全文获取类型
收费全文 | 3491篇 |
免费 | 89篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 41篇 |
综合类 | 6篇 |
化学工业 | 878篇 |
金属工艺 | 124篇 |
机械仪表 | 80篇 |
建筑科学 | 48篇 |
矿业工程 | 3篇 |
能源动力 | 299篇 |
轻工业 | 185篇 |
水利工程 | 22篇 |
石油天然气 | 7篇 |
无线电 | 340篇 |
一般工业技术 | 806篇 |
冶金工业 | 470篇 |
原子能技术 | 25篇 |
自动化技术 | 268篇 |
出版年
2023年 | 38篇 |
2022年 | 81篇 |
2021年 | 109篇 |
2020年 | 87篇 |
2019年 | 86篇 |
2018年 | 142篇 |
2017年 | 77篇 |
2016年 | 83篇 |
2015年 | 77篇 |
2014年 | 112篇 |
2013年 | 218篇 |
2012年 | 160篇 |
2011年 | 195篇 |
2010年 | 157篇 |
2009年 | 143篇 |
2008年 | 121篇 |
2007年 | 117篇 |
2006年 | 93篇 |
2005年 | 79篇 |
2004年 | 67篇 |
2003年 | 81篇 |
2002年 | 50篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 68篇 |
1998年 | 155篇 |
1997年 | 100篇 |
1996年 | 93篇 |
1995年 | 50篇 |
1994年 | 53篇 |
1993年 | 53篇 |
1992年 | 38篇 |
1991年 | 40篇 |
1990年 | 35篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 41篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有3602条查询结果,搜索用时 15 毫秒
61.
62.
Shappell NW Billey LO Forbes D Matheny TA Poach ME Reddy GB Hunt PG 《Environmental science & technology》2007,41(2):444-450
Anaerobic lagoons and treatment wetlands are used worldwide to treat wastewater from dense livestock production facilities; however, there is very limited data on the hormonal activity of the wastewater effluent produced by these treatment systems. The objectives of this experiment were to measure (1) the hormonal activity of the initial effluent and (2) the effectiveness of a lagoon-constructed wetland treatment system for producing an effluent with a low hormonal activity. Wastewater samples were taken in April, July, and November 2004 and July 2005 from a lagoon-constructed wetland system at a swine farrowing facility. Estrogenic activity (in vitro E-screen assay), 17 beta-estradiol (E2), and testosterone concentrations (LC/MS-MS) were measured. A high correlation was found between estradiol equivalents determined by E-screen and LC/MS-MS (R2 = 0.82). Nutrient removal was measured to ensure that the wetlands were functioning in a manner similar to literature reports. Nutrient removals were typical for treatment wetlands: TKN 59-75% and orthophosphate 0-18%. Wetlands decreased estrogenic activity by 83-93%. Estrone was the most persistent estrogenic compound. Constructed wetlands produced effluents with estrogenic activity below the lowest equivalent E2 concentration known to have an effect on fish (10 ng/L or approximately 37 x 10(-12) M). 相似文献
63.
Nasirullah Rizwan Shariff Umesha Shankara Shetty Reddy Sunki Yella 《International Journal of Food Science & Technology》2010,45(7):1395-1402
Edible vegetable oil blends, such as coconut:linseed; coconut:safflower; coconut:sunflower; coconut:rice‐bran oils; in the ratio of 70:30 and 60:40 v/v and pure coconut oil (CNO) were interesterified using sodium methoxide 0.5% and subsequently refined to prepare nutritionally superior flowable CNO blends which remained liquid even at sub‐zero temperatures. The slip melting point of chemically interesterified fats could not be determined as they are liquified just after removing from freezing chamber in comparison with the slip melting point of 21.5–26.5 °C for their uninteresterified counterparts. These interesterified fats were liquid and flowable at 6 °C for more than 4 h in a cooling chamber and their solidification temperature ranged between ?2.0 and ?5.5 °C. Free fatty acids showed an increasing trend from 0.35% to 2.0% resulting in decrease in triglycerides After refining these oil blends showed values similar to their controls. However, iodine value of interesterified and uninteresterified oils were close to each other. Differential scanning calorimetry showed the onset of crystallisation at lower temperatures and lower solid fat content for interesterified fats. A nutritionally superior combination of CNO blend which is flowable at low temperature could be prepared. 相似文献
64.
