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   6828篇
  免费   97篇
  国内免费   19篇
电工技术   63篇
综合类   59篇
化学工业   2086篇
金属工艺   249篇
机械仪表   123篇
建筑科学   487篇
矿业工程   48篇
能源动力   402篇
轻工业   672篇
水利工程   78篇
石油天然气   97篇
武器工业   2篇
无线电   243篇
一般工业技术   1071篇
冶金工业   168篇
原子能技术   92篇
自动化技术   1004篇
  2023年   29篇
  2022年   244篇
  2021年   345篇
  2020年   169篇
  2019年   182篇
  2018年   85篇
  2017年   194篇
  2016年   237篇
  2015年   226篇
  2014年   326篇
  2013年   1110篇
  2012年   573篇
  2011年   219篇
  2010年   268篇
  2009年   272篇
  2008年   178篇
  2007年   252篇
  2006年   172篇
  2005年   231篇
  2004年   132篇
  2003年   108篇
  2002年   137篇
  2001年   97篇
  2000年   99篇
  1999年   98篇
  1998年   65篇
  1997年   42篇
  1996年   51篇
  1995年   38篇
  1994年   37篇
  1993年   33篇
  1992年   32篇
  1991年   18篇
  1990年   33篇
  1989年   19篇
  1988年   64篇
  1987年   73篇
  1986年   63篇
  1985年   37篇
  1984年   29篇
  1983年   32篇
  1982年   47篇
  1981年   51篇
  1980年   46篇
  1979年   46篇
  1978年   28篇
  1977年   22篇
  1976年   13篇
  1975年   4篇
  1971年   7篇
排序方式: 共有6944条查询结果,搜索用时 328 毫秒
981.
The advent of 2D nanostructured materials as advanced fillers for polymer matrix composites has opened the doors to a plethora of new industrial applications requiring both electric and thermal management. Unique properties, in fact, can arise from accurate selection and processing of 2D fillers and their matrix. Here, we report an innovative family of nanocomposite membranes based on polyurethane (PU) and graphene nanoplatelets (GNPs), designed to improve thermal comfort in functional textiles. GNP particles were thoroughly characterized (through Raman, atomic force microscopy, high-resolution TEM, scanning electron microscope), and showed high crystallinity (ID/IG = 0.127), low thickness (D50 < 6–8 layers), and high lateral dimensions (D50 ≈ 3 μm). When GNPs were loaded (up to 10% wt/wt) into the PU matrix, their homogeneous dispersion resulted in an increase of the in-plane thermal conductivity of composite membranes up to 471%. The thermal dissipation of membranes, alone or coupled with cotton fabric, was further evaluated by means of an ad hoc system designed to simulate a human forearm. The results obtained provide a new strategy for the preparation of membranes suitable for technical textiles, with improved thermal comfort.  相似文献   
982.
Anemia, characterized by a decrease of the hemoglobin level in the blood and a reduction in carrying capacity of oxygen, is a major public health problem which affects people of all ages. The methods used to treat anemia are blood transfusion and oral administration of iron-based supplements, but these treatments are associated with a number of side effects, such as nausea, vomiting, constipation, and stomach pain, which limit its long-term use. In addition, oral iron supplements are poorly absorbed in the intestinal tract, due to overexpression of hepcidin, a peptide hormone that plays a central role in iron homeostasis. In this review, we conducted an analysis of the literature on biologically active compounds and plant extracts used in the treatment of various types of anemia. The purpose of this review is to provide up-to-date information on the use of these compounds and plant extracts, in order to explore their therapeutic potential. The advantage of using them is that they are available from natural resources and can be used as main, alternative, or adjuvant therapies in many diseases, such as various types of anemia.  相似文献   
983.
Notch pathway is a highly conserved intracellular signaling route that modulates a vast variety of cellular processes including proliferation, differentiation, migration, cell fate and death. Recently, the presence of a strict crosstalk between Notch signaling and inflammation has been described, although the precise molecular mechanisms underlying this interplay have not yet been fully unravelled. Disruptions in Notch cascade, due both to direct mutations and/or to an altered regulation in the core components of Notch signaling, might lead to hypo- or hyperactivation of Notch target genes and signaling molecules, ultimately contributing to the onset of autoinflammatory diseases. To date, alterations in Notch signaling have been reported as associated with three autoinflammatory disorders, therefore, suggesting a possible role of Notch in the pathogenesis of the following diseases: hidradenitis suppurativa (HS), Behçet disease (BD), and giant cell arteritis (GCA). In this review, we aim at better characterizing the interplay between Notch and autoinflammatory diseases, trying to identify the role of this signaling route in the context of these disorders.  相似文献   
984.
