全文获取类型
收费全文 | 3663篇 |
免费 | 80篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 271篇 |
金属工艺 | 16篇 |
机械仪表 | 38篇 |
建筑科学 | 28篇 |
矿业工程 | 2篇 |
能源动力 | 29篇 |
轻工业 | 310篇 |
水利工程 | 6篇 |
石油天然气 | 15篇 |
无线电 | 83篇 |
一般工业技术 | 148篇 |
冶金工业 | 2701篇 |
原子能技术 | 2篇 |
自动化技术 | 89篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 44篇 |
2021年 | 44篇 |
2020年 | 34篇 |
2019年 | 38篇 |
2018年 | 42篇 |
2017年 | 41篇 |
2016年 | 37篇 |
2015年 | 40篇 |
2014年 | 56篇 |
2013年 | 76篇 |
2012年 | 65篇 |
2011年 | 87篇 |
2010年 | 60篇 |
2009年 | 60篇 |
2008年 | 51篇 |
2007年 | 55篇 |
2006年 | 47篇 |
2005年 | 28篇 |
2004年 | 22篇 |
2003年 | 22篇 |
2002年 | 22篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 92篇 |
1998年 | 900篇 |
1997年 | 520篇 |
1996年 | 267篇 |
1995年 | 177篇 |
1994年 | 156篇 |
1993年 | 171篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1990年 | 19篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 22篇 |
1978年 | 3篇 |
1977年 | 56篇 |
1976年 | 139篇 |
1975年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有3746条查询结果,搜索用时 15 毫秒
991.
S Ahn S Maudsley LM Luttrell RJ Lefkowitz Y Daaka 《Canadian Metallurgical Quarterly》1999,274(3):1185-1188
Some forms of G protein-coupled receptor signaling, such as activation of mitogen-activated protein kinase cascade as well as resensitization of receptors after hormone-induced desensitization, require receptor internalization via dynamin-dependent clathrin-coated pit mechanisms. Here we demonstrate that activation of beta2-adrenergic receptors (beta2-ARs) leads to c-Src-mediated tyrosine phosphorylation of dynamin, which is required for receptor internalization. Two tyrosine residues, Tyr231 and Tyr597, are identified as the major phosphorylation sites. Mutation of these residues to phenylalanine dramatically decreases the c-Src-mediated phosphorylation of dynamin following beta2-AR stimulation. Moreover, expression of Y231F/Y597F dynamin inhibits beta2-AR internalization and the isoproterenol-stimulated mitogen-activated protein kinase activation. Thus, agonist-induced, c-Src-mediated tyrosine phosphorylation of dynamin is essential for its function in clathrin mediated G protein-coupled receptor endocytosis. 相似文献
992.
Patrícia Aparecida Pimenta Pereira Vanessa Rios de Souza Taísa Rezende Teixeira Fabiana Queiroz Soraia Vilela Borges João de Deus Souza Carneiro 《Food Hydrocolloids》2013
The addition of salts to carrageenan and locust bean gum gels functions to improve the characteristics of texture, thereby increasing gel strength. This effect is widely studied in gels of model systems but is studied to a lesser extent in complex systems, such as fruit preserves. The objective of this study was to evaluate the effect of adding salts on the rheological behavior of functional sugar-free guava preserves, as well as to correlate the rheological parameters. To this end, three types of texture properties were analyzed (texture profile, stress relaxation and uniaxial compression) in functional sugar-free guava preserves prepared with different concentrations of KCl and CaCl2 salt. The analyses were performed with a texturometer (Stable Micro Systems, Model TA - XT2i), and the parameters were analyzed using a Scott-Knott test at 5% probability, principal components analysis and Pearson correlation. CaCl2 was more effective for improving the characteristics of texture, especially gel strength (concentration near the F3: 0.33%), whereas KCl addition degraded gel strength. In the analysis of test relaxation, the Maxwell model parameters provided better discrimination between samples than the Peleg model parameters. Positive and negative correlations were observed, and the parameters of hardness, adhesiveness and elastic modulus ideal (E1) were the most correlated with other rheological parameters. 相似文献
993.
