全文获取类型
收费全文 | 35080篇 |
免费 | 2348篇 |
国内免费 | 1481篇 |
专业分类
电工技术 | 511篇 |
技术理论 | 1篇 |
综合类 | 2338篇 |
化学工业 | 19267篇 |
金属工艺 | 1405篇 |
机械仪表 | 758篇 |
建筑科学 | 224篇 |
矿业工程 | 323篇 |
能源动力 | 782篇 |
轻工业 | 1287篇 |
水利工程 | 41篇 |
石油天然气 | 1859篇 |
武器工业 | 447篇 |
无线电 | 1777篇 |
一般工业技术 | 5108篇 |
冶金工业 | 641篇 |
原子能技术 | 157篇 |
自动化技术 | 1983篇 |
出版年
2024年 | 47篇 |
2023年 | 364篇 |
2022年 | 540篇 |
2021年 | 781篇 |
2020年 | 710篇 |
2019年 | 675篇 |
2018年 | 705篇 |
2017年 | 834篇 |
2016年 | 1020篇 |
2015年 | 1032篇 |
2014年 | 1687篇 |
2013年 | 1706篇 |
2012年 | 2168篇 |
2011年 | 2712篇 |
2010年 | 2035篇 |
2009年 | 2258篇 |
2008年 | 1939篇 |
2007年 | 2510篇 |
2006年 | 2275篇 |
2005年 | 2092篇 |
2004年 | 1710篇 |
2003年 | 1586篇 |
2002年 | 1426篇 |
2001年 | 1175篇 |
2000年 | 1022篇 |
1999年 | 819篇 |
1998年 | 672篇 |
1997年 | 467篇 |
1996年 | 401篇 |
1995年 | 331篇 |
1994年 | 299篇 |
1993年 | 232篇 |
1992年 | 169篇 |
1991年 | 120篇 |
1990年 | 107篇 |
1989年 | 56篇 |
1988年 | 46篇 |
1987年 | 32篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
171.
The effect of tetramethylammonium cations (TMA+) on TiO2 crystal morphology in hydrothermal conditions has been studied. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. The morphologies including besom-like particle, nanosheet and nanotube have been observed. The different ways TMA+ cations in the hydrothermal bases affect the crystal growth manner are suggested to be responsible for the different morphologies of the as-synthesized samples. 相似文献
172.
Template-free nanosized ZSM-5 seeds with an average size of 15 nm were prepared from a synthesis solution with the composition 12Na2O:100SiO2:2Al2O3:2500H2O. By the use of these seeds, thin ZSM-5 zeolite membranes were prepared on the outer surface of a porous α-alumina tube with a pore size of 2 μm in a gel system by varying-concentration synthesis with organic-free template. The first composition synthesis sol-gel was the same as seeds of molar composition and the second one was 12Na2O:100SiO2:2Al2O3:5000H2O at 180 ℃ for 10 h, respectively. XRD shows that the film consists of well-crystallized ZSM-5 zeolite. SEM investigation indicats that the zeolite films on the supports are defect free and the film thickness is approximately 8 μm. The permeances for H2, N2, CH4 and CO2 are 8.94×10-7 , 3.27×10-7 , 3.9×10-7 , 3.14×10-7 and 0.874×10-7 mol·m2·s-1·Pa-1 , respectively. The ideal selectivity of membrane at room temperature for H2/CO2, H2/N2, H2/CH4 are 2.84, 2.73 and 2.29, respectively. 相似文献
173.
端基封闭法合成双环戊二烯改性不饱和聚酯 总被引:13,自引:0,他引:13
研究端基封闭法合成双环戊二烯(DCPD)改性不饱和聚能工艺条件对产品性能的影响。研究结果表明,合成反应的最佳工艺条件为总酸酐:丙二醇:DCPD=1:1.1:0.1─0.16;封端反应温度130─140℃催化剂量为总重量的0.02%─0.03%;聚酯酸值50mgkOH·g ̄(-1)时滴加DCPD,滴加时间控制在1─2小时;加成反应时间为2小时左右。 相似文献
174.
