全文获取类型
收费全文 | 405658篇 |
免费 | 6667篇 |
国内免费 | 1390篇 |
专业分类
电工技术 | 7615篇 |
综合类 | 377篇 |
化学工业 | 58478篇 |
金属工艺 | 14109篇 |
机械仪表 | 11704篇 |
建筑科学 | 11219篇 |
矿业工程 | 1195篇 |
能源动力 | 11047篇 |
轻工业 | 42944篇 |
水利工程 | 3724篇 |
石油天然气 | 1635篇 |
武器工业 | 13篇 |
无线电 | 55077篇 |
一般工业技术 | 75503篇 |
冶金工业 | 74963篇 |
原子能技术 | 5576篇 |
自动化技术 | 38536篇 |
出版年
2021年 | 2533篇 |
2019年 | 2456篇 |
2018年 | 3856篇 |
2017年 | 3910篇 |
2016年 | 4159篇 |
2015年 | 3468篇 |
2014年 | 5744篇 |
2013年 | 19343篇 |
2012年 | 10275篇 |
2011年 | 14742篇 |
2010年 | 11346篇 |
2009年 | 12942篇 |
2008年 | 13967篇 |
2007年 | 14320篇 |
2006年 | 12804篇 |
2005年 | 12014篇 |
2004年 | 11707篇 |
2003年 | 11401篇 |
2002年 | 10497篇 |
2001年 | 10643篇 |
2000年 | 9412篇 |
1999年 | 10091篇 |
1998年 | 23409篇 |
1997年 | 17072篇 |
1996年 | 13218篇 |
1995年 | 10859篇 |
1994年 | 9667篇 |
1993年 | 9254篇 |
1992年 | 7001篇 |
1991年 | 6674篇 |
1990年 | 6307篇 |
1989年 | 5984篇 |
1988年 | 5742篇 |
1987年 | 4805篇 |
1986年 | 4756篇 |
1985年 | 5905篇 |
1984年 | 5521篇 |
1983年 | 4762篇 |
1982年 | 4431篇 |
1981年 | 4391篇 |
1980年 | 4130篇 |
1979年 | 4028篇 |
1978年 | 3724篇 |
1977年 | 4501篇 |
1976年 | 6055篇 |
1975年 | 3084篇 |
1974年 | 2973篇 |
1973年 | 2851篇 |
1972年 | 2291篇 |
1971年 | 1965篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Wireless Networks - Orthogonal frequency-division multiplexing with random multiple access (OFDRMA) is discussed for down-link communications, whereby a single base-station transmits information... 相似文献
22.
During the service life of structural sealant glazing (SSG) facades, the load-bearing capacity of the silicone bonds needs to be guaranteed. Laboratory tests can assess the durability of SSG-systems based on mechanical characteristics of the bond after simultaneous exposure to both climatic and mechanical loads. This article studies how the material characteristics of two common structural sealants are affected by laboratory and field exposure. Dynamic mechanical analysis (DMA) confirms a reduction in the dynamic modulus of exposed silicone samples. Results from thermogravimetric analysis, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering/wide-angle X-ray scattering show differences between the two sealants and indicate no/minor changes in the composition and morphology of the laboratory and field exposed sealants. Mechanical characterization methods, such as DMA, and tensile and shear testing of the structural bond, are shown to be sensitive toward the combined climatic and mechanical loadings, and are hence suitable for studying degradation mechanisms of structural sealants. 相似文献
23.
24.
Kexin Jiao Laurence J. Walsh Sao Ivanovski Pingping Han 《International journal of molecular sciences》2021,22(9)
Periodontitis is a chronic complex inflammatory disease associated with a destructive host immune response to microbial dysbiosis, leading to irreversible loss of tooth-supporting tissues. Regeneration of functional periodontal soft (periodontal ligament and gingiva) and hard tissue components (cementum and alveolar bone) to replace lost tissues is the ultimate goal of periodontal treatment, but clinically predictable treatments are lacking. Similarly, the identification of biomarkers that can be used to accurately diagnose periodontitis activity is lacking. A relatively novel category of molecules found in oral tissue, circular RNAs (circRNAs) are single-stranded endogenous, long, non-coding RNA molecules, with covalently circular-closed structures without a 5’ cap and a 3’ tail via non-classic backsplicing. Emerging research indicates that circRNAs are tissue and disease-specific expressed and have crucial regulatory functions in various diseases. CircRNAs can function as microRNA or RNA binding sites or can regulate mRNA. In this review, we explore the biogenesis and function of circRNAs in the context of the emerging role of circRNAs in periodontitis pathogenesis and the differentiation of periodontal cells. CircMAP3K11, circCDK8, circCDR1as, circ_0062491, and circ_0095812 are associated with pathological periodontitis tissues. Furthermore, circRNAs are expressed in periodontal cells in a cell-specific manner. They can function as microRNA sponges and can form circRNA–miRNA–mRNA networks during osteogenic differentiation for periodontal-tissue (or dental pulp)-derived progenitor cells. 相似文献
25.
