全文获取类型
收费全文 | 411814篇 |
免费 | 6561篇 |
国内免费 | 1376篇 |
专业分类
电工技术 | 7696篇 |
综合类 | 349篇 |
化学工业 | 61753篇 |
金属工艺 | 14280篇 |
机械仪表 | 11878篇 |
建筑科学 | 11641篇 |
矿业工程 | 869篇 |
能源动力 | 11119篇 |
轻工业 | 43841篇 |
水利工程 | 3311篇 |
石油天然气 | 1834篇 |
武器工业 | 13篇 |
无线电 | 55378篇 |
一般工业技术 | 76629篇 |
冶金工业 | 74951篇 |
原子能技术 | 5569篇 |
自动化技术 | 38640篇 |
出版年
2021年 | 2665篇 |
2019年 | 2447篇 |
2018年 | 3844篇 |
2017年 | 3913篇 |
2016年 | 4148篇 |
2015年 | 3430篇 |
2014年 | 5720篇 |
2013年 | 19285篇 |
2012年 | 10207篇 |
2011年 | 14683篇 |
2010年 | 11290篇 |
2009年 | 12892篇 |
2008年 | 13918篇 |
2007年 | 14286篇 |
2006年 | 12778篇 |
2005年 | 11966篇 |
2004年 | 11578篇 |
2003年 | 11279篇 |
2002年 | 10914篇 |
2001年 | 11133篇 |
2000年 | 10272篇 |
1999年 | 10769篇 |
1998年 | 24011篇 |
1997年 | 17587篇 |
1996年 | 13903篇 |
1995年 | 10979篇 |
1994年 | 9770篇 |
1993年 | 9354篇 |
1992年 | 7121篇 |
1991年 | 6791篇 |
1990年 | 6399篇 |
1989年 | 6107篇 |
1988年 | 5860篇 |
1987年 | 4885篇 |
1986年 | 4833篇 |
1985年 | 5979篇 |
1984年 | 5600篇 |
1983年 | 4831篇 |
1982年 | 4498篇 |
1981年 | 4448篇 |
1980年 | 4209篇 |
1979年 | 4080篇 |
1978年 | 3771篇 |
1977年 | 4548篇 |
1976年 | 6097篇 |
1975年 | 3115篇 |
1974年 | 3011篇 |
1973年 | 2890篇 |
1972年 | 2318篇 |
1971年 | 2003篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
A. J. Wright A. Wong L. L. Diosady 《Food research international (Ottawa, Ont.)》2003,36(9-10):1069-1072
A Ni catalyst was added to a cis-selective Pd catalyst in an attempt to further improve the Pd catalyst's cis-selectivity and activity for canola oil hydrogenation. The system was tested under reaction conditions known to be suitable for cis-selective hydrogenation with the Pd catalyst (50 ppm Pd, 70 °C, and 5.2 MPa). Although inactive on its own under these conditions, the addition of 100 ppm Ni increased the hydrogenation activity (from 2.12 to 2.49 10−2 min−1). Further addition of Ni up to 1000 ppm resulted in no further improvements in activity. The trans isomer contents of the oils hydrogenated with Pd and the Pd/Ni systems were similar. The level of conjugated dienes decreased rapidly during hydrogenation with both Pd alone and with the Pd/Ni combination and no changes in conjugation were detected in the presence of the Ni catalyst alone. The increased activity of the Pd/Ni system over Pd alone was attributed to adsorption of catalyst poisons from the oil by Ni. 相似文献
952.
Butler Emily A.; Egloff Boris; Wlhelm Frank H.; Smith Nancy C.; Erickson Elizabeth A.; Gross James J. 《Canadian Metallurgical Quarterly》2003,3(1):48
At times, people keep their emotions from showing during social interactions. The authors' analysis suggests that such expressive suppression should disrupt communication and increase stress levels. To test this hypothesis, the authors conducted 2 studies in which unacquainted pairs of women discussed an upsetting topic. In Study 1, one member of each pair was randomly assigned to (a) suppress her emotional behavior, (b) respond naturally, or (c) cognitively reappraise in a way that reduced emotional responding. Suppression alone disrupted communication and magnified blood pressure responses in the suppressors' partners. In Study 2, suppression had a negative impact on the regulators' emotional experience and increased blood pressure in both regulators and their partners. Suppression also reduced rapport and inhibited relationship formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
953.