LM Higgins SA McDonald N Whittle N Crockett JG Shields TT MacDonald 《Canadian Metallurgical Quarterly》1999,162(1):486-493
The role of GRP78/BiP in coordinating endoplasmic reticular (ER) protein processing with mRNA translation was examined in GH3 pituitary cells. ADP-ribosylation of GRP78 and eukaryotic initiation factor (eIF)-2alpha phosphorylation were assessed, respectively, as indices of chaperone inactivation and the inhibition of translational initiation. Inhibition of protein processing by ER stress (ionomycin and dithiothreitol) resulted in GRP78 deribosylation and eIF-2 phosphorylation. Suppression of translation relative to ER protein processing (cycloheximide) produced approximately 50% ADP-ribosylation of GRP78 within 90 min without eIF-2 phosphorylation. ADP-ribosylation was reversed in 90 min by cycloheximide removal in a manner accelerated by ER stressors. Cycloheximide sharply reduced eIF-2 phosphorylation in response to ER stressors for about 30 min; sensitivity returned as GRP78 became increasingly ADP-ribosylated. Reduced sensitivity of eIF-2 to phosphorylation appeared to derive from the accumulation of free, unmodified chaperone as proteins completed processing without replacements. Prolonged (24 h) incubations with cycloheximide resulted in the selective loss of the ADP-ribosylated form of GRP78 and increased sensitivity of eIF-2 phosphorylation in response to ER stressors. Brefeldin A decreased ADP-ribosylation of GRP78 in parallel with increased eIF-2 phosphorylation. The cytoplasmic stressor, arsenite, which inhibits translational initiation through eIF-2 phosphorylation without affecting the ER, also produced ADP-ribosylation of GRP78. 相似文献
994.
995.
Juan José Goncalves Fidel Castro José Alberto Teixeira Dosinda González-Mendizabal 《Chemical Engineering Communications》2013,200(1):94-115
In this work, the fluid-dynamic of a slurry bubble column provided with a tube bank operating in cross flow was studied. The main objective was to determine the influence of the air velocity, the slurry velocity, and the solid concentration in the gas holdup and solid distribution inside a bed with internals. Pilot scale equipment with a column of square traverse section (0.144 m 2 ) of stainless steel with 2.20 m height was used. The column base has a truncated pyramidal shape with an inclination angle to the vertical of 20°. In the central part of the equipment, there is a bank of 49 tubes ( D =2.54 cm and L =38 cm) in an aligned arrangement ( S_L=S_T=4.4\,\rm cm ). The three-phase system used was compressed air, tap water, and sieved sand ( D_p=0.0505\,\rm cm ). The velocities of liquid and gas phases were varied in the range from 0.31 to 1.24 cm/s and from 1.41 to 3.15 cm/s, respectively, and the solids load concentration from 0 to 30% w/w. According to the results, when the liquid and gas phase velocities increase, the gas holdup, \varepsilon_G , increases, while when the solids load concentration increases, \varepsilon_G presents a local maximum at intermediate values, \varepsilon_G being the largest for the two-phase system. Analogously, the axial profiles of solids concentration showed a local maximum in the central region of the column, exactly in the area of the tube bank. In the traverse direction, the solids concentration increases gradually heading to the center of the column. These profiles, axial and traverse, become more uniform as the air velocity increases and the slurry as well. In addition, according to expectations, the solids concentration increases in each point of the column as the load concentration is increased in the system. 相似文献
996.
G.F. Teixeira M.A. ZagheteG. Gasparotto M.G.S. CostaJ.W.M. Espinosa E. LongoJ.A. Varela 《Journal of Alloys and Compounds》2012,512(1):124-127
Micro-cube-shaped lead zirconate titanate was synthesized using the microwave-assisted hydrothermal method. Photoluminescence and field emission scanning electron microscopy were used for monitoring the formation of mesocrystals. Based on these results, a growth mechanism was then proposed which involved nanoparticle aggregation, nanoplate self-assembly on specific architecture and the final formation of mesoscopic micro-cube-shaped lead zirconate titanate. 相似文献
997.
