全文获取类型
收费全文 | 2623篇 |
免费 | 49篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 17篇 |
综合类 | 16篇 |
化学工业 | 119篇 |
金属工艺 | 32篇 |
机械仪表 | 13篇 |
建筑科学 | 12篇 |
矿业工程 | 7篇 |
能源动力 | 10篇 |
轻工业 | 82篇 |
水利工程 | 9篇 |
石油天然气 | 5篇 |
无线电 | 35篇 |
一般工业技术 | 161篇 |
冶金工业 | 2110篇 |
原子能技术 | 5篇 |
自动化技术 | 47篇 |
出版年
2024年 | 4篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 35篇 |
2012年 | 39篇 |
2011年 | 48篇 |
2010年 | 35篇 |
2009年 | 34篇 |
2008年 | 42篇 |
2007年 | 33篇 |
2006年 | 21篇 |
2005年 | 27篇 |
2004年 | 15篇 |
2003年 | 22篇 |
2002年 | 18篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 81篇 |
1998年 | 649篇 |
1997年 | 383篇 |
1996年 | 244篇 |
1995年 | 140篇 |
1994年 | 124篇 |
1993年 | 143篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 17篇 |
1988年 | 31篇 |
1987年 | 21篇 |
1986年 | 21篇 |
1985年 | 17篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1978年 | 4篇 |
1977年 | 63篇 |
1976年 | 115篇 |
1975年 | 7篇 |
1966年 | 2篇 |
排序方式: 共有2680条查询结果,搜索用时 15 毫秒
51.
Diego Castaño José Patricio Díaz Varela Antoni Torrens 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2011,15(7):1449-1455
In this paper, we show that free algebras in the variety of residuated lattices and some of its subvarieties are directly
indecomposable and show, as a consequence, the direct indecomposability of free algebras for some classes of their bounded
implicative subreducts. 相似文献
52.
R Ottman JH Lee WA Hauser S Hong D Hesdorffer N Schupf TA Pedley ML Scheuer 《Canadian Metallurgical Quarterly》1993,43(12):2526-2530
Methods for standardized classification of epileptic seizures are important for both clinical practice and epidemiologic research. In this study, we developed a strategy for standardized classification using a semistructured telephone interview and operational diagnostic criteria. We interviewed 1,957 adults with epilepsy ascertained from voluntary organizations. To confirm and expand the seizure history, we also interviewed a first-degree relative for 67% of subjects and obtained medical records for 59%. Three lay reviewers used all available information to classify seizures. To assess reliability, each reviewer classified a sample of subjects assigned to the others. In addition, an expert physician classified a sample of subjects assigned to two of the reviewers. Agreement was "moderate-substantial" for generalized-onset seizures, both for the comparisons between pairs of lay reviewers and for the neurologist versus lay reviewers. Agreement was "substantial-almost perfect" for partial-onset seizures, both for pairs of lay reviewers and for the neurologist versus lay reviewers. These results suggest that seizures can be reliably classified by lay reviewers, using operational criteria applied to symptoms ascertained in a semistructured telephone interview. 相似文献
53.
The relative effect of protozoan and bacterial predators on the survival of Escherichia coli in estuarine water samples was examined. Predacious protozoa exerted their major influence on E. coli destruction during the first 2 days of a 10-day-decline period. Inhibition of protozoa after day 2 had little effect on E. coli survival. Bacterial predators also contributed to E. coli destruction but in natural estuarine water samples were maintained at lower levels due to "grazing" by predacious protozoa. 相似文献
54.
TA Reader 《Canadian Metallurgical Quarterly》1976,50(1):11-30
The structure and function of the digestive gland of the gastropod mollusc, Bithynia tentaculata, was investigated using ultrastructural, histochemical, and cytochemical techniques. The digestive gland was shown to be composed of two main cell types, the "digestive" cells and "secretory" cells. The digestive cells appeared to be concerned with the absorption and digestion of nutrients, while secretory cells produced digestive enzymes and calcareous concretions. Undifferentiated cells were scattered between these two main cell types. The pathological effects of larval digeneans on the digestive gland were also investigated, at the ultrastructural level. In such infected snails the digestive gland appeared to be degenerating. The significance of this tissue destruction was briefly discussed. 相似文献
55.
PDF417二维条码肖像图片压缩编码的优化算法研究 总被引:1,自引:0,他引:1
针对PDF417二维条码存储空间有限的问题,提出了一种基于小波变换的有损图像压缩算法,通过这个算法,可以将静态图片信息加入PDF417条码中,并能够满足在指定字节数情况下保证高质量地压缩图像,该文在分析小波变换等算法理论的基础上,详细介绍了PDF417二维条码肖像图片压缩编码的优化算法及该算法的实验结果与美国Symbol公司的PC2VQ算法结果对比。 相似文献
56.
