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   824篇
  免费   14篇
  国内免费   2篇
电工技术   9篇
综合类   1篇
化学工业   192篇
金属工艺   10篇
机械仪表   27篇
建筑科学   106篇
矿业工程   2篇
能源动力   26篇
轻工业   87篇
水利工程   8篇
无线电   56篇
一般工业技术   161篇
冶金工业   17篇
原子能技术   2篇
自动化技术   136篇
  2024年   12篇
  2023年   12篇
  2022年   17篇
  2021年   30篇
  2020年   28篇
  2019年   31篇
  2018年   19篇
  2017年   26篇
  2016年   36篇
  2015年   32篇
  2014年   36篇
  2013年   59篇
  2012年   41篇
  2011年   43篇
  2010年   40篇
  2009年   31篇
  2008年   46篇
  2007年   39篇
  2006年   31篇
  2005年   33篇
  2004年   23篇
  2003年   17篇
  2002年   23篇
  2001年   7篇
  2000年   19篇
  1999年   16篇
  1998年   21篇
  1997年   11篇
  1996年   13篇
  1995年   4篇
  1994年   7篇
  1993年   5篇
  1992年   1篇
  1991年   4篇
  1990年   1篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1980年   3篇
  1979年   1篇
  1978年   2篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1971年   4篇
排序方式: 共有840条查询结果,搜索用时 0 毫秒
701.
Computational fluid dynamics (CFD) simulations in combination with droplet population balances lead to a practical standard for calculating the flow pattern – and thus the residence time distribution – in horizontal separators of any size based on available process data. The implementation of the droplet behavior also enables the calculation of a droplet-specific separator efficiency. The method development was carried out at identical plants at three different locations. The CFD simulations were successfully validated with experimental data from the participating industrial partners.  相似文献   
702.
    
Thermal energy storage is considered an important element of future energy systems. However, it is mandatory that the storage technologies work reliably. More complex systems are usually more prone to failure. As system size increases and functionalities can be separated, a more differentiated analysis is necessary. Large-scale applications often involve intrinsic redundancy because scale-up to some extent is realized through numbering-up. Therefore, failures of individual components do not cause total outage of the thermal energy storage, but only a certain loss in performance. A special feature of some thermochemical storage technologies is that separate parts of the whole system provide the functionalities of charging and discharging. Consequently, many failure modes do not cause a complete loss of functionality, but only of one of the two functionalities.  相似文献   
703.
    
Chemotherapy causes intestinal mucositis, which includes villous atrophy and altered mucosal barrier function. However, there is an uncertainty regarding how the reduced small-intestinal surface area affects the mucosal permeability of the small marker probe mannitol (MW 188), and how the mucosa responds to luminal irritants after chemotherapy. The aims in this study were to determine (i) the relationship between chemotherapy-induced villus atrophy and the intestinal permeability of mannitol and (ii) how the mucosa regulate this permeability in response to luminal ethanol and sodium dodecyl sulfate (SDS). This was investigated by treating rats with a single intraperitoneal dose of doxorubicin, irinotecan, or 5-fluorouracil. After 72 h, jejunum was single-pass perfused and mannitol permeability determined at baseline and after 15 min luminal exposure to 15% ethanol or 5 mg/mL SDS. Tissue samples for morphological analyses were sampled from the perfused segment. All three chemotherapeutics caused a similar 30% reduction in villus length. Mannitol permeability increased with irinotecan (1.3-fold) and 5-fluorouracil (2.5-fold) and was reduced with doxorubicin (0.5-fold), suggesting that it is not epithelial surface area alone that regulates intestinal permeability to mannitol. There was no additional increase in mannitol permeability induced by luminal ethanol or SDS in the chemotherapy-treated rats compared to controls, which may be related to the relatively high basal permeability of mannitol compared to other common low-permeability probes. We therefore suggest that future studies should focus on elucidating the complex interplay between chemotherapy in combination with luminal irritants on the intestinal permeability of other probes.  相似文献   
704.
705.
    
