全文获取类型
收费全文 | 3105篇 |
免费 | 68篇 |
国内免费 | 3篇 |
学科分类
工业技术 | 3176篇 |
出版年
2021年 | 26篇 |
2020年 | 20篇 |
2019年 | 40篇 |
2018年 | 30篇 |
2017年 | 44篇 |
2016年 | 48篇 |
2015年 | 40篇 |
2014年 | 49篇 |
2013年 | 173篇 |
2012年 | 89篇 |
2011年 | 147篇 |
2010年 | 117篇 |
2009年 | 107篇 |
2008年 | 168篇 |
2007年 | 142篇 |
2006年 | 128篇 |
2005年 | 141篇 |
2004年 | 100篇 |
2003年 | 81篇 |
2002年 | 79篇 |
2001年 | 70篇 |
2000年 | 54篇 |
1999年 | 62篇 |
1998年 | 177篇 |
1997年 | 127篇 |
1996年 | 84篇 |
1995年 | 73篇 |
1994年 | 73篇 |
1993年 | 72篇 |
1992年 | 40篇 |
1991年 | 25篇 |
1990年 | 34篇 |
1989年 | 41篇 |
1988年 | 38篇 |
1987年 | 35篇 |
1986年 | 25篇 |
1985年 | 30篇 |
1984年 | 24篇 |
1983年 | 36篇 |
1982年 | 32篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 28篇 |
1976年 | 29篇 |
1975年 | 14篇 |
1974年 | 13篇 |
1973年 | 14篇 |
1972年 | 13篇 |
排序方式: 共有3176条查询结果,搜索用时 15 毫秒
51.
Bret J. Chisholm William D. Richards Timothy E. Banach Sofia Soloveichik James F. Kelley Greg R. Bradtke Sandeep Dhawan 《应用聚合物科学杂志》2006,100(6):4762-4771
Structure–property relationships have been developed for sulfonated poly(butylene terephthalate) copolymers. The compositional variables investigated were sulfonate content, molecular weight, and polymer endgroup composition, and the fundamental polymer properties evaluated were melt viscosity, crystallization kinetics, and impact strength. It was found that all compositional variables significantly affect all of the polymer properties of interest. The most interesting effect is the influence of polymer endgroup composition on polymer properties. The trends indicate that the carboxylic acid endgroups form intermolecular interactions with sodium sulfonate groups, resulting in a decrease in the strength of intermolecular ionic interactions between sodium sulfonate groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4662–4771, 2006 相似文献
52.
A range of 18 diesel fuels and 21 kerosene fuels from mainly Australian petroleum and synthetic fuel sources, including coal, shale and peat, was investigated. Compositional details were defined as the weight per cent abundances of n-alkanes, branched plus cyclic saturates, single-ring aromatics, doublering aromatics and polynuclear aromatics, using both h.p.l.c. and 13C n.m.r. techniques. Relationships between fuel composition and a range of fuel properties were sought. Simple linear relationships between property values and compositional data were used. Explicit correlative expressions were derived using multiple linear regression analysis, with the coefficient of multiple determination, R2, indicating the quality of the fit between observed and calculated property values. In most cases good correlations were achieved. For diesels the properties investigated, with R2 values in parentheses, were: inverse specific gravity (0.99); 13C n.m.r. aromaticity (0.99); 1H n.m.r. aromaticity (0.88); cetane index (0.97); aniline point (0.96); diesel index (0.98); and FIA-measured aromatics content (0.77). For kerosenes the properties, with R2 values in parentheses, were: 13C n.m.r. aromaticity (0.98); 1H n.m.r. aromaticity (0.97); smoke point (0.88); and FIA-measured aromatics content (0.94). The results are shown to be of value in assessing the potential and limitations of hydrotreating as a process for upgrading synfuels. 相似文献
53.
Hydrophobically modified alkali-soluble emulsion (HASE) polymers are an important class of rheology modifiers for waterborne
coatings applications. They are typically prepared as terpolymers by emulsion polymerization of ethyl acrylate (EA), methacrylic
acid (MAA), and an associative macromonomer. The viscosity development and shear responses of HASE solutions depend on a number
of factors. This article presents rheological data reflecting the impacts of three key variables: hydrophobe size, acid content,
and molecular weight, on model HASE thickening and rheological performance. The relative contributions of hydrophobic association,
chain expansion, and polymer chain length are discussed.
In steady shear flow, all thickener solutions approached some constant low-shear viscosity at small deformation rates. At
the same molar composition, larger hydrophobe size resulted in higher viscosity development and greater shear thinning behavior.
The amount of acid monomer in HASE polymers can influence the balance between hydrophobic attraction and electrostatic repulsion
forces. It was found that a minimum of 15 wt% MAA was required to effect dissolution and thickening of the model HASE polymers.
Increasing the MAA level yielded higher zero-shear viscosity and storage modulus G’ with maximal values being obtained at
40% MAA.
The molecular weight of the model thickeners was controlled by the amount of chain transfer agent (CTA) added during polymerization.
When the CTA level was below 0.1 wt% based on total monomers, the polymer solutions displayed shear-thinning behavior. A small
increase in CTA concentration beyond 0.1% resulted in a dramatic change to Newtonian flow, and the solution viscosity was
nearly two orders of magnitude lower.
The model thickeners were also tested in a vinyl acrylic architectural paint formulation. The effects of each individual factor
on paint thickener efficiency, high-shear, and low-shear properties are discussed and compared with solution rheology for
predictive relationships.
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 11–12, 2003, in Philadelphia,
PA. 相似文献
54.
