全文获取类型
收费全文 | 104759篇 |
免费 | 2478篇 |
国内免费 | 4980篇 |
专业分类
电工技术 | 3760篇 |
技术理论 | 1篇 |
综合类 | 2455篇 |
化学工业 | 10838篇 |
金属工艺 | 7944篇 |
机械仪表 | 5431篇 |
建筑科学 | 5499篇 |
矿业工程 | 7927篇 |
能源动力 | 1505篇 |
轻工业 | 15571篇 |
水利工程 | 3965篇 |
石油天然气 | 5091篇 |
武器工业 | 923篇 |
无线电 | 9338篇 |
一般工业技术 | 18013篇 |
冶金工业 | 4005篇 |
原子能技术 | 2185篇 |
自动化技术 | 7766篇 |
出版年
2023年 | 634篇 |
2022年 | 766篇 |
2021年 | 809篇 |
2020年 | 643篇 |
2019年 | 868篇 |
2018年 | 945篇 |
2017年 | 498篇 |
2016年 | 701篇 |
2015年 | 939篇 |
2014年 | 2059篇 |
2013年 | 1574篇 |
2012年 | 5757篇 |
2011年 | 7230篇 |
2010年 | 2597篇 |
2009年 | 2115篇 |
2008年 | 5103篇 |
2007年 | 5282篇 |
2006年 | 4667篇 |
2005年 | 4466篇 |
2004年 | 4108篇 |
2003年 | 3499篇 |
2002年 | 3475篇 |
2001年 | 3377篇 |
2000年 | 2735篇 |
1999年 | 2072篇 |
1998年 | 1520篇 |
1997年 | 1392篇 |
1996年 | 1510篇 |
1995年 | 1577篇 |
1994年 | 1434篇 |
1993年 | 1330篇 |
1992年 | 1697篇 |
1991年 | 1662篇 |
1990年 | 1995篇 |
1989年 | 1802篇 |
1988年 | 2361篇 |
1987年 | 2854篇 |
1986年 | 2442篇 |
1985年 | 2751篇 |
1984年 | 2492篇 |
1983年 | 2274篇 |
1982年 | 2429篇 |
1981年 | 2089篇 |
1980年 | 1623篇 |
1979年 | 1005篇 |
1978年 | 633篇 |
1966年 | 442篇 |
1965年 | 640篇 |
1964年 | 636篇 |
1956年 | 508篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
1.
边坡位移的时间序列曲线存在复杂的非线性特性,传统的预测模型精度不足以满足预测要求。为此提出了基于变分模态分解的鸟群优化-核极限学习机的预测模型,并用于河北省某水泥厂的边坡位移预测。该方法首先采用VMD把边坡位移序列分解为一系列的有限带宽的子序列,再对各子序列分别采用相空间重构并用核极限学习机预测,采用鸟群算法优化相空间重构的嵌入维度和KELM中惩罚系数和核参数三个数值,以取得最优预测模型。最后将各个子序列预测值叠加,得到边坡位移的最终预测值。结果表明:和KELM、BSA-KELM、EEMD-BSA-KELM模型相比,基于VMD的BSA-KELM预测精度更高,为边坡位移的预测提供一种有效的方法。 相似文献
2.
3.
我们整个的项目是围绕着倡节能,促环保进行的,将节能环保与现代技术相连接。拯救地球、保护环境、节约能源,是我们共同的责任。该平台可以清楚的看见个人或集体使用水电量的多少与变化,还可以通过记录将个人的使用与官方平均数据相比较,从而根据此来设置一些等级和奖励,来激励学生时刻节约资源的行动。我们进行了生态学,物理学,心理学等方面的了解和探究,但在网络平台搭建的过程中遇到了很棘手的问题,在IC卡的制作方面我们的能力和条件还不足以满足IC卡的制作,经过探讨我们转换思路使问题得到了比较好的解决。最后我们进行了项目的宣传工作,该项目取得了阶段性的良好进展。 相似文献
4.
At present, the development and implementation of digital transformation are the keys to promoting high-quality industry development. The new digital fabrication method of robotic 3D printing is a research area being studied by many to tackle the issue of the declining productivity of traditional construction methods. Although many studies have been done, most of the current 3D printing projects are facing limitations in terms of scale. In order to bridge the gap, this article proposed a mass customization 3D printing framework system for large-scale projects. This article discusses how mass customization is made possible through the joint operation of the FUROBOT software and 3D printing hardware. By taking the east gate of Nanjing Happy Valley Plaza as a case study, the article demonstrates and studies the feasibility of the large-scale mass customization 3D printing framework system. 相似文献
5.
6.
Site-specific seismic hazard analysis is crucial for designing earthquake resistance structures, particularly in seismically active regions. Shear wave velocity ( V S) is a key parameter in such analysis, although the economy and other factors restrict its direct field measurement in many cases. Various V S–SPT– N correlations are routinely incorporated in seismic hazard analysis to estimate the value of V S. However, many uncertainties question the reliability of these estimated V S values. This paper comes up with a statistical approach to take care of such uncertainties involved in V S calculations. The measured SPT– N values from all the critical boreholes were converted into statistical parameters and passed through various correlations to estimate V S at different depths. The effect of different soil layers in the boreholes on the Vs estimation was also taken into account. Further, the average shear wave velocity of the top 30 m soil cover ( V S30) is estimated after accounting for various epistemic and aleatoric uncertainties. The scattering nature of the V S values estimated using different V S– N correlations was reduced significantly with the application of the methodology. Study results further clearly demonstrated the potential of the approach to eliminate various uncertainties involved in the estimation of V S30 using general and soil-specific correlations. 相似文献
7.