Penedo Frank J.; Dahn Jason R.; Gonzalez Jeffrey S.; Molton Ivan; Carver Charles S.; Antoni Michael H.; Roos Bernard A.; Schneiderman Neil 《Canadian Metallurgical Quarterly》2003,22(2):220
This study evaluated relations among optimism, perceived stress management skills (PSMS), and positive mood in 46 men who had surgical treatment for localized prostate cancer. The authors found that optimism, PSMS, and positive mood scores were positively correlated. Positive mood was unrelated to demographic and disease-related control variables. In a hierarchical regression model controlling for PSMS, the relationship between optimism and positive mood became nonsignificant, whereas PSMS remained a correlate of positive mood. Results suggest that the relationship between optimism and positive mood may be mediated by belief in being able to use stress management techniques effectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
954.
Yunlei Li Dick de Ridder Robert P.W. Duin Marcel J.T. Reinders 《Pattern recognition》2008,41(1):320-330
Samples can be measured with different precisions and reliabilities in different experiments, or even within the same experiment. These varying levels of measurement noise may deteriorate the performance of a pattern recognition system, if not treated with care. Here we seek to investigate the benefit of incorporating prior knowledge about measurement noise into system construction. We propose a kernel density classifier which integrates such prior knowledge. Instead of using an identical kernel for each sample, we transform the prior knowledge into a distinct kernel for each sample. The integration procedure is straightforward and easy to interpret. In addition, we show how to estimate the diverse measurement noise levels in a real world dataset. Compared to the basic methods, the new kernel density classifier can give a significantly better classification performance. As expected, this improvement is more obvious for small sample size datasets and large number of features. 相似文献
955.
J. Hladik 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1938,76(5):483-485
Zusammenfassung Es wird ein Verfahren mitgeteilt mit welchem es gelingt, die Wasseraufnahmefähigkeit der Mehle als maximale Wasseraufnahme in objektiver Weise verläßlich ziffernmäßig festzustellen. Dieses Verfahren ermöglicht zugleich, die Mehle je nach ihrem Feinheitsgrade zu unterscheiden. Das ziemlich einfache Verfahren ist geeignet, um die wirkliche Wasseraufnahmefähigkeit mit den anderen Eigenschaften der Mehle zu vergleichen, Zusammenhänge mit denselben zu ermitteln und insbesondere auch den Backwert der Mehle zu beurteilen. 相似文献
956.
In this article we survey a number of predeployed secure key distribution (PSKD) schemes proposed in the technical literature. We also propose a new time-based PSKD (TPSKD), which operates under the assumption of loose time synchronization, and discuss the performance of the scheme. Since the TPSKD scheme uses time information, which would typically already be available in sensor nodes, the cost of the scheme?s implementation is low. 相似文献
957.
Ohne Zusammenfassung 相似文献
958.
Steensgaard J. Zhiqing Zhang Wenhuan Yu Sarhegyi A. Lucchese L. Dae-Ik Kim Temes G.C. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(5):1289-1296
Incremental data converters (IDCs) are useful in instrumentation and measurement applications, where low-frequency analog signals need to be converted into digital form with high accuracy and low power dissipation. They are particularly well suited for applications where a single analog-digital converter is multiplexed between many channels. This paper proposes an exact design methodology for IDCs, which optimizes the signal-to-noise ratio of the converter under practical design constraints. The process also allows the designer to apportion the noise budget in an arbitrary manner between thermal and quantization noise. The design process is illustrated by an example which describes the optimization of a third-order multiplexed IDC. 相似文献
959.
In this work, we have created a new type of structure, the nanopore active layer, for achieving quantization of carrier states in a semiconductor. The nanopore structure consists of a periodic two-dimensional array of localized energy barriers perturbing an otherwise conventional quantum well. This perturbation leads to the formation of intraband forbidden energy gaps which are observed experimentally. 相似文献
960.
J.A. Giroto A.C.S.C. Teixeira C.A.O. Nascimento R. Guardani 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2361-2369
This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), were tested under different conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based on the evolution of the TOC–time curves. Under specific reaction conditions, the formation and coalescence of solid particles was visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be coupled with solid separation systems, which may reduce the treatment cost. 相似文献