全文获取类型
收费全文 | 25653篇 |
免费 | 2293篇 |
国内免费 | 1350篇 |
专业分类
电工技术 | 1532篇 |
技术理论 | 6篇 |
综合类 | 1729篇 |
化学工业 | 4584篇 |
金属工艺 | 1495篇 |
机械仪表 | 1591篇 |
建筑科学 | 2017篇 |
矿业工程 | 797篇 |
能源动力 | 679篇 |
轻工业 | 1893篇 |
水利工程 | 468篇 |
石油天然气 | 1499篇 |
武器工业 | 155篇 |
无线电 | 3013篇 |
一般工业技术 | 3170篇 |
冶金工业 | 1312篇 |
原子能技术 | 274篇 |
自动化技术 | 3082篇 |
出版年
2024年 | 126篇 |
2023年 | 448篇 |
2022年 | 757篇 |
2021年 | 1040篇 |
2020年 | 850篇 |
2019年 | 706篇 |
2018年 | 773篇 |
2017年 | 882篇 |
2016年 | 796篇 |
2015年 | 1066篇 |
2014年 | 1348篇 |
2013年 | 1575篇 |
2012年 | 1807篇 |
2011年 | 1987篇 |
2010年 | 1474篇 |
2009年 | 1425篇 |
2008年 | 1457篇 |
2007年 | 1431篇 |
2006年 | 1384篇 |
2005年 | 1143篇 |
2004年 | 766篇 |
2003年 | 706篇 |
2002年 | 760篇 |
2001年 | 597篇 |
2000年 | 580篇 |
1999年 | 622篇 |
1998年 | 503篇 |
1997年 | 403篇 |
1996年 | 396篇 |
1995年 | 326篇 |
1994年 | 310篇 |
1993年 | 201篇 |
1992年 | 153篇 |
1991年 | 119篇 |
1990年 | 92篇 |
1989年 | 71篇 |
1988年 | 52篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 13篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
Fabrication and Characterization of Electrospun Dopants/PS Composite Fibers with Porous and Hollow‐Porous Structures 下载免费PDF全文
Lidong Tian Junwei Gu Xingfeng Lei Zhaoyuan Lv Mingtao Qiao Changjie Yin Qiuyu Zhang 《大分子材料与工程》2016,301(5):625-635
Three different dopants are used to fabricate electrospun dopants/polystyrene (dopants/PS) composite fibers from PS solution and PS sol. The relative humidity and the influence of the dopants on the morphologies, diameter, porous structures, and dopant distribution of electrospun PS fibers are investigated. Compared to those obtained from PS solution, electrospun dopants/PS composite fibers from PS sol with hollow‐porous and multichannel hollow‐porous structures present significant advantages due to the multi‐stage degree of interfacial structure and diversity of the internal environment. In comparison to coaxial electrospun PS fibers, the electrospun dopants/PS composite fibers from PS sol obtained in one step have an improved yield and a simplified technological process simultaneously, leading to significant competitiveness in fields such as catalysis, fluidics gas storage, and sensing.
995.
ZrO2是一种高熔点金属氧化物,同时具有弱酸性和弱碱性以及氧化性与还原性,具有p型半导体性质,易产生氧空穴,是理想的催化材料。通过添加不同质量分数的ZrO2(0~5%) 作为助剂,采用分步沉淀法制备系列CuO/Fe2O3-ZrO2催化剂,通过XRD、N2物理吸附-脱附、H2-TPR和CO2-TPD等表征技术,考察ZrO2助剂对CuO/Fe2O3水煤气变换催化剂催化性能的影响。结果表明,适量ZrO2(质量分数1%)的添加,削弱了CuFe2O4中铜铁物种之间的协同作用,增加了催化剂中可被还原的铜物种的数量,形成较多的弱碱性位点,有利于增加活性中心铜的数量,具有较好的水煤气变换反应活性和热稳定性。 相似文献
996.
含硫纤维素衍生物的研究进展 总被引:1,自引:0,他引:1
简述了近年来在含硫纤维素衍生物方面的研究进展。将含硫纤维素衍生物分为巯基纤维素与费原酯棉、水溶性含硫纤维素衍生物和聚硫醚纤维素三大类,对含硫纤维素衍生物的合成、应用及其与金属离子作用机理作了论述。 相似文献
997.
氟喹诺酮类抗菌药物的合成与开发 总被引:11,自引:0,他引:11
简要介绍了诺氟沙星、依诺沙星、培氟沙星等 10种氟喹诺酮类抗菌药物的工业合成方法。对国内的研究开发情况作了总结。 相似文献
998.
