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91.
Experimental peak capacities for capillary gas chromatography (GC), capillary liquid chromatography (CLC), and capillary electrochromatography (CEC) were compared. To obtain a meaningful comparison, the following constraints were applied. First, the same sample (mixture of alkylbenzenes) was used as a test mixture for all three techniques; second, the same packing material and column diameter were used in CLC and CEC; and third, isothermal conditions were used in GC, while isocratic conditions were used both in CLC and in CEC. Comparison of peak capacities for the same total column efficiency (approximately 36000 plates) showed that the peak capacity of GC is greater than those of the liquid-phase separation techniques. Comparison of CEC and CLC for constant retention factor was also carried out. For this condition, the results depend on the particle size used; for 3-microm porous particles, CEC had a peak capacity larger than CLC due to higher efficiency from the flow profile generated by electroosmotic flow. However, when 1.5-microm nonporous particles were used, the peak capacities were approximately the same for both techniques. The effect of linear velocity on peak capacity was also studied for all three techniques. Practical conditions aimed at increasing peak capacities of liquid-phase separation techniques are discussed. 相似文献
92.
Medina MB 《International journal of food microbiology》2001,69(3):199-208
Research at USDA attempts to eliminate or reduce Escherichia coli contamination in meat and poultry foods by understanding the attachment mechanisms. This study utilizes a surface plasmon resonance (SPR) biosensor to determine the interactions of the immobilized E. coli O157:H7 surface with collagen I and selected polysaccharides. The binding and dissociation kinetics of collagen I with E. coli surface molecules had a mean affinity constant (K) of 3 x l0(8) (M(-1)) while the dissociation rate was 4.4 x l0(-5) (S(-1)). Using the SPR biosensor, carrageenan, sodium alginate and pectin were evaluated for their interactions with collagen I and the E. coli surface. Results showed 89% to 100% inhibition by carrageenans and about 50% by sodium alginate and less than 10% by pectin. The biosensor binding studies were augmented by the scanning electron microscopy studies, which also showed the attachment of E. coli to the collagen fibrils of the bovine tissues. These studies serve as the basis for developing new strategies to block bacterial attachment or detach pathogens from animal carcasses. 相似文献
93.
Jack J. W. A. van Loon F. Javier Medina Hilde Stenuit Eric Istasse Marc Heppener Roberto Marco 《Microgravity science and technology》2007,19(5-6):9-32
From the autumn of 2001 till spring of 2005 a series of six flights to the International Space Station, ISS, were conducted using the Russian Soyuz manned launcher. These flights initially known as ‘taxi-missions’, were characterized by the participation and co-funding from both the European Space Agency, ESA, and the five national delegations from France, Italy, Belgium, Spain, and the Netherlands. The national participation was reflected both in the flight of a cosmonaut/astronaut, originating from the country co-sponsoring the flight as well as in the origin of the majority of experiments and other activities carried out during these missions. In these six Soyuz missions: Andromède (October 2001), Marco Polo (April 2002), Odissea (October 2002), Cervantes (October 2003), DELTA (April 2004) and Eneide (April 2005), some more than one hundred experiments were carried out. These experiments covered the areas of basic and applied research and technology in biology, human physiology, fluid and plasma physics, material science and Earth observation. Also a significant number of education activities were part of these missions. This paper gives a complete overview of these missions, of all science, education and related activities performed. The perspectives of these activities in the light of the space exploration programs in the XXI century and some of the uncertainties and paradoxes are discussed. 相似文献
94.
Isabel Matía Fernando González-Camacho Roberto Marco John Z. Kiss Gilbert Gasset Jack van Loon Francisco Javier Medina 《Microgravity science and technology》2007,19(5-6):128-132
In an experiment conducted in the “Cervantes” Spanish Soyuz Mission, a 10-day flight to the International Space Station, Arabidopsis seeds were germinated, seedlings grew for 4 days at 22ºC, and they were fixed in flight with paraformaldehyde. A ground 1 g control experiment was replicated, and an additional experiment in simulated microgravity, using a Random Positioning Machine, was performed in the same conditions. Structural, morphometric and immunocytochemical data were compared. Glutaraldehyde-fixed seedlings similarly grown in the Space Shuttle (STS-84 Mission) were also used for ultrastructural and morphometric studies. Seedlings grown for 4 days in real or simulated weightlessness showed a longer size than the ground 1 g control. Root meristematic cells showed an enhanced proliferating rate, but ribosome biogenesis was reduced, as inferred from the nucleolar size and from the levels of the nucleolar protein nucleolin. This could be the consequence of the acceleration of the cell cycle, with shortening of its phases. Weightlessness induces stress in the plant, influencing cellular processes decisive for development and morphogenesis. This stress may endanger the plant and would require the action of compensating specialized defence mechanisms. 相似文献
95.
