全文获取类型
收费全文 | 56539篇 |
免费 | 2727篇 |
国内免费 | 198篇 |
专业分类
电工技术 | 869篇 |
综合类 | 93篇 |
化学工业 | 10837篇 |
金属工艺 | 2068篇 |
机械仪表 | 3071篇 |
建筑科学 | 1236篇 |
矿业工程 | 52篇 |
能源动力 | 2157篇 |
轻工业 | 4067篇 |
水利工程 | 252篇 |
石油天然气 | 210篇 |
武器工业 | 1篇 |
无线电 | 10025篇 |
一般工业技术 | 11236篇 |
冶金工业 | 5817篇 |
原子能技术 | 632篇 |
自动化技术 | 6841篇 |
出版年
2023年 | 533篇 |
2022年 | 833篇 |
2021年 | 1405篇 |
2020年 | 992篇 |
2019年 | 1010篇 |
2018年 | 1334篇 |
2017年 | 1327篇 |
2016年 | 1649篇 |
2015年 | 1302篇 |
2014年 | 2031篇 |
2013年 | 3483篇 |
2012年 | 3196篇 |
2011年 | 3907篇 |
2010年 | 2977篇 |
2009年 | 3169篇 |
2008年 | 2917篇 |
2007年 | 2461篇 |
2006年 | 2244篇 |
2005年 | 1938篇 |
2004年 | 1850篇 |
2003年 | 1699篇 |
2002年 | 1651篇 |
2001年 | 1290篇 |
2000年 | 1205篇 |
1999年 | 1182篇 |
1998年 | 2195篇 |
1997年 | 1436篇 |
1996年 | 1204篇 |
1995年 | 961篇 |
1994年 | 724篇 |
1993年 | 683篇 |
1992年 | 490篇 |
1991年 | 494篇 |
1990年 | 417篇 |
1989年 | 404篇 |
1988年 | 321篇 |
1987年 | 275篇 |
1986年 | 254篇 |
1985年 | 231篇 |
1984年 | 199篇 |
1983年 | 151篇 |
1982年 | 152篇 |
1981年 | 130篇 |
1980年 | 129篇 |
1979年 | 102篇 |
1978年 | 94篇 |
1977年 | 123篇 |
1976年 | 158篇 |
1975年 | 80篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Polyamide/epoxysilane (coupling agent) composites were reacted with poly(dimethylsiloxane) (PDMS), a condensation product of diethoxydimethylsilane (DEDMS), by a sol–gel process. Polyamide–PDMS nanocomposites were obtained. The existence of the condensation product of DEDMS and the reaction between the epoxy group and the polyamide were confirmed with Fourier transform infrared, attenuated total reflection, and wide‐scanning X‐ray photoelectron spectroscopy. Atomic force microscopy and contact‐angle measurements showed that the surface properties of polyamide were greatly improved by the addition of PDMS. The pyrolysis temperature of polyamide with PDMS was approximately 400°C, and the pyrolysis temperature was similar to that of pure polyamide. Also, the char contents increased with the addition of PDMS. The glass‐transition temperature of polyamide with or without PDMS was approximately 140°C according to differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1947–1955, 2004 相似文献
952.
Ju-Yeon Lee 《Polymer Bulletin》1995,35(1-2):73-78
Summary 4-(2-Vinyloxyethoxy)-4-nitrostilbene 2 was prepared by the reaction of 4-hydroxy-4-nitrostilbene 1 with 2-iodoethyl vinyl ether. Monomer 2 was polymerized with cationic initiators to obtain a poly(ethyl vinyl ether) with the NLO-phore 4-oxy-4-nitrostilbene in the side chain. The resulting polymer 3 was soluble in common solvents such as chloroform and DMSO. The inherent viscosities of polymer 3 were in the range of 0.25–0.30 dL/g in chloroform. Polymer 3 showed a good thermal stability in TGA thermogram. Solution-cast films were cloudy and brittle with a Tg of 63°C. 相似文献
953.
A supercritical fluid extraction method has been applied to test the feasibility of tocopherol concentration from soybean
sludge with carbon dioxide at temperatures and pressures ranging from 35 to 70°C and 200 to 400 bar, respectively. The supercritical
solubility of the esterified soybean sludge was over 4–6 times greater than that of the original soybean sludge. By a simple
batch-type one-stage method the tocopherols in the esterified soybean sludge could be concentrated up to 40 wt%. The overall
results of the present study show that soybean sludge initially containing about 13–14 wt% tocopherols may require a countercurrent
multistage column to be highly and effectively concentrated. 相似文献
954.
Jin-Hae Chang Bong-Ku Choi Jae-Hoon Kim Soo-Min Lee Myung-Sik Bang 《Polymer Engineering and Science》1997,37(9):1564-1571
A thermotropic liquid crystalline polymer (LCP) with an alkyl side-group was synthesized. Blends of the LCP with polycarbonate (PC) were prepared by coprecipitatton from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of PC, and significant viscosity reductions were observed in the temperature range of 200–230°C. Blends of different LCP compositions were extruded with different draw ratio from a capillary rheometer. The ultimate tensile strength showed a maximum at a 10 wt% LCP composition in the blends. It decreased for compositions greater the 10 wt% LCP, whereas the initial modulus increased with increasing LCP content. The morphology of the blends was found to be affected by their compositions. Scanning electron microscopy (SEM) studies revealed finely dispersed spherical LCP domains in the PC matrix. The SEM micrographs also showed a poor adhesion between the two phases. 相似文献
955.
