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   1789篇
  免费   0篇
电工技术   7篇
化学工业   57篇
金属工艺   16篇
机械仪表   2篇
建筑科学   20篇
能源动力   10篇
轻工业   18篇
水利工程   1篇
石油天然气   5篇
无线电   23篇
一般工业技术   37篇
冶金工业   1565篇
原子能技术   4篇
自动化技术   24篇
  2021年   3篇
  2019年   3篇
  2018年   4篇
  2017年   4篇
  2016年   3篇
  2015年   3篇
  2014年   5篇
  2013年   14篇
  2012年   6篇
  2011年   8篇
  2010年   3篇
  2009年   8篇
  2008年   6篇
  2007年   13篇
  2006年   10篇
  2005年   4篇
  2004年   11篇
  2003年   12篇
  2002年   3篇
  2001年   8篇
  2000年   4篇
  1999年   30篇
  1998年   446篇
  1997年   291篇
  1996年   172篇
  1995年   111篇
  1994年   84篇
  1993年   101篇
  1992年   20篇
  1991年   14篇
  1990年   26篇
  1989年   24篇
  1988年   20篇
  1987年   16篇
  1986年   12篇
  1985年   5篇
  1984年   5篇
  1983年   6篇
  1982年   4篇
  1981年   16篇
  1980年   24篇
  1978年   4篇
  1977年   65篇
  1976年   139篇
  1975年   3篇
  1974年   2篇
  1972年   2篇
  1971年   2篇
  1969年   2篇
  1955年   2篇
排序方式: 共有1789条查询结果,搜索用时 15 毫秒
991.
ABSTRACT:  In order to understand the development of the microbial population within a hot-drinks vending machine a new machine was placed in a staff area of a university campus vending only hot chocolate. The machine was cleaned weekly using a detergent based protocol. Samples from the mixing bowl, dispense area, and drink were taken over a 19-wk period and enumerated using plate count agar. Bacillus cereus was identified using biochemical methods. Vended drinks were sampled at 0, 3, 6, and 9 min after vending; the hot chocolate powder was also sampled. Over the 1st 8 wk, a significant increase in the microbial load of the machine components was observed. By the end of the study, levels within the vended drink had also increased significantly. Inactivation of the automatic flush over a subsequent 5-wk period led to a statistically but not operationally significant increase in the microbial load of the dispense area and vended drink. The simple weekly clean had a significant impact on the microbial load of the machine components and the vended drink. This study demonstrated that a weekly, detergent-based cleaning protocol was sufficient to maintain the microbial population of the mixing bowl and dispense point in a quasi-steady state below 3.5 log CFU/cm2 ensuring that the microbial load of the vended drinks was maintained below 3.4 log CFU/mL. The microbial load of the drinks showed no significant changes over 9 min after vending, suggesting only spores are present in the final product.  相似文献   
992.
This study investigated the effect of anxiety on play processes in 43 first-, second-, and third-grade children. Using a mood-induction procedure, this study compared processes in play among children randomized to an anxious or neutral mood-induction procedure. Children were assessed using the Affect in Play Scale pre- and post-mood-induction. In addition, this study examined relationships between pretend play processes and self-reported state and trait anxiety levels using the State Trait Anxiety Inventory for Children. Findings demonstrated a significant negative relationship between baseline state anxiety level and organization of the play narrative. Consistent with previous research, children in both conditions significantly improved on multiple play scores over time. Although pretend play processes were not significantly affected by condition assignment, further analysis with a more sensitive measure of affect in play revealed a significant interaction between state anxiety and condition assignment on the amount of positive affect expressed in play. Results indicate that play processes can improve with time and greater state anxiety may impact organization and affective processes in play. Implications for play therapy are discussed in terms of the potential impact anxiety has on play processes. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
993.
Pressurized water reactors circulate high-temperature water that slowly corrodes Inconel and stainless steel system surfaces, and the nickel/iron based corrosion products deposit in regions of the fuel where sub-cooled nucleate boiling occurs. The deposited corrosion products, called ‘crud’, can have an adverse impact on fuel performance. Boron can concentrate within the crud in the boiling regions of the fuel leading to a phenomenon known as axial offset anomaly (AOA). In rare cases, fuel clad integrity can be compromised because of crud-induced localized corrosion (CILC) of the zirconium-based alloy. Westinghouse and the Electric Power Research Institute have committed to understanding the crud transport process and develop a risk assessment software tool called boron-induced offset anomaly (BOA) to avoid AOA and CILC. This paper reviews the history of the BOA model development and new efforts to develop a micro-scale model called MAMBA for use in the Consortium for Advanced Light Water Reactor Simulation (CASL) program.  相似文献   
994.
Evaluating the Impacts of Real-Time Pricing on the Usage of Wind Generation   总被引:1,自引:0,他引:1  
One of the impediments to large-scale use of wind generation within power systems is its nondispatchability and variable and uncertain real-time availability. Operating constraints on conventional generators such as minimum generation points, forbidden zones, and ramping limits as well as system constraints such as power flow limits and ancillary service requirements may force a system operator to curtail wind generation in order to ensure feasibility. Furthermore, the pattern of wind availability and electricity demand may not allow wind generation to be fully utilized in all hours. One solution to these issues, which could reduce these inflexibilities, is the use of real-time pricing (RTP) tariffs which can both smooth-out the diurnal load pattern in order to reduce the impact of binding unit operating and system constraints on wind utilization, and allow demand to increase in response to the availability of costless wind generation. We use and analyze a detailed unit commitment model of the Texas power system with different estimates of demand elasticities to demonstrate the potential increases in wind generation from implementing RTP.  相似文献   
995.
996.
997.
998.
999.
1000.
PURPOSE: In superficial urothelial tumors of the bladder, p53 status is currently the most informative pretreatment parameter to define a population at higher risk for invasive carcinoma. Also, in T1 tumors, occurrence of muscular invasion is often related to an early relapse following BCG therapy. With the knowledge of biological parameters able to identify the group of initial BCG therapy non-responders, it would be possible to offer earlier treatment to the patients who need a more aggressive mode of therapy. The aim of this work was to study the predictive value of the p53 tumor status on the early BCG therapy response. MATERIALS AND METHODS: The population included a selected group of 43 patients presenting T1 bladder tumors with no carcinoma in situ (Tis), treated by transurethral resection (TUR) followed by intravesical BCG therapy. Clinical outcome was analyzed in relation to usual clinical and histopathological parameters, and pretreatment p53 tumor status was assayed by an immunohistochemical technique using DO7 monoclonal antibody. For 16 specimens, p53 gene was investigated using a Single Strand Conformation Polymorphism (SSCP) analysis and sequence determination. RESULTS: p53 anomalies were strongly correlated to smoking behavior (p = 0.003) and tumoral grade (p = 0.025). Univariate analysis revealed an absence of correlation between p53 immunostaining and initial, one and two years response-rate to BCG therapy. However, longterm followup revealed a trend between positive staining and disease progression. The p53 molecular study validated the use of DO7 immunostaining in detection of p53 anomalies. CONCLUSIONS: In T1 bladder tumors, pretreatment p53 determination was not useful to define a group of early BCG non-responders. Thus, p53 status and immunological response induced by BCG endovesical therapy are two independent events.  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