The conjugation of organometallic groups to current β-lactam antibiotics is a field of increasing study due to the ability of certain organometallic groups to enhance the antibiotic potency of these drugs. Herein, we report the antibacterial properties of two metallocenyl (ferrocenyl and ruthenocenyl) 7-aminocephalosporanic acid (7-ACA) antibiotic conjugates. Continuing a trend we found in our previous studies, the ruthenocenyl conjugate showed greater antibacterial activity than its ferrocenyl counterpart. Compared with the previously published 7-aminodesacetoxycephalosporanic acid (7-ADCA) conjugates, the 3-acetyloxymethyl group significantly improved the compounds’ activity. Furthermore, the Rc-7-ACA compound was more active against clinical Staphylococcus aureus isolates than the ampicillin reference. Noticeably, neither of the two new compounds showed an undesirable toxic effect in HeLa and L929 cells at the concentrations at which they displayed strong antibacterial effects. The antibacterial activity of the two metallocenyl 7-ACA derivatives was further confirmed by scanning electron microscopy (SEM). SEM micrographs showed that bacteria treated with metallocenyl 7-ACA derivatives feature cell wall damage and morphology changes. Using a CTX-M-14 β-lactamase competition assay based on nitrocefin hydrolysis, we showed that the Rc-7-ACA bound more favorably to CTX-M-14 than its ferrocenyl counterpart, again confirming the superiority of the ruthenocenyl moiety over the ferrocenyl one in interacting with proteins. We also report a 1.47 Å resolution crystal structure of Rc-7-ACA in complex with the CTX-M-14 E166A mutant, an enzyme sharing a similar active site configuration with penicillin-binding proteins, the molecular target of β-lactam antibiotics. These results strengthen the case for the antibacterial utility of the Rc and Fc groups.  相似文献   
985.
Water-soluble, early lanthanide(III) mono- and bisporphyrin complexes possess very similar UV–Vis absorption as well as photophysical and photochemical properties, as a consequence of a special type of aggregation, through the peripheral substituents. In the absence of the bidentate, O-donor acetate ligand, bisporphyrin can form too, which has slightly redshifted and broadened absorption bands, compared to those of the monoporphyrin. Also the bisporphyrin displays a blueshifted and less intense fluorescence, related to the free-base porphyrin. The formation of complexes and the transformation between the mono- and bisporphyrins are very slow reactions in dark at room temperature. These reactions are accelerated by the photolysis of the system, which are considerable by-processes of the photoredox degradation. Depending on the wavelength of irradiation, two types of photoproducts can appear: during the photolysis at the Soret-band, a radical type intermediate can be observed, which disappears in dark. However, during the irradiation at the Q-bands, a new photoproduct appears, which is stable in dark and undetectable in the case of post-transition metal ions' out-of-plane porphyrin complexes.  相似文献   
986.
Hop terpenes might be oxidized during kettle boiling into more water soluble compounds that could contribute to ‘hoppy’ aroma of kettle hopped lager beers. Our current research proves that the boiling process induces significant changes in the hop oil volatile profile. The discrimination between volatile profiles of unboiled and boiled hop essential oil was evaluated via principal component and cluster analysis (PCA and CA). HS–SPME–GC–MS analysis revealed quantitative changes (e.g. increases in the levels of oxygenated α-humulene and β-caryophyllene derivatives) as well as qualitative changes (i.e. detection of compounds, not found in unboiled hop essential oil) in the hop oil volatile profile upon boiling. Many of these compounds were previously found in lager beer and may therefore contribute to beer flavor. Interestingly, the analytical difference between unboiled and boiled hop essential oil proved to be more pronounced as the initial hop essential oil concentration used for boiling was increased. In addition, lager beers spiked with boiled hop oil were described as ‘hoppy/spicy’ during sensory evaluations. Therefore, the newly formed products and hop oil constituents that are characterized by an increased recovery after boiling, are candidate compounds for ‘hoppy’ aroma in real brewing practice.  相似文献   
987.
