全文获取类型
收费全文 | 5178篇 |
免费 | 340篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 73篇 |
综合类 | 15篇 |
化学工业 | 980篇 |
金属工艺 | 103篇 |
机械仪表 | 162篇 |
建筑科学 | 211篇 |
矿业工程 | 6篇 |
能源动力 | 193篇 |
轻工业 | 360篇 |
水利工程 | 30篇 |
石油天然气 | 21篇 |
无线电 | 851篇 |
一般工业技术 | 1051篇 |
冶金工业 | 465篇 |
原子能技术 | 25篇 |
自动化技术 | 1014篇 |
出版年
2024年 | 7篇 |
2023年 | 32篇 |
2022年 | 106篇 |
2021年 | 137篇 |
2020年 | 110篇 |
2019年 | 129篇 |
2018年 | 143篇 |
2017年 | 119篇 |
2016年 | 144篇 |
2015年 | 147篇 |
2014年 | 212篇 |
2013年 | 437篇 |
2012年 | 299篇 |
2011年 | 302篇 |
2010年 | 270篇 |
2009年 | 284篇 |
2008年 | 282篇 |
2007年 | 258篇 |
2006年 | 222篇 |
2005年 | 183篇 |
2004年 | 149篇 |
2003年 | 170篇 |
2002年 | 140篇 |
2001年 | 115篇 |
2000年 | 101篇 |
1999年 | 112篇 |
1998年 | 166篇 |
1997年 | 117篇 |
1996年 | 80篇 |
1995年 | 72篇 |
1994年 | 52篇 |
1993年 | 55篇 |
1992年 | 42篇 |
1991年 | 28篇 |
1990年 | 36篇 |
1989年 | 34篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1973年 | 8篇 |
排序方式: 共有5560条查询结果,搜索用时 15 毫秒
991.
Due to the high cost of adsorbents and their thermal regeneration in recent years,much research has focused on the search for cheaper adsorbents for treating wastewater from textile industry.The single component adsorption of an acidic dye,Acid Yellow 117,and a basic dye,Methylene Blue,onto several adsorbents—bamboo,waste wood,bamboo char,waste wood char,bamboo activated carbon,wood activated carbon and active carbon F400 were conducted.Based on a Langmuir analysis,the monolayer adsorption capacities were determined.Three of the adsorbents were selected for binary layer adsorption to check the multilayer concept and the potential application for better adsorbent usage.The two cheapest adsorbents,bamboo and wood are compared with the commercial activated carbon F400,and all three systems were successful. 相似文献
992.
JY Yeh MS Coumar HY Shiao TJ Lin YC Lee HC Hung S Ko FM Kuo MY Fang YL Huang JT Hsu TK Yeh SR Shih YS Chao JT Horng HP Hsieh 《ChemMedChem》2012,7(9):1546-1550
From a high-throughput screening (HTS) hit with inhibitory activity against virus-induced cytophathic in the low micromolar range, we have developed a potent anti-influenza lead through careful optimization without compromising the drug-like properties of the compound. An orally bioavailable compound was identified as a lead agent with nanomolar activity against influenza, representing a 140-fold improvement over the initial hit. 相似文献
993.
Ning Han Jared J Hou Fengyun Wang SenPo Yip Hao Lin Ming Fang Fei Xiu Xiaoling Shi TakFu Hung Johnny C Ho 《Nanoscale research letters》2012,7(1):632
One of the challenges to prepare high-performance and uniform III-V semiconductor nanowires (NWs) is to control the crystal structure in large-scale. A mixed crystal phase is usually observed due to the small surface energy difference between the cubic zincblende (ZB) and hexagonal wurtzite (WZ) structures, especially on non-crystalline substrates. Here, utilizing Au film as thin as 0.1 nm as the catalyst, we successfully demonstrate the large-scale synthesis of pure-phase WZ GaAs NWs on amorphous SiO2/Si substrates. The obtained NWs are smooth, uniform with a high aspect ratio, and have a narrow diameter distribution of 9.5 ± 1.4 nm. The WZ structure is verified by crystallographic investigations, and the corresponding electronic bandgap is also determined to be approximately 1.62 eV by the reflectance measurement. The formation mechanism of WZ NWs is mainly attributed to the ultra-small NW diameter and the very narrow diameter distribution associated, where the WZ phase is more thermodynamically stable compared to the ZB structure. After configured as NW field-effect-transistors, a high ION/IOFF ratio of 104 − 105 is obtained, operating in the enhancement device mode. The preparation technology and good uniform performance here have illustrated a great promise for the large-scale synthesis of pure phase NWs for electronic and optical applications. 相似文献
994.
