全文获取类型
收费全文 | 2817篇 |
免费 | 92篇 |
国内免费 | 9篇 |
学科分类
工业技术 | 2918篇 |
出版年
2023年 | 26篇 |
2022年 | 43篇 |
2021年 | 76篇 |
2020年 | 70篇 |
2019年 | 65篇 |
2018年 | 86篇 |
2017年 | 60篇 |
2016年 | 66篇 |
2015年 | 58篇 |
2014年 | 78篇 |
2013年 | 176篇 |
2012年 | 105篇 |
2011年 | 107篇 |
2010年 | 75篇 |
2009年 | 88篇 |
2008年 | 87篇 |
2007年 | 77篇 |
2006年 | 84篇 |
2005年 | 61篇 |
2004年 | 46篇 |
2003年 | 45篇 |
2002年 | 45篇 |
2001年 | 22篇 |
2000年 | 41篇 |
1999年 | 64篇 |
1998年 | 200篇 |
1997年 | 135篇 |
1996年 | 101篇 |
1995年 | 60篇 |
1994年 | 63篇 |
1993年 | 58篇 |
1992年 | 38篇 |
1991年 | 31篇 |
1990年 | 22篇 |
1989年 | 42篇 |
1988年 | 33篇 |
1987年 | 30篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 31篇 |
1980年 | 26篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 26篇 |
1976年 | 36篇 |
1974年 | 14篇 |
1973年 | 16篇 |
排序方式: 共有2918条查询结果,搜索用时 15 毫秒
41.
42.
Poly(keto-amines) such as poly(4-methyl-3-iminophenacyls) and poly(2-methyl-4-iminophenacyls) were prepared by self-polycondensation of 4-methyl-3-aminophenacyl chloride and 2-methyl-4-aminophenacyl chloride under different experimental conditions. All the polymer samples were insoluble in common organic solvents. They were characterized by elemental analysis, IR spectral studies, estimation of M?n by non-aqueous conductometric titration and study of thermal properties by DTA. The properties of P4M3IP and P2M4IP were compared with those of poly(4-iminophenacyls). 相似文献
43.
Graft copolymerization of methyl methacrylate (MMA) onto guar gum (GG) in aqueous slurry has been carried out using hydrogen peroxide (H2O2) as initiator. The copolymers were characterized by infrared spectroscopy. The grafting parameters like percent grafting, grafting efficiency, percent add-on, and the grafting frequency were determined, and the effect of reaction time, concentration of initiator, and [GG]/[MMA] ratios on the grafting parameters have been discussed. The decrease in % add-on at increasing concentration of H2O2 indicated enhancement in the rate of homopolymerization of methyl methacrylate. 相似文献
44.
Yinzhong Guo Vijay M. Mannari Pulin Patel John L. Massingill 《Journal of Coatings Technology and Research》2006,3(4):327-331
A series of soybean oil phosphate ester polyols (SOPEP) was prepared by reaction of fully epoxidized soybean oil with phosphoric
acid and simultanoeous hydrolysis in the presence of a polar solvent. The polyols were characterized by determination of acid
value, oxirane number, hydroxyl value, molecular weight (GPC), and FTIR spectra. These polyols with varying amounts of acid
phosphate groups could be self-emulsified to form aqueous dispersions after neutralization with organic base. These aqueous
dispersion showed varying degrees of stability and their appearance ranged from opaque dispersions to translucent to clear
solutions. Waterborne coating compositions were prepared using these aqueous dispersions as principal components and their
thermally cured film properties were studied. it was found that by careful selection and formulation, SOPEPs can be successfully
used for low-VOC waterborne coating formulations. SOPEPs with 3.5% phosphate ester content showed visibly superior corrosion
resistance properties. 相似文献
45.
A new method for predicting elastic moduli M of heterogeneous polymer compositions is proposed. It is based on a phenomenological adjustment between parallel and series models for upper and lower bound moduli MU and ML. Thus, where ?H is the volume fraction of hard phase, ?S is the volume fraction of soft phase, and n is the only adjustable parameter since the upper and lower bound moduli are given by and where MH and MS are the moduli of the pure hard and soft phases, respectively. Predicted values of M are in agreement with measured values in a number of systems which include polyblends and composite materials of fixed morphology. The significance of n is discussed relative to concentrations in the area of a phase transition for the polyblends or relative to phase morphology in the case of fixed morphology compositions. Interestingly, the relationship, by analogy, is in agreement with measured values of polyblend melt viscosities. 相似文献
46.
