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   3908篇
  免费   129篇
  国内免费   13篇
电工技术   37篇
综合类   2篇
化学工业   450篇
金属工艺   82篇
机械仪表   61篇
建筑科学   47篇
矿业工程   1篇
能源动力   68篇
轻工业   106篇
水利工程   1篇
石油天然气   4篇
无线电   395篇
一般工业技术   434篇
冶金工业   2011篇
原子能技术   28篇
自动化技术   323篇
  2023年   5篇
  2021年   21篇
  2020年   27篇
  2019年   27篇
  2018年   49篇
  2017年   47篇
  2016年   46篇
  2015年   50篇
  2014年   69篇
  2013年   183篇
  2012年   99篇
  2011年   130篇
  2010年   119篇
  2009年   121篇
  2008年   126篇
  2007年   106篇
  2006年   75篇
  2005年   70篇
  2004年   66篇
  2003年   75篇
  2002年   47篇
  2001年   46篇
  2000年   55篇
  1999年   116篇
  1998年   693篇
  1997年   360篇
  1996年   263篇
  1995年   143篇
  1994年   129篇
  1993年   133篇
  1992年   27篇
  1991年   44篇
  1990年   36篇
  1989年   58篇
  1988年   45篇
  1987年   37篇
  1986年   36篇
  1985年   47篇
  1984年   6篇
  1983年   15篇
  1982年   11篇
  1981年   15篇
  1980年   20篇
  1978年   9篇
  1977年   42篇
  1976年   76篇
  1975年   11篇
  1974年   4篇
  1973年   3篇
  1955年   3篇
排序方式: 共有4050条查询结果,搜索用时 55 毫秒
1.
2.
Neural Computing and Applications - With an increase in online longitudinal users’ interactions, capturing users’ precise preferences and giving accurate recommendations have become an...  相似文献   
3.
运动饮料配方设计概论   总被引:7,自引:0,他引:7  
运动中,人体生理发生一系列的变化,包括水分损失、血糖/糖原消耗、电解质损失等,导致运动中/后的疲劳和运动能力下降。以运动中人体生理特点为基础,通过讨论运动前/中/后补充水、碳水化合物及电解质的问题,论证了运动饮料配方设计的原理依据。  相似文献   
4.
Bandpass filters with an optimal rejection bandwidth are designed using parallel-coupled stepped impedance resonators (SIRs). The fundamental (f/sub o/) and higher order resonant harmonics of an SIR are analyzed against the length ratio of the high-Z and low-Z segments. It is found that an optimal length ratio can be obtained for each high-Z to low-Z impedance ratio to maximize the upper rejection bandwidth. A tapped-line input/output structure is exploited to create two extra transmission zeros in the stopband. The singly loaded Q(Q/sub si/) of a tapped SIR is derived. With the aid of Q/sub si/, the two zeros can be independently tuned over a wide frequency range. When the positions of the two zeros are purposely located at the two leading higher order harmonics, the upper rejection band can be greatly extended. Chebyshev bandpass filters with spurious resonances up to 4.4f/sub o/, 6.5f/sub o/, and 8.2f/sub o/ are fabricated and measured to demonstrate the idea.  相似文献   
5.
Cell cycle-dependent tumor necrosis factor apoptosis   总被引:1,自引:0,他引:1  
To determine if tumor necrosis factor (TNF)-mediated apoptosis affects cells at defined stages of the cell cycle, WEHI-164/2F (WEHI) cells were synchronized at G0-G1 after 3-day cultures in medium containing RPMI 1640 and 0.5% FCS (RPMI-0.5% FCS). The arrested WEHI cells (60-75% in G0-G1) showed increased sensitivity to TNF killing, measured as 48-h 3-(5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assays, and 15-h apoptosis by propidium iodide staining and flow cytometry analysis. The TNF killing kinetics of G0-G1-arrested cells was similar to controls, and TNF did not accelerate or retard cell cycle progression of the arrested cells after feeding with fresh RPMI-0.5% FCS. However, TNF inhibited WEHI DNA synthesis as early as 1 h after treatment, and inhibition was proportionate to sensitivity to TNF-induced apoptosis. WEHI cells treated with TNF showed a higher percentage of cells in S phase with concomitant decrease in G0-G1 and G2-M. When cultured for 3-18 h in fresh RPMI-0.5% FCS to allow progression of the G0-G1-arrested cells toward the G1-S boundary, WEHI cells became more sensitive to TNF killing, especially at the 3-9 h time points. Moreover, TNF did not degrade [125I]5-iodo-2'-deoxyuridine-labeled WEHI DNA if the labeled cells were precultured for 9 h in fresh RPMI-0.5% FCS to allow them to pass S phase before the addition of TNF. These results show that TNF-induced apoptosis of WEHI cells is connected to cell cycle events; WEHI targets receive the TNF cytotoxic signal mainly at the G1-S boundary and begin to die by apoptosis as they exit from S phase.  相似文献   
6.
7.
8.
Structural investigation on monocrystalline CuInSe2 samples has been made. From the single crystal results, the space group of CuInSe2 was confirmed to be Iˉ42d and the crystal solidification direction was investigated. Compositional uniformity of the ingots was established by EPMA and it was found that the indium concentration was greater than that for copper. Systematic annealing experiments were carried out in vacuum at different temperatures (as low as 160° C) and for different times. Large variation in resistivity was observed after the annealing treatment. P-type samples were found to convert to n-type after the heat-treatments.  相似文献   
9.
Plant seeds store triacylglycerols as energy sources for germination and postgerminative growth of seedlings. The triacylglycerols are preserved in small, discrete, intracellular organelles called oil bodies. A new method was developed to purify seed oil bodies. The method included extraction, flotation by centrifugation, detergent washing, ionic elution, treatment with a chaotropic agent, and integrity testing by use of hexane. These processes subsequently removed non-specifically associated or trapped proteins within the oil bodies. Oil bodies purified by this method maintained their integrity and displayed electrostatic repulsion and steric hindrance on their surface. Compared with the previous procedure, this method allowed higher purification of oil bodies, as demonstrated by SDS-PAGE using five species of oilseeds. Oil bodies purified from sesame were further analyzed by two-dimensional gel electrophoresis and revealed two potential oleosin isoforms. The integrity of oil bodies in germinating sesame seedlings was examined by hexane extraction. Our results indicated that consumption of triacylglycerols reduced gradually the total amount of oil bodies in seedlings, whereas no alteration was observed in the integrity of remaining oil bodies. This observation implies that oil bodies in germinating seeds are not degraded simultaneously. It is suggested that glyoxisomes, with the assistance of mitochondria, fuse and digest oil bodies one at a time, while the remaining oil bodies are preserved intact during the whole period of germination.  相似文献   
10.
A 78-year-old Chinese woman presented with recurrent postprandial abdominal pain. Computerised tomography revealed a small bowel tumour causing volvulus of a segment of the small bowel. Laparotomy confirmed an extraluminal ileal tumour with partial volvulus of the involved small bowel segment. Small bowel resection was done. Histological and ultrastructural studies confirmed a gastrointestinal autonomic nerve tumour. We review the medical literature on this rare tumour.  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