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   4233篇
  免费   181篇
  国内免费   5篇
电工技术   55篇
综合类   4篇
化学工业   750篇
金属工艺   44篇
机械仪表   70篇
建筑科学   160篇
矿业工程   6篇
能源动力   151篇
轻工业   384篇
水利工程   54篇
石油天然气   14篇
无线电   243篇
一般工业技术   809篇
冶金工业   1098篇
原子能技术   24篇
自动化技术   553篇
  2023年   23篇
  2022年   15篇
  2021年   83篇
  2020年   68篇
  2019年   68篇
  2018年   106篇
  2017年   84篇
  2016年   93篇
  2015年   61篇
  2014年   104篇
  2013年   279篇
  2012年   220篇
  2011年   273篇
  2010年   201篇
  2009年   211篇
  2008年   236篇
  2007年   235篇
  2006年   187篇
  2005年   176篇
  2004年   165篇
  2003年   144篇
  2002年   141篇
  2001年   85篇
  2000年   69篇
  1999年   61篇
  1998年   77篇
  1997年   73篇
  1996年   69篇
  1995年   65篇
  1994年   73篇
  1993年   65篇
  1992年   61篇
  1991年   35篇
  1990年   42篇
  1989年   49篇
  1988年   43篇
  1987年   43篇
  1986年   39篇
  1985年   43篇
  1984年   31篇
  1983年   29篇
  1982年   22篇
  1981年   35篇
  1980年   13篇
  1979年   27篇
  1978年   13篇
  1977年   20篇
  1976年   10篇
  1975年   8篇
  1972年   7篇
排序方式: 共有4419条查询结果,搜索用时 15 毫秒
1.
Aqueous solutions of poly(vinylpyrrolidone) (PVP) of various concentrations (20, 25, and 28 wt%) were successfully spun into fibers by centrifugal spinning. The pristine PVP fibers were annealed and carbonized to produce flexible carbon fibers for use as binder-free anodes in lithium-ion batteries. These flexible carbon fibers were prepared by developing a novel three-step heat treatment to reduce the residual stresses in the pristine PVP precursor fibers, and to prevent fiber degradation during carbonization. The thermogravimetric analysis data showed that the annealed fibers yielded a residual mass percentage of 36.0% while the pristine PVP fibers suffered a higher mass loss and only retained 26.5% of original mass above 450 °C (under nitrogen). The electrochemical performance of the carbon-fiber anodes was evaluated by conducting galvanostatic charge/discharge, rate performance, and cycle voltammetry experiments. The 20, 25, and 28 wt% derived binder-free anodes delivered specific charge capacities of 205, 189, and 275 mAh g−1, respectively, after the first cycle at a current density of 100 mA g−1. The results obtained in this work indicate that a feasible pathway towards a large-scale production of carbon-fiber anodes from a 100% aqueous solution can be achieved via centrifugal spinning and subsequent heat treatment.  相似文献   
2.
The research analyses decisions as evaluative outcomes regarding project value. The UK-French Hinkley Point C Nuclear Power Station provides the case study. Value is traditionally assessed as inputs and outputs. Here, value is conceptualized as a co-created value proposition at the front-end with implications for realization post-completion. Service-dominant logic (SDL) provides the theoretical lens and contributes to a methodological approach for examining projects. Decision-making outcomes provide the evidence from a range of data sources, including reports and commentaries. The methods are interpretative. The findings show that decision-making extends beyond the time-cost-quality/scope dimensions. The long-term issues regarding value realized are often overlooked. Stakeholders and individual actors have mainly focused upon managing political and financial risks, especially time and cost. The research poses challenges to project management analysis, SDL and research design in assessing evidence. Addressing these issues facilitates a knowledge contribution to SDL theorization and the field of project management.  相似文献   
3.
4.
Neural Computing and Applications - With an increase in online longitudinal users’ interactions, capturing users’ precise preferences and giving accurate recommendations have become an...  相似文献   
5.
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits.  相似文献   
6.
