全文获取类型
收费全文 | 1388篇 |
免费 | 234篇 |
国内免费 | 125篇 |
专业分类
电工技术 | 22篇 |
综合类 | 127篇 |
化学工业 | 198篇 |
金属工艺 | 14篇 |
机械仪表 | 8篇 |
建筑科学 | 225篇 |
矿业工程 | 75篇 |
能源动力 | 50篇 |
轻工业 | 88篇 |
水利工程 | 645篇 |
石油天然气 | 176篇 |
武器工业 | 4篇 |
无线电 | 5篇 |
一般工业技术 | 28篇 |
冶金工业 | 18篇 |
原子能技术 | 9篇 |
自动化技术 | 55篇 |
出版年
2024年 | 7篇 |
2023年 | 37篇 |
2022年 | 65篇 |
2021年 | 77篇 |
2020年 | 73篇 |
2019年 | 59篇 |
2018年 | 43篇 |
2017年 | 60篇 |
2016年 | 54篇 |
2015年 | 57篇 |
2014年 | 91篇 |
2013年 | 87篇 |
2012年 | 128篇 |
2011年 | 109篇 |
2010年 | 65篇 |
2009年 | 85篇 |
2008年 | 60篇 |
2007年 | 95篇 |
2006年 | 77篇 |
2005年 | 71篇 |
2004年 | 55篇 |
2003年 | 58篇 |
2002年 | 47篇 |
2001年 | 31篇 |
2000年 | 27篇 |
1999年 | 18篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1951年 | 1篇 |
排序方式: 共有1747条查询结果,搜索用时 15 毫秒
121.
S. E. Jørgensen 《Lakes & Reservoirs: Research and Management》1998,3(2):139-142
This paper proposes an alternative parameter estimation procedure. Usually the parameters that yield the highest sensitivity are calibrated by trial and error or by an automatic calibration procedure. If the number of parameters to be calibrated is more than 3-5, this procedure is very time consuming. The presented procedure is based on the assumption that the biological components in an ecosystem model attempt to develop such properties that they become best possible survivors, i.e. develop as much biomass as possible. It has previously been proposed that the survival of the entire ecosystem can be measured by use of the thermodynamic function exergy, which measures the distance from thermodynamic equilibrium and accounts for the biomass and its information content. If these assumptions are correct, it should be possible to determine the combination of parameters which gives the highest exergy. The paper presents the use of this idea in combination with a normal calibration. The parameters, which are less known from the literature and still yield a relatively high sensitivity, are determined by use of the above-mentioned exergy principle. The parameters that are known within relatively narrow ranges from the literature are calibrated by the normal procedure. The method has been used on a concrete lake modelling study and given good results. This combination method seems therefore to offer clear advantages, particularly for models with a relatively high number of sensitive parameters (> 5), which otherwise would require a very cumbersome calibration. 相似文献
122.
国内湖泊水质污染及富营养化治理 总被引:2,自引:0,他引:2
湖泊水质污染及生态恢复是我国当前水环境保护所面临的主要问题。在国内湖泊富营养化防治调研的基础上,对我国重点治理的“三湖”水环境状况及治理对策进行了总结与分析,提出国内湖泊治理存在的问题和对策,以及官厅水库水污染防治应注意的问题。 相似文献
123.
The component solubilities in NaCl–RbCl–H2O, KCl–CsCl–H2O and KBr–CsBr–H2O systems at 25 C were calculated by using the Pitzer ion interaction model and its extended HW models. Excellent agreement with experimental solubilities indicated that the models can be successfully used to calculate the component solubilities. This study affords the necessary parameters for solubility predictions of complicated systems containing rubidium and caesium and establishes a theoretical basis for the separation of these valuable metals from salt lake brine. 相似文献
124.
该文依据宿鸭湖水库水质的实际监测资料,采用指数法对水库的水环境进行地表水环境质量评价和水库富营养化评价,采用秩相关系数法对近5年水库水质变化趋势进行分析和评价,提出污染防治对策.结果表明,宿鸭湖水库水质基本满足地表水水域环境功能,水库富营养化程度为轻度富营养化,近5年来水质变化趋势稳定;通过提出针对性的对策和建议,可以进一步降低污染物水平,保障水库综合效益的发挥. 相似文献
125.
