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31.
Minella M Rogora M Vione D Maurino V Minero C 《The Science of the total environment》2011,409(18):3463-3471
A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5 m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients (•OH, 3CDOM* and CO3-•) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals •OH and CO3−•. Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical •OH source) and the summer maxima of DOC (•OH sink and 3CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving •OH and CO3−• would be most important in spring, while the reactions involving 3CDOM* would be most important in summer. 相似文献
32.
南水北调东线工程对南四湖环境的影响及对策 总被引:11,自引:2,他引:11
南水北调东线工程对南四湖环境的影响及对策措施涉及多个学科领域,在分析南四湖水环境现状的基础上,论述了东线工程对南四湖环境的主要有利影响和主要不利影响,提出了对策措施与建议,得出有利影响远大于不利影响,不对南四湖及周边地区环境造成持久不利影响的结论. 相似文献
33.
龙潭湖公园进水口现名为“龙门”,是全湖之水源,位于湖面之东隅,靠近护城河。河水沿着地下隧道过闸口(龙门)注入湖内。为了使水闸免于外露,采取了勾连搭歇山式的水榭建筑,前为敞厅后为室,前厅供游息赏景之用,后室为水闸电机操作间,恰好达到了一举双收的效用。 相似文献
34.
Solving the problem at the source: Controlling Mn release at the sediment-water interface via hypolimnetic oxygenation 总被引:3,自引:0,他引:3
One of the primary goals of hypolimnetic oxygenation systems (HOx) from a drinking water perspective is to suppress sediment-water fluxes of reduced chemical species (e.g., manganese and iron) by replenishing dissolved oxygen (O2) in the hypolimnion. Manganese (Mn) in particular is becoming a serious problem for water treatment on a global scale. While it has been established that HOx can increase sediment O2 uptake rates and subsequently enhance the sediment oxic zone via elevated near-sediment O2 and mixing, the influence of HOx on sediment-water fluxes of chemical species with more complicated redox kinetics like Mn has not been comprehensively evaluated.This study was based on Mn and O2 data collected primarily in-situ to characterize both the sediment and water column in a drinking-water-supply reservoir equipped with an HOx. While diffusive Mn flux out of the sediment was enhanced by HOx operation due to an increased concentration driving force across the sediment-water interface, oxygenation maintained elevated near-sediment and porewater O2 levels that facilitated biogeochemical cycling and subsequent retention of released Mn within the benthic region. Results show that soluble Mn levels in the lower hypolimnion increased substantially when the HOx was turned off for as little as ∼48 h and the upper sediment became anoxic. Turning off the HOx for longer periods (i.e., several weeks) significantly impaired water quality due to sediment Mn release. Continual oxygenation maintained an oxic benthic region sufficient to prevent Mn release to the overlying source water. 相似文献
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首先对宁波平原圩田景观的发展沿革进行论述。其次,剖析了鄞西圩区、宁波市与日月二湖在圩田水系整理方面的关系,并梳理了日月二湖的景观营建过程,指出日月二湖的布局结构体现了圩田水利系统和开垦方式,是该区域圩田景观的特定表达。并分析日月二湖与宁波平原中的众多聚落公共空间的发育具有相似性,两者很大程度上都源于圩田开垦机制。最后,将视野扩大至东南系列小平原,进一步揭示出这些地区以圩田景观为基础的传统湖泊景观营建的共性特征,这为理解中国东南滨海平原地区类似的传统风景营建提供了一种新的视角。 相似文献
38.
Short-term bacterial community composition dynamics in response to accumulation and breakdown of Microcystis blooms 总被引:1,自引:0,他引:1
Short-term bacterial community composition (BCC) dynamics in response to accumulation and breakdown of Microcystis blooms were examined by conducting in situ mesocosm experiments with varying levels of Microcystis sp. biomass, ranging from 15 to 3217 μg/L as measured by chlorophyll-a concentration in the freshwater water column. The BCC was assessed by means of terminal restriction fragment length polymorphism (T-RFLP) of 16S ribosomal RNA genes followed by cloning and sequencing of selected samples. The results showed that the composition of both free-living and particle-attached bacterial communities changed during the accumulation and breakdown phases of a Microcystis bloom, and differences were also evident with different levels of Microcystis biomass. The relative abundance of bacteria affiliated with Micrococcineae and Legionellales increased in general after amendment with Microcystis. Significant correlation between the relative abundance of Micrococcineae and breakdown of Microcystis biomass was also observed. Canonical correspondence analysis (CCA) showed that the changes in the free-living and particle-attached bacterial community were mostly related to the changes in the concentrations of chlorophyll-a, dissolved organic carbon (DOC), dissolved oxygen (DO) and pH, which were mainly induced by the breakdown of Microcystis biomass. Overall, our study revealed the following: i) accumulation of Microcystis blooms and their breakdown have strong impacts on bacterial community composition; ii) there might be saprophytic association between Micrococcineae and decomposition of Microcystis biomass; iii) it is necessary to reveal potential associations between Legionellales organisms and Microcystis blooms in eutrophic freshwater lakes. 相似文献
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Hypolimnetic oxygenation systems (HOx) are increasingly used in lakes and reservoirs to elevate dissolved oxygen (O2) while preserving stratification, thereby decreasing concentrations of reduced chemical species in the hypolimnion. By maintaining an oxic zone in the upper sediment, HOx suppress fluxes of reduced soluble species from the sediment into the overlying water. However, diminished HOx performance has been observed due to HOx-induced increases in sediment O2 uptake. Based on a series of in situ O2 microprofile and current velocity measurements, this study evaluates the vertical O2 distribution at the sediment-water interface as a function of HOx operation. These data were used to determine how sediment O2 uptake rate (JO2) and sediment oxic-zone depth (zmax) were affected by applied oxygen-gas flow rate, changes in near-sediment mixing and O2 concentration, and proximity to the HOx. The vertical sediment-water O2 distribution was found to be strongly influenced by oxygenation on a reservoir-wide basis. Elevated JO2 and an oxic sediment zone were maintained during continuous HOx operation, with zmax increasing linearly with HOx flow rate. In contrast, JO2 decreased to zero and the sediment became anoxic as the vertical O2 distribution at the sediment-water interface collapsed during periods when the HOx was turned off and near-sediment mixing and O2 concentrations decreased. JO2 and zmax throughout the reservoir were found to be largely governed by HOx-induced mixing rather than O2 levels in the water column. By quantifying how JO2 and zmax vary in response to HOx operations, this work (1) characterizes how hypolimnetic oxygenation affects sediment O2 dynamics, (2) contributes to the optimization of water quality and management of HOx-equipped lakes and reservoirs, and (3) enhances understanding of the effect of mixing and O2 concentrations in other systems. 相似文献