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   814篇
  免费   36篇
  国内免费   1篇
电工技术   12篇
综合类   4篇
化学工业   224篇
金属工艺   13篇
机械仪表   12篇
建筑科学   51篇
矿业工程   3篇
能源动力   11篇
轻工业   65篇
水利工程   15篇
无线电   52篇
一般工业技术   171篇
冶金工业   31篇
原子能技术   3篇
自动化技术   184篇
  2023年   6篇
  2022年   7篇
  2021年   29篇
  2020年   11篇
  2019年   17篇
  2018年   14篇
  2017年   18篇
  2016年   34篇
  2015年   25篇
  2014年   28篇
  2013年   40篇
  2012年   39篇
  2011年   52篇
  2010年   31篇
  2009年   33篇
  2008年   44篇
  2007年   53篇
  2006年   41篇
  2005年   15篇
  2004年   16篇
  2003年   19篇
  2002年   18篇
  2001年   11篇
  2000年   12篇
  1999年   26篇
  1998年   11篇
  1997年   13篇
  1996年   9篇
  1995年   13篇
  1994年   13篇
  1993年   9篇
  1992年   11篇
  1991年   9篇
  1990年   11篇
  1989年   11篇
  1988年   9篇
  1987年   10篇
  1986年   9篇
  1985年   7篇
  1984年   4篇
  1983年   6篇
  1982年   3篇
  1980年   5篇
  1979年   5篇
  1978年   11篇
  1977年   7篇
  1975年   3篇
  1973年   4篇
  1927年   2篇
  1901年   2篇
排序方式: 共有851条查询结果,搜索用时 18 毫秒
1.
Growing evidence is showing that acetylation plays an essential role in cancer, but studies on the impact of KDAC inhibition (KDACi) on the metabolic profile are still in their infancy. Here, we analyzed, by using an iTRAQ-based quantitative proteomics approach, the changes in the proteome of KRAS-mutated non-small cell lung cancer (NSCLC) A549 cells in response to trichostatin-A (TSA) and nicotinamide (NAM) under normoxia and hypoxia. Part of this response was further validated by molecular and biochemical analyses and correlated with the proliferation rates, apoptotic cell death, and activation of ROS scavenging mechanisms in opposition to the ROS production. Despite the differences among the KDAC inhibitors, up-regulation of glycolysis, TCA cycle, oxidative phosphorylation and fatty acid synthesis emerged as a common metabolic response underlying KDACi. We also observed that some of the KDACi effects at metabolic levels are enhanced under hypoxia. Furthermore, we used a drug repositioning machine learning approach to list candidate metabolic therapeutic agents for KRAS mutated NSCLC. Together, these results allow us to better understand the metabolic regulations underlying KDACi in NSCLC, taking into account the microenvironment of tumors related to hypoxia, and bring new insights for the future rational design of new therapies.  相似文献   
2.
Advanced manufacturing system technologies are difficult to evaluate using ordinary financial measures owing to the presence of risk and significant intangible factors. In this paper a methodology is proposed that quantifies financial, strategic, and tactical attributes of each alternative. Attribute values are denned for each period of project life. Both project life and attributes are treated as random variables. Attributes are discounted to the current time and the multiple objectives are combined by composite programming. The distribution of the combined objective is estimated. The procedure is demonstrated on an actual case study.  相似文献   
3.
Research on achievement goal orientation in sport has relied primarily on traditional statistical methodology to examine group mean differences. Unfortunately, examination of the measurement model is generally ignored prior to means testing. This study reports an application of structural equation modeling (SEM) in testing measurement invariance and latent mean structure of the Task and Ego Orientation in Sport Questionnaire (TEOSQ; Duda & Nicholls, 1989) using male and female college students. A confirmatory factor analysis for testing invariance revealed invariant measurement properties and factor structures across gender, indicating that task and ego orientation are similarly conceptualized by male and female students. Subsequent testing of latent mean structures, however, showed significant gender differences with respect to ego orientation, but no difference in task orientation. The SEM procedures used in the present study demonstrate additional construct validity and internal consistency reliability for the TEOSQ and, by confirming its factor structure, provide a sound psychometric basis for its continued use in substantive studies focusing on the comparison of achievement goal orientation across gender.  相似文献   
4.
