全文获取类型
收费全文 | 26430篇 |
免费 | 2296篇 |
国内免费 | 1034篇 |
专业分类
电工技术 | 1437篇 |
技术理论 | 1篇 |
综合类 | 1544篇 |
化学工业 | 4538篇 |
金属工艺 | 1543篇 |
机械仪表 | 1553篇 |
建筑科学 | 2123篇 |
矿业工程 | 783篇 |
能源动力 | 778篇 |
轻工业 | 1894篇 |
水利工程 | 471篇 |
石油天然气 | 1293篇 |
武器工业 | 208篇 |
无线电 | 2954篇 |
一般工业技术 | 3414篇 |
冶金工业 | 1215篇 |
原子能技术 | 354篇 |
自动化技术 | 3657篇 |
出版年
2024年 | 139篇 |
2023年 | 530篇 |
2022年 | 879篇 |
2021年 | 1224篇 |
2020年 | 976篇 |
2019年 | 763篇 |
2018年 | 800篇 |
2017年 | 998篇 |
2016年 | 856篇 |
2015年 | 1094篇 |
2014年 | 1294篇 |
2013年 | 1596篇 |
2012年 | 1637篇 |
2011年 | 1785篇 |
2010年 | 1493篇 |
2009年 | 1413篇 |
2008年 | 1350篇 |
2007年 | 1253篇 |
2006年 | 1238篇 |
2005年 | 1201篇 |
2004年 | 759篇 |
2003年 | 666篇 |
2002年 | 585篇 |
2001年 | 501篇 |
2000年 | 531篇 |
1999年 | 633篇 |
1998年 | 594篇 |
1997年 | 470篇 |
1996年 | 508篇 |
1995年 | 417篇 |
1994年 | 347篇 |
1993年 | 267篇 |
1992年 | 207篇 |
1991年 | 173篇 |
1990年 | 124篇 |
1989年 | 102篇 |
1988年 | 99篇 |
1987年 | 66篇 |
1986年 | 45篇 |
1985年 | 33篇 |
1984年 | 31篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1972年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Bearing performance degradation assessment based on lifting wavelet packet decomposition and fuzzy c-means 总被引:4,自引:0,他引:4
Bearing performance degradation assessment is crucial to realize condition-based maintenance. In this paper, a new method for it is proposed based on lifting wavelet packet decomposition and fuzzy c-means. Feature vectors are composed of the node energies of lifting wavelet packet decomposition. Normal and final failure data are used as training samples to build assessment model utilizing fuzzy c-means, and the subjection of tested data to normal state is defined as the degradation indicator, which has intuitionistics explanation related to degradation degree. Results of its application to accelerated bearing life test show that this indicator can reflect effectively performance degradation of bearing. And after discussing the influence of outliers in training set, a robust strategy is proposed. 相似文献
992.
潘政文 《智能建筑电气技术》2009,3(5):81-83
通过分析试验和检查用消火栓的功能要求,指出该处消火栓设置按钮的必要性,从防雷电电磁脉冲角度提出了试验和检查用消火栓按钮的设置原则;通过对设计上常用的消火栓按钮接线方式的分析,提出了消火栓按钮接线的最佳方案。 相似文献
993.
Biochemical characteristics and thermal inhibition kinetics of polyphenol oxidase extracted from Thompson seedless grape 总被引:2,自引:0,他引:2
Polyphenol oxidase (PPO) was isolated from Thompson seedless grape (Vitis vinifera ‘Thompson Seedless’), and its biochemical characteristics were studied. The PPO showed activity to catechol and D, L-DOPA, but not towards monophenol
l-Tyrosine, diphenols guaiacol and caffeic acid, and triphenols pyrogallic acid and gallic acid. Apparent Michaelis–Menten
constant (K
m) and maximum velocity of the reaction (V
max) values were 45.0 ± 0.05 mM and 500.0 ± 15.3 OD400 nm/min for catechol, and 34.6 ± 0.03 mM and 384.6 ± 11.7 OD478 nm/min for D, L-DOPA, respectively. The obtained similar specificity values of V
max/K
m ratio of catechol and D, L-DOPA indicated their similar affinity to Thompson seedless PPO. The most effective inhibitor was
l-cysteine, followed in decreasing order by ascorbic acid, sodium metabisulfite, EDTA, NaCl, and citric acid. It was discovered
that metal ions of Mg2+ and Cu2+ increased, while Zn2+ and K+ reduced the PPO activity. Sugars showed inhibition on the PPO activity, with higher effect by sucrose and lower effect by
fructose and glucose. Optimum pH and temperature for grape PPO activity were 6.0 and 25 °C with 10 mM catechol as substrate.
