全文获取类型
收费全文 | 149782篇 |
免费 | 14882篇 |
国内免费 | 9158篇 |
专业分类
电工技术 | 11650篇 |
技术理论 | 2篇 |
综合类 | 18117篇 |
化学工业 | 18528篇 |
金属工艺 | 6381篇 |
机械仪表 | 10420篇 |
建筑科学 | 18239篇 |
矿业工程 | 6659篇 |
能源动力 | 4992篇 |
轻工业 | 10049篇 |
水利工程 | 6482篇 |
石油天然气 | 6869篇 |
武器工业 | 1990篇 |
无线电 | 9897篇 |
一般工业技术 | 19402篇 |
冶金工业 | 5723篇 |
原子能技术 | 2359篇 |
自动化技术 | 16063篇 |
出版年
2024年 | 648篇 |
2023年 | 1801篇 |
2022年 | 3414篇 |
2021年 | 3968篇 |
2020年 | 4524篇 |
2019年 | 3955篇 |
2018年 | 3855篇 |
2017年 | 4791篇 |
2016年 | 5356篇 |
2015年 | 5518篇 |
2014年 | 9047篇 |
2013年 | 8719篇 |
2012年 | 11445篇 |
2011年 | 11582篇 |
2010年 | 8930篇 |
2009年 | 9270篇 |
2008年 | 8590篇 |
2007年 | 10567篇 |
2006年 | 9319篇 |
2005年 | 7818篇 |
2004年 | 6443篇 |
2003年 | 5588篇 |
2002年 | 4697篇 |
2001年 | 3915篇 |
2000年 | 3454篇 |
1999年 | 3018篇 |
1998年 | 2351篇 |
1997年 | 2055篇 |
1996年 | 1707篇 |
1995年 | 1530篇 |
1994年 | 1290篇 |
1993年 | 952篇 |
1992年 | 849篇 |
1991年 | 602篇 |
1990年 | 491篇 |
1989年 | 490篇 |
1988年 | 350篇 |
1987年 | 206篇 |
1986年 | 174篇 |
1985年 | 84篇 |
1984年 | 75篇 |
1983年 | 42篇 |
1982年 | 51篇 |
1981年 | 55篇 |
1980年 | 38篇 |
1979年 | 36篇 |
1978年 | 17篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Enhanced gravity, or centrifugal, separators have revolutionised gold processing over the past decades, significantly increasing the recovery of fine (−100 μm) free gold. One of the main drawbacks of centrifugal gravity concentrators is the large volume of water required (even if it is all recycled). With water becoming an ever increasingly important “commodity”, reducing this is of importance both from an environmental and a monetary point of view. This work investigated operating a laboratory scale Knelson Concentrator with a dry feed and using air as the fluidising medium. The feed used was a synthetic mixture of tungsten and quartz, used to mimic a gold ore. The response surface method and central composite design techniques were used to design the experiments and to model the results, with the experimental variables being the bowl speed (G-Level), air fluidising pressure and the feed rate. The models corresponded well to the experimental results, indicating that for this experimental setup, the optimal conditions were a bowl G-Level of 40 G, a feed rate of 220 g/min and an air fluidising pressure of 8 psi. 相似文献
62.
使用钡盐法对铬废水处理,对p H值在废水中的初值、反映温度计量结果、重铬酸钾的浓度等,在回收六价铬的影响效果进行了分析。对废水中的六价铬使用了源自吸收的分光光度法回收。经过处理后,废水中的p H为8~9的时候,六价铬的回收在9%。废水中的六价铬随着其浓度不断上升增加。超过10℃的时候,六价铬的反应没有非常大的影响,但是当温度降低到10℃以下的时候,回收率就逐步下降了。经过处理之后,六价铬的浓度达到了0.276 7 mg/L,达到了相关规定的标准。 相似文献
63.
测向误差的减小一直以来都是无线电测向精度提高的一个难点,对于不同的测向体制所采用的减小测向误差的方法都不尽相同。本文主要介绍的是相关干涉仪测向体制的基本原理以及通过内插法的应用来减小测向误差的方法。 相似文献
64.
Sumeng Wei Yuling Yang Xiao Feng Shanshan Li Lei Zhou Jingyu Wang Xiaozhi Tang 《International Journal of Food Science & Technology》2020,55(7):2691-2699
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics. 相似文献
65.
ABSTRACTImproving the hydration resistance of CaO particle in manufacturing and application of free CaO-containing materials has practical significance. In this study, CaO granules was made from Ca(OH)2 particles, which were fabricated by the granulation method. The results showed that the hydration resistance of the CaO granules which was prepared under 1700?r?min?1 was the best, the CaO granules was sintered well in calcination process, the shell of CaO granules was relatively dense, which improves the hydration resistance of CaO granules, and the rate of hydration weight increment was 0.58% after placed in the air for 20 days under a temperature of 10–14°C and a relative humidity of 57–81%. 相似文献
66.
