全文获取类型
收费全文 | 6828篇 |
免费 | 634篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 41篇 |
综合类 | 1篇 |
化学工业 | 2276篇 |
金属工艺 | 87篇 |
机械仪表 | 164篇 |
建筑科学 | 261篇 |
矿业工程 | 19篇 |
能源动力 | 204篇 |
轻工业 | 2049篇 |
水利工程 | 59篇 |
石油天然气 | 42篇 |
无线电 | 271篇 |
一般工业技术 | 852篇 |
冶金工业 | 332篇 |
原子能技术 | 25篇 |
自动化技术 | 784篇 |
出版年
2024年 | 22篇 |
2023年 | 105篇 |
2022年 | 393篇 |
2021年 | 456篇 |
2020年 | 250篇 |
2019年 | 294篇 |
2018年 | 296篇 |
2017年 | 314篇 |
2016年 | 349篇 |
2015年 | 228篇 |
2014年 | 353篇 |
2013年 | 549篇 |
2012年 | 489篇 |
2011年 | 540篇 |
2010年 | 403篇 |
2009年 | 404篇 |
2008年 | 344篇 |
2007年 | 278篇 |
2006年 | 220篇 |
2005年 | 159篇 |
2004年 | 137篇 |
2003年 | 113篇 |
2002年 | 100篇 |
2001年 | 62篇 |
2000年 | 61篇 |
1999年 | 63篇 |
1998年 | 114篇 |
1997年 | 71篇 |
1996年 | 43篇 |
1995年 | 31篇 |
1994年 | 32篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1956年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有7467条查询结果,搜索用时 28 毫秒
171.
Diana Tomás Joana Rodrigues Ana Varela Maria Manuela Veloso Wanda Viegas Manuela Silva 《International journal of molecular sciences》2016,17(2)
Genomic diversity of Portuguese accessions of Avena species—diploid A. strigosa and hexaploids A. sativa and A. sterilis—was evaluated through molecular and cytological analysis of 45S rDNA, and other repetitive sequences previously studied in cereal species—rye subtelomeric sequence (pSc200) and cereal centromeric sequence (CCS1). Additionally, retrotransposons and microsatellites targeting methodologies—IRAP (inter-retrotransposon amplified polymorphism) and REMAP (retrotransposon-microsatellite amplified polymorphism)—were performed. A very high homology was detected for ribosomal internal transcribed sequences (ITS1 and ITS2) between the species analyzed, although nucleolar organizing regions (NOR) fluorescent in situ hybridization (FISH) analysis revealed distinct number of Nor loci between diploid and hexaploid species. Moreover, morphological diversity, evidenced by FISH signals with different sizes, was observed between distinct accessions within each species. pSc200 sequences were for the first time isolated from Avena species but proven to be highly similar in all genotypes analyzed. The use of primers designed for CCS1 unraveled a sequence homologous to the Ty3/gypsy retrotransposon Cereba, that was mapped to centromeric regions of diploid and hexaploid species, being however restricted to the more related A and D haplomes. Retrotransposon-based methodologies disclosed species- and accessions-specific bands essential for the accurate discrimination of all genotypes studied. Centromeric, IRAP and REMAP profiles therefore allowed accurate assessment of inter and intraspecific variability, demonstrating the potential of these molecular markers on future oat breeding programs. 相似文献
172.
Vincenza Ferraro Ana P. Carvalho Clara Piccirillo Manuela M. Santos Paula M. L. Castro Manuela E. Pintado 《Materials science & engineering. C, Materials for biological applications》2013,33(6):3111-3120
Different valuable compounds, which can be employed in medicine or in other industries (i.e. food, agrochemical, pharmaceutical) can be recovered from by-products and waste from the fish canning industries. They include lipids, proteins, bio-polymers, minerals, amino acids and enzymes; they can be extracted from wastewaters and/or from solid residues (head, viscera, skin, tails and flesh) generated along the canning process, through the filleting, cooking, salting or smoking stages.In this review, the opportunities for the extraction and the valorisation of bioactive compounds from sardine, sardine-type fish and mackerel canning residues are examined and discussed. These are amongst the most consumed fishes in the Mediterranean area; moreover, canning is one of the most important and common methods of preservation. The large quantities of by-products generated have great potentials for the extraction of biologically desirable high added value compounds. 相似文献
173.
Schmidt Jaison Dairon Ebertz De Marchi Ana Carolina Bertoletti 《Universal Access in the Information Society》2017,16(4):921-928
Universal Access in the Information Society - This paper aims to present the results of a systematic review focused on usability evaluation methods for serious games (SG) of mobile devices... 相似文献
174.
Liliana Martelo Alfonso Jiménez Artur JM Valente Hugh D Burrows Ana T Marques Michael Forster Ullrich Scherf Mercedes Peltzer Sofia M Fonseca 《Polymer International》2012,61(6):1023-1030
Films of neat and plasticized biodegradable poly(lactic acid) (PLA) matrices containing anionic conjugated polyelectrolytes, poly[9,9‐bis(4‐phenoxybutylsulfonate)]fluorene‐2,7‐diyl‐alt‐arylenes, with 1,4‐phenylene and 4,4″‐p‐terphenylene, respectively, as arylene groups or a neutral poly(9,9‐dialkylfluorene) for comparison were prepared by solution casting. These films were characterized using differential scanning calorimetry, thermogravimetry, scanning electron microscopy and fluorescence spectroscopy. In addition, the effects of plasticizer on the thermal properties and the oxygen permeability of the PLA films were measured through the oxygen transmission rate. Results show that it is possible to obtain thin, optically transparent and luminescent films with potential in oxygen sensing, exhibiting good thermal and photochemical stability. At high polyelectrolyte content, evidence is found for phase separation and aggregate formation and it is no longer possible to obtain completely homogeneous films. The possibility of incorporating the cationic metal complex tris(2,2′‐bipyridyl)ruthenium(II) into plasticized PLA films containing conjugated polyelectrolytes for dual‐wavelength ratiometric luminescence sensing is also discussed. Copyright © 2012 Society of Chemical Industry 相似文献
175.
Matias Urbieta Ana Oliveira João Araújo Armanda Rodrigues Ana Moreira Sílvia Gordillo Gustavo Rossi 《Innovations in Systems and Software Engineering》2014,10(1):59-75
Spatial concerns of Web geographical information systems (Web-GIS) are inherently crosscutting and volatile: crosscutting because they affect multiple functionalities of Web-GIS systems, and volatile because their status may change often. If these concerns are not modularized properly, the quality of Web-GIS services, particularly with regard to adaptation and evolution, can be severely compromised. This paper uses aspect-orientation to model crosscutting and volatile spatial concerns. By modeling both types of concerns, crosscutting and volatile, as candidate aspects, one can use dynamic weaving to add or remove them from a system at runtime. The aspect-oriented approach proposed starts with the identification and specification of crosscutting concerns and follows by composing these using modeling aspects using a transformation approach, an aspect-oriented modeling technique. The conflicts that can emerge due to the composition order are also taken into consideration. Finally, this paper proposes a set of reusable GIS crosscutting concerns, documenting them in a concern catalogue. 相似文献
176.
Diego Carvalho Soares Flávia Maria Santoro Fernanda Araujo Baião 《Journal of Network and Computer Applications》2013,36(6):1451-1465
Knowledge Management aims to promote the growth, communication and preservation of knowledge within an organization, which includes managing the appropriate resources to facilitate knowledge sharing and reuse. Business Process-Oriented Knowledge Management focuses on discovering and representing the dynamic conversion of existing knowledge among participants involved in executing business processes. In this context, Knowledge-Intensive Processes are a very important and challenging specific subclass of processes, since they strongly involve socialization and informal exchanges of knowledge among participants. This paper describes in detail a method for semi-automatic discovery of relevant information characterizing Knowledge-Intensive Processes, as well as the results of further evaluation of the method. Our approach draws on the informal exchange of existing knowledge in collaborative tools such as e-mails. The output is a conceptual map that describes the main elements of a Knowledge-Intensive Process, as well as their relationships. The results from the case study conducted to evaluate the method in an organization underlined the prospects for using collaborative environments to discover the way agents perform their activities. 相似文献
177.
178.
Frederik Ziebell Ana Martin-Villalba Anna Marciniak-Czochra 《Journal of the Royal Society Interface》2014,11(94)
In the adult hippocampus, neurogenesis—the process of generating mature granule cells from adult neural stem cells—occurs throughout the entire lifetime. In order to investigate the involved regulatory mechanisms, knockout (KO) experiments, which modify the dynamic behaviour of this process, were conducted in the past. Evaluating these KOs is a non-trivial task owing to the complicated nature of the hippocampal neurogenic niche. In this study, we model neurogenesis as a multicompartmental system of ordinary differential equations based on experimental data. To analyse the results of KO experiments, we investigate how changes of cell properties, reflected by model parameters, influence the dynamics of cell counts and of the experimentally observed counts of cells labelled by the cell division marker bromodeoxyuridine (BrdU). We find that changing cell proliferation rates or the fraction of self-renewal, reflecting the balance between symmetric and asymmetric cell divisions, may result in multiple time phases in the response of the system, such as an initial increase in cell counts followed by a decrease. Furthermore, these phases may be qualitatively different in cells at different differentiation stages and even between mitotically labelled cells and all cells existing in the system. 相似文献
179.
This paper addresses the use of high order dissimilarity models in data mining problems. We explore dissimilarities between triplets of nearest neighbors, called dissimilarity increments (DIs). We derive a statistical model of DIs for d-dimensional data (d-DID) assuming that the objects follow a multivariate Gaussian distribution. Empirical evidence shows that the d-DID is well approximated by the particular case d=2. We propose the application of this model in clustering, with a partitional algorithm that uses a merge strategy on Gaussian components. Experimental results, in synthetic and real datasets, show that clustering algorithms using DID usually outperform well known clustering algorithms. 相似文献
180.