全文获取类型
收费全文 | 526篇 |
免费 | 50篇 |
国内免费 | 81篇 |
专业分类
电工技术 | 54篇 |
综合类 | 26篇 |
化学工业 | 106篇 |
金属工艺 | 73篇 |
机械仪表 | 19篇 |
建筑科学 | 39篇 |
矿业工程 | 23篇 |
能源动力 | 12篇 |
轻工业 | 44篇 |
水利工程 | 12篇 |
石油天然气 | 55篇 |
武器工业 | 3篇 |
无线电 | 40篇 |
一般工业技术 | 95篇 |
冶金工业 | 12篇 |
原子能技术 | 8篇 |
自动化技术 | 36篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 28篇 |
2021年 | 32篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 26篇 |
2014年 | 30篇 |
2013年 | 31篇 |
2012年 | 41篇 |
2011年 | 37篇 |
2010年 | 33篇 |
2009年 | 21篇 |
2008年 | 33篇 |
2007年 | 26篇 |
2006年 | 32篇 |
2005年 | 19篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有657条查询结果,搜索用时 15 毫秒
11.
采用碱处理法制备了多级孔ZSM-5分子筛,并分别以多级孔ZSM-5分子筛和常规ZSM-5分子筛作为酸性组分制备了加氢裂化催化剂。采用氮气吸附-脱附、X射线衍射光谱、吡啶吸附红外光谱、氨气吸附-脱附、透射电镜等分析手段对分子筛样品进行表征。采用高压固定床微型反应装置对四氢萘在加氢裂化催化剂上的加氢裂化反应性能进行评价。结果表明:在反应温度350 ℃、氢分压4
MPa、氢/油体积比500/1、质量空速5.9 h-1、反应时间2 h的反应条件下,与常规ZSM-5分子筛加氢裂化催化剂相比,多级孔ZSM-5分子筛加氢裂化催化剂对四氢萘的转化率提升了10百分点以上,BTX收率提升了2~8百分点,开环反应选择性提高了约20百分点。这是因为介孔的引入提高了四氢萘对分子筛内部酸性位点的可接近性,是提高其开环反应选择性和BTX收率的关键因素。 相似文献
12.
13.
综合能源系统包含了大量的不确定因素,因此需要考虑综合能源系统在不确定环境下的运行状态。文中基于解析法和近似法,提出一种辐射状供热网络概率潮流快速计算方法。首先通过正态分布函数的数字特征得到管道流量的均值与方差,然后利用连续型随机变量的性质得到了节点温度的均值与方差,当求得热电联产机组热出力概率分布后可得机组电出力概率分布,最后求得电网各状态变量的概率分布。文中方法不需要迭代即可计算出稳态潮流与概率潮流,且不存在收敛性问题。该方法能在保证计算精度的同时,极大地提高计算速度,可为综合能源系统的不确定性分析和风险评估提供参考。 相似文献
14.