ADSP-TS101 is a high performance DSP with good properties of parallel processing and high speed. According to the real-time processing requirements of underwater acoustic communication algorithms, a real-time parallel processing system with multi-channel synchronous sample, which is composed of multiple ADSP-TS101s, is designed and carried out. For the hardware design, field programmable gate array (FPGA) logical control is adopted for the design of multi-channel synchronous sample module and cluster/data flow associated pin connection mode is adopted for multiprocessing parallel processing configuration respectively: And the software is optimized by two kinds of communication ways: broadcast writing way through shared bus and point-to-point way through link ports. Through the whole system installation, connective debugging, and experiments in a lake, the results show that the real-time parallel processing system has good stability and real-time processing capability and meets the technical design requirements of real-time processing. 相似文献
126.
根据2013年1~12月对桂湖浮游藻类的调查和监测结果,分析藻类种群组成和优势种、细胞密度、马卡列夫(Margalef)和香农—韦弗(Shannon-Weaver)生物多样性指数等生物特征参数的变化,从生物学角度对桂湖水质进行评价,为桂林两江四湖水环境的综合治理和生态保护提供基础资料和理论依据。 相似文献
127.
As regards river restoration, it is fundamental to better link human pressures and environmental responses and to take into consideration not only target species or habitat but diverse ecological elements. This permits to assess sustainable restoration plan, especially concerning sediment augmentation below dams. The use of a hierarchical multicriteria approach on the Ain River permits us to assess a diagnosis of sediment deficit impact integrating several morphological (channel shifting, river bed degradation and river bed coarsening) and ecological components (Riparian and floodplain lake and fish communities). Our diagnosis also integrates a temporal and spatial approach better to link human pressures and environmental responses and to identify the dam effects amongst other drivers (e.g. grazing decline and channel regulation). The results confirm causality links between sediment deficit and slight channel bed degradation (0.01 m.year?1) or channel bed paving and thus highlight the impact of the dam on the drying of the riparian forest and on former channel community. However, the relationship between incision and reduction in active channel lateral mobility is more difficult to establish. The role of sediment deficit in the current variability of the riparian regeneration capacity and, thereby, landscape diversity along the lower valley remains unclear. This study also confirms the relevance of using different ecological indicators, notably because all components present different adjustment time scales, whereas some of them are more sensitive to other impacts. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
128.
为了解洞庭湖区枯水期的水体总磷的污染情况,利用MODIS反射率与同步的总磷(TP)浓度实测数据进行相关性分析,得出最优波段组合b1-b5。建立了三次多项式反演模型,并运用模型反演得到2005、2009及2013年枯水期3期洞庭湖区总磷的分布图,湖区水体主要以Ⅳ类水质和Ⅴ类水质为主,进一步采用以TP为基准的修正营养指数(TSIM)公式得出洞庭湖区的营养状态分布情况。结果表明:2005-2013年洞庭湖水体营养指数呈现略下降又上升的趋势。洞庭湖区湖水趋于富营养化状态,且东洞庭湖最严重,南洞庭湖次之,西洞庭湖最轻,洞庭湖湖体水质劣于入湖口水质。 相似文献
129.
保持白洋淀的水生态,对于华北地区的生态环境和社会经济发展有重大意义。白洋淀的反复干淀,引起了各级领导和广大群众的关注,要求水利部门从根本上扭转这种局面,建立保持白洋淀水生态的长效机制。2006—2009年从黄河调水保证了白洋淀水生态环境的持续健康,取得了显著的经济效益和社会效益。 相似文献
130.
不断恶化的水质变化趋势需要对湖泊的水生生态进行更为广泛和深入的研究。物质的迁移和混合过程直接影响着化学和生物组分的分布,对于维系整个湖泊生态系统非常重要,理解这个复杂的过程有助于更好地保护和利用湖泊资源。为了更好地定量分析瑞士阿尔卑纳赫湖中物质的迁移路径,在研究中,用CE—QUAL—W2模型(二维)模拟物质的迁移和混合过程,与实测结果吻合良好,表明该模型较为准确地模拟了迁移和混合过程,为该模型应用于水质模拟和预测打下了坚实的基础。为了更好地反映物质的迁移过程,还采用热平衡方法计算了垂直扩散系数,并且证明单独的CTD监测能够获取可靠的垂直扩散系数,不必同时进行温度计链的监测。 相似文献