全文获取类型
收费全文 | 112679篇 |
免费 | 23180篇 |
国内免费 | 1358篇 |
专业分类
电工技术 | 3224篇 |
综合类 | 2866篇 |
化学工业 | 48102篇 |
金属工艺 | 2015篇 |
机械仪表 | 2285篇 |
建筑科学 | 3188篇 |
矿业工程 | 1146篇 |
能源动力 | 2969篇 |
轻工业 | 26058篇 |
水利工程 | 479篇 |
石油天然气 | 3450篇 |
武器工业 | 75篇 |
无线电 | 9746篇 |
一般工业技术 | 19737篇 |
冶金工业 | 2905篇 |
原子能技术 | 539篇 |
自动化技术 | 8433篇 |
出版年
2024年 | 282篇 |
2023年 | 786篇 |
2022年 | 1702篇 |
2021年 | 2467篇 |
2020年 | 4624篇 |
2019年 | 7156篇 |
2018年 | 6382篇 |
2017年 | 7311篇 |
2016年 | 7244篇 |
2015年 | 7026篇 |
2014年 | 7997篇 |
2013年 | 8875篇 |
2012年 | 8519篇 |
2011年 | 8309篇 |
2010年 | 6382篇 |
2009年 | 6007篇 |
2008年 | 5546篇 |
2007年 | 6170篇 |
2006年 | 5715篇 |
2005年 | 4749篇 |
2004年 | 4137篇 |
2003年 | 3763篇 |
2002年 | 3461篇 |
2001年 | 2946篇 |
2000年 | 2656篇 |
1999年 | 1895篇 |
1998年 | 968篇 |
1997年 | 747篇 |
1996年 | 644篇 |
1995年 | 526篇 |
1994年 | 467篇 |
1993年 | 391篇 |
1992年 | 289篇 |
1991年 | 233篇 |
1990年 | 175篇 |
1989年 | 113篇 |
1988年 | 77篇 |
1987年 | 93篇 |
1986年 | 67篇 |
1985年 | 76篇 |
1984年 | 74篇 |
1983年 | 37篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
12.
Konstantinos Spyrou Matteo Calvaresi Evmorfia K. Diamanti Theodoros Tsoufis Dimitrios Gournis Petra Rudolf Francesco Zerbetto 《Advanced functional materials》2015,25(2):263-269
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. 相似文献
13.
14.
《Egyptian Journal of Petroleum》2015,24(1):49-57
Series of MCM-41 supported sulfated Zirconia (SZ) catalysts with different loadings (2.5–7.5% wt.) were prepared using direct impregnation method. The acquired solid catalysts were characterized structurally and chemically using X-RD, HRTEM, BET, FT-IR, Raman spectroscopy and TPD analysis. The acidity of the solid catalysts was investigated through cumene cracking and isopropanol dehydration at different temperatures. As the SZ loading increases, the surface acidity of the mesoporous catalysts was enhanced, this was reflected by the higher catalytic activity toward cumene cracking and isopropanol dehydration. 相似文献
15.
Esteban Vera Pingitore María Silvina Juárez Tomás Birgitt Wiese 《Drug development and industrial pharmacy》2015,41(6):942-952
Context: The administration of pharmabiotics is a promising alternative to antimicrobial drugs for the treatment and/or prevention of female urogenital infections.Objective: To design pharmabiotic formulations including bioactive ingredients of microbial origin combined with non-microbial substances and then to evaluate the stability of the combinations during freeze-drying and storage.Materials and methods: Different formulations including Lactobacillus gasseri CRL 1263, Lactobacillus salivarius CRL 1328, salivaricin CRL 1328 (a bacteriocin) and non-microbial compounds (lactose, inulin and ascorbic acid) were assayed, and the ingredients were freeze-dried together or separately. The formulations were stored in gelatin capsules at 4?°C for 360?d.Results: The viability of lactobacilli was affected to different extents depending on the strains and on the formulations assayed. L. salivarius and ascorbic acid were successfully combined only after the freeze-drying process. Salivaricin activity was not detected in formulations containing L. gasseri. However, when combined with ascorbic acid, lactose, inulin or L. salivarius, the bacteriocin maintained its activity for 360?d. The selected microorganisms proved to be compatible for their inclusion in multi-strain formulations together with lactose, inulin and ascorbic acid. Salivaricin could be included only in a L. salivarius CRL 1328 single-strain formulation together with non-microbial substances.Conclusions: This study provides new insights into the design of urogenital pharmabiotics combining beneficial lactobacilli, salivaricin CRL 1328 and compounds with different functionalities. 相似文献
16.
《Food Control》2015
Consumption of vegetables is increasing due to demand for healthy products in peoples' diets. To reduce microbial contamination and maintain freshness, industrial processes in Portugal rely on minimally processing of vegetables with hypochlorite as sanitizer. Formation of toxic chlorine derivatives has raised concern restrictions to its use and alternatives with whey permeate as a disinfection agent has been attempted. The aim of this work was to evaluate the bio potential of fermented cheese whey, for use on disinfection of minimally processed lettuce organically grown.Assays were made with whey obtained from inoculated milk during cheese processing, fermented for 120 h at 37 °C, after which, among other carbohydrates, lactic acid was measured by HPLC, giving average yields of 18 g L−1.The sanitizing effect of whey, undiluted, 75 and 50% solutions, was compared with 110 ppm sodium hypochlorite, after rinsing. Aerobic Microorganisms (AM), Psychrotrophic Microorganisms (PM) and Enterobacteriaceae (ENT), were used as indicators for hygiene quality. For a level of significance of P < 0.05, the hygiene quality standards of lettuce samples, were better using 75% whey solution (AM 6.62, PM 7.48 cfu g−1), than using sodium hypochlorite (AM 7.48, PM 8.15 cfu g−1), for the 7 days of shelf life studied. Evaluation of Enterobacteriaceae showed significant differences after 3 days, between water (ENT 4.98 cfu g−1) sodium hypochlorite (ENT 4.81 cfu g−1) and 75% solution of whey (ENT 4.63 cfu g−1).Considering the actual limitations imposed to chlorine sanitation, these results point a good alternative to the food industry, especially for organic fresh vegetables, which are chemical free brands. 相似文献
17.
Joon‐Young Jun Sosuke Nakajima Koji Yamazaki Yuji Kawai Hajime Yasui Yasuyuki Konishi 《International Journal of Food Science & Technology》2015,50(4):871-877
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria. 相似文献
18.
The principles and design of “active” self‐propelling particles that can convert energy, move directionally on their own, and perform a certain function is an emerging multidisciplinary research field, with high potential for future technologies. A simple and effective technique is presented for on‐demand steering of self‐propelling microdiodes that move electroosmotically on water surface, while supplied with energy by an external alternating (AC) field. It is demonstrated how one can control remotely the direction of diode locomotion by electronically modifying the applied AC signal. The swimming diodes change their direction of motion when a wave asymmetry (equivalent to a DC offset) is introduced into the signal. The data analysis shows that the ability to control and reverse the direction of motion is a result of the electrostatic torque between the asymmetrically polarized diodes and the ionic charges redistributed in the vessel. This novel principle of electrical signal‐coded steering of active functional devices, such as diodes and microcircuits, can find applications in motile sensors, MEMs, and microrobotics. 相似文献
19.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity 下载免费PDF全文
20.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures. 相似文献