全文获取类型
收费全文 | 74129篇 |
免费 | 17352篇 |
国内免费 | 1467篇 |
专业分类
电工技术 | 2561篇 |
技术理论 | 2篇 |
综合类 | 2240篇 |
化学工业 | 23117篇 |
金属工艺 | 2445篇 |
机械仪表 | 2985篇 |
建筑科学 | 4627篇 |
矿业工程 | 917篇 |
能源动力 | 1683篇 |
轻工业 | 9166篇 |
水利工程 | 794篇 |
石油天然气 | 2638篇 |
武器工业 | 201篇 |
无线电 | 11377篇 |
一般工业技术 | 15898篇 |
冶金工业 | 2651篇 |
原子能技术 | 405篇 |
自动化技术 | 9241篇 |
出版年
2024年 | 144篇 |
2023年 | 627篇 |
2022年 | 943篇 |
2021年 | 1584篇 |
2020年 | 2434篇 |
2019年 | 3971篇 |
2018年 | 4001篇 |
2017年 | 4476篇 |
2016年 | 4849篇 |
2015年 | 5233篇 |
2014年 | 5519篇 |
2013年 | 7103篇 |
2012年 | 4780篇 |
2011年 | 4730篇 |
2010年 | 4794篇 |
2009年 | 4487篇 |
2008年 | 4020篇 |
2007年 | 3883篇 |
2006年 | 3646篇 |
2005年 | 3112篇 |
2004年 | 2529篇 |
2003年 | 2342篇 |
2002年 | 2258篇 |
2001年 | 1961篇 |
2000年 | 1966篇 |
1999年 | 1548篇 |
1998年 | 1008篇 |
1997年 | 877篇 |
1996年 | 851篇 |
1995年 | 654篇 |
1994年 | 569篇 |
1993年 | 399篇 |
1992年 | 351篇 |
1991年 | 269篇 |
1990年 | 206篇 |
1989年 | 172篇 |
1988年 | 141篇 |
1987年 | 109篇 |
1986年 | 87篇 |
1985年 | 64篇 |
1984年 | 62篇 |
1983年 | 34篇 |
1982年 | 39篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 37 毫秒
991.
Fabrication and characterization of PFSI/ePTFE composite proton exchange membranes of polymer electrolyte fuel cells 总被引:1,自引:0,他引:1
PFSI/ePTFE composite proton exchange membranes were fabricated by impregnating perfluorosulfonic acid resin (PFSI resin, Nafion) into chemically modified expanded PTFE (ePTFE) matrix. Chemical modification of sodium-naphthalene treatment and N-methylol acrylamide (NMA) grafting decreased the contact angle of the as-received ePTFE from 125 ± 0.5° to 67 ± 0.5°, effectively converting the as-received hydrophobic ePTFE to a hydrophilic ePTFE matrix. The composite membrane fabricated with the hydrophilic ePTFE have higher impregnated PFSI loading, much lower porosity and better PTFE/PFSI interface contact, as compared to the composite membranes with the as-received ePTFE. This leads to much lower gas permeability and significantly improves the durability under an accelerated dry/wet cycle test. The fuel cell made from the PFSI/ePTFE composite membranes with hydrophilic ePTFE showed superior performance as compared to that with the composite membrane made from the as-received ePTFE and Nafion 211 membrane. 相似文献
992.
993.
The photopolymerization of wood coatings under UV and visible light in industrial type conditions has been investigated. The inhibiting effect of the phenolic compounds found in wood extractives, especially quercetin, on the final properties of the coating (hardness, gel content) as well as the polymerization kinetics (rates, final conversion) has been discussed. Model clear‐coating formulations — based on an acrylate oligomer, a reactive diluent and a bis‐acylphosphine oxide as photo‐initiator — have been used. This article focuses on the influence of the nature of the acrylate oligomer (polyester, epoxy, polyurethane), the type of phenolic derivative (POHs) and the irradiation conditions (UV conveyor, Xe lamp). It appears that lead to through the strong inner‐filter effect in the presence of quercetin is responsible for the loss of all the observed properties. In order to mimic what happens at the wood–coating interface, the role of the diffusion of the phenolic derivatives have been also investigated and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3285–3298, 2007 相似文献
994.