5.
The presence of protease inhibitors in soybean prohibits the utilisation of the raw beans for food and feed. However, little information is available about environmental influences and the effects of nitrogen and sulphur supply on the antinutritional constituents of soybean. As these factors may influence protease inhibitors, soybean genotypes segregated according to the presence or absence of the Kunitz trypsin inhibitor have been evaluated for trypsin inhibitor activity (TIA) in field trials. TIA was affected significantly by environment (geographical location), fertilisation treatment and genotype. Environmental means of TIA were between 69.5 and 104.8 mg g?1. Nitrogen application, which caused an increase in seed protein content, resulted in a reduction in TIA by about 15% as compared with the control. Remarkably, simultaneous application of nitrogen and sulphur in the form of ammonium sulphate had a similar reductive effect on TIA to that of nitrogen application alone, although soybean protease inhibitors are rich in sulphur amino acids. Significant genetic variation in TIA was found both within the genotype class with the Kunitz inhibitor present as well as within the class lacking this inhibitor. The results suggest that TIA of soybean may be modified considerably by genetic improvement and appropriate agronomic management. Copyright © 2003 Society of Chemical Industry  相似文献   
6.
Summary Bavarian cereals and wheat flour from the 1987 harvest were analysed for nivalenol (NIV) and deoxynivalenol (DON) using high performance liquid chromatography (HPLC) and for T-2 toxin and zearalenone (ZEA) by enzyme-linked-immunosorbent as say (ELISA). The study included 190 field samples of wheat, barley, rye and oat with visibly damaged ears, 45 samples of wheat intended for feed production and two series of wheat flour (type 550) and whole wheat flour collected in October 1987 and June 1988. The field samples examined showed a high DON contamination of wheat (87%) with an average of 3.96 mg/kg and a maximum of 43.8 mg/kg. Mean levels between 0.33 mg/kg and 0.27 mg/kg DON could be detected in barley, rye and oat. Of the wheat samples, 58% contained ZEA with a maximum of 1.560 mg/kg. The highest levels of ZEA were detected in samples which also showed high concentrations of DON. The NIV and T-2 toxin levels were comparatively low. Thirty percent of the samples showed NIV concentrations between 0.04 mg/kg and 0.29 mg/kg and 38% contained between 0.005 and 0.60 mg/kg of T-2. In the wheat samples for feed production, only DON was detected with an average of 0.190 mg/kg and a maximum of 0.75 mg/kg. The highest DON levels (0.58 mg/kg) from October 1987 were found in the wheat flour samples which were lower than the highest DON concentration (3.24 mg/kg) detected in the samples collected during June 1988. This fact was probably due to a substantial amount of non-contaminated wheat from 1986. The toxin concentrations in the whole wheat flour were not higher than in the type 550 flour. The regional distribution of the mean DON concentrations showed the highest levels in Middle and Lower-Franconia.
