全文获取类型
收费全文 | 34762篇 |
免费 | 3180篇 |
国内免费 | 2380篇 |
专业分类
电工技术 | 443篇 |
技术理论 | 1篇 |
综合类 | 1903篇 |
化学工业 | 17283篇 |
金属工艺 | 1973篇 |
机械仪表 | 434篇 |
建筑科学 | 805篇 |
矿业工程 | 475篇 |
能源动力 | 3424篇 |
轻工业 | 2962篇 |
水利工程 | 182篇 |
石油天然气 | 1688篇 |
武器工业 | 1286篇 |
无线电 | 1163篇 |
一般工业技术 | 3660篇 |
冶金工业 | 1295篇 |
原子能技术 | 704篇 |
自动化技术 | 641篇 |
出版年
2024年 | 126篇 |
2023年 | 984篇 |
2022年 | 1231篇 |
2021年 | 1381篇 |
2020年 | 1434篇 |
2019年 | 1383篇 |
2018年 | 1241篇 |
2017年 | 1295篇 |
2016年 | 1209篇 |
2015年 | 1267篇 |
2014年 | 1996篇 |
2013年 | 2182篇 |
2012年 | 2261篇 |
2011年 | 2493篇 |
2010年 | 1935篇 |
2009年 | 1996篇 |
2008年 | 1683篇 |
2007年 | 2066篇 |
2006年 | 1815篇 |
2005年 | 1546篇 |
2004年 | 1356篇 |
2003年 | 1211篇 |
2002年 | 963篇 |
2001年 | 848篇 |
2000年 | 749篇 |
1999年 | 642篇 |
1998年 | 477篇 |
1997年 | 410篇 |
1996年 | 381篇 |
1995年 | 318篇 |
1994年 | 293篇 |
1993年 | 231篇 |
1992年 | 206篇 |
1991年 | 134篇 |
1990年 | 119篇 |
1989年 | 91篇 |
1988年 | 60篇 |
1987年 | 62篇 |
1986年 | 31篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1980年 | 11篇 |
1964年 | 9篇 |
1961年 | 5篇 |
1959年 | 5篇 |
1957年 | 8篇 |
1955年 | 8篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A combinatorial process has been developed for the high throughput production and evaluation of surface coatings. The workflow designed for the production of arrays of liquid coatings involves the robotic transfer of aliquots of solutions of raw materials to an array of glass vials and mixing of the coatings using an unconventional magnetic stirring process. An investigation of the capability of the workflow to accurately and repeatedly prepare coating arrays was conducted as a function of solution viscosity and aliquot size. In addition, mixing capability was evaluated as a function of solution viscosity, total solution volume, and mechanism of stirring. Overall, the results of the study indicated that adequate accuracy and repeatability of the coating preparation process can be achieved as long as raw material solutions are designed such that viscosity is below about 250 cP and aliquot sizes are above about 75 μl. With regard to mixing capability, total solution volume was found to have a profound affect as did the stirring mechanism. 相似文献
32.
《无机及分析化学》在多媒体教学的应用及思考 总被引:1,自引:0,他引:1
对多媒体技术在无机及分析化学教学的应用进行了,阐述和分析,指出使用多媒体教学应注意的问题。 相似文献
33.
Nickel electrodes were prepared by electrodeposition in electrolytes of various anionic compositions. The deposition conditions and bath types were evaluated with special emphasis on the electrocatalytic properties for the oxygen evolution reaction (OER). Electrochemical characterizations in a 5 mol/L KOH solution at 25°C showed that the electrode deposited from the chloride bath, having a low Tafel slope of 50 mV/dec and an overpotential of 396 mV at 100 mA/cm2, is the most catalytically active among electrodes prepared in electrolytes of various anionic compositions. The electrode activity for the OER is related to the real surface areas, which depend on the anion compositions in the deposition bath and the deposition conditions. 相似文献
34.
George M. Campbell 《Chemical Engineering Communications》1990,98(1):223-230
The room temperature adsorption of PuF6(g) on a solid substrate was compared to the adsorption of UF6(g) on the same surface. Significantly more PuF6(g) was adsorbed at pressures in the range of 1.2 to 0.2torr, accompanied by the evolution of molecular fluorine. The adsorbed UF6 was easily desorbed by reducing the pressure. Most of the adsorbed PuF6 remained on the surface when subjected to the same treatment. 相似文献
35.
