全文获取类型
收费全文 | 57300篇 |
免费 | 6771篇 |
国内免费 | 4038篇 |
专业分类
电工技术 | 5134篇 |
技术理论 | 3篇 |
综合类 | 5517篇 |
化学工业 | 9324篇 |
金属工艺 | 2334篇 |
机械仪表 | 4447篇 |
建筑科学 | 3918篇 |
矿业工程 | 2160篇 |
能源动力 | 5335篇 |
轻工业 | 1201篇 |
水利工程 | 5477篇 |
石油天然气 | 6555篇 |
武器工业 | 638篇 |
无线电 | 1837篇 |
一般工业技术 | 4491篇 |
冶金工业 | 2987篇 |
原子能技术 | 1426篇 |
自动化技术 | 5325篇 |
出版年
2024年 | 111篇 |
2023年 | 817篇 |
2022年 | 1517篇 |
2021年 | 1835篇 |
2020年 | 1949篇 |
2019年 | 1670篇 |
2018年 | 1549篇 |
2017年 | 1969篇 |
2016年 | 2315篇 |
2015年 | 2304篇 |
2014年 | 3272篇 |
2013年 | 3874篇 |
2012年 | 4087篇 |
2011年 | 4651篇 |
2010年 | 3162篇 |
2009年 | 3428篇 |
2008年 | 3121篇 |
2007年 | 3677篇 |
2006年 | 3475篇 |
2005年 | 3129篇 |
2004年 | 2567篇 |
2003年 | 2309篇 |
2002年 | 1859篇 |
2001年 | 1548篇 |
2000年 | 1362篇 |
1999年 | 1085篇 |
1998年 | 908篇 |
1997年 | 765篇 |
1996年 | 717篇 |
1995年 | 667篇 |
1994年 | 562篇 |
1993年 | 409篇 |
1992年 | 343篇 |
1991年 | 209篇 |
1990年 | 219篇 |
1989年 | 163篇 |
1988年 | 117篇 |
1987年 | 92篇 |
1986年 | 62篇 |
1985年 | 31篇 |
1984年 | 43篇 |
1983年 | 34篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 18篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 25篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
41.
Xianjin Li Tianyu Li Pengcheng Xu Congxin Xie Yunhe Zhang Xianfeng Li 《Advanced functional materials》2021,31(22):2100133
Bromine-based flow batteries (Br-FBs) are considered one of the most promising energy storage systems due to their features of high energy density and low cost. However, they generally suffer from uncontrolled diffusion of corrosive bromine particularly at high temperatures. That is because the interaction between polybromide anions and the commonly used complexing agent (N–methyl–N–ethyl–pyrrolidinium bromide [MEP]) decreases with increasing temperatures, which causes serious self-discharge and capacity fade. Herein, a novel bromine complexing agent, 1–ethyl–2–methyl–pyridinium bromide (BCA), is introduced in Br-FBs to solve the above problems. It is proven that BCA can combine with polybromide anions very well even at a high temperature of 60 °C. Moreover, the BCA contributes to decreasing the electrochemical polarization of Br−/Br2 couple, which in turn improves their power density. As a result, a zinc–bromine flow battery with BCA as the complexing agent can achieve a high energy efficiency of 84% at 40 mA cm−2, even at high temperature of 60 °C and it can stably run for more than 400 cycles without obvious performance decay. This paper provides an effective complexing agent to enable a wide temperature range Br-FB. 相似文献
42.
This paper discusses the capability of Guo et al.'s (2021) equations to determine the discharge of radial gates under submerged flow conditions. It was concluded that Guo et al.'s (2021) equations are associated with error reduction compared to the Incomplete Self-Similarity (ISS) theory and the calibration method. However, it does not have a significant advantage over Energy-Momentum (E-M) approach. Employing E-M principles, new equations were proposed to determine the discharge of radial gates, which has some advantages compared to Guo et al. (2021), such as (1) error reduction under partially and fully submerged flow conditions, (2) least dependence on the empirical constants, (3) uniformity of form over the entire submerged condition, and (4) no need to classify the submerged flow. Field calibration showed that the proposed equations in the present study for a single gate predict the discharge of parallel radial gates with a mean absolute error of less than 4.5% subject to the submerged operation of all open gates. 相似文献
43.
We investigate nonlinear phase dynamics of an ideal kink mode, induced by E × B flow. Here the phase is the cross phase(θ_c) between perturbed stream function of velocity■ and magnetic field ■, i.e. θ_c= θ_φ-θ_ψ. A dimensionless parameter, analogous to the Richardson number,■(γ_(kink): the normalized growth rate of the pure kink mode; ■: normalized E × B shearing rate) is defined to measure the competition between phase pinning by the current density and phase detuning by the flow shear. When R_i 1, θ_c is locked to a fixed value,corresponding to the conventional eigenmode solution. When R_i≤1, θ_c enters a phase slipping or oscillating state, corresponding to a nonmodal solution. The nonlinear phase dynamics method provides a more intuitive explanation of the complex dynamical behavior of the kink mode in the presence of E × B shear flow. 相似文献
44.
