全文获取类型
收费全文 | 15806篇 |
免费 | 1164篇 |
国内免费 | 119篇 |
专业分类
电工技术 | 253篇 |
综合类 | 69篇 |
化学工业 | 4203篇 |
金属工艺 | 408篇 |
机械仪表 | 527篇 |
建筑科学 | 606篇 |
矿业工程 | 36篇 |
能源动力 | 1112篇 |
轻工业 | 1492篇 |
水利工程 | 211篇 |
石油天然气 | 286篇 |
武器工业 | 4篇 |
无线电 | 1628篇 |
一般工业技术 | 2927篇 |
冶金工业 | 594篇 |
原子能技术 | 122篇 |
自动化技术 | 2611篇 |
出版年
2024年 | 72篇 |
2023年 | 328篇 |
2022年 | 669篇 |
2021年 | 993篇 |
2020年 | 843篇 |
2019年 | 918篇 |
2018年 | 1043篇 |
2017年 | 941篇 |
2016年 | 954篇 |
2015年 | 595篇 |
2014年 | 883篇 |
2013年 | 1571篇 |
2012年 | 1010篇 |
2011年 | 1054篇 |
2010年 | 750篇 |
2009年 | 684篇 |
2008年 | 497篇 |
2007年 | 428篇 |
2006年 | 355篇 |
2005年 | 257篇 |
2004年 | 230篇 |
2003年 | 185篇 |
2002年 | 147篇 |
2001年 | 130篇 |
2000年 | 124篇 |
1999年 | 115篇 |
1998年 | 177篇 |
1997年 | 138篇 |
1996年 | 118篇 |
1995年 | 77篇 |
1994年 | 62篇 |
1993年 | 76篇 |
1992年 | 54篇 |
1991年 | 48篇 |
1990年 | 56篇 |
1989年 | 47篇 |
1988年 | 31篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 37篇 |
1983年 | 33篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 35篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Masoud Eshghizadeh Ali Talebi Mohamad-Taghi Dastorani 《Water Resources Management》2018,32(10):3473-3487
In this study, LAPSUS model is modified to enhance the effective rainfall estimation by SCS curve number method. The LAPSUS model calculates discharge based on effective rainfall and routs it towards lower neighbouring grid cells following the multiple flow direction principle. Then, the sediment transport capacity and sediment transport rate are calculated in each grid cell. Finally, erosion or sedimentation is calculated by comparing the sediment transport rate with the sediment already in the transport of each grid cell. The amount of rainfall, curve number, convergence factor, discharge exponent, slope exponent, erodibility factor, and sedimentation ability factor are inputted to the application page of the modified model that was created in the C++ programming. The outputs of the model are runoff and erosion maps in ASCII format. Evaluating performance of the modified model showed a high accuracy of its results. The value of the coefficient of determination (R2) calculated 0.99 for runoff and 0.97 for erosion. The Nash-Sutcliffe efficiency was 0.96 for runoff and 0.97 for erosion. The value of the precision index calculated 0.81 for both runoff and erosion. Also, the nRMSE calculated 3% for both runoff and erosion. The result showed that the modified model capable to estimate the runoff and erosion on a landscape in a micro sub-catchment scale. 相似文献
992.
993.
Max Teplitski Jason T. Noel Ali Alagely Michelle D. Danyluk 《Food research international (Ottawa, Ont.)》2012,45(2):576-586
Despite the fact that plants are not traditionally considered as hosts for human enteric pathogens, recent evidence suggests that non-typhoidal Salmonella and enterovirulent Escherichia coli recognize plants and rely on a specific set of genes to multiply in plant-associated environments, eventually causing dramatic outbreaks of illness. The advent of sensitive functional genomics tools, including differential fluorescence induction and in vivo expression technology, set the stage for the characterization of the genes and behaviors used by enterics to colonize, persist and proliferate within plants and the associated microbial communities. Meta-analysis of published data suggests that Salmonella and enterovirulent E. coli persist in plants using strategies that differ from those in phytobacteria. Virulence genes were upregulated in E. coli O157:H7 in the presence of lettuce leaf exudates, however Salmonella SPI-1 genes associated with gastroenteritis were dispensable during plant growth. Microarray and mutant studies of plant responses to human pathogens reveal that plants generally do not recognize Salmonella and enterovirulent E. coli as phytopathogens or beneficial symbionts, although the full spectrum of plant responses to enterics remains to be elucidated. Defining plant responses to human enteric pathogens becomes increasingly important as the feasibility of breeding for resistance to these organisms is being evaluated. 相似文献
994.
