全文获取类型
收费全文 | 105773篇 |
免费 | 11479篇 |
国内免费 | 6704篇 |
专业分类
电工技术 | 8589篇 |
技术理论 | 8篇 |
综合类 | 8521篇 |
化学工业 | 15788篇 |
金属工艺 | 5777篇 |
机械仪表 | 7034篇 |
建筑科学 | 8749篇 |
矿业工程 | 3478篇 |
能源动力 | 3329篇 |
轻工业 | 8228篇 |
水利工程 | 2549篇 |
石油天然气 | 5051篇 |
武器工业 | 1305篇 |
无线电 | 13076篇 |
一般工业技术 | 11087篇 |
冶金工业 | 4163篇 |
原子能技术 | 1428篇 |
自动化技术 | 15796篇 |
出版年
2024年 | 597篇 |
2023年 | 1965篇 |
2022年 | 3865篇 |
2021年 | 5309篇 |
2020年 | 3823篇 |
2019年 | 3091篇 |
2018年 | 3380篇 |
2017年 | 3787篇 |
2016年 | 3440篇 |
2015年 | 4937篇 |
2014年 | 6051篇 |
2013年 | 7097篇 |
2012年 | 8232篇 |
2011年 | 8318篇 |
2010年 | 7761篇 |
2009年 | 7352篇 |
2008年 | 7007篇 |
2007年 | 6449篇 |
2006年 | 6075篇 |
2005年 | 4774篇 |
2004年 | 3405篇 |
2003年 | 2621篇 |
2002年 | 2691篇 |
2001年 | 2244篇 |
2000年 | 1841篇 |
1999年 | 1638篇 |
1998年 | 1157篇 |
1997年 | 959篇 |
1996年 | 895篇 |
1995年 | 709篇 |
1994年 | 592篇 |
1993年 | 393篇 |
1992年 | 356篇 |
1991年 | 251篇 |
1990年 | 194篇 |
1989年 | 166篇 |
1988年 | 103篇 |
1987年 | 70篇 |
1986年 | 61篇 |
1985年 | 42篇 |
1984年 | 38篇 |
1983年 | 23篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 33篇 |
1979年 | 19篇 |
1977年 | 10篇 |
1976年 | 20篇 |
1959年 | 11篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
首先从材料力学角度分析了抚顺石化公司干法腈纶装置原进口切断刀盘圆环失效的原因 ,认为此种切断刀盘圆环系二维增强结构层压板 ,层间没有纤维增强 ,需要解决由二维增强向三维增强的过渡。给出了改进办法 ,寻求到三维增强的替代材料。同时介绍了机械加工测试及在线实验 相似文献
72.
Jiuxin Jiang Bo Zhu Peiling Wang Weiwu Chen Dongsheng Yan Hanrui Zhuang Yibing Cheng 《Journal of the American Ceramic Society》2005,88(4):950-953
The Pr α-sialon powders prepared by self-propagating high-temperature synthesis (SHS), consisting of 55 wt% Pr α-sialon and 45 wt% of β-sialon (abbreviated as α' and β'), were hot-pressed at 1800°C for 1 h. The results showed that Pr α' phase would transfer to β' with the appearance of JEM phase (Pr(Si6− z Al z )(N10− z O z )) after sintering, thus resulting in the increase of β' phase to 86 wt%. The addition of Y2 O3 into SHS-ed Pr α' powders as the starting materials restrains the transformation of α' to β' and prevents the formation of JEM phase as well. The nucleation mechanism of Pr α' grain during hot-pressing was investigated in terms of transmission electron microscope and energy-dispersive spectrometer analysis. Two nucleation modes of Pr α' grains were found, i.e., nucleating on the undissolved Pr α' grains and on the nuclei of (Pr, Y) α' grains precipitated from liquid phase. 相似文献
73.
74.
This paper presents a comparative study how reactor configuration, sludge loading and air flowrate affect flow regimes, hydrodynamics, floc size distribution and sludge solids-liquid separation properties. Three reactor configurations were studied in bench scale activated sludge bubble column reactor (BCR), air-lift reactor (ALR) and aerated stirred reactor (ASR). The ASR demonstrated the highest capacity of gas holdup and resistance, and homogeneity in flow regimes and shearing forces, resulting in producing large numbers of small and compact flocs. The fluid dynamics in the ALR created regularly directed recirculation forces to enhance the gas holdup and sludge flocculation. The BCR distributed a high turbulent flow regime and non-homogeneity in gas holdup and mixing, and generated large numbers of larger and looser flocs. The sludge size distributions, compressibility and settleability were significantly influenced by the reactor configurations associated with the flow regimes and hydrodynamics. 相似文献
75.
