全文获取类型
收费全文 | 8834篇 |
免费 | 1440篇 |
国内免费 | 736篇 |
专业分类
电工技术 | 210篇 |
综合类 | 1021篇 |
化学工业 | 424篇 |
金属工艺 | 356篇 |
机械仪表 | 439篇 |
建筑科学 | 1687篇 |
矿业工程 | 918篇 |
能源动力 | 316篇 |
轻工业 | 134篇 |
水利工程 | 2070篇 |
石油天然气 | 774篇 |
武器工业 | 117篇 |
无线电 | 643篇 |
一般工业技术 | 512篇 |
冶金工业 | 260篇 |
原子能技术 | 109篇 |
自动化技术 | 1020篇 |
出版年
2024年 | 15篇 |
2023年 | 145篇 |
2022年 | 303篇 |
2021年 | 351篇 |
2020年 | 355篇 |
2019年 | 335篇 |
2018年 | 289篇 |
2017年 | 406篇 |
2016年 | 410篇 |
2015年 | 432篇 |
2014年 | 639篇 |
2013年 | 597篇 |
2012年 | 724篇 |
2011年 | 696篇 |
2010年 | 499篇 |
2009年 | 507篇 |
2008年 | 508篇 |
2007年 | 580篇 |
2006年 | 512篇 |
2005年 | 467篇 |
2004年 | 369篇 |
2003年 | 311篇 |
2002年 | 246篇 |
2001年 | 240篇 |
2000年 | 192篇 |
1999年 | 163篇 |
1998年 | 130篇 |
1997年 | 84篇 |
1996年 | 92篇 |
1995年 | 90篇 |
1994年 | 72篇 |
1993年 | 43篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1964年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
41.
随着经济高速增长和城市化进程不断加快,华北平原区域性空气污染问题愈演愈烈。针对该区域开展长时序气溶胶光学厚度时空分布特征和潜在源分析研究,对华北平原大气污染治理具有重要意义。基于长时序MODIS/Terra C6.1 MOD04_L2气溶胶光学厚度产品,分析华北平原气溶胶光学厚度的时空分布特征,并利用后向轨迹聚类分析讨论华北平原7个重点城市气团输送的季节变化,并以污染较为严重的河北石家庄为例进行潜在源分析和浓度权重分析,探究影响其大气质量的污染物潜在源区。结果表明:2011~2020年华北平原气溶胶光学厚度月均值呈显著的周期性变化,以年为周期,每个周期内峰值一般出现在6月至8月; 气溶胶光学厚度月际年内呈单峰分布,峰值出现在6月(0.75),最小值出现在12月(0.37); 气溶胶光学厚度季均值从大到小依次为夏季(0.67)、春季(0.59)、冬季(0.49)、秋季(0.46); 10年间气溶胶光学厚度呈下降趋势,整体下降幅度达36.84%,其中2011年最高(0.72),2018年最低(0.45); 华北平原7个重点城市春、夏、秋、冬四季主要受短距离气团输送影响较大,长距离气团输送影响较小; 2014~2020年河北石家庄的空气质量优良天数占比相对较小,空气质量状况差,影响其空气质量的污染物多为本地生成,同时也受周边省市近距离输送的影响。 相似文献
42.
Large-Scale Particle Image Velocimetry (LSPIV) has emerged as a reliable technology to measure river surface flow velocity distribution and can be applied to estimate river discharge. Fewer studies have explored the capability of surface turbulence measurements using LSPIV. In this paper, LSPIV is applied to evaluate statistics of surface turbulence of a natural river. Turbulence measurements including velocity fluctuation, velocity spectra and the dissipation rate of turbulent kinetic energy (TKE) are validated by comparing with those measured by an Acoustic Doppler Velocimeter (ADV). Traditionally, estimation of stream discharge through LSPIV needs a secondary measurement to determine river bathymetry and water depth. A new method is presented here to demonstrate that for a fully developed and channel-controlled flow, the cross section geometry can be estimated from the combined measurements of surface mean velocity and the dissipation rate, following the Manning-Strickler formula. Therefore, river discharge can be estimated with LSPIV along with a calibrated Manning's roughness, without additional bathymetry survey. The proposed new method is applied to measure discharge in Milwaukee River (Milwaukee, Wisconsin, U.S.A.), which agreed well with data obtained from a nearby streamgage station. 相似文献
43.
