全文获取类型
收费全文 | 82841篇 |
免费 | 15793篇 |
国内免费 | 156篇 |
专业分类
电工技术 | 1404篇 |
综合类 | 66篇 |
化学工业 | 26285篇 |
金属工艺 | 2455篇 |
机械仪表 | 3952篇 |
建筑科学 | 2692篇 |
矿业工程 | 25篇 |
能源动力 | 2873篇 |
轻工业 | 10401篇 |
水利工程 | 548篇 |
石油天然气 | 132篇 |
武器工业 | 2篇 |
无线电 | 13245篇 |
一般工业技术 | 20517篇 |
冶金工业 | 4400篇 |
原子能技术 | 668篇 |
自动化技术 | 9125篇 |
出版年
2024年 | 24篇 |
2023年 | 539篇 |
2022年 | 677篇 |
2021年 | 1671篇 |
2020年 | 2334篇 |
2019年 | 3961篇 |
2018年 | 4196篇 |
2017年 | 4427篇 |
2016年 | 5179篇 |
2015年 | 4816篇 |
2014年 | 5500篇 |
2013年 | 7588篇 |
2012年 | 5711篇 |
2011年 | 6014篇 |
2010年 | 5196篇 |
2009年 | 5192篇 |
2008年 | 4673篇 |
2007年 | 3899篇 |
2006年 | 3536篇 |
2005年 | 2971篇 |
2004年 | 2805篇 |
2003年 | 2704篇 |
2002年 | 2479篇 |
2001年 | 2149篇 |
2000年 | 1992篇 |
1999年 | 1350篇 |
1998年 | 1600篇 |
1997年 | 1031篇 |
1996年 | 823篇 |
1995年 | 570篇 |
1994年 | 480篇 |
1993年 | 420篇 |
1992年 | 304篇 |
1991年 | 287篇 |
1990年 | 267篇 |
1989年 | 246篇 |
1988年 | 209篇 |
1987年 | 178篇 |
1986年 | 127篇 |
1985年 | 118篇 |
1984年 | 95篇 |
1983年 | 66篇 |
1982年 | 38篇 |
1981年 | 41篇 |
1980年 | 31篇 |
1979年 | 31篇 |
1978年 | 31篇 |
1977年 | 39篇 |
1976年 | 61篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
Solutions of rare earth modifier (RES) and epoxy chloropropane (ECP) grafting modification method were used for the surface treatment of aramid fiber. Tensile properties of both the aramid/epoxy composites and single fibers were tested. The effects of RES concentration on tensile properties of aramid/epoxy composites were investigated in detail to explore an optimum amount of rare earth elements in solution for modifying aramid fiber. The fracture surface morphologies of tensile specimens were observed and analyzed with the aid of SEM. The experimental results show that rare earth treatment is superior to ECP grafting treatment in promoting interfacial adhesion between the aramid fiber and epoxy matrix. Meanwhile, the tensile strengths of single fibers were almost not affected by RES treatment. The optimum performance is obtained when the content of rare earth elements is 0.5 wt %. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1037–1041, 2004 相似文献
992.
Richard Kotek Dong‐Wook Jung Joon Ho Kim Brent Smith Patricia Guzman Benjamin Schmidt 《应用聚合物科学杂志》2004,92(3):1724-1730
The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180°C. Fiber weight loss increased with an increasing heat‐setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well‐developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 μm. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat‐setting temperature. A temperature of 180°C is the upper limit for heat‐setting PTT filaments but seems to be the most effective for making porous fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1724–1730, 2004 相似文献
993.
A series of soluble novel polyesterimides was synthesized from diamines [a mixture of 2,2‐bis(4‐(4‐aminophenoxy)phenyl)propane (BAPP) with amine‐terminated polysiloxane (ATPS) in various mole ratios] and the ester‐group‐containing dianhydrides. The ester group containing dianhydrides in turn was synthesized by the transesterification reaction of trimellitic anhydride (TMA) with diacetate ester of hydroquinone (HQ), 4,4′‐dihydrophenyl (BP), 1,6‐hexanediol, or ethylene glycol. The resulted polyesterimides were characterized by using Fourier‐transform infrared spectroscopy, inherent viscosity, solubility, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The polyesterimides of BP and HQ had relatively high glass transition temperatures in the range of 214.7–227.2 and 195.7–210.5°C, respectively. The glass transitions decreased rather slowly with the increase in polysiloxane content. Thermal stability and the weight‐loss behavior of polyesterimides were studied by TGA. All polyesterimides of BP and HQ (BPI and HQI) showed no significant weight loss below 500°C in a N2 environment, and the decomposition temperatures (Td5%) of BPI and HQI were >520°C. Most polyesterimides were soluble in polar aprotic solvents and m‐cresol. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 730–738, 2004 相似文献
994.
The synergistic effects of boron nitride (BN) powder and die on the rheology and processability of metallocene‐catalyzed low density polyethylene (mLDPE) were investigated. The processability in the extrusion process is closely related to the interfacial properties between the polymer melts and the die wall. BN powder was added to mLDPE to reduce the friction coefficient and surface energy. Adding 0.5 wt% BN powder to mLDPE was very effective in improving the processability and the extrudate appearance. To study the effect of die surface property, three different dies were applied in capillary extrusion. One was conventional tungsten carbide (TC) die, and the others were hot‐pressed BN (hpBN) die and hot‐pressed BN composite (hpBNC) die. The applications of these BN dies were quite effective in delaying surface melt fracture (sharkskin) and postponing gross melt fracture to higher shear rate compared to the TC die. These improvements result from the fact that BN dies reduce the wall shear stress significantly and promote slip. The synergistic effect of processability could be obtained when both BN powder and hpBN die were used together. 相似文献
995.