This paper investigates the N-policy M/M/1 queueing system with working vacation and server breakdowns. As soon as the system becomes empty, the server begins a working vacation. The server works at a lower service rate rather than completely stopping service during a vacation period. The server may break down with different breakdown rates during the idle, working vacation, and normal busy periods. It is assumed that service times, vacation times, and repair times are all exponentially distributed. We analyze this queueing model as a quasi-birth–death process. Furthermore, the equilibrium condition of the system is derived for the steady state. Using the matrix-geometric method, we find the matrix-form expressions for the stationary probability distribution of the number of customers in the system and system performance measures. The expected cost function per unit time is constructed to determine the optimal values of the system decision variables, including the threshold N and mean service rates. We employ the particle swarm optimization algorithm to solve the optimization problem. Finally, numerical results are provided, and an application example is given to demonstrate the applicability of the queueing model. 相似文献
67.
Design and Fabrication of Concentration‐Gradient Generators with Two and Three Inlets in Microfluidic Chips 下载免费PDF全文
A simple and low‐cost method for designing and fabricating concentration‐gradient generators with two and three inlets is proposed which can generate different concentration gradients at varying flow velocities. The microchannel structure was designed in S‐shape and left‐right symmetry. The concentration‐gradient generator was simulated based on the finite element method. The microchannels were processed on a computer numerical control (CNC) engraving and milling machine on poly(methylmethacrylate) substrate, and then two concentration‐gradient generators were fabricated by hot bonding technology. The results of experiment and simulation were compared to prove the feasibility of the method. Flow velocity was an important factor for generating different concentration gradients. The concentration‐gradient profiles of the generators with two and three inlets present approximately linear and quadratic curves. 相似文献
68.
《Food Control》2015
A diverse range of genetic elements has been used to develop genetically modified organisms (GMOs) over the last 18 years. Screening methods that target few elements, such as the Cauliflower Mosaic Virus 35S promoter (P-35S) and Agrobacterium tumefaciens nopaline terminator (T-nos), are not sufficient to screen GMOs. In the present study, a multiplex PCR system for all globally commercialized GM soybean events was developed to easily trace the events. For this purpose, screening elements of 24 GM soybean events were investigated and 9 screening targets were selected and divided into three individual triplex PCR systems: P-35S, ribulose-1,5-bisphosphate carboxylase small subunit promoter of Arabidopsis thaliana, T-nos, T-35S, pea E9 terminator, open reading frame 23 terminator of A. tumefaciens, proteinase inhibitor II terminator of potato, acetohydroxy acid synthase large subunit terminator of A. thaliana, and the revealed 3′ flanking sequences of DP-305423-1. The specificity of the assays was confirmed using thirteen GM soybean events as the respective positive/negative controls. The limit of detection of each multiplex set, as determined using certified reference materials of specific GM events, ranged from 0.03 to 0.5%, depending upon target. Furthermore, 26 food samples that contained soybean ingredients, which were purchased from the USA, China, Japan, and Korea, were analyzed, 17 of which contained one or more GM soybean events. These results suggest that the developed screening method can be used to efficiently track and identify 24 GM soybean events in food and feed. 相似文献
69.
The aim of the study was to identify the importance of individual food product attributes (the use of preservatives, processing method, shelf-life period and nutritional value) as well as their relation to the purchase behaviour. To achieve this, consumer preferences were decomposed in conditions of full access to information, and data was compared with actual consumer behaviour related to making purchasing decisions in front of the store shelf. Based on data from 338 respondents, conjoint analysis and repeated ANOVA measurements were carried out, allowing to eliminate individual behavioural patterns. The results showed a dissonance between the consumers attitudes towards the attributes and their shopping behaviour. The processing method was the most important declared attribute for consumers, meanwhile this information was the least searched for during purchase. At the same time, shelf-life period marked as the least important was the main information searched for by consumers when shopping. The results also show a clear dislike towards the use of microwaves as a preservation method, while traditional thermal preservation was marked as the most positive for consumers. In addition, consumers were classified into 3 heterogeneous groups, identifying differences in the preferences of food attributes. The obtained results have practical value relating not only to the preferences of individual attributes, but also to their various variants. The results can be a guide for companies to properly label food products. The indicated dissonance illustrates the educational gap and related insufficient motivation to get to know the product before buying it. This is extremely important in connection with technological development and new food processing methods. 相似文献
70.