全文获取类型
收费全文 | 20290篇 |
免费 | 1439篇 |
国内免费 | 55篇 |
学科分类
工业技术 | 21784篇 |
出版年
2023年 | 261篇 |
2022年 | 138篇 |
2021年 | 648篇 |
2020年 | 475篇 |
2019年 | 540篇 |
2018年 | 655篇 |
2017年 | 698篇 |
2016年 | 818篇 |
2015年 | 683篇 |
2014年 | 964篇 |
2013年 | 1396篇 |
2012年 | 1424篇 |
2011年 | 1743篇 |
2010年 | 1278篇 |
2009年 | 1268篇 |
2008年 | 1130篇 |
2007年 | 938篇 |
2006年 | 793篇 |
2005年 | 708篇 |
2004年 | 684篇 |
2003年 | 578篇 |
2002年 | 526篇 |
2001年 | 411篇 |
2000年 | 349篇 |
1999年 | 322篇 |
1998年 | 544篇 |
1997年 | 340篇 |
1996年 | 265篇 |
1995年 | 177篇 |
1994年 | 172篇 |
1993年 | 134篇 |
1992年 | 101篇 |
1991年 | 80篇 |
1990年 | 76篇 |
1989年 | 80篇 |
1988年 | 49篇 |
1987年 | 49篇 |
1986年 | 34篇 |
1985年 | 38篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The novel hybrid polyoxazoline‐grafted multiwalled carbon nanotubes (POZO‐grafted MWNTs) were synthesized by the reaction of partially hydrolyzed polyoxazolines (Hydrolyzed‐POZO) and MWNTs having carboxylic acid groups (MWNT‐COOH) in the presence of DCC as a condensing agent. Hydrolyzed‐POZO (degree of hydrolysis, 20.2 mol % by 1H‐NMR) were produced from the hydrolysis of polyoxazolines in an aqueous NaOH solution at reflux for 72 h. MWNT‐COOH were prepared by acid treatment of pristine MWNTs. The composition, structure, thermal property, and surface morphology of the novel hybrid POZO‐grafted MWNTs were fully characterized by FT‐IR, Raman, 1H‐NMR, DSC, TGA, SEM, and TEM. The obtained POZO‐grafted MWNTs are well soluble in various organic solvents and water. It was observed that the glass transition temperature (Tg) of POZO‐grafted MWNTs was lower than that of Hydrolyzed‐POZO due to the absence of hydrogen bonding interactions between Hydrolyzed‐POZO itself caused by the incorporation with MWNTs. It was also found that Hydrolyzed‐POZO was homogeneously attached to the surfaces of MWNTs through the “grafting‐to” method. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
992.
Recent experiments on the observation of collisions of single nanoparticles (NPs) with an electrode through amplification of the current by electrocatalysis are described. Systems in which the particles adhere to the electrode upon collision produce a step and staircase response, while those in which particles only interact for a short time with the electrode produce a spike or blip, with little change in the steady state current. Examples of both behaviors, e. g., Pt NPs on a Au electrode for hydrazine oxidation (staircase response) and IrOx NPs on a Pt electrode for water oxidation (blip response) are shown. Controlling the nature of the electrode surface is important in generating useful responses, for example, in the case of gold NPs on an oxidized Pt electrode for borohydride oxidation. 相似文献
993.
This article presents the ternary phase diagram for methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and n‐hexane system at 70°C. It was constructed by both theoretical calculations and online laser light scattering (LLS) technique. In situ polymerization of MMA in a nonpolar nonsolvent carried out in a LLS cell provides a new means for the accurate detection of the cloud points of highly viscous polymer mixtures, with polymer weight fractions over 0.6. The ternary phase diagram measured in this study can be used to design the reaction conditions for the precipitation and/or dispersion polymerization in a nonpolar nonsolvent medium where polymerization kinetics as well as polymer particle morphologies are strongly affected by thermodynamic phase separation phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
994.
Cheol Soo Choi Pushpankur Ghoshal Malathi Srinivasan Sheene Kim Gary Cline Mulchand S. Patel 《Lipids》2010,45(11):987-995
The pyruvate dehydrogenase complex (PDC) plays a critical role in lipid synthesis and glucose homeostasis in the fed and fasting
states. The central role of the liver in the maintenance of glucose homeostasis has been established by studying changes in
key enzymes (including PDC) and the carbon-flux via several pathways under different metabolic states. In the present study
we have developed a murine model of liver-specific PDC deficiency using Cre-loxP technology to investigate its consequences
on lipid and carbohydrate metabolism. There was no incorporation of glucose-carbon into fatty acids by liver in vitro from
liver-specific Pdha1 knockout (L-PDHKO) male mice due to absence of hepatic PDC activity. Interestingly, there was a compensatory increase in
lipogenic capacity in epididymal adipose tissue from L-PDHKO mice. Both fat and lean body mass were significantly reduced
in L-PDHKO mice, which might be explained by an increase in total energy expenditure compared with wild-type littermate mice.
Furthermore, both liver and peripheral insulin sensitivities measured during a hyperinsulinemic-euglycemic clamp were improved
in L-PDHKO mice. The findings presented here demonstrate (i) the indispensable role of PDC for lipogenesis from glucose in
liver and (ii) specific adaptations in lipid and glucose metabolism in the liver and adipose tissue to compensate for loss
of PDC activity in liver only. 相似文献
995.
