全文获取类型
收费全文 | 488篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 1篇 |
综合类 | 1篇 |
化学工业 | 61篇 |
机械仪表 | 13篇 |
建筑科学 | 27篇 |
矿业工程 | 3篇 |
轻工业 | 81篇 |
石油天然气 | 3篇 |
无线电 | 9篇 |
一般工业技术 | 196篇 |
原子能技术 | 2篇 |
自动化技术 | 92篇 |
出版年
2024年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 48篇 |
2011年 | 57篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 60篇 |
2007年 | 49篇 |
2006年 | 32篇 |
2005年 | 31篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 20篇 |
2001年 | 20篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1968年 | 5篇 |
1967年 | 3篇 |
1966年 | 8篇 |
排序方式: 共有489条查询结果,搜索用时 31 毫秒
31.
32.
In this study, the adsorption of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) from landfill leachate onto single-walled carbon nanotubes (SWCNTs) was investigated. Different leachate solutions were prepared by altering the pH, ionic strength, and dissolved organic carbon (DOC) in the solutions to mimic the varying water conditions that occur in leachate during the various stages of waste decomposition. The youngest and oldest leachate solutions contained varying DOC and background chemistry and were represented by leachate Type A (pH = 5.0; DOC = 2500 mg/L; conductivity = 12,500 μS/cm; [Ca2+] = 1200 mg/L; [Mg2+] = 470 mg/L) and Type E (pH = 7.5; DOC = 250 mg/L; conductivity = 3250 μS/cm; [Ca2+] = 60 mg/L; [Mg2+] = 180 mg/L). These solutions were subsequently combined in different ratios to produce intermediate solutions, labeled B-D, to replicate time-dependent changes in leachate composition. Overall, a larger fraction of EE2 was removed as compared to BPA, consistent with its higher log KOW value. The total removal of BPA and EE2 decreased in older leachate solutions, with the adsorptive capacity of SWCNTs decreasing in the order of leachate Type A > Type B > Type C > Type D > Type E. An increase in the pH from 3.5 to 11 decreased the adsorption of BPA by 22% in young leachate and by 10% in old leachate. The changes in pH did not affect the adsorption of EE2 in the young leachate, but did reduce adsorption by 32% in the old leachate. Adjusting the ionic strength using Na+ did not significantly impact adsorption, while increasing the concentration of Ca2+ resulted in a 12% increase in the adsorption of BPA and a 19% increase in the adsorption of EE2. DOC was revealed to be the most influential parameter in this study. In the presence of hydrophilic DOC, represented by glucose in this study, adsorption of the endocrine disrupting compounds (EDCs) onto the SWCNTs was not affected. In the absence of SWCNTs, hydrophobic DOC (i.e., humic acid) adsorbed 15-20% of BPA and EE2. However, when the humic acid and SWCNTs were both present, the overall adsorptive capacity of the SWCNTs was reduced. Hydrophobic (π-π electron donor-acceptor) interactions between the EDCs and the constituents in the leachate, as well as interactions between the SWCNTs and the EDCs, are proposed as potential adsorption mechanisms for BPA and EE2 onto SWCNTs. 相似文献
33.
The intake of fat, saturated and monounsaturated FA (SFA and MUFA), and omega-6 and omega-3 PUFA has been estimated in 641
Belgian women (age 18-39 y). Their food intake was recorded using a 2-d food diary. The PUFA included were linoleic (LA),
alpha-linolenic (LNA), arachidonic (AA), eicosapentaeonoic (EPA), docosapentaenoic (DPA) and docosahexaenoic (DHA) acids.
The mean total fat intake corresponded to 34.3% of total energy intake (E). The mean intake of the FA groups corresponded
to 13.7%, 13.1%, and 6.0% of E, for SFA, MUFA, and PUFA, respectively. The mean intake of LA was 5.3% of E and of LNA was
0.6% of E, with a mean LA/LNA ratio of 8.7. The mean intake of AA was 0.03% of E. The mean intake of EPA, DPA, and DHA was
0.4%, 0.01%, and 0.06% of E, respectively. According to the Belgian recommendations, the total fat and SFA intake was too
high for about three-quarters of the population. The mean LA and overall n-6 PUFA intake corresponded with the recommendation,
with part of the population exceeding the upper level. Conversely, the population showed a large deficit for LNA and n-3 PUFA.
The major food source for LA and LNA was fats and oils, followed by cereal products. The main sources of long-chain PUFA were
fish and seafood, and meat, poultry, and eggs. From a public health perspective, it seems desirable to tackle the problem
of low n-3 PUFA intake. 相似文献
34.
Bacteria are widespread, abundant, geochemically reactive components of aquatic environments. In particular, iron-oxidizing bacteria, are involved in the oxidation and subsequent precipitation of ferrous ions. Due to this property, they have been applied in drinking water treatment processes, in order to accelerate the removal of ferrous iron from groundwaters. Iron also exerts a strong influence on arsenic concentrations in groundwater sources, while iron oxides are efficient adsorbents in arsenic removal processes. In the present study, the removal of arsenic (III and V), during biological iron oxidation has been investigated. The results showed that both inorganic forms of arsenic could be efficiently treated, for the concentration range of interest in drinking water (50-200microg/L). In addition, the oxidation of trivalent arsenic was found to be catalyzed by bacteria, leading to enhanced overall arsenic removal, because arsenic in the form of arsenites cannot be efficiently sorbed onto iron oxides. This method comprises a cost competitive technology, which can find application in treatment of groundwaters with elevated concentrations of iron and arsenic. 相似文献
35.