In this study, we report on a unique, one-step fabrication technique enabling the simultaneous synthesis of vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with dual height scales through alcohol catalyzed chemical vapor deposition (ACCVD). Regions of VA-MWCNTs with different heights were well separated from each other leading to a self-patterning on the surface. We devised a unique layer-by-layer process for application of catalyst and inhibitor precursors on oxidized Si (100) surfaces before the ACCVD step to achieve a hierarchical arrangement. Patterning could be controlled by adjusting the molarity and application sequence of precursors. Contact angle measurements on these self-patterned surfaces indicated that manipulation of these hierarchical arrays resulted in a wide range of hydrophobic behavior changing from that of a sticky rose petal to a lotus leaf. 相似文献
995.
Periodic zinc oxide (ZnO) nanomeshes of different thicknesses were deposited on single-layer graphene to form back-gated field effect transistors (GFETs). The GFETs exhibit tunable electronic properties, featuring n- and p-type characteristics by merely controlling the thickness of the ZnO nanomesh layer. Furthermore, the effect of thermal strain on the GFETs from the substrate is suppressed by the ZnO nanomesh, which improves the thermal stability of the GFETs. This nanopatterning technique could modulate the electronic properties of the GFETs effectively. 相似文献
996.
Yen-Pin Tsai Jung-Chung Hung Li-Chao Yin Chinghua Hung 《The International Journal of Advanced Manufacturing Technology》2012,60(9-12):1207-1213
A homemade apparatus was used to apply ultrasonic-vibration to assist the glass hot embossing processes. To operate at high temperatures for glass hot embossing, the ultrasonic vibration system was appropriately designed with an embedded cooling system, and an ultrasonic horn was specifically modified for high-temperature use. Molds with both V-groove and Fresnel structures were manufactured for hot embossing experiments on PSK-100 glass. The heights of the molded structures were increased significantly with the assistance of ultrasonic vibration. This technology demonstrates the capability to upgrade the performance of the glass hot embossing process. 相似文献
997.
Transparent exopolymer particle removal in different drinking water production centers 总被引:1,自引:0,他引:1
Van Nevel S Hennebel T De Beuf K Du Laing G Verstraete W Boon N 《Water research》2012,46(11):3603-3611
Transparent exopolymer particles (TEP) have recently gained interest in relation to membrane fouling. These sticky, gel-like particles consist of acidic polysaccharides excreted by bacteria and algae. The concentrations, expressed as xanthan gum equivalents L−1 (μg Xeq L−1), usually reach hundred up to thousands μg Xeq L−1 in natural waters. However, very few research was performed on the occurrence and fate of TEP in drinking water, this far. This study examined three different drinking water production centers, taking in effluent of a sewage treatment plant (STP), surface water and groundwater, respectively. Each treatment step was evaluated on TEP removal and on 13 other chemical and biological parameters. An assessment on TEP removal efficiency of a diverse range of water treatment methods and on correlations between TEP and other parameters was performed. Significant correlations between particulate TEP (>0.4 μm) and viable cell concentrations were found, as well as between colloidal TEP (0.05-0.4 μm) and total COD, TOC, total cell or viable cell concentrations. TEP concentrations were very dependent on the raw water source; no TEP was detected in groundwater but the STP effluent contained 1572 μg Xeq L−1 and the surface water 699 μg Xeq L−1. Over 94% of total TEP in both plants was colloidal TEP, a fraction neglected in nearly every other TEP study. The combination of coagulation and sand filtration was effective to decrease the TEP levels by 67%, while the combination of ultrafiltration and reverse osmosis provided a total TEP removal. Finally, in none of the installations TEP reached the final drinking water distribution system at significant concentrations. Overall, this study described the presence and removal of TEP in drinking water systems. 相似文献
998.
