全文获取类型
收费全文 | 1335篇 |
免费 | 45篇 |
专业分类
电工技术 | 61篇 |
化学工业 | 409篇 |
金属工艺 | 28篇 |
机械仪表 | 31篇 |
建筑科学 | 20篇 |
能源动力 | 60篇 |
轻工业 | 107篇 |
水利工程 | 7篇 |
石油天然气 | 1篇 |
无线电 | 102篇 |
一般工业技术 | 301篇 |
冶金工业 | 105篇 |
原子能技术 | 29篇 |
自动化技术 | 119篇 |
出版年
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 29篇 |
2020年 | 18篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 32篇 |
2015年 | 28篇 |
2014年 | 57篇 |
2013年 | 101篇 |
2012年 | 57篇 |
2011年 | 106篇 |
2010年 | 84篇 |
2009年 | 51篇 |
2008年 | 70篇 |
2007年 | 62篇 |
2006年 | 51篇 |
2005年 | 50篇 |
2004年 | 55篇 |
2003年 | 41篇 |
2002年 | 38篇 |
2001年 | 23篇 |
2000年 | 32篇 |
1999年 | 21篇 |
1998年 | 47篇 |
1997年 | 34篇 |
1996年 | 29篇 |
1995年 | 24篇 |
1994年 | 19篇 |
1993年 | 15篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1380条查询结果,搜索用时 671 毫秒
861.
The purpose of this study is to propose new thermal index for outdoor and non-uniform environments with heat conduction, such as when a person sits on a bench at a park. This paper describes mathematically the theory of how solar radiation and heat conduction, as well as air temperature, humidity, air velocity and longwave radiation, are incorporated into the new index and how these thermal factors that may not be uniform are treated. Another important feature is that separate indices are generated for each factor while the new index is derived. It is expected that the new index will help us to understand how much each factor affects the human thermal comfort in outdoor and non-uniform environments with heat conduction. 相似文献
862.
The present study investigated the application of zero valent iron to remediate the arsenic in naturally contaminated groundwater. A performance evaluation was conducted in the laboratory on groundwater contaminated with artificial arsenic using sodium arsenate (Na2HAsO4.7H2O) to simulate the arsenic concentration in the groundwater. Batch and column experiments were performed to evaluate the arsenic removal capacity by zero valent iron and the removal mechanism. The flow rate (up-flow mode) was maintained for 180 days in each column. The results from both the batch and the column experiments showed that more than 99% of the arsenic was removed successfully. In the column experiments, the arsenic was efficiently removed and the arsenic concentration in the treated water decreased to below the limit of 10 μg /L (WHO's standard) even when the columns were packed with only 25% ZVI by volume. We used SEM and XRD to characterize the surface morphology and the corrosion layer which formed on pristine ZVI and arsenic-treated ZVI to elucidate the arsenic removal mechanism. XRD and SEM results revealed that ZVI gradually converted to a magnetite/maghemite corrosion product mixed with lepidocrocite. Adsorption followed by co-precipitation was an important pathway to removing the arsenic by ZVI. Our results suggest that ZVI, combined with sand, is a suitable candidate for the ex-situ treatment of groundwater in the neutral pH range and in the presence of dissolved oxygen. 相似文献
863.
