全文获取类型
收费全文 | 7803篇 |
免费 | 498篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 59篇 |
综合类 | 5篇 |
化学工业 | 1986篇 |
金属工艺 | 101篇 |
机械仪表 | 146篇 |
建筑科学 | 289篇 |
矿业工程 | 13篇 |
能源动力 | 244篇 |
轻工业 | 1350篇 |
水利工程 | 98篇 |
石油天然气 | 31篇 |
无线电 | 490篇 |
一般工业技术 | 1167篇 |
冶金工业 | 1002篇 |
原子能技术 | 14篇 |
自动化技术 | 1312篇 |
出版年
2024年 | 12篇 |
2023年 | 76篇 |
2022年 | 188篇 |
2021年 | 279篇 |
2020年 | 203篇 |
2019年 | 224篇 |
2018年 | 278篇 |
2017年 | 256篇 |
2016年 | 312篇 |
2015年 | 240篇 |
2014年 | 305篇 |
2013年 | 620篇 |
2012年 | 528篇 |
2011年 | 668篇 |
2010年 | 405篇 |
2009年 | 387篇 |
2008年 | 369篇 |
2007年 | 381篇 |
2006年 | 263篇 |
2005年 | 191篇 |
2004年 | 209篇 |
2003年 | 178篇 |
2002年 | 170篇 |
2001年 | 103篇 |
2000年 | 90篇 |
1999年 | 114篇 |
1998年 | 348篇 |
1997年 | 218篇 |
1996年 | 144篇 |
1995年 | 97篇 |
1994年 | 70篇 |
1993年 | 71篇 |
1992年 | 30篇 |
1991年 | 31篇 |
1990年 | 29篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 7篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 35篇 |
1973年 | 5篇 |
1967年 | 4篇 |
排序方式: 共有8307条查询结果,搜索用时 15 毫秒
61.
María Esther Diupotex-Chong Néstor J Cazzaniga Alejandra Hernández-Santoyo José Miguel Betancourt-Rule 《Biocell》2004,28(3):279-285
Mitotic chromosomes of the freshwater snail Pomacea patula catemacensis (Baker 1922) were analyzed on gill tissue of specimens from the type locality (Lake Catemaco, Mexico). The diploid number of chromosomes is 2n = 26, including nine metacentric and four submetacentric pairs; therefore, the fundamental number is FN = 52, No sex chromosomes could be identified. The same chromosome number and morphology were already reported for P. flagellata, i.e., the other species of the genus living in Mexico. The basic haploid number for family Ampullariidae was reported to be n = 14 in the literature; so, its reduction to n = 13 is probably an apomorphy of the Mexican Pomacea snails. Lanistes bolteni, from Egypt, also shows n = 13, but its karyotype is much more asymmetrical, and seems to have evolved independently from P. flagellata and P. patula catemacensis. The nominotypical subspecies, P. patula patula (Reeve 1856), is a poorly known taxon, whose original locality is unknown. A taxonomical account is presented here, and a Mexican origin postulated as the most parsimonious hypothesis. 相似文献
62.
Imperfection in information can be considered a crosscutting concern that manifests itself in diverse kinds of imprecision, uncertainty, or inconsistency in the data models of a software system. The extension of existing programming and querying interfaces for the different aspects of information imperfection requires a proper modularization of the different concerns of numerical imprecision handling, so that the extensions do not interfere with existing programming practices and do not obscure the original design. Aspect‐oriented design (AOD) enables such a form of nonintrusive extensions to be added to existing software libraries, clearly separating fuzziness or other imperfections in data as a differentiated concern that can be considered from the early phases of development. In this article, a general framework for aspect‐based extension of data models and fuzzy databases is described, and some design and implementation issues of such AOD‐based extensions on OJB database libraries are described as a case study. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 1199–1216, 2006. 相似文献
63.
Raquel Alves dos Santos Teresinha Rosa Cabral Isabel Rosa Cabral Lusania Maria Greggi Antunes Cristiane Pontes Andrade Plínio Cerqueira dos Santos Cardoso Marcelo de Oliveira Bahia Claudia Pessoa José Luis Martins do Nascimento Rommel Rodríguez Burbano Catarina Satie Takahashi 《Biocell》2008,32(2):195-200
Physalis angulata L (Solanaceae) is a medicinal plant from North of Brazil, whose different extracts and infusions are commonly used in the popular medicine for the treatment of malaria, asthma, hepatitis, dermatitis and rheumatism. However, the genotoxic effects of P. angulata on human cells is not well known. The main purpose of the present study was to evaluate the in vitro genotoxic effects of aqueous extract of P. angulata using the comet assay and the micronucleus assay in human lymphocytes provided from 6 healthy donors. Treatments with P. angulata extracts were performed in vitro in order to access the extent of DNA damage. The comet assay has shown that treatments with P. angulata at 0.5, 1.0, 2.0, 3.0 and 6.0 microg/mL in culture medium were genotoxic. Lymphocytes treated with P. angulata at the concentrations of 3.0 and 6.0 microg/mL in culture medium showed a statistically significant increase in the frequency of micronucleus (p<0.05), however, the cytokinesis blocked proliferation index (CBPI) was not decreased after P. angulata treatment. In conclusion, the present work demonstrated the genotoxic effects of P. angulata extract on human lymphocytes in vitro. 相似文献
64.
