全文获取类型
收费全文 | 19747篇 |
免费 | 1043篇 |
国内免费 | 633篇 |
专业分类
电工技术 | 659篇 |
综合类 | 516篇 |
化学工业 | 1740篇 |
金属工艺 | 1114篇 |
机械仪表 | 537篇 |
建筑科学 | 887篇 |
矿业工程 | 300篇 |
能源动力 | 346篇 |
轻工业 | 811篇 |
水利工程 | 238篇 |
石油天然气 | 335篇 |
武器工业 | 65篇 |
无线电 | 1737篇 |
一般工业技术 | 1418篇 |
冶金工业 | 586篇 |
原子能技术 | 171篇 |
自动化技术 | 9963篇 |
出版年
2024年 | 34篇 |
2023年 | 137篇 |
2022年 | 255篇 |
2021年 | 371篇 |
2020年 | 288篇 |
2019年 | 274篇 |
2018年 | 290篇 |
2017年 | 313篇 |
2016年 | 344篇 |
2015年 | 377篇 |
2014年 | 674篇 |
2013年 | 899篇 |
2012年 | 1336篇 |
2011年 | 3697篇 |
2010年 | 1650篇 |
2009年 | 1513篇 |
2008年 | 1136篇 |
2007年 | 1006篇 |
2006年 | 894篇 |
2005年 | 998篇 |
2004年 | 909篇 |
2003年 | 943篇 |
2002年 | 574篇 |
2001年 | 496篇 |
2000年 | 414篇 |
1999年 | 233篇 |
1998年 | 259篇 |
1997年 | 186篇 |
1996年 | 132篇 |
1995年 | 151篇 |
1994年 | 119篇 |
1993年 | 80篇 |
1992年 | 39篇 |
1991年 | 51篇 |
1990年 | 40篇 |
1989年 | 52篇 |
1988年 | 33篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 18篇 |
1984年 | 41篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
M.S. Thompson Author Vitae Author Vitae 《Polymer》2008,49(2):345-373
Poly(ethylene oxide) (PEO) oligomers are employed extensively in pharmaceutical and biomedical arenas mainly due to their excellent physical and biological properties, including solubility in water and organic solvents, lack of toxicity, and absence of immunogenicity. PEO can be chemically modified and reacted with, or adsorbed onto, other molecules and surfaces. Sophisticated applications for PEO have increased the demand for PEO oligomers with tailored functionalities, and heterobifunctional PEOs are often needed. This review discusses the synthesis and applications of heterobifunctional PEO oligomers possessing amine, carboxylate, thiol, and maleimide functional groups. 相似文献
102.
Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (dj) and electrospun fiber diameter (df), and scaling laws existed between them, i.e., dj-Q0.61 and df-Q0.33. The diameter reduction ratios of Do/dj (Do is the needle diameter) and dj/df were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (ηo) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the ηo effect on the electrospinning process. Our results showed that the ηo-dependence of dj and df also followed simple scaling laws: dj-ηo0.06, and df-ηo0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation. 相似文献
103.
The effect of end groups (2NH2) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH2)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH3, and 2CH3)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH2) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH2) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH2)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH2)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
104.
Han‐Lang Wu Chen‐Chi M. Ma Chun‐Chieh Lin Yie‐Chan Chiu Chih‐Yuan Chen Chin‐Lung Chiang 《应用聚合物科学杂志》2008,107(5):3236-3243
Poly(arylene ether benzonitrile) (PAEBN) was synthesized with 2,6‐dichlorobenzonitrile and biphenol. PAEBNs with various molecular weights (MWs), 1,640,000 and 185,000 g/mol, were synthesized by control of the stoichiometry of the monomers and were blended with sulfonated poly(ether ether ketone) (SPEEK). The effects of MW on the water uptake, swelling, methanol permeability, and proton conductivity of the SPEEK/PAEBN blend membranes were investigated. The molecular mobility of the SPEEK/PAEBN blends was also examined in this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
105.
Dr Maher Boulos Author Vitae 《Metal Powder Report》2004,59(5):16-21
It may be a truism to say that round powders pack better, but spheroidisation of powder particles is one of the successful commercial applications of induction plasma technology and can play a key role in substantial improvement of powder quality and fluidity… 相似文献
106.
107.
A. Ardeshir Goshtasby Author Vitae 《Computer aided design》2003,35(5):487-494
Formulations for parametric circles and spheres in terms of rational Gaussian (RaG) curves and surfaces are introduced. With the proposed formulations, a full circle is generated by interpolating a closed RaG curve to the vertices of an equilateral triangle, and a full sphere is generated by interpolating a closed RaG surface to the vertices of an octahedron with equilateral triangular faces. Generation of circles and spheres in this manner is very intuitive and easy to remember as the weights are all 1 and the nodes are all unique and uniformly spaced. 相似文献
108.
109.
海洋钻井液有机物添加剂生物降解性评价 总被引:1,自引:0,他引:1
随着海洋石油的勘探开发,钻井液有机添加剂不可避免地进入海洋.因此在海洋勘探开发过程中应选择环保性能好,即生物降解性能好的有机物添加剂。用累计耗氧量法测定了海洋钻井液有机添加剂的生物降解性,研究评价了有机添加剂的生物降解规律和机理,探讨了有机物生物降解性同其化学结构的内在联系,为海洋勘探开发过程中选择环保性能好的有机物添加剂提供理论依据。总结实验结果发现:淀粉类(如DFD-140和FI-E1等)最容易生物降解;其次是纤维素类(如MV-CMC等)和烯类单体聚合物(如PAM和PHP);而沥青类、两性离子类则难以生物降解,有的甚至对生物降解起抑制作用。 相似文献
110.
Solution-chemistry analysis of ammonium bicarbonate consumption in rare-earth-element precipitation 总被引:2,自引:0,他引:2
R. Chi Z. Zhou Z. Xu Y. Hu G. Zhu S. Xu 《Metallurgical and Materials Transactions B》2003,34(5):611-617
A solution-chemistry analysis is applied to estimating the consumption of ammonium bicarbonate in the recovery of rare-earth
(RE) elements from leachates of weathered clays. The theoretical analysis shows that a two-step process is needed for recovering
RE from the leachates of the weathered clays by precipitation using ammonium bicarbonate. The first step is a precipitation
at solution pH 5 to remove impurities such as Fe and Al. The second step is to precipitate RE by adjusting the solution pH
above 8. The consumption of ammonium bicarbonate was found to depend on the concentration of RE elements and impurities in
the leachates. The total amount of ammonium bicarbonate consumption for the entire process was determined experimentally,
and the results showed an excellent agreement with that calculated based on solution-chemistry analysis. The decomposition
of H2CO3 was identified as one of the main causes of ammonium bicarbonate overdose, accounting for up to 41 pct in comparison to 20
pct consumption for the removal of impurities. The amount of ammonium bicarbonate required in terms of the NH4HCO3: RE2O3 (RE oxides) molar ratio was found to be 4:1 for maximal RE recovery. An overall RE recovery around 90 pct was achieved with
a product purity being about 90 pct. 相似文献