全文获取类型
收费全文 | 6596篇 |
免费 | 602篇 |
国内免费 | 101篇 |
专业分类
电工技术 | 53篇 |
综合类 | 61篇 |
化学工业 | 3669篇 |
金属工艺 | 127篇 |
机械仪表 | 114篇 |
建筑科学 | 104篇 |
矿业工程 | 22篇 |
能源动力 | 77篇 |
轻工业 | 1614篇 |
水利工程 | 11篇 |
石油天然气 | 63篇 |
武器工业 | 4篇 |
无线电 | 258篇 |
一般工业技术 | 527篇 |
冶金工业 | 35篇 |
原子能技术 | 68篇 |
自动化技术 | 492篇 |
出版年
2024年 | 5篇 |
2023年 | 49篇 |
2022年 | 661篇 |
2021年 | 691篇 |
2020年 | 127篇 |
2019年 | 162篇 |
2018年 | 206篇 |
2017年 | 221篇 |
2016年 | 308篇 |
2015年 | 316篇 |
2014年 | 314篇 |
2013年 | 325篇 |
2012年 | 290篇 |
2011年 | 382篇 |
2010年 | 245篇 |
2009年 | 363篇 |
2008年 | 418篇 |
2007年 | 333篇 |
2006年 | 230篇 |
2005年 | 206篇 |
2004年 | 186篇 |
2003年 | 161篇 |
2002年 | 128篇 |
2001年 | 107篇 |
2000年 | 128篇 |
1999年 | 94篇 |
1998年 | 83篇 |
1997年 | 75篇 |
1996年 | 53篇 |
1995年 | 37篇 |
1994年 | 58篇 |
1993年 | 37篇 |
1992年 | 24篇 |
1991年 | 34篇 |
1990年 | 23篇 |
1989年 | 28篇 |
1988年 | 18篇 |
1987年 | 19篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1984年 | 10篇 |
1983年 | 22篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 4篇 |
排序方式: 共有7299条查询结果,搜索用时 15 毫秒
31.
32.
In an organization operating in the bancassurance sector we identified a low-risk IT subportfolio of 84 IT projects comprising together 16,500 function points, each project varying in size and duration, for which we were able to quantify its requirements volatility. This representative portfolio stems from a much larger portfolio of IT projects. We calculated the volatility from the function point countings that were available to us. These figures were aggregated into a requirements volatility benchmark. We found that maximum requirements volatility rates depend on size and duration, which refutes currently known industrial averages. For instance, a monthly growth rate of 5% is considered a critical failure factor, but in our low-risk portfolio we found more than 21% of successful projects with a volatility larger than 5%. We proposed a mathematical model taking size and duration into account that provides a maximum healthy volatility rate that is more in line with the reality of low-risk IT portfolios. Based on the model, we proposed a tolerance factor expressing the maximal volatility tolerance for a project or portfolio. For a low-risk portfolio its empirically found tolerance is apparently acceptable, and values exceeding this tolerance are used to trigger IT decision makers. We derived two volatility ratios from this model, the π-ratio and the ρ-ratio. These ratios express how close the volatility of a project has approached the danger zone when requirements volatility reaches a critical failure rate. The volatility data of a governmental IT portfolio were juxtaposed to our bancassurance benchmark, immediately exposing a problematic project, which was corroborated by its actual failure. When function points are less common, e.g. in the embedded industry, we used daily source code size measures and illustrated how to govern the volatility of a software product line of a hardware manufacturer. With the three real-world portfolios we illustrated that our results serve the purpose of an early warning system for projects that are bound to fail due to excessive volatility. Moreover, we developed essential requirements volatility metrics that belong on an IT governance dashboard and presented such a volatility dashboard. 相似文献
33.
control with limited communication and message losses 总被引:2,自引:0,他引:2
We propose an H∞ approach to a remote control problem where the communication is constrained due to the use of a shared channel. The controller employs a periodic time sequencing scheme for message transmissions from multiple sensors and to multiple actuators of the system. It further takes into account the information on the random message losses that occur in the channel. An exact characterization for controller synthesis is obtained and is stated in terms of linear matrix inequalities. Furthermore, an analysis on the loss probabilities of the messages to accomplish stabilization is carried out. The results are illustrated through a numerical example. 相似文献
34.