Inès Thabti Walid Elfalleh Hédia Hannachi Ali Ferchichi Maria Da Graça Campos 《Journal of Functional Foods》2012,4(1):367-374
The total polyphenol and flavonoids in leaves of Morus alba var. alba, Morus alba var. rosa and Morus rubra were determined and identification of their components was carried out. The total content of phenolics varied between 345.20 and 631.53 mg gallic acid equivalents (GAE)/100 g dry weight (DW) basis. The total amount of flavonoids ranged between 193.87 and 398.33 mg rutin equivalents (RE)/100 g DW. Thirteen compounds were isolated by chromatography, and their structures determined to be mainly flavonol glycosides and phenolic acids. Three novel components were identified as kaempferol-7-O-glucoside, quercetin-3-O-β-glucoside-7-O-α-rhamnoside and quercetin-3-O-rhamnoside-7-O-glucoside, for the first time from mulberry leaves. Others known compounds were also identified. 相似文献
995.
Songül Cakmakci Engin Gundogdu Ali A. Hayaloglu Elif Dagdemir Mustafa Gurses Bulent Cetin Deren Tahmas‐Kahyaoglu 《International Journal of Food Science & Technology》2012,47(11):2405-2412
The objective of this study is to characterise the gross chemical and microbiological status and identify the volatile compounds of mouldy Civil cheeses. A total of forty‐one samples were surveyed, and gross compositional status of the cheeses was (as mean values): 6.5 for pH, 6.2% for fat‐in‐dry matter, 51.8% for moisture and 15.3% for water‐soluble nitrogen (as% of total nitrogen). Chemical composition of the cheese samples varied widely. Mouldy Civil cheese has similar pH values and moisture contents when compared with blue‐type cheeses, but it has distinct feature for fat contents. The microbiological counts of the samples were found to be high and some samples contained coliform bacteria. A total of 95 volatiles, including esters (28), acids (6), ketones (12), aldehydes (3), alcohols (15), terpenes (10), sulphur compounds (3) and miscellaneous (18), were identified in the volatile fractions of the cheeses, and principal volatile groups were esters, alcohols and ketones. 相似文献
996.
In this work a simple, rapid and sensitive method using dispersive liquid–liquid microextraction (DLLME) combined with UV–Vis spectrophotometry has been developed for the preconcentration and determination of trace amounts of aziridine in food simulants. The method is based on derivatization of aziridine with Folin's reagent (1,2-naphthoquione-4-sulphonic acid) and extraction of color product using DLLME technique. Some important parameters, such as reaction conditions, and type and volume of extraction solvent and disperser solvent were studied and optimized. Under optimum conditions, a linear calibration curve in the range of 2.0–350 ng mL?1 of aziridine was obtained. Detection limit based on 3Sb was 1.0 ng mL?1, and the relative standard deviation for 50 ng mL?1 of aziridine was 2.49c (n?=?7). The proposed method was applied for the determination of aziridine in food simulants. 相似文献
997.
