全文获取类型
收费全文 | 8682篇 |
免费 | 1314篇 |
国内免费 | 446篇 |
专业分类
电工技术 | 154篇 |
综合类 | 526篇 |
化学工业 | 3663篇 |
金属工艺 | 492篇 |
机械仪表 | 367篇 |
建筑科学 | 275篇 |
矿业工程 | 121篇 |
能源动力 | 193篇 |
轻工业 | 1099篇 |
水利工程 | 40篇 |
石油天然气 | 644篇 |
武器工业 | 99篇 |
无线电 | 604篇 |
一般工业技术 | 1534篇 |
冶金工业 | 193篇 |
原子能技术 | 84篇 |
自动化技术 | 354篇 |
出版年
2024年 | 35篇 |
2023年 | 170篇 |
2022年 | 222篇 |
2021年 | 275篇 |
2020年 | 320篇 |
2019年 | 304篇 |
2018年 | 264篇 |
2017年 | 340篇 |
2016年 | 529篇 |
2015年 | 565篇 |
2014年 | 634篇 |
2013年 | 686篇 |
2012年 | 605篇 |
2011年 | 668篇 |
2010年 | 443篇 |
2009年 | 524篇 |
2008年 | 397篇 |
2007年 | 539篇 |
2006年 | 459篇 |
2005年 | 416篇 |
2004年 | 324篇 |
2003年 | 271篇 |
2002年 | 233篇 |
2001年 | 198篇 |
2000年 | 188篇 |
1999年 | 116篇 |
1998年 | 115篇 |
1997年 | 96篇 |
1996年 | 102篇 |
1995年 | 67篇 |
1994年 | 60篇 |
1993年 | 47篇 |
1992年 | 49篇 |
1991年 | 30篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
纳米碳酸钙的制备及表征 总被引:4,自引:0,他引:4
研究了以氧化钙和二氧化碳为原料,化学法制备纳米碳酸钙的工艺条件、添加剂的影响及形态。结果表明:中间体氢氧化钙的初始浓度、二氧化碳的流量、反应温度、搅拌速度及添加剂等在控制制备纳米碳酸钙颗粒的形状和尺寸中均十分重要。透射电镜观察结果表明:通过控制反应及添加剂,可以得到尺寸规整的链锁形、纺锤形和球形纳米碳酸钙。表面能谱证实产品为高纯的碳酸钙。X射线衍射和电子衍射的结果进一步表明:所制纳米碳酸钙均属方解石型六方晶系,a0=0.498 9 nm,c0=1.706 2 nm;为多晶结构。 相似文献
103.
104.
以碳酸钠作缚酸剂,1,6-二溴-2-萘氧乙酰肼(2)与芳酰氯反应制得N,N'-二酰基肼,后者在voch作用下,脱水环化成2-(1,6-二溴-2-萘氧甲基)-5-芳基-1,3,4-噁二唑类化合物。其结构经元素分析、IR、1^HNMB和MS表征。 相似文献
105.
本研究旨在制备两种琉璃苣叶水溶性多糖,进一步探究其结构特征,并评价其降血糖、抗癌和免疫活性。采用纤维素酶辅助提取(BLP-1)和微波辅助提取法(BLP-2)制备琉璃苣叶水溶性多糖,并比较了BLP-1和BLP-2的理化性质,通过分析α-葡萄糖苷酶和α-淀粉酶的抑制效果来评价BLP-1和BLP-2的降血糖活性,通过检测HepG2、MX-1和A549细胞的抑制率来评价抗癌活性,通过检测RAW246.7的免疫因子分泌来评价免疫活性。结果表明,BLP-1和BLP-2具有不同的多糖和蛋白质含量。BLP-1和BLP-2由阿拉伯糖(Ara)、半乳糖(Gal)、葡萄糖(Glc)、木糖(Xyl)组成,但摩尔比组成不同,其分子量分别为20.1和22.6KDa。热重分析(TGA)表明BLP-2比BLP-1具有更稳定的结构。这两种多糖具有抑制α-葡萄糖苷酶和α-淀粉酶活性、抑制HepG-2、A549和MX-1癌细胞增殖以及激活巨噬细胞RAW 264.7细胞分泌免疫细胞因子以介导细胞免疫反应的潜力。两种多糖可作为新功能食品和医药产品中的生物活性成分,为进一步研究两种多糖的构效关系提供了理论依据。 相似文献
106.