175.
176.
疏水缔合型聚丙烯酰胺的合成与性能评价 总被引:1,自引:0,他引:1
为了提高高相对分子质量的聚丙烯酰胺的抗温抗盐性能,利用自制的两亲表面活性单体与丙烯酰胺共聚合成了疏水缔合型聚丙烯酰胺并进行室内评价。结果表明,在高温、高盐、高钙条件下,合成的疏水缔合型聚丙烯酰胺具有良好的增粘性和较强的热稳定性;克服了疏水缔合型聚合物在盐水中溶解性差的问题,可用各种矿化度的盐水和油田产出污水配制;具有良好的无机盐增粘性能和抗温性能。 相似文献
177.
N,N′-二(β-十八酰氧基)乙基乙二胺二乙酸钠的合成及性能研究 总被引:1,自引:1,他引:0
用 N,N′-二羟乙基乙二胺、氯乙酸钠合成了 N,N′-二羟乙基乙二胺二乙酸钠(中间体),中间体再与硬脂酰氯反应制备了一种新型 Gemini 两性表面活性剂 N,N′-二(β-十八酰氧基)乙基乙二胺二乙酸钠。对产物合成条件进行了考察,优化的反应条件为:n(硬脂酰氯):n(中间体)=2.5,溶剂 V(水):V(氯仿)=1:2,pH=9.0~10.0,反应温度15~20℃,反应时间5 h。通过红外光谱和质谱分析确定了产物结构,并测试了产物的表面性能。结果表明,在25℃时,该产物的临界胶束浓度为0.24 mmol/L,临界胶束浓度下的表面张力为35.7 mN/m;即时泡沫高度为250 mm,5 min 后泡沫高度为220 mm;乳化时间为22.48 min(甲苯-水物系)和4.65 min(正己烷-水物系),亲水-亲油平衡值为5.4,等电点为 pH 3.3~6.5。 相似文献
178.
以硫脲和水合肼合成了可用于检验醛的试剂——4-氨基-3-肼基-5-巯基-1,2,4-三唑(别名:紫醛),其结构通过红外光谱、核磁进行了确定。试验表明,紫醛对醛的检验敏感、专一、快速、操作简单。 相似文献
179.
180.
A method for the synthesis of novel sulfated ionomer of styrene–butadiene–styrene triblock copolymer (SBS) was developed. SBS was first epoxidized by performic acid in the presence of a phase‐transfer catalyst; this was followed by a ring‐opening reaction with an aqueous solution of alkali salt of bisulfate. The optimum conditions for the ring‐opening reaction of the epoxidized SBS with an aqueous solution of KHSO4 were studied. During the ring‐opening reaction, both phase‐transfer catalyst and ring‐opening catalyst were necessary to enhance the conversion of epoxy groups to ionic groups. The products were characterized with Fourier transform infrared spectrophotometry and transmission electron microscopy (TEM). After the potassium ions of the ionomer were substituted with lead ions, the lead sulfated ionomer exhibited dark spots under TEM. Some properties of the sulfated ionomer were studied. With increasing ionic groups or ionic potential of the cations, the water absorbency and emulsifying volume of the ionomer and the intrinsic viscosity of the ionomer solution increased, whereas the oil absorbency decreased. The sulfated ionomer possessed excellent emulsifying properties compared with the sulfonated SBS ionomer. The sodium sulfated ionomers in the presence of 10% zinc stearate showed better mechanical properties than the original SBS. When the ionomer was blended with crystalline polypropylene, a synergistic effect occurred with respect to the tensile strength. The ionomer behaved as a compatibilizer for blending equal amounts of SBS and oil‐resistant chlorohydrin rubber. In the presence of 3% ionomer, the blend exhibited much better mechanical properties and solvent resistance than the blend without the ionomer. SEM photographs indicated improved compatibility between the two components of the blend in the presence of the ionomer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献