采用气相色谱法,氢火焰离子化检测器,选用3%OV-17填充柱,正十三烷为内标,气化室和检测器温度为180℃,柱温120℃,对3溴4氟苯甲醛进行定量测定。该方法简单、快速、准确、适用,标准偏差0.26%,变异系数0.27%,平均回收率100.1%。 相似文献
995.
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
996.
A series of novel copolymers, poly(methacryloyl‐2‐oxy‐1,2,3‐propanetricarboxylic acid‐co‐exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthalic acid) [poly(MTCA‐co‐ETAc)], poly(methacryloyl‐2‐oxy‐1,2,3‐propanetricarboxylic acid‐co‐hydrogenethyl‐exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthalate) [poly(MTCA‐co‐HEET)], and poly(methacryloyl‐2‐oxy‐1,2,3‐propanetricarboxylic acid‐co‐α‐ethoxy‐exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthaloyl‐5‐fluorouracil) [poly(MTCA‐co‐EETFU)], were prepared from corresponding monomers by photopolymerizations at 25°C for 48 h. The polymers were identified by FTIR, 1H‐NMR, and 13C‐NMR spectroscopies. The number‐average molecular weights of the fractionated polymers determined by GPC were in the range from 9400 to 14,900 and polydispersity indices were 1.2–1.4. The in vitro IC50 values of polymers against mouse mammary carcinoma (FM3A), mouse leukemia (P388), and human histiocytic lymphoma (U937) as cancer cell lines and mouse liver cells (AC2F) as a normal cell line were much higher compared to that of 5‐fluorouracil (5‐FU). The in vivo antitumor activities of monomers and polymers against mice bearing sarcoma 180 tumor cell line were better than those of 5‐FU. The inhibition of DNA replication and antiangiogenesis activities of MTCA and copolymers were better compared to those of 5‐FU. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 57–64, 2004 相似文献
997.
998.
Water molecules adsorbed on a double-walled carbon nanotube (DWCNT) serve as charge trapping centers when present in low density and as electron donors when present in high density. There is a discontinuous change between the low- and high-density regions. H2O molecules are apt to be adsorbed on the outer surface of DWCNTs, and in this case the electrical transport properties are extremely sensitive to environment, which suggests that DWCNTs are hole doped and act as an electric dipole with the inner tube. 相似文献
999.
The thermal properties of amorphous gelatin films and gelatin films with renatured structural order were measured by using conventional and temperature modulated differential scanning calorimetry (DSC). Different amounts of gelatin structural order associated with a melting enthalpic change in the DSC measurement were prepared based on different gelatin drying conditions. Two consecutive heating and cooling DSC measurements on the gelatin films showed that there was no change in the glass‐transition temperature (Tg) for the amorphous gelatin but there was a decrease in the Tg for the structural gelatin on the second DSC scan. This decrease was attributed to the plasticizing effect from the release of originally hydrogen‐bonded water associated with the structural gelatin. In addition, a reversing endotherm observed upon melting of the structural gelatin during a temperature modulated DSC measurement indicated that the transition of bound water to free water occurred as the partial triple‐helix gelatin melted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1795–1801, 2006 相似文献
1000.
The row‐nucleated lamellar crystalline structure of high‐density polyethylene (HDPE) films was prepared by applying elongation stress to HDPE melt during T‐die cast film extrusion and subsequently annealing the extruded films. This unusual crystalline structure was analyzed in terms of lamellar crystalline orientation, long‐period lamellar spacing, crystallite size, and degree of crystallinity. The contribution of melt‐extension represented by draw‐down‐ratio (DDR) to the overall orientation was found to be most noticeable than other processing variables. Meanwhile, the long‐period lamellar spacing, the crystallite size, and the degree of crystallinity were influenced predominantly by the annealing temperature. Finally, the processing (melt extension and annealing temperature) – structure (lamellar crystalline structure) – property (hard elasticity) relationship of HDPE films was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3326–3333, 2007 相似文献