全文获取类型
收费全文 | 177330篇 |
免费 | 22567篇 |
国内免费 | 5390篇 |
专业分类
电工技术 | 8448篇 |
技术理论 | 11篇 |
综合类 | 8452篇 |
化学工业 | 40213篇 |
金属工艺 | 7862篇 |
机械仪表 | 9552篇 |
建筑科学 | 13039篇 |
矿业工程 | 3736篇 |
能源动力 | 4807篇 |
轻工业 | 15231篇 |
水利工程 | 2717篇 |
石油天然气 | 8302篇 |
武器工业 | 998篇 |
无线电 | 22659篇 |
一般工业技术 | 28022篇 |
冶金工业 | 7651篇 |
原子能技术 | 1371篇 |
自动化技术 | 22216篇 |
出版年
2024年 | 567篇 |
2023年 | 2286篇 |
2022年 | 3932篇 |
2021年 | 5521篇 |
2020年 | 5421篇 |
2019年 | 6360篇 |
2018年 | 6655篇 |
2017年 | 7525篇 |
2016年 | 7498篇 |
2015年 | 8751篇 |
2014年 | 10417篇 |
2013年 | 12787篇 |
2012年 | 11122篇 |
2011年 | 11450篇 |
2010年 | 10652篇 |
2009年 | 10124篇 |
2008年 | 9403篇 |
2007年 | 8995篇 |
2006年 | 9088篇 |
2005年 | 7870篇 |
2004年 | 5766篇 |
2003年 | 5280篇 |
2002年 | 4910篇 |
2001年 | 4396篇 |
2000年 | 4529篇 |
1999年 | 4450篇 |
1998年 | 3628篇 |
1997年 | 2977篇 |
1996年 | 2705篇 |
1995年 | 2238篇 |
1994年 | 1865篇 |
1993年 | 1355篇 |
1992年 | 1074篇 |
1991年 | 809篇 |
1990年 | 623篇 |
1989年 | 530篇 |
1988年 | 434篇 |
1987年 | 260篇 |
1986年 | 236篇 |
1985年 | 157篇 |
1984年 | 130篇 |
1983年 | 96篇 |
1982年 | 91篇 |
1981年 | 73篇 |
1980年 | 56篇 |
1979年 | 38篇 |
1978年 | 14篇 |
1977年 | 34篇 |
1976年 | 16篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Huyong Yan Guoyin Wang Di Wu Yu Huang Mingsheng Shang Jianjun Xu Kun Shan Xiaoyu Shi Jianhua Dong Lei Feng Botian Zhou Ye Yuan Yufei Zhao 《Water Resources Management》2017,31(5):1435-1456
In the field of water quality management, it is vital to determine the main precursory anomalies from the precursor of intricate water bloom in the context of a given area. In this paper, a water bloom precursor analysis method, based on two direction singular rough set, was proposed. This approach was produced on the basis of the different sections and pre-water bloom of water bloom precursor anomalies and characteristic of elements transferred in singular rough set. For testing the validity of two direction singular rough set application in water bloom precursor analysis, Xiangxi River, which is one of the typical tributaries of Three Gorges Reservoir in China, was selected as study area. The result showed that compared with other indexes, pH and dissolved oxygen (DO) are the most valuable indicators of water bloom in the precursory anomalies. Furthermore, regarding with water bloom precursory anomalies in Xiangxi River, most of the nutrient loading and biological community are the key indicators. Hence, this method can determine the main precursory anomaly for water bloom in the study area, which provides powerful knowledge support to water quality specialists for them to comprehensively analyze precursory anomaly so as to find out its relationship with occurrence law of water bloom. 相似文献
992.
Medium-Term Hydro Generation Scheduling (MTHGS) with Chance Constrained Model (CCM) and Dynamic Control Model (DCM) 总被引:1,自引:0,他引:1
Jianzhong Zhou Mengfei Xie Zhongzhen He Hui Qin Liu Yuan 《Water Resources Management》2017,31(11):3543-3555
Medium-Term Hydro Generation Scheduling (MTHGS) plays an important role in the operation of hydropower systems. In the first place, this paper presents a Chance Constrained Model for solving the optimal MTHGS problem. The model recognizes the impact of inflow uncertainty and the constraints involving hydrologic parameters subjected to uncertainty are described as probabilistic statements. It aims at providing a more practical technique compared to the traditional deterministic approaches used for MTHGS. The stochastic inflow is expressed as a simple discrete-time Markov chain and Stochastic Dynamic Programming is adopted to solve the model. Then in order to use the information of long-term inflow forecast to improve dispatching decisions, a Dynamic Control Model is developed. Short-term forecast results of the current period and long-term forecast results of the remaining period are treated as inputs of the model. Finally, the two methods are applied to MTHGS of Xiluodu hydro plant in China. The results are compared to those obtained from Deterministic Dynamic Programming with hindsight and advantages and disadvantages of the two methods are analyzed. 相似文献
993.
994.
995.
996.
2016年"鲇鱼"台风期间,省溪源水库遭遇建库以来最大洪水,水库通过预泄滕库、避潮错峰等方式成功防御,通过详细介绍"鲇鱼"台风期间水雨情特点以及调度过程,汲取经验,为今后水库洪水调度提供参考。 相似文献
997.
MAH接枝EPDM增韧PA66的研究 总被引:7,自引:0,他引:7
研究了MAH(马来酸酐)接枝三元乙丙橡胶(EPDM—g-MAH)对尼龙66(PA66)的增韧作用。利用SEM(扫描电镜)观察了共混体系的微观形貌(形态结构),并运用小角激光散射(SALS)方法研究了EPDM的加入对PA66结晶性能的影响。结果表明,未接枝的EPDM与PA66的相容性很差,而EPDM—g—MAH与PA66相容性明显增加,EPDM-g—MAH粒子均匀分散在PA66中,共混体系力学性能有很大提高。随着EPDM—g—MAH用量的增加,PA66球晶尺寸变小,共混体系界面结合更加紧密。 相似文献
998.
999.
Preparation and characterization of porous carbon beads and their application in dispersing small metal crystallites 总被引:2,自引:0,他引:2
Porous carbon beads were prepared by the pyrolysis of poly(vinylidene chloride) beads that were synthesized by suspension polymerization. After prolysis treatment at 180–300 °C under argon stream, the polymeric beads were further carbonized at 1000 °C for 3 h under argon stream to acquire porous carbon beads, of which the specific surface area was about 1000 m2/g, and pore size was mainly in the width range of 0.8–1.2 nm. The carbon structure and surface chemical composition characterized by X-ray diffraction and X-ray photoelectron spectroscopy, depended on the preparation temperature and the relations between them were examined. The characterization of the carbon beads by scanning electron microscopy, atomic force microscopy presented the morphological structure of the carbon beads surface and a global view of pores. The dispersion of nickel crystallites on the carbon beads surface was characterized by electron microprobe analysis. This study reveals that uniform surface morphological structure leads to the fine dispersion of metal crystallites. 相似文献
1000.
Estimating discharge in gravel‐bed river using non‐contact ground‐penetrating and surface‐velocity radars 下载免费PDF全文
Discharge measurement is a critical task for gravel‐bed channels. Under high‐flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage–discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact‐type velocity measuring is also subject to measurement errors and/or instrument failures by the high‐flow velocities, driftwood, stumps, and debris. This study developed a new real‐time method to estimate river discharge in gravel‐bed channels. A systematic measuring technology combining ground‐penetrating radar and surface‐velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross‐sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel‐bed reach of the Cho‐Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage–discharge relation and the index‐velocity method. The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage–discharge and index‐velocity methods. 相似文献