Vorkommen von Fusarium Mykotoxinen in bayerischem Getreide der Ernte 1987
Zusammenfassung Cerealien und Weizenmehle der bayerischen Ernte 1987 wurden mittels hochauflösender Flüssigchromatographie (HPLC) auf Nivalenol (NIV) und Deoxynivalenol (DON) Bowie mit Enzymimmunoassay auf T-2 Toxin und Zearalenon (ZEA) analysiert. Die Untersuchungen umfaßten 190 Feldproben von Weizen, Gerste, Roggen und Hafer, die alle optisch erkennbaren Fusarienbefall aufwiesen, 45 Futterweizenproben Bowie zwei Probenserien von Weizenmehlen der Type 550 und Vollkornweizenmehlen, die im October 1987 und im Juni 1988 gezogenwurden. — Die Untersuchungen der Feldproben ergaben eine hohe DON-Kontamination des Weizens (87%) mit einem durchschnittlichen Gehalt von 3,96 mg/kg und einem Maximalgehalt von 43,8 mg/kg. In Gerste, Roggen und Hafer konnten durchschnittlich zwischen 0,33 mg/kg und 0,27 mg/kg DON-nachgewiesen werden. 58% der Winterweizenproben wiesen Zearalenon mit einem Maximalgehalt von 1,56 mg/kg auf. Die höchsten ZEA-Werte wurden in Proben ermittelt, die gleichzeitig einen hohen DON-Gehalt aufwiesen. Die Konzentrationen von NIV und T-2 Toxin waren vergleichsweise niedrig. 30% der Proben hatten NIV-Gehalte zwischen 0,04 mg/kg und 0,29 mg/kg und 38% enthielten T-2 Toxin zwischen 0,005 mg/kg und 0,06 mg/kg. In den Futterweizenproben konnte DON als einziges Toxin mit einem Gehalt von durchschnittlich 0,19 mg/kg und maximal 0,75 mg/kg festgestellt werden. Die Weizenmehle, die im October 1987 gezogen wurden, wiesen maximal 0,58 mg/kg DON auf. Die Gehalte lagen damit medriger als die der Mehlproben vom Juni 1988, die maximal 3,24 mg/kg und durchschnittlich 0,26 mg/kg DON enthielten. Dieser Sachverhalt könnte auf Anteile von nicht kontaminiertem Weizen der Ernte 86 an den im October gezogenen Mehlproben zurückgeführt werden. Die Toxingehalte der Vollkornmehle waren nicht höher als die der Weizenmehle der Type 550. Die höchsten Durchschnittsgehalte von DON wurden in Mittel- und Unterfranken festgestellt.
  相似文献   
7.
As heterogeneous data from different sources are being increasingly linked, it becomes difficult for users to understand how the data are connected, to identify what means are suitable to analyze a given data set, or to find out how to proceed for a given analysis task. We target this challenge with a new model-driven design process that effectively codesigns aspects of data, view, analytics, and tasks. We achieve this by using the workflow of the analysis task as a trajectory through data, interactive views, and analytical processes. The benefits for the analysis session go well beyond the pure selection of appropriate data sets and range from providing orientation or even guidance along a preferred analysis path to a potential overall speedup, allowing data to be fetched ahead of time. We illustrate the design process for a biomedical use case that aims at determining a treatment plan for cancer patients from the visual analysis of a large, heterogeneous clinical data pool. As an example for how to apply the comprehensive design approach, we present Stack'n'flip, a sample implementation which tightly integrates visualizations of the actual data with a map of available data sets, views, and tasks, thus capturing and communicating the analytical workflow through the required data sets.  相似文献   
8.
    
Zusammenfassung Zur Bestimmung biogener Amine aus Schlachtgeflügel wird ein einfach durchzuführendes Analysenverfahren beschrieben. Die Amine wurden mit 0,6m-Perchlorsäure extrahiert, nach Dansylierung auf einer RP-18 Säule aufgetrennt und bei 254 nm detektiert. Innerhalb von 7 min konnte eine gute Auftrennung von 8 Aminen erreicht werden. Zur quantitativen Erfassung von Spermin und Spermidin mußte der Extrakt zusätzlich über Amberlite CG 50 gereinigt werden. Die Wiederfindungsraten betrugen 82% bis 96%, die Nachweisgrenzen 0,2 bis 0,5 g pro g Hühnerhaut. Bei Schlachtgeflügel eignen sich Putrescin und Cadaverin gut als Leitsubstanzen für den einsetzenden Verderb, da sie bereits ab Gesamtkoloniezahlen von etwa 105 pro cm2 nachweisbar sind, und ihre Konzentration mit zunehmendem Verderb rasch ansteigen.