Hybrid materials based on a new polyhedral oligomeric silsesquioxane, octa(2,3-epoxypropyl)silsesquioxane (OE) with diamines of 4,4′-methylenedianiline (DDM) and 5-trifluoromethyl-1,3-phenylenediamine (FPA) were prepared and characterized. OE was synthesized from cage-structured octaallylsilsesquioxane (OA) with m-chloroperbenzoicacid. The FTIR studies suggested that the N-H bond in diamines was not completely reacted with epoxy group due to steric hindrance and also extensive hydrogen bonding existed in the hybrid materials. The retention of the cage structure in the prepared hybrid materials was suggested by the FTIR and 29Si NMR studies. The OE/FPA hybrid materials had superior thermal/mechanical characteristics than the OE/DDM due to the higher rigidity of the FPA than that of DDM or the silicon-fluorine interaction enhancing crosslinking reaction or hydrogen bonding. The prepared OE/FPA had a Tg of 170 °C, which was higher than diglycidyl ether of bisphenyl A (DGEBA)/DDM at the same stoichiometric ratio. It also had excellent thermal, mechanical, and dielectric characteristics with high storage modulus of 1.8 GPa (30 °C) and 0.3 GPa (250 °C), low coefficient of thermal expansion of 86 μm/m °C, and dielectric constant of 2.19. Thus, it can be high performance materials with potential applications for electronic packaging. 相似文献
956.
Ji Hye Yoon Sang Beom Choi You Jin Oh Min Jeong Seo Young Ho Jhon Tae-Bum Lee Daejin Kim Seung Hoon Choi Jaheon Kim 《Catalysis Today》2007,120(3-4):324-329
A new mixed-valent iron MOF, formulated as Fe3O(F4BDC)3(H2O)3·(DMF)3.5 (1), has been synthesized by using a perfluorinated linear dicarboxylate to link trigonal prismatic Fe3(μ3-O)(O2C–)6 clusters. The structure refinement based on single crystal X-ray diffraction data collected from 1 reveals the material exhibits the acs topology with large channels along the crystallographic c-axis. Due to the presence of fluorine atoms the organic link, 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylate (F4BDC), has a 63° torsion angle between the carboxylate and aromatic planes, resulting in larger channels compared to those in the isoreticular material MOF-235. While few iron-based MOFs have demonstrated porosity, nitrogen and hydrogen sorption experiments carried out at 77 K proved the porosity of outgassed 1, which has a Langmuir surface are of 635 m2/g and a gravimetric capacity of 0.9 wt% of hydrogen at 1 bar. 相似文献
957.
Hyun‐Ah Kang Gyu‐Jong Jeon Moo‐Yeal Lee Ji‐Won Yang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2002,77(2):205-210
A series of alginate‐derived polymeric surfactants (APSs) with a linear alkyl group (C8, C12, C16) was synthesized by oxidation followed by reductive amination of 2,3‐dialdehydic alginate. The products were characterized by measuring IR spectra, NMR spectra, surface tension and critical micelle concentration (cmc). They were also tested for the solubilization of azobenzene and adsorption of heavy metal. In the case of 40% CHO‐C8 APSs, the lowest interfacial tension value (31.5 m Nm?1) was obtained at the cmc value of 1.35 g dm?3. The dissolving capacity of 40% CHO‐C8 APS towards azobenzene was 27 times greater than that of alginate. The overall cobalt (Co2+) removal efficiency by adsorption using APSs was high compared with that of sodium alginate at pH 3, 5 and 7. Equilibrium aspects of cobalt adsorption onto 10% CHO‐APSs were studied, and the results show that APSs had high equilibrium capacities for cobalt uptake, 115.5 mgg?1. © 2002 Society of Chemical Industry 相似文献
958.
Summary Isothermal cure kinetics ofEPON HPT 1071/DDS system have been performed by means of differential scanning calorimetry. The maximum cure rate and the extent of conversion at various DDS concentrations were studied as a function of cure temperature. Maximum cure rate increases with increasing cure temperature and DDS concentration. At various DDS concentrations, the maximum cure rate occured between 19–22% conversion. In order to evaluate the kinetic parameters, numerical calculations by means of a Newton-Raphson technique and experimental results obtained from the peak of reaction rate curve were undertaken. 相似文献
959.
A high pressure differential scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer with a prism liquid cell (PLC) were used to monitor the reaction kinetics of styrene-unsaturated polyester resins at elevated curing temperatures and pressures. The thermal method is easy to perform but provides only an overall reaction exotherm. The spectroscopic method can detect the detailed reaction mechanism of copolymerizations. It is, however, less quantitative and the calculation is much more time-consuming compared to the thermal analysis. Reactions of two unsaturated polyester resins with different molecular structure were measured by these two methods. Results showed that applying cure pressure on unsaturated polyester resins reduced the reaction rate but increased the final conversion. The styrene reaction was enhanced more than the polyester reaction at high curing temperatures. 相似文献
960.