全文获取类型
收费全文 | 5381篇 |
免费 | 459篇 |
国内免费 | 202篇 |
专业分类
电工技术 | 11篇 |
综合类 | 328篇 |
化学工业 | 3384篇 |
金属工艺 | 115篇 |
机械仪表 | 41篇 |
建筑科学 | 57篇 |
矿业工程 | 91篇 |
能源动力 | 50篇 |
轻工业 | 439篇 |
水利工程 | 26篇 |
石油天然气 | 1004篇 |
武器工业 | 19篇 |
无线电 | 67篇 |
一般工业技术 | 347篇 |
冶金工业 | 48篇 |
原子能技术 | 3篇 |
自动化技术 | 12篇 |
出版年
2024年 | 6篇 |
2023年 | 54篇 |
2022年 | 77篇 |
2021年 | 87篇 |
2020年 | 103篇 |
2019年 | 139篇 |
2018年 | 122篇 |
2017年 | 163篇 |
2016年 | 198篇 |
2015年 | 174篇 |
2014年 | 267篇 |
2013年 | 310篇 |
2012年 | 383篇 |
2011年 | 339篇 |
2010年 | 288篇 |
2009年 | 290篇 |
2008年 | 243篇 |
2007年 | 368篇 |
2006年 | 366篇 |
2005年 | 338篇 |
2004年 | 282篇 |
2003年 | 269篇 |
2002年 | 254篇 |
2001年 | 182篇 |
2000年 | 175篇 |
1999年 | 139篇 |
1998年 | 119篇 |
1997年 | 60篇 |
1996年 | 55篇 |
1995年 | 48篇 |
1994年 | 33篇 |
1993年 | 25篇 |
1992年 | 34篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1984年 | 4篇 |
1980年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有6042条查询结果,搜索用时 484 毫秒
1.
2.
3.
4.
This study assessed the collection efficiency (CE) of two popularly used sampling devices (BioSampler and Coriolis sampler) for fungal aerosols. Phosphate‐buffered saline (PBS) supplemented with or without surfactant (Tween‐20, Tween‐80, or Triton X‐100) and antifoam agent was prepared and used as collection liquids. The agar impactor (BioStage) was simultaneously operated with liquid‐based samplers to collect fungi from seven sites located at a university building, public library, and animal farming. Fungal concentrations determined by liquid samplers were divided by those by BioStage, and the ratio values represented CE. Results indicate that the CE of BioSampler was superior to that of Coriolis (P = 0.0001) and the PBS containing surfactant collected fungi better than that without surfactant (P < 0.0001), whereas antifoam agent showed no influence (P = 0.8). Moreover, fungal concentrations determined by BioSampler with surfactant‐added PBS were statistically indifferent from those by BioStage (P > 0.05) with a Spearman correlation coefficient of 0.81‐0.83 (P < 0.01). In addition to sampler and collection liquid, sampling location was also identified as a significant CE factor (P = 0.006), implying potential influences by fungal genera in the studied fields. Overall, BioSampler with surfactant‐supplemented PBS (eg, Triton X‐100) is recommended considering the great CE and compatibility with a variety of analytical assays. 相似文献
5.
以马来酸酐和2-丁基辛醇为原料,经酯化得到相应的双酯,以乙醇作混相促进剂,使双酯与亚硫酸氢钠进行磺化反应,合成了磺基琥珀酸双2-丁基辛酯钠盐。采用正交试验对酯化反应条件进行了优化。合成产物的临界胶束浓度(cmc)值为3.58×10-6mol/L,表面张力(γcmc)为27.568mN/m。 相似文献
6.
清洁压裂液在煤层气井压裂中的应用 总被引:5,自引:0,他引:5
清洁压裂液自1997年首次被斯伦贝谢公司研制出以来,已经在国内外油气井的压裂改造中取得了良好的效果。由于清洁压裂液易于彻底破胶、流变性好、携砂能力强,可以提高压裂规模且对地层伤害较小,中联煤层气有限责任公司在陕西省韩城地区选用清洁压裂液对煤层进行了压裂试验,共压裂3口井、8层煤层,施工成功率100%,并取得了良好的压裂效果,压完后的火把高度2~4 m,平均砂比均在30%以上,最高单层加砂68 m3,压后放喷液显示完全破胶(未添加任何破胶剂),放喷初期黏度一般低于10 mPa·s,放喷4 h后黏度均低于5 mPa·s。此次清洁压裂液成功应用于煤层压裂改造在国内外尚属首次,为大规模改造煤层同时尽量降低煤层伤害提供了一条新的途径,文章对清洁压裂液及煤层特点所做的室内研究情况及现场应用情况进行了详细的介绍。 相似文献
7.
高分子表面活性剂对超声辐照下苯乙烯乳液聚合的影响 总被引:1,自引:0,他引:1
在超声辐照引发苯乙烯乳液聚合中加入一种新型的以羧甲基纤维素为基础的高分子表面活性剂(CMC—A9),讨论了高分子表面活性剂对反应动力学的影响。实验表明,超声辐照下初级自由基并非由通常认为的高分子表面活性剂产生,而是十二烷基硫酸钠在超声辐照下断裂,产生自由基。通过对反应动力学的研究,发现超声辐照下乳液聚合机理不同于常规乳液聚合,聚合反应过程只有两个阶段,即加速期和减速期,不存在恒速期。加入CMC—A9高分子表面活性剂,可以在较短的时间内和较低的超声功率下达到较高的单体转化率。 相似文献
8.
十二酰胺丙基二甲基羟乙基氯化铵与十二烷基硫酸钠水溶液的表面吸附和胶束形成 总被引:1,自引:0,他引:1
利用十二酰胺丙基二甲胺和氯乙醇反应 ,合成了十二酰胺丙基二甲基羟乙基氯化铵 (DDHA)阳离子表面活性剂 ,将其与十二烷基硫酸钠 (SDS)以不同摩尔比进行混合 ,测定了混合系统的表面张力 ,计算了单一系统和混合系统的饱和吸附量、分子最小截面积 ,表面层和胶束中 DDHA的摩尔分率及分子间相互作用参数 ,目视观察了混合系统的浑浊情况。结果表明 :在降低γcmc和 cmc方面 ,DDHA SDS混合系统有协同效应 ,表面层和胶束的组成与二组分配比有关 ,但是非对称的 ,等物质的量混合物中 ,DDHA在胶束和表面层中具有较大的摩尔分数。DDHA与 SDS在实验测定的各混合系统中都不出现混浊 相似文献
9.
BaMgAl10O17∶Eu2 (BAM) was prepared in the microemulsion system and its phase behavior was studied. There exists a small region in the reverse microemulsion system where the dispersed particles are of spherical form. In this way, BAM blue phosphor with good dispersion can be synthesized. The microemulsion phase diagrams of the pseudo-ternary system (Triton X-100/cosurfactant-oil-BAM brine) were first established intuitively by the dilution method. The microstructure of microemulsions was determined through eyeballing, conductance technique, and polar optical microscopy. Its phase behavior is affected by various factors, such as temperature (room temperature, 30, 40 ℃), oil, surfactants, and cosurfactants in microemulsions. According to the phase diagrams, the microemulsion system of Triton X-100/1-hexanol-hexane-BAM brine was chosen to prepare the precursor. The BAM phosphor can be obtained via sintering the precursor at a comparatively low temperature. The phosphors were characterized by XRD and vacuum ultraviolet (VUV) spectra. 相似文献
10.
Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non‐ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69–6.82 MPa and the temperature range 274.05–277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non‐ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献