Determination of biogenic amines by RP-HPLC for monitoring microbial spoilage of poultry
Summary A simple high-performance liquid chromatographic (HPLC) analysis is described for the determination of biogenic amines in broiler carcasses. The clean-up procedure consists of an extraction with 0.6M-perchloric acid, formation of dansyl derivatives, separation by a RP-18 column and UV detection at 254 nm. Within 7 min eight amines could be separated. The quantitative determination of spermidine and spermine requires an additional ion-exchange clean-up with Amberlite CG 50 after the extraction. This procedure gives recoveries of 82%–96% with detection limits of 0.2–0.5 g/g of broiler skin. Putrescine and cadaverine are good indicators for the onset of spoilage of poultry carcasses, since both amines could be detected at total colony counts of 105 cfu/cm2 and their concentration increases rapidly with advancing decomposition.
  相似文献   
9.
The glycine conjugation pathway in humans is involved in the metabolism of natural substrates and the detoxification of xenobiotics. The interactions between the various substrates in this pathway and their competition for the pathway enzymes are currently unknown. The pathway consists of a mitochondrial xenobiotic/medium-chain fatty acid: coenzyme A (CoA) ligase (ACSM2B) and glycine N-acyltransferase (GLYAT). The catalytic mechanism and substrate specificity of both of these enzymes have not been thoroughly characterised. In this study, the level of evolutionary conservation of GLYAT missense variants and haplotypes were analysed. From these data, haplotype variants were selected (156Asn > Ser, [17Ser > Thr,156Asn > Ser] and [156Asn > Ser,199Arg > Cys]) in order to characterise the kinetic mechanism of the enzyme over a wide range of substrate concentrations. The 156Asn > Ser haplotype has the highest frequency and the highest relative enzyme activity in all populations studied, and hence was used as the reference in this study. Cooperative substrate binding was observed, and the kinetic data were fitted to a two-substrate Hill equation. The coding region of the GLYAT gene was found to be highly conserved and the rare 156Asn > Ser,199Arg > Cys variant negatively affected the relative enzyme activity. Even though the 156Asn > Ser,199Arg > Cys variant had a higher affinity for benzoyl-CoA (s0.5,benz = 61.2 µM), kcat was reduced to 9.8% of the most abundant haplotype 156Asn > Ser (s0.5,benz = 96.6 µM), while the activity of 17Ser > Thr,156Asn > Ser (s0.5,benz = 118 µM) was 73% of 156Asn > Ser. The in vitro kinetic analyses of the effect of the 156Asn > Ser,199Arg > Cys variant on human GLYAT enzyme activity indicated that individuals with this haplotype might have a decreased ability to metabolise benzoate when compared to individuals with the 156Asn > Ser variant. Furthermore, the accumulation of acyl-CoA intermediates can inhibit ACSM2B leading to a reduction in mitochondrial energy production.  相似文献   
10.
Tendinopathies are painful, disabling conditions that afflict 25% of the adult human population. Filling an unmet need for realistic large-animal models, we here present an ovine model of tendon injury for the comparative study of adult scarring repair and fetal regeneration. Complete regeneration of the fetal tendon within 28 days is demonstrated, while adult tendon defects remained macroscopically and histologically evident five months post-injury. In addition to a comprehensive histological assessment, proteome analyses of secretomes were performed. Confirming histological data, a specific and pronounced inflammation accompanied by activation of neutrophils in adult tendon defects was observed, corroborated by the significant up-regulation of pro-inflammatory factors, neutrophil attracting chemokines, the release of potentially tissue-damaging antimicrobial and extracellular matrix-degrading enzymes, and a response to oxidative stress. In contrast, secreted proteins of injured fetal tendons included proteins initiating the resolution of inflammation or promoting functional extracellular matrix production. These results demonstrate the power and relevance of our novel ovine fetal tendon regeneration model, which thus promises to accelerate research in the field. First insights from the model already support our molecular understanding of successful fetal tendon healing processes and may guide improved therapeutic strategies.  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