Jack Shih-Chieh Hsu Tung-Ching Lin Guang-Ting Zheng Yu-Wen Hung 《International Journal of Project Management》2012,30(1):27-36
This study investigates the role of users as knowledge co-producers in different stages of the information system development project. Data collected from 269 IS professionals supported our hypotheses that common knowledge has an impact on requirement determination, which, in turn, leads to better project performance. User-IS relationship can substitute the effect of common knowledge on requirement determination in the design stage and user review can ensure that the obtained requirements are actually carried out by developers in the development stage. As a result, higher project performance can be obtained. Discussion of the results and conclusions is also provided. 相似文献
999.
Nguyen HD Cao B Mishra B Boyanov MI Kemner KM Fredrickson JK Beyenal H 《Water research》2012,46(1):227-234
The presence and importance of microenvironments in the subsurface at contaminated sites were suggested by previous geochemical studies. However, no direct quantitative characterization of the geochemical microenvironments had been reported. We quantitatively characterized microscale geochemical gradients (dissolved oxygen (DO), H2, pH, and redox potential) in Hanford 300A subsurface sediment biofilms. Our results revealed significant differences in geochemical parameters across the sediment biofilm/water interface in the presence and absence of U(VI) under oxic and anoxic conditions. While the pH was relatively constant within the sediment biofilm, the redox potential and the DO and H2 concentrations were heterogeneous at the microscale (<500-1000 μm). We found microenvironments with high DO levels (DO hotspots) when the sediment biofilm was exposed to U(VI). On the other hand, we found hotspots (high concentrations) of H2 under anoxic conditions both in the presence and in the absence of U(VI). The presence of anoxic microenvironments inside the sediment biofilms suggests that U(VI) reduction proceeds under bulk oxic conditions. To test this, we operated our biofilm reactor under air-saturated conditions in the presence of U(VI) and characterized U speciation in the sediment biofilm. U LIII-edge X-ray absorption spectroscopy (XANES and EXAFS) showed that 80-85% of the U was in the U(IV) valence state. 相似文献
1000.
Jean-Gilles Beaubrun J Cheng CM Chen KS Ewing L Wang H Agpaoa MC Huang MC Dickey E Du JM Williams-Hill DM Hamilton B Micallef SA Rosenberg Goldstein RE George A Joseph SW Sapkota AR Jacobson AP Tall BD Kothary MH Dudley K Hanes DE 《Food microbiology》2012,31(2):199-209
The most commonly used method for serotyping Salmonella spp. is based on the Kaufmann–White scheme, and is composed of serological reactions using antibodies to LPS agglutinins. The multiplex PCR used in this investigation was established by Kim et al. to serotype the 30 most common clinical Salmonella serotypes, as determined by CDC. The PCR assay consists of two five-plex reactions and a single two-plex PCR reaction, based on six genetic loci from Salmonella enterica serotype Typhimurium and four loci from S. enterica serotype Typhi. In this investigation, we further evaluated the method for serotyping Salmonella spp. using a reference collection, environmental samples collected from a Mid-Atlantic region tomato farm study, four food matrices spiked with different Salmonella serotypes and a proficiency test. The PCR assay was first evaluated using DNA isolated from pure cultures of isolates obtained from various clinical and environmental samples, and then DNA isolated from broth cultures of food matrices of “Red round” and Roma tomatoes, Romaine lettuce, green onions and Serrano peppers spiked with serotypes Newport, Typhimurium, Javiana and Saintpaul, respectively. The results showed that the PCR assay correctly serotyped Salmonella spp. from the clinical, environmental, spiked food matrices, and proficiency test samples. These findings are significant because the PCR assay was successful in the identification of Salmonella in the spiked samples in a broth culture containing other non-salmonella organism. This method may be a useful resource for the food safety community. 相似文献