为了定量、客观、全面地评价光学镜头的像质,介绍了光学镜头调制传递函数的测试。先简要叙述了测试的原理,并给出计算公式;然后介绍了测试步骤,其中包括固定、穿轴、测试中心视场和测试轴外视场;最后介绍了测试时的注意事项,包括对测试工装的要求、对测试平面的要求和正、负轴外视场测试值相差较大时的处理办法。 相似文献
76.
锅炉和循环水处理系统的氧腐蚀是各种腐蚀中最严重的一种。因此,对给水进行除氧处理应该是最有效的防止腐蚀的方法。本文针对新研制出的新型活性铁除氧剂,又研制出与之相配套的除氧设备。该设备具有理想的除氧效果,常温操作,结构简单,弥补了过去一些除氧设备的不足。 相似文献
77.
CMC samples obtained by gel filtration on a preparative scale were used to calibrate an agarose column. The relation between molecular weight and the peak elution volume for monodisperse samples were calculated as well as the relation between band broadening and the peak elution volume. In the calculations of the molecular weight distribution curves of the studied CMC samples, consideration was given to the variable band broadening by proper transformations of the experimental data, thus making it possible to obtain numerical solutions free from oscillations. The method admits a rapid determination of the molecular weight distribution of cellulose and related materials. 相似文献
78.
Anodic aluminum oxide (AAO) membrane can be used as template for the synthesized nanostructures. In this article, we have prepared the AAO membrane by using electrooxidation of aluminum substrate in phosphoric acid, and fabricated poly(2,5‐di‐n‐butoxyphenylene) (BuO–PPP) nanofibril arrays by oxidative coupling polymerization of 1,4‐di‐n‐butoxybenzene (DBB) within the pores of the AAO template membrane. The detailed molecular structure of the polymer nanofibrils was characterized by using infrared and 1H nuclear magnetic resonance spectra, and estimated to consist of almost equal fractions of 1,4‐ and 1,3‐ linkages. We have used transmission electron microscopy, scanning electron microscopy, and atom force microscopy to confirm the morphologies and images of the AAO template membrane and the fabricated nanometer scale of BuO–PPP nanofibril arrays. The experimental results demonstrated that the pores of the AAO membrane were regular and uniform, and parallel each other, and the BuO–PPP chains in the narrowest template‐synthesized nanofibrils were oriented parallel to the porous axes of the AAO membrane and perpendicular to the surface of the aluminum substrate. The polymer chain orientation was partially responsible for the enhanced conductivity. The ultraviolet absorption spectrum of the BuO–PPP nanofibril arrays shown that the polymer contains a better extended π‐conjugation system along poly‐(p‐phenylene) backbone, which resulted in longer wavelength shift of the absorption band, the absorption maxima were located at 258 nm (E1 absorption band) and 332 nm (E2 absorption band), respectively. Photoluminescence spectrum of the BuO–PPP nanofibril arrays exhibited a blue emission. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 425–430, 2004 相似文献
79.
钟原 《网络安全技术与应用》2014,(6):208-209
随着全球网络技术与移动通信设备的融合发展,“大数据”时代已经引起社会各界的重点关注。苹果、三星、华为、IBM、微软、腾讯等国际知名企业都开始建构出“大数据”时代的企业生态系统。本文将对“大数据”时代的企业生态系统的演化和建构进行深入分析。 相似文献
80.
用共沉淀法制备Fe3O4磁流体,总结出用十二烷基磺酸钠与聚乙二醇作为表面活性剂制备水基磁流体的合适条件:(1)反应温度为室温或不高于35℃;(2)表面活性剂十二烷基磺酸钠的最佳用量为0.0030~0.0040 g/80 mL;(3)第一次包裹的最佳pH为9~10;(4)聚乙二醇作为第二次包裹的表面活剂时,体系最佳温度为40℃左右;(5)表面活性剂聚乙二醇的最佳用量为0.0050~0.0060 g/80 mL。通过实验制得了能稳定存在180 d的水基磁流体。并用透射电镜、红外光谱、分光光度计、古埃磁天平等进行了初步表征。 相似文献