Lubomír Pospíšil Magdaléna Hromadová Jana Bulí?ková Salvatore Filippone Zhu Guan Yongmin Zhang 《Carbon》2010,48(1):153-1408
The formal redox potentials of electron transfer reactions of fullerene, methanofullerene, fullerene-cyclodextrin complex and methanofullerene conjugates with cyclodextrins in aqueous and dimethylsulfoxide solutions are reported. These new compounds are surface active and retain the redox activity of C60 even in aqueous medium. Compounds have been characterized by an electrochemical admittance technique, which offers an advantage of separating faradaic and capacitive properties. Observed difference of formal redox potentials of the free fullerene forms and their cyclodextrin-containing compounds were used to determine the binding enhancement. Results are interpreted in terms of inter-molecular host-guest interactions of C60-cyclodextrin conjugates. 相似文献
996.
Simple preparation of ordered mesoporous carbons assisted by an organosilicate as a linking material
Wooyoung Kim Nam Dong Kim Mi Yeong Kang Ji Bong Joo In Kyu Song Jung Rag Yoon Jongheop Yi 《Carbon》2010,48(15):4566-4569
Ordered mesoporous carbon materials (OMCs) were prepared from a silica–carbon composite assisted by 3-mercaptopropyltrimethoxysilane (MPTMS) in an aqueous phase. The obtained OMCs have a high surface area, large pore volume and uniform pore structure. MPTMS plays an important role in linking the polymer part with silica part to form a mesoporous structure. Importantly, the amount of MPTMS used is an important determinant in the development of a uniform mesoporosity. The method described herein has some important advantages over existing methods, such as simplified synthesis steps for the preparation of OMCs, the fact that the aqueous phase can be used and that the resulting materials have a high surface area of more than 1700 m2/g. 相似文献
997.
Bokkyu Choi 《Electrochimica acta》2010,55(28):8771-6701
Fuel cell/battery (FCB) systems are promising power generation/energy storage systems because of their bi-functionality as fuel cells and as secondary batteries. We investigated the required charging after the discharged manganese dioxide (MnOOH) by oxygen gas under the rest condition and during the fuel cell operation mode using manganese dioxide as a positive electrode for the FCB system. Electrochemical characterization was performed using cyclic voltammetry and galvanostatic measurements. Additionally, changes in the crystal structure and the chemical functional groups during the electrode reactions were monitored by X-ray diffractometry and Fourier transform infrared spectroscopy. The results indicated that MnOOH formed via the electrochemical discharge of manganese dioxide (MnO2) and that the oxyhydroxide can be chemically transformed back to MnO2 with gaseous oxygen (O2). The recharged MnO2 can be used as the cathode in a fuel cell with an O2 supply and it can also be electrochemically discharged without an O2 supply. In addition, we confirmed that MnO2 does not convert to Mn3O4 during the charge/discharge cycles if the redox reaction is maintained within a restricted range where a homogeneous process exists between MnO2 and MnOOH. The results in this study suggest that the FCB system can be constructed using MnO2 as the positive electrode and a metal hydride (MH) as the negative electrode, which can be rapidly charged to more than 70% of the theoretical capacity within 10 min using pressurized H2 and electrochemically discharged, in an alkaline electrolyte. This system possesses a high-power generation efficiency, a high-energy density and a high load-following capability. 相似文献
998.
Spinel lithium manganese oxide was synthesized via co-precipitation. The prepared lithium manganese oxide powder was further heated at 700 °C for 15 h under pressurized (3 bar) oxygen atmosphere. The resultant exhibited a highly crystalline cubic spinel phase with space group Fd3m, as confirmed by X-ray diffraction. The spinel compound exhibited a slightly smaller lattice constant than a conventional spinel compound, even though the cationic ratio of Li/Mn is the same for both compounds. Chemical titration of the Mn component showed that heat treatment under a 3 bar oxygen atmosphere resulted in slightly higher average Mn oxidation state, indicating that the amount of Mn4+ increased after the treatment. The Li1.05Mn1.95O3.99 electrode exhibited improved cycling performance, namely, 96.3% of capacity retention during 100 cycles at elevated temperature (60 °C). The details of the structure and electrochemistry of the electrode are discussed. 相似文献
999.
1000.
IhnSung Cho IlHyun Beak JaeCheon Jo JuMi Park SeokHyung Oh JaeYoun Jung 《Journal of Mechanical Science and Technology》2010,24(6):1363-1368
The bent-axis type of piston pump driven by the piston rod works by the piston rod driving the cylinder block; because of
this the taper angle of the piston rod and the swivel angle between the cylinder block and the shaft are important design
factors. If these factors cannot satisfy the conditions for optimum design, the friction loss between the cylinder bore and
the piston increases, and the pump can fail to work under conditions of severe friction and wear. Since the piston reciprocates
in the cylinder bore with high velocity, at the same time rotating on its own axis and revolving on the center of the cylinder
block, a decrease of the volume efficiency is generated because of the leakage between the cylinder bore and the piston. Therefore,
to prevent this, the piston ring is designed to be at the end of the piston, and the friction characteristics between the
piston ring and the cylinder bore require further research due to their great influence on the performance of the piston pump.
Thus, in this paper, the elastohydrodynamic lubrication (EHL) analysis of the film thickness, the pressure distribution, and
the friction force, have been studied between the piston ring and the cylinder bore in the bent-axis type of piston pump.
The analyzed results show that the friction force is influenced by the rotating speed and the discharge pressure. 相似文献