Ya-Fei Zhao Wen-Jing Ren Ying Zhang Jin-Rong He Hai-Yan Yin Yang Liao Patrizia Rubini Jan M. Deussing Alexei Verkhratsky Zeng-Qiang Yuan Peter Illes Yong Tang 《International journal of molecular sciences》2022,23(3)
Extracellular adenosine 5′-triphosphate (ATP) in the brain is suggested to be an etiological factor of major depressive disorder (MDD). It has been assumed that stress-released ATP stimulates P2X7 receptors (Rs) at the microglia, thereby causing neuroinflammation; however, other central nervous system (CNS) cell types such as astrocytes also possess P2X7Rs. In order to elucidate the possible involvement of the MDD-relevant hippocampal astrocytes in the development of a depressive-like state, we used various behavioral tests (tail suspension test [TST], forced swim test [FST], restraint stress, inescapable foot shock, unpredictable chronic mild stress [UCMS]), as well as fluorescence immunohistochemistry, and patch-clamp electrophysiology in wild-type (WT) and genetically manipulated rodents. The TST and FST resulted in learned helplessness manifested as a prolongation of the immobility time, while inescapable foot shock caused lower sucrose consumption as a sign of anhedonia. We confirmed the participation of P2X7Rs in the development of the depressive-like behaviors in all forms of acute (TST, FST, foot shock) and chronic stress (UCMS) in the rodent models used. Further, pharmacological agonists and antagonists acted in a different manner in rats and mice due to their diverse potencies at the respective receptor orthologs. In hippocampal slices of mice and rats, only foot shock increased the current responses to locally applied dibenzoyl-ATP (Bz-ATP) in CA1 astrocytes; in contrast, TST and restraint depressed these responses. Following stressful stimuli, immunohistochemistry demonstrated an increased co-localization of P2X7Rs with a microglial marker, but no change in co-localization with an astroglial marker. Pharmacological damage to the microglia and astroglia has proven the significance of the microglia for mediating all types of depression-like behavioral reactions, while the astroglia participated only in reactions induced by strong stressors, such as foot shock. Because, in addition to acute stressors, their chronic counterparts induce a depressive-like state in rodents via P2X7R activation, we suggest that our data may have relevance for the etiology of MDD in humans. 相似文献
999.
Yue Yin Cong Guo Hongyan Shi Jianhua Zhao Fang Ma Wei An Xinru He Qing Luo Youlong Cao Xiangqiang Zhan 《International journal of molecular sciences》2022,23(4)
The R2R3-MYB is a large gene family involved in various plant functions, including carotenoid biosynthesis. However, this gene family lacks a comprehensive analysis in wolfberry (Lycium barbarum L.) and other Solanaceae species. The recent sequencing of the wolfberry genome provides an opportunity for investigating the organization and evolutionary characteristics of R2R3-MYB genes in wolfberry and other Solanaceae species. A total of 610 R2R3-MYB genes were identified in five Solanaceae species, including 137 in wolfberry. The LbaR2R3-MYB genes were grouped into 31 subgroups based on phylogenetic analysis, conserved gene structures, and motif composition. Five groups only of Solanaceae R2R3-MYB genes were functionally divergent during evolution. Dispersed and whole duplication events are critical for expanding the R2R3-MYB gene family. There were 287 orthologous gene pairs between wolfberry and the other four selected Solanaceae species. RNA-seq analysis identified the expression level of LbaR2R3-MYB differential gene expression (DEGs) and carotenoid biosynthesis genes (CBGs) in fruit development stages. The highly expressed LbaR2R3-MYB genes are co-expressed with CBGs during fruit development. A quantitative Real-Time (qRT)-PCR verified seven selected candidate genes. Thus, Lba11g0183 and Lba02g01219 are candidate genes regulating carotenoid biosynthesis in wolfberry. This study elucidates the evolution and function of R2R3-MYB genes in wolfberry and the four Solanaceae species. 相似文献
1000.
将不同配比的聚丙烯(PP)和乙烯-乙酸乙烯共聚物(EVA)进行共混,测试了共混物的拉伸强度和冲击强度;用差示扫描量热法研究了共混物的结晶性能;用扫描电镜(SEM)二次电子成像系统分析了试样的断口形貌,研究了EVA含量对共混物力学性能的影响。结果表明:EVA的加入提高了EVA/PP共混体系的韧性,同时降低了PP的结晶度。 相似文献