全文获取类型
收费全文 | 81768篇 |
免费 | 8380篇 |
国内免费 | 6906篇 |
专业分类
电工技术 | 6257篇 |
技术理论 | 3篇 |
综合类 | 6413篇 |
化学工业 | 14715篇 |
金属工艺 | 14191篇 |
机械仪表 | 5146篇 |
建筑科学 | 4531篇 |
矿业工程 | 1995篇 |
能源动力 | 5743篇 |
轻工业 | 1505篇 |
水利工程 | 5501篇 |
石油天然气 | 7154篇 |
武器工业 | 751篇 |
无线电 | 2608篇 |
一般工业技术 | 8426篇 |
冶金工业 | 4749篇 |
原子能技术 | 1876篇 |
自动化技术 | 5490篇 |
出版年
2024年 | 405篇 |
2023年 | 1280篇 |
2022年 | 2267篇 |
2021年 | 2787篇 |
2020年 | 2911篇 |
2019年 | 2606篇 |
2018年 | 2356篇 |
2017年 | 3134篇 |
2016年 | 3244篇 |
2015年 | 3288篇 |
2014年 | 4604篇 |
2013年 | 5353篇 |
2012年 | 5401篇 |
2011年 | 6382篇 |
2010年 | 4569篇 |
2009年 | 4939篇 |
2008年 | 4215篇 |
2007年 | 5117篇 |
2006年 | 4891篇 |
2005年 | 4233篇 |
2004年 | 3726篇 |
2003年 | 3315篇 |
2002年 | 2719篇 |
2001年 | 2241篇 |
2000年 | 1939篇 |
1999年 | 1631篇 |
1998年 | 1272篇 |
1997年 | 1103篇 |
1996年 | 979篇 |
1995年 | 889篇 |
1994年 | 750篇 |
1993年 | 556篇 |
1992年 | 465篇 |
1991年 | 288篇 |
1990年 | 307篇 |
1989年 | 230篇 |
1988年 | 150篇 |
1987年 | 111篇 |
1986年 | 82篇 |
1985年 | 43篇 |
1984年 | 57篇 |
1983年 | 39篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1975年 | 6篇 |
1959年 | 28篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
用试井方法确定注水后地层渗透率的变化 总被引:1,自引:0,他引:1
大港油田已进入开发中后期,高含水油田占73%,开发初期的一些参数已不适合现在开发的需要。研究出一套用试井方法确定注水以后地层渗透率变化的方法,对大港油田的增储上产具有重要意义。 相似文献
92.
In industrial systems, the formation of biofilms can cause many problems, such as an increase in the flow resistance of pipelines, energy losses in fluid transport and heat exchangers, product contamination, materials deterioration, and biocorrosion. As a result, biofilms contribute substantially to economic losses in the industry. Corrosion is particularly an issue in the petroleum industry and its implications range from down-hole completion through petroleum processing units. Much of this corrosion is attributed to microbial activities. This paper proposes a mathematical model for predicting substrate concentration for such microbial growth. Substrate concentrations in the system and near the biofilm surface are one of the parameters that has a great effect in determining the extent of the problems associated with biofilms. In this study, a convective-diffusion model under various flow conditions (stagnant, laminar, and turbulent) has been solved using the finite difference technique, employing the alternating direction implicit (ADI) method. The model assumes that a liquid containing substrate and bacteria is flowing in a pipeline with known concentrations at the inlet and then predicts the variation of the transient (as a function of time) substrate concentration along the pipeline and as a function of the pipe radius. The model is then used to predict and estimate the substrate concentration profiles on the biofilm surface under different environmental conditions. A parametric study was also conducted to study the effect of the different parameters influencing the substrate concentration profiles in the system and on the biofilm surface. 相似文献
93.
R. Tao 《Chemical engineering science》2006,61(7):2186-2190
Molecular dynamical simulation has been carried out to investigate the structure and dynamics of a dipolar fluid under strong shear. Dipolar fluid consists of polarizable particles, which have an induced dipole moment in the applied field direction. Shear stress is perpendicular to the field direction. When shear stress is small, the flow has a flowing-chain structure. If shear stress increases to pass a critical value, flowing-chain structure changes to flowing layer structure. Each layer is parallel to the flow direction and shear direction. Within one layer, particles form strings in the flow direction. 相似文献
94.
95.
Xueyuan ZhangWenle He Inger Odnevall Wallinder Jinshan PanChristofer Leygraf 《Corrosion Science》2002,44(9):2131-2151
Instantaneous corrosion rates of naturally patinated copper of varying age (16 months, 138 and 145 years) have been determined during continuous rain events in the laboratory with electrochemical impedance spectroscopy using a two-electrode cell. The two-electrode cell was found to yield the same information in bulk rainwater as a conventional three-electrode cell.Relatively constant corrosion rates, between 0.2 and 0.6 μm/y, were determined for samples having a two-layer structure with an inner brownish layer of cuprous oxide and an outer greenish layer of basic copper salts (138, 145 years). Samples with cuprous oxide as the dominating phase of the patina (16 months) showed higher and somewhat increasing corrosion rates during a rain event (from 0.6 to 1.2 μm/y). During a continuous rain event, corrosion rates were found to be approximately 10 (brownish patina) and 25 times (greenish patina) lower than corresponding instantaneous runoff rates. The first flush phenomena of the runoff process, with an increased concentration during first flush and a relatively constant concentration during steady state, was indirectly seen as an increase in solution conductivity during the first rain volume followed by relative constant value. The contribution of the concentration in the first flush to the total annual runoff rate was significant for panels having a greenish layer (138, 145 years) whereas it was negligible for panels having a brownish layer (16 months). 相似文献
96.
97.
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
98.
In this work, the filiform corrosion behaviour of powder painted aluminium profiles was studied, and the coating barrier properties together with adhesion to the substrate were analysed. Samples coated with a traditional painting procedure (one powder layer application followed by curing), and other samples coated using a special cycle to obtain wood grain effect were compared using accelerated filiform corrosion tests. Moreover, in order to better understand the degradation mechanisms of painted metal substrates, thermal stresses were applied to accelerate the natural weathering. The effects of the thermal aging were analysed by electrochemical impedance spectroscopy. 相似文献
99.
本文探讨了高速钢在高温形变过程中碳化物析出的行为及奥氏体组织状态对析出的影响。用透射电镜和扫描电镜分析了不同热处理状态奥氏体的组织结构,分析了高温形变过程中碳化物析出的部位,颗粒尺寸及形态。试验表明, 碳化物主要在奥氏体的缺陷处呈点状和点列状析出,大小为20mμ。处于回复状态的奥氏体缺陷诱发碳化物析出,析出碳化物钉札缺陷阻止再结晶进行。当再结晶驱动力较大时,由于动态再结晶充分发展,使缺陷大量消除,碳化物析出显著地减少。 相似文献
100.
Yu. V. Balaban-Irmenin N. G. Fokina 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2007,41(5):306-312
The effect of internal-corrosion inhibitors on heating-system pipelines is investigated. Tests were conducted on a testing
device for polarization measurements under conditions corresponding to the Rostov Heat-Supply System. The concentration of
OEDP-zinc, which provides a high degree of protection from general corrosion, is determined. The reagent has been successfully
incorporated into the Rostov No. 2 TPP.
__________
Translated from élektricheskie Stantsii, No. 7, July 2007, pp. 37–43. 相似文献