全文获取类型
收费全文 | 24633篇 |
免费 | 2460篇 |
国内免费 | 1353篇 |
专业分类
电工技术 | 1464篇 |
技术理论 | 3篇 |
综合类 | 2099篇 |
化学工业 | 4213篇 |
金属工艺 | 1368篇 |
机械仪表 | 1315篇 |
建筑科学 | 1922篇 |
矿业工程 | 779篇 |
能源动力 | 566篇 |
轻工业 | 2663篇 |
水利工程 | 472篇 |
石油天然气 | 1148篇 |
武器工业 | 176篇 |
无线电 | 2473篇 |
一般工业技术 | 2798篇 |
冶金工业 | 1264篇 |
原子能技术 | 371篇 |
自动化技术 | 3352篇 |
出版年
2024年 | 104篇 |
2023年 | 354篇 |
2022年 | 734篇 |
2021年 | 874篇 |
2020年 | 702篇 |
2019年 | 596篇 |
2018年 | 619篇 |
2017年 | 733篇 |
2016年 | 651篇 |
2015年 | 978篇 |
2014年 | 1245篇 |
2013年 | 1555篇 |
2012年 | 1611篇 |
2011年 | 1721篇 |
2010年 | 1600篇 |
2009年 | 1543篇 |
2008年 | 1582篇 |
2007年 | 1470篇 |
2006年 | 1376篇 |
2005年 | 1142篇 |
2004年 | 990篇 |
2003年 | 951篇 |
2002年 | 1179篇 |
2001年 | 995篇 |
2000年 | 622篇 |
1999年 | 523篇 |
1998年 | 356篇 |
1997年 | 269篇 |
1996年 | 245篇 |
1995年 | 212篇 |
1994年 | 171篇 |
1993年 | 141篇 |
1992年 | 112篇 |
1991年 | 85篇 |
1990年 | 66篇 |
1989年 | 59篇 |
1988年 | 45篇 |
1987年 | 34篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
181.
Summary The ring-opening polymerization of 2-phenyl-1,3,-6,2-trioxaphosphocane (4), an eight-membered cyclic phosphonite, has been investigated. Cationic initiators of PhCH2-Cl and MeOTf gave polymers, whereas anionic and radical initiators did not yield polymer. The structure of polymer was examined by IR, 1H, 31P, and 31C NMR spectroscopy of polymers and elemental analysis as well as the alkaline hydrolysis products. The polymer consisted of two different units, i.e., the major part is the normal phosphinate structure 5 and the minor part is the isomerized unit 6 in 7% with PhCH2Cl initiation and in 34% with MeOTf initiator. The difference in nature of propagating species from these two initiators are discussed in connection with their reactivities.On leave from the Institute of Chemistry, Academia Sinica, Beijing, China 相似文献
182.
183.
FCC汽油降烯烃技术进展 总被引:21,自引:0,他引:21
介绍了近年来国内外FCC汽油降烯烃的技术进展,并对FCC汽油降烯技术及相关措施的未来应用前景进行了分析。 相似文献
184.
185.
过氧化脲可通过持续释放活性氧达到牙齿美白的目的,适用于各种原因引起的着色牙齿的美白。它可同时美白多个牙齿,美白效率高、费用低、使用方便和刺激性小,详细介绍了国内外专利配方及其使用效果;总结了国内外对过氧化脲牙齿美白剂的应用研究和对牙釉质、牙本质的影响;指出了国外研究的发展趋势,结合我国的实际情况对我国开发过氧化脲牙齿美白剂的方向提出了建议。 相似文献
186.
Langmuir吸附方程的应用 总被引:2,自引:0,他引:2
本文总结了Langmuir方程在吸附分离过程中的应用。利用Langmuir方程得到直观表达混合气组分气体间吸附强弱关系及分离的难易程度的x-y图,推导了Lewis关系式。 相似文献
187.
Recent laboratory research has indicated that coal fly ash derived from subbituminous and bituminous type coals is a sink for atmospheric mercury (Hg), however lignite-based ash was found to emit Hg to the air. Solids collected from systems with components that enhance Hg removal (i.e. activated carbon injection (ACI), flue gas desulfurization (FGD), and selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR)) may have higher Hg concentrations and therefore a higher potential for Hg release. For this study we investigated the potential for Hg release to the air and water from coal combustion products (CCPs) collected from coal-fired units with FGD equipment, SCR and SNCR equipment, and sorbent injection for Hg removal. In the laboratory study, most dry samples acted as sinks for atmospheric Hg in the dark at 25 °C. When exposed to light or increased temperature (45 °C), deposition of Hg to the fly ash substrates in most cases continued but decreased. Wet FGD samples emitted Hg. However, they became a sink for atmospheric Hg or exhibited low Hg emission rates when dried. Mercury flux in the dark at 25 °C was correlated with fly ash carbon content (LOI). Most liquid extracts derived using the synthetic precipitation leaching procedure (SPLP EPA method 1312) had very low Hg concentrations (<13 ng/l). 相似文献
188.
A novel aromatic amine organo‐modifier synthesized in our previous work was used to treat montmorillonite (MMT) and the organo‐modified MMT was used to prepare poly(etherimide) (PEI)/MMT nanocomposites by a melt intercalation method. MMT treated by this amine exhibited large layer‐to‐layer spacing and a high ion‐exchange ratio (>95%). The nanocomposites were characterized with X‐ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical analysis, a universal tester, thermogravimetric analysis, and by differential scanning calorimetry. The results of XRD and TEM showed that the nanocomposites formed exfoliated structures even when the MMT content was 10 wