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91.
Helen E. Hermes Henrich Frielinghaus Wim Pyckhout-Hintzen Dieter Richter 《Polymer》2006,47(6):2147-2155
A new model is presented which can describe quantitatively the small angle neutron scattering from montmorillonite-type clay dispersions and polymer-clay nanocomposites. The model is shown to be able to describe well the data from a series of dilute montmorillonite in water dispersions in which the deuterium content of the water phase is varied. The fits combined with information from other techniques suggest strongly that H-D exchange occurs in the montmorillonite-water dispersions. Deviations from Q−2 behaviour often observed experimentally for clay dispersions are convincingly explained by the presence of a small proportion of tactoids. 相似文献
92.
Vasudev P. Saraf Wolfgang G. Glasser Garth L. Wilkes James E. McGrath 《应用聚合物科学杂志》1985,30(5):2207-2224
Hydroxypropyl lignin-based thermosetting polyurethanes were synthesized with excess hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI) by solution casting. Four polyethylene glycols (PEG) of molecular weight 400, 600, 1000, and 4000 were mixed with lignin polyol to incorporate different proportions of soft segment into the network prior to crosslinking. Neither thermal nor mechanical and limited small angle x-ray scattering (SAXS) analysis provided distinct evidence for phase separation and microstructure formation. The study examines the effect of the soft segment in relation to chain length and weight contribution on the thermal and mechanical properties of the final networks. A significant sensitivity of glass transition temperature (Tg), of swelling in DMF, and of the mechanical properties to soft segment content was observed. Some of this sensitivity must, however, be attributed to differences in crosslink density since the polyol to diisocyanate weight ratio was kept constant throughout the synthesis series. The magnitude of the change of the different properties was found to be influenced by both glycol content and glycol molecular weight. The Tg of the network decreased from 105°C to as low as 38°C (HDI), and from 158°C to 70°C (TDI), with incorporation of up to 17.8% glycol, and it was greater with lower molecular weight glycols than with higher ones at any weight fraction. Swelling in DMF increased as expected with soft segment content. Mechanical properties were affected most if HDI and lower molecular weight glycols were used. The uniformity in structure, reduction in brittleness, and considerable improvement in mechanical properties with inclusion of minor PEG contents indicates that lignin-based network polyurethanes can be synthesized with controllable performance characteristics. 相似文献
93.
Addition of H2 to a NO/NH3/O2/H2O feed for selective catalytic reduction of nitrogen oxide over Ag/Al2O3 catalysts causes an unusual enhancement of activity, e.g., the marginal activity (<10%) of 1 wt% Ag impregnated on γ-Al2O3 or mesoporous Al2O3 modifications is boosted to nearly 100% over a broad temperature range from 200 to 550°C at a space velocity of 30,000cm3g?1h?1). Contrary, silver on SiO2 or α-Al2O3 shows no improvement of activity in the presence of H2. The effect is tentatively attributed to a higher percentage of intermediary nano-sized Ag clusters on high-surface area Al2O3 in the presence of hydrogen. This promotes oxygen activation and hence NO oxidation to reactive intermediate nitrite species. The required dispersion of Ag cannot be stabilized on SiO2 or α-Al2O3. 相似文献
94.
Copolymers of 1,1-diphenylethylene (DPE) behave in a very special way in radical polymerization. Particularly, the behavior of MMA-DPE copolymers in radical polymerization is investigated. The results reveal that the semiquinoid structure of the precursor polymer identified in a previous contribution is activated by the attack of free radicals and thus, in a second stage polymerization with a second monomer, block copolymers are formed. The block copolymer yield depends strongly on the ratio between the amount of DPE-containing precursor polymer and the initiator and monomer concentration used in the second stage. The mechanism proposed is able to explain at least qualitatively all experimental results including the restriction of this mode of control of radical polymerization to the formation of diblock copolymers only. 相似文献
95.
