全文获取类型
收费全文 | 67317篇 |
免费 | 7720篇 |
国内免费 | 4154篇 |
专业分类
电工技术 | 5594篇 |
技术理论 | 2篇 |
综合类 | 6026篇 |
化学工业 | 9827篇 |
金属工艺 | 3963篇 |
机械仪表 | 4648篇 |
建筑科学 | 5396篇 |
矿业工程 | 2143篇 |
能源动力 | 1765篇 |
轻工业 | 6567篇 |
水利工程 | 1789篇 |
石油天然气 | 2654篇 |
武器工业 | 821篇 |
无线电 | 7581篇 |
一般工业技术 | 6741篇 |
冶金工业 | 2557篇 |
原子能技术 | 988篇 |
自动化技术 | 10129篇 |
出版年
2024年 | 189篇 |
2023年 | 1265篇 |
2022年 | 2542篇 |
2021年 | 3437篇 |
2020年 | 2624篇 |
2019年 | 1931篇 |
2018年 | 2213篇 |
2017年 | 2435篇 |
2016年 | 2127篇 |
2015年 | 3192篇 |
2014年 | 4158篇 |
2013年 | 4757篇 |
2012年 | 5573篇 |
2011年 | 5669篇 |
2010年 | 5306篇 |
2009年 | 4862篇 |
2008年 | 4720篇 |
2007年 | 4544篇 |
2006年 | 3875篇 |
2005年 | 3154篇 |
2004年 | 2236篇 |
2003年 | 1591篇 |
2002年 | 1468篇 |
2001年 | 1162篇 |
2000年 | 1071篇 |
1999年 | 808篇 |
1998年 | 405篇 |
1997年 | 396篇 |
1996年 | 344篇 |
1995年 | 280篇 |
1994年 | 201篇 |
1993年 | 157篇 |
1992年 | 113篇 |
1991年 | 88篇 |
1990年 | 58篇 |
1989年 | 62篇 |
1988年 | 50篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 6篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 20篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1959年 | 9篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
通过对AAOA-MBR工艺在实际工程中的应用,分析该工艺处理城市污水的节能减排效能。实践表明AAOA-MBR工艺具有很强的抗冲击负荷能力,在进水质水量大幅度波动、且碳源匮乏的情况下,仍能取得良好的处理效果。实际工程运行四年来,厂区出水各项指标均稳定优于城镇污水处理厂污染物排放标准(GB 18918-2002)中的一级A标准,其中COD、BOD5、SS、NH3-N去除率分别达到可分别达到90.14%、98.25%、95.58%和98.2%;通过对运行期间污水处理量与耗电量相关关系进行回归分析可知,当处理水量达到设计规模时,其吨水耗电量预测为0.31kWh/m3。同时,基于对污水处理系统的沿程水质检测,优化进水水量分配和内循环回流比并进行产水泵联动改造,可进一步提高系统节能减排效果。 相似文献
22.
The mechanical properties of complex concentrated alloys (CCAs) depend on their formed phases and corresponding microstructures.The data-driven prediction of the phase formation and associated mechanical properties is essential to discovering novel CCAs.The present work collects 557 samples of various chemical compositions,comprising 61 amorphous,167 single-phase crystalline,and 329 multi-phases crystalline CCAs.Three classification models are developed with high accuracies to category and understand the formed phases of CCAs.Also,two regression models are constructed to predict the hard-ness and ultimate tensile strength of CCAs,and the correlation coefficient of the random forest regression model is greater than 0.9 for both of two targeted properties.Furthermore,the Shapley additive expla-nation (SHAP) values are calculated,and accordingly four most important features are identified.A significant finding in the SHAP values is that there exists a critical value in each of the top four fea-tures,which provides an easy and fast assessment in the design of improved mechanical properties of CCAs.The present work demonstrates the great potential of machine learning in the design of advanced CCAs. 相似文献
23.
