全文获取类型
收费全文 | 16680篇 |
免费 | 1120篇 |
国内免费 | 844篇 |
专业分类
电工技术 | 1061篇 |
综合类 | 794篇 |
化学工业 | 5262篇 |
金属工艺 | 1622篇 |
机械仪表 | 614篇 |
建筑科学 | 921篇 |
矿业工程 | 173篇 |
能源动力 | 253篇 |
轻工业 | 934篇 |
水利工程 | 59篇 |
石油天然气 | 470篇 |
武器工业 | 109篇 |
无线电 | 1459篇 |
一般工业技术 | 1959篇 |
冶金工业 | 528篇 |
原子能技术 | 244篇 |
自动化技术 | 2182篇 |
出版年
2024年 | 43篇 |
2023年 | 222篇 |
2022年 | 469篇 |
2021年 | 594篇 |
2020年 | 437篇 |
2019年 | 397篇 |
2018年 | 317篇 |
2017年 | 387篇 |
2016年 | 513篇 |
2015年 | 534篇 |
2014年 | 759篇 |
2013年 | 948篇 |
2012年 | 995篇 |
2011年 | 1274篇 |
2010年 | 991篇 |
2009年 | 1067篇 |
2008年 | 972篇 |
2007年 | 1140篇 |
2006年 | 1082篇 |
2005年 | 837篇 |
2004年 | 684篇 |
2003年 | 607篇 |
2002年 | 533篇 |
2001年 | 412篇 |
2000年 | 356篇 |
1999年 | 286篇 |
1998年 | 230篇 |
1997年 | 182篇 |
1996年 | 164篇 |
1995年 | 109篇 |
1994年 | 95篇 |
1993年 | 108篇 |
1992年 | 85篇 |
1991年 | 74篇 |
1990年 | 64篇 |
1989年 | 64篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 55篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1978年 | 35篇 |
1977年 | 39篇 |
1976年 | 43篇 |
1975年 | 48篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The adsorption and inhibition effect of 6-benzylaminopurine (BAP) on cold rolled steel (CRS) in 1.0 M HCl at 25-50 °C was studied by weight loss and potentiodynamic polarization methods. The results showed that BAP was a good inhibitor in 1.0 M HCl, and the inhibition efficiency (IE) increased with the inhibitor concentration. The adsorption of BAP on the CRS surface obeyed the Langmuir adsorption isotherm equation. Both thermodynamic parameters (adsorption heat ΔH0, adsorption free energy ΔG0 and adsorption entropy ΔS0) and kinetic parameters (apparent activation energy Ea and pre-exponential factor A) were calculated and discussed. Polarization curves showed that BAP acted as a mixed-type inhibitor in hydrochloric acid. Good agreement between weight loss and polarization methods was obtained. The adsorbed film on CRS surface containing optimum dose of BAP was investigated by Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM). Quantum chemical calculation was applied to elucidate the adsorption mode of the inhibitor molecule onto steel surface. Depending on the results, the inhibitive mechanism was proposed from the viewpoint of adsorption theory. 相似文献
992.
993.
994.
2-氨基-6-羟基-3,5-二硝基吡啶(AHDNP)是合成聚对苯亚乙基吡啶并咪 二唑(PPIO)重要前体.本文以2,6-二氯吡啶为原料经单硝化、单氨解、再硝化先合成中间体2-氨基-6-氯-3,5-二硝基吡啶(ACDNP),纯度为95.60%,总收率41.00%以上;最后在K2CO3的碱性水溶液中70℃条件下单水解,成功合成出AHDNP,提纯后总收率为82.07%,纯度为98.13%.AHDNP的结构经过FT-IR、MS、13C NMR 准确定性和表征.合成过程操作方便、产品质量优异、经济性良好及易于产业化,为进一步研发合成新型高性能材料PPIO及其新单体提供技术基础及中间体来源. 相似文献
995.
Factors Affecting the Durability of Ti-6Al-4V/Epoxy Bonds 总被引:1,自引:0,他引:1
Factors influencing the durability of Ti-6Al-4V/epoxy interphases were studied by determining chemical and physical properties of Ti-6Al-4V adherend surfaces and by characterizing the strength and durability of Ti-6Al-4V/epoxy bonds.
Ti-6Al-4V adherend surfaces were oxidized either by chemical etch or anodization. Four principal pretreatments were studied: chromic acid anodization (CAA), sodium hydroxide anodization (SHA), phosphate fluoride acid etch (P/F) and TURCO basic etch (TURCO). The oxides were characterized by SEM, STEM, profilometry, contact angles and XPS.
