全文获取类型
收费全文 | 3723篇 |
免费 | 163篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 53篇 |
综合类 | 9篇 |
化学工业 | 600篇 |
金属工艺 | 62篇 |
机械仪表 | 64篇 |
建筑科学 | 170篇 |
矿业工程 | 29篇 |
能源动力 | 113篇 |
轻工业 | 427篇 |
水利工程 | 29篇 |
石油天然气 | 8篇 |
无线电 | 371篇 |
一般工业技术 | 495篇 |
冶金工业 | 828篇 |
原子能技术 | 13篇 |
自动化技术 | 622篇 |
出版年
2023年 | 22篇 |
2022年 | 24篇 |
2021年 | 50篇 |
2020年 | 66篇 |
2019年 | 53篇 |
2018年 | 81篇 |
2017年 | 85篇 |
2016年 | 92篇 |
2015年 | 83篇 |
2014年 | 98篇 |
2013年 | 231篇 |
2012年 | 146篇 |
2011年 | 189篇 |
2010年 | 177篇 |
2009年 | 175篇 |
2008年 | 187篇 |
2007年 | 188篇 |
2006年 | 148篇 |
2005年 | 109篇 |
2004年 | 107篇 |
2003年 | 119篇 |
2002年 | 88篇 |
2001年 | 59篇 |
2000年 | 70篇 |
1999年 | 79篇 |
1998年 | 256篇 |
1997年 | 160篇 |
1996年 | 107篇 |
1995年 | 74篇 |
1994年 | 67篇 |
1993年 | 68篇 |
1992年 | 34篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 38篇 |
1988年 | 26篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 10篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 19篇 |
1976年 | 27篇 |
1973年 | 7篇 |
1972年 | 7篇 |
排序方式: 共有3893条查询结果,搜索用时 109 毫秒
11.
这个最新设计实例介绍了一种以少量无源器件来设计简单的高频LC振荡器的方法。但为获得最佳结果,稳定振荡器的实际硬件设计需要更多的器件且更为复杂。图1显示一种具有自动电平输出幅度控制以及能提供具有较低谐波含量正弦波输出缓冲的18MHz稳定振荡器(参考文献2)。此外,本设计实例还用英飞凌科技公司(Infineon Technologies)的廉价BF998型双栅极MOSFET替换了原来的JFET振荡器,该双栅极MOSFET可从DigiKey及其它公司购买。 相似文献
12.
Ricardo Beristain‐Cardoso Anne‐Claire Texier Reyes Sierra‐Álvarez Jim A Field Elías Razo‐Flores Jorge Gómez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1197-1203
BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO?/NO3? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH3COO?/NO3? (0.85, 0.72 and 0.62) with a constant S2?/NO3? molar ratio of 0.13 were evaluated. At a CH3COO?/NO3? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g?1 NO3?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g?1 CH3COO?‐C consumed. Sulfide was partially oxidized to S0, and 71% of the S2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO?/NO3? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g SO42?‐S g?1 S2? consumed. CONCLUSIONS: The CH3COO?/NO3? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. Copyright © 2008 Society of Chemical Industry 相似文献
13.
14.
PJ Jenkins MA Satta M Simmgen WM Drake C Williamson DG Lowe K Britton SL Chew RV Thakker GM Besser 《Canadian Metallurgical Quarterly》1997,47(6):747-751
We report a patient with a metastatic parathyroid carcinoma and medullary carcinoma of the thyroid. This patient represents a variation of the multiple endocrine neoplasia syndrome (MEN) type 2A. There was no evidence of a phaeochromocytoma. The case illustrates the difficulties that may be encountered in localising the source of PTH secretion; the patient underwent four unsuccessful exploratory operations of the neck and mediastinum before further investigations revealed a single metastatic deposit of parathyroid carcinoma involving the first thoracic vertebra. PCR amplification and sequencing of the RET oncogene from the metastatic parathyroid carcinoma and genomic DNA revealed a heterozygous mutation (Cys634Tyr) in exon 11, as has previously been described to occur in MEN 2A. In addition, loss of tumour heterozygosity was demonstrated at loci from chromosomes 1, 2, 3p, 13q and 16p. This represents the first report of a parathyroid carcinoma in a MEN2A patient, in which the multiple allelic deletions are consistent with the generalised losses observed in aggressive tumours. 相似文献
15.
