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981.
This paper presents a finite element solution to the problem of low Peclet number fluid flow in the thermal entrance region of a round pipe. The velocity is assumed to be laminar and fully developed throughout the pipe and the fluid temperature is kept uniform atX = —∞. The pipe wall is adiabatic at X ≤ 0 and cooled convectively at X ≥ 0. The solutions include temperature distributions and Nusselt numbers for the parameters, Bi = 0.04, 0.4, 4, 20 and Pe = 1, 3, 5, 10, 20, 30, which are in excellent agreement with the existing analytic solution except in the region near the singular point Δ A temperature discrepancy in the analytic solution at this point is physically impossible. The finite element method overcomes this mathematical difficulty and shows a greater value in the Nusselt number due to a higher wall temperature at X ≥ 0. 相似文献
982.
Hyun Gyu Kim Dong Won Hwang Sang Won Bae Jong Hyeon Jung Jae Sung Lee 《Catalysis Letters》2003,91(3-4):193-198
Highly donor-doped (110) layered perovskite materials, La2Ti2O7, with high surface areas were synthesized by the polymerizable complex (PC) method. Relative to La2Ti2O7 prepared by the solid state reaction (SSR) method, PC catalysts showed higher surface areas, crystallization at lower temperatures, higher phase purity, more uniform morphology and better-distributed nickel on the outer surface of La2Ti2O7. All these factors led to higher photocatalytic activity for overall water splitting under UV irradiation. The quantum yield of the reaction over La2Ti2O7 prepared by the PC method was as high as 27%, which was about twofold greater than that over La2Ti2O7 prepared by the SSR method. 相似文献
983.
Hyung Joon Cha Kyoung Ro Kim Byeong Hee Hwang Dae Hee Ahn Young Je Yoo 《Korean Journal of Chemical Engineering》2007,24(5):812-815
Glucoamylase that hydrolyses starch to glucose is one of the important industrial enzymes for ethanol production industry.
Therefore, genetic production of recombinant glucoamylase has been widely studied. Previously, we reported secreted production
of Saccharomyces diastaticus-originated glucoamylase in Saccharomyces cerevisiase expression system using its own signal sequence and the SUC2 promoter that is regulated by glucose level in culture medium. In the present work, we performed a comparative study between
batch and fed-batch bioreactor cultures for secreted production of recombinant glucoamylase. Through maintaining low glucose
levels in the culture broth, we obtained about 7-fold higher secreted production levels of glucoamlyase in fed-batch culture.
Fed-batch culture strategy also enhanced (∼3.1-fold) secretion efficiency of recombinant glucoamylase in S. cerevisiae. 相似文献
984.
Reducing steel slag (RSS) was mainly acquired from five electric-arc furnace (EAF) steelmaking plants (among them, the products
of two plants were carbon steel and those of other plants were stainless steel) for research tests. The chemical properties,
compound compositions, activities and contents of main expansive compounds were tested. The results showed that the field
sampled RSS had a very high crystallinity and hydraulicity with main chemical compositions close to those of Portland cement.
It can be known from the study that in case of C/S ratio higher than 2.0, the main compound compositions are C2S, C3S, C2F and f-CaO. However, after the RSS was stored for six months, an obvious variation occurred with potential pre-hydration in RSS,
where the SO3 content was slightly reduced and the compressive activity index was obviously higher than that at the 28th day. 相似文献
985.
Humic acid, a natural organic matter, was separated with a polyamide (PA) composite membrane with a molecular weight cutoff (MWCO) of 500 g/mol. The PA composite membrane was prepared by the interfacial polymerization of piperazine and trimesoyl chloride on a polysulfone support with an MWCO of about 30,000 g/mol. The separation conditions through the membrane were varied, and factors affecting the permeation performance of the membranes, such as the concentration, pH, and storage time of the humic acid solutions, were studied. The surface chemistry of the membrane changed dynamically as a function of the operating time during the permeation tests, and the size and ζ potential of the colloid of humic acid solutions under different conditions were characterized with a ζ potentiometer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2847–2853, 2002 相似文献
986.
