全文获取类型
收费全文 | 14643篇 |
免费 | 1705篇 |
国内免费 | 976篇 |
专业分类
电工技术 | 2894篇 |
综合类 | 1507篇 |
化学工业 | 844篇 |
金属工艺 | 1144篇 |
机械仪表 | 971篇 |
建筑科学 | 465篇 |
矿业工程 | 304篇 |
能源动力 | 333篇 |
轻工业 | 340篇 |
水利工程 | 181篇 |
石油天然气 | 451篇 |
武器工业 | 303篇 |
无线电 | 3805篇 |
一般工业技术 | 1490篇 |
冶金工业 | 473篇 |
原子能技术 | 505篇 |
自动化技术 | 1314篇 |
出版年
2024年 | 20篇 |
2023年 | 151篇 |
2022年 | 222篇 |
2021年 | 326篇 |
2020年 | 345篇 |
2019年 | 312篇 |
2018年 | 304篇 |
2017年 | 497篇 |
2016年 | 586篇 |
2015年 | 639篇 |
2014年 | 838篇 |
2013年 | 879篇 |
2012年 | 1137篇 |
2011年 | 1219篇 |
2010年 | 933篇 |
2009年 | 920篇 |
2008年 | 974篇 |
2007年 | 1173篇 |
2006年 | 967篇 |
2005年 | 839篇 |
2004年 | 631篇 |
2003年 | 575篇 |
2002年 | 520篇 |
2001年 | 441篇 |
2000年 | 318篇 |
1999年 | 263篇 |
1998年 | 202篇 |
1997年 | 205篇 |
1996年 | 173篇 |
1995年 | 144篇 |
1994年 | 132篇 |
1993年 | 101篇 |
1992年 | 76篇 |
1991年 | 64篇 |
1990年 | 55篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1972年 | 1篇 |
1963年 | 2篇 |
1959年 | 2篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Tomasz Pdzinski Katarzyna Grzyb Konrad Skotnicki Piotr Filipiak Krzysztof Bobrowski Chryssostomos Chatgilialoglu Bronislaw Marciniak 《International journal of molecular sciences》2021,22(9)
Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO•) play an important role, being the most aggressive towards biomolecules. The reactions of HO• with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO• generated by ionizing radiation in aqueous solutions under anoxic conditions. We performed the identification and quantification of transient species by pulse radiolysis and of final products by LC-MS and high-resolution MS/MS after γ-radiolysis. By parallel photochemical experiments, using 3-carboxybenzophenone (CB) triplet with the model peptide, we compared the outcomes in terms of short-lived intermediates and stable product identification. The result is a detailed mechanistic scheme of Met oxidation by HO•, and by CB triplets allowed for assigning transient species to the pathways of products formation. 相似文献
3.
通过对AAOA-MBR工艺在实际工程中的应用,分析该工艺处理城市污水的节能减排效能。实践表明AAOA-MBR工艺具有很强的抗冲击负荷能力,在进水质水量大幅度波动、且碳源匮乏的情况下,仍能取得良好的处理效果。实际工程运行四年来,厂区出水各项指标均稳定优于城镇污水处理厂污染物排放标准(GB 18918-2002)中的一级A标准,其中COD、BOD5、SS、NH3-N去除率分别达到可分别达到90.14%、98.25%、95.58%和98.2%;通过对运行期间污水处理量与耗电量相关关系进行回归分析可知,当处理水量达到设计规模时,其吨水耗电量预测为0.31kWh/m3。同时,基于对污水处理系统的沿程水质检测,优化进水水量分配和内循环回流比并进行产水泵联动改造,可进一步提高系统节能减排效果。 相似文献
4.
采用扫描电镜和超高分辨透射电镜,对具有良好冲制性能的新型锆合金薄板成品带材进行含晶粒、第二相粒子等在内的显微组织研究,并探索真空退火处理条件下温度对带材显微组织的影响。结果显示:新型锆合金薄板成品带材晶粒平均尺寸2.17 μm,存在{0001}<1010>和{0001}<1120>两种织构,大部分晶粒<1120>平行带材RD方向,较少晶粒<1010>平行带材RD方向;第二相粒子分布在晶粒内部及晶界,平均尺寸114 nm,尺寸较大的为不规则椭圆形的Zr-Nb-Fe相,尺寸较小的为圆形的β-Nb相;热处理退火温度降低,带材晶粒尺寸减小,第二相粒子细小弥散分布;新型锆合金薄板成品带材良好冲制性能主要源于轧制积累应变诱发再结晶过程进行充分,导致晶粒细小及孪晶发生破碎;相对轧制变形,退火对带材冲制性能影响不显著。 相似文献
5.