Cancer is a leading cause of death worldwide and according to the World Health Organization (WHO) accounted for 10 million deaths in 2020. Promising theranostic (therapy and diagnostic) agents in the treatment of cancer are nanomaterials, which have come to the forefront because of their small size approaching those of protein complexes in the human body, and of their easy functionalization giving access to nanocomposite materials with diverse functions (fluorescence, magnetic, stimuli-responsiveness, etc.), and improved biocompatibility. Among them, affinity nanoparticles, often decorated with highly specific targeting ligands such as antibodies, aptamers, lectins and peptides, have enabled enhanced binding and exquisite recognition of biomarkers overexpressed in cancer cells. In this review, we describe an emerging class of targeting ligands, molecularly imprinted polymer hydrogel nanoparticles for their application in the early detection of disease, with the aim to improve diagnosis and treatment.  相似文献   
706.
    
Intensive forest harvesting has increased in Fennoscandia over the last few decades. Similar developments may follow throughout Europe as renewable energy replaces fossil fuels. The international literature suggests that intensive harvesting could increase ecological risks to yield, carbon stores, soil fertility, and biodiversity, but geographically specific knowledge is sparse in many countries, and results do not extend beyond 5–30 years after harvesting. We use Denmark as a case for discussing future directions. Forest history is described, and research on ecological effects and their inclusion in governance is reviewed. Denmark was almost completely deforested by the early 1800s, but centuries of afforestation have resulted in a current forest cover of 14.3%. Research commonly uses stem‐only harvesting as a reference against which to compare intensive harvesting impacts, but pristine forests would be a more useful reference for ecological processes and biodiversity. However, pristine forests are almost non‐existent in Europe, and non‐intervention, self‐regulating forests provide an alternative. Governance and positions of non‐governmental organizations in Denmark focus more on general forest management impacts and conservation of light‐demanding biodiversity associated with historic coppicing and grazing than on intensive harvesting. The energy sector drives the development of new governance to verify forest biomass sustainability, but the national knowledge base for such verification is limited. As part of a larger solution, we suggest establishing a network of non‐intervention, self‐regulating forests that can serve as a reference for long‐term research and monitoring of intensive harvesting impacts. This would support the application of adaptive management strategies, and continuous improvements of best management practice guidelines. WIREs Energy Environ 2016, 5:588–610. doi: 10.1002/wene.206 This article is categorized under:
  • Bioenergy > Economics and Policy
  • Bioenergy > Climate and Environment
  • Energy and Development > Climate and Environment
  相似文献   
707.
708.
Induced chemical defense reactions are widespread in marine brown algae. Despite the evidence that the biosynthesis of defense metabolites can be up-regulated upon herbivory, we do not know how this regulation of biosynthetic pathways to secondary metabolites is achieved in brown algae. In higher plants, the phytohormone jasmonic acid (JA) is crucial for the mediation of induced chemical defenses, and several findings of this metabolite from marine sources have been reported. We tested the hypothesis that JA or related metabolites play a role in induced brown algal defense. Quantification of oxylipins with a detection limit around 20 ng g−1 algal tissue did not reveal the presence of JA in the seven examined brown algal species Dictyota dichotoma, Colpomenia peregrina, Ectocarpus fasciculatus, Fucus vesiculosus, Himanthalia elongata, Saccharina latissima (formerly Laminaria saccharina), and Sargassum muticum. Moreover, treatment with ecologically relevant concentrations of JA and methyl jasmonate did not lead to a significant change in the profile of medium- and non-polar metabolites of the tested algae. Only when high concentrations of ≥500 μg ml−1 medium of the phytohormones were applied that a metabolic response which could be attributed to unspecific stress was observed. Bioassays with D. dichotoma that focused on medium- and non-polar compounds confirmed the lack of a biological role of JA and methyl jasmonate in the induction of algal induced chemical defenses. The phytohormone-treated samples did not exhibit any increased defense potential towards the amphipod Ampithoe longimana and the isopod Paracerceis caudata. JA and related phytohormones, known to be active in higher plants, thus appear to play no role in brown algae for induction of the defense chemicals studied here.  相似文献   
709.
    
A supply system geared to renewable energy sources requires a high degree of flexibility to ensure system stability. Load management can make a big contribution. The chemical industry as one of the largest consumers of electrical energy can play an important role there. The analysis of the so far conducted studies shows great potential for the chlor‐alkali process and air liquefaction. The variable costs are comparable to other flexibility options. To determine the realizable potential further investigations are needed.  相似文献   
710.
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