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991.
The reaction of NO2, CH4 and O2 was studied using low levels of methane compared to NO2 and O2 over protonic and cobalt‐exchanged ferrierite, ZSM‐5 and mordenite zeolites. Results suggest that two reaction pathways at
low and high temperatures may be involved in the lean selective catalytic reduction (SCR) of NO2 by methane. At low temperatures, the reduction of NO2 to NO and N2 might be the initial reaction step. It is likely that NO2 or its adsorbed precursors initiate the reaction of methane at low temperatures. At high temperatures, the oxidation of NO
and combustion of methane with oxygen might be involved. No appreciable differences were observed in the reduction of NO2 over Co‐zeolites as compared to known results of NO reduction over these materials. However, enhanced N2 formation rate was observed on H‐zeolites starting from NO2 instead of data reported for NO. Furthermore, it appears that the active sites for SCR are both acid and metal sites.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
992.
Porosity effect on microstructure,mechanical, and fluid dynamic properties of Ti2AlC by direct foaming and gel‐casting 下载免费PDF全文
Marek Potoczek Anna Chmielarz Murilo D. de M. Innocentini Izabela C. P. da Silva Paolo Colombo Barbara Winiarska 《Journal of the American Ceramic Society》2018,101(12):5346-5357
In this study, Ti2AlC foams were fabricated by direct foaming and gel‐casting using agarose as gelling agent. Slurry viscosity, determined by the agarose content (at a fixed solids loading), as well as surfactant concentration and foaming time were the key parameters employed for controlling the foaming yield, and hence the foam porosity after sintering process. Fabricated foams having total porosity in the 62.5‐84.4 vol% range were systematically characterized to determine their pore size and morphology. The effect of the foam porosity on the room‐temperature compression strength and elastic modulus was also determined. Depending on the amount of porosity, the compression strength and Young's modulus were found to be in the range of 9‐91 MPa and 7‐52 GPa, respectively. Permeability to air flow at temperatures up to 700°C was investigated. Darcian (k1) and non‐Darcian (k2) permeability coefficients displayed values in the range 0.30‐93.44 × 10?11 m2 and 0.39‐345.54 × 10?7 m, respectively. The amount of porosity is therefore a very useful microstructural parameter for tuning the mechanical and fluid dynamic properties of Ti2AlC foams. 相似文献
993.
994.
Wen-Hao Tan Leiling Tao Kevin M. Hoang Mark D. Hunter Jacobus C. de Roode 《Journal of chemical ecology》2018,44(11):1040-1044
Many plants express induced defenses against herbivores through increasing the production of toxic secondary chemicals following damage. Phytochemical induction can directly or indirectly affect other organisms within the community. In tri-trophic systems, increased concentrations of plant toxins could be detrimental to plants if herbivores can sequester these toxins as protective chemicals for themselves. Thus, through trophic interactions, induction can lead to either positive or negative effects on plant fitness. We examined the effects of milkweed (Asclepias spp.) induced defenses on the resistance of monarch caterpillars (Danaus plexippus) to a protozoan parasite (Ophryocystis elektroscirrha). Milkweeds contain toxic secondary chemicals called cardenolides, higher concentrations of which are associated with reduced parasite growth. Previous work showed that declines in foliar cardenolides caused by aphid attack render monarch caterpillars more susceptible to infection. Here, we ask whether cardenolide induction by monarchs increases monarch resistance to disease. We subjected the high-cardenolide milkweed A. curassavica and the low-cardenolide A. syriaca to caterpillar grazing, and reared infected and uninfected caterpillars on these plants. As expected, monarchs suffered less parasite growth and disease when reared on A. curassavica than on A. syriaca. We also found that herbivory increased cardenolide concentrations in A. curassavica, but not A. syriaca. However, cardenolide induction in A. curassavica was insufficient to influence monarch resistance to the parasite. Our results suggest that interspecific variation in cardenolide concentration is a more important driver of parasite defense than plasticity via induced defenses in this tri-trophic system. 相似文献
995.