J.J. Hwang C.K. Chen R.F. Savinell C.C. Liu J. Wainright 《Journal of Applied Electrochemistry》2004,34(2):217-224
A three-dimensional numerical model is developed to simulate the transport phenomena on the cathodic side of a polymer electrolyte membrane fuel cell (PEMFC) that is in contact with parallel and interdigitated gas distributors. The computational domain consists of a flow channel together with a gas diffusion layer on the cathode of a PEMFC. The effective diffusivities according to the Bruggman correlation and Darcy's law for porous media are used for the gas diffusion layer. In addition, the Tafel equation is used to describe the oxygen reduction reaction (ORR) on the catalyst layer surface. Three-dimensional transport equations for the channel flow and the gas diffusion layer are solved numerically using a finite-volume-based numerical technique. The nature of the multi-dimensional transport in the cathode side of a PEMFC is illustrated by the fluid flow, mass fraction and current density distribution. The interdigitated gas distributor gives a higher average current density on the catalyst layer surface than that with the parallel gas distributor under the same mass flow rate and cathode overpotential. Moreover, the limiting current density increased by 40% by using the interdigitated flow field design instead of the parallel one. 相似文献
987.
The preparation of poly(vinyl alcohol) (PVA) fibers by multi-step drawing was examined. The high draw ratio was attained when the drawing just before melting point was repeated. The influences of the draw ratio on mechanical and thermal properties of the fibers were studied. We utilized the wide angle x-ray diffraction (WAXD) as a medium to observe the erystallinity and the orientation of PVA fibers to study their effects on the physical properties of the fibers. With various coagulation bath concentration, both the tenacity and Young's modulus of fibers would increase as the draw ratios increased, the elongation would decrease at the same time. The tenacity was able to reach 41.0 cN/tex with the Young's modulus being 856.2 cN/tex; also, as the draw ratios increased, both crystallinity and orientation would increase. The crystallinity was about 67.2 % and the orientation was about 86.4%. 相似文献
988.
The effect of reaction gas and catalyst on the growth of carbon nanotubes (CNTs) in the anodic aluminum oxide (AAO) nano-template was investigated. A mechanism of CNT growth was proposed, which involves the competitive catalytic carbon deposition between on the Co catalyst particles electrodeposited at the bottom of the pores and on the AAO template itself. Presence of H2 in the reacting gas mixture significantly affected the morphology and the wall structure of synthesized CNTs: CNTs of high crystallinity grew out of pores with H2 while no CNTs overgrew in the absence of H2. CNT synthesis by CO disproportionation showed a lower growth rate and a higher degree of ordering than those grown by C2H2 pyrolysis. The unified mechanism of CNT growth on AAO template is also proposed. 相似文献
989.
Won Joon Choi Hee‐Joon Kim Kwan Han Yoon Oh Hyeong Kwon Chang Ik Hwang 《应用聚合物科学杂志》2006,100(6):4875-4879
Poly(ethylene terephthalate) (PET)/clay nanocomposite was prepared by the direct polymerization with clay‐supported catalyst. The reaction degree of catalyst against the cation exchange capacity of clay was 8 wt %. The intercalation of PET chains into the silicate layers was revealed by X‐ray diffraction studies. SEM morphology of the nanocomposite showed a good dispersion of clay‐supported catalyst, ranging from 30 to 100 nm. The intercalated and exfoliated clay‐supported catalyst in PET matrix was also observed by TEM. The improvement of O2 permeability for PET/clay‐supported catalyst composite films over the pure PET is approximately factors of 11.3–15.6. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4875–4879, 2006 相似文献
990.
Ouk?Sub?LeeEmail author Guan?Hee?Kim Myun?Soo?Kim Jai?Sug?Hwang 《Journal of Mechanical Science and Technology》2003,17(6):787-795
Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions
such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson
Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high
strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A16061T-6
and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique. 相似文献