Availability of bone marrow stromal cells in three-dimensional coculture with hepatocytes and transplantation into liver-damaged mice 总被引:5,自引:0,他引:5
Takeda M Yamamoto M Isoda K Higashiyama S Hirose M Ohgushi H Kawase M Yagi K 《Journal of Bioscience and Bioengineering》2005,100(1):77-81
Rat bone marrow stromal cells (BMSCs) were cultured in porous hydroxyapatite (HA) disks for 2 weeks to form a cell layer on the surface. Freshly isolated hepatocytes were then inoculated into both BMSC-cultured and non-treated HA disks. Hepatocytes cocultured with BMSCs secreted significantly more albumin than those in monoculture in vitro. The cell-packed HA disks were implanted into the peritoneal cavity of Nagase analbuminemia rats (NARs), and 4 weeks later, blood samples were collected to measure the albumin concentration. The cotransplantation of BMSCs with hepatocytes significantly increased the serum albumin concentration in NARs. The HA disks coculturing mice hepatocytes and BMSCs were also implanted into mice, in which liver damage had been induced using carbon tetrachloride and phenobarbital. The decreased serum albumin level in liver-damaged mice was completely recovered by the transplantation of hepatocytes and BMSCs. The serum level of IL-6 in liver-damaged mice was also increased by the cotransplantation of BMSCs and hepatocytes. Thus, the transplantation of BMSCs appears to have a systemic effect on recipients through the increase in the serum cytokine level as well as a local effect on cotransplanted hepatocytes. 相似文献
864.
Mitoma Y Uda T Egashira N Simion C Tashiro H Tashiro M Fan X 《Environmental science & technology》2004,38(4):1216-1220
Detoxification of highly toxic polychlorinated aromatic compounds such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and dioxin-like compounds such as coplanar polychlorinated biphenyls (co-PCBs) under mild conditions (atmospheric pressure and room temperature) was achieved by a simple stirring operation for 24 h using metallic calcium in ethanol, without any tedious decomposition procedures and harsh conditions such as high temperature and/or high pressure. Metallic calcium can be kept stable under atmospheric conditions for a long period as compared to metallic sodium since the surface is coated with CaCO3, which is formed in the contact with air. Moreover, ethanol, which is one of the safest solvents for humans, acts not only as a solvent but also as an accelerator due to its ablility to remove the carbonated coating. This decomposition method for PCDDs, PCDFs, and co-PCBs therefore is one of the most economical and environmentally friendly detoxification methods with respect to the input energy and safety of reagents used. Concentration for each isomer of PCDDs, PCDFs, and co-PCBs was reduced in 98.32-100% conversions by treatment in ethanol at room temperature. The toxicity equivalency quantity (TEQ), which was measured by the HRGC-HRMS analysis, for the total residues of isomers was reduced from 22,000 to 210 pg TEQ/mL of hexane (conversion: 99.05%) at room temperature. By refluxing over 24 h, the conversion increased up to 99.45%. 相似文献
865.
Spaghetti was prepared using dies made of different materials. The surface was observed using digital and optical microscopes, and was rougher for the spaghettis prepared using the Teflon, polypropylene, polycarbonate, aluminum, and bronze dies in this order. The extrusion velocity when passing through the die was faster, the bulk density was higher, and the rupture strength was greater for the spaghetti having the smoother surface. The die material did not affect the gelatinization temperature. The water sorption curves in boiling water containing 0.5% (w/v) sodium chloride were also observed. The curves were expressed by an equation of the hyperbolic type except for the early stage of sorption in order to estimate the equilibrium amount of water sorbed based on the bone‐dry sample. The momentarily‐sorbed amount of water, which is a hypothetical quantity to characterize the initial water intake, was estimated by fitting the experimental points within 60 s. The amount was higher for the spaghetti having the rougher surface. 相似文献
866.
Naohiro Hamaoka Junki Shimajiri Masayuki Abe Masashi Hosokawa Kazuo Miyashita 《Journal of food science》2013,78(9):C1348-C1353
A novel seafood paste was developed by the fermentation of scallop ovary using rice malt (koji) and yeast culture. Chemical analysis of the product showed the formation of high level of free amino acids and organic acids during the fermentation. The product color and flavor resembled to Japanese traditional soybean miso. The contents of total lipids (TLs) extracted from the fermented products were ranged from 9.18% to 11.59% or 11.38% to 13.57%/dry sample weight. Although the TL was rich in oxidatively unstable polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), little decrease was found in these PUFAs during the fermentation, showing the high oxidative stability of the TL from the fermented scallop ovary. Moreover, the oxidative stability of the TL extracted from the fermented products increased with increasing the fermentation time. This would be mainly due to the formation of lipid soluble antioxidants such as tocopherols, which might be derived from yeast used for fermentation. 相似文献
867.
Alignment methods of nematic liquid crystals (LCs) by surface photoreactions on substrate surfaces were initially proposed around 1990, and the photoalignment technology of nematic LCs has recently been integrated into the LC device fabrication industry due to its profitable features. Accumulated efforts in this field have revealed that applications of photoalignment processes are not limited to conventional nematic LCs but that a variety of functional materials can also be manipulated according to this principle. Target materials have now been extended to thermotropic smectic LCs, discotic LCs, LC polymers, block copolymers, gel networks, conjugated polymers, and organic semiconductors and lyotropic systems including chromonic LCs and inorganic–organic mesostructured hybrids. Through these photochemical approaches, many types of photopatterning for both topographical and orientational modulations have become feasible. This article reviews photoalignment processes applied to a wide range of materials, surveying relatively recent work. Some important related alignment and patterning processes are also introduced to clarify the significance of these photoalignment techniques. 相似文献
868.
Stearoyl-coenzyme A desaturase-1 (SCD1) is a rate-limiting enzyme that catalyzes the biosynthesis of monounsaturated fatty acids from saturated fatty acids. Recently, SCD1 down-regulation has been implicated in the prevention of obesity, and the improvement of insulin and leptin sensitivity. In this study, we examined the effect of fucoxanthin, a marine carotenoid, on hepatic SCD1 in obese mouse models of hyperleptinemia KK-A y and leptin-deficiency ob/ob. In KK-A y mice, providing a diet containing 0.2 % fucoxanthin for 2 weeks markedly suppressed SCD1 mRNA and protein expressions in the liver. The fatty acid composition of liver lipids was also affected by an observed decrease in the ratio of oleic acid to stearic acid. Furthermore, serum leptin levels were significantly decreased in hyperleptinemia KK-A y mice after 2 weeks of fucoxanthin feeding. However, the suppressive effects of fucoxanthin on hepatic SCD1 and body weight gain were not observed in ob/ob mice. These results show that fucoxanthin down-regulates SCD1 expression and alters fatty acid composition of the liver via regulation of leptin signaling in hyperleptinemia KK-A y mice but not in leptin-deficient ob/ob mice. 相似文献
869.
Mechanical treatments of veratrylglycerol-β-syringaldehyde ether (M) were conducted with a ceramic ball mill or a vibration ball mill in the presence of water and n-paraffin alcohols which were used as ·OH scavengers. Addition of 1% each of the alcohols to the milling process of Compound (M) greatly decreased the yields of the products, e.g. veratryl alcohol 2, vanillin 3, syringaldehyde 4, 3,5-dimethoxy-p-benzoquinone 5, 3,5-dimethoxy-p-hydroquinone 6 and others. Another addition of n-paraffin alcohols to aqueous media during the millings also significantly reduced the concentration of H2O2. When phthalic hydrazide (P) was treated in the mills in the aqueous media, triacetoxyphthalazine (1A), 3-acetoxyphthalic acid (2A) and other products were separated from the acetates of the reaction mixtures. Results mentioned above disclosed the generation of ·O2H, ·OH, and ·H in the aqueous media during the mechanical treatments. 相似文献
870.
Ryousuke Ishikawa Pil Ju Ko Masashi Bando Yasuyoshi Kurokawa Adarsh Sandhu Makoto Konagai 《Nanoscale research letters》2013,8(1):534
Carrier doping of graphene is one of the most challenging issues that needs to be solved to enable its use in various applications. We developed a carrier doping method using radical-assisted conjugated organic molecules in the liquid phase and demonstrated all-wet fabrication process of doped graphene films without any vacuum process. Charge transfer interaction between graphene and dopant molecules was directly investigated by spectroscopic studies. The resistivity of the doped graphene films was drastically decreased by two orders of magnitude. The resistivity was improved by not only carrier doping but the improvement in adhesion of doped graphene flakes. First-principles calculation supported the model of our doping mechanism. 相似文献