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   77185篇
  免费   2684篇
  国内免费   230篇
电工技术   777篇
综合类   666篇
化学工业   12571篇
金属工艺   1255篇
机械仪表   1501篇
建筑科学   1947篇
矿业工程   461篇
能源动力   1503篇
轻工业   8476篇
水利工程   923篇
石油天然气   212篇
武器工业   6篇
无线电   3331篇
一般工业技术   8560篇
冶金工业   27231篇
原子能技术   409篇
自动化技术   10270篇
  2024年   123篇
  2023年   462篇
  2022年   844篇
  2021年   1123篇
  2020年   744篇
  2019年   921篇
  2018年   1614篇
  2017年   1789篇
  2016年   2229篇
  2015年   1755篇
  2014年   1716篇
  2013年   2914篇
  2012年   4043篇
  2011年   4614篇
  2010年   2422篇
  2009年   2484篇
  2008年   2169篇
  2007年   2033篇
  2006年   1643篇
  2005年   4188篇
  2004年   3390篇
  2003年   2783篇
  2002年   1558篇
  2001年   1253篇
  2000年   784篇
  1999年   1137篇
  1998年   8130篇
  1997年   5103篇
  1996年   3413篇
  1995年   1961篇
  1994年   1510篇
  1993年   1577篇
  1992年   409篇
  1991年   469篇
  1990年   432篇
  1989年   437篇
  1988年   424篇
  1987年   338篇
  1986年   308篇
  1985年   320篇
  1984年   168篇
  1983年   158篇
  1982年   227篇
  1981年   273篇
  1980年   282篇
  1979年   115篇
  1978年   143篇
  1977年   747篇
  1976年   1610篇
  1975年   140篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
2.
In this study, amaranth flour was used as an ingredient to prepare gluten-free cookies. The production process and attributes of amaranth cookies were characterised, and the potential use of amaranth flour as a functional ingredient was analysed. Cookies exhibited a non-uniform reddish brown colour and a cookie factor ratio of 4.5 ± 0.6. Storage studies indicated that after 3 weeks at room temperature cookies presented slight variations in the texture. Simulated gastrointestinal digestion of this product was able to release peptides capable of exerting potential antithrombotic and antihypertensive activities, IC50 values of 0.22 ± 0.04 and 0.23 ± 0.03 mg mL−1 protein, respectively. This work demonstrates for the first time that food made with amaranth flour exerts potential antithrombotic and antihypertensive activity. In conclusion, these amaranth cookies could be an alternative way of incorporating potentially health beneficial products for people who choose a conscious diet, including coeliac or vegan consumers.  相似文献   
3.
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.  相似文献   
4.
5.
6.
7.
8.
ABSTRACT

This paper presents an empirical assessment of four state-of-the-art risk-averse approaches to deal with the capacitated lot-sizing problem under stochastic demand. We analyse two mean-risk models based on the semideviation and on the conditional value-at-risk risk measures, and alternate first and second-order stochastic dominance approaches. The extensive computational experiments based on different instances characteristics and on a case-study suggest that CVaR exhibits a good trade-off between risk and performance, followed by the semideviation and first-order stochastic dominance approach. For all approaches, enforcing risk-aversion helps to reduce the cost-standard deviation substantially, which is usually accomplished via increasing production rates. Overall, we can say that very risk-averse decision-makers would be willing to pay an increased price to have a much less risky solution given by CVaR. In less risk-averse settings, though, semideviation and first-order stochastic dominance can be appealing alternatives to provide significantly more stable production planning costs with a marginal increase of the expected costs.  相似文献   
9.
10.
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