical CT were useful in evaluating endobronchial lesions.  相似文献   
6.
The nature of the events whereby the reactive intermediates resulting from the bioactivation of bromobenzene and furosemide induce hepatotoxicity is unknown. To examine a role for disturbances in intracellular calcium homeostasis, secondary to a depletion in cellular reduced glutathione (GSH) and reduced protein thiols (PSHs), isolated mouse hepatocytes were exposed to cytotoxic concentrations of bromobenzene or furosemide. Cytosolic calcium concentration, as well as thiol status, was determined. The incubation of hepatocytes with 3.0 mM bromobenzene, and subsequent additions (1.2 mM) of the agent every hour, resulted in significant GSH depletion. The loss of plasma membrane integrity at 1.5 h preceded both a rise in the cytosolic Ca2+ concentration and depletion of total PSH content. Furosemide (1.0 mM) produced a 70% depletion in cellular GSH content in isolated hepatocytes. The initiation of cell damage occurred concurrently with both a rise in the cytosolic Ca2+ concentration and a depletion of total PSH content 4 h following furosemide addition. Since the increase in cytosolic Ca2+ did not precede cytotoxicity, these results do not support an initiating role for Ca2+ deregulation in bromobenzene and furosemide hepatotoxicities. In addition, depletion of PSH content did not correlate with bromobenzene- or furosemide-induced cytotoxicity.  相似文献   
7.
8.
To realize a stable supply of electric power in an automobile, an accurate and reliable detection method of SOC (state‐of‐charge) in a lead acid battery is required. However the dynamics of the battery is very complicated. The characteristics of the battery greatly change due to its degradation. Moreover a automobile has many driving patterns, which are unknown beforehand. Thus it is not easy to detect the SOC analytically. In this paper, to overcome this problem, a new on‐line SOC detection method with a radial basis function neural network is proposed. In order to increase the detection accuracy of degraded batteries, physical values related to the degradation degree are used as input signal in the neural network. The detection accuracies for different sized batteries and various degradation states are investigated.  相似文献   
9.
An improved T-Ω method that can analyze magnetic fields produced not only by eddy currents but also by magnetizing currents is proposed. The method is applied to the analysis of 3-D eddy-current models with holes. The usefulness of the method is investigated by comparing calculated results with measured results and with results obtained by the A-Φ method. The T-Ω method has the advantage that the CPU time can be considerably reduced when most of the analyzed region is current-free and the eddy current flows two-dimensionally. The method is especially effective when the shape of the winding is simple and the distribution of magnetizing current is known beforehand. It is not effective when most of the analyzed region is current-carrying  相似文献   
10.
A 64-Mb dynamic RAM (DRAM) has been developed with a meshed power line (MPL) and a quasi-distributed sense-amplifier driver (qDSAD) scheme. It realizes high speed, tRAS=50 ns (typical) at Vcc=3.3 V, and 16-b input/output (I/O). This MPL+qDSAD scheme can reduce sensing delay caused by the metal layer resistance. Furthermore, to suppress crosstalk noise, a VSS shield peripheral layout scheme has been introduced, which also widens power line widths. This 64-Mb DRAM was fabricated with 0.4-μm CMOS technology using KrF excimer laser lithography. A newly developed memory cell structure, the tunnel-shaped stacked-capacitor cell (TSSC), was adapted to this 64-Mb DRAM  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