This review of the literature on varietal change in sub-Saharan Africa looks in detail at adoption of new varieties of bananas in Uganda, cassava in Nigeria, potato in Kenya, sweetpotato in Uganda and yams in Côte d’Ivoire. The review explored three hypotheses about drivers of varietal change. There was a strong confirmation for the hypothesis that insufficient priority given to consumer-preferred traits by breeding programmes contributes to the limited uptake of modern varieties (MVs) and low varietal turnover. Lack of evidence meant the second hypothesis of insufficient attention to understanding and responding to gender differences in consumer preferences for quality and post-harvest traits was unresolved. The evidence on the third hypothesis about the informal seed system contributing to slow uptake of MVs was mixed. In some cases, the informal system has contributed to rapid uptake of MVs, but often it appears to be a barrier with inconsistent varietal naming a major challenge.  相似文献   
988.
The aim of this study was to test two different innovative plasma assisted approaches to prolong ricotta shelf life. In one test the ricotta cheese is directly exposed to the plasma effects, and in the other one the plasma is indirectly applied (i.e. blowing the plasma effluents on the substrate). This last approach is innovative and very promising because in this way, plasma treatment can be assured at moments or at places where no plasma source can be used or is available. To the aim, treated and untreated samples were stored at 4 °C for a period of 8 days, during which microbiological, sensory analyses and pH measurements were carried out. Tests were repeated more times to also taken into account product variability. Results highlighted that both treatments in all tests were effective to control microbial proliferation and preserve sensory quality. Specifically, a significant shelf life prolongation was recorded, ranging between 50% and 100%, depending to the type of treatment and on the initial microbial contamination.Industrial relevanceBoth direct and indirect plasma treatments tested have led to a shelf life increase of up 2 days, which is a very promising result for a fresh product such as artisanal ricotta. The current paper offers the first example in literature of “gentle” and efficacious treatment of fresh perishable products by gas effluents plasma-enriched by reactive oxygen or nitrogen species. The easy implementation of the proposed indirect approach and the easily customizable CAP system at room temperature could gain great attention from fresh dairy sector, with economic advantages and benefits also for the environment.  相似文献   
989.
Package design influences consumers’ expectations of a product’s sensory properties and expected healthiness and/or tastiness, and potentially also changes actual product perception during consumption. The robustness of these effects is far from clear, however. This study investigated the influence of package cues signalling either hedonic or healthy product properties on expectations and subsequent product evaluation over repeated consumption.In a between-subjects design, 92 participants evaluated product expectations and taste perceptions of a chocolate-sesame flavoured biscuit with a package emphasizing either its healthy (n = 44) or hedonic (n = 48) aspects, both at a central location (CLT) and during six home use tests (HUT), using both explicit (questionnaires) and implicit (IAT) measures.Package design significantly affected (p < 0.05) consumers’ expectations of the product. They expected the biscuit to be tastier, less attractive and less healthy in the hedonic package condition, and less tasty, more attractive and healthier in the healthy package condition. However, these effects did not transfer to actual product evaluations upon tasting, either blind or tasting in combination with viewing the package during the HUTs. Implicit attitudes did change as a result of repeated exposures, depending on the package consumers were provided with, indicating product-package interactions over time (p < 0.05).In conclusion, package design influences product expectations and associations with its healthiness and attractiveness, which is of relevance in product choice and purchase settings. However, at the stage of (repeated) consumption, intrinsic (sensory) properties become the dominant drivers of products’ sensory and hedonic evaluations, and the impact of package cues seems less potent.  相似文献   
990.
Consumers assess products not only based on their physical aspects but also on their emotion-evoking components. Many methods, such as EsSense Profile®, GEOS, and ScentMove, have been developed for evaluating various kinds of products. Research has suggested the need for developing a specialized lexicon for specific food or beverage categories. The English emotion lexicon, the Coffee Drinking Experience1(CDE), was developed specifically for coffee. However, while emotions can be expressed by words, they can also be affected by culture and context. Thus, our objectives are 1) to develop coffee emotion lexicons in Korean and Chinese, 2) to compare the differences of emotions evoked while consuming different kinds of coffee, and 3) to compare the differences between Chinese and Korean consumers while consuming the same coffee samples. To address these aims, we conducted two studies. First, we conducted a consumer-led translation of 86 emotion terms from the CDE into Korean and Chinese. Second, consumers checked the intensity of emotion terms while drinking six commercial coffee samples. The order of the Chinese and Korean consumers’ overall preferences was the same: all-in-one coffee received higher scores than black coffee. Finally, using a logistic stepwise regression analysis, the Chinese and Korean lexicons were reduced to 53 and 29 terms, respectively.  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