The enzyme was heat stable between 10 and 25 °C, but showed significant activity loss at temperatures higher than 40 °C and
completely inactivation at 70 °C for 10 min. Thermal inactivation of PPO showed a first-order kinetic with an activation energy
(E
a) of 146.1 ± 10.8 kJ/mol at pH 6.0. 相似文献
994.
Qiu P Guan H Dong P Li S Ho CT Pan MH McClements DJ Xiao H 《Molecular nutrition & food research》2011,55(4):613-622
Scope: Previously, we reported that 5‐hydroxy polymethoxyflavones (5OH‐PMFs) isolated from orange, namely 5‐hydroxy‐6,7,8,3′,4′‐pentamethoxyflavone, 5‐hydroxy‐3,6,7,8,3′,4′‐hexamethoxyflavone (5HHMF) and 5‐hydroxy‐6,7,8,4′‐tetramethoxyflavone (5HTMF), potently induced apoptosis and cell‐cycle arrest in multiple human colon cancer cells. Herein, using isogenic variants of HCT116 human colon cancer cells, we investigated the effects of p53, Bax and p21 on the apoptosis and cell‐cycle arrest induced by different 5OH‐PMFs. Methods and results: Annexin V/PI co‐staining assay demonstrated that 5HHMF and 5HTMF significantly induced apoptosis in HCT116 (p53+/+) cells but not in HCT116 (p53?/?) cells. Furthermore, 5HHMF and 5HTMF significantly induced apoptosis in HCT116 (Bax+/?) cells, whereas their pro‐apoptotic effects on HCT116 (Bax?/?) cells were marginal. All three 5OH‐PMFs increased G0/G1 cell population of HCT116 (p53+/+) cells, and these effects were abolished in HCT116 (p53?/?) and HCT116 (p21?/?) cells. Immunoblotting analysis showed that 5HHMF and 5HTMF increased the levels of cleaved caspase‐3, cleaved PARP in both HCT116 (p53+/+) and HCT116 (Bax+/?) cells and these effects were much weaker in HCT116 (p53?/?) and HCT116 (Bax?/?) cells. Conclusion: Our results demonstrated that 5OH‐PMFs, especially 5HHMF and 5HTMF, induce apoptosis and cell‐cycle arrest by p53‐, Bax‐ and p21‐dependent mechanism. 相似文献
995.
Rongrong Huang Xiaodan Pan Jingang Lv Wei Zhong Fang Yan Feixia Duan 《International Journal of Food Properties》2018,21(1):2193-2204
The objective of this study was to investigate the effects of explosion puffing on the nutritional composition, physical properties, and digestibility of grains including millet, barley, black rice, rice, glutinous rice, and wheat. Explosion puffing of grains resulted in the nutritional composition with higher total sugar content and lower moisture, starch and fat contents. Although the protein content scarcely changed comparing with the untreated grains, the solubility declined significantly. Moreover, explosion puffing could significantly improve the physical properties including the water absorption index, water solubility index and gelatinization degree. The in vitro digestion experiment was employed to investigate the influences of explosion puffing on the starch hydrolysis rate and free amino acid content, and it was indicated that the digestibility of the starch and protein in grains was highly improved. The results demonstrated that explosion puffing is a suitable technique to improve the physical properties and digestibility of grains, which provided the theoretic foundation for the use of explosion puffing technology in coarse cereal processing. 相似文献
996.
997.
Xiaolin Yao Xinrong Zhu Siyi Pan Yapeng Fang Fatang Jiang Glyn O. Phillips Xiaoyun Xu 《Food chemistry》2012
The inhibitory activities of two polymethoxylated flavone (PMFs) monomers (nobiletin and tangeretin) have been investigated against Pseudomonas fluorescens and Pseudomonas aeruginosain vitro. The effects on cell morphology, the release of cell constituents, the synthesis of proteins and the activities of key dehydrogenase were examined to elucidate their antibacterial mechanism. The concentration of transaminase and reducing sugar in bacterial solutions increased significantly when treated with nobiletin and tangeretin. Electron microscopy showed that the structure of the bacterial cells was destroyed and accompanied with induced cells plasmolysis. Nobiletin and tangeretin also inhibited the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), and reduced proteins synthesis in bacterial cells. It is proposed that nobiletin and tangeretin destroyed the permeability of the cell membrane, with release of the cell constituents, leading to metabolic dysfunction, inhibition of protein synthesis, and eventually to cell pyknosis and death. 相似文献
998.
999.
报道了8种新型双核穴合物的合成,通过1HNMR、ES-MS、IR以及元素分析对其结构进行了确证.结果证明,[Cu2L](ClO4)2·MeCN具有螺旋结构,其他双核穴合物中SCN-或OH-离子与金属离子配位. 相似文献
1000.