Jiaxiang Guo Zhiyong Yuan Xiangyun Liao Yaoyi Bai Qianfeng Lai 《Computer Animation and Virtual Worlds》2015,26(3-4):337-345
The vessel wall and the blood flow interact and influence each other, and real‐time coupling between them is of great importance to the virtual surgery as well as the research and diagnosis of vascular disease. On the basis of smoothed particle hydrodynamics (SPH), we present a new approach to solve non‐Newtonian viscous force of blood and a parallel mixed particles‐based coupling method for blood flow and vessel wall. Meanwhile, we also design a proxy particle‐based vessel wall force visualization method. Our method is as follows. Firstly, we solve the non‐Newtonian viscous forces of blood through the SPH method to discretize the Casson equation. Secondly, in each time step, we combine blood particles and sampling proxy particles on the blood vessel wall to form mixed particles and calculate the interaction forces through the SPH method between every pair of the neighboring mixed particles inside the graphics processing unit. Thirdly, the forces of the proxy particles will be mapped to the color display of the proxy particle. Experimental results demonstrate that our method is able to implement real‐time sizeable coupling of blood flow and vessel wall while mainly ensuring physical authenticity and it can also provide real‐time and obvious information about vessel wall force distribution. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
Xiangyun Wang Hu Zhang Hao Xu Peipei Qi Xiaofeng Ji Qiang Wang Xinquan Wang 《Food Analytical Methods》2013,6(1):133-140
Currently, methamidophos, the main metabolite of acephate in the plants, has been paid particular attention in the risk evaluation of acephate because of its severely accurate toxicity, but the chirality of methamidophos and acephate has not been taken into account. In this study, a chiral separation and analysis method was developed to help evaluate the risks posing to the environment and human health. The efficiency of four commercial chiral capillary columns to accomplish enantioseparation of these two pesticides was firstly evaluated, and the chromatographic condition on the chose column BGB-176 SE was optimized. An analytical method for determination and confirmation of the enantiomers in vegetables by gas chromatography–tandem mass spectrometry was then developed with the column. QuEChERS was adopted to extract and clean the residues in vegetables. The mean recovery rates of quintuplicate results in cabbage and pakchoi ranged from 71.87 to 81.45 %; the relative standard deviation was less than 8.81 %. The limits of detection of enantiomers of acephate and methamidophos were 0.008 and 0.005 mg/kg, respectively. After the application of the method to vegetables from a market, it was proved that the metabolism of acephate and methamidophos in plants should be enantioselective. 相似文献
16.
17.
Growth of carbon nanotubes on natural organic precursors by chemical vapor deposition 总被引:1,自引:0,他引:1
Some plant tissues are rich in transition metal Fe. So, we explored the use of black jew’s-ear fungus and black sesame seeds as catalyst precursors to prepare carbon nanotubes by chemical vapor deposition. Each catalyst particle arises from the metal content of a single cell of the precursor, hence the distribution of catalyst particles is uniform. Their size and composition are almost identical. Carbon nanotube arrays can grow when black sesame seeds are used as catalyst precursors. Carbon nanotubes with diameters 80 nm and length greater than 100 μm can grow when black jew’s-ear fungus are used. 相似文献
18.
Yaofeng Li Xiangyun Chen Xiaofang Tang Chundong Zhang La Wang Peng Chen Minhui Pan Cheng Lu 《International journal of molecular sciences》2015,16(3):6266-6280
Silk gland cells undergo multiple endomitotic cell cycles during silkworm larval ontogeny. Our previous study demonstrated that feeding is required for continued endomitosis in the silk gland cells of silkworm larvae. Furthermore, the insulin signaling pathway is closely related to nutritional signals. To investigate whether the insulin signaling pathway is involved in endomitosis in silk gland cells, in this study, we initially analyzed the effects of bovine insulin on DNA synthesis in endomitotic silk gland cells using 5-bromo-2''-deoxyuridine (BrdU) labeling technology, and found that bovine insulin can stimulate DNA synthesis. Insulin signal transduction is mainly mediated via phosphoinositide 3-kinase (PI3K)/Akt, the target of rapamycin (TOR) and the extracellular signal-regulated kinase (ERK) pathways in vertebrates. We ascertained that these three pathways are involved in DNA synthesis in endomitotic silk gland cells using specific inhibitors against each pathway. Moreover, we investigated whether these three pathways are involved in insulin-stimulated DNA synthesis in endomitotic silk gland cells, and found that the PI3K/Akt and TOR pathways, but not the ERK pathway, are involved in this process. These results provide an important theoretical foundation for the further investigations of the mechanism underlying efficient endomitosis in silk gland cells. 相似文献
19.
超滤膜污染的成因及模型表征研究进展 总被引:1,自引:0,他引:1
文章从超滤膜的理化性质、分离的料液性质和运行操作条件三方面介绍了超滤膜污染的成因,阐述了膜污染的数学模型研究概况,并对膜污染未来的研究方向进行了展望。 相似文献
20.