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   2969篇
  免费   100篇
  国内免费   1篇
电工技术   59篇
综合类   4篇
化学工业   1026篇
金属工艺   52篇
机械仪表   31篇
建筑科学   196篇
矿业工程   30篇
能源动力   32篇
轻工业   385篇
水利工程   10篇
石油天然气   1篇
无线电   152篇
一般工业技术   409篇
冶金工业   235篇
原子能技术   28篇
自动化技术   420篇
  2022年   37篇
  2021年   37篇
  2020年   31篇
  2019年   29篇
  2018年   50篇
  2017年   42篇
  2016年   67篇
  2015年   85篇
  2014年   74篇
  2013年   118篇
  2012年   117篇
  2011年   160篇
  2010年   107篇
  2009年   111篇
  2008年   115篇
  2007年   136篇
  2006年   117篇
  2005年   107篇
  2004年   103篇
  2003年   73篇
  2002年   67篇
  2001年   56篇
  2000年   51篇
  1999年   53篇
  1998年   72篇
  1997年   59篇
  1996年   56篇
  1995年   54篇
  1994年   67篇
  1993年   43篇
  1992年   44篇
  1991年   42篇
  1990年   28篇
  1989年   38篇
  1988年   23篇
  1987年   28篇
  1986年   34篇
  1985年   37篇
  1984年   38篇
  1983年   33篇
  1982年   32篇
  1981年   27篇
  1980年   29篇
  1978年   25篇
  1977年   27篇
  1976年   27篇
  1975年   37篇
  1974年   20篇
  1973年   24篇
  1970年   30篇
排序方式: 共有3070条查询结果,搜索用时 0 毫秒
1.
ABSTRACT

The digital age of the future is ‘not out there to be discovered’, but it needs to be ‘designed’. The design challenge has to address questions about how we want to live, work, and learn (as individuals and as communities) and what we value and appreciate, e.g.: reflecting on quality of life and creating inclusive societies. An overriding design trade-off for the digital age is whether new developments will increase the digital divide or will create more inclusive societies. Sustaining inclusive societies means allowing people of all ages and all abilities to exploit information technologies for personally meaningful activities. Meta-design fosters the design of socio-technical environments that end-user developers can modify and evolve at use time to improve their quality of life and favour their inclusion in the society. This paper describes three case studies in the domain of assistive technologies in which end users themselves cannot act as end-user developers, but someone else (e.g.: a caregiver or a clinician) must accept this role requiring multi-tiered architectures. The design trade-offs and requirements for meta-design identified in the context of the case studies and other researchers’ projects are described to inform the development of future socio-technical environments focused on social inclusion.  相似文献   
2.
3.
Semi‐Markovian processes (SMP) serve as a versatile means to model various traffic types generated by sources or superposed from links in ATM networks. An efficient discrete time analysis method is proposed for SMP/G/1 queueing systems to evaluate ATM switches with non‐renewal input. Some basic results are derived for the autocorrelation function of semi‐Markovian processes and for the effect of state space reduction on autocorrelation, which show how to represent correlated traffic with given characteristic by an adequate SMP model of limited size. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
4.
AIMS: This series analyses the results of conservative surgery for large lower pole breast cancers by lumpectomy associated with a bilateral remodelling mammoplasty, in order to avoid residual deformities. METHODS: This retrospective study concerns 50 patients with a lower pole breast cancer treated between 1986 and 1996 by lumpectomy, mammoplasty and irradiation. The contralateral breast was immediately made symmetrical in all cases. The mean tumour size was 32.5 mm. RESULTS: The mean weight of the lumpectomy specimen was 270 g. Resection margins were tumour-free in 90% of cases. The main complication observed was delayed healing, thus postponing post-operative treatment in 6.5% of cases. The median follow-up was 48 months. The 5-year actuarial ipsilateral local recurrence rate was 7% and 5-year actuarial metastasis-free and overall survival rates were 81 and 97%, respectively. Cosmesis was satisfactory in 85% of patients. We observed better results when radiotherapy was performed after rather than prior to surgery (92 vs. 67%: NS). CONCLUSIONS: Performing a bilateral mammoplasty at the time of initial surgery for large breast cancers situated in the lower quadrants of the breast facilitates larger lumpectomies with good cosmetic results.  相似文献   
5.
6.
Gries  D. Marsh  D. 《Computer》1989,22(11):49-56
This report describes the results of a survey completed in December 1988 on the production and employment of PhDs and faculty in PhD-granting computer science/engineering departments during the 1987-8 academic year. All 127 computer science (CS) departments (115 US and 12 Canadian) participated. In addition, 34 departments offering the PhD in computer engineering (CE) were included. Throughout the report. CE statistics are reported separately so that comparisons with previous years can be made for CS. The intent is to merge all statistics for CS and CE after several years  相似文献   
7.
8.
9.
10.
Amino-substituted cyclopropenylium salts ( 11a,b ) react with diazomethyl compounds ( 12a-i ) in dichloromethane or acetonitrile in the presence of a base (ethyldiisopropylamine, 1,5-diazabicyclo[4.3.0] non-5-ene) to form 4-aminopyridazines ( 13a-i ) specifically. The reaction is interpreted in terms of an initial electrophilic diazoalkane substitution to give diazomethylcyclopropenes ( 11 + 12 → 14 ) which undergo a [1.5]-cyclisation to form the betaines 16 which, in turn, isomerise with opening of the bridging bond to give the aminopyridazines 13 . In a similar manner, the tris[amino] cyclopropenylium salts 8a,b and 10a-c are converted to the 3,4,5-tris[amino]-pyridazines ( 21a-k ) by treatment with diazomethyl compounds ( 12a, c-f ).  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