Kun Yang Yachun Wang Penghui Lei Tiankai Yao Dong Zhao Jie Lian 《Journal of the European Ceramic Society》2021,41(12):6018-6028
Chemical durability of lanthanide zirconates (A2Zr2O7) (A = La-Yb) under near-field environments is important for evaluating their application as potential nuclear waste forms. In this work, A2Zr2O7 (A = La-Yb) are synthesized by spark plasma sintering with controlled microstructure and their chemical durability are evaluated in a nitric acid solution (pH = 1). Scanning transmission electron microscopy analysis reveals an amorphous passivation film either enriched with Zr or lanthanide. The complex chemistry of the passivation films can be correlated with a transition in corrosion mechanisms from a preferential release of lanthanide in La2Zr2O7 to a preferential release of Zr in Er2Zr2O7 and Yb2Zr2O7. These results suggest a dominant mechanism of incongruent dissolution and surface reorganization for the formation of passivation films. Strong correlations are identified between the leaching rates and cation ionic size, ionic potential, electronegativity differences between A-site cation and Zr, and bonding valence sum of oxygen, suggesting important impacts of structural and bonding characteristics in controlling chemical durability of lanthanide zirconates. 相似文献
24.
Yuan Cheng Jie Xing Xu Li Lixu Xie Yining Xie Zhi Tan Jianguo Zhu 《Journal of the American Ceramic Society》2022,105(8):5213-5221
Although KNN-based ceramics with high electrical properties are obtained through a variety of strategies, the temperature sensitivity is still one of the key technical bottlenecks hindering practical applications. Here, we use a new strategy, meticulously tailoring phase boundary, to refine the ferroelectric boundary of KNN-based ceramics, leading to high piezoelectricity companied with improving temperature stability. The highest d33 value in this system reaches 501 pC/N with a TC ∼ 240°C, whereas a large strain of ∼0.134% can be kept with 10% lower deterioration until 100°C. The origin of high piezoelectricity is mainly attributed to the well-preserved multiphase coexistence and the appearance of nanodomains, which greatly facilitate the polarization rotation. Instead of the changed intrinsic thermal insensitivity, the precision phase boundary engineering plays an important role in strengthening the temperature stability of electric-induced strain. This work provides a simple and effective method to obtain both high electrical properties and excellent thermal stability in KNN-based ceramics, which is expected to promote the practical applications in the future. 相似文献
25.
26.
The process of cemented carbides manufacturing requires rapid and field elemental analytical techniques to control and evaluate the properties of products. Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is such a potential elemental analytical technique. In this work, a portable LIBS instrument combined with a CF method was developed for the analysis of cemented carbides. Three batches of cemented compact carbides without reference samples were analyzed. Qualitative and quantitative analysis of the samples were achieved by using the portable LIBS instrument combined with CF method. To validate the analysis results, X-ray fluorescence spectrometry (XRF) was used to analyze the samples as well. The results of CF-LIBS agreed well with the results of XRF, with relative errors between ?29.53 and 24.70%. The results demonstrated that the portable LIBS instrument combined with CF method was capable for direct and rapid analysis without any need of standard measurements. Notably, with the portable LIBS instrument combined with CF method, acceptable accuracy could be obtained, which is promising for practical field applications. 相似文献
27.
28.
以碘吸附值为评价指标,活化时间、活化温度和浸渍比为影响因素,采用响应面法试验设计对磷酸活化法制备咖啡渣活性炭的工艺条件进行优化,并通过静态吸附试验研究了不同吸附时间、溶液pH值和吸附温度条件下,活性炭对水溶液中Cr(Ⅵ)吸附性能的影响,最后利用Langmuir、Freundlich吸附等温方程、准一级动力学方程、准二级动力学方程和颗粒内部扩散方程进行拟合。试验结果表明,制备咖啡渣活性炭的最佳工艺条件为活化时间1 h、活化温度498℃、浸渍比1.72;在此条件下活性炭得率为30.4%,碘吸附值为(799±16)mg/g,比表面积为1 006 m2/g,孔容为0.779 cm3/g、微孔孔容为0.051 cm3/g、平均孔径为3.088 nm。较低pH值和较高温度能够促进活性炭对Cr(Ⅵ)的吸附;Langmuir等温方程能够更好地描述活性炭对Cr(Ⅵ)的吸附效果;活性炭对Cr(Ⅵ)的吸附分3个阶段:快速吸附阶段、慢速吸附阶段和吸附平衡阶段,10 min内可完成吸附总量的79%,360 min内达到吸附平衡,该吸附过程符合准二级吸附动力学方程。分析表明咖啡渣活性炭对Cr(Ⅵ)的吸附主要为单分子层的化学吸附。 相似文献
29.
30.