ABSTRACT Fish crackers are semi-prepared starch-based products which must be expanded just prior to consumption. This work aims at the experimental and theoretical study of the thin-layer drying process of fish crackers in a thin disc geometry. The process was carried out in an insulated cabinet dryer and the experimental kinetic drying data were fitted using the analytical solutions resulting from both a drying model governed by the Fick' s second law and a model based on the lumped system, highlighting the adequacy of each of them. Therefore, it was possible to calculate the mass transfer coefficients for seven different blends offish crackers. Also, the effect of the drying time on the bulk density of the puffed product was evaluated for these seven blends. Both the kinetic drying parameters and the optimal bulk density responses were analyzed using the Simplex-Lattice Design over a mixture triangle within a minimal number of experiments. 相似文献
998.
Gas–liquid interfacial area in the oxygen absorption to oil‐in‐water emulsions in an airlift reactor
The present work includes an exhaustive study about gas–liquid interfacial area between gas phase and liquid heterogeneous medium generated in an airlift bioreactor. The system studied is composed by water, methyl ricinoleate (MR), and Tween‐80, since it is the base of the medium used for the production of γ‐decalactone, a peach‐like aroma compound of industrial interest that can be produced biotechnologically through the biotransformation of ricinoleic acid, by the yeast Yarrowia lipolytica. Experimental results allow describing the hydrodynamic behaviour of the gas phase into the biphasic medium. 相似文献
999.
Flávio C. Cabrera Deuber L. S. Agostini Renivaldo J. dos Santos Silvio R. Teixeira Miguel A. Rodríguez‐Pérez Aldo E. Job 《应用聚合物科学杂志》2013,130(1):186-192
Natural rubber/gold nanoparticles membranes (NR/Au) were studied by ultrasensitive detection and chemical analysis through surface‐enhanced Raman scattering and surface‐enhanced resonance Raman scattering in our previous work (Cabrera et al., J. Raman Spectrosc. 2012, 43, 474). This article describes the studies of thermal stability and mechanical properties of SERS‐active substrate sensors. The composites were prepared using NR membranes obtained by casting the latex solution as an active support (reducing/establishing agents) for the incorporation of colloidal gold nanoparticles (AuNPs). The nanoparticles were synthesized by in situ reduction at different times. The characterization of these sensors was carried out by thermogravimetry, differential scanning calorimetry, scanning electron microscopy (SEM) microscopy, and tensile tests. It is suggested an influence of nanoparticles reduction time on the thermal degradation of NR. There is an increase in thermal stability without changing the chemical properties of the polymer. For the mechanical properties, the tensile rupture was enhanced with the increase in the amount of nanoparticles incorporated in the material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
1000.
Athanasios Bamis Dimitrios Lymberopoulos Thiago Teixeira Andreas Savvides 《Personal and Ubiquitous Computing》2010,14(6):473-487
The in-house monitoring of elders using intelligent sensors is a very desirable service that has the potential of increasing
autonomy and independence while minimizing the risks of living alone. Because of this promise, the efforts of building such
systems have been spanning for decades, but there is still a lot of room for improvement. Driven by the recent technology
advances in many of the required components, in this article, we present a scalable framework for detailed behavior interpretation.
Our framework supports in-house monitoring of elders using an intelligent gateway and a set of cheap commercially available
sensors, in addition to more advanced camera-based human localization sensors and a client for GPS-enabled mobile phones that
provides monitoring when outdoors. In this article, we report our experiences and present our current progress in three main
components: sensors, middleware, and behavior interpretation mechanisms spanning from simple programmable rule-based alerts
to algorithms for extracting the temporal routines of individuals. 相似文献