首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1156篇
  免费   101篇
  国内免费   1篇
电工技术   5篇
化学工业   666篇
金属工艺   15篇
机械仪表   15篇
建筑科学   39篇
矿业工程   6篇
能源动力   30篇
轻工业   242篇
水利工程   6篇
石油天然气   5篇
无线电   27篇
一般工业技术   126篇
冶金工业   21篇
原子能技术   1篇
自动化技术   54篇
  2024年   2篇
  2023年   28篇
  2022年   146篇
  2021年   227篇
  2020年   50篇
  2019年   55篇
  2018年   44篇
  2017年   59篇
  2016年   77篇
  2015年   49篇
  2014年   60篇
  2013年   70篇
  2012年   60篇
  2011年   60篇
  2010年   34篇
  2009年   50篇
  2008年   37篇
  2007年   29篇
  2006年   25篇
  2005年   16篇
  2004年   15篇
  2003年   13篇
  2002年   10篇
  2001年   6篇
  2000年   5篇
  1999年   6篇
  1998年   5篇
  1997年   2篇
  1996年   1篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   3篇
  1990年   1篇
  1989年   2篇
  1987年   1篇
  1985年   1篇
  1984年   3篇
  1982年   1篇
排序方式: 共有1258条查询结果,搜索用时 15 毫秒
31.
One of the main goals of recent bioinorganic chemistry studies has been to design and synthesize novel substances to treat human diseases. The promising compounds are metal-based and metal ion binding components such as vanadium-based compounds. The potential anticancer action of vanadium-based compounds is one of area of investigation in this field. In this study, we present five oxovanadium(IV) and dioxovanadium(V) complexes as potential PTP1B inhibitors with anticancer activity against the MCF-7 breast cancer cell line, the triple negative MDA-MB-231 breast cancer cell line, and the human keratinocyte HaCaT cell line. We observed that all tested compounds were effective inhibitors of PTP1B, which correlates with anticancer activity. [VO(dipic)(dmbipy)]·2 H2O (Compound 4) and [VOO(dipic)](2-phepyH)·H2O (Compound 5) possessed the greatest inhibitory effect, with IC50 185.4 ± 9.8 and 167.2 ± 8.0 nM, respectively. To obtain a better understanding of the relationship between the structure of the examined compounds and their activity, we performed a computer simulation of their binding inside the active site of PTP1B. We observed a stronger binding of complexes containing dipicolinic acid with PTP1B. Based on our simulations, we suggested that the studied complexes exert their activity by stabilizing the WPD-loop in an open position and limiting access to the P-loop.  相似文献   
32.
Brain injury, especially traumatic brain injury (TBI), may induce severe dysfunction of extracerebral organs. Cardiac dysfunction associated with TBI is common and well known as the brain–heart crosstalk, which broadly refers to different cardiac disorders such as cardiac arrhythmias, ischemia, hemodynamic insufficiency, and sudden cardiac death, which corresponds to acute disorders of brain function. TBI-related cardiac dysfunction can both worsen the brain damage and increase the risk of death. TBI-related cardiac disorders have been mainly treated symptomatically. However, the analysis of pathomechanisms of TBI-related cardiac dysfunction has highlighted an important role of melatonin in the prevention and treatment of such disorders. Melatonin is a neurohormone released by the pineal gland. It plays a crucial role in the coordination of the circadian rhythm. Additionally, melatonin possesses strong anti-inflammatory, antioxidative, and antiapoptotic properties and can modulate sympathetic and parasympathetic activities. Melatonin has a protective effect not only on the brain, by attenuating its injury, but on extracranial organs, including the heart. The aim of this study was to analyze the molecular activity of melatonin in terms of TBI-related cardiac disorders. Our article describes the benefits resulting from using melatonin as an adjuvant in protection and treatment of brain injury-induced cardiac dysfunction.  相似文献   
33.
