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   35979篇
  免费   4549篇
  国内免费   2384篇
电工技术   819篇
综合类   2347篇
化学工业   9204篇
金属工艺   606篇
机械仪表   1151篇
建筑科学   428篇
矿业工程   1293篇
能源动力   402篇
轻工业   11732篇
水利工程   152篇
石油天然气   1357篇
武器工业   193篇
无线电   2381篇
一般工业技术   1490篇
冶金工业   1400篇
原子能技术   492篇
自动化技术   7465篇
  2024年   269篇
  2023年   667篇
  2022年   1113篇
  2021年   1388篇
  2020年   1570篇
  2019年   1301篇
  2018年   1264篇
  2017年   1443篇
  2016年   1528篇
  2015年   1730篇
  2014年   2245篇
  2013年   2684篇
  2012年   3477篇
  2011年   3108篇
  2010年   2139篇
  2009年   1995篇
  2008年   1864篇
  2007年   2310篇
  2006年   2022篇
  2005年   1544篇
  2004年   1223篇
  2003年   1081篇
  2002年   807篇
  2001年   680篇
  2000年   607篇
  1999年   496篇
  1998年   406篇
  1997年   363篇
  1996年   266篇
  1995年   247篇
  1994年   167篇
  1993年   143篇
  1992年   151篇
  1991年   107篇
  1990年   95篇
  1989年   69篇
  1988年   49篇
  1987年   50篇
  1986年   36篇
  1985年   46篇
  1984年   41篇
  1983年   32篇
  1982年   22篇
  1981年   13篇
  1980年   14篇
  1979年   7篇
  1978年   6篇
  1977年   6篇
  1959年   6篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A standard method for the extraction of tiger nut milk has been introduced. It has been shown that, although milling duration improves the yield of tiger nut milk solids and its nutrient composition, there is a quantifiable loss of nutrient in the pressing residue during milk extraction. Milling duration improved the colloidal stability of the milk against creaming during 16 h of storage. A higher milling intensity resulted in the aggregation of biological polymers which resulted in colloidal destabilisation. Milling improved the lightness and stability and reduced browning rate of the tiger nut milk during storage. This report is important for the production of tiger nut milk of consistent and comparable characteristics. Milling has been introduced as a processing method for the qualitative and quantitative modulation of the properties of tiger nut milk. It is recommended to develop further strategies to improve the colloidal stability of tiger nut milk as a beverage.  相似文献   
2.
用水提取婴幼儿奶粉中的碘,亚铁氰化钾和乙酸锌盐析法沉淀蛋白,过滤后可以得到澄清处理液。用电感耦合等离子体质谱对提取样液进行测定,130Te作为内标物进行定量分析。该方法简便快捷,检出限为0.10 mg/kg加标回收率为90.8%~109%,相关系数0.999,精密度试验RSD2%。  相似文献   
3.
Aiming to environment protection, green solvents are crucial for commercialization of solution-processed optoelectronic devices. In this work, d-limonene, a natural product, was introduced as the non-aromatic and non-chlorinated solvent for processing of polymer light-emitting diodes (PLEDs) and organic field effect transistors (OFETs). It was found that d-limonene could be a good solvent for a blue-emitting polyfluorene-based random copolymer for PLEDs and an alternating copolymer FBT-Th4(1,4) with high hole mobility (μh) for OFETs. In comparisons to routine solvent-casted films of the two conjugated polymers, the resulting d-limonene-deposited films could show comparable film qualities, based on UV–vis absorption spectra and observations by atomic force microscopy (AFM). With d-limonene as the processing solvent, efficient blue PLEDs with CIE coordinates of (0.16, 0.16), maximum external quantum efficiency of 3.57%, and luminous efficiency of 3.66 cd/A, and OFETs with outstanding μh of 1.06 cm2 (V s)−1 were demonstrated. Our results suggest that d-limonene would be a promising non-aromatic and non-chlorinated solvent for solution processing of conjugated polymers and molecules for optoelectronic device applications.  相似文献   
4.
ABSTRACT

This paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance.  相似文献   
5.
通过认真学习《细节决定成败》,结合井矿盐开采的实际,分别以生产过程中的三个细节为主,讨论了在采输卤生产技术控制中的细节的重要性。  相似文献   
6.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %.  相似文献   
7.
本文提出了一种基于信息融合的物体三维特征的提取方法,该方法利用两幅互相配准的三维测距图像和灰度图像,来提取多面体的三维特征。首先,通过分析灰度图像中的灰度变化及测距图像中的测距值变化,分别求取各自图像中物体的特征点及特征边;然后,利用两配准图像之间的对应关系,求得所有特征点、面与多边形在三维测距图像中的三维表示;接着,通过分析三维测距图像中所测得的各候选平面上特定点与边处的曲率及法向,验证候选平面  相似文献   
8.
聂幼华 《食品与机械》1996,(5):16-18,20
本文对芝麻营养保健成分的提取进行了系统的研究。确定了芝麻营养原液的制取工艺。为充分发挥芝麻的营养保健作用开辟了新的途径。  相似文献   
9.
本文研究了HPMBP与伯胺N_(1923)的二甲苯溶液,从盐酸介质中协同萃取希土(Ⅲ)的机理。用斜率法、恒摩尔法确定了协萃配合物的组成为:RNH_3Ln(PMBP)_4。求得关于Pr(Ⅲ)协萃反应的平衡常数及协萃配合物的生成常数分别为:logK_(12)=-1.95;logβ_(12)=3.94。实验发现,协萃系数(R)随希土元素的原子序数(Z)递变而呈现“双峰效应”。还研究了协萃配合物的IR,NMR谱。  相似文献   
10.
A new efficient method for synthesising nitriles, important organic reagents, is reported in this paper. In an environmentally benign solvent‐free system, aryl carboxylic acids were converted into the corresponding nitriles via one‐pot reactions, by amidation with ethyl carbamate followed by dehydration with thionyl chloride, in excellent yields. The results showed that the method has the advantages of lower cost, higher yield, less pollution and greater ease of work‐up. Copyright © 2008 Society of Chemical Industry  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