M. P. Murari R. Murari S. Parthasarathy C. A. Guy V. V. Kumar B. Malewicz Wolfgang J. Baumann 《Lipids》1990,25(10):606-612
Described is a reaction sequence for the total synthesis of lyso platelet activating factor (lysoPAF; 1-O-alkyl-sn-glycero-3-phosphocholine) and its enantiomer. The procedure is versatile and yields optically pure isomers of defined chain
length. The synthesis is equally suited for the preparation of lysoPAF analogues and its enantiomers with unsaturation in
the long aliphatic chain. First,rac-1(3)-O-alkylglycerol is prepared by alkylation ofrac-isopropylideneglycerol with alkyl methanesulfonate followed by acid-catalyzed removal of the ketal group. The primary hydroxy
group of alkylglycerol is then protected by tritylation, the secondary hydroxy group is acylated, and the protective trityl
group is removed under mild acidic conditions with boric acid on silicic acid, essentially without acyl migration. Condensation
of the diradylglycerol with bromoethyl dichlorophosphate in diethyl ether, hydrolysis of the resulting chloride, and nucleophilic
displacement of the bromine with trimethylamine givesrac-1-O-alkyl-2-acylglycero-3-phosphocholine in good overall yield. The racemic alkylacylglycerophosphocholine is finally treated
with snake venom phospholipase A2 (Ophiophagus hannah) which affords 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) of natural configuration in optically pure form. The “unnatural” 3-O-alkyl-2-O-acyl-sn-glycerol-1-phosphocholine enantiomer, which is not susceptible to phospholipase A2 cleavage, gives 3-O-alkyl-sn-glycero-1-phosphocholine upon deacylation with methanolic sodium hydroxide. Homogeneity and structure of the intermediates
and final products were ascertained by carbon-13 nuclear magnetic resonance spectroscopy on monomeric solutions. 相似文献
96.
Johannes Konnerth Andreas Jger Josef Eberhardsteiner Ulrich Müller Wolfgang Gindl 《应用聚合物科学杂志》2006,102(2):1234-1239
Seven different polymers used frequently as adhesives and/or matrix polymers in wood, wood composites, and natural fiber‐reinforced composites were studied by uniaxial tensile tests and nanoindentation. It was shown that the elastic modulus, the hardness, the creep factor, and the elastic‐, plastic‐, and viscoelastic work of indentation of the seven different polymers is essentially the same regardless whether the polymers were tested in the form of pure films or in situ, i.e., in an adhesive bond line with spruce wood. An excellent correlation was found between the elastic modulus measured by tensile tests and the elastic modulus measured by nanoindentation. In spite of the good correlation, the elastic modulus measured by nanoindentation is significantly higher than the elastic modulus measured by tensile tests. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1234–1239, 2006 相似文献
97.
98.
Thomas Fehn Felix Kugler Beatrice Tübke Rainer Schweppe Phillip Mebert Wolfgang Krcmar Ulrich Teipel 《化学,工程师,技术》2021,93(5):771-780
Due to the growing energy requirements, the proportion of external thermal insulation composite systems (ETICS) installed has increased significantly during the past 50 years. Due to the longevity of these systems, ETICS waste is currently accumulating. Owing to the complex construction as well as a multitude of differently installed materials and substances of the past generations, there are many uncertainties and problems with the clean and low-pollutant processing of such systems. In the frame of this work, the ETICS were processed and sorted before being screened for ingredients or pollutants as well as for the purity of the recovered material fractions. 相似文献
99.
Silica gel or zeolites AlPO-5 and SAPO-34 are recommended as adsorbents in water-driven heat pumps because of their selective water uptake. Secondary energy, like solar energy, can be used for regeneration of loaded adsorbers. In case of the availability of only low energy levels, the use of dealuminated Y zeolite (DAY) is the better choice because of the infinitely variation of its hydrophilic properties by tailoring of the framework Si/Al ratio. Actual data on the hydrothermal stability of DAY are lacking. Thus, we report on the long-term behavior of DAY zeolites with different Si/Al ratios. 相似文献
100.
Chaudry Oliver Friedberger Andreas Grimm Alexandra Uder Michael Nagel Armin Michael Kemmler Wolfgang Engelke Klaus 《Magma (New York, N.Y.)》2021,34(3):367-376
Magnetic Resonance Materials in Physics, Biology and Medicine - To develop a precise semi-automated segmentation of the fascia lata (FL) of the thigh to quantify IMAT volume in T1w MR images and... 相似文献