26.
Dr. Ana G. Enderle Dr. Matteo Bosso Rüdiger Groß Magdalena Heiland Dr. Mariela Bollini Dr. María J. Culzoni Prof. Dr. Frank Kirchhoff Prof. Dr. Jan Münch Prof. Dr. Carsten Streb 《ChemMedChem》2021,16(17):2727-2730
Polyoxometalates (POMs), molecular metal oxide anions, are inorganic clusters with promising antiviral activity. Herein we report increased anti-HIV-1 activity of a POM when electrostatically combined with organic counter-cations. To this end, Keggin-type cerium tungstate POMs have been combined with organic methyl-caffeinium (Caf) cations, and their cytotoxicity, antiviral activity and mode of action have been studied. The novel compound, Caf4K[β2-CeSiW11O39]×H2O, exhibits sub-nanomolar antiviral activity and inhibits HIV-1 infectivity by acting on an early step of the viral infection cycle. This work demonstrates that combination of POM anions and organic bioactive cations can be a powerful new strategy to increase antiviral activity of these inorganic compounds. 相似文献
27.
Nitsa Buaron Antonella Mangraviti Francesco Volpin Ann Liu Mariangela Pedone Eric Sankey Dina Aranovich Itay Adar Fausto J. Rodriguez Abraham Nyska Riki Goldbart Tamar Traitel Henry Brem Betty Tyler Joseph Kost 《Advanced functional materials》2021,31(44):2100643
Treating neuroinflammation-related injuries and disorders through manipulation of neuroinflammation functions is being heralded as a new therapeutic strategy. In this study, a novel pectic galactan (PG) polysaccharide based gene therapy approach is developed for targeting reactive gliosis in neuroinflammation. Galectin-3 (Gal-3) is a cell protein with a high affinity to β-galactoside sugars and is highly expressed in reactive gliosis. Since PG carries galactans, it can target reactive gliosis via specific carbohydrate interaction between galactan and Gal-3 on the cell membrane, and therefore can be utilized as a carrier for delivering genes to these cells. The carrier is synthesized by modifying quaternary ammonium groups on the PG. The resulting quaternized PG (QPG) is found to form complexes with plasmid DNA with a mean diameter of 100 nm and have the characteristics required for targeted gene therapy. The complexes efficiently condense large amounts of plasmid per particle and successfully bind to Gal-3. The in vivo study shows that the complexes are biocompatible and safe for administration and can selectively transfect reactive glial cells of an induced cortical lesion. The results confirm that this PG-based delivery system is a promising platform for targeting Gal-3 overexpressing neuroinflammation cells for treating neuroinflammation-related injuries and neurodegenerative diseases. 相似文献
28.
Belcher Calvin H. Zheng Baolong MacDonald Benjamin E. Langlois Eric D. Lehman Benjamin Pearce Charles Delaney Robert Apelian Diran Lavernia Enrique J. Monson Todd C. 《Journal of Materials Science》2022,57(9):5518-5532
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic... 相似文献
29.
Journal of Materials Science - The crystallographic orientation of TiB is one of the main factors that influence the microstructure and texture evolution of Ti-TiB composites. Different... 相似文献
30.
利用水力空化过程产生局部的高温、高压、高射流以及强大的剪切力等极端化学物理条件改质处理沙特重质原油,试验结果表明:沙特重质原油经过水力空化改质后粘度由13.61降低至7.22mm2/s,残碳由7.16%降低至6.48%,实沸点蒸馏后减压渣油降低1个百分点。进一步采用APPI FT-IR MS、XRD、FT-IR、SEM和粒度分布等技术研究了水力空化改质对沙重原油分子组成,沥青质团聚体微晶结构、沥青质胶束粒径分布、沥青质官能团、沥青质形貌等方面的影响,从分子角度阐述空化改质重油的机理。研究结果表明:水力空化改质后沙重原油分子量分布、芳烃类化合物缔合作用变小;沥青质对低DBE化合物吸附性能降低;沥青质团聚体微晶结构更加松散;沥青质胶束粒度分布降低;沥青质分子相互团聚作用力减弱。进一步考察了水力空化改质前后减压渣油延迟焦化性能,改质处理后焦炭产率降低1.85个百分点,液体收率和气体产率分别增加1.52和0.33个百分点,水力空化改质对沥青质性质、结构特点的改善能够有效的提高其加工性能。 相似文献