全文获取类型
收费全文 | 54968篇 |
免费 | 6419篇 |
国内免费 | 2767篇 |
专业分类
电工技术 | 1321篇 |
技术理论 | 9篇 |
综合类 | 3104篇 |
化学工业 | 22723篇 |
金属工艺 | 3172篇 |
机械仪表 | 1311篇 |
建筑科学 | 2452篇 |
矿业工程 | 1068篇 |
能源动力 | 2554篇 |
轻工业 | 4246篇 |
水利工程 | 313篇 |
石油天然气 | 3645篇 |
武器工业 | 294篇 |
无线电 | 2933篇 |
一般工业技术 | 10387篇 |
冶金工业 | 2995篇 |
原子能技术 | 530篇 |
自动化技术 | 1097篇 |
出版年
2024年 | 357篇 |
2023年 | 1406篇 |
2022年 | 2338篇 |
2021年 | 2415篇 |
2020年 | 2207篇 |
2019年 | 2069篇 |
2018年 | 1869篇 |
2017年 | 2049篇 |
2016年 | 2232篇 |
2015年 | 2091篇 |
2014年 | 3124篇 |
2013年 | 3417篇 |
2012年 | 3892篇 |
2011年 | 4080篇 |
2010年 | 2978篇 |
2009年 | 3068篇 |
2008年 | 2423篇 |
2007年 | 3109篇 |
2006年 | 3053篇 |
2005年 | 2580篇 |
2004年 | 2174篇 |
2003年 | 1934篇 |
2002年 | 1560篇 |
2001年 | 1290篇 |
2000年 | 1161篇 |
1999年 | 917篇 |
1998年 | 809篇 |
1997年 | 604篇 |
1996年 | 537篇 |
1995年 | 440篇 |
1994年 | 375篇 |
1993年 | 295篇 |
1992年 | 243篇 |
1991年 | 203篇 |
1990年 | 169篇 |
1989年 | 96篇 |
1988年 | 75篇 |
1987年 | 75篇 |
1986年 | 54篇 |
1985年 | 93篇 |
1984年 | 78篇 |
1983年 | 70篇 |
1982年 | 59篇 |
1981年 | 6篇 |
1980年 | 16篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 9篇 |
1959年 | 6篇 |
1951年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Using nickel-2,2′-dipyridyl complex as a template, N-vinyl-2-pyrrolidone as the metal coordination functional monomer, and ethylene glycol dimethacrylate as the crosslinker, polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membrane as the supported membrane, metal complex imprinted polymeric membranes were prepared. The association constant of template-monomer interaction in the prepolymerization solution was estimated to be 4.38 × 104 (L/mol)2 by spectrophotometric titration analysis. The attenuated total reflection Fourier transform infrared spectroscopy and scanning electron micrograph characterization indicated that the surface of the support PVDF membrane was completely coated by the imprinted polymer layer after modification. The imprinted membranes exhibited the selective permeability for the template in certain nickel acetate solution. The molecularly imprinted membranes gave higher permeation separation factors at about pH 6, whereas increasing pressure would lower the separation ability. The effects of ion concentration, cations and counterions, ligand selectivity, pH, and trans-membrane pressure were investigated and the permeation performances of the imprinted membranes could be regarded as facilitated transport mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
82.
T. Jeevananda Siddaramaiah Taek Su Lee Joong Hee Lee O. M. Samir R. Somashekar 《应用聚合物科学杂志》2008,109(1):200-210
Polyaniline/carboxylated multi-walled carbon nanotube (PAni/c-MWNT) nanocomposites have been synthesized by micellar aided emulsion polymerization with various c-MWNTs compositions, viz., 0.5, 1, 5, and 10 wt %. The microcrystalline parameters such as the nanocrystal size (〈N〉), lattice strain (g), interplanar distance (dhkl), width of the crystallite size distribution, surface weighted crystal size (Ds), and volume of the ordered regions were calculated from the X-ray data by using two mathematical models, namely the Exponential distribution and Reinhold distribution methods. The effects of heat ageing on the microcrystalline parameters of the PAni/c-MWNT nanocomposites were also studied and the results are correlated. The thermal stability and electrical resistivity of the PAni/c-MWNT nanocomposites were examined with thermogravimetric analysis (TGA) and a conventional two-probe method. The TGA data indicate that the thermal stability of the nanocomposites improved after the incorporation of c-MWNTs. The influence of temperature on the resistivity of the nanocomposites was also measured. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
83.