Interaction‐Feature Enhanced Multiuser Model Learning for a Home Environment Using Ambient Sensors 下载免费PDF全文
Activity recognition (AR) is a key enabler for a context‐aware smart home since knowing what the residents’ current activities helps a smart home provide more desirable services. This is why AR is often used in assistive technologies for cognitively impaired people to evaluate their abilities to undertake activities of daily living. In a real‐life scenario, multiple‐resident AR has been considered as a very challenging problem, primarily due to the complexity of data association. In addition, most prior research has not considered the potential interpersonal interactions among residents to simplify complexity, especially in an environment monitored by ambient sensors. In this study, we propose two types of multiuser activity models, both of which are derived from an interaction‐feature enhanced multiuser model learning framework. These two models consider interpersonal interactions and data association for multiuser AR using ambient sensors. We then compare their performance with the other two baseline models with or without consideration of data association and interpersonal interactions. The experimental results show that the derived models outperform other baseline classifiers. Therefore, the proposed approach can increase the opportunities for providing context‐aware services for a multiresident smart home. 相似文献
996.
Recently, Gregori et al. have discussed (Fuzzy Sets Syst 2011;161:2193–2205) the so‐called strong fuzzy metrics when looking for a class of completable fuzzy metric spaces in the sense of George and Veeramani and state the question of finding a nonstrong fuzzy metric space for a continuous t‐norm different from the minimum. Later on, Gutiérrez García and Romaguera solved this question (Fuzzy Sets Syst 2011;162:91–93) by means of two examples for the product and the Lukasiewicz t‐norm, respectively. In this direction, they posed to find further examples of nonstrong fuzzy metrics for continuous t‐norms that are greater than the product but different from minimum. In this paper, we found an example of this kind. On the other hand, Tirado established (Fixed Point Theory 2012;13:273–283) a fixed‐point theorem in fuzzy metric spaces, which was successfully used to prove the existence and uniqueness of solution for the recurrence equation associated with the probabilistic divide and conquer algorithms. Here, we generalize this result by using a class of continuous t‐norms known as ω‐Yager t‐norms. 相似文献
997.
Composites based on natural rubber (NR) and containing organophilic and pristine layered silicates of natural and synthetic origin were produced by melt compounding and sulfur curing. The curing, thermomechanical, and mechanical properties of the mixes, which contained 10 phr (parts per hundred parts of rubber) silicates, were determined. The dispersion of the silicates was studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Organophilic clays accelerated the sulfur curing of NR, which was believed to occur because of a complexation reaction in which the amine groups of the clay intercalants participated. The property improvements caused by the fillers were ranked as follows: organophilic clays > pristine synthetic layered silicate (sodium fluorohectorite) > pristine natural clay (purified sodium bentonite) > precipitated nonlayered silica (used as a reference). This was attributed to partial intercalation of the organophilic clay by NR on the basis of XRD and TEM results and to the high aspect ratio of the fluorohectorite. Apart from intercalation, severe confinement (i.e., the collapse of the interlayer distance) of the organoclays was observed. This peculiar feature was traced to the formation of a zinc coordination complex, which extracted the amine intercalant of the organoclays, thus causing the collapse of the layers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 813–819, 2004 相似文献
998.
Salvador Hernndez Salvador Pereira‐Pech Arturo Jimnez Vicente Rico‐Ramírez 《加拿大化工杂志》2003,81(5):1087-1091
Several thermally coupled distillation sequences have been proposed to improve the thermal inefficiency of conventional distillation sequences. Particularly, for the separation of ternary mixtures, structures that perform a lateral extraction in one of the columns of the integrated arrangement have been shown to provide significant energy savings. The structure of existing sequences, based on conventional distillation columns, might provide the basis for alternate thermally coupled designs. In this paper, it is shown how a thermally coupled system derived from an indirect conventional sequence can provide energy savings through a proper optimization of the interconnecting streams. 相似文献
999.
The liquid-liquid equilibrium for the quaternary system of o-xylene(1)+water(2)+propionic acid(3)+1-butanol(4) was measured
at 298.15 K and atmospheric pressure. Binodal curves, tie-lines, a distribution curve, and a selectivity curve for the quaternary
system have been determined in order to investigate the effect of binary solvents, oxylene and 1-butanol, on extracting propionic
acid from aqueous solution. In addition, these experimental tie line data were also compared with the values predicted by
the UNIFAC model. In this study, the UNIFAC model was capable of predicting the compositions of this quaternary system within
an average RMSD of 1.13 mol%.
This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November
3 and 4, 2004. 相似文献
1000.
We have studied the effect of the amount Φc of a reactive compatibilizer on the rheological properties of a polyethylene/polyamide blend, under steady shear and transient extensional flows. Here, we propose to describe the viscosity η(γ) and the first normal stress coefficient γ1(γ) using a Carreau‐type power‐law model, which is a three‐parameter model. A single model is sufficient to express the behavior of γ1(γ) On the other hand, the complete η(γ) curve is described by the superposition of two Carreau models, in relation to the presence of two relaxation mechanisms. Moreover, the extentional viscosity ηE(?), estimated using the end pressure drop observed in capillary flow experiments, is expressed by a two‐parameter power‐law model. 相似文献