全文获取类型
收费全文 | 40853篇 |
免费 | 2825篇 |
国内免费 | 1007篇 |
专业分类
电工技术 | 1600篇 |
技术理论 | 4篇 |
综合类 | 1557篇 |
化学工业 | 7449篇 |
金属工艺 | 1786篇 |
机械仪表 | 2061篇 |
建筑科学 | 1803篇 |
矿业工程 | 761篇 |
能源动力 | 1511篇 |
轻工业 | 2710篇 |
水利工程 | 475篇 |
石油天然气 | 1024篇 |
武器工业 | 148篇 |
无线电 | 6332篇 |
一般工业技术 | 6456篇 |
冶金工业 | 3040篇 |
原子能技术 | 451篇 |
自动化技术 | 5517篇 |
出版年
2024年 | 110篇 |
2023年 | 520篇 |
2022年 | 961篇 |
2021年 | 1354篇 |
2020年 | 1068篇 |
2019年 | 930篇 |
2018年 | 1083篇 |
2017年 | 1124篇 |
2016年 | 1066篇 |
2015年 | 1224篇 |
2014年 | 1674篇 |
2013年 | 2472篇 |
2012年 | 2419篇 |
2011年 | 2815篇 |
2010年 | 2186篇 |
2009年 | 2288篇 |
2008年 | 2279篇 |
2007年 | 2035篇 |
2006年 | 1793篇 |
2005年 | 1468篇 |
2004年 | 1284篇 |
2003年 | 1345篇 |
2002年 | 1559篇 |
2001年 | 1309篇 |
2000年 | 947篇 |
1999年 | 816篇 |
1998年 | 1123篇 |
1997年 | 814篇 |
1996年 | 655篇 |
1995年 | 550篇 |
1994年 | 434篇 |
1993年 | 379篇 |
1992年 | 278篇 |
1991年 | 236篇 |
1990年 | 245篇 |
1989年 | 221篇 |
1988年 | 187篇 |
1987年 | 168篇 |
1986年 | 140篇 |
1985年 | 135篇 |
1984年 | 113篇 |
1983年 | 84篇 |
1982年 | 76篇 |
1981年 | 64篇 |
1980年 | 82篇 |
1979年 | 53篇 |
1978年 | 61篇 |
1977年 | 63篇 |
1976年 | 82篇 |
1975年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献
92.
Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene] (MEH‐PPV)/silica nanoparticle hybrid films were prepared and characterised. Three kinds of materials were compared: parent MEH‐PPV, MEH‐PPV/silica (hybrid A films), and MEH‐PPV/coupling agent MSMA/silica (hybrid B films), in which MSMA is 3‐(trimethoxysilyl) propyl methacrylate. It was found that the hybrid B films could significantly prevent macrophase separation, as evidenced by scanning electron and fluorescence microscopy. Furthermore, the thermal characteristics of the hybrid films were largely improved in comparison with the parent MEH‐PPV. The UV‐visible absorption spectra suggested that the incorporation of MSMA‐modified silica into MEH‐PPV could confine the polymer chain between nanoparticles and thus increase the conjugation length. The photoluminescence (PL) studies also indicated enhancement of the PL intensity and quantum efficiency by incorporating just 2 wt% of MSMA‐modified silica into MEH‐PPV. However, hybrid A films did not show such enhancement of optoelectronic properties as the hybrid B films. The present study suggests the importance of the interface between the luminescent organic polymers and the inorganic silica on morphology and optoelectronic properties. Copyright © 2004 Society of Chemical Industry 相似文献
93.
Temperature and pH‐responsive interpenetrating polymer network (IPN) hydrogels, constructed with poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA), by a sequential IPN method, were studied. The characterization of IPN hydrogels was investigated by Fourier‐transform infrared spectroscopy, differential scanning calorimetry (DSC) and swelling under various conditions. The IPN hydrogels exhibited relatively high swelling ratios, in the range 230–380 %, at 25 °C. The swelling ratios of the PMAA/PVA IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the amounts of freezing and non‐freezing water. The amount of free water increased with increasing PMAA content in the IPN hydrogels. Copyright © 2004 Society of Chemical Industry 相似文献
94.
Trieu-Kien Truong Yaotsu Chang Yan-Haw Chen Lee C.D. 《Communications, IEEE Transactions on》2005,53(5):749-754
In this paper, two algebraic decoders for the (103, 52, 19) and (113, 57, 15) quadratic residue codes, which have lengths greater than 100, are presented. The results have been verified by software simulation that programs in C++ language have been executed to check possible error patterns of both quadratic residue codes. 相似文献
95.
96.
97.
Jen-Chwen Lin T. Leo Ngai Y. Austin Chang 《Metallurgical and Materials Transactions A》1986,17(7):1241-1245
Defect equilibria for binary semiconducting compound phases which exhibit ionized native donor and acceptor defects were considered,
and equations describing the pressure-temperature-composition relationships for these compound phases were derived. These
equations were used to analyze experimental data from the literature for tin telluride. Excellent agreement was obtained between
calculated thermodynamic and phase boundary values and experimental data. The approach presented is readily extended to obtain
equations for the thermodynamic properties of ternary and higher order semiconducting compound phases. 相似文献
98.
S H Yoon J H Collins D Musale S Sundararajan S P Tsai G A Hallsby J F Kong J Koppes P Cachia 《Water science and technology》2005,51(6-7):151-157
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works. 相似文献
99.
Dielectric reliability in Al2O3(2–3.1nm)–HfO2(3nm) stack capacitor with Metal–Insulator–Si(MIS) structure is investigated in this paper. We propose an optimized capacitor process through the Time–Dependent Dielectric Breakdown (TDDB) data under various process conditions. Furthermore, due to asymmetric current at both negative and positive voltage stress polarities, we show different lifetime extrapolation by a fluence–driven model. As a result, the maximum allowed operating voltage is projected to be 1.7V (failure rate 10ppm during 10year @ 85°C) for Data “0” retention lifetime. 相似文献
100.
This study used different metals to modify Rh/Al2O3 catalysts for NO reduction in a simulated waste incineration flue gas containing 6% O2. The characteristics of the modified catalysts were analyzed using BET, TEM and XRD. The results of the experiment reveal that Na addition can significantly affect the properties of Rh/Al2O3 catalysts on the BET surface area and Rh metal dispersion. Furthermore, Na addition was found to significantly enhance the NO conversion of Rh/Al2O3 at 250–350 °C. On the contrary, Cu, Ni, and Co addition was found to have slight suppression effects. 相似文献