全文获取类型
收费全文 | 58372篇 |
免费 | 7006篇 |
国内免费 | 4158篇 |
专业分类
电工技术 | 5184篇 |
技术理论 | 9篇 |
综合类 | 5942篇 |
化学工业 | 9397篇 |
金属工艺 | 2166篇 |
机械仪表 | 4301篇 |
建筑科学 | 5559篇 |
矿业工程 | 2159篇 |
能源动力 | 5326篇 |
轻工业 | 1452篇 |
水利工程 | 6880篇 |
石油天然气 | 3964篇 |
武器工业 | 642篇 |
无线电 | 1838篇 |
一般工业技术 | 4508篇 |
冶金工业 | 2986篇 |
原子能技术 | 1386篇 |
自动化技术 | 5837篇 |
出版年
2024年 | 249篇 |
2023年 | 872篇 |
2022年 | 1681篇 |
2021年 | 1991篇 |
2020年 | 2020篇 |
2019年 | 1698篇 |
2018年 | 1588篇 |
2017年 | 1996篇 |
2016年 | 2219篇 |
2015年 | 2327篇 |
2014年 | 3505篇 |
2013年 | 3882篇 |
2012年 | 3922篇 |
2011年 | 4673篇 |
2010年 | 3253篇 |
2009年 | 3555篇 |
2008年 | 3295篇 |
2007年 | 3893篇 |
2006年 | 3651篇 |
2005年 | 3163篇 |
2004年 | 2637篇 |
2003年 | 2350篇 |
2002年 | 1874篇 |
2001年 | 1571篇 |
2000年 | 1311篇 |
1999年 | 1097篇 |
1998年 | 880篇 |
1997年 | 746篇 |
1996年 | 691篇 |
1995年 | 613篇 |
1994年 | 508篇 |
1993年 | 397篇 |
1992年 | 333篇 |
1991年 | 216篇 |
1990年 | 218篇 |
1989年 | 166篇 |
1988年 | 118篇 |
1987年 | 84篇 |
1986年 | 60篇 |
1985年 | 34篇 |
1984年 | 47篇 |
1983年 | 32篇 |
1982年 | 22篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 22篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
桥梁颤振气动导数识别的迭代法 总被引:3,自引:1,他引:2
本文提出一种利用自由振动响应通过年顿-拉夫逊迭代同时识别出桥梁全部8个颤振气动导的方法。此法具有对迭代初值要求不高,识别结果稳定的特点,并具有一定的抗噪声干扰能力。数字仿真与实物试验结果表明本文方法有效,可行。 相似文献
154.
155.
A new definition of the flooding point in a two-phase counter-current trickle bed column has been proposed. Based on this point a versatile correlation of liquid hold-up has been formulated. The coefficients of this correlation are invariant to the change of physical properties of liquid, type and size of the packing forming the bed and gas velocity. This conclusion has been reached from the analysis of experiments with four different liquids irrigating the bed and three types of packing of various size. The versatile correlation can be used also re-currently to calculate flooding hold-up and flooding liquid rate from two known values of liquid hold-up for a given gas rate. 相似文献
156.
157.
Influences of land use/cover on water quality in the upper and middle reaches of River Njoro, Kenya 总被引:1,自引:0,他引:1
William A. Shivoga Mucai Muchiri Samuel Kibichi Jethro Odanga Scott N. Miller Tracy J. Baldyga Eric M. Enanga Maina C. Gichaba 《Lakes & Reservoirs: Research and Management》2007,12(2):97-105
Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land‐cover types and subwatersheds contributing run‐off to the sampling sites in the River Njoro. Standard Digital Elevation Model‐based routines were used to establish the watershed area contributing run‐off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land‐use types and the size of the subwatersheds. The mid‐stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large‐scale farming with intense, well‐preserved riparian and in‐stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small‐scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid‐reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land‐use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near‐stream land uses. We suggest that conservation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem. 相似文献
158.
159.
In various medium‐to‐large‐scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat‐release rate and smoke‐production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi‐directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
160.
从流域和区域对水资源需求及环境保护要求出发,提出了在大樟溪干流刘岐、岩前和莒口增设鱼道、取消船闸和航运的建议;从流域环境保护要求提出了主要水库的最小下泄流量;根据大樟溪流域人口、经济及土地资源的状况,提出了从泉州、莆田和福州等水资源受益区安置移民缓解土地资源紧张的模式来提高龙湘水库的调节库容,以提高流域及区域对水资源需求与调配能力,确保河道生态安全、生产生活用水安全等流域规划的新思路、新理念。 相似文献