全文获取类型
收费全文 | 5344篇 |
免费 | 384篇 |
国内免费 | 198篇 |
专业分类
电工技术 | 212篇 |
综合类 | 258篇 |
化学工业 | 940篇 |
金属工艺 | 246篇 |
机械仪表 | 217篇 |
建筑科学 | 353篇 |
矿业工程 | 118篇 |
能源动力 | 126篇 |
轻工业 | 484篇 |
水利工程 | 204篇 |
石油天然气 | 105篇 |
武器工业 | 74篇 |
无线电 | 427篇 |
一般工业技术 | 603篇 |
冶金工业 | 781篇 |
原子能技术 | 75篇 |
自动化技术 | 703篇 |
出版年
2024年 | 14篇 |
2023年 | 61篇 |
2022年 | 134篇 |
2021年 | 160篇 |
2020年 | 119篇 |
2019年 | 114篇 |
2018年 | 123篇 |
2017年 | 126篇 |
2016年 | 152篇 |
2015年 | 210篇 |
2014年 | 267篇 |
2013年 | 322篇 |
2012年 | 347篇 |
2011年 | 390篇 |
2010年 | 302篇 |
2009年 | 310篇 |
2008年 | 306篇 |
2007年 | 314篇 |
2006年 | 227篇 |
2005年 | 211篇 |
2004年 | 151篇 |
2003年 | 147篇 |
2002年 | 128篇 |
2001年 | 101篇 |
2000年 | 72篇 |
1999年 | 83篇 |
1998年 | 184篇 |
1997年 | 124篇 |
1996年 | 101篇 |
1995年 | 59篇 |
1994年 | 49篇 |
1993年 | 62篇 |
1992年 | 22篇 |
1991年 | 26篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 30篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 19篇 |
1977年 | 25篇 |
1976年 | 51篇 |
1974年 | 12篇 |
排序方式: 共有5926条查询结果,搜索用时 0 毫秒
101.
102.
Redona Hafizi Faik Imeri Bisera Stepanovska Tanturovska Roxana Manaila Stephanie Schwalm Sandra Trautmann Roland H. Wenger Josef Pfeilschifter Andrea Huwiler 《International journal of molecular sciences》2022,23(11)
Erythropoietin (Epo) is a crucial hormone regulating red blood cell number and consequently the hematocrit. Epo is mainly produced in the kidney by interstitial fibroblast-like cells. Previously, we have shown that in cultures of the immortalized mouse renal fibroblast-like cell line FAIK F3-5, sphingosine 1-phosphate (S1P), by activating S1P1 and S1P3 receptors, can stabilize hypoxia-inducible factor (HIF)-2α and upregulate Epo mRNA and protein synthesis. In this study, we have addressed the role of intracellular iS1P derived from sphingosine kinases (Sphk) 1 and 2 on Epo synthesis in F3-5 cells and in mouse primary cultures of renal fibroblasts. We show that stable knockdown of Sphk2 in F3-5 cells increases HIF-2α protein and Epo mRNA and protein levels, while Sphk1 knockdown leads to a reduction of hypoxia-stimulated HIF-2α and Epo protein. A similar effect was obtained using primary cultures of renal fibroblasts isolated from wildtype mice, Sphk1−/−, or Sphk2−/− mice. Furthermore, selective Sphk2 inhibitors mimicked the effect of genetic Sphk2 depletion and also upregulated HIF-2α and Epo protein levels. The combined blockade of Sphk1 and Sphk2, using Sphk2−/− renal fibroblasts treated with the Sphk1 inhibitor PF543, resulted in reduced HIF-2α and Epo compared to the untreated Sphk2−/− cells. Exogenous sphingosine (Sph) enhanced HIF-2α and Epo, and this was abolished by the combined treatment with the selective S1P1 and S1P3 antagonists NIBR-0213 and TY52156, suggesting that Sph was taken up by cells and converted to iS1P and exported to then act in an autocrine manner through S1P1 and S1P3. The upregulation of HIF-2α and Epo synthesis by Sphk2 knockdown was confirmed in the human hepatoma cell line Hep3B, which is well-established to upregulate Epo production under hypoxia. In summary, these data show that sphingolipids have diverse effects on Epo synthesis. While accumulation of intracellular Sph reduces Epo synthesis, iS1P will be exported to act through S1P1+3 to enhance Epo synthesis. Furthermore, these data suggest that selective inhibition of Sphk2 is an attractive new option to enhance Epo synthesis and thereby to reduce anemia development in chronic kidney disease. 相似文献
103.
