全文获取类型
收费全文 | 90599篇 |
免费 | 9640篇 |
国内免费 | 6806篇 |
专业分类
电工技术 | 5518篇 |
技术理论 | 10篇 |
综合类 | 8551篇 |
化学工业 | 19835篇 |
金属工艺 | 2033篇 |
机械仪表 | 4193篇 |
建筑科学 | 2424篇 |
矿业工程 | 1788篇 |
能源动力 | 1393篇 |
轻工业 | 1957篇 |
水利工程 | 1395篇 |
石油天然气 | 4645篇 |
武器工业 | 1168篇 |
无线电 | 10518篇 |
一般工业技术 | 7606篇 |
冶金工业 | 1647篇 |
原子能技术 | 888篇 |
自动化技术 | 31476篇 |
出版年
2024年 | 137篇 |
2023年 | 1133篇 |
2022年 | 2056篇 |
2021年 | 2798篇 |
2020年 | 2883篇 |
2019年 | 2307篇 |
2018年 | 2080篇 |
2017年 | 2501篇 |
2016年 | 2823篇 |
2015年 | 3316篇 |
2014年 | 5484篇 |
2013年 | 5105篇 |
2012年 | 6369篇 |
2011年 | 7230篇 |
2010年 | 5526篇 |
2009年 | 5700篇 |
2008年 | 5842篇 |
2007年 | 6951篇 |
2006年 | 6032篇 |
2005年 | 5482篇 |
2004年 | 4626篇 |
2003年 | 4035篇 |
2002年 | 3280篇 |
2001年 | 2567篇 |
2000年 | 2164篇 |
1999年 | 1651篇 |
1998年 | 1312篇 |
1997年 | 1006篇 |
1996年 | 849篇 |
1995年 | 756篇 |
1994年 | 638篇 |
1993年 | 474篇 |
1992年 | 339篇 |
1991年 | 291篇 |
1990年 | 236篇 |
1989年 | 161篇 |
1988年 | 130篇 |
1987年 | 98篇 |
1986年 | 78篇 |
1985年 | 104篇 |
1984年 | 81篇 |
1983年 | 84篇 |
1982年 | 73篇 |
1981年 | 46篇 |
1980年 | 27篇 |
1979年 | 49篇 |
1978年 | 20篇 |
1977年 | 25篇 |
1976年 | 15篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
针对目前工业CT图像转换为3D打印G代码方法效率低的问题,提出一种基于邻层数据匹配的工业CT图像直接转换成G代码的方法。首先采用Canny算子提取工业CT图像的轮廓,然后处理轮廓分叉问题,实现邻层间几何信息数据匹配,其次进行邻层间轮廓插值以满足3D打印层间厚度要求,从而避免"阶梯效应",最后通过填充编码得到用于3D打印的G代码。使用本文提出的方法,轮毂CT图像转换为G代码的时间为10.5 s,耗时远小于其他间接转换方法;3D打印出的轮毂无"阶梯效应",平均尺寸误差率为0.25%。实验结果表明,该方法不涉及中间格式,转换效率高,转换误差与传统方法相当,适用于具有复杂内腔结构的零件。 相似文献
2.
To benefit from recent advances in modeling and computational algorithms,as well as the availability of new covariance data,sensitivity and uncertainty analyses are needed to quantify the impact of uncertain sources on the design parameters of small prismatic high-temperature gas-cooled reactors(HTGRs).In particular,the contribution of nuclear data to the keff uncertainty is an important part of the uncertainty analysis of small-sized HTGR physical calculations.In this study,a small-sized HTGR designed by China Nuclear Power Engineering Co.,Ltd.was selected for keff uncertainty analysis during full lifetime burnup calculations.Models of the cold zero power(CZP)condition and full lifetime burnup process were constructed using the Reactor Monte Carlo Code RMC for neutron transport calculation,depletion calculation,and sensitivity and uncertainty analysis.For the sensitivity analysis,the Contribution-Linked eigenvalue sensitivity/Uncertainty estimation via Track length importance Characterization(CLUTCH)method was applied to obtain sensitive infor-mation,and the"sandwich"method was used to quantify the keff uncertainty.We also compared the keff uncertainties to other typical reactors.Our results show that 235U is the largest contributor to keff uncertainty for both the CZP and depletion conditions,while the contribution of 239Pu is not very significant because of the design of low discharge burnup.It is worth noting that the radioactive capture reaction of 28Si significantly contributes to the keff uncer-tainty owing to its specific fuel design.However,the keff uncertainty during the full lifetime depletion process was relatively stable,only increasing by 1.12%owing to the low discharge burnup design of small-sized HTGRs.These numerical results are beneficial for neutronics design and core parameters optimization in further uncertainty prop-agation and quantification study for small-sized HTGR. 相似文献
3.