Critical depth is a significant parameter in the designing and management of open channels and related hydraulic structures, understanding the flow characteristics and calculations of varied flows (gradually, spatially, etc.). The trapezoidal cross sections are the most commonly used geometric sections in the network of water transmission and distribution channels, thus discussing its geometrical and hydraulic parameters is inevitable. The used nonlinear and mathematical relationships governing the critical depth problem in the trapezoidal channels are implicit and complex, hence the methods of trial and error, graphical and numerical are used to calculate it. In the present study, new explicit equations are presented based on mathematical analysis of the critical depth problem in the trapezoidal channel. Mathematical analysis has led to completely mathematical and analytical solutions having a definite physical (hydraulic) concept. Having the explicit equations provided by the ease of calculation process with no limitation of the application range and high accuracy are the advantages of this analysis. The accuracy of the presented equations is desired and determined according to the required accuracy. The data used for verification of the results are based on the critical flow condition (Froude number equal to 1), which has been generated in a wide and practical range of the geometric and hydraulic characteristics of the channel. Also, the calculated values are compared with the real values of the considered parameter. 相似文献
44.
All supercritical free overfalls were almost considered as frictionless flow or pseudo-uniform flow before, the effect of friction had not been paid due attention. Currently, a new mathematical model is proposed to analyze supercritical rectangular free overfall by Boussinesq-type energy equation accounting for frictional effect. A computational approach of loop iteration algorithm is utilized to simultaneously calculate the implicit water surface profile by Runge-Kutta method, end-depth-ratio, and discharge. Subsequently, the dependency of discharge on end depth and Nikuradse equivalent sand roughness for different slope is illustrated. Comparison of computed results with experimental observations reveals satisfactory agreement. Additionally, the present energy approach leads to more accurate results than the momentum method for high roughness. Finally, to aid application for engineers, an explicit solution of discharge for practical application in the commonly using range is also proposed. The most important purpose of this study is to present a general computational approach, which could be used for the rough supercritical free overfalls of any other cross-sections. 相似文献
45.
Knowledge distillation has become a key technique for making smart and light-weight networks through model compression and transfer learning. Unlike previous methods that applied knowledge distillation to the classification task, we propose to exploit the decomposition-and-replacement based distillation scheme for depth estimation from a single RGB color image. To do this, Laplacian pyramid-based knowledge distillation is firstly presented in this paper. The key idea of the proposed method is to transfer the rich knowledge of the scene depth, which is well encoded through the teacher network, to the student network in a structured way by decomposing it into the global context and local details. This is fairly desirable for the student network to restore the depth layout more accurately with limited resources. Moreover, we also propose a new guidance concept for knowledge distillation, so-called ReplaceBlock, which replaces blocks randomly selected in the decoded feature of the student network with those of the teacher network. Our ReplaceBlock gives a smoothing effect in learning the feature distribution of the teacher network by considering the spatial contiguity in the feature space. This process is also helpful to clearly restore the depth layout without the significant computational cost. Based on various experimental results on benchmark datasets, the effectiveness of our distillation scheme for monocular depth estimation is demonstrated in details. The code and model are publicly available at : https://github.com/tjqansthd/Lap_Rep_KD_Depth. 相似文献
46.
提出钢表层脱碳层深度测定的一种新方法,即电子探针面分析法。对热轧态高碳工具钢75Cr1、淬火齿轮钢20CrMnTi、冷轧退火低碳车厢板SH1100钢3个典型钢种完成脱碳层深度的测定试验,结果表明:对于珠光体-铁素体型中高碳钢的脱碳层深度测定,金相法测定值是电子探针面分析法测定值的77%左右;对于淬回火钢的脱碳层深度测定,电子探针面分析法的测量精度在10 μm以下,约是显微硬度法测量精度的十分之一;对于脱碳层深度不易准确测定的低碳钢,电子探针面分析法通过较大区域范围的平均碳含量变化曲线来测定脱碳层深度,测量结果准确。电子探针面分析法在脱碳层深度测定方面具有钢种组织状态不限、试样形状不限、数据统计性好、测量精度高、易操作等优势,可在业内大力推广。 相似文献
47.
48.
含铁、锰高的水带有黄色和异味,工业用水则会在产品上形成黄斑,影响质量,必须严格控制铁、锰在水中的含量。砷是人体非必须元素,单质砷的毒性较低而砷的化合物均有剧毒,减少人体对砷的摄入量非常重要。文章对地下水联合除铁、除锰、除砷及其原理进行探讨。 相似文献
49.
以辽河油田齐28区块地质特征为依据,以现代钻井工艺理论为准则,以现代计算技术最优化科学理论为手段,确定了合理的开发井参数并设计了有效技术措施。主要设计内容有合理的地层划分、井身结构设计、钻具组合设计等几个方面,为该区块钻井工程的后续设计和施工提供了技术支持。 相似文献
50.