全文获取类型
收费全文 | 2690篇 |
免费 | 36篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 8篇 |
综合类 | 1篇 |
化学工业 | 210篇 |
金属工艺 | 15篇 |
机械仪表 | 57篇 |
建筑科学 | 24篇 |
矿业工程 | 3篇 |
能源动力 | 9篇 |
轻工业 | 143篇 |
水利工程 | 7篇 |
石油天然气 | 5篇 |
无线电 | 31篇 |
一般工业技术 | 87篇 |
冶金工业 | 2060篇 |
原子能技术 | 2篇 |
自动化技术 | 65篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 30篇 |
2021年 | 49篇 |
2020年 | 26篇 |
2019年 | 30篇 |
2018年 | 24篇 |
2017年 | 24篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 56篇 |
2012年 | 50篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 26篇 |
2008年 | 32篇 |
2007年 | 24篇 |
2006年 | 30篇 |
2005年 | 20篇 |
2004年 | 11篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 20篇 |
1999年 | 84篇 |
1998年 | 623篇 |
1997年 | 364篇 |
1996年 | 226篇 |
1995年 | 143篇 |
1994年 | 104篇 |
1993年 | 122篇 |
1992年 | 13篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 20篇 |
1980年 | 28篇 |
1978年 | 6篇 |
1977年 | 66篇 |
1976年 | 160篇 |
1975年 | 3篇 |
1964年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有2727条查询结果,搜索用时 31 毫秒
71.
Effect of reduced dietary sodium on blood pressure: a meta-analysis of randomized controlled trials 总被引:1,自引:0,他引:1
JP Midgley AG Matthew CM Greenwood AG Logan 《Canadian Metallurgical Quarterly》1996,275(20):1590-1597
OBJECTIVE:- To ascertain whether restriction of dietary sodium lowers blood pressure in hypertensive and normotensive individuals. DATA SOURCES:- An English-language computerized literature search, restricted to human studies with Medical Subject Heading terms, "hypertension," "blood pressure," "vascular resistance," "sodium and dietary," "diet and sodium restricted," "sodium chloride," "clinical trial," "randomized controlled trial," and "prospective studies," was conducted. Bibliographies of review articles and personal files were also searched. TRIAL SELECTION:- Trials that had randomized allocation to control and dietary sodium intervention groups, monitored by timed sodium excretion, with outcome measures of both systolic and diastolic blood pressure were selected by blinded review of the methods section. DATA EXTRACTION:- Two observers extracted data independently, using purpose-designed forms, and discrepancies were resolved by discussion. DATA SYNTHESIS:- The 56 trials that met our inclusion criteria showed significant heterogeneity. Publication bias was also evident. The mean reduction (95% confidence interval) in daily urinary sodium excretion, a proxy measure of dietary sodium intake, was 95 mmol/d (71-119 mmol/d) in 28 trials with 1131 hypertensive subjects and 125 mmol/d (95-156 mmol/d) in 28 trials with 2374 normotensive subjects. After adjustment for measurement error of urinary sodium excretion, the decrease in blood pressure for a 100-mmol/d reduction in daily sodium excretion was 3.7 mm Hg (2.35-5.05 mm Hg) for systolic (P<.001) and 0.9 mm Hg (-0.13 to 1.85 mm Hg) for diastolic (P=.09) in the hypertensive trials, and 1.0 mm Hg (0.51-1.56 mm Hg) for systolic (P<.001) and 0.1 mm Hg (-0.32 to 0.51 mm Hg) for diastolic (P=.64) in the normotensive trials. Decreases in blood pressure were larger in trials of older hypertensive individuals and small and nonsignificant in trials of normotensive individuals whose meals were prepared and who lived outside the institutional setting. CONCLUSION:- Dietary sodium restriction for older hypertensive individuals might be considered, but the evidence in the normotensive population does not support current recommendations for universal dietary sodium restriction. 相似文献
72.
Dimas Cassimiro Nascimento Carlos Eduardo Pires Demetrio Gomes Mestre 《Applied Intelligence》2016,45(2):530-548
Deduplication is the task of identifying the entities in a data set which refer to the same real world object. Over the last decades, this problem has been largely investigated and many techniques have been proposed to improve the efficiency and effectiveness of the deduplication algorithms. As data sets become larger, such algorithms may generate critical bottlenecks regarding memory usage and execution time. In this context, cloud computing environments have been used for scaling out data quality algorithms. In this paper, we investigate the efficacy of different machine learning techniques for scaling out virtual clusters for the execution of deduplication algorithms under predefined time restrictions. We also propose specific heuristics (Best Performing Allocation, Probabilistic Best Performing Allocation, Tunable Allocation, Adaptive Allocation and Sliced Training Data) which, together with the machine learning techniques, are able to tune the virtual cluster estimations as demands fluctuate over time. The experiments we have carried out using multiple scale data sets have provided many insights regarding the adequacy of the considered machine learning algorithms and proposed heuristics for tackling cloud computing provisioning. 相似文献
73.
A neural network with asymmetric basis functions for feature extraction of ECG P waves. 总被引:1,自引:0,他引:1
E de Azevedo Botter C R Nascimento T Yoneyama 《Neural Networks, IEEE Transactions on》2001,12(5):1252-1255
In this work a simple neural network with asymmetric basis functions is proposed as a feature extractor for P waves in electrocardiographic signals (ECG). The neural network is trained using the classical backward-error-propagation algorithm. The performance of the proposed network was tested using actual ECG signals and compared with other types of neural feature extractors. 相似文献
74.