Mohamed A.El-Nemr Ibrahim M.A.Ismail Nabil M.Abdelmonem Ahmed El Nemr Safaa Ragab 《中国化学工程学报》2021,36(8):199-222
Watermelon peel residues were used to produce a new biochar by dehydration method. The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI) ions from aqueous solution has been investigated. Three biochars, Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, were made from watermelon peel via dehydration with 50% sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH_2 or Triethylenetetramine(TETA) to give Melon-BO-TETA. The prepared biochars were characterized by BET, BJH,SEM, FT-IR, TGA, DSC and EDAX analyses. The highest removal percentage of Cr(VI) ions was 69% for Melon-B,98% for Melon-BO-NH_2 and 99% for Melon-BO-TETA biochars of 100 mg·L~(-1) Cr(VI) ions initial concentration and 1.0 g·L~(-1) adsorbents dose. The unmodified biochar(Melon-B) and modified biochars(Melon-BO-NH_2 and Melon-BO-TETA) had maximum adsorption capacities(Qm) of 72.46, 123.46, and 333.33 mg·g~(-1), respectively.The amination of biochar reduced the pore size of modified biochar, whereas the surface area was enhanced.The obtained data of isotherm models were tested using different error function equations. The Freundlich,Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, respectively. The adsorption rate was primarily controlled by pseudo-second–order rate model. Conclusively, the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process. The adsorption for the Melon-B, Melon-BO-NH_2 and Melon-BO-TETA could be explained for acid–base interaction and hydrogen bonding interaction. 相似文献
8.
为了研究钨合金破片样品在爆轰驱动下的破碎行为,以93W-Ni-Fe作为研究对象,对两种不同工艺得到的钨合金破片样品进行了静态压溃性能、动态力学性能和爆轰驱动破碎性实验;采用扫描电子显微镜进行金相研究,结合原始破片及爆轰加载后的回收破片微观形貌分析,实现破片在爆轰加载后的完整性预估。结果表明,在两种破片静态压溃性能相当的情况下,其动态应力应变曲线以及爆轰驱动后的破碎率也会出现明显差异,因此静态压溃性实验不足以表征破片的爆轰驱动完整率,但与动态力学性能以及金相研究结合后,发现动态应力应变曲线无明显应变硬化行为的破片更容易发生破碎,且破片微观形貌出现大量孔隙以及晶粒分布不均匀现象,说明结合动态力学性能分析可有效预估钨合金破片样品的爆轰驱动破碎行为。 相似文献
9.
Daniel T. Payne Mandeep K. Chahal V clav B&rcaron ezina Whitney A. Webre Katsuhiko Ariga Francis D Souza Jan Labuta Jonathan P. Hill 《Frontiers of Chemical Science and Engineering》2020,14(1):28
Chiral 1,1’-binaphthyl-linked diporphyrin ‘tweezers’ (R)-1/(S)-1 and the corresponding zinc(II) complexes (R)-2/(S)-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee) determinations) were evaluated. Tris(1-n-dodecyl)porphyrins were used for the first time as the interacting units. Host capabilities of the diporphyrin tweezers were investigated by titrations with (R,R)- and (S,S)-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and 1H nuclear magnetic resonance (1H-NMR) methods. Chiral configurations could also be differentiated using CD or 1H-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10−6 mol·L−1). The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R,R)- and (S,S)-CHDA. Non-metallated (R)-1/(S)-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest. This work demonstrates the utility of 1,1’-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers. 相似文献
10.
Pablo Salcedo-Abraira Sergio M.F.Vilela Artem A.Babaryk Maria Cabrero-Antonino Pedro Gregorio Fabrice Salles Sergio Navalon Hermenegildo Garcia Patricia Horcajada 《Nano Research》2021,14(2):450-457
A novel microporous two-dimensional(2D)Ni-based phosphonate metal-organic framework(MOF;denoted as IEF-13)has been successfully synthesized by a simple and green hydrothermal method and fully characterized using a combination of experimental and computational techniques.Structure resolution by single-crystal X-ray diffraction reveals that IEF-13 crystallizes in the triclinic space group Pi having bi-octahedra nickel nodes and a photo/electroactive tritopic phosphonate ligand.Remarkably,this material exhibits coordinatively unsaturated nickel(II)sites,free-P03H2and-P03H acidic groups,a C02accessible microporosity,and an exceptional thermal and chemical stability.Further,its in-deep optoelectronic characterization evidences a photoresponse suitable for photocatalysis.In this sense,the photocatalytic activity for challenging H2generation and overall water splitting in absence of any co-catalyst using UV-Vis irradiation and simulated sunlight has been evaluated,constituting the first report for a phosphonate-MOF photocatalyst.IEF-13 is able to produce up to 2,200 fimol of H2per gram using methanol as sacrificial agent,exhibiting stability,maintaining its crystal structure and allowing its recycling.Even more,170μmol of H2per gram were produced using IEF-13 as photocatalyst in the absence of any co-catalyst for the overall water splitting,being this reaction limited by the 02reduction.The present work opens new avenues for further optimization of the photocatalytic activity in this type of multifunctional materials. 相似文献