The expected amount of plant nitrogen (N) at harvest which originates from soil N supply is of high relevance for N fertilization planning. Due to mineralization–immobilisation turnover processes, soil N supply is influenced by N fertilization which complicates its assessment. The soil N supply consists of two components: the soil mineral N measured at early spring and the ‘effective’ N mineralization (Mineff) under winter wheat (Triticum aestivum L.). Mineff was defined as the difference between crop N uptake (Ncrop) at harvest and N supply. Our aim was the identification and quantification of climate and site-related factors in order to achieve an improved assessment of the site-specific (long term average) Mineff. We used N rate experiments from 411 collective seasons, carried out at 98 sites across Germany in order to analyze the impact of climate and site-related factors on Mineff. Quadratic curves were fitted in order to describe the grain N uptake as a function of N supply. A fixed marginal N efficiency was defined in order to analyze Mineff at a reasonable N supply. Starting with estimates for Mineff as function of preceding crop, we found that climate (average temperature during May, annual rainfall) and site-related factors have a significant influence on Mineff. In order to ensure that the regression model is transferable to unknown sites, a “leave one site out” cross validation was carried out. Compared to considering preceding crop only (reference), the regression model reduced the RMSE by 9.5 (calibration) or 8.3 (cross validation) kg N/ha. 相似文献
996.
Andrey Oliveira de Souza Aur lio Moreira Luiz Ant nio Tavernard Pereira Neto Ant nio Carlos Brandao de Araujo Heleno Bispo da Silva Sidinei Kebler da Silva Jose Jailson Nicacio Alves 《中国化学工程学报》2019,27(1):21-31
This study aimed to describe a Computational Fluid Dynamics(CFD) procedure using the ANSYS CFX software 16.1 and Design of Experiments for the determination of volume and extension of explosive atmospheres due to fugitive emissions of flammable gases.The multidimensional statistical sampling technique Latin Hypercube was used, which defined 100 simulations of random methane gas leak conditions.The CFD model proved to be robust in predicting the extension and volume of the explosive atmosphere for orifice diameters from 0.1 to2.5 mm, pressure from 0.1 MPa to 12 MPa and temperatures from 0 ℃ to 400 ℃.It was found that the calculation domain must be parameterized 8 m in length for each millimeter of the diameter of the source of release to ensure the predictions.In order not to lose precision for very small diameters, the mesh was parameterized with 50 elements along the orifice diameter.It was proved that gravity does not influence the extension and volume of the explosive atmosphere at sonic emissions.The deviation from the ideal gas behavior in the reservoir,achieved by applying the Soave–Redlich–Kwong equation of state, also has not significantly influenced the extension and volume of the explosive atmosphere.The results showed that the size of the explosive atmosphere varies directly with the diameter of the source emission and reservoir pressure, and inversely with the temperature of the reservoir.The diameter of the source is the parameter that has the major effect on the extension of the explosive atmosphere, followed by the pressure and lastly the temperature of the reservoir. 相似文献
997.
Oliveira TW Leandro CG de Jesus Deiró TC dos Santos Perez G da França Silva D Druzian JI Couto RD Barreto-Medeiros JM 《Lipids》2011,46(11):1071-1074
The main goal of the present study was to evaluate the long-term effects of a perinatal palatable high-fat diet on the food
intake and cholesterol profile of adult rats. Male Wistar rats (aged 22 days) were divided into two groups according to their
mother’s diet during gestation and lactation (C
p, n = 10; pups from control mothers; and HLp
n = 10; pups from mothers fed a palatable high-fat diet). At the 76th day, pups were housed individually for 14 days, and daily
food consumption was determined during a period of 6 days. Blood from 100-day-old rats was sampled by cardiac puncture. Fasting
(12 h) serum glucose, total cholesterol, LDL-C, HDL-C, triglycerides (TG), and VLDL-C levels were determined. The measurement
of food intake was higher in the animals submitted to a hyperlipidic diet during the perinatal period. Serum total cholesterol,
LDL-C, HDL-C, TG, VLDL-C and glycemia were increased in the HLp group compared to the control group. Our findings show that an early life environment with a high-fat diet can contribute
to metabolic disease in later life. 相似文献
998.