Gerardo Gabriel Acosta Miguel Angel Mayosky José Maria Catalfo 《Applied Intelligence》1994,4(1):53-66
This article proposes a scheme for the on-line adjustment of three mode controller settings based on experimental measurements of closed-loop performance. It uses a recently developed heuristic tuning procedure to identify estimated process parameters. This method may give rise to conflicting estimates. Fuzzy Set theory is applied to manage the situation in terms of a fuzzy conjunction to combine the various estimates. PID control was chosen because of its wide use in the industrial environment due to driving simplicity and robustness. The article shows design, development, and computer simulation aspects. 相似文献
65.
德国的珠宝设计散发着一种典型的德国气质,就像德国的宝马、奔驰一样,远远看来,没有特别的装饰,朴实略显厚重,但是,近距离观察,就会因为无瑕疵的工艺和细节的经典处理而感动,心跳不已。德国人就是这样,用他们的工艺撼动人类,而不由得你不赞叹:精工亦是艺术。 相似文献
66.
S Contreras M Rodríguez F al Momani C Sans S Esplugas 《Canadian Metallurgical Quarterly》2003,37(13):3164-3171
The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD5/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L-1, 0.48 for BOD21/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS-1 h-1. 相似文献
67.
Jose Miguel Leiva-Murillo Antonio Artés-Rodríguez 《Neural Networks, IEEE Transactions on》2007,18(5):1433-1441
In this paper, we present a novel scheme for linear feature extraction in classification. The method is based on the maximization of the mutual information (MI) between the features extracted and the classes. The sum of the MI corresponding to each of the features is taken as an heuristic that approximates the MI of the whole output vector. Then, a component-by-component gradient-ascent method is proposed for the maximization of the MI, similar to the gradient-based entropy optimization used in independent component analysis (ICA). The simulation results show that not only is the method competitive when compared to existing supervised feature extraction methods in all cases studied, but it also remarkably outperform them when the data are characterized by strongly nonlinear boundaries between classes. 相似文献
68.
69.
A Fernandez Rodríguez M Arrabal Martín JF Domínguez Molinero JL Mijan Ortiz J Sánchez Tamayo A Zuluaga Gómez 《Canadian Metallurgical Quarterly》1995,19(8):620-626
A prospective study was conducted on 374 patients with urinary lithiasis, aiming to analyze the participation of oxalate in the lithogenesis and composition of the calcium oxalate calculi, alone or associated to other factors. METHODOLOGY: Metabolic urinary study of the patient and analysis of calculi with infrared spectrography and optical microscopy. RESULTS: 26.3% patients had hyperoxaluria and 77.5% of the calculi contain calcium oxalate; these are 167 cases of calcium oxalate, 110 of oxalate and calcium phosphate and 13 cases of mixed calcium oxalate and uric acid lithiasis. 43.4% patients with pure monohydrate calcium oxalate calculi have hypercalciuria, 22.6% hyperoxaluria and 19% hyperuricosuria. Dihydrated calcium oxalate calculi are related to high hypercalciuria in 65% cases and to significant hyperoxaluria in 35% cases. 45% patients present a single lithogenic factor, either hypercalciuria (49.6%), hyperoxaluria (20.6%), hyperuricosuria (13.74%), hypocitraturia (9%), urinary infection (1.5%), A.T.R. (2.25%) or acid oliguria (3%). 相似文献
70.
Many school systems, in both the developed and developing world, are implementing educational technology to assist in student learning. However, there is no clear consensus on how to evaluate these new technologies. This paper proposes a comprehensive methodology for estimating the value of a new educational technology in three steps: benefit analysis, through the administration of a well-designed experiment; cost analysis, which incorporates costs to weigh against the benefits; and feasibility analysis, which introduces real-world concerns that may affect the ability to actually implement the technology. To illustrate the methodology, a case study from Chile is used where portable educational video games were introduced into first and second grade classrooms with the aim of improving learning in mathematics and language. This paper demonstrates the importance of all three steps in the evaluation process and provides a framework for future analyses. 相似文献