以枯草杆菌为菌种液体培养制备碱性磷酸酶,研究确定了培养的最佳工艺条件,并对碱性磷酸酶的酶促反应动力学性质进行了初步探讨。结果表明,枯草杆菌制备碱性磷酸酶的最佳工艺条件为:40℃,pH值7.4振荡培养10h,酶活最高。对碱性磷酸酶的动力学性质研究表明,该酶催化底物磷酸苯二钠水解反应的最适pH值8.8,最适温度52℃,米氏常数Km值为2.94mmol/L。 相似文献
36.
利用快速测长法研究了混合材对碱—碳酸盐反应的影响。通过试验证明混合材能减缓碱—碳酸盐反应的速度,但不能有效地抑制碱—碳酸盐反应,并初步探讨了混合材不能有效地抑制碱—碳酸盐反应的机理。 相似文献
37.
Guerbet十四醇的合成与表征 总被引:4,自引:1,他引:4
以正庚醇为原料 ,通过Guerbet反应合成Guerbet十四醇 (2 戊基壬醇 ,C14 GA)。用IR、NMR和元素分析测定了C14 GA的结构 ,并研究了反应温度和用料比对其产率的影响。实验结果如下 :(1)在较优化的反应条件下 (正庚醇的总加入量为 1mol,在实验过程中 ,先加入 1/ 3mol庚醇和 1/ 4mol的KOH ,在 16 0℃下反应 2h ,然后再加入剩下的 2 / 3mol庚醇和 4g 5 %Pd -C催化剂 ,在 15 5℃下反应 6h)合成产物 ,其产率可达到 5 4 2 0 % ;(2 )所合成的产物与试图要得到的Guerbet十四醇 (2 戊基壬醇 ,C14 GA)含有相同的基团 (2×—CH3、10×—CH2 —、1×CH、1×—CH2 —O—和 1×—OH) ,而且 ,所合成的产物中 ,w (C) =79 0 6 % ,w (H ) =13 6 2 % ,与从Guerbet十四醇分子式计算的理论值w(C) =78 5 0 % ,w (H) =14 0 1%基本一致。可见所合成的产物正是Guerbet十四醇 (C14 GA) 相似文献
38.
Studies were undertaken on the isolation and identification of reaction products of ammonium nitrate phosphate (ANP) fertilizers containing 30, 50 and 70 per cent water-soluble phosphorus (WSP) of total phosphorus in representative soils of the vertisol, oxisol, alfisol, entisol, mollisol and aridisol groups of India. ANP fertilizers were applied in solid form to soil, and reaction products formed at and around the site of ANP fertilizer placement were identified after six weeks incubation in moist soils by X-ray diffraction technique. DCPD (dicalcium phosphate dihydrate- CaHPO4 · 2H2O) was the major reaction product of ANP fertilizers containing 30 and 50 per cent WSP in vertisol, entisol, aridisol, mollisol, oxisol and alfisol, and of ANP containing 70 per cent WSP in vertisol, entisol, alfisol, aridisol and mollisol. DCP (dicalcium phosphate-CaHPO4) was detected with ANP of 30 and 50 per cent WSP in the vertisol, alfisol, entisol, mollisol and aridisol groups of soils. In addition to DCPD, FePO4 · 2H2O (metastrengite) and AlPO4 · 2H2 O-monoclinic (metavariscite) were formed in alfisol and oxisol soils with ANP of 30 and 50 per cent WSP. FePO4 · 2H2O and AlPO4 · 2H2O (metavariscite) were identified in alfisol and oxisol soils while AlPO4 · 2H2O-orthorhombic (variscite) was formed in alfisol soils with ANP of 70 per cent WSP. 相似文献
39.
The polyesterification and isomerization reaction of 1,6-hexane diol and maleic anydride in a melt without catalyst was studied by 13C and 1H n.m.r. spectroscopy. The structure and concentration of oligoester species during the polyesterification and isomerization were determined depending on the reaction temperature and time. According to the number and configuration of repeating units determined from 1H n.m.r. spectra kinetics of both reactions were also considered. The degree of isomerization is continuously increasing in the investigated reaction range. 相似文献
40.
甲酸甲酯合成与转化的催化技术 总被引:3,自引:0,他引:3
本文评述了甲酸甲酯(MF)合成与转化的催化技术,展示了从MF出发发展C_1化学的可能途径,在MF的合成方面详细地分析了从甲醇出发的羰化法、脱氢法和氧化法催化技术,简介了我们的有关研究工作。 相似文献