全文获取类型
收费全文 | 16615篇 |
免费 | 3912篇 |
国内免费 | 2453篇 |
专业分类
电工技术 | 751篇 |
技术理论 | 2篇 |
综合类 | 1438篇 |
化学工业 | 717篇 |
金属工艺 | 646篇 |
机械仪表 | 700篇 |
建筑科学 | 3726篇 |
矿业工程 | 4364篇 |
能源动力 | 289篇 |
轻工业 | 369篇 |
水利工程 | 638篇 |
石油天然气 | 1691篇 |
武器工业 | 65篇 |
无线电 | 1219篇 |
一般工业技术 | 932篇 |
冶金工业 | 674篇 |
原子能技术 | 44篇 |
自动化技术 | 4715篇 |
出版年
2024年 | 458篇 |
2023年 | 1176篇 |
2022年 | 2117篇 |
2021年 | 2045篇 |
2020年 | 1863篇 |
2019年 | 1144篇 |
2018年 | 719篇 |
2017年 | 589篇 |
2016年 | 570篇 |
2015年 | 616篇 |
2014年 | 1171篇 |
2013年 | 722篇 |
2012年 | 1182篇 |
2011年 | 1122篇 |
2010年 | 902篇 |
2009年 | 853篇 |
2008年 | 682篇 |
2007年 | 795篇 |
2006年 | 752篇 |
2005年 | 657篇 |
2004年 | 472篇 |
2003年 | 465篇 |
2002年 | 353篇 |
2001年 | 303篇 |
2000年 | 307篇 |
1999年 | 227篇 |
1998年 | 159篇 |
1997年 | 130篇 |
1996年 | 115篇 |
1995年 | 64篇 |
1994年 | 68篇 |
1993年 | 41篇 |
1992年 | 26篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1959年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
阿尔塔什水利枢纽工程是我国在建面板堆石坝工程之一,其深厚的砂砾石覆盖层和庞大的坝体,在施工和运行过程中均会对防渗墙的应力应变产生较大的影响,处理不好直接会影响到大坝整体防渗效果和工程安全。如何在保证施工质量的前提下,优化施工方案,改善防渗墙应力状况,是施工技术研究重点。通过对防渗墙的受力特性、深厚覆盖层的工程特性分析和研究,从防渗墙成墙槽段划分、墙段连接技术、强漏失地层成槽技术和固壁泥浆配比等关键技术上进行优化和改进,有效的消减了防渗墙在坝体填筑和蓄水过程中的应力应变集中,保证防渗墙的成墙质量和运行效果。 相似文献
82.
In this study, poly(ethylene terephthalate) (PET)/SiO2 nanocomposites were synthesized by in situ polymerization and melt‐spun to fibers. The superfine structure and properties of PET/SiO2 fibers were studied in detail by means of TEM, DSC, SEM, and a universal tensile machine. According to the TEM, SiO2 nanoparticles were well dispersed in the PET matrix at a size level of 10–20 nm. The DSC results indicated that the SiO2 nanoparticles might act as a marked nucleating agent promoting the crystallization of the PET matrix from melt but which inhibited the crystallization from the glassy state, owing to the “crosslink” interaction between the PET and SiO2 nanoparticles. The tensile strength of 5.73 MPa was obtained for the fiber from PET/0.1 wt % SiO2, which was 17% higher than that of the pure PET. The fibers were treated with aqueous NaOH. SEM photographs showed that more and deeper pits were introduced onto PET fibers, which provided shortcuts for disperse dye and diffused the reflection to a great extent. According to the K/S values, the color strength of the dyeing increased with increasing SiO2 content. It is found that the deep dyeability of PET fibers was improved greatly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
83.
84.
