全文获取类型
收费全文 | 53158篇 |
免费 | 5372篇 |
国内免费 | 2077篇 |
专业分类
电工技术 | 12601篇 |
技术理论 | 2篇 |
综合类 | 3824篇 |
化学工业 | 5092篇 |
金属工艺 | 2408篇 |
机械仪表 | 2008篇 |
建筑科学 | 7448篇 |
矿业工程 | 2955篇 |
能源动力 | 1469篇 |
轻工业 | 2508篇 |
水利工程 | 2674篇 |
石油天然气 | 3507篇 |
武器工业 | 237篇 |
无线电 | 3368篇 |
一般工业技术 | 2618篇 |
冶金工业 | 2481篇 |
原子能技术 | 853篇 |
自动化技术 | 4554篇 |
出版年
2024年 | 121篇 |
2023年 | 458篇 |
2022年 | 1118篇 |
2021年 | 1476篇 |
2020年 | 1419篇 |
2019年 | 1107篇 |
2018年 | 1010篇 |
2017年 | 1339篇 |
2016年 | 1507篇 |
2015年 | 1776篇 |
2014年 | 3871篇 |
2013年 | 3023篇 |
2012年 | 4153篇 |
2011年 | 4382篇 |
2010年 | 3278篇 |
2009年 | 3315篇 |
2008年 | 2925篇 |
2007年 | 3597篇 |
2006年 | 3468篇 |
2005年 | 2897篇 |
2004年 | 2479篇 |
2003年 | 2300篇 |
2002年 | 1966篇 |
2001年 | 1760篇 |
2000年 | 1409篇 |
1999年 | 1103篇 |
1998年 | 719篇 |
1997年 | 552篇 |
1996年 | 489篇 |
1995年 | 437篇 |
1994年 | 295篇 |
1993年 | 196篇 |
1992年 | 141篇 |
1991年 | 126篇 |
1990年 | 81篇 |
1989年 | 79篇 |
1988年 | 65篇 |
1987年 | 36篇 |
1986年 | 28篇 |
1985年 | 13篇 |
1984年 | 27篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1963年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 498 毫秒
21.
随着我国环境保护法规《大气污染防治法》的修订和《涂料征收消费税通知》的公布,探讨了其对船舶涂料企业的冲击及其应对措施。 相似文献
22.
Luc Rochette Loubna Mazini Gabriel Malka Marianne Zeller Yves Cottin Catherine Vergely 《International journal of molecular sciences》2020,21(23)
The potential use of stem cell-based therapies for the repair and regeneration of various tissues and organs is a major goal in repair medicine. Stem cells are classified by their potential to differentiate into functional cells. Compared with other sources, adipose-derived stem cells (ADSCs) have the advantage of being abundant and easy to obtain. ADSCs are considered to be tools for replacing, repairing, and regenerating dead or damaged cells. The capacity of ADSCs to maintain their properties depends on the balance of complex signals in their microenvironment. Their properties and the associated outcomes are in part regulated by reactive oxygen species, which mediate the oxidation-reduction state of cells as a secondary messenger. ADSC therapy has demonstrated beneficial effects, suggesting that secreted factors may provide protection. There is evidence that ADSCs secrete a number of cytokines, growth factors, and antioxidant factors into their microenvironment, thus regulating intracellular signaling pathways in neighboring cells. In this review, we introduce the roles of ADSCs in the protection of cells by modulating inflammation and immunity, and we develop their potential therapeutic properties. 相似文献
23.
Seyedeh Nooshin Banitaba Dariush Semnani Elahe Heydari‐Soureshjani Behzad Rezaei Ali A Ensafi Ahmadreza Taghipour‐Jahromi 《Polymer International》2020,69(8):675-687
In this study, solvent‐free nanofibrous electrolytes were fabricated through an electrospinning method. Polyethylene oxide (PEO), lithium perchlorate and ethylene carbonate were used as polymer matrix, salt and plasticizer respectively in the electrolyte structures. Keggin‐type hetero polyoxometalate (Cu‐POM@Ru‐rGO, Ni‐POM@Ru‐rGO and Co‐POM@Ru‐rGO (POM, polyoxometalate; rGO, reduced graphene oxide)) nanoparticles were synthesized and inserted into the PEO‐based nanofibrous electrolytes. TEM and SEM analyses were carried out for further evaluation of the synthesized filler structures and the electrospun nanofibre morphologies. The fractions of free ions and crystalline phases of the as‐spun electrolytes were estimated by obtaining Fourier transform infrared and XRD spectra, respectively. The results showed a significant improvement in the ionic conductivity of the nanofibrous electrolytes by increasing filler concentrations. The highest ionic conductivity of 0.28 mS cm?1 was obtained by the introduction of 0.49 wt% Co‐POM@Ru‐rGO into the electrospun electrolyte at ambient temperature. Compared with solution‐cast polymeric electrolytes, the electrospun electrolytes present superior ionic conductivity. Moreover, the cycle stability of the as‐spun electrolytes was clearly improved by the addition of fillers. Furthermore, the mechanical strength was enhanced with the insertion of 0.07 wt% fillers to the electrospun electrolytes. The results implied that the prepared nanofibres are good candidates as solvent‐free electrolytes for lithium ion batteries. © 2020 Society of Chemical Industry 相似文献
24.
文章分析了网络安全等级保护2.0时期国家标准的新变化对等级测评结论可能产生的影响,并用实际案例和数据论述了以往描述的基于测评指标和基于测评对象的定量分析方法存在的局限性。根据网络安全等级保护国家标准结构和内容的新特点,结合新的等级测评结论表述方法,文章提出了调整和优化定量计算产生等级测评结论的思路,给出了缺陷扣分的原理和缺陷扣分的定量计算方法,并比较了各种定量计算方法在计算结果上的差异,提出了适合新标准的测评结论定量计算公式。 相似文献
25.
This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied. 相似文献
26.
通过对接轨站设置位置和布置图型主要影响因素的分析。按照能够充分反映接轨站作业特点的交接方式。对接轨站所采用的布置图型进行了归纳和分类。 相似文献
27.
28.
异构分层无线网络中基于逗留时间的动态流量均衡算法研究 总被引:1,自引:1,他引:0
为使异构分层无线网络能服务更多的移动用户,提出了一种基于逗留时间的动态流量均衡算法.该算法首先根据用户移动模型计算其在小区内的逗留时间,然后基于小区呼叫到达率和重叠覆盖小区的流量状态来确定一个周期内呼叫转移的数量,最后依据逗留时间门限值将重负载小区中满足条件的呼叫转移到轻负载的重叠覆盖小区中.为降低切换呼叫掉线率,还对异构网间的呼叫切换策略做了改进.仿真实验结果表明,本算法在新呼叫阻塞率和切换呼叫掉线率等性能指标上比传统方法有显著的提高. 相似文献
29.
30.