FV Elmslie M Rees MP Williamson M Kerr MJ Kjeldsen KA Pang A Sundqvist ML Friis D Chadwick A Richens A Covanis M Santos A Arzimanoglou CP Panayiotopoulos D Curtis WP Whitehouse RM Gardiner 《Canadian Metallurgical Quarterly》1997,6(8):1329-1334
The epilepsies are a group of disorders characterised by recurrent seizures caused by episodes of abnormal neuronal hyperexcitability involving the brain. Up to 60 million people are affected worldwide and genetic factors may contribute to the aetiology in up to 40% of patients. The most common human genetic epilepsies display a complex pattern of inheritance. These are categorised as idiopathic in the absence of detectable structural or metabolic abnormalities. Juvenile myoclonic epilepsy (JME) is a distinctive and common variety of familial idiopathic generalised epilepsy (IGE) with a prevalence of 0.5-1.0 per 1000 and a ratio of sibling risk to population prevalence (lambda(s)) of 42. The molecular genetic basis of these familial idiopathic epilepsies is entirely unknown, but a mutation in the gene CHRNA4, encoding the alpha4 subunit of the neuronal nicotinic acetylcholine receptor (nAChR), was recently identified in a rare Mendelian variety of idiopathic epilepsy. Chromosomal regions harbouring genes for nAChR subunits were therefore tested for linkage to the JME trait in 34 pedigrees. Significant evidence for linkage with heterogeneity was found to polymorphic loci encompassing the region in which the gene encoding the alpha7 subunit of nAChR (CHRNA7) maps on chromosome 15q14 (HLOD = 4.4 at alpha = 0.65; Z(all) = 2.94, P = 0.0005). This major locus contributes to genetic susceptibility to JME in a majority of the families studied. 相似文献
16.
Uwe Helmke Robert C. Williamson 《Mathematics of Control, Signals, and Systems (MCSS)》1995,8(1):27-49
The problem of parametrizing single hidden layer scalar neural networks with continuous activation functions is investigated. A connection is drawn between realization theory for linear dynamical systems, rational functions, and neural networks that appears to be new. A result of this connection is a general parametrization of such neural networks in terms of strictly proper rational functions. Some existence and uniqueness results are derived. Jordan decompositions are developed, which show how the general form can be expressed in terms of a sum of canonical second order sections. The parametrization may be useful for studying learning algorithms.This work was supported by the Australian Research Council, the Australian Telecommunications and Electronics Research Board, and the Boeing Commencai Aircraft Company (thanks to John Moore). 相似文献
17.
18.
The abrasion characteristics of Tencel fabrics were evaluated by Martindale abrasion and laundering, and the breakdown mechanism of fibers was surveyed by scanning electron microscopy. The fabric was subjected to pad‐dry‐cure treatment with two different types of modified dimethyloldihydroxyethylene urea resins (Reaktant DH and Reaktant FC). Although the degree of dry abrasion varied with different resins, the damage exhibited by individual fibers differed little from untreated to resin‐treated; the major mechanism of abrasion was through friction, and the mechanism of fiber failure was multiple splitting and transverse cracking. In untreated Tencel, the characteristic feature of wet abrasion was massive fibrillation, and in crosslinked fabrics, the wet abrasion mechanism was through fiber slippage and slicing action, although in the Reaktant FC‐treated fabric, the wet abrasion mechanism was more through slicing than through fiber splitting. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1391–1398, 2006 相似文献
19.
The yeast ARS element, six years on: a progress report 总被引:24,自引:0,他引:24
D H Williamson 《Yeast (Chichester, England)》1985,1(1):1-14
20.
It is shown that the well known two-pass sequential local transformation algorithm for computing a distance transformation in rectangular domains may fail in some convex integer domains, but that a four-pass algorithm is sufficient in all two-dimensional convex domains. For non-convex domains the number of passes necessary is shown to be generally greater. Two propagation algorithms for computing the distance transformation are described and shown theoretically and experimentally to be computationally more efficient than the sequential local transformation algorithm in non-convex domains of complex shape. The relationship of the distance transformation in non-convex domains to some more general transformations is explored. 相似文献