Germplasm with shorter duration than that of the currently grown varieties is being generated to maximize productivity of irrigated rice. However, short-duration varieties often produce yields lower than the medium- and long-duration varieties. Experiments were conducted during the 1980–82 dry and wet seasons to increase productivity through the use of very early-maturing rices and the improved management of nitrogen (N) fertilizers.Results over three years showed that IR58 and IR9729-67-3 (growth duration 100 ± 5 days) yield as well as or higher than IR36 although earlier maturing. They generally had a higher productivity (kg ha–1 day–1) than IR36 (110 ± 5 days).Three years' data suggest that the improved timing of broadcast applications of urea in split doses increased grain yield comparable with the basal incorporation of slow-release sulfur-coated urea (SCU) or deep point-placement of urea supergranules (USG).Results on elite breeding lines showed that the early-maturing IR9729-67-3 produced higher protein yield ha–1 than longer duration varieties such as IR8 and IR42 in the dry season. Furthermore, contrary to earlier results, single basal incorporation of slow-release SCU increased the protein yield of rice by 53 kg ha–1 and deep point-placement of USG by 43 kg ha–1 over split application of prilled urea. 相似文献
85.
锦屏一级水电站作为世界第一高的拱坝,在超高的水头和复杂的地质条件下,在底层灌浆洞中进行了超过170 m的深孔帷幕灌浆。施工中克服了各种不利条件,解决了多种非常规的施工技术难题,其经验可为其他类似工程提供参考。 相似文献
86.
248nm深紫外光刻胶 总被引:11,自引:3,他引:11
本文从化学增幅技术的产生,深紫外248nm胶主体树脂及PAG发展历程、溶解抑制剂、存在的工艺问题及解决途径多个方面综述了深紫外248nm胶的发展与进步. 相似文献
87.
88.
汉语的基本块识别是汉语句法语义自动分析中的重要任务之一。传统的方法大多数直接将汉语基本块识别任务转化成词层面的一个序列标注问题,采用CRF模型来处理。虽然,在许多评测中得到最好的结果,但基于词为标注单位,在实用中受限于自动分词系统以及汉语词特征的稀疏性。为此,该文给出了一种以字为标注单位,以字为原始输入层,来构建汉语的基本块识别的深层神经网络模型,并通过无监督方法,学习到字的C&W和word2vec两种分布表征,将其作为深层神经网络模型的字的表示层的初始输入参数来强化模型参数的训练。实验结果表明,使用五层神经网络模型,以[-3,3]窗口的字的word2vec分布表征,其准确率、召回率和F值分别达到80.74%,73.80%和77.12%,这比基于字的CRF高出约5%。这表明深层神经网络模型在汉语的基本块识别中是有作用的。 相似文献
89.
传统灰色GM(1,1)预测模型对非负递增时间序列有较好的预测精度,但对波动幅度较大的时间序列预测精度较低。为了提高预测精度,本文在趋势曲线模型和自记忆理论的基础上,建立趋势曲线-自记忆组合预测模型,将该模型应用于深基坑位移预测中,并与灰色GM(1,1)预测模型和趋势曲线预测模型比较,该模型具有较高的预测精度。 相似文献
90.
In order to understand the change rules of stress-displacement in surrounding rocks of dynamic pressure roadways in deep mines and to obtain a theoretical basis for analyses of roadway stability and designs of support,we established a coupling equation of adjacent rock strength,mining stress and supporting resistance on the basis of an elastic-plastic theory of mechanics.We obtained an analytical solution for stress and displacement distribution of elastic and plastic regions in surrounding rock of dynamic pressure roadway..Based on this theory,we have analyzed the changes in stress-displacement in elastic and plastic regions of surrounding rocks of dynamic pressure roadways in the Haizi Coal Mine.The results show that:1) radial and tangential stress change violently within the first 4 m from the inner surface of a roadway after excavation;radial stress increases while tangential stress decreases within a range of about 6 m from the inner surface of the roadway as a function of q3;2) radial and tangential stress increase with an increase in the mining pressure coefficient k;the increase in the rate of tangential stress is greater than that of radial stress;3) the radial displacement of the inner surface of roadways decreases with an increase in q3,provided that k remains unchanged. 相似文献