This work presents a new adsorption technique where the adsorbent (powdered activated carbon-PAC) is in the form of suspended flocs formed with water-soluble polymer flocculants. Thus, the adsorption of a typical dye, methylene blue (MB), was studied onto polyacrylamide flocs of PAC (PACF) in a fluidized bed reactor. The technique is based on the fact that the adsorption capacity of PAC does not decrease after flocculation because the adsorbed polymer occupies only a few surface sites, in the form of trains, loops, and tails. Moreover, the adsorption was found to proceed through a rapid mass transfer of MB to the adsorbing PAC flocs, in the same extent as onto PAC. Because of the rapid settling characteristics of the aggregates formed, the two phase separations, loaded PAC and solution, become easier. Thus, the technique offers the advantages of conducting simultaneously both adsorption and solid/liquid separation all in one single stage. Results obtained showed that high MB removal values can be attained in a fluidized bed reactor (>90%) and that PACF presents a much higher adsorption capacity (breakthrough points) than granulated activated carbon (GAC) in the same adsorbing bed. It is believed that this technique highly broadens the potential of the use of powdered activated carbon or other similar ultrafine adsorbents. 相似文献
36.
Decsi T Boehm G Tjoonk HM Molnár S Dijck-Brouwer DA Hadders-Algra M Martini IA Muskiet FA Boersma ER 《Lipids》2002,37(10):959-965
Long-chain PUFA play an important role in early human neurodevelopment. Significant inverse correlations were reported between
values of trans isomeric and long-chain PUFA in plasma lipids of preterm infants and children aged 1–15 yr as well as in venous cord blood
lipids of full-term infants. Here we report FA compositional data of cord blood vessel wall lipids in 308 healthy, full-term
infants (gestational age: 39.7±1.2 wk, birth weight: 3528±429 g, mean±SD). The median (interquartile range) of the sum of
18-carbon trans FA was 0.22 (0.13)% w/w in umbilical artery and 0.16 (0.10)% w/w in umbilical vein lipids. Nonparametric correlation analysis
showed significant inverse correlations between the sum of 18-carbon trans FA and both arachidonic acid and DHA in artery (r=−0.38, P<0.01, and r=−0.20, P<0.01) and vein (r=−0.36, P<0.01, and −0.17, P<0.01) wall lipids. In addition, the sum of 18-carbon trans FA was significantly positively correlated to Mead acid, a general indicator of EFA deficiency, in both artery (r=+0.35, P<0.01) and vein (r=+0.31, P<0.01) wall lipids. The present results obtained in a large group of full-term infants suggest that maternal trans FA intake is inversely associated with long-chain PUFA status of the infant at birth. 相似文献
37.
This paper describes a statistical image reconstruction method for X-ray computed tomography (CT) that is based on a physical model that accounts for the polyenergetic X-ray source spectrum and the measurement nonlinearities caused by energy-dependent attenuation. We assume that the object consists of a given number of nonoverlapping materials, such as soft tissue and bone. The attenuation coefficient of each voxel is the product of its unknown density and a known energy-dependent mass attenuation coefficient. We formulate a penalized-likelihood function for this polyenergetic model and develop an ordered-subsets iterative algorithm for estimating the unknown densities in each voxel. The algorithm monotonically decreases the cost function at each iteration when one subset is used. Applying this method to simulated X-ray CT measurements of objects containing both bone and soft tissue yields images with significantly reduced beam hardening artifacts. 相似文献
38.
Microdosimetric characteristics of 28 kVp mammography X ray spectra were studied for several target/added filtration combinations (Mo/Mo, Rh/Rh, Rh/Al, W/Rh, Mo/Rh). Monte Carlo techniques were used to model X ray production from mammography units and to calculate distributions of absorbed dose and energy imparted in breast tissue. The results show that the dose averaged lineal energy is about 5.0 keV.micron-1, about 25% higher than for general diagnostic imaging X ray spectra. Significant differences in lineal energy between the five X ray qualities were noted, with the highest value for the commonly used Mo/Mo combination. Spectral hardening with depth in the tissues causes a 5% decrease in lineal energy over 5 cm. No significant differences were found for the different tissue compositions. 相似文献
39.
40.
A three-stage continuous culture system was used to segregate the component microbial groups of a methanogenic hexanoate-degrading association enriched from anaerobic refuse. The inhibitory effects of o-cresol concentrations (2-20 mM) on the fermentative, acetogenic, sulphate-reducing and methanogenic bacteria were then assessed in the presence of either 1.4 or 3.5 mM sulphate in the influent medium. The sulphate-reducing bacteria (SRB) in the 1.4 mM sulphate-supplemented systems were the most sensitive to o-cresol, with 29.3 and 56.6% inhibition on supplementation with 4 and 6 mM o-cresol, respectively. With 3.5mM supplementation, inhibition was 4.5 and 19.4%, respectively. Methanogenesis was not inhibited by concentrations < 10 mM o-cresol, and complete inhibition was recorded only at concentrations > or = 10 mM. Both fermentation and acetogenesis were affected by inhibition of the electron sinks. The increase in influent sulphate concentration promoted electron flow to sulphidogenesis, as predicted on thermodynamic criteria, but did not affect the relative sensitivity of the different physiological groups. 相似文献