全文获取类型
收费全文 | 294852篇 |
免费 | 24699篇 |
国内免费 | 16761篇 |
专业分类
电工技术 | 19075篇 |
技术理论 | 54篇 |
综合类 | 41021篇 |
化学工业 | 31156篇 |
金属工艺 | 11592篇 |
机械仪表 | 16462篇 |
建筑科学 | 38178篇 |
矿业工程 | 15114篇 |
能源动力 | 8823篇 |
轻工业 | 14988篇 |
水利工程 | 14363篇 |
石油天然气 | 11879篇 |
武器工业 | 2924篇 |
无线电 | 21180篇 |
一般工业技术 | 22980篇 |
冶金工业 | 16006篇 |
原子能技术 | 2917篇 |
自动化技术 | 47600篇 |
出版年
2024年 | 650篇 |
2023年 | 2803篇 |
2022年 | 5215篇 |
2021年 | 6732篇 |
2020年 | 6965篇 |
2019年 | 6105篇 |
2018年 | 5607篇 |
2017年 | 6914篇 |
2016年 | 8281篇 |
2015年 | 9354篇 |
2014年 | 16536篇 |
2013年 | 15495篇 |
2012年 | 19614篇 |
2011年 | 20855篇 |
2010年 | 16672篇 |
2009年 | 17565篇 |
2008年 | 16565篇 |
2007年 | 21169篇 |
2006年 | 19991篇 |
2005年 | 17505篇 |
2004年 | 14880篇 |
2003年 | 13306篇 |
2002年 | 10958篇 |
2001年 | 9320篇 |
2000年 | 7942篇 |
1999年 | 6483篇 |
1998年 | 4969篇 |
1997年 | 4362篇 |
1996年 | 4004篇 |
1995年 | 3469篇 |
1994年 | 3093篇 |
1993年 | 2343篇 |
1992年 | 2039篇 |
1991年 | 1537篇 |
1990年 | 1338篇 |
1989年 | 1147篇 |
1988年 | 905篇 |
1987年 | 607篇 |
1986年 | 460篇 |
1985年 | 404篇 |
1984年 | 374篇 |
1983年 | 273篇 |
1982年 | 239篇 |
1981年 | 192篇 |
1980年 | 144篇 |
1979年 | 122篇 |
1978年 | 76篇 |
1977年 | 80篇 |
1976年 | 66篇 |
1975年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Effect of Cerium on Expression and Activity of MMP-9 from Human Carcinoma of Bladder Cell Line 总被引:1,自引:0,他引:1
Rareearthshaveledtowidespreadinterestsinlifescience ,whilethescientistsdoresearchesdeeplyinmedicalandbiochemicalfields .Rareearthsplaypotentialrolesininhibitingcancer ,andalargenum berofscientistsdedicatethemselvestoit[1] .Thema trixmetalloproteinases (MMPs)areafamilyofatleast1 7humanzinc dependentendopeptidasesthatareca pableofdegradingalmostallextracellularmatrix(ECM)components .Theyareessentialinmanyphys iologicalprocessesandseveralpathologicalconditions ,suchastumorprogression .MMPsare… 相似文献
992.
The relation between the initial unbalance and the output signal of bridge circuits when acted upon simultaneously by the
physical factor being measured and the temperature of the surroundings when the bridge is supplied from a voltage or current
source is investigated. Analytic relations are obtained which explain the temperature dependence of the useful output voltage
under external physical action.
__________
Translated from Izmeritel’naya Tekhnika, No. 1, pp. 48–49, 2007. 相似文献
993.
选煤厂洗水闭路循环改造及效果 总被引:1,自引:1,他引:0
根据生产实际中洗水不能闭路循环的问题 ,因地制宜进行改造和加强管理 ,实现洗水闭路循环。 相似文献
994.
Heat transfer characteristics of a swirling impinging jet have been experimentally examined using a combined particle image velocimetry (PIV) and laser‐induced fluorescence (LIF) technique for simultaneous measurement of velocity and temperature fields. The present study shows that the radial width of the jet stretches with increasing swirl intensity, and that the stretching phenomenon contributes to the maximum local heat transfer coefficient. At the stagnation region, the flow near the heated surface is mixed intermittently by reverse flows toward upstream, and spatial distributions of temperature are correlated with instantaneous velocity vector maps. The dynamic behavior of recirculation zones, attributed to swirl number Sw and impinging distance, mainly determines the turbulent heat transfer at the stagnation region. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 663–673, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10120 相似文献
995.
形状记忆聚氨酯的结构与性能研究 总被引:1,自引:0,他引:1
以 2 ,4 -甲苯二异氰酸酯 (2 ,4 -TDI)、不同分子量的聚己二酸丁二醇酯 (PBAG)和 1,4-丁二醇 (BDO)为原料合成了具有形状记忆功能的聚氨酯材料。通过DSC、弯曲实验和力学实验 ,研究了形状记忆聚氨酯的性能 ,发现软段高度结晶和硬段聚集形成硬段微区是其具有较好形状记忆性能的必要条件。 相似文献
996.
997.
岩盐钻井水溶双井连通开采工艺的研究与推广 总被引:1,自引:0,他引:1
文章就全国井矿盐采区多年的开采工艺技术,进行了系统的研究与总结,并提出了岩盐钻井水溶开采双井连通的各种开采工艺及其关键技术,具有很强的适用性和推广价值。 相似文献
998.
Hyun-Chul Kim Author VitaeDaijin KimAuthor Vitae Sung Yang Bang Author Vitae 《Pattern recognition》2003,36(5):1095-1105
Linear discriminant analysis (LDA) is a data discrimination technique that seeks transformation to maximize the ratio of the between-class scatter and the within-class scatter. While it has been successfully applied to several applications, it has two limitations, both concerning the underfitting problem. First, it fails to discriminate data with complex distributions since all data in each class are assumed to be distributed in the Gaussian manner. Second, it can lose class-wise information, since it produces only one transformation over the entire range of classes. We propose three extensions of LDA to overcome the above problems. The first extension overcomes the first problem by modelling the within-class scatter using a PCA mixture model that can represent more complex distribution. The second extension overcomes the second problem by taking different transformation for each class in order to provide class-wise features. The third extension combines these two modifications by representing each class in terms of the PCA mixture model and taking different transformation for each mixture component. It is shown that all our proposed extensions of LDA outperform LDA concerning classification errors for synthetic data classification, hand-written digit recognition, and alphabet recognition. 相似文献
999.
With the assumption that the bed shear stress fluctuates in a lognormal fashion, the probability density function (PDF) of the standardized bed shear stress is derived as a function of the relative shear stress intensity. The PDF is more skewed with larger relative intensities, but approaches a Gaussian function when the relative intensity is small. The computed PDF agrees well with the reported experimental data for flows over a smooth boundary. The higher-order moments of the bed shear stress, skewness, and kurtosis, are shown analytically to be also dependent on the relative intensity. The theoretical dependencies are then compared to a number of measurements available in the literature. The Reynolds number effect on the relative intensity is also discussed. 相似文献
1000.
本文分析了造成ora-01555错误的原因,并提出解决办法。ora-01555错误一直是DBA与developer争论的焦点,解决其问题应是双方协调的结果。 相似文献