首页 | 官方网站   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   1713篇
  免费   126篇
  国内免费   1篇
工业技术   1840篇
  2024年   4篇
  2023年   14篇
  2022年   30篇
  2021年   105篇
  2020年   48篇
  2019年   92篇
  2018年   72篇
  2017年   68篇
  2016年   83篇
  2015年   68篇
  2014年   84篇
  2013年   126篇
  2012年   128篇
  2011年   142篇
  2010年   114篇
  2009年   106篇
  2008年   93篇
  2007年   72篇
  2006年   68篇
  2005年   47篇
  2004年   52篇
  2003年   29篇
  2002年   15篇
  2001年   17篇
  2000年   20篇
  1999年   10篇
  1998年   16篇
  1997年   25篇
  1996年   12篇
  1995年   9篇
  1994年   6篇
  1993年   9篇
  1992年   4篇
  1991年   7篇
  1990年   6篇
  1988年   5篇
  1986年   1篇
  1985年   7篇
  1984年   1篇
  1983年   5篇
  1982年   1篇
  1981年   1篇
  1980年   4篇
  1979年   2篇
  1978年   3篇
  1977年   1篇
  1976年   2篇
  1975年   1篇
  1974年   3篇
  1973年   1篇
排序方式: 共有1840条查询结果,搜索用时 31 毫秒
991.
Sideritis species have been used in folk medicine for their antimicrobial, antiulcerogenic, digestive and anti‐inflammatory properties. Over the years, the phytochemistry of the genus Sideritis has been studied, and various terpenoids, sterols, coumarins and especially flavonoid aglycones and glycosides have been identified. In particular, species from the Balkan Peninsula have been studied and were found to be rich in flavonoids, with valuable antioxidant activity. In the folk medicine of the Balkan countries, Sideritis raeseri is used as a herbal tea in the treatment of inflammation, gastrointestinal disorders and coughs, and also as a tonic, whereas extracts are used as a component of dietary supplements for anaemia. Its dried inflorescences are used to prepare a beverage called ‘mountain tea’. In light of the considerable interest generated in the chemistry, pharmacological properties and commercial value of S. raeseri Boiss. & Heldr., we review and summarise the available literature on these plants. The review details the chemical composition of the essential oil, its mineral and polyphenol contents, the naming of these plants and their physicochemical characterisation, and the nuclear magnetic resonance spectral data and biological properties associated with the plant extracts, with a focus on their potential chemotherapeutic applications. © 2016 Society of Chemical Industry  相似文献   
992.
Regeneration is the most efficient way of managing used oil. It saves money by preventing costly cleanups and liabilities that are associated with mismanagement of used oil, it helps to protect the environment and it produces a technically renewable resource by enabling an indefinite recycling potential. There are a variety of processes and licensors currently offering ways to deal with used oils. Selecting a regeneration technology for used oil involves "cross-matching" key criteria. Therefore, the first prototype of spent oil regeneration (SPORE), a decision support tool, has been developed to help decision-makers to assess the available technologies and select the preferred used oil regeneration options. The analysis is based on technical, economical and environmental criteria. These criteria are ranked to determine their relative importance for a particular used oil regeneration project. The multi-criteria decision analysis (MCDA) is the core of the SPORE using the PROMETHEE II algorithm.  相似文献   
993.
A therapy-specific worsening of cardiovascular stability during bicarbonate dialysis (BD) with respect to acetate-free biofiltration (AFB) have been previously reported. We further investigated the impact of the 2 therapies on electrocardiographic parameters in order to gain novel insight into the cardiac responses. Holter ECG acquired during hypotension-free sessions (12 BD + 12 AFB) were retrospectively analyzed. R-R intervals were extracted from ECG recordings. An autoregressive spectral technique was used to compute low- and high-frequency (LF and HF) components of heart rate variability (HRV). QT interval duration was measured with a computer-assisted technique and corrected for HR. In BD the LF component of HRV after an initial increase was slowly depressed with respect to AFB (p < 0.05). QT duration showed a significant (p < 0.01) hemodialysis-induced reduction. QT shortening was more pronounced (p < 0.05) in BD than in AFB (-31 vs. -10 ms), even after correction for HR (p < 0.05). Cardiac electrical activity is significantly affected by the hemodialysis technique. The decrease in the LF component of HRV and the QT shortening are coherent with the worse cardiovascular tolerance observed in BD and with the hypothesis of an enhanced production of endogenous nitric oxide.  相似文献   
994.
The aim of this paper is to test a technique called partial directed coherence (PDC) and its modification (squared PDC; sPDC) for the estimation of human cortical connectivity by means of simulation study, in which both PDC and sPDC were studied by analysis of variance. The statistical analysis performed returned that both PDC and sPDC are able to estimate correctly the imposed connectivity patterns when data exhibit a signal-to-noise ratio of at least 3 and a length of at least 27 s of nonconsecutive recordings at 250 Hz of sampling rate, equivalent, more generally, to 6750 data samples.  相似文献   
995.
Hydrogen production via water-gas shift (WGS) reaction using heavy oil residues as syngas source is an attractive way to improve refinery margin. However, this low cost syngas may present significant concentration of sulfur, leading to poisoning of usual WGS catalysts. Searching for sulfur tolerant catalysts, the performance of niobia supported platinum, gold and copper catalysts was evaluated under near-industrial conditions, in the absence and presence of H2S. Cu/Nb2O5 catalyst was inactive, even under clean conditions. Au/Nb2O5 presented higher activity and complete deactivation when exposed to sulfur, but recovered its catalytic activity with the removal of H2S from the reaction mixture, indicating a reversible deactivation. Pt/Nb2O5 catalyst was the most suitable among the catalysts evaluated to be used in sour conditions, not deactivating when exposed to 50 ppm and 1000 ppm of H2S.  相似文献   
996.