All adhesive bonding was carried out using a structural epoxy, FM-300U. Both lap shear and wedge test samples were tested in hot, wet environments. The results lead to the conclusion that the interfacial area between the adhesive and adherend is the primary factor affecting bond durability. 相似文献
Ti-6Al-4V adherend surfaces were oxidized either by chemical etch or anodization. Four principal pretreatments were studied: chromic acid anodization (CAA), sodium hydroxide anodization (SHA), phosphate fluoride acid etch (P/F) and TURCO basic etch (TURCO). The oxides were characterized by SEM, STEM, profilometry, contact angles and XPS.
All adhesive bonding was carried out using a structural epoxy, FM-300U. Both lap shear and wedge test samples were tested in hot, wet environments. The results lead to the conclusion that the interfacial area between the adhesive and adherend is the primary factor affecting bond durability. 相似文献
996.
目的 在大肠杆菌中表达、纯化重组靶向毒素hIL6(T22)-PE38,并检测其细胞毒性。方法以PHis-hIL6(T22)-PE38质粒为模板,PCR扩增hIL6(T22)-PE38基因,插入表达载体pET-28a(+)的NcoⅠ和XhoⅠ多克隆位点,构建重组表达质粒,分别转化至大肠杆菌BL21(DE3)、Rosettablue(DE3)和BL21(DE3)pLysS中,IPTG诱导表达,并对表达条件进行优化。表达产物经亲和层析纯化后,检测其细胞毒性。结果重组表达质粒pET-28a-hIL6(T22)-PE38经双酶切和测序证明构建正确。表达的重组毒素相对分子质量约56 000,在大肠杆菌Rosettablue(DE3)中表达量最高。最适诱导表达条件为:1 mmol/L IPTG 28℃诱导4 h。重组毒素能选择性地杀伤人骨髓瘤细胞U266和鼠骨髓瘤细胞SP2/0,体外对U266和SP2/0细胞的IC50分别为0.5~1.0和1.0~1.5μg/ml。结论重组靶向毒素hIL6(T22)-PE38在大肠杆菌中成功获得可溶性表达,纯化的蛋白可明显选择性杀伤U266和SP2/0细胞。 相似文献
997.
998.
本文以自制的2-环己基对甲酚为原料,在酸性催化剂条件下,以水为溶剂,与甲醛水溶液缩合反应合成了抗氧剂2,2’-亚甲基双(6-环己基-4-甲基苯酚)又称抗氧剂ZKF。本工艺采用廉价的甲醛水溶液代替国内外多数工艺中采用的甲缩醛或多聚甲醛,并以水为溶剂代替了有机溶剂,水溶液可循环使用5次,实现了清洁生产并降低了产品成本。产品收率为90.2%,产品纯度99.3%。 相似文献
999.
4′ 羟基联苯 4 甲酸与甲醇反应,合成了4′ 羟基联苯 4 甲酸甲酯。后者与1,6 二溴己烷反应合成了目标化合物4′ (6 溴己氧基)联苯 4 甲酸甲酯,反应工艺条件为:以无水乙醇为溶剂,n(4′ 羟基联苯 4 甲酸甲酯)∶n(碳酸钾)∶n(1,6 二溴己烷)=1∶1 5∶3,80℃反应8h,收率达60 8%。两步总收率57 6%。目标化合物经IR,1HNMR和元素分析确证了分子结构。 相似文献
1000.
The effect of sodium montmorillonite source on the morphology and properties of nylon 6 nanocomposites was examined using equivalent experimental conditions. Sodium montmorillonite samples acquired from two well-known mines, Yamagata, Japan, and Wyoming, USA, were ion exchanged with the same alkyl ammonium chloride compound. The resulting organoclays were extruded with a high molecular weight grade of nylon 6 under the same processing conditions. Quantitative analysis of TEM photomicrographs of the two nanocomposites reveal a slightly larger average particle length and a slightly higher degree of platelet exfoliation for the Yamagata based nanocomposite than the Wyoming version, thus, translating into a higher particle aspect ratio. The stress-strain behavior of the nanocomposites appears to reflect the nanocomposite morphology, in that higher stiffness and strengths are attainable with the increased particle aspect ratio. Moreover, the trends in stiffness behavior between the two types of nanocomposites may be explained by conventional composite theory. 相似文献