Mendes MP Ribeiro L Nascimento J Condesso de Melo T Stigter TY Buxo A 《Water science and technology》2012,66(10):2162-2169
The Water Framework Directive establishes that the river basin management plans must have a summary of the pressures and impacts of human activities, such as agriculture, on the chemical and quantitative status of groundwater bodies. In order to identify those areas where a potential impact from agricultural activities on groundwater bodies exists, but currently lacking groundwater monitoring data, a methodology was developed that combines the use of gross nitrogen balance values with the results of a specific vulnerability assessment index. A farm management efficiency parameter is added, to identify the factors that contribute to nitrogen use efficiency and to assess the near-future scenarios. This methodology allows the identification of significant pressures that may be responsible for a groundwater body failing good status where there is no representative monitoring network. 相似文献
75.
AG Lobanok ON Zinchekko SL Romanov VV Smetanin LT Bogomazova 《Canadian Metallurgical Quarterly》1976,45(4):620-624
Identical distribution of C2- and Cx-cellulase activities of enzyme complexes produced by Trichoderma lignorum on a medium with lactose, a soluble "inductor", and on a medium with cellulose was found by means of disc elestrophoresis in polyacrylamide gel. The maximum rate of synthesis of cellulases on the medium with lactose was registered during the highest deceleration, and even complete cessation, of the fungal growth. During this phase, only one electrophoretically homogeneous cellulase component with Rf of 0.44 possessing all types of the cellulase activity is present in the cultural broth. In the course of growth of the fungus on cellulose after 48 hours, also only one electrophoretically homogeneous component with Rf of 0.44 was found in the cultural broth when the rate of the substrate degradation was highest. The appearance of minor protein components with the activity of cellulase at later stages of cultivation after cessation of the fungal growth is supposed to be caused by modification of the main cellulase component with Rf of 0.44 by the growth medium. 相似文献
76.
In experiments with unanaesthetized rabbits the influences of electric stimulation of the dentate fascia (DF) on the extracellularly recorded spontaneous and evoked activity of the CA3 neurones were investigated. Stimulation of a fixed locus in the DF during recording in the CA3 by a microelectrode, shifted along the longitudinal axis of the hippocampus, supported the notion of the topical, "segmental" organization of connections between the DF and CA3. A relatively narrow "active zone" (approximately 700 nm) appeared in the CA3 during the threshold DF stimulation: it was bordered by zones with predominantly inhibitory responses to stimulation. The CA3 neurones in the "active zone" rapidly lost their reactivity to sensory stimuli. In the "inhibitory" and "zero" zones the normal level of reactivity to sensory stimuli was preserved. 相似文献
77.
BCI Meeting 2005--workshop on signals and recording methods. 总被引:4,自引:0,他引:4
Jonathan R Wolpaw Gerald E Loeb Brendan Z Allison Emanuel Donchin Omar Feix do Nascimento William J Heetderks Femke Nijboer William G Shain James N Turner 《IEEE transactions on neural systems and rehabilitation engineering》2006,14(2):138-141
This paper describes the highlights of presentations and discussions during the Third International BCI Meeting in a workshop that evaluated potential brain-computer interface (BCI) signals and currently available recording methods. It defined the main potential user populations and their needs, addressed the relative advantages and disadvantages of noninvasive and implanted (i.e., invasive) methodologies, considered ethical issues, and focused on the challenges involved in translating BCI systems from the laboratory to widespread clinical use. The workshop stressed the critical importance of developing useful applications that establish the practical value of BCI technology. 相似文献
78.
E. P. Muniz J. R. C. Proveti R. D. Pereira B. Segatto P. S. S. Porto V. P. Nascimento M. A. Schettino E. C. Passamani 《Journal of Materials Science》2013,48(4):1543-1554
The kinetics of formation of NiFe2O4 nanoparticles were investigated where the nanoparticles were produced by the proteic-sol–gel method using coconut water followed by annealing in (i) air, (ii) air in the presence of boron nitride (BN), or (iii) nitrogen. The sample dried at 473 K for 5.5 h was composed of small disordered NiFe2O4 nanoparticles in a superparamagnetic state as determined from Mössbauer spectroscopy. In general, heat treatment at high temperature leads to a nanocomposite rich in NiFe2O4. In air, annealing at 1173 K for 8 h favored the formation of the magnetically ordered NiFe2O4 inverse spinel structure, with bulk characteristics and average crystal sizes of approximately 66 nm. In a nitrogen atmosphere and in compacted BN powder under air atmosphere, the NiFe2O4 spinel structure stabilized for temperatures up to 873 and 773 K, respectively, however, decomposition of the NiFe2O4 phase into other undesired structures was observed above 873 K. 相似文献
79.
80.
Aula Alwattar Athir Haddad Quan Zhou Tatiana Nascimento Ryan Greenhalgh Eliton Medeiros Jonny Blaker Adam Parry Peter Quayle Stephen Yeates 《Polymer International》2019,68(3):360-368
Fluorescent markers are critical for tracking the position and movement of molecules both in vivo and in vitro. Conventionally, synthetic dyes are non‐covalently added to polymers for fluorescent tracking, but often diffuse away. Here we demonstrate, for the first time, a facile method for the synthesis of fluorescent poly(lactic acid) nano‐/microfibres for biomedical applications using solution spin blowing. Pyrene‐end‐capped poly(l ‐lactide) (PLLA) derivatives were synthesised using the ring‐opening polymerisation of l ‐lactide and they were characterised using spectroscopic and thermal analyses. Submicrometre‐sized fluorescent fibres were produced from these PLLA derivatives using solution blow spinning techniques generating polymer blends and core–shell fibres. Such system could be further exploited to incorporate electrically conductive carbon allotropes via the pyrene aromaticity, producing fluorescent and electrically active fibres for in vitro monitoring and electrical stimulation. © 2018 Society of Chemical Industry 相似文献