Hunter’s classification is the most adopted method for describing coarse woody debris (CWD) decay stages; however, wood chemical characterization is often lacking. This study explores the sugar profiles of living silver fir (Abies alba Mill.) trees and CWD samples in Hunter’s five-decay stages, evaluating the trends and variability in sugar content in CWD samples during decomposition. Wood cores from living trees and CWD samples from two different forest sites in Trentino (Italy) were analyzed after extraction using ion-exchange chromatography, equipped with pulsed amperometric and charge aerosol detectors (IC-PAD-CAD). Detailed monosaccharides, disaccharides, and sugar alcohol profiles of living wood and CWD samples were described. Cellobiose, arabinose, maltose, and trehalose showed similar trend in both the sites. Principal component analysis (PCA) highlighted the good capability of sugar profiles to well characterize and discriminate silver fir wood samples among Hunter’s categories of wood decomposition.  相似文献   
997.
Although there are some models available in the literature for paste drying in spouted beds, few of them have focused on transient analysis of dynamical systems. Our objective was to integrate experiments and simulations of a dynamic model to investigate the transient response to disturbances and interruptions in the feed flow during paste drying in a spouted bed with inert particles. The spouted bed consisted of a cylindrical column with 50.0?cm of height and 20.0?cm of diameter. Drying tests were performed at inlet gas temperatures of 70?°C and 100?°C and inlet air flow 30% above the minimum spouting velocity. A 5% w/w suspension of calcium carbonate was used as paste material, and glass spheres of 2.2?mm were used as inert materials. Different patterns of step function changes were tested in the paste feed flow rate. A lumped parameter model was used to predict mass and heat transfer during the drying. Experiments and simulations were in good agreement.  相似文献   
998.
In educational environments an improvement in the quality of interior lighting has a direct benefit in increasing productivity and alertness of students and teachers, as well as very important implications for the energy efficiency of th eeducation facilities but when a replacement with different lighting is analyzed, research may be tarnished by users’ preformed opinions, influenced by manufacturers and advertising. Consequently, it is necessary to understand the users’ point of view, even before of being subjected to any change in the lighting stimulus. Based on the Kansei Engineering framework, the general objective of this paper is to evaluate and compare the subjective evaluation of students’ pre-formed opinions to lighting provided by two types of lamps (fluorescentandLED). The subjective assessment of 427 university students has been compared over four years. The results show significant differences in students’ subjective evaluation. This finding highlights the existence of symbolic or functional attributes of the usefulness perceived by the student that could influence on investigations in which different types of lighting are compared.  相似文献   
999.
The patterns of longitudinal and peripheral growth were analyzed in human autopod cartilage anlagen (fetal developmental stage 20th–22nd week) through morphometric assessment of chondrocyte parameter size, shape, alignment and orientation between peripheral and central sectors of the anlage transition zone defined by primary ossification center and the epiphyseal basis. The aim was to correlate the chondrocyte dynamics with the longitudinal and peripheral growth. A further comparison was carried out between the corresponding sectors of the postnatal (3–5 months old) growth plate cartilage documenting: (1) the different chondrocyte framework and the new peripheral mechanism; (2) the opposite direction of fetal periosteal ossification versus the Lacroix bone bark. Measurement of multiple parameters (% lac area, % total matrix area, total lac density and mean single lac area), which characterize the cartilage Anlage growth, suggested the following correlations with chondrocyte duplication rate: (a) slow duplication rate ≈ coupled, intralacunar chondrocytes (in central epiphysis); (b) repeated/frequent cell duplications ≈ clusters (in the basal epiphyseal layer); (c) clusters of chondrocytes before becoming hypertrophic were stacked up on the top of each other (both in the Anlage transition zone or in the columns of metaphyseal growth plate); (d) enhanced osteoclastic resorption of the Lacroix bone bark lower end, extended to the more external metaphyseal trabeculae counterbalancing the discrepancy between the epiphyseal and the diaphyseal circumferential growth.  相似文献   
1000.
In an effort to characterize colostrum microbial diversity and its potential associations with early-lactation clinical mastitis, we used high-throughput sequencing of the 16S rRNA gene to investigate the bovine colostrum microbiome. A prospective observational study was conducted that included 70 Holstein cows; colostrum samples were collected from all 4 mammary gland quarters. Colostrum samples were categorized according to whether the quarter was diagnosed (CMC) or not diagnosed (NCMC) with clinical mastitis during the first 30 d postpartum. Colostrum samples were dominated by Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Fusobacteria, and Tenericutes phyla, with the 6 most common taxa [order (o), family (f), and genus (g)] being g_Staphylococcus, g_Prevotella, f_Ruminococcaceae, o_Bacteroidales, o_Clostridiales, and g_Pseudomonas. The colostrum microbiota of primiparous cows was significantly richer (higher number of bacterial species) than that of multiparous cows, and differences in colostrum taxonomic structure between parities were also observed. The microbial community of NCMC samples of primiparous cows was significantly more diverse than that of CMC samples, and the relative abundances of the Tenericutes and Fusobacteria phyla as well as the Mycoplasma and Fusobacterium genera were significantly higher in NCMC than in CMC samples of primiparous cows. The colostrum core microbiome, defined as the bacterial taxa common to all colostrum samples examined, was composed of 20 taxa and included bacterial genera already known to be associated with mastitis (e.g., Staphylococcus, Mycoplasma, and Streptococcus spp.). Our results indicate that the colostrum microbiome of primiparous cows differs from that of multiparous cows, and it harbors some diversity and taxonomic markers of mammary gland health specific to primiparous cows only.  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-23

京公网安备 11010802026262号