An oxygen plasma treatment has been used to improve the adhesion of amorphous hydrogenated carbon (a‐C:H) films onto surfaces of recycled poly(ethylene terephthalate) (PET). Modifications produced by the oxygen plasma on the PET surface in chemical bonds and morphology were investigated by X‐ray photoelectron spectroscopy and atomic force microscopy, respectively. Contact angle measurements were used to study the changes in the surface wettability. Adhesion of the a‐C:H film onto the PET surface was investigated by the tape test method. It was observed that the improvement in film adhesion is in good correlation with the increase in surface roughness, due to plasma etching, and with the appearance of oxygen‐related functional groups at the surface. The results of this study indicate that a‐C:H‐coated recycled PET can be used in food packaging. The a‐C:H film could be used as a functional barrier to reduce or prevent migration of contaminants from the polymer to the package content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
999.
M. A. del Valle F. R. Díaz J. L. Torres P. P. Zamora M. A. Godoy J. C. Bernède 《应用聚合物科学杂志》2010,115(1):107-115
The nucleation and growth mechanism of some homopolymers of aniline (six monomers were studied: 3,5‐dichloroaniline, 2,5‐dichloroaniline, 2,6‐dichloroaniline, 2,3‐dichloroaniline, 2,5‐dibromoaniline, and 2,6‐dibromoaniline), synthesized by potentiostatic methods, was determined with a mathematical model that considers different contributions from current–time transients with a gold‐disc electrode. Deconvolution of the transients for the dichlorinated monomers showed IN3Dct and PN3Ddif contributions (where IN3Dct refers to an instantaneous nucleation and three‐dimensional growth mechanism under charge‐transfer control and PN3Ddif refers to a progressive nucleation and three‐dimensional growth mechanism under diffusion control), whereas IN2D and PN3Ddif components and IN2D, IN3Dct, and PN3Ddif components (where IN2D refers to an instantaneous nucleation and two‐dimensional growth mechanism) were needed for 2,5‐dibromoaniline and 2,6‐dibromoaniline, respectively. The percentage of the contribution of the current–time transient to the total charge was worked out for each monomer. The effect of the scan rate on the voltammetric profile during the potentiodynamic electrosynthesis of the polymers was studied too. Curves of the current versus the square root of the potential scan rate were recorded for a selected group of monomers, and the slope was considered an estimation of the diffusion coefficient of the respective monomer. Furthermore, the electrosynthesized polymers were characterized with Fourier transform infrared, ultraviolet–visible, X‐ray photoelectron spectroscopy, and scanning electron microscopy. Microanalysis, used to establish the ratio of the atomic percentages of P and N for each polymer synthesized at a constant potential, was performed for doped and undoped polymers. This parameter was a measure of the degree of electrochemical doping. The conductivity of the doped and undoped polymers was also measured. Hence, the systematic characterization of this analogue series of monomers allows, before generalization, an adequate experimental design to prepare polymers with the properties required for their use. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
1000.
Filiberto González Garcia Maria Elena Leyva Marcia Gomes Oliveira Alvaro Antonio Alencar De Queiroz Alexandre Zirpoli Simões 《应用聚合物科学杂志》2010,117(4):2213-2219
The mechanical and adhesive properties of epoxy formulations based on diglycidyl ether of bisphenol A cured with various aliphatic amines were evaluated in the glass state. Impact and uniaxial compression tests were used to determine the impact energy, elastic modulus and yield stress, respectively. The adhesion tests were carried out in steel–steel joints using single‐lap shear, T‐peel, and impact adhesive joints geometry. The better mechanical and adhesive behavior of the networks is obtained when exists high flexibility of chain between crosslink and/or high elastic modulus. The 1‐(2‐aminoethyl)piperazine epoxy network presents the best adhesive properties, high flexibility, and the largest impact energy. However, it possesses low elastic modulus and yield stress. Also, exhibits increases in peel strength and impact energy while reductions in lap shear strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献