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   263143篇
  免费   3487篇
  国内免费   827篇
电工技术   5166篇
综合类   334篇
化学工业   37827篇
金属工艺   10324篇
机械仪表   8527篇
建筑科学   6271篇
矿业工程   1088篇
能源动力   6507篇
轻工业   23167篇
水利工程   2583篇
石油天然气   3916篇
武器工业   68篇
无线电   34934篇
一般工业技术   50457篇
冶金工业   47499篇
原子能技术   5450篇
自动化技术   23339篇
  2021年   2054篇
  2019年   2064篇
  2018年   3494篇
  2017年   3567篇
  2016年   3774篇
  2015年   2353篇
  2014年   4087篇
  2013年   11434篇
  2012年   6651篇
  2011年   8981篇
  2010年   7076篇
  2009年   7949篇
  2008年   8778篇
  2007年   8710篇
  2006年   7891篇
  2005年   7239篇
  2004年   6965篇
  2003年   6808篇
  2002年   6451篇
  2001年   6525篇
  2000年   6229篇
  1999年   6323篇
  1998年   14406篇
  1997年   10418篇
  1996年   8195篇
  1995年   6490篇
  1994年   5800篇
  1993年   5660篇
  1992年   4598篇
  1991年   4259篇
  1990年   4096篇
  1989年   3825篇
  1988年   3674篇
  1987年   3204篇
  1986年   3112篇
  1985年   3662篇
  1984年   3443篇
  1983年   3077篇
  1982年   2896篇
  1981年   3010篇
  1980年   2802篇
  1979年   2685篇
  1978年   2530篇
  1977年   3007篇
  1976年   3630篇
  1975年   2369篇
  1974年   2338篇
  1973年   2348篇
  1972年   1876篇
  1971年   1763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.
The contamination of honey with hepatotoxic pyrrolizidine alkaloids (PAs) is a well-known hazard for food safety. While management strategies and controls of the honey industry aim to reduce the PA levels, uncertainties remain with regard to the safety of regionally produced and marketed honey. In addition, a previous study showed large differences of results obtained after various periods of storage and apparent differences between the analytical results of different laboratories. Therefore, this study aimed at examining these uncertainties by monitoring the impact of storage on the PA and PA N-oxide (PANO) content of two freshly harvested honeys and on possible demixing effects caused by pollen settling. Additionally, three analytical approaches – target analysis with matrix-matched calibration or standard addition and a sum parameter method – were applied for a comparative analysis of 20 honeys harvested in summer 2016. All samples originated from Schleswig-Holstein in Northern Germany where the PA plant Jacobaea vulgaris is currently observed on a massive scale. The results of the time series analyses showed that PANO levels markedly decreased within a few weeks and practically reached the LOD 16 weeks after harvest. Tertiary PAs, by contrast, remained stable and did not increase as a consequence of PANO decrease. The experiments on a putative demixing, which may result in a heterogeneous distribution of PAs/PANOs, revealed that there was no such effect during storage of up to 12 weeks. A comparison of the PA/PANO levels obtained by different analytical approaches showed that in some cases the sum parameter method yielded much higher levels than the target approaches, whereas in other cases, the target analysis with standard addition found higher levels than the other two methods. In summary, the results of this study highlight uncertainties regarding the validity and comparability of analytical results and consequently regarding health risk assessment.  相似文献   
3.
4.
Here we report some recent biophysical issues on the preparation of solute-filled lipid vesicles and their relevance to the construction of “synthetic cells.” First, we introduce the “semi-synthetic minimal cells” as the liposome-based cell-like systems, which contain a minimal number of biomolecules required to display simple and complex biological functions. Next, we focus on recent aspects related to the construction of synthetic cells. Emphasis is given to the interplay between the methods of synthetic cell preparation and the physics of solute encapsulation. We briefly introduce the notion of structural and compositional “diversity” in synthetic cell populations.  相似文献   
5.
The viability and β‐galactosidase activity of four Lactobacillus strains in milk drink containing gums during 28 days of refrigerated storage at 4 °C were assessed. The population of Lactobacillus rhamnosus GGB101 and Lactobacillus rhamnosus GGB103 were maintained, whereas the population of Lactobacillus reuteri DSM20016 and Lactobacillus reuteri SD2112 significantly decreased. The recommended level of 6 log CFU g?1 was exceeded for all tested trains throughout storage. The highest viable number of Lactobacillus rhamnosus GGB103 (8.76 ± 0.03 log CFU mL?1) was obtained in the product containing carrageenan–maltodextrin. The addition of guar–locust bean–carrageenan led to 20‐fold increase in the level of β‐galactosidase activity for L. rhamnosus GGB101 (1208 ± 2.12 Miller units mL?1) compared to the control (61 ± 2.83 Miller units mL?1). Our results suggested that gums could be added to milk to improve viability and enhance β‐galactosidase activity of Lactobacillus.  相似文献   
6.
7.
8.
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