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   219706篇
  免费   6268篇
  国内免费   2824篇
电工技术   5871篇
技术理论   5篇
综合类   3622篇
化学工业   35055篇
金属工艺   9976篇
机械仪表   7670篇
建筑科学   7933篇
矿业工程   1906篇
能源动力   5812篇
轻工业   21117篇
水利工程   2611篇
石油天然气   5137篇
武器工业   403篇
无线电   24518篇
一般工业技术   37794篇
冶金工业   34773篇
原子能技术   4833篇
自动化技术   19762篇
  2022年   2021篇
  2021年   3005篇
  2020年   2194篇
  2019年   2283篇
  2018年   3309篇
  2017年   3418篇
  2016年   3415篇
  2015年   3318篇
  2014年   4903篇
  2013年   10419篇
  2012年   7606篇
  2011年   9686篇
  2010年   7972篇
  2009年   8740篇
  2008年   8759篇
  2007年   8475篇
  2006年   7529篇
  2005年   6836篇
  2004年   5958篇
  2003年   5287篇
  2002年   5208篇
  2001年   5046篇
  2000年   4790篇
  1999年   4947篇
  1998年   11096篇
  1997年   7984篇
  1996年   6172篇
  1995年   4737篇
  1994年   3943篇
  1993年   3812篇
  1992年   2820篇
  1991年   2696篇
  1990年   2528篇
  1989年   2538篇
  1988年   2463篇
  1987年   2171篇
  1986年   2120篇
  1985年   2392篇
  1984年   2205篇
  1983年   2025篇
  1982年   1891篇
  1981年   1959篇
  1980年   1814篇
  1979年   1824篇
  1978年   1778篇
  1977年   2108篇
  1976年   2694篇
  1975年   1561篇
  1974年   1550篇
  1973年   1609篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
71.
This paper is concerned with the problem of joint input and state estimation for linear stochastic systems with direct feedthrough. Based on the fact that each unknown input between any two time steps is always bounded, a novel improved algorithm is proposed. Compared with existing results, this algorithm can effectively enhance estimation accuracy. Moreover, the stability of the algorithm is also discussed. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed approach.  相似文献   
72.
电动机的初期故障信号一般较弱,不易辨别,而状态空间法在小信号的处理中灵敏度很高。为达到对电动机故障的诊断和识别,试图把状态空间法应用到对电动机的故障诊断中,先通过推导,从数学理论层面分析了状态空间法对于电动机故障信号的可辨别性,再使用Matlab软件搭建状态空间的辨别模型,把实验台测试的三组数据导入到模型中进行测试。测试的结果有力地证明了此方法的可行性,并能克服快速傅里叶变换(FFT)中数据采集量较大、分辨率不高的缺点。  相似文献   
73.
The dynamic characteristics of a saw gin as a subsystem with lumped and distributed parameters are considered in the paper. On the basis of investigation of the machine assembly, graphs are drawn that allow establishing the maximum values of the angle of relative rotation and the angle of rotation of the saw cylinder shaft under torsion.  相似文献   
74.
75.
76.
77.
78.
79.
Enhancement of the dissolution rate of the poorly water-soluble hypoglycemic agent, gliclazide, by the aid of lyophilization was investigated. Mannitol, sodium lauryl sulfate (SLS) and polyvinyl pyrrolidone (PVP-k-30) were employed in different weight ratios (43%, 56% and 64% w/w, respectively) as water-soluble excipients in the formulation. Lyophilized systems were found to exhibit extremely higher in vitro dissolution rate compared to the unprocessed drug powder. Solid state characterization of the lyophilized systems using X-ray powder diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques revealed that dissolution enhancement was attributable to transformation of gliclazide from the crystalline to an amorphous state in the solid dispersion formed during the lyophilization process. The gastrointestinal absorption and hypoglycemic effect of the lyophilized gliclazide/SLS system were investigated following oral administration to Albino rabbits. Cmax and area under the plasma concentration–time curve of gliclazide (AUC0–12) after administration of the lyophilized formulations were significantly higher than those obtained after administration of the unprocessed gliclazide.  相似文献   
80.
The high cost and potential toxicity of biodegradable polymers like poly(lactic‐co‐glycolic)acid (PLGA) has increased the interest in natural and modified biopolymers as bioactive carriers. This study characterized the physical stability (water sorption and state transition behavior) of selected starch and proteins: octenyl succinate–modified depolymerized waxy corn starch (DWxCn), waxy rice starch (DWxRc), phytoglycogen, whey protein concentrate (80%, WPC), whey protein isolate (WPI), and α‐lactalbumin (α‐L) to determine their potential as carriers of bioactive compounds under different environmental conditions. After enzyme modification and particle size characterization, glass transition temperature and moisture isotherms were used to characterize the systems. DWxCn and DWxRc had increased water sorption compared to native starch. The level of octenyl succinate anhydrate (OSA) modification (3% and 7%) did not reduce the water sorption of the DWxCn and phytoglycogen samples. The Guggenheim–Andersen–de Boer model indicated that native waxy corn had significantly (P < 0.05) higher water monolayer capacity followed by 3%‐OSA‐modified DWxCn, WPI, 3%‐OSA‐modified DWxRc, α‐L, and native phytoglycogen. WPC had significantly lower water monolayer capacity. All Tg values matched with the solid‐like appearance of the biopolymers. Native polysaccharides and whey proteins had higher glass transition temperature (Tg) values. On the other hand, depolymerized waxy starches at 7%‐OSA modification had a “melted” appearance when exposed to environments with high relative humidity (above 70%) after 10 days at 23 °C. The use of depolymerized and OSA‐modified polysaccharides blended with proteins created more stable blends of biopolymers. Hence, this biopolymer would be suitable for materials exposed to high humidity environments in food applications.  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