In silico comparison of 34 putative pks genes in Aspergillus niger strain CBS 513.88 versus A. niger strain ATCC 1015 genome revealed significant nucleotide identity (>95% covering a minimum of 99% of the gene sequence) for 31 of these genes (approximately 91%). A. niger CBS 513.88 harbors three putative pks genes (An01g01130, An11g05940, and An15g07920), for which nucleotide identity was not found in A. niger ATCC 1015. To compare the results of the in silico analysis with the in vivo situation, experimental data were obtained for a large number of A. niger strains obtained from different substrates and geographical regions. Three putative pks genes that were found to be variable between the two A. niger strains using bioinformatics tools were in fact strain-specific genes based on experimental data. The PCR amplification signals for the An01g01130, An11g05940, and An15g07920 pks genes were detected in only 97%, 71%, and 26% of the strains, respectively. Southern blot analyses confirmed the PCR data. Because one of the strain-specific pks genes (An15g07920) is located in a putative ochratoxin cluster, we focused our investigation on that region. We assessed the ochratoxin production capability of the 119 A. niger strains and found a positive association between the presence of this pks gene and the capability of the respective strain to produce ochratoxin.  相似文献   
34.
Determination of Iron Species in Samples of Iron-Fortified Food   总被引:1,自引:0,他引:1  
The paper presents the determination of iron forms in food products. The procedure of sample extraction was developed and optimized, preserving the content of particular forms of iron. The colorimetric method using 2,2′-bipirydyl (measurements at 520 nm) was applied in Fe(II) determinations, while in Fe(III) determinations, the colorimetric method with potassium thiocyanate (measurements at 470 nm) was applied. The total content of iron was determined by the technique of atomic absorption spectrometry, which allowed for the determination of iron content in organic and inorganic complex compounds. Detection limits of 1 mg kg?1 were obtained for all determined iron forms, with the precision ranging between 0.7 % and 1.5 % for 10 mg kg?1 concentration. The optimized analytical procedure was applied in the determinations of iron forms in iron-fortified food products.  相似文献   
35.
The LC–MS/MS technique was applied to the stability study of several flavonoids and phenolic acids in honey samples during the ultrasonic extraction (USE) and microwave-assisted extraction (MAE). Phenolic compounds from the standard mixture were stable under ultrasounds action with the mean recovery of (90.4% ± 7.1%), but during microwave-assisted extraction the benzoic acid derivatives and aglycones of flavonoids showed lower recovery (70–80%). In honey matrix, the phenolic acids and the glycosides exhibited the high stability for MAE and USE treatments. However, the recoveries of tested aglycones were below 10%. In the presence of an artificial sugar matrix, flavonols were almost completely degraded after successive treatment under MAE and USE conditions. The obtained results indicated that standard addition method for flavonoids quantification in honey samples should not be recommended. Application of the USE conditions provided higher and/or similar extraction yields for phenolic acids than usually applied shaking with solvent. It also allowed shortening the time required for the whole sample preparation procedure. Phenolic acids and glycosides such as quercetrin, rutin and hesperidin appeared to be stable under such conditions.  相似文献   
36.
BACKGROUND: In Equatorial Guinea, as a result of the recent growth of the oil industry, there is an opportunity to address important public health problems through public and private initiatives. To propose effective nutrition and public health strategies, it is important first to have reliable information on the nutritional status of the population and the underlying factors affecting it. OBJECTIVE: To assess the nutritional status and the prevalence of anemia among Equatoguinean children in a nationally representative sample and to identify the risk factors associated with the nutritional problems detected. METHODS: The study was a cross-sectional survey using a multistaged, stratified, cluster-selected sample. The survey included a sociodemographic, health, and dietary questionnaire and measurement of hematocrit and anthropometric features, from which nutritional indicators based on the National Center for Health Statistics (NCHS) reference and the World Health Organization (WHO) standards were calculated. Logistic regression models were used for the multivariate analysis. A total of 552 children aged 0 to 60 months were surveyed. RESULTS: The overall prevalence of stunting (< -2 height-for-age z-scores [HAZ]) was 29.7% based on the NCHS reference and 35.2% based on WHO standards; the risk factors associated with stunting were age (p < .0001), low socioeconomic status (p = .01), and fishing by a member of the household (p = .003) The prevalence of mild anemia (hemoglobin < 110 g/L) was 69.3%, and that of moderate or severe anemia (hemoglobin < 80 g/L) was 8.3%. The only significant risk factor associated with moderate to severe anemia was low household socioeducational level (p = .01). CONCLUSIONS: Stunting and anemia are public health problems in Equatorial Guinea. Integrated strategies, including fighting poverty and improving maternal education, should be undertaken.  相似文献   
37.
