全文获取类型
收费全文 | 17654篇 |
免费 | 1802篇 |
国内免费 | 976篇 |
专业分类
电工技术 | 1183篇 |
技术理论 | 3篇 |
综合类 | 1328篇 |
化学工业 | 2694篇 |
金属工艺 | 983篇 |
机械仪表 | 1180篇 |
建筑科学 | 1560篇 |
矿业工程 | 474篇 |
能源动力 | 475篇 |
轻工业 | 1213篇 |
水利工程 | 309篇 |
石油天然气 | 868篇 |
武器工业 | 171篇 |
无线电 | 2122篇 |
一般工业技术 | 2055篇 |
冶金工业 | 913篇 |
原子能技术 | 178篇 |
自动化技术 | 2723篇 |
出版年
2024年 | 143篇 |
2023年 | 347篇 |
2022年 | 653篇 |
2021年 | 900篇 |
2020年 | 664篇 |
2019年 | 511篇 |
2018年 | 525篇 |
2017年 | 559篇 |
2016年 | 551篇 |
2015年 | 761篇 |
2014年 | 905篇 |
2013年 | 974篇 |
2012年 | 1070篇 |
2011年 | 1086篇 |
2010年 | 1008篇 |
2009年 | 918篇 |
2008年 | 995篇 |
2007年 | 912篇 |
2006年 | 883篇 |
2005年 | 825篇 |
2004年 | 671篇 |
2003年 | 507篇 |
2002年 | 523篇 |
2001年 | 450篇 |
2000年 | 435篇 |
1999年 | 420篇 |
1998年 | 351篇 |
1997年 | 327篇 |
1996年 | 299篇 |
1995年 | 242篇 |
1994年 | 206篇 |
1993年 | 179篇 |
1992年 | 121篇 |
1991年 | 88篇 |
1990年 | 86篇 |
1989年 | 79篇 |
1988年 | 47篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 20篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 13篇 |
1973年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Plasminogen activator-inhibitor C-1 (PAI-1) plays a critical role in the regulation of fibrinolysis, serving as the primary inhibitor of tissue-type plasminogen activator. Elevated levels of PAI-1 are a risk factor for recurrent myocardial infarction, and locally increased PAI-1 expression has been described in atherosclerotic human arteries. Recent studies have shown that the administration of angiotensin converting enzyme inhibitors reduces the risk of recurrent myocardial infarction in selected patients. Since angiotensin II (Ang II) has been reported to induce PAI-1 production in cultured astrocytes, we have hypothesized that one mechanism that may contribute to the beneficial effect of angiotensin converting enzyme inhibitors is an effect on fibrinolytic balance. In the present study, we examined the interaction of Ang II with cultured bovine aortic endothelial cells (BAECs) and the effects of this peptide on the production of PAI-1. 125I-Ang II was found to bind to BAECs in a saturable and specific manner, with an apparent Kd of 1.4 nM and Bmax of 74 fmol per mg of protein. Exposure of BAECs to Ang II induced dose-dependent increases in PAI-1 antigen in the media and in PAI-1 mRNA levels. Induction of PAI-1 mRNA expression by Ang II was not inhibited by pretreating BAECs with either Dup 753 or [Sar1, Ile8]-Ang II, agents that are known to compete effectively for binding to the two major angiotensin receptor subtypes. These data indicate that Ang II regulates the expression of PAI-1 in cultured endothelial cells and that this response is mediated via a pharmacologically distinct form of the angiotensin receptor. 相似文献
23.
ElectrochemicalInvestigationontheFormationofDyFeAloyinMoltenChloridesLiuGuankun(刘冠昆),TongYexiang(童叶翔),HongHuichan(洪惠婵),Yang... 相似文献
24.
Several fly ash samples from different countries were analyzed for dibromopolychlorodibenzo-p-dioxins and -dibenzofurans (DBPCDD/Fs) using capillary column gas chromatography/high-resolution mass spectrometry. Concentrations of these compounds ranged from low to high parts-per-trillion (pptr) depending on the location where the samples were collected. The mass spectrometer, operated at greater than 10,000 mass resolution in combination with the high resolving power of capillary column GC, permitted characterization of DBPCDD/Fs in municipal waste incinerator fly ash for the first time. The isomer patterns of tetra- through octa-congener groups of DBPCDD/Fs are remarkably similar regardless of where the fly ash originated, indicating common mechanisms of formation of these compounds in the incinerators. 相似文献
25.
MPC系统模块结构中的流场研究 总被引:5,自引:0,他引:5
本研究中,应用Simple数值计算方法开发了求解MPC系统模块结构中二维流场分布的计算软件。为了验证计算结果的精确性,用多普勒测速仪实测了用有机玻璃制成的MPC模块二维模型的流场,模拟计算结果与实测值对比取得了较好的一致性。四种不同流出角的MPC模块平均总压损失计算结果表明,已开发的软件可作为设计低流阻MPC模块的良好工具。 相似文献
26.
Ling Tong 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(2):431-436
This paper introduce the experiment about a new type of quasi-optic cavity Making a experimental model, measuring all parameters of the cavity, giving experiment results. It shows that theoritical research in reference[1] is correct Its results coincide with theory. At same time, it also indicates the cavity is hopeful device in MMW. 相似文献
27.
28.
29.
Conlon P.J. Tong Y.P. French P.M.W. Taylor J.R. Shestakov A.V. 《Electronics letters》1994,30(9):709-710
Sub-100 fs pulse generation from a Kerr lens modelocked Cr4+ :YAG laser has been demonstrated for the first time, yielding femtosecond pulses tunable from 1.49 to 1.56 μm with pulses as short as 90 fs obtained at 1.53 μm 相似文献
30.
An annular slot antenna on a dielectric half-space 总被引:1,自引:0,他引:1
The radiation properties of both singly and multiply fed annular slot antennas on a dielectric/air interface have been analyzed using Galerkin's method applied in the Hankel transform domain. The validity of our method has been confirmed through comparison with both theoretical and experimental results. The magic slot configuration has also been studied. The polarization diversity of this radiator makes it suitable for implementing a quasioptical balanced mixer 相似文献