四针状氧化锌纳米材料的发射稳定性研究 总被引:1,自引:0,他引:1
采用四针状氧化锌纳米材料作为阴极发射体制作了真空场发射二极管,观察其阴极发射电流的稳定性。在实验过程中,阴极发射电流的波动幅度在2%以下,说明四针状氧化锌纳米发射体具有较好的发射稳定性。 相似文献
104.
三聚氰胺甲醛树脂改性及其纤维的性能 总被引:1,自引:0,他引:1
三聚氰胺甲醛树脂是热固性高聚物,成纤性差,成纤纤维韧性差;通过苯代三聚氰胺、聚乙烯醇(PVA)对三聚氰胺树脂进行改性,提高了树脂溶液的可纺性,所制纤维的柔韧性得到了提高。通过红外光谱、SEM、TG-DTA研究了纤维的结构、形态及耐热性。 相似文献
105.
本文利用热力学分析了铁尾矿中主体元素可能发生的反应并对生成的产物进行了预测.理论分析表明,尾矿中Fe3O4和FeTiO3的还原是逐级进行的,虽有中间产物的产生,但随温度的升高,最终转化为Fe3Si和Ti(C,N),这为合成制备Fe-Si-Ti多相材料提供了理论基础.在热力学分析的基础上,采用碳热还原氮化法制备了Fe3Si-Ti(C,N)多相材料,并借助XRD和SEM对烧结体的物相和显微形貌进行了表征.结果表明,1300℃以上时,产物的主晶相为Fe3Si和Ti(C,N),与热力学分析结果吻合.通过SEM分析可知,生成的Ti(C,N)相富集在Fe3Si相的周围,形成一种高硬度、耐磨、抗腐蚀的复合材料,表明这是一条从废弃尾矿制得良好的耐磨材料的绿色工艺. 相似文献
106.
ao.Univ.-Prof. DI Dr. Friedrich Schöberl DI Bernhard Zeiringer Mag. Christian Moritz 《?sterreichische Wasser- und Abfallwirtschaft》2014,66(5-6):190-205
The EU Water Framework Directive commits member states to achieve good ecological status in all waterbodies. Artificial or heavily modified waterbodies must reach at least its good ecological potential. In view of these requirements, simple and feasible methods are required in order to evaluate habitat suitability for relevant target species in larger river reaches. Well-developed models for determining the relationship between stream flows and habitat for target species mainly based on micro- and meso-scale already exist. However, the application of such models is complex and time-consuming and consequently limited to relatively short river segments. The objective of this study is to develop a simplified applicable assessment model to evaluate habitat conditions for selected target fish. This model uses hydro-morphological indicators for the habitat assessment and relies on correlative relations between habitat suitability and hydro-morphological features of river stretches (average Froude-number, relative flow width, mean bed slope, relative water depth and flow velocity). The indicators were determined as reach-related averages, derived from 2D model simulations (hydraulic and habitat-specific). Particular emphasis was laid on using a wide range of river stretches with different hydro-morphological characteristics (hydrology, bed substratum, bed structures, degree of braiding, sinuosity of the river course, mean bed width and bed slope). As a result, a set of model equations enables the evaluation of fish habitat conditions in river stretches as a function of flow and morphology. The habitat suitability assessment focuses on four preselected target species: brown trout, European grayling and for low slope rivers common nase and barbel. 相似文献
107.
108.
109.
基于IEC 61850的电力设备远程控制方法 总被引:1,自引:0,他引:1
远程控制已成为确保电力系统安全稳定运行的重要技术手段,IEC 61850对电力设备的远程控制提出了更高的要求。以增强安全的操作前选择控制的有限状态机为基础,提出了基于IEC 61850的电力远动系统的远程控制模型。结合实际应用的需要,设计了基于IEC 61850的远方控制接口,实现了对智能电子设备(IED)的远程访问控制,对断路器进行了断开与闭合操作。基于上述研究所开发的系统通过了在某地区电网进行的工业现场试验并试运行,验证了模型的正确性和方案的可行性。 相似文献
110.