38.
The HaLoop approach to large-scale iterative data analysis   总被引:1,自引:0,他引:1  
The growing demand for large-scale data mining and data analysis applications has led both industry and academia to design new types of highly scalable data-intensive computing platforms. MapReduce has enjoyed particular success. However, MapReduce lacks built-in support for iterative programs, which arise naturally in many applications including data mining, web ranking, graph analysis, and model fitting. This paper (This is an extended version of the VLDB 2010 paper “HaLoop: Efficient Iterative Data Processing on Large Clusters” PVLDB 3(1):285–296, 2010.) presents HaLoop, a modified version of the Hadoop MapReduce framework, that is designed to serve these applications. HaLoop allows iterative applications to be assembled from existing Hadoop programs without modification, and significantly improves their efficiency by providing inter-iteration caching mechanisms and a loop-aware scheduler to exploit these caches. HaLoop retains the fault-tolerance properties of MapReduce through automatic cache recovery and task re-execution. We evaluated HaLoop on a variety of real applications and real datasets. Compared with Hadoop, on average, HaLoop improved runtimes by a factor of 1.85 and shuffled only 4 % as much data between mappers and reducers in the applications that we tested.  相似文献   
39.
The aim of this study is to answer the question of whether improvements in the health of the elderly in European countries could compensate for population ageing on the supply side of the labour market. We propose a state-of-health-specific (additive) decomposition of the old-age dependency ratio into an old-age healthy dependency ratio and an old-age unhealthy dependency ratio in order to participate in a discussion of the significance of changes in population health to compensate for the ageing of the labour force. Applying the proposed indicators to the Eurostat's population projection for the years 2010-2050, and assuming there will be equal improvements in life expectancy and healthy life expectancy at birth, we discuss various scenarios concerning future of the European labour force. While improvements in population health are anticipated during the years 2010-2050, the growth in the number of elderly people in Europe may be expected to lead to a rise in both healthy and unhealthy dependency ratios. The healthy dependency ratio is, however, projected to make up the greater part of the old-age dependency ratio. In the European countries in 2006, the value of the old-age dependency ratio was 25. But in the year 2050, with a positive migration balance over the years 2010-2050, there would be 18 elderly people in poor health plus 34 in good health per 100 people in the current working age range of 15-64. In the scenarios developed in this study, we demonstrate that improvements in health and progress in preventing disability will not, by themselves, compensate for the ageing of the workforce. However, coupled with a positive migration balance, at the level and with the age structure assumed in the Eurostat's population projections, these developments could ease the effect of population ageing on the supply side of the European labour market.  相似文献   
40.
The murine monoclonal antibody BR55-2 is directed against thetumor-associated antigen Lewis Y oligosaccharide. The LewisY core antigen is a difucosylated structure consisting of fourhexose units. Analysis of binding profiles of lactoseries isomericstructures by BR55–2 suggest that the binding epitopeincludes the OH-4 and OH-3 groups of the ß-D-galactoseunit, the 6-CH3 groups of the two fucose units and the N-acetylgroup of the subterminal ß-D-N-acetylglucosamine (ßDGlcNAc).To elucidate the molecular recognition properties of BR55–2for the Y antigen, BR55–2 was cloned, sequenced and itsthree-dimensional structure was examined by molecular modeling.The crystal structure of BR96, another anti-Lewis Y antibody,solved in complex with a nonoate methyl ester Lewis Y tetrasaccharide,and the lectin IV protein in complex with a Lewis b tetrasaccharidecore were used as a guide to probe the molecular basis for BR55–2antigen recognition and specificity. Our modeling study showsthat BR55–2 shares similar recognition features for thedifucosylated type 2 lactoseries Lewis Y structure observedin the BR96-sugar complex. We observe that a major source ofspecificity for the Lewis Y structure by anti-Y antibodies emanatesfrom interaction with the ß-D-N-acetylglucosamineresidue and the nature of the structures extended at the reducingsite of the fucosylated lactosoamine.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号