As a highly complex and time-varying process, gas-water two-phase flow is commonly encountered in industries. It has a variety of typical flow states and transition flow states. Accurate identification and monitoring of flow states is not only beneficial to further study of two-phase flow but also helpful for stable operation and economic efficiency of process industry. Combining canonical variate analysis (CVA) and Gaussian mixture model (GMM), a strategy called multi-CVA-GMM is proposed for flow state monitoring in gas-water two-phase flow. CVA is used to extract flow state features from the perspective of correlation between historical data and future data, which solves the cross correlation and temporal correlation of multi-sensor measurement data. GMM calculates the possibility that the current flow state belongs to each typical flow pattern and judges the current flow state by probability indicators. It is conducive to follow-up use of Bayesian inference probability and Mahalanobis distance-based (BID) indicator for flow state monitoring, which avoids repeated traversal of multiple CVA-GMM models and improves the efficiency of the monitoring process. The probability indicators can also be used to analyze transition flow states. The method combining the probabilistic idea of GMM with the deterministic idea of multimodal modeling can accurately identify the current flow state and effectively monitor the evolution of flow state. The multi-CVA-GMM method is validated by using the measured data of the horizontal flow loop of gas-water two-phase flow experimental facility, and its effectiveness is proved. 相似文献
45.
46.
47.
To identify conveniently multiphase flow regimes in subsea pipeline-risers, we study in this paper experimentally two-phase flows in a 1657 m long pipeline with an S-shaped riser to simulate field experiment, within a wide range of gas and liquid velocities. Three flow regimes, namely severe slugging, transitional flows, and stable flows, are analyzed based on three differential pressure and one pressure signals at the top of the riser; comparatively speaking, the positions of these signals in the experimental system are similar to those of the sea level signals in industrial fields, which are easy and less expensive to obtain. The obtained signals are decomposed into six scales via a multi-scale wavelet analysis, and further four statistical parameters on each scale are extracted, including mean values, standard deviations, ranges, and mean values of absolute. We compared the effects of six SVM classifiers with different kernel functions on the recognition rate of flow regimes, and it is found the recognition rates of SVM classifier with quadratic and cubic kernel functions are the highest. Further, the principal component analysis is employed to reduce the dimension of statistical parameters and it indicates that the recognition rate tends to increase with the rising number of principal components from 1 to 6, and it remains constant if the principal component number is further increased. Moreover, The results suggest that the recognition rate obtained from the pressure difference between the top of the riser and the separator peaks, and then it comes that from the pressure signal at the top of the riser, and that for the pressure difference signal at the top of the riser is the least satisfying one. As for the optimal differential pressure signals between the top of the riser and the separator, the results show that the recognition rate increases rapidly from 70.2% to 90.4% when the sample duration rising from 2.3 s to 18.6 s, and when the sample duration exceeds 74.4 s, the recognition rate exceeds 92.9% and remains unchanged. 相似文献
48.
49.
M.R. Fatahi 《Canadian Metallurgical Quarterly》2019,58(2):140-155
Enhanced gravity concentrators such as Knelson concentrator (KC) are extensively used in the mineral processing industry. The complexities of KC bowl geometry and variation of feed characteristics have forced process engineers to design empirically new units using laboratory and pilot-scale Knelson concentrators. However, numerical modelling methods such as computational fluid dynamics (CFD) and discrete element method (DEM) provide a better insight of flow behaviour of fluid and particulate solid phases inside these processing units. This article reports findings of CFD simulations for single-phase water flow inside the laboratory KC. An available standard 7.5-cm laboratory KC bowl was numerically simulated using realisable k-ε turbulence model to resolve the turbulence dispersion of existing transitional flow regime. The effects of relative centrifugal force (RCF) intensity and bed fluidisation water flow rate on the water velocity and pressure distributions were studied. Simulations confirmed the swirling flow pattern governing inside the bowl. The results revealed that the impact of RCF intensity on the water field values is greater than that of bed fluidisation water flow rate. Both velocity and pressure variations inside the bowl rings followed a linear trend. 相似文献
50.
大直径厚壁气瓶内部淬火时的流动换热过程极其复杂,受到多种因素的影响,而研究气瓶内部压强和温度的变化规律对改善流动换热效果、提高产品组织性能具有重要的理论指导意义。以914 mm厚壁气瓶和瓶内流体为研究对象,建立了二维等效流 固耦合模型;采用多喷嘴系统对气瓶内外进行喷水淬火,研究了气瓶总长、喷水流速及淬火时间对瓶内压强及内壁温度的影响,通过间歇淬火试验验证了数学模型的正确性。结果发现,气瓶长度对瓶内压强和瓶壁温度的影响显著,喷水流速次之,当喷水流速大于8 m/s后,水量对瓶壁的冷却效果大大降低;气瓶内壁长度方向的温度梯度分别随气瓶总长的增加和淬火时间的延长而减小,但基本不受喷水量的影响。 相似文献