Katharina Nekolla Sabine Sellner Marc Praetner Karina Mildner Dagmar Zeuschner Fritz Krombach 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(14):1882-1890
So‐called membrane nanotubes are cellular protrusions between cells whose functions include cell communication, environmental sampling, and protein transfer. It has been previously reported that systemically administered carboxyl‐modified quantum dots (cQDs) are rapidly taken up by perivascular macrophages in skeletal muscle of healthy mice. Expanding these studies, it is found, by means of in vivo fluorescence microscopy on the mouse cremaster muscle, rapid uptake of cQDs not only by perivascular macrophages but also by tissue‐resident cells, which are localized more than 100 μm distant from the closest vessel. Confocal microscopy on muscle tissue, immunostained for the membrane dye DiI, reveals the presence of continuous membranous structures between MHC‐II‐positive, F4/80‐positive cells. These structures contain microtubules, components of the cytoskeleton, which clearly colocalize with cQDs. The cQDs are exclusively found inside endosomal vesicles. Most importantly, by using in vivo fluorescence microscopy, this study detected fast (0.8 μm s?1, mean velocity), bidirectional movement of cQDs in such structures, indicating transport of cQD‐containing vesicles along microtubule tracks by the action of molecular motors. The findings are the first to demonstrate membrane nanotube function in vivo and they suggest a previously unknown route for the distribution of nanomaterials in tissue. 相似文献
96.
Karina C.M. Dall’Agno Osmar Norberto de Souza 《Expert systems with applications》2013,40(7):2568-2574
Protein structure prediction (PSP) is a long standing problem in structural biology and bioinformatics. Within the PSP problem loop refinement is a major bottleneck. In this article we report the latest version of the CReF expert predictor system for the PSP problem with emphasis on loop refinement of the approximate 3-D structure 1ZDD_P of the Z34C mini protein predicted by CReF. We designed a loop refinement protocol based on seven molecular dynamics (MD) simulations runs at different temperatures. We found that, by letting the loop residues move freely during dynamics at 325 K and restraining the internal coordinates of the correctly predicted helical structures, while allowing them to move relative to each other, the refinement protocol was very effective in predicting an accurate loop conformation in the first 100 ps of a 1000 ps MD simulation. The quality of the predictions was confirmed by the RMSD between refined and experimental structures which varied from 0.6 to 1.3 Å. In addition, stereochemical analyses showed that 100% of all residues of the refined 1ZDD_P, including those in the loop, populates the most favorable core regions of the Ramachandran plot. Our study suggests that the proposed protocol may be suitable to refine more complex mini proteins with different classes and architectures. 相似文献
97.
Rigoberto Medina 《国际强度与非线性控制杂志
》2013,23(13):1496-1509
》2013,23(13):1496-1509
We give sufficient conditions for the exponential stability of a class of perturbed time‐varying difference equations with multiple delays and slowly varying coefficients. Under appropriate growth conditions on the perturbations, combined with the ‘freezing’ technique, we establish explicit conditions for global exponential stability. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
98.
Vanina A. Angelini Joaquín Orejas María I. Medina Elizabeth Agostini 《Journal of hazardous materials》2011
Chlorophenols are harmful pollutants, frequently found in the effluents of several industries. For this reason, many environmental friendly technologies are being explored for their removal from industrial wastewaters. The aim of the present work was to study the scale up of 2,4-dichlorophenol (2,4-DCP) removal from synthetic wastewater, using Brassica napus hairy roots and H2O2 in a discontinuous stirred tank reactor. We have analyzed some operational conditions, because the scale up of such process was poorly studied. High removal efficiencies were obtained (98%) in a short time (30 min). When roots were re-used for six consecutive cycles, 2,4-DCP removal efficiency decreased from 98 to 86%, in the last cycle. After the removal process, the solutions obtained from the reactor were assessed for their toxicity using an acute test with Lactuca sativa L. seeds. Results suggested that the treated solution was less toxic than the parent solution, because neither inhibition of lettuce germination nor effects in root and hypocotyl lengths were observed. Therefore, we provide evidence that Brassica napus hairy roots could be effectively used to detoxify solutions containing 2,4-DCP and they have considerable potential for a large scale removal of this pollutant. Thus, this study could help to design a method for continuous and safe treatment of effluents containing chlorophenols. 相似文献
99.
A. Morato C. Alonso F. Medina J.L. Garreta J.E. Sueiras Y. Cesteros P. Salagre D. Tichit B. Coq 《Catalysis Letters》2001,77(1-3):141-146
Several fluoride type perovskites, with formula KMg1–x
Pd
x
F3, have been prepared for the first time. The enlargement of their cell parameters has been associated with the insertion of Pd into the structure. After reduction, these new compounds, when tested in the hydrodechlorination reaction of CCl2F2 and CHClF2, showed higher selectivities to CHClF2 and CH2F2, respectively, than other Pd catalysts supported on KMgF3. 相似文献
100.
Rafael Peña Aurelio Medina Olimpo Anaya-Lara James R. McDonald 《Renewable Energy》2009,34(5):1204-1209
A procedure to estimate the capacity of minihydro plants based on water flow time series forecasting is presented. First, the classic method used for this purpose is introduced and then a set of methodologies to assess the feasibility of minihydro generation and to determine system capacity based on time series forecast is described. The water flow time series is processed to determine the theoretical power generation and to assess if a minihydro plant can be installed. Finally the characteristics of each of the electro-mechanical components for the proposed minihydro plant are selected. 相似文献