Smectite clays treated with quaternary ammonium salts have been utilized for decades in paints, greases, cosmetics, and personal care products as rheological modifiers. They have also been used in industrial wastewater treatment extensively. In more recent times these surface modified clays have demonstrated benefits in polymer/clay nanocomposites. The use of quaternary ammonium modifiers limits the usefulness of these composites in food packaging because they are not approved for direct food contact. It would be advantageous to have surface modifying chemicals acceptable for direct food contact in these composites. This article reports research conducted on a promising surface modifier pentaerythritol stearate (PS), which is approved by the FDA for inclusion in food as a preservative. The surface modification of montmorillonite with PS is reported in detail as well as the production of nanocomposites with selected polymers made with the modified clay. Molecular modeling and purification of commercial PS samples indicate that the mono‐ and diesters are the critical surface modifiers, although the as received commercial material works well in forming intercalated clay complexes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
84.
简要介绍了全板电镀镍金加工过程中镀金面发白现象及改善措施。特别是针对高位发白(或粗糙)的产生原因和处理过程进行较为详细的描述,并对工艺在此处理过程中存在问题进行了简要剖析。 相似文献
85.
The continuous production of hydrogen from cyclohexanes is achieved effectively using Pt/ACF (ACF = activated carbon fiber) catalysts in a fixed-bed flow reactor. The Pt catalysts are more effective than a Pd/ACF catalyst for the reaction. Besides cyclohexane, methylcyclohexane, 1,4-dimethylcyclohexane, and p-menthane can also be employed as hydrogen source in the reaction system. 相似文献
86.
The Wabash River Integrated Methanol and Power Production from Clean Coal Technologies (IMPPCCT) project is investigating an Early Entrance Coproduction Plant (EECP) concept to evaluate integrated electrical power generation and methanol production from coal and other carbonaceous feedstocks. Research, development and testing (RD&T) that is currently being conducted under the project is evaluating cost effective process systems for removing contaminants, particularly sulfur species, from the generated gas which contains mainly synthesis gas (syngas), CO2 and steam at concentrations acceptable for the methanol synthesis catalyst. The RD&T includes laboratory testing followed by bench-scale and field testing at the SG Solutions Gasification Plant located in West Terre Haute, Indiana. Actual synthesis gas produced by the plant was utilized at system pressure and temperature for bench-scale field testing. 相似文献
87.
建立了AMl级别的最大重迭对称性分子轨道计算方案(MOSMO)。采用通常的半经验分子轨道方法AMl级别中完全相同的参数,计算了各种分子的几何参数等。所得计算结果与实验值及HF/6-31G*从头算方法计算结果相符,说明提出的计算方案是可行的。同时,由于提出的计算方案过程简单,更易推广使用到从头算方法难以解决的大分子体系和超分子体系的结构和性质研究。 相似文献
88.
89.
无氢类金刚石碳膜的研究进展 总被引:1,自引:0,他引:1
介绍了无氢类金刚石碳膜的制备方法 ,它们的机械、光学、电学性能 ,将无氢与含氢的类金刚石碳膜进行了简单比较 ,总结及探讨了它们的应用 相似文献
90.
Frank J. Owens 《Materials Letters》2007,61(10):1997-1999
Molecular orbital calculations of the ionization potential of single wall carbon nanotubes having donor NH2 and acceptor NO2 groups bonded to the side walls and ends and boron and nitrogen substituted for carbon show substantial increases in ionization potential compared to carbon nanotubes with no functional groups and no carbon substitutions. The presence of a carbon vacancy on the side wall also causes a substantial increase in the ionization potential. The effect of tube length on the ionization energy is also calculated. The calculations also suggest that at appropriate levels of boron and nitrogen doping the armchair carbon nanotubes could be high temperature organic ferromagnetic materials. 相似文献