Elisa Bertino Giovanna Guerrini Marco Mesiti 《Journal of Intelligent Information Systems》2008,30(1):55-92
Measuring the structural similarity between an XML document and a DTD has many relevant applications that range from document
classification and approximate structural queries on XML documents to selective dissemination of XML documents and document
protection. The problem is harder than measuring structural similarity among documents, because a DTD can be considered as
a generator of documents. Thus, the problem is to evaluate the similarity between a document and a set of documents. An effective
structural similarity measure should face different requirements that range from considering the presence and absence of required
elements, as well as the structure and level of the missing and extra elements to vocabulary discrepancies due to the use
of synonymous or syntactically similar tags. In the paper, starting from these requirements, we provide a definition of the
measure and present an algorithm for matching a document against a DTD to obtain their structural similarity. Finally, experimental
results to assess the effectiveness of the approach are presented. 相似文献
35.
36.
37.
In this paper, we present an analysis and synthesis approach for guaranteeing that the phase of a single-input, single-output closed-loop transfer function is contained in the interval [−b1;,b1;] for a given b1;>0 at all frequencies. Specifically, we first derive a sufficient condition involving a frequency domain inequality for guaranteeing a given phase constraint. Next, we use the Kalman–Yakubovich–Popov theorem to derive an equivalent time domain condition. In the case where bVlW-zSkzk" alt="View the MathML source" title="View the MathML source" align="absbottom" border="0" height=16 width="39"/>, we show that frequency and time domain sufficient conditions specialize to the positivity theorem. Furthermore, using linear matrix inequalities, we develop a controller synthesis approach for guaranteeing a phase constraint on the closed-loop transfer function. Finally, we extend this synthesis approach to address mixed gain and phase constraints on the closed-loop transfer function. 相似文献
38.
Patricia Bondia Rocío Jurado Santiago Casado José M. Domínguez‐Vera Natividad Gálvez Cristina Flors 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(17)
The combination of complementary techniques to characterize materials at the nanoscale is crucial to gain a more complete picture of their structure, a key step to design and fabricate new materials with improved properties and diverse functions. Here it is shown that correlative atomic force microscopy (AFM) and localization‐based super‐resolution microscopy is a useful tool that provides insight into the structure and emissive properties of fluorescent β‐lactoglobulin (βLG) amyloid‐like fibrils. These hybrid materials are made by functionalization of βLG with organic fluorophores and quantum dots, the latter being relevant for the production of 1D inorganic nanostructures templated by self‐assembling peptides. Simultaneous functionalization of βLG fibers by QD655 and QD525 allows for correlative AFM and two‐color super‐resolution fluorescence imaging of these hybrid materials. These experiments allow the combination of information about the topography and number of filaments that compose a fibril, as well as the emissive properties and nanoscale spatial distribution of the attached fluorophores. This study represents an important step forward in the characterization of multifunctionalized hybrid materials, a key challenge in nanoscience. 相似文献
39.
40.
Carbon Nanodot‐Sensitized Modulation of Alzheimer's β‐Amyloid Self‐Assembly,Disassembly, and Toxicity 下载免费PDF全文
You Jung Chung Kayoung Kim Byung Il Lee Chan Beum Park 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(34)
The self‐assembly of amyloidogenic peptides into β‐sheet‐rich aggregates is a general feature of many neurodegenerative diseases, including Alzheimer's disease, which signifies the need for the effective attenuation of amyloid aggregation toward alleviating amyloid‐associated neurotoxicity. This study reports that photoluminescent carbon nanodots (CDs) can effectively suppress Alzheimer's β‐amyloid (Aβ) self‐assembly and function as a β‐sheet breaker disintegrating preformed Aβ aggregates. This study synthesizes CDs using ammonium citrate through one‐pot hydrothermal treatment and passivates their surface with branched polyethylenimine (bPEI). The bPEI‐coated CDs (bPEI@CDs) exhibit hydrophilic and cationic surface characteristics, which interact with the negatively charged residues of Aβ peptides, suppressing the aggregation of Aβ peptides. Under light illumination, bPEI@CDs display a more pronounced effect on Aβ aggregation and on the dissociation of β‐sheet‐rich assemblies through the generation of reactive oxygen species from photoactivated bPEI@CDs. The light‐triggered attenuation effect of Aβ aggregation using a series of experiments, including photochemical and microscopic analysis, is verified. Furthermore, the cell viability test confirms the ability of photoactivated bPEI@CDs for the suppression of Aβ‐mediated cytotoxicity, indicating bPEI@CDs' potency as an effective anti‐Aβ neurotoxin agent. 相似文献