Javier Viguri Raquel Onandí a Roberto Arce Angel Irabien 《Chemical Engineering Communications》2005,192(11):1490-1504
In the present study the characterization and distillation of alkyd paint waste have been carried out in order to establish the technical viability of organic solvents recovery and to decide upon the best environmental management for the waste stream from a paint spray-booth application in an automotive component factory. The paint is a black primer based on an alkyd resin with toluene and xylene as solvents, black carbon as pigment, fillers, and other minor components.
The paint, paint wastes, and distillation wastes have been characterized by determination of the physicochemical properties of the solid (solvents content and flash point) and determination of ecotoxicity (EC50), total organic carbon (TOC), and metals concentration of the leachates. The highly volatile matter (HVM) content, determined by the weight loss at 200°C, has been used as a parameter to relate with the hazardous wastes regulations based on the characterization parameters EC50, TOC, and flash point.
Distillation experiments have been performed in a simple batch mode with mixtures of paint waste, water, and additives in order to obtain high efficiencies in the recovery of volatile organic compounds and to obtain a final solid with nonhazardous behavior and good manageability qualities. A fractional factorial design (23-1) of experiments was carried out in order to study the influence of the distillation variables: water/paint waste ratio (2/1-3/1 (g/g)), temperature (110°-145°C), alkaline additives (Na(OH),CaO, Ca(OH)2), and amount of other additives (wt.% of bentonite, cement, and Ca(OH)2) on the solvent recovery, [% VOCs]Recovery, on the residual volatile organic compounds, [% VOCs]Distillation Waste, and on the total organic content (TOC) of the waste leachates. The present work shows the quantitative results of the alkyd paint waste distillation process under optimum conditions. 相似文献
The paint, paint wastes, and distillation wastes have been characterized by determination of the physicochemical properties of the solid (solvents content and flash point) and determination of ecotoxicity (EC50), total organic carbon (TOC), and metals concentration of the leachates. The highly volatile matter (HVM) content, determined by the weight loss at 200°C, has been used as a parameter to relate with the hazardous wastes regulations based on the characterization parameters EC50, TOC, and flash point.
Distillation experiments have been performed in a simple batch mode with mixtures of paint waste, water, and additives in order to obtain high efficiencies in the recovery of volatile organic compounds and to obtain a final solid with nonhazardous behavior and good manageability qualities. A fractional factorial design (23-1) of experiments was carried out in order to study the influence of the distillation variables: water/paint waste ratio (2/1-3/1 (g/g)), temperature (110°-145°C), alkaline additives (Na(OH),CaO, Ca(OH)2), and amount of other additives (wt.% of bentonite, cement, and Ca(OH)2) on the solvent recovery, [% VOCs]Recovery, on the residual volatile organic compounds, [% VOCs]Distillation Waste, and on the total organic content (TOC) of the waste leachates. The present work shows the quantitative results of the alkyd paint waste distillation process under optimum conditions. 相似文献
107.