Linear polyethers possess unusually high CO2 solubility and, hence, selectivity due to the presence of accessible ether linkages that can interact with the quadrupolar moment of CO2 molecules. In this work, membranes derived from crosslinked poly(propylene glycol) diacrylate (PPGda) oligomers differing in molecular weight (M), as well as PPGda nanocomposites containing either an organically-modified montmorillonite clay or a methacrylate-terminated fumed silica are investigated and compared with highly CO2-selective poly(ethylene glycol) diacrylate (PEGda) homopolymer and nanocomposite membranes previously reported. The rheological and permeation properties of PPGda depend sensitively on M, with the elastic modulus decreasing, but CO2 permeability and CO2/H2 selectivity increasing, with increasing M. Incorporation of either nanofiller into PPGda enhances the elastic modulus and reduces the gas permeability in the resultant nanocomposites without strongly affecting CO2/H2 selectivity. Blending PPGda and PEGda prior to chemical crosslinking yields binary membranes that exhibit intermediate gas-transport properties accurately described by a linear rule of mixtures. 相似文献
47.
Effect of temperature, solvent power, and molecular weight on the adsorption of poly methyl methacrylate (PMMA) on aluminium silicate has been studied. Kinetics of adsorption have been also investigated at 30° and 45 °C. The values of rate constants at these temperatures are 1.4 · 10?2 and 1.0 · 10?2 min?1 respectively. The adsorption data have been analysed according to the Langmuir and the Simha -Frisch -Eirich (SFE) isotherms. The results could be adequately explained in terms of the Langmuir isotherm. 相似文献
48.
Supported 12-tungstophosphoricacid (12-TPA) and 12-tunstosilicicacid (12-TSA) were used as heterogeneous catalysts for liquid-phase
tert-butylation of m-cresol, an industrial important reaction. Alkylation reactions have been carried out with supported 12-TPA by varying different
parameters such as % loading of 12-tungstophosphoricacid onto support, mole ratio of alcohol to m-cresol, reaction temperature, amount of the catalyst, reaction time and calcination temperature to optimize the conditions.
To see the effect of the acidity on the reaction, the same reaction was studied over supported 12-TSA. Both the catalysts
give 100% selectivity for o-isomer with different % conversion. The difference in catalyst performance of both the catalyst
was correlated with the value of total acidity as well as Bronsted acidity. 相似文献
49.
Graft copolymers were synthesized by graft copolymerization of butyl acrylate (BA) onto sodium salt of partially carboxymethylated starch (Na‐PCMS). Ceric ammonium nitrate (CAN), a redox initiator, was used for initiation of graft copolymerization reaction. All the experiments were run with Na‐PCMS having degree of substitution, DS = 0.35. The grafting reaction was characterized by parameters such as % total conversion (%Ct), % grafting (%G), % grafting efficiency (%GE), and % add‐on. Graft copolymers were characterized by infrared spectral analysis and scanning electron microscopy. Variables affecting graft copolymerization reaction such as nitric acid concentration, reaction time, reaction temperature, and ceric ion concentration were investigated. The results revealed that 0.3M CAN as initiator, 0.3M HNO3, with reaction time 4–4.5 h at 25–30°C were found as suitable parameters for maximum yield of graft copolymerization reaction. © 2006 Wiley Periodicals, Inc. JAppl Polym Sci 102: 3334–3340, 2006 相似文献
50.
Analysis of the frequency distributions of breaking load, tenacity, and ratio of cell wall thickness to ribbon width (C/R) for single cotton fibers in this study has indicated that they can all be represented by β-distributions. This suggests that a parallel model of element configurations exists in which there is a uniform distribution of elemental strengths in single cotton fibers before as well as after slack mercerization. In the case of breaking load and tenacity, the distributions are positively skewed and the skewness decreases on slack mercerization, suggesting that quite a few potentially weak places have been either completely removed or at least strengthened. The changes in C/R ratio on slack mercerization for cottons having a range of maturity have been examined and discussed. The dependence of properties such as breaking load, tenacity, and linear density on cell wall to ribbon width ratio (C/R) have also been studied. 相似文献