全文获取类型
收费全文 | 4860篇 |
免费 | 125篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 90篇 |
综合类 | 5篇 |
化学工业 | 737篇 |
金属工艺 | 84篇 |
机械仪表 | 85篇 |
建筑科学 | 162篇 |
矿业工程 | 33篇 |
能源动力 | 86篇 |
轻工业 | 362篇 |
水利工程 | 21篇 |
石油天然气 | 13篇 |
无线电 | 806篇 |
一般工业技术 | 681篇 |
冶金工业 | 1226篇 |
原子能技术 | 52篇 |
自动化技术 | 564篇 |
出版年
2021年 | 42篇 |
2020年 | 34篇 |
2019年 | 36篇 |
2018年 | 57篇 |
2017年 | 42篇 |
2016年 | 56篇 |
2015年 | 48篇 |
2014年 | 79篇 |
2013年 | 276篇 |
2012年 | 129篇 |
2011年 | 170篇 |
2010年 | 120篇 |
2009年 | 159篇 |
2008年 | 148篇 |
2007年 | 191篇 |
2006年 | 168篇 |
2005年 | 151篇 |
2004年 | 128篇 |
2003年 | 145篇 |
2002年 | 113篇 |
2001年 | 103篇 |
2000年 | 95篇 |
1999年 | 135篇 |
1998年 | 368篇 |
1997年 | 246篇 |
1996年 | 166篇 |
1995年 | 148篇 |
1994年 | 124篇 |
1993年 | 117篇 |
1992年 | 77篇 |
1991年 | 75篇 |
1990年 | 66篇 |
1989年 | 53篇 |
1988年 | 62篇 |
1987年 | 40篇 |
1986年 | 42篇 |
1985年 | 43篇 |
1984年 | 38篇 |
1983年 | 45篇 |
1982年 | 47篇 |
1981年 | 48篇 |
1980年 | 44篇 |
1979年 | 40篇 |
1978年 | 31篇 |
1977年 | 59篇 |
1976年 | 54篇 |
1975年 | 45篇 |
1974年 | 21篇 |
1973年 | 25篇 |
1972年 | 32篇 |
排序方式: 共有5007条查询结果,搜索用时 15 毫秒
171.
Development of Simplified Heterocyclic Acetogenin Analogues as Potent and Selective Trypanosoma brucei Inhibitors 下载免费PDF全文
Dr. Gordon J. Florence Andrew L. Fraser Dr. Eoin R. Gould Elizabeth F. King Stefanie K. Menzies Dr. Joanne C. Morris Marie I. Thomson Dr. Lindsay B. Tulloch Marija K. Zacharova Prof. Dr. Terry K. Smith 《ChemMedChem》2016,11(14):1503-1506
Neglected tropical diseases caused by parasitic infections are an ongoing and increasing concern. They are a burden to human and animal health, having the most devastating effect on the world′s poorest countries. Building upon our previously reported triazole analogues, in this study we describe the synthesis and biological testing of other novel heterocyclic acetogenin‐inspired derivatives, namely 3,5‐isoxazoles, furoxans, and furazans. Several of these compounds maintain low‐micromolar levels of inhibition against Trypanosoma brucei, whilst having no observable inhibitory effect on mammalian cells, leading to the possibility of novel lead compounds for selective treatment. 相似文献
172.
173.
Janet M Snyder Jerry W King Ki-Souk Nam 《Journal of the science of food and agriculture》1996,72(1):25-30
Meat products that were exposed to a warehouse fire were collected and examined to identify contaminants present in the samples. An extraction method using supercritical carbon dioxide at 100 atm and 60°C was developed to analyse and characterise volatile and semi-volatile compounds from the samples. The major volatile compounds were lipid oxidation products, such as hexanal and nonanal. Volatiles concentrations from fire-exposed meat products were compared to control samples to determine compositional differences. Aromatic and polycyclic aromatic hydrocarbons were identified, and naphthalene was measured in suspected fire-damaged meat products. Direct supercritical extraction from the meat samples proved to be a rapid and reproducible method to assess contamination in commercial meat products. 相似文献
174.
Several surface treatments, using both commercially available coupling agents and reagents containing multiple amines, were applied to commingled continuous as-received AS4 carbon reinforcing fiber/liquid crystal polymer (LCP) matrix fibers. Unidirectional composites (normally 60 vol% carbon fiber) were prepared from as-received and treated commingled fibers and characterized. To estimate the effect the effect of the treatments on fiber-matrix adhesion, short beam shear (SBS) tests were conducted, the failure surfaces were examined, and spectroscopic studies wee performed. The mean SBS strength of the as-received unidirectional AS4 carbon fiber/LCP matrix composite system was 49 MPa. The best coupling agent and amine treatments yielded increases in composite shear strength of ∼ 10 to 20%, relative to the as-received AS4/LCP system. For the amine treatments, ESCA and FTIR analyses suggested of both the carbon and LCP fibers may have caused the increased adhesion. Moreover, SEM analysis of the failure surfaces of SBS specimens from composites prepared with the treated fibers may have caused the increased adhesion. Moreover, SEM analysis of the failure surfaces of SBS specimens from composites prepared with the treated fibers (both with coupling agents and amines) showed that strong fiber-matrix adhesion was present. That is, failure occurred in the LCP matrix material. 相似文献
175.
Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst proneness.As such,it is of high practical value to correctly evaluate rock brittleness.However,the definition and measurement method of rock brittleness have been very diverse and not yet been standardized.In this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly discussed.The development and role of rock brittleness in different fields of rock engineering are also studied.Eighty brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are discussed.The results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock brittleness.On the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness.It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness.This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term. 相似文献
176.
Harmon SM King JK Gladden JB Chandler GT Newman LA 《Environmental science & technology》2004,38(2):650-656
This study used an experimental model to evaluate methylmercury accumulation when the soil of a constructed wetland is amended with sulfate. The model was planted with Schoenoplectus californicus and designed to reduce wastestream metals and metal-related toxicity. The soil was varied during construction to provide a control and two sulfate treatments which were equally efficient at overall mercury and copper removal. After an initial stabilization period, methylmercury concentrations in porewater were up to three times higher in the sulfate-treated porewater (0.5-1.6 ng/L) than in the control (<0.02-0.5 ng/L). Mean percent methylmercury was 9.0% in the control with 18.5 and 16.6% in the low- and high-sulfate treatments, respectively. Methylmercury concentrations measured in mesocosm surface water did not reflect the differences between the control and the sulfate treatments that were noted in porewater. The mean bulk sediment methylmercury concentration in the top 6 cm of the low-sulfate treatment (2.33 ng/g) was significantly higher than other treatment means which ranged from 0.96 to 1.57 ng/g. Total mercury in sediment ranged from 20.8 to 33.4 ng/g, with no differences between treatments. Results suggest that the non-sulfate-amended control was equally effective in removing metals while keeping mercury methylation low. 相似文献
177.
A rapid and selective liquid chromatography–electrospray ionisation mass spectrometry (LC–ESI-MS) method to screen citrus samples for limonoid glucosides and estimate their relative concentrations has been developed. This method utilises a phenyl stationary phase, whereas previous methods have relied on C-18. Samples may be analysed directly without treatment other than dilution. Peak areas from the extracted deprotonated molecular ion mass signals for individual limonoid glucosides were normalised against the sum of the areas to establish their relative concentrations. The method was successfully applied to the analysis of various juice, extracts, and liquid samples of partially purified limonoid glucosides. 相似文献
178.
Bohaychuk VM Gensler GE King RK Manninen KI Sorensen O Wu JT Stiles ME McMullen LM 《Journal of food protection》2006,69(9):2176-2182
A total of 800 meat and poultry products were purchased from the retail marketplace in Edmonton, Alberta, Canada. The products consisted of raw ground beef, chicken legs, pork chops, and ready-to-eat fermented sausage, roast beef, processed turkey breast, chicken wieners, and beef wieners. The samples were analyzed to determine the prevalence of Shiga toxin-producing Escherichia coli, Salmonella, Campylobacter spp., and Listeria monocytogenes. Shiga toxin-producing E. coli 022: H8 was found in one raw ground beef sample. Salmonella and Campylobacter were found in 30 and 62% of raw chicken legs, respectively. L. monocytogenes was found in 52% of raw ground beef, 34% of raw chicken legs, 24% of raw pork chops, 4% of fermented sausages, 3% of processed turkey breast, 5% of beef wieners, and 3% of chicken wieners. The occurrence of pathogens in this study is similar to that in retail products in many other international locales. 相似文献
179.
ABSTRACT: Adequate cooking of meat is necessary to inactivate microbial pathogens. This is particularly important for ground meat products and some variety meats where pathogens can be present internally. Consumers are being advised on appropriate temperatures to which meat products should be cooked, and to use a meat thermometer to ensure these temperatures are reached. However, consumers are more likely to assess cooking status by the color of the meat or juice. This article reviews the factors that can influence the final color of cooked meat. In most instances, these factors influence color by modifying the meat pigment myoglobin prior to and during cooking. Many factors can prolong the pink "uncooked" color in meat, including high pH, modified atmosphere packaging, rapid thawing, low fat content, nitrite, and irradiation. Such factors may lead to overcooking and loss of food quality, and consumer rejection. Alternatively, factors that cause "premature browning" of meat, where the interior of the product looks cooked but a microbiologically safe temperature has not been reached, are food safety issues. Pale, soft exudative meats can prematurely brown, as can meats packaged under oxygenated conditions, frozen in bulk or thawed over long periods, or those that have had salts or lean finely textured beef added. Meats cooked from a frozen state or irradiated in aerobic conditions might also be at risk, but this might depend on meat species. In summary, the color of cooked meat is not a good indicator of adequate cooking, and the use of a food thermometer is recommended. 相似文献
180.
The porosity of a typical activated carbon is investigated with small angle neutron scattering (SANS), using the contrast matching technique, by changing the hydrogen/deuterium content of the absorbed liquid (toluene) to extract the carbon density at different scattering vector (Q) values and by measuring the p/p0 dependence of the SANS, using fully deuterated toluene. The contrast matching data shows that the apparent density is Q-dependent, either because of pores opening near the carbon surface during the activation processor or changes in D-toluene density in nanoscale pores. For each p/p0 value, evaluation of the Porod Invariant yields the fraction of empty pores. Hence, comparison with the adsorption isotherm, shows that the fully dry powder undergoes densification when liquid is added. An algebraic function is developed to fit the SANS signal at each p/p0 value hence yielding the effective Kelvin radii of the liquid surfaces as a function of p/p0. These values, when compared with the Kelvin equation, show that the resultant surface tension value is accurate for the larger pores but tends to increase for small (nanoscale) pores. The resultant pore size distribution is less model-dependent than for the traditional methods of analyzing the adsorption isotherms. 相似文献