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   1335篇
  免费   44篇
  国内免费   9篇
电工技术   12篇
综合类   25篇
化学工业   150篇
金属工艺   10篇
机械仪表   25篇
建筑科学   39篇
矿业工程   4篇
能源动力   28篇
轻工业   69篇
水利工程   5篇
石油天然气   4篇
无线电   118篇
一般工业技术   124篇
冶金工业   634篇
原子能技术   7篇
自动化技术   134篇
  2023年   3篇
  2022年   9篇
  2021年   16篇
  2020年   10篇
  2019年   14篇
  2018年   17篇
  2017年   15篇
  2016年   25篇
  2015年   13篇
  2014年   26篇
  2013年   44篇
  2012年   37篇
  2011年   47篇
  2010年   37篇
  2009年   38篇
  2008年   33篇
  2007年   29篇
  2006年   43篇
  2005年   18篇
  2004年   28篇
  2003年   24篇
  2002年   23篇
  2001年   11篇
  2000年   26篇
  1999年   46篇
  1998年   203篇
  1997年   128篇
  1996年   92篇
  1995年   34篇
  1994年   39篇
  1993年   45篇
  1992年   11篇
  1991年   23篇
  1990年   16篇
  1989年   11篇
  1988年   22篇
  1987年   16篇
  1986年   6篇
  1985年   14篇
  1984年   6篇
  1982年   7篇
  1981年   8篇
  1980年   6篇
  1979年   3篇
  1978年   2篇
  1977年   15篇
  1976年   31篇
  1974年   3篇
  1972年   3篇
  1971年   2篇
排序方式: 共有1388条查询结果,搜索用时 31 毫秒
121.
Twelve young adults were treated with either melatonin, 3 mg or 6 mg, or placebo, at two different times before an early evening nap (18.00-20.00 h) according to a balanced double-blind Latin square design. Polysomnographic monitoring revealed that both dosages of melatonin significantly shortened sleep latency and increased total sleep time in comparison to placebo, irrespective of the time of administration. Subjects also tended to assess their sleep as 'deeper' after melatonin treatment. Based on previous data and the present results, it was concluded that exogenous melatonin exerts hypnotic effects only when circulating levels of endogenous melatonin are low.  相似文献   
122.
BT Holt  NL Parks  GA Engh  JM Lawrence 《Canadian Metallurgical Quarterly》1997,20(12):1121-4; discussion 1124-5
One hundred thirty-six primary total knee arthroplasty patients were randomized for the use of closed-suction, nonreinfusable wound drains. Blood loss was identical in the drained and undrained groups. Forty percent of undrained wounds compared with 0% of drained wounds required dressing reinforcement. Sixty-nine percent of undrained wounds compared with 39% of drained wounds developed ecchymosis, measuring 92 cm2 in the undrained group and 28 cm2 in the drained group. This study concludes that a simple wound drain effectively minimizes the undesirable accumulation of blood in the surrounding soft tissues and the postoperative wound dressing after total knee arthroplasty.  相似文献   
123.
The integrin alpha 4 beta 7 and mucosal addressin cell adhesion molecule-1 (MAdCAM-1) are molecules involved in the normal recirculation of lymphocytes between the blood and the gastrointestinal tract. These molecules may play a complementary and significant role in animal models of colitis. We have investigated the structural interaction between alpha 4 beta 7 and MAdCAM-1. Site-directed mutagenesis studies of the MAdCAM-1 molecule has led to the identification of the amino acid residue (LDT) in the loop between beta strands C and D of the Ig-superfamily-like folds being involved in the adhesive and cell activation functions of MAdCAM-1 with alpha 4 beta 7.  相似文献   
124.
Contrast-enhanced T1-weighted spin-echo magnetic resonance imaging (MRI) has demonstrated that Gd-diethylenetriaminepentaacetate (Gd-DTPA), which normally does not cross the blood-brain or blood-CSF barriers, does so approximately 40 min after administration of glucose to a vitamin B1 deficient rat. The period of the onset of this blood-CSF or blood-brain barrier dysfunction coincides with our previous observations of accumulation of glutamate or glutamate derivatives following an equivalent glucose load under identical conditions of thiamin deficiency, consistent with a relationship between these two observations. The dysfunction was reversed when a thiamin deficient animal was made thiamin replete.  相似文献   
125.
126.
A new system has been developed for dynamic project management and control known as Planning Orientated Evaluation Methods (POEM) which has been considered as a core project evaluation system incorporating cost and time analysts. The performance control gives the manager a direct influence on the project completion date and rate of spend.  相似文献   
127.
High-current snapback characteristics of MOSFETs   总被引:1,自引:0,他引:1  
The high-current snapback characteristics of MOSFETs with different channel lengths and widths, gate oxide thicknesses, and substrate dopings were studied to determine their effectiveness in electrostatic discharge stress protection. Filamentary conduction was not observed for currents up to 7 mA/μm of channel width for a pulsewidth of 500 ns. MOSFETs with shorter channel lengths require lower voltages to sustain the same current, independent of gate oxide thickness. Increasing the substrate doping does not necessarily reduce the high current voltage. These trends can be explained using a simple lateral n-p-n bipolar transistor snapback model  相似文献   
128.
This paper proposes new integer approximations of the lapped transforms, called the integer lapped transforms (ILT), and studies their applications to image coding. The ILT are derived from a set of orthogonal sinusoidal transforms having short integer coefficients, which can be implemented with simple integer arithmetic. By employing the same scaling constants in these integer sinusoidal transforms, integer versions of the lapped orthogonal transform (LOT), the lapped biorthogonal transform (LBT), and the hierarchical lapped biorthogonal transform (HLBT) are developed. The ILTs with 5-b integer coefficients are found to have similar coding gain (within 0.06 dB) and image coding performances as their real-valued counterparts. Furthermore, by representing these integer coefficients as sum of powers-of-two coefficients (SOPOT), multiplier-less lapped transforms with very low implementation complexity are obtained. In particular, the implementation of the eight-channel multiplier-less integer LOT (ILOT), LBT (ILBT), and HLBT (IHLBT) require 90 additions and 44 shifts, 98 additions and 59 shifts, and 70 additions and 38 shifts, respectively.  相似文献   
129.
130.
An 8-Gb multi-level NAND Flash memory with 4-level programmed cells has been developed successfully. The cost-effective small chip has been fabricated in 70-nm CMOS technology. To decrease the chip size, a one-sided pad arrangement with compacted core architecture and a block address expansion scheme without block redundancy replacement have been introduced. With these methods, the chip size has been reduced to 146 mm/sup 2/, which is 4.9% smaller than the conventional chip. In terms of performance, the program throughput reaches 6 MB/s at 4-KB page operation, which is significantly faster than previously reported and very competitive with binary Flash memories. This high performance has been achieved by the combination of the multi-level cell (MLC) programming with write caches and with the program voltage compensation technique for neighboring select transistors. The read throughput reaches 60 MB/s using 16I/O configuration.  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