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   727篇
  免费   19篇
电工技术   33篇
化学工业   119篇
金属工艺   19篇
机械仪表   14篇
建筑科学   7篇
能源动力   19篇
轻工业   74篇
无线电   76篇
一般工业技术   137篇
冶金工业   150篇
原子能技术   39篇
自动化技术   59篇
  2023年   3篇
  2022年   5篇
  2021年   10篇
  2020年   3篇
  2019年   4篇
  2018年   7篇
  2017年   12篇
  2016年   13篇
  2015年   13篇
  2014年   18篇
  2013年   36篇
  2012年   34篇
  2011年   30篇
  2010年   22篇
  2009年   20篇
  2008年   35篇
  2007年   27篇
  2006年   24篇
  2005年   10篇
  2004年   20篇
  2003年   24篇
  2002年   22篇
  2001年   15篇
  2000年   20篇
  1999年   21篇
  1998年   65篇
  1997年   26篇
  1996年   32篇
  1995年   21篇
  1994年   13篇
  1993年   15篇
  1992年   18篇
  1991年   15篇
  1990年   9篇
  1989年   12篇
  1988年   12篇
  1987年   6篇
  1986年   2篇
  1985年   4篇
  1984年   4篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   3篇
  1978年   4篇
  1977年   7篇
  1976年   8篇
  1975年   6篇
  1974年   3篇
  1972年   2篇
排序方式: 共有746条查询结果,搜索用时 328 毫秒
61.
We have developed an incentive‐rewarding mechanism that stimulates activities in social networking services (SNSs), including content uploading and link establishment. We particularly focus on changing the reward assignment ratio based on the different risks users perceive when uploading content with different privacy settings: public‐open and friend‐limited. Learning‐based simulation allowed us to observe that SNS activity, which we measured as the amount of browsed content within a certain period, can be controlled by a rewarding assignment ratio. We then analyzed how the amount of uploaded content and the increase of established links affect SNS activity. Results suggested that the optimal reward assignment ratio to maximize SNS activity changes depending on the total amount of available reward resources. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
62.
In order to solve a power consumption problem of the driver stage in the cathode-follower RF system, a grid-cathode driving scheme is investigated by means of an isolation transformer. A very low output impedance can be realized together with a voltage gain a few tens of times higher than that of a cathode-follower. The model system has been tested under frequency modulation in the 1-3-MHz range at 40-Hz repetition; the output impedance is less than 30 Ω and the driver voltage 62 V to produce a 1.2-kV peak at the cavity gap  相似文献   
63.
Dispersed generators such as wind power systems, photovoltaic systems, and cogeneration systems are expected to mitigate the environmental burden of energy consumption, and their installation has been promoted recently. Micro‐Grid is focused on as a method to solve some problems in a commercial electric power line when installing a large number of dispersed generators, and some demonstrative research on Micro‐Grid for large‐scale systems is being carried out now. Also, small cogeneration systems for houses, such as gas engines and fuel cells, are expected to improve CO2 emissions. However, if the power and heat demand of a family are relatively small or are unbalanced, the cogeneration system does not operate effectively. The authors have studied the application of Micro‐Grid for home energy supply, and have developed a control system to solve this problem. The system achieves a reduction of CO2 emissions and energy costs by sharing electric power and heat among some houses with cogeneration systems. This paper presents an outline of the newly developed system, and in particular describes the effect of the reduction in CO2 emissions compared with a conventional energy supply method, and the case in which dispersed generators are installed in some houses and operate independently. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(3): 19–27, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20879  相似文献   
64.
65.
We report a simple method for the fabrication of reproducible, clean, and stable MgB2 superconducting tips. The quality of these tips has been verified by imaging the surface of a thin Au(111) film sample, using a low temperature scanning tunneling microscopy (STM). Using the MgB2 superconducting tip, high-quality semiatomically resolved STM surface images of the thin Au(111) film sample have been observed, which unambiguously indicates that the fabrication of relatively superconducting MgB2, suitable for use as STM tips, is feasible.  相似文献   
66.