To enhance chemical stability and suppress of aggregation of magnetite nanoparticles (MNPs), which are used as a support for thermoresponsive copolymer immobilization, silica coating of the MNPs is applied via the electrooxidation method. Although the resulting silica coated-MNPs also formed aggregates, the size distribution of the aggregate shifted to smaller size range. Because of that, the surface area available for copolymer immobilization increased approximately 6.7 times at maximum as compared with that of the uncoated MNPs. It contributed to the increase of the amount of the immobilized copolymer on the silica-coated MNPs, which is approximately four times larger than that on the uncoated MNPs. Fe3O4 dissolution test confirmed enhancement of chemical stability of MNPs. The thermoresponsive copolymer immobilized on the silica-coated MNPs shows the ability to recycle Cu(II) ion from Cu(II) containing solution by changing temperature with significantly shorter time than those in other thermoresponsive adsorbents in gel form. 相似文献
4.
Since the discovery in 1922 of 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl stable free radical (DPPH·), the chemistry of such open-shell compounds has developed continuously, allowing for both theoretical and practical advances in the free radical chemistry area. This review presents the important, general and modern aspects of the chemistry of hydrazyl free radicals and the science behind it. 相似文献
5.
6.
Haijie Li Yuting Shang Wenrui Huang Bingfeng Xue Xiaomeng Zhang Zhe Cui Peng Fu Xinchang Pang Qingxiang Zhao Minying Liu 《应用聚合物科学杂志》2021,138(39):51017
Succinic acid is an important synthetic monomer but it is difficult to use it as a precursor for synthesizing high molecular weight polyamide, due to its tendency to perform intra-cyclization reaction at high temperature. In order to solve this problem, in this paper, the direct solid-state polymerization (DSSP) method with the initial reactant, nylon salt which was composed of 1, 5-diaminopentane, succinic acid, and terephthalic acid, was applied to synthesize the bio-based copolyamide PA 5T/54. In comparison with the conventional melting polymerization method, the DSSP method can prevent the cyclization reaction of succinic acid effectively due to the lower reacting temperature as well as the restriction effect of the nylon salt. As a result, the product fabricated by DSSP method has higher molecular weight and much lighter color from red to white. Therefore, the DSSP method is advantageous for the synthesis of the polymers or copolymers composed of the succinic acid as the monomer. Furthermore, the polymerization mechanism proposed in this work can serve as a guidance for the design of the molecular structure and control of the polymerization process. 相似文献
7.
An on-site laboratory with direct access to cleaned and conditioned steel mill gases was recently put into operation. The long-term performance and stability of Clariant's MegaMax®800 methanol synthesis catalyst utilizing steel mill gases is currently being investigated. First test results revealed that in order to investigate deactivation mechanisms arising from particular properties of the cleaned steel mill gases, the overlaying effect of thermal deactivation of the catalyst has to be minimized. 相似文献
8.
9.
Dr. Yan Zhang Dr. Bekir Engin Eser Prof. Dr. Zheng Guo 《Chembiochem : a European journal of chemical biology》2021,22(12):2146-2153
Recently discovered endogenous mammalian lipids, fatty acid esters of hydroxy fatty acids (FAHFAs), have been proved to have anti-inflammatory and anti-diabetic effects. Due to their extremely low abundancies in vivo, forging a feasible scenario for FAHFA synthesis is critical for their use in uncovering biological mechanisms or in clinical trials. Here, we showcase a fully enzymatic approach, a novel in vitro bi-enzymatic cascade system, enabling an effective conversion of nature-abundant fatty acids into FAHFAs. Two hydratases from Lactobacillus acidophilus were used for converting unsaturated fatty acids to various enantiomeric hydroxy fatty acids, followed by esterification with another fatty acid catalyzed by Candida antarctica lipase A (CALA). Various FAHFAs were synthesized in a semi-preparative scale using this bi-enzymatic approach in a one-pot two-step operation mode. In all, we demonstrate that the hydratase-CALA system offers a promising route for the synthesis of optically pure structure-diverse FAHFAs. 相似文献
10.
This paper analyses the perception of Artificial Intelligence (AI) by individuals in Spain and the factors associated with it. It uses data from 6308 individuals from a 2018 Spanish survey. A binary logit regression model is formulated and estimated for the attitude towards robots and AI and its possible determinants. As main results are that a gender gap is detected, and that people have a negative attitude if they are not interested in scientific discoveries and technological developments and if AI and robots are not useful at work. 相似文献