Wax esters were isolated from commercial orange roughy (Hoplostethus atlanticus) oil by column chromatography and fractionated by argentation thin layer chromatography. Following transesterification, the
resultant fatty acid methyl esters and fatty alcohols were analyzed by gas chromatography. both acyl- and alkyl-moieties were
mainly of the monoene structure within the 16∶1–22∶1 range. After derivatization, the positions of the double bonds of even
numbered fatty acid and fatty alcohol isomers were located by chromatography-mass spectrometry and compared.
Results of these positional analyses indicate that the primary desaturation reactions takes place in the Δ9 position of pre-existing
(C14 to C24) acyl chains. It is proposed that acyl components from 18∶1 are subjected to chain elongation to form a mixture of 24∶1 isomers
as the final product. Apart from the 24∶1 acyl moiety of the wax esters, in which the double bond was almost exclusively in
the Δ15 position, de novo biosynthetic reactions on acids and alcohols appear to yield related acyl- and alkyl-moieties of
resynthesized wax esters. 相似文献
55.
Fatty acid monoesters of propylene glycol (1,2-propanediol) are good water-in-oil emulsifiers. These esters were synthesized
enzymatically to overcome the problems associated with chemical processes. APseudomonas lipase was added to reaction mixtures containing propylene glycol and various acyl donors (fatty acids, fatty acid ethyl
esters, fatty acid anhydrides and triglycerides) in organic solvents, and the mixtures were shaken at 30°C. The products were
analyzed by gas chromatography. The yield of monoesters was affected by the acyl donors, organic solvents, temperature, water
content, pH memory and reaction time. The anhydrous (lyophilized) enzyme and fatty acid anhydrides were best for monoester
production. The optimum pH ranges were 4–5 and 8–10. The yields of propylene glycol monolaurate, monomyristate, monopalmitate,
monostearate and monooleate with 50 mM fatty acid anhydrides as acyl donors were 97.2, 79.6, 83.7, 89.7 and 93.4 mM, respectively;
those with 50 mM fatty acids as acyl donors were 37.3, 28.7, 28.7, 35.3 and 36.2 mM, respectively. The yields of propylene
glycol monopalmitate, monostearate and monooleate with 50 mM triglycerides as acyl donors were 87.4, 65.1 and 83.2 mM, respectively. 相似文献
56.
Steven Swier Yong Sung Chun Jeffrey Gasa Montgomery T. Shaw R.A. Weiss 《Polymer Engineering and Science》2005,45(8):1081-1091
Sulfonated poly(ether ketone ketone) ionomers (SPEKK) with ion‐exchange capacities (IEC) between 0.2 and 3.4 meq/g were prepared by sulfonating PEKK with a mixture of concentrated and fuming sulfuric acids. Sulfonation occurs only on the phenyl rings attached to ether and ketone groups. The glass transition temperature of the dry SPEKK ionomers increased linearly with increasing IEC, and the ionomers were thermally stable to ~250°C, above which desulfonation occurred. Water‐swollen ionomers exhibited microphase separated morphologies, and the average correlation length determined by small angle X‐ray scattering increased with increasing IEC. The proton conductivity of hydrated SPEKK membranes measured by impedance spectroscopy ranged from ~10–3 to 10–1 S/cm as the IEC increased from ~1.0 to 2.4 meq/g. Single cell performance curves on membrane‐electrode assemblies (MEA) indicated that the SPEKK membranes approached the performance of Nafion? for an IEC of 2 meq/g. POLYM. ENG. SCI., 45:1081–1091, 2005. © 2005 Society of Plastics Engineers 相似文献
57.
B. S. Goodrich E. R. Hesterman K. S. Shaw R. Mykytowycz 《Journal of chemical ecology》1981,7(5):817-827
A study has been made of the volatile constituents in the vapors collected from fecal pellets of wild rabbits,Oryctolagus cuniculus. Measurements of changes in the heart rates of adult male rabbits exposed to the effluent of a gas chromatographic capillary column were used to indicate the presence of compounds which may be of behavioral significance. Combined with the use of high-resolution columns in gas chromatography and gas chromatography-mass spectrometry, this approach has implicated several classes of compounds, including volatile fatty acids and phenols, which in certain absolute or relative concentrations may be involved in the formation of signals of territorial importance. 相似文献
58.
In this paper, we describe a procedure for the processing of SiC-whisker-reinforced MoSi2 composites via tape casting. Based on the characteristics of SiC whiskers and MoSi2 powder in aqueous and nonaqueous solvents, a slip formulation (solvent, dispersant, binder, etc.) has been developed. The formulation developed allows for a uniform distribution of SiC whiskers in the matrix, easy separation of the tapes from the polymeric carrier, convenient control of both tape thickness and orientation of SiC whiskers, and a low binder burnout temperature. The latter is important for the prevention of the oxidation of MoSi2 powder during the binder burnout in an oxidizing atmosphere. 相似文献
59.
60.
M. T. Shaw 《Polymer Engineering and Science》1977,17(4):266-268
A method for determining the melt viscosity and molecular weight of ultra high molecular weight polyethylene (UHMWPE) is described. The method, based on squeeze flow, was used to characterize seventeen UHM W-PE samples varying in molecular weight from 0.6 × 106 to 5.1 × 106 and in viscosity from 2.9 × 106 to 3.4 × 109 poise. A correlation between melt viscosity and molecular weight was demonstrated, but the reliability of a molecular weight determination decreased somewhat as molecular weight increased. As a predictor of melt processability, the method provides the speed and simplicity heretofore lacking in UHMW-PE characterization by solution viscosity while retaining high reproducibility. 相似文献