G. Brankovic Z. Brankovic M. R. Davolos M. Cilense J. A. Varela 《Materials Characterization》2004,52(4-5):243-251
The influence of dopants commonly used in SnO2 varistor ceramics, such as CoO, Cr2O3 or Nb2O5, on the structural properties of SnO2 was investigated. Several SnO2-based ceramics containing only one of the dopants were prepared and characterized. Spectroscopic investigations [visible, near infrared (IR) and IR region] were performed to obtain information about dopants valence states inside the ceramics, as well as about their influence on electronic structure of the material. Structural properties were investigated by X-ray diffraction analysis and mechanisms of dopant incorporation were proposed. Obtained results were confirmed with results of the electrical measurements. Microstructural changes in doped ceramics were investigated by scanning electron microscopy (SEM) analysis that showed great differences in densities, grain size, and morphology of the SnO2 ceramics depending on type of dopants and their distribution. 相似文献
57.
M Harmsen TA Oosterlaken C Tangerman H Snippe CA Kraaijeveld 《Canadian Metallurgical Quarterly》1993,43(2):137-146
3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34) is the rate limiting step in the mevalonate pathway that produces isoprenoids and cholesterol. Inhibitors of HMG-CoA reductase are teratogenic in vivo and induce neural tube defects in rat embryo culture, effects which appear unrelated to cholesterol deficiency. This study is the first to localize HMG-CoA reductase mRNA by in situ hybridization (ISH). Expression of reductase mRNA was examined in post-implantation rat embryos, and for control purposes in rat liver and UT-1 cells, using a digoxigenin-11 (dig-11) labelled cRNA probe. Eighteen-day fetal liver showed heavy but patchy hybridization, and adult rat liver showed strong hybridization only on some periportal hepatocytes, which was absent in livers of fasted animals. UT-1 cells stimulated to overexpress HMG-CoA reductase mRNA were strongly positive with the same probe. Control hybridizations with sense strand RNA probe, or with cRNA probe on pre-RNased tissue were negative. Strong hybridization signal for HMG-CoA reductase mRNA was observed in all tissues of the post-implantation rat embryo, from egg cylinder to 30 somite stages (7 to 12 days). Heavy signal was noted in primitive ectoderm and neural tube. The wide embryonic and extraembryonic distribution and abundance of HMG-CoA reductase mRNA may reflect developmental requirements for products of the mevalonate pathway, e.g., isoprenoids for post-translational farnesylation of p21ras. 相似文献
58.
塔程程 《吉林化工学院学报》2021,38(8):76-79
信息检索课程的系统化讲授,对于大学生优化信息检索行为,提高信息检索使用效率具有不容忽视的教学辅助作用.立足问卷调查形成的一系列相关数据,探讨大学生信息检索行为存在问题,最终在课程教学中提出优化大学生信息检索的对策:明确信息检索目的,提升实施效果;有效提升检索行为实施频率,增强综合质量;使得信息获取多元发展,优化成效凸显... 相似文献
59.
A. Paz-Lopez G. Varela J.A. BecerraS. Vazquez-Rodriguez R.J. Duro 《Science of Computer Programming》2013
Ambient Intelligence (AmI) systems need to be as transparent as possible, that is, their users should perceive only the effects of the features presented to them and, in some cases, some kind of interface. They should not be conscious of how these features are implemented, from a hardware or from a software point of view. 相似文献
60.
M. A. P. Almeida L. S. Cavalcante M. Siu Li J. A. Varela E. Longo 《Journal of Inorganic and Organometallic Polymers and Materials》2012,22(1):264-271
Manganese tungstate (MnWO4) nanorods were prepared at room temperature by the co-precipitation method and synthesized after processing in a microwave-hydrothermal
(MH) system at 140 °C for 6–96 min. These nanorods were structurally characterized by X-ray diffraction (XRD), Rietveld refinements
and Fourier transform (FT)-Raman spectroscopy. The growth direction, shape and average size distribution of nanorods were
observed by means of transmission electron microscopy (TEM) and high resolution TEM (HR-TEM). The optical properties of the
nanorods were investigated by ultraviolet visible (UV-vis) absorption and photoluminescence (PL) measurements. XRD patterns,
Rietveld refinement data and FT-Raman spectroscopy indicate that the MnWO4 precipitate is not a single phase structure while the nanorods synthesized by MH processing have a wolframite-type monoclinic
structure without deleterious phases. FT-Raman spectra exhibited the presence of 17 Raman-active modes from 50 to 1,000 cm−1. TEM and HR-TEM micrographs indicated that the nanorods are aggregated due to surface energy by Van der Waals forces and
grow along the [100] direction. UV–vis absorption measurements confirmed non-linear values for the optical band gap (from
3.2 to 2.72 eV), which increased as the MH processing time increased. The structural characterizations indicated that the
presence of defects in the MnWO4 precipitate promotes a significant contribution to maximum PL emission, while MnWO4 nanorods obtained by MH processing decrease the PL emission due to the reduction of defects in the lattice. 相似文献