全文获取类型
收费全文 | 313197篇 |
免费 | 4246篇 |
国内免费 | 711篇 |
专业分类
电工技术 | 6241篇 |
综合类 | 564篇 |
化学工业 | 47300篇 |
金属工艺 | 10377篇 |
机械仪表 | 8907篇 |
建筑科学 | 8080篇 |
矿业工程 | 884篇 |
能源动力 | 8663篇 |
轻工业 | 31380篇 |
水利工程 | 2587篇 |
石油天然气 | 3682篇 |
武器工业 | 8篇 |
无线电 | 39922篇 |
一般工业技术 | 58960篇 |
冶金工业 | 57971篇 |
原子能技术 | 5494篇 |
自动化技术 | 27134篇 |
出版年
2021年 | 2287篇 |
2019年 | 2163篇 |
2018年 | 3641篇 |
2017年 | 3468篇 |
2016年 | 3570篇 |
2015年 | 2570篇 |
2014年 | 4496篇 |
2013年 | 14520篇 |
2012年 | 7466篇 |
2011年 | 10242篇 |
2010年 | 7991篇 |
2009年 | 9219篇 |
2008年 | 9718篇 |
2007年 | 9706篇 |
2006年 | 8611篇 |
2005年 | 8008篇 |
2004年 | 7865篇 |
2003年 | 7608篇 |
2002年 | 7450篇 |
2001年 | 7607篇 |
2000年 | 7268篇 |
1999年 | 7606篇 |
1998年 | 17731篇 |
1997年 | 12904篇 |
1996年 | 10161篇 |
1995年 | 7947篇 |
1994年 | 7258篇 |
1993年 | 6991篇 |
1992年 | 5371篇 |
1991年 | 5108篇 |
1990年 | 5013篇 |
1989年 | 4849篇 |
1988年 | 4745篇 |
1987年 | 3960篇 |
1986年 | 4065篇 |
1985年 | 4809篇 |
1984年 | 4372篇 |
1983年 | 4101篇 |
1982年 | 3688篇 |
1981年 | 3831篇 |
1980年 | 3507篇 |
1979年 | 3504篇 |
1978年 | 3287篇 |
1977年 | 3897篇 |
1976年 | 4911篇 |
1975年 | 2872篇 |
1974年 | 2717篇 |
1973年 | 2746篇 |
1972年 | 2257篇 |
1971年 | 1997篇 |
排序方式: 共有10000条查询结果,搜索用时 225 毫秒
81.
Detailed study on fusion characteristics of rigid poly(vinyl chloride) nanocomposites: The comparison of using multiple regression analysis and artificial neural network
下载免费PDF全文
![点击此处可从《乙烯基与添加剂工艺杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fusion behavior of poly(vinyl chloride) (PVC) compounds plays an important role in the development of physical properties of processed material. The fusion characteristics in PVC processing are governed by material variables that affect the fusion with some interactions. In this research, the aim was to characterize the effects of formulation ingredients on fusion characteristics of PVC. Four material parameters, including the contents of nanoclay (NC), azodicarbonamide, calcium stearate, and processing aid, are proposed as affecting variables. The fusion time (FT) as well as fusion factor (FF) are considered fusion indicators and are experimentally determined in some different levels of affecting parameters. The multivariable regression analysis (MRA) and the Artificial Neural Network (ANN) modeling are considered as two analytical methods. The regression analysis result for the FT denotes, in part, significant linear and quadratic effects of NC and also its significant interactions with azodicarbonamide and calcium stearate, whereas that of FF indicates only a linear effect of NC. ANN modeling is performed with a three‐layer (input, hidden, and output) neural network. The results of the comparison of the MRA and ANN predictions with experimental values are reported as the correlation coefficient (R2), mean‐square error, and mean absolute percentage error for both FF and FT parameters. The obtained values clearly denote that the ANN results are more precise and especially more general than those of MRA. However, in the case of FT, improvement of the ANN modeling is much greater than that of FF. J. VINYL ADDIT. TECHNOL., 21:147–155, 2015. © 2014 Society of Plastics Engineers 相似文献
82.
83.
Verbovitskii Yu. V. Denis R. V. Shtender V. V. Zavalii I. Yu. 《Powder Metallurgy and Metal Ceramics》2015,54(3-4):220-226
Powder Metallurgy and Metal Ceramics - Multiphase La 2 MgNi 9 alloys are synthesized by induction melting. The crystalline structures of all phases in the alloys are determined with X-ray... 相似文献
84.
85.
86.
Joo H. Kang Eujin Um Alexander Diaz Harry Driscoll Melissa J. Rodas Karel Domansky Alexander L. Watters Michael Super Howard A. Stone Donald E. Ingber 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(42):5657-5666
Magnetic nanoparticles have been employed to capture pathogens for many biological applications; however, optimal particle sizes have been determined empirically in specific capturing protocols. Here, a theoretical model that simulates capture of bacteria is described and used to calculate bacterial collision frequencies and magnetophoretic properties for a range of particle sizes. The model predicts that particles with a diameter of 460 nm should produce optimal separation of bacteria in buffer flowing at 1 L h−1. Validating the predictive power of the model, Staphylococcus aureus is separated from buffer and blood flowing through magnetic capture devices using six different sizes of magnetic particles. Experimental magnetic separation in buffer conditions confirms that particles with a diameter closest to the predicted optimal particle size provide the most effective capture. Modeling the capturing process in plasma and blood by introducing empirical constants (ce), which integrate the interfering effects of biological components on the binding kinetics of magnetic beads to bacteria, smaller beads with 50 nm diameters are predicted that exhibit maximum magnetic separation of bacteria from blood and experimentally validated this trend. The predictive power of the model suggests its utility for the future design of magnetic separation for diagnostic and therapeutic applications. 相似文献
87.
88.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
89.
90.