《低温学》2018
A Stirling/pulse tube hybrid cryocooler (SPC), comprised of a Stirling cryocooler as the first stage and a pulse tube cryocooler as the second stage, features the ability of shifting cooling capacity between stages by adjusting the movement of the displacer in the first stage. Such an ability allows an SPC to accommodate itself to time-varying heat loads at different temperatures, which makes it a competitive candidate in space applications. However, due to the gas coupling, there exists a significant mutual effect between stages which endows an SPC with special thermodynamic characteristics and has a significant effect on the SPC’s capability of shifting cooling capacity between stages. With the phasor analysis and the thermodynamic analysis, this paper establishes an idealized model of an SPC. The model is then used to study the effect of the second stage on the first stage and reveal the condition that an SPC is able to shift cooling capacity between stages. Also, the model is compared with a Sage numerical model and the two models are consistent on the overall trend. Though it is unable to reflect reality precisely, the idealized model can interpret the mechanism and highlight some of the essential nature of an SPC, which will eventually benefit the appropriate design of an SPC. 相似文献
6.
7.
The Caputo and Caputo–Fabrizio derivative are applied to study a second‐grade nanofluid over a vertical plate. A comparative analysis is presented to study the unsteady free convection of a second‐grade nanofluid with a new time–space fractional heat conduction. The governing equations with mixed time–space fractional derivatives are non‐dimensionalized and solved numerically, and a comparison between the Caputo and the Caputo–Fabrizio models is made. It is found that the temperature is higher for the Caputo–Fabrizio fractional model than the Caputo model, but the higher velocity only exists near the vertical plate for the Caputo–Fabrizio model than the Caputo model. Moreover, the velocity for the Caputo model will exceed the Caputo–Fabrizio model as y evolves. 相似文献
8.
9.
采用SPM (Sulfuric-Peroxide Mixtures, 98wt%H2SO4+30wt%H2O2)+兆声(方法1)和氧等离子体+HPM (Hydrochloric/Peroxide Mixture, 37wt%HCl+30wt%H2O2+DIH2O)+兆声(方法2)两种清洗方法对多层介质膜脉宽压缩光栅进行清洗, 并对清洗前后样品的表面元素含量、衍射效率、表面粗糙度、表面温升以及激光损伤阈值等参数进行测量以评估两种清洗方法清洗效果。在入射角70°, 脉宽12 ns, s偏振, 波长1064 nm的激光辐照下, 经过清洗方法1清洗后的光栅样品单脉冲激光损伤阈值为7.55 J/cm 2, 而方法2清洗后的样品损伤阈值为5.32 J/cm 2。另外, 虽然经过方法2清洗后样品表面杂质含量更低, 但是在衍射效率、表面粗糙度和表面温升都劣于经方法1清洗后的样品, 进一步分析发现方法2中氧等离子体清洗过程引入的Fe元素影响了其样品损伤性能和温升性能。因此, SPM清洗方法可以作为多层介质膜脉宽压缩光栅提升抗激光损伤性能的优化清洗方案。 相似文献
10.
《中国有色金属学会会刊》2021,31(12):3800-3813
The Fe−Ni−TiO2 nanocomposite coatings were electrodeposited by pulse frequency variation. The results showed that the nanocomposite with a very dense coating surface and a nanocrystalline structure was produced at higher frequencies. By increasing the pulse frequency from 10 to 500 Hz, the iron and TiO2 nanoparticles contentswere increased in expense of nickel content. XRD patterns showed that by increasing the frequency to 500 Hz, an enhancement ofBCC phase was observed and the grain size of deposits was reduced to 35 nm. The microhardness and the surface roughness were increased to 647 HV and 125 nm at 500 Hz due to the grain size reduction and higher incorporation of TiO2 nanoparticles into the Fe−Ni matrix (5.13 wt.%). Moreover, the friction coefficient and wear rate values were decreased by increasing the pulse frequency;while the saturation magnetization and coercivity values of the composite deposits were increased. 相似文献