Impact of zinc salts on heat-induced aggregation of natural actomyosin from yellow stripe trevally 总被引:2,自引:0,他引:2
Impact of zinc sulphate (ZnSO4) and zinc chloride (ZnCl2) on heat-induced aggregation of natural actomyosin (NAM) extracted from yellow stripe trevally (Selaroides leptolepis) was investigated. In the presence of ZnSO4 or ZnCl2, the transition temperature (Tmax) of myosin shifted from 47.83 ± 0.30 °C to 46.05 ± 0.36 and 46.49 ± 0.49 °C, with the coincidental decreases in ΔH from 1.07 ± 0.03 J/g to 0.63 ± 0.02 and 0.67 ± 0.04 J/g, respectively (P < 0.05). Additionally, Ca2+–ATPase activity of NAM decreased with increasing the concentrations of ZnSO4 or ZnCl2 during heating up to 40 °C. During heating from 20 to 75 °C, higher turbidity, surface hydrophobicity and disulphide bond formation were obtained in NAM added with ZnSO4 or ZnCl2 at temperatures ranging from 40 to 75 °C, compared with the control. Nevertheless, a higher aggregation was found in NAM added with ZnSO4, compared with ZnCl2. Zeta potential (ζ) analysis suggested that the surface of NAM added with ZnSO4 became less negatively charged, compared with that of ZnCl2 counterpart. Transmission electron microscopy showed that the structure of NAM was highly interconnected, finer and denser when zinc salts, especially ZnSO4 were incorporated. Therefore, ZnSO4 could be used to induce aggregation of fish muscle proteins, thereby improving gelling property of fish mince or surimi. 相似文献
998.
Emna B. Saafi‐Ben Salah Guido Flamini Amira El Arem Manel Issaoui Samia Dabbou Leila BenYahia Ali Ferchichi Mohamed Hammami Lotfi Achour 《International Journal of Food Science & Technology》2012,47(9):1903-1908
This paper reports a discrimination study based on the physico‐chemical characteristics, fatty acids and profile of volatile compounds of the seeds from seven date palm varieties (Phoenix dactylifera L.) grown in Tunisia. Date seeds contained 10.49–14.76% moisture; 6.28–11.2% fat (on a dry weight basis); 2.67–12.85% protein; 0.91–6.06% reducing sugar; 0.61–2.98% sucrose and 0.97–1.17% ash. Gas liquid chromatography revealed that the oil fraction of the date palm seeds contained eighteen fatty acids, with oleic acid (30.77–42.50%) and lauric acid (18.51–27.48%) as the main unsaturated and saturated ones. Volatile profile showed differences among varieties. In total, forty‐five compounds were identified, mainly alcohols, aldehydes and unsaturated hydrocarbons ones. This study provides evidence that the seeds of date may be a potential source of valuable nutrients with interesting functionality. 相似文献
999.
This article presents the method and results of wellbore stability analysis for three common reservoir lithologies consisting of a consolidated sandstone, a shaly sandstone, and a limestone formation. The effect of stress anisotropy on the mechanical stability of wellbores is evaluated while varying the inclination angle from 0 to 90°, for both the Mohr-Coulomb and the Drucker-Prager failure criteria. The selected failure criterion, and the in-situ rock stress regime are found to have significant effects on the safe drilling fluid density required to maintain wellbore integrity. According to some field examples, the Drucker-Prager failure criterion appears to systematically mimic rock conditions more realistically than the Mohr-Coulomb failure criterion. The simulated consolidated sandstone formation is found more stable with lesser drilling fluid density, at any inclination angle, than the simulated shaly sandstone formation. The simulated limestone formation is even more stable than the consolidated sandstone at all inclination angles since it requires lighter fluid density to prevent wellbore collapse. For all these rock types, the higher the deviation angle (from vertical), the higher the drilling fluid density needed for maintaining wellbore integrity. For the depth and rock conditions simulated, both consolidated and shaly sands are unstable in a strike-slip stress regime, but stable in an extensional stress regime. The simulated limestone formation was found stable in both stress regimes. However, in an extensional stress regime, the limestone formation required lighter fluid density to maintain wellbore integrity than in a strike-slip stress regime. This article introduces the theory of using a practically-oriented model to assess the mechanical stability of a wellbore in a linearly-elastic stress field. The model can be used to determine the range of mechanically stable well inclinations for a given formation, and to suggest drilling-fluid density programs tailored to efficient and safe drilling. 相似文献
1000.
An LiMn2O4 electrode was prepared based on mixed-metals (gold–titanium) codeposition method. By this method, titanium oxide is also incorporated into the electroactive film formed on substrate electrode. Formation of titanium oxide on the spinel surface avoids dissolution of Mn from the spinel at elevated temperatures. TiO2can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the LiMn2O4 spinel can be improved by the surface modification with TiO2. This action improves cyclability for lithium battery performance and reduces capacity fades of LiMn2O4 at elevated temperatures. 相似文献