BACKGROUND: We postulated that pathophysiologic processes under nonpulsatile circulation are related to the behavior of the sympathetic nerve activity that regulates tissue perfusion. METHODS: Pulsatile and nonpulsatile pumps were installed in parallel in the left heart bypass circuit of anesthetized goats (n = 9) so that pulsatile circulation could be converted to nonpulsatile circulation instantly. At 5 minutes before and after systemic depulsation, we measured hemodynamic indices, renal nerve activity, and regional blood flow of the brain, heart, and renal cortex. RESULTS: Renal nerve activity was significantly elevated after systemic depulsation (15.6 +/- 9.3 versus 19.4 +/- 9.8 microV), when mean aortic pressure remained almost constant. The renal cortical flow was significantly reduced after depulsation (3.61 +/- 1.23 versus 2.93 +/- 1.19 mL.min-1.g-1), whereas no significant difference was found in the regional blood flow of the brain or the heart. CONCLUSIONS: The significant reduction of renal cortical blood flow after systemic depulsation is associated with a significant increase in renal nerve activity. Our results suggest that increased renal nerve activity plays an important role in the reduction of renal function after systemic depulsation.  相似文献   
67.
The murine mortalin genes, mot-1 and mot-2, are members of the hsp70 family of proteins and differ from each other by only two amino acid residues. Mot-1 is expressed in normal cells and has pancytosolic cellular distribution whereas mot-2 is found in the perinuclear region of immortal cells. We report here that a high level of expression of mot-2 protein resulted in malignant transformation of cells as analysed by anchorage independent growth and nude mice assays. A high level of protein expression is attributed to the 900 bp 3' untranslated region of the cDNA which does not have any transforming activity per se. Mortalin cDNA clones isolated from human transformed cells were also found to have transforming activity in similar assays and a high level of expression was apparent in some of the human immortalized cells that showed non-pancytosolic mortalin immunofluorescence. Taken together, the data suggest that nonpancytosolic mortalin may have a role in tumorigenesis.  相似文献   
68.
We describe two infants in whom rhombencephalosynapsis was diagnosed with MR imaging in vivo. In contrast to Dandy-Walker malformation, the vermian maldevelopment in this anomaly is characterized by an absence of the anterior vermis and a deficiency of the posterior vermis. The cerebellar hemispheres are fused. In an attempt to identify the pathogenesis of these anatomic manifestations, we question the traditional concept of the embryologic development of the cerebellar primordium.  相似文献   
69.
In order to clarify the cell kinetics of colorectal villous tumors (VT), 21 villous adenomatous areas and 12 carcinomatous areas within villous adenomas were investigated for proliferative activity and apoptosis and compared with a series of 41 tubular tumors (TT), demonstrating elements of intramucosal carcinomas as well as tubular adenomas (so-called carcinoma in tubular adenoma). Proliferation was estimated in terms of Ki-67 labeling indices and mitotic indices, and apoptosis was assessed by DNA nick-end labeling to give apoptotic indices. Apoptotic indices of villous adenomatous and carcinomatous regions were significantly lower than the values for their tubular counterparts. Ki-67 labeling indices were also significantly lower for adenoma components. Apoptotic indices, Ki-67 labeling indices and mitotic indices increased with atypia raised in tubular adenoma components. Correlations of mitotic indices with apoptotic indices, Ki-67 labeling indices with apoptotic indices and mitotic indices with Ki-67 labeling indices were found for each villous tumor group and tubular tumor group, and the apoptosis and proliferation ratios for villous tumors were relatively low, suggesting a tendency for greater growth due to less cell deletion. Although this is only one of the biological features of villous tumor groups, it might play a major role in generation of malignancy.  相似文献   
70.
Hormone-sensitive lipase (HSL) catalyzes the rate-limiting step in adipocyte lipolysis. We have studied the effect of glucose and long chain fatty acids on the HSL mRNA content of 3T3-F442A adipocytes. Exposure of the cells for 32 h to a medium without glucose led to a decrease by a factor of 2.5-3 in the HSL mRNA without a change in C/EBP alpha mRNA or triglyceride content of the adipocytes. The reduction in HSL mRNA level was accompanied by a decrease in HSL total activity. The effect of glucose exposure was observed after 24 h of exposure and was reversible. Treatment of the adipocytes with oleate did not affect HSL expression. These data show that glucose modulates HSL gene expression and hence could participate in the regulation of adipose tissue lipolysis.  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