Wardlaw GD Arey JS Reddy CM Nelson RK Ventura GT Valentine DL 《Environmental science & technology》2008,42(19):7166-7173
Natural seeps contribute nearly half of the oil entering the coastal ocean. However, environmental fate studies generally monitor fewer than 5% of these petroleum compounds. Hence, the rates and relevance of physical, chemical, and biological weathering processes are unknown for the large majority of hydrocarbons, both released from natural seeps and also from human activities. To investigate the specific compositional changes occurring in petroleum during subsurface degradation and submarine seepage, we studied the natural oil seeps offshore Santa Barbara, California with comprehensive, two-dimensional gas chromatography (GC x GC). With this technique, we quantified changes in the molecular diversity and abundance of hydrocarbons between subsurface reservoirs, a proximal sea floor seep, and the sea surface overlying the seep. We also developed methods to apportion hydrocarbon mass losses due to biodegradation, dissolution, and evaporation, for hundreds of tracked compounds that ascended from the subsurface to the sea floor to the sea surface. The results provide the first quantitative evidence of broad metabolic specificity for anaerobic hydrocarbon degradation in the subsurface and reveal new trends of rapid hydrocarbon evaporation at the sea surface. This study establishes GC x GC as a powerful technique for differentiating biological and physical weathering processes of complex mixtures at a molecular level. 相似文献
65.
L. N. Srikar B. K. Khuntia G. V. S. Reddy B. R. Srinivasa 《Journal of the science of food and agriculture》1993,63(3):319-322
Dry-salted mackerel and pink perch were stored at two temperatures: ambient (26·8 ± 3·3°C) and 2·5 ± 1°C. Changes in moisture content, salt content, water activity (aw), peroxide value (PV), free fatty acid content (FFA), total volatile base nitrogen (TVBN) content, halophilic bacterial count and sensory scores for overall acceptability were studied. Loss of moisture and absorption of salt were considerably higher in the products stored at ambient temperature. The decrease in aw was more pronounced at ambient temperature than at the lower temperature. Although the chemical indices of freshness (PV, FFA and TVBN) and the halophilic counts showed increasing trends, they were considerably lower in the products stored at the lower temperature. Sensory evaluation for overall acceptability indicated that storage at the lower temperature could considerably extend the shelf-life of salted fish. 相似文献
66.
Contribution of biomass burning to atmospheric polycyclic aromatic hydrocarbons at three European background sites 总被引:2,自引:0,他引:2
Mandalakis M Gustafsson O Alsberg T Egebäck AL Reddy CM Xu L Klanova J Holoubek I Stephanou EG 《Environmental science & technology》2005,39(9):2976-2982
Radiocarbon analysis of atmospheric polycyclic aromatic hydrocarbons (PAHs) from three background areas in Sweden, Croatia, and Greece was performed to apportion their origin between fossil and biomass combustion. Diagnostic ratios of PAHs implied that wood and coal combustion was relatively more important in the northern European site, while combustion of fossil fuels was the dominant source of PAHs to the two central-southern European background sites. The radiocarbon content (delta14C) of atmospheric PAHs in Sweden ranged between -388 per thousand and -381 per thousand, while more depleted values were observed for Greece (-914 per thousand) and Croatia (-888 per thousand). Using a 14C isotopic mass balance model it was calculated that biomass burning contributes nearly 10% of the total PAH burden in the studied southern European atmosphere with fossil fuel combustion making up the 90% balance. In contrast, biomass burning contributes about 50% of total PAHs in the atmosphere at the Swedish site. Our results suggest that the relative contributions of biomass burning and fossil fuels to atmospheric PAHs may differ considerably between countries, and therefore, different national control strategies might be needed if a further reduction of these pollutants is to be achieved on a continental-global scale. 相似文献
67.
