首页 | 官方网站   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   266058篇
  免费   18192篇
  国内免费   8942篇
工业技术   293192篇
  2024年   1056篇
  2023年   3810篇
  2022年   6578篇
  2021年   8877篇
  2020年   6506篇
  2019年   5607篇
  2018年   6423篇
  2017年   7518篇
  2016年   7288篇
  2015年   9008篇
  2014年   11109篇
  2013年   13991篇
  2012年   15747篇
  2011年   17539篇
  2010年   13456篇
  2009年   13266篇
  2008年   12447篇
  2007年   12058篇
  2006年   12351篇
  2005年   13622篇
  2004年   9565篇
  2003年   8216篇
  2002年   6516篇
  2001年   5827篇
  2000年   5458篇
  1999年   6529篇
  1998年   11626篇
  1997年   8320篇
  1996年   6636篇
  1995年   4897篇
  1994年   3957篇
  1993年   3364篇
  1992年   2030篇
  1991年   1635篇
  1990年   1369篇
  1989年   1184篇
  1988年   1010篇
  1987年   736篇
  1986年   622篇
  1985年   518篇
  1984年   296篇
  1983年   289篇
  1982年   303篇
  1981年   337篇
  1980年   331篇
  1979年   166篇
  1978年   167篇
  1977年   681篇
  1976年   1419篇
  1975年   146篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
3.
4.
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   
5.
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions.  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-23

京公网安备 11010802026262号