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   637108篇
  免费   7859篇
  国内免费   2468篇
电工技术   12030篇
综合类   945篇
化学工业   90187篇
金属工艺   24748篇
机械仪表   19055篇
建筑科学   14548篇
矿业工程   3004篇
能源动力   15615篇
轻工业   50614篇
水利工程   6289篇
石油天然气   10869篇
武器工业   111篇
无线电   80402篇
一般工业技术   123117篇
冶金工业   127982篇
原子能技术   13853篇
自动化技术   54066篇
  2021年   4652篇
  2019年   4598篇
  2018年   7804篇
  2017年   7910篇
  2016年   8315篇
  2015年   5488篇
  2014年   9363篇
  2013年   27100篇
  2012年   15323篇
  2011年   21148篇
  2010年   16714篇
  2009年   19165篇
  2008年   20237篇
  2007年   20283篇
  2006年   18035篇
  2005年   16683篇
  2004年   16502篇
  2003年   16022篇
  2002年   15458篇
  2001年   15723篇
  2000年   14924篇
  1999年   15901篇
  1998年   40632篇
  1997年   28355篇
  1996年   21894篇
  1995年   16660篇
  1994年   14599篇
  1993年   14578篇
  1992年   10666篇
  1991年   10080篇
  1990年   9780篇
  1989年   9453篇
  1988年   8801篇
  1987年   7676篇
  1986年   7699篇
  1985年   8751篇
  1984年   7974篇
  1983年   7236篇
  1982年   6850篇
  1981年   7046篇
  1980年   6725篇
  1979年   6301篇
  1978年   6183篇
  1977年   7207篇
  1976年   9412篇
  1975年   5449篇
  1974年   5292篇
  1973年   5337篇
  1972年   4417篇
  1971年   3948篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
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   
3.
4.
5.
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   
6.
The use of field robots can greatly decrease the amount of time, effort, and associated risk compared to if human workers were to carryout certain tasks such as disaster response. However, transportability and reliability remain two main issues for most current robot systems. To address the issue of transportability, we have developed a lightweight modularizable platform named AeroArm. To address the issue of reliability, we utilize a multimodal sensing approach, combining the use of multiple sensors and sensor types, and the use of different detection algorithms, as well as active continuous closed‐loop feedback to accurately estimate the state of the robot with respect to the environment. We used Challenge 2 of the 2017 Mohammed Bin Zayed International Robotics Competition as an example outdoor manipulation task, demonstrating the capabilities of our robot system and approach in achieving reliable performance in the fields, and ranked fifth place internationally in the competition.  相似文献   
7.
8.
9.
10.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  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