Bacterial infections remain a leading threat to global health because of the misuse of antibiotics and the rise in drug-resistant pathogens. Although several strategies such as photothermal therapy and magneto-thermal therapy can suppress bacterial infections, excessive heat often damages host cells and lengthens the healing time. Here, a localized thermal managing strategy, thermal-disrupting interface induced mitigation (TRIM), is reported, to minimize intercellular cohesion loss for accurate antibacterial therapy. The TRIM dressing film is composed of alternative microscale arrangement of heat-responsive hydrogel regions and mechanical support regions, which enables the surface microtopography to have a significant effect on disrupting bacterial colonization upon infrared irradiation. The regulation of the interfacial contact to the attached skin confines the produced heat and minimizes the risk of skin damage during thermoablation. Quantitative mechanobiology studies demonstrate the TRIM dressing film with a critical dimension for surface features plays a critical role in maintaining intercellular cohesion of the epidermis during photothermal therapy. Finally, endowing wound dressing with the TRIM effect via in vivo studies in S. aureus infected mice demonstrates a promising strategy for mitigating the side effects of photothermal therapy against a wide spectrum of bacterial infections, promoting future biointerface design for antibacterial therapy.  相似文献   
7.
Carbene‐metal‐amides (CMAs) are a promising family of donor–bridge–acceptor molecular charge‐transfer (CT) emitters for organic light‐emitting diodes. A universal approach is demonstrated to tune the energy of their CT emission. A blueshift of up to 210 meV is achievable in solid state via dilution in a polar host matrix. The origin of this shift has two components: constraint of thermally‐activated triplet diffusion, and electrostatic interactions between guest and polar host. This allows the emission of mid‐green CMA archetypes to be tuned to sky blue without chemical modifications. Monte‐Carlo simulations based on a Marcus‐type transfer integral successfully reproduce the concentration‐ and temperature‐dependent triplet diffusion process, revealing a substantial shift in the ensemble density of states in polar hosts. In gold‐bridged CMAs, this shift does not lead to a significant change in luminescence lifetime, thermal activation energy, reorganization energy, or intersystem crossing rate. These discoveries offer new insight into coupling between the singlet and triplet manifolds in CMA materials, revealing a dominant interaction between states of CT character. The same approach is employed using materials which have been chemically modified to alter the energy of their CT state directly, shifting the emission of sky‐blue chromophores into the practical blue range.  相似文献   
8.
Malus sieversii is considered the progenitor of modern apple (Malus pumila) cultivars and to represent a valuable source of genetic diversity. Despite the importance of M. sieversii as a source of disease resistance, stress tolerance, and novel fruit traits, little is known about gene function and diversity in M. sieversii. Notably, a publicly annotated genome sequence for this species is not available. In the current study, the FOX (Full-length cDNA OvereXpressing) gene hunting system was used to construct a library of transgenic lines of Arabidopsis in which each transgenic line overexpresses a full-length gene obtained from a cDNA library of the PI619283 accession of M. sieversii. The cDNA library was constructed from mRNA obtained from bark tissues collected in late fall–early winter, a time at which many abiotic stress-adaptative genes are expressed. Over 4000 apple FOX Arabidopsis lines have been established from the pool of transgenic seeds and cDNA inserts corresponding to various Gene Ontology (GO) categories have been identified. A total of 160 inserts appear to be novel, with no or limited homology to M. pumila, Arabidopsis, or poplar. Over 1300 lines have also been screened for freezing resistance. The constructed library of transgenic lines provides a valuable genetic resource for exploring gene function and diversity in Malus sieversii. Notably, no such library of t-DNA lines currently exists for any Malus species.  相似文献   
9.
The objective of this study was to evaluate the effect of sample presentation (tissue type) and maturity (ripe and unripe) on the classification of banana (Musa Cavendish) samples sourced from two different geographical regions and analysed using mid infrared (MIR) spectroscopy. The coefficient of determination (R2) and the standard error of cross-validation (SECV) obtained using partial least squares discriminant analysis were 0.83 (0.33), 0.75 (0.25) and 0.94 (0.19) for the prediction of maturity, geographical origin and tissue type, respectively. No effect of either of type of tissue (e.g. pulp or peel) or maturity was observed. The results of this study demonstrated that MIR spectroscopy might be used to classify the origin of the banana samples at different degrees of ripeness. However, one of the limitations of this study is on the number of samples analysed and further validation must be recommended using samples from other sources, regions and harvest seasons.  相似文献   
10.
Indigenous community members along the Slave River in Canada have voiced their concerns for the health of ecosystems under pressure from resource extraction, hydroelectric development and global climate change. We present a test case of traditional knowledge and scientific results about the spawning and migration patterns of fish in the Slave River and Delta. This dual knowledge system approach elucidates the broader connectivity of local study regions and can improve monitoring programmes by extending beyond the usual context/confines of the present or recent past, increasing the spatial and temporal range of system information.  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