Malaysian population widely consumes the cereal-based foods, oilseeds, nuts, and spices in their daily diet. Mycotoxigenic fungi are well known to invade food products under storage conditions and produce mycotoxins that have threat to human and animal health. Therefore, determining toxigenic fungi and aflatoxin B(1) (AFB1) in foods used for human consumption is of prime importance to develop suitable management strategies and to minimize risk. Ninety-five food products marketed in Penang, Malaysia were randomly collected from different supermarkets and were analyzed for presence of Aspergillus spp. by agar plate assay and AFB1 by enzyme-linked immunosorbent assay (ELISA). A. flavus was the dominant fungi in all foods followed by A. niger. Fifty-five A. flavus strains were tested for their ability to produce aflatoxins on rice grain substrate. Thirty-six (65.4%) strains out of 55 produced AFB1 ranging from 1700 to 4400 μg/kg and 17 strains (31%) produced AFB2 ranging from 620 to 1670 μg/kg. Natural occurrence of AFB1 could be detected in 72.6% food products ranging from 0.54 to 15.33 μg/kg with a mean of 1.95 μg/kg. Maximum AFB1 levels were detected in peanut products ranging from 1.47 to 15.33 μg/kg. AFB1 levels detected in all food products were below the Malaysian permissible limits (<35 μg/kg). Aspergillus spp. and AFB1 was not detected in any cookies tested. Although this survey was not comprehensive, it provides valuable information on aflatoxin levels in foods marketed in Malaysia. 相似文献
68.
Ramakrishna?Chetana Ponnachanna?Chengappa?Srinivasa Sunki?Reddy?Yella ReddyEmail author 《European Food Research and Technology》2005,220(2):136-141
Moisture sorption data are useful in choosing suitable packaging material having a desirable water vapour barrier property in addition to determining the stability of the product. The sorption isotherms of milk burfi, one of the important Indian traditional milk-based sweets, using sugar and sugar substitutes were determined. The product was prepared replacing sugar with sorbitol, maltodextrin (MD)+polydextrose (PD), and PD alone, along with aspartame to give an equi-sweetness level compared to sugar. The isotherms followed typical sigmoidal shape, characteristic of sugar-rich products. The curve for burfi with sorbitol shifted to the left compared to that of sugar, whereas for those prepared with MD+PD or PD, the curves are similar to that of burfi made with sugar. Several models were chosen to fit sorption behaviour and the Guggenheim-Anderson-De Boer model showed a better fit compared to other models. 相似文献
69.
70.
Analyzing the radiocarbon ((14)C) content of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate matter can provide estimates on the source contributions from biomass burning versus fossil fuel. The relative importance of these two sources to ambient PAHs varies considerably across regions and even countries, and hence there is a pressing need to apportion these sources. In this study, we advanced the radiocarbon analysis from bulk carbon to compound class specific radiocarbon analysis (CCSRA) to determine Δ(14)C and δ(13)C values of PAHs in PM(2.5) samples for investigating biomass burning and fossil fuel source contributions to PAHs from one of the Southeastern Aerosol Research and Characterization (SEARCH) sites in North Birmingham (BHM), Alabama during winter (December 2004-February 2005) and summer (June-August 2005) by accelerator mass spectrometry. To compare our ambient samples to known sources, we collected and analyzed fenceline samples from the vicinity of a coke plant in BHM. As expected, PAHs from the coke plant fenceline samples had very low radiocarbon levels. Its Δ(14)C varied from -990 to -970‰, indicating that 97 to 99% were of fossil source. PAHs in the ambient PM(2.5) had Δ(14)C from -968 to -911 ‰, indicating that 92-97% of PAHs were from fossil fuel combustion. These levels indicated the dominance of fossil sources of ambient PAHs. The radiocarbon level of ambient PAHs was higher in winter than in summer. Winter samples exhibited depleted δ(13)C value and enriched Δ(14)C value because of the increased contribution of PAHs from biomass burning source. However, biomass burning contributed more to heavier PAHs (modern source accounting for 6-8%) than lighter ones with a modern contribution of 3%. 相似文献