Analysis of the polyethylene glycol glucosides and FA esters thereof by atmospheric-pressure ionization MS 总被引:1,自引:0,他引:1
Xin?Jin Jinzong?YangEmail author Bingtao?Tang Minggui?Zhu Ning?Yu Yi?Liu 《Journal of the American Oil Chemists' Society》2003,80(6):519-524
Polyethylene glycol (PEG) glucosides (PEGG) and the PEGG esters of lauric acid were analyzed by atmospheric-pressure ionization
MS (API-MS) with electrospray ionization. Straightforward mass characterization of the complex mixtures could be achieved
without prior chromatographic separation. The constituents were identified on the basis of quasi-molecular ions. Individual
components could be observed as protonated molecular ions [M+H]+ and/or as their NH4
+, Na+, or K+ adducts in positive ion mode. The mass spectrometric investigation showed that mixtures of PEGG consisted of monoglucoside,
diglucoside, polyglucoside, and free PEG. The esterification product is a mixture of two types of nonionic surfactants: PEG-laurates
and PEGG-laurates. The reasons for distortion of the quasi-molecular ion intensities and the stabilization of adduct ions
were discussed. The rapid and highly sensitive API-MS analysis technique proposed here is well suited for direct characterization
of complex mixtures and suitable for development as a routine analytical method. 相似文献
108.
改性磁性壳聚糖微球的制备、表征及性能研究 总被引:3,自引:0,他引:3
以(NH4)2Fe(SO4)2.6H2O、NH4Fe(SO4)2.12H2O和壳聚糖为原料,经羟丙基化、胺基化,采用一步包埋法制备了一种新型的多胺基化磁性壳聚糖微球。通过正交实验法确定了磁性微球的最佳制备条件,即搅拌速度1200r/min,壳聚糖用量3.0g,环氧氯丙烷用量2.5mL,乙二胺用量2.5mL。并用IR、TG、XRD和SEM对其结构及形貌进行了表征。结果表明,Fe3O4磁性粒子已包埋了一层胺基化壳聚糖。磁性微球胺基含量为2.302mmol/g;呈较规则的球形,平均粒径为209nm,且具有顺磁性和良好的耐酸性。 相似文献
109.
A metric of the 3D image quality of autostereoscopic displays based on optical measurements is proposed. This metric uses each view's luminance contrast, which is defined as the ratio of maximum luminance at each viewing position to total luminance at that position. Conventional metrics of the autostereoscopic display based on crosstalk, which uses “wanted” and “unwanted” lights. However, in case of the multiple‐views‐type autostereoscopic displays, it is difficult to distinguish exactly which lights are wanted lights and which are unwanted lights. This paper assumes that the wanted light has a maximum luminance at the good stereoscopic viewing position, and the unwanted light also has a maximum luminance at the worst pseudo‐stereoscopic viewing position. By using the maximum luminance that is indexed by view number of the autostereoscopic display, the proposed method enables characterizing stereoscopic viewing conditions without using wanted/unwanted light. A 3D image quality metric called “stereo luminance contrast,” the average of both eyes' contrast, is proposed. The effectiveness of the proposed metric is confirmed by the results of optical measurement analyses of different types of autostereoscopic displays, such as the two‐view, scan‐backlight, multi‐view, and integral. 相似文献
110.
Variable temperature13C MAS NMR spectra are reported for13CO-enriched KFe2Mn(CO)12 as a solid and also as dispersed clusters on a carbon support. The spectrum of KFe2Mn(CO)12 at 300 K agrees with the proposed structure for this cluster and shows that the cluster is static. Two bridging carbonyl resonances are clearly resolved and, by comparison with13C MAS NMR spectra of Mn2(CO)10 and Fe2(CO)9, all terminal resonances for the cluster can be assigned. When the cluster is supported on carbon, two broad resonances are observed at room temperature which are assignable to KFe2Mn(CO)12 and a decomposition product, Mn2(CO)10. The carbonyl ligands in both supported clusters are completely averaged, and KFe2Mn(CO)12 on the carbon surface demonstrates fluxional behavior similar to that observed for the cluster in solution. For this fluxional process, activation energies of 0.6 kcal/mol and 0.5 kcal/mol are estimated for carbon-supported KFe2Mn(CO)12 and Mn2(CO)10, respectively. 相似文献