全文获取类型
收费全文 | 63387篇 |
免费 | 4323篇 |
国内免费 | 1085篇 |
专业分类
电工技术 | 1541篇 |
技术理论 | 3篇 |
综合类 | 1487篇 |
化学工业 | 11365篇 |
金属工艺 | 2075篇 |
机械仪表 | 2302篇 |
建筑科学 | 2962篇 |
矿业工程 | 1008篇 |
能源动力 | 1552篇 |
轻工业 | 6904篇 |
水利工程 | 832篇 |
石油天然气 | 1653篇 |
武器工业 | 162篇 |
无线电 | 4764篇 |
一般工业技术 | 10025篇 |
冶金工业 | 11674篇 |
原子能技术 | 422篇 |
自动化技术 | 8064篇 |
出版年
2024年 | 170篇 |
2023年 | 790篇 |
2022年 | 1001篇 |
2021年 | 1846篇 |
2020年 | 1468篇 |
2019年 | 1319篇 |
2018年 | 2242篇 |
2017年 | 2296篇 |
2016年 | 2284篇 |
2015年 | 1997篇 |
2014年 | 2570篇 |
2013年 | 4159篇 |
2012年 | 3830篇 |
2011年 | 3718篇 |
2010年 | 3133篇 |
2009年 | 2793篇 |
2008年 | 3049篇 |
2007年 | 2744篇 |
2006年 | 2330篇 |
2005年 | 2000篇 |
2004年 | 1627篇 |
2003年 | 1460篇 |
2002年 | 1395篇 |
2001年 | 1035篇 |
2000年 | 985篇 |
1999年 | 1197篇 |
1998年 | 3815篇 |
1997年 | 2404篇 |
1996年 | 1666篇 |
1995年 | 1067篇 |
1994年 | 941篇 |
1993年 | 850篇 |
1992年 | 375篇 |
1991年 | 339篇 |
1990年 | 282篇 |
1989年 | 277篇 |
1988年 | 260篇 |
1987年 | 212篇 |
1986年 | 211篇 |
1985年 | 231篇 |
1984年 | 196篇 |
1983年 | 140篇 |
1982年 | 172篇 |
1981年 | 181篇 |
1980年 | 160篇 |
1979年 | 135篇 |
1978年 | 121篇 |
1977年 | 201篇 |
1976年 | 417篇 |
1975年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Jianmou Lu Yanli Huang Shunyan Ren 《International Journal of Control, Automation and Systems》2020,18(5):1250-1263
This paper investigates the general decay synchronization and general decay H∞ synchronization problems of multi-weighted coupled reaction-diffusion 相似文献
73.
Ningning Fu Jiaxing Li Ming Wang Lili Ren Youqing Luo 《International journal of molecular sciences》2020,21(22)
An obligate mutualistic relationship exists between the fungus Amylostereum areolatum and woodwasp Sirex noctilio. The fungus digests lignin in the host pine, providing essential nutrients for the growing woodwasp larvae. However, the functional properties of this symbiosis are poorly described. In this study, we identified, cloned, and characterized 14 laccase genes from A. areolatum. These genes encoded proteins of 508 to 529 amino acids and contained three typical copper-oxidase domains, necessary to confer laccase activity. Besides, we performed molecular docking and dynamics simulation of the laccase proteins in complex with lignin compounds (monomers, dimers, trimers, and tetramers). AaLac2, AaLac3, AaLac6, AaLac8, and AaLac10 were found that had low binding energies with all lignin model compounds tested and three of them could maintain stability when binding to these compounds. Among these complexes, amino acid residues ALA, GLN, LEU, PHE, PRO, and SER were commonly present. Our study reveals the molecular basis of A. areolatum laccases interacting with lignin, which is essential for understanding how the fungus provides nutrients to S. noctilio. These findings might also provide guidance for the control of S. noctilio by informing the design of enzyme mutants that could reduce the efficiency of lignin degradation. 相似文献
74.
75.
Shuncheng Liu Kejian Wang Zhongfeng Zhang Yueqing Ren Lanlan Chen Xiaojie Sun Wenbin Liang 《Polymer Engineering and Science》2020,60(10):2640-2652
Three kinds of ethylene-octene copolymers (POE) were melt-blended with high-density polyethylene (PE-HD) in different proportions. Detailed characterizations were conducted to analyze their structural differences of POE and its effects in toughening PE-HD. The higher molecular weight POE can improve the toughness of PE-HD. 60:40 PE-HD/POE is elongated to break up to 700% while impact strength is 84.7 kJ/m2 at −30°C, which is 21-fold of PE-HD. In the brittle to ductile transition (BDT) during impact, the fracture mechanism changes from the crazing mode to the shear yield-plastic deformation mode. The BDT temperature decreases as the POE molecular weight and its content increase. The interface strength in tension is estimated to access their effects. The Boltzmann-type models were successfully extended to describe the typical S-shaped curves in BDT of notched impact strength vs POE content or temperature. The supplementary decay model is suggested for the attenuation in toughening. Transition map in impact is proposed to select the use range of composition (c ) and temperature (T ) for high toughness. The curves are converted into 3D graph of T -c -impact strength for illustrating their coupling-separate effects, and further into the contour map of impact strength in T -c space for finding their partial equivalence. 相似文献
76.
Ricardo Martínez-Corona Gerardo Vázquez Marrufo Carlos Cortés Penagos Luis Alberto Madrigal-Pérez Juan Carlos González-Hernández 《Yeast (Chichester, England)》2020,37(1):149-162
Lipases are hydrolytic enzymes that break the ester bonds of triglycerides, generating free fatty acids and glycerol. Extracellular lipase activity has been reported for the nonconventional yeast Kluyveromyces marxianus, grown in olive oil as a substrate, and the presence of at least eight putative lipases has been detected in its genome. However, to date, there is no experimental evidence on the physiological role of the putative lipases nor their structural and catalytic properties. In this study, a bioinformatic analysis of the genes of the putative lipases from K. marxianus L-2029 was performed, particularly identifying and characterizing the extracellular expected enzymes, due to their biotechnological relevance. The amino acid sequence of 10 putative lipases, obtained by in silico translation, ranged between 389 and 773 amino acids. Two of the analysed putative proteins showed a signal peptide, 25 and 33 amino acids long for KmYJR107Wp and KmLIP3p, and a molecular weight of 44.53 and 58.23 kDa, respectively. The amino acid alignment of KmLIP3p and KmYJR107Wp with the crystallized lipases from a patatin and the YlLip2 lipase from Yarrowia lipolytica, respectively, revealed the presence of the hydrolase characteristic motifs. From the 3D models of putative extracellular K. marxianus L-2029 lipases, the conserved pentapeptide of each was determined, being GTSMG for KmLIP3p and GHSLG for KmYJR107Wp; besides, the genes of these two enzymes (LIP3 and YJR107W) are apparently regulated by oleate response elements. The phylogenetic analysis of all K. marxianus lipases revealed evolutionary affinities with lipases from abH15.03, abH23.01, and abH23.02 families. 相似文献
77.
Li Wei Ren Yinghui Li Chenfang Li Zhipeng Li Maojun 《The International Journal of Advanced Manufacturing Technology》2020,106(3):921-935
The International Journal of Advanced Manufacturing Technology - The wear of micro-grinding tools less than 1 mm in diameter is crucial for achieving acceptable surface quality and accurate... 相似文献
78.
This study aims to evaluate the tribological behaviour of 3Y-TZP/Ta (20 vol%) ceramic-metal composites and 3Y-TZP monolithic ceramic prepared by spark plasma sintering (SPS) against ultrahigh molecular weight polyethylene (UHMWPE). According to the results of pin (UHMWPE)-on-flat wear test under dry conditions, the UHMWPE – 3Y-TZP/Ta system exhibited lower volume loss and friction coefficient than the UHMWPE – monolithic ceramic combination due to the presence of an autolubricating layer that provides sufficient lubrication for reducing the friction. Owing to the lubrication of the liquid media, under wet conditions obtained using simulated body fluid (SBF), similar behaviour is observed in both cases. Additionally, the ceramic and biocomposite materials were subjected to a low temperature degradation (LTD) process (often referred to as “ageing”) to evaluate the changes in the tribological behaviour after this treatment. In this particular case, the wear properties of the UHMWPE-biocomposite system were found to be less influenced by ageing in contrast to the case of the UHMWPE-zirconia monolithic material. In addition to their exceptional mechanical performance, 3Y-TZP/Ta composites also showed high resistance to low temperature degradation and good tribological properties, making them promising candidates for biomedical applications, especially for orthopaedic implants. 相似文献
79.
Yang Yang Yibei Zhou Juan Ren Qiaoji Zheng Kwok Ho Lam Dunmin Lin 《Journal of the European Ceramic Society》2018,38(2):557-566
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d33~400 pC/N), inverse piezoelectric coefficient (d33*~547 pm/V) and planar electromechanical coupling factor (kp~58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response. 相似文献
80.
Natural Computing - The fiber stretching process plays the key role in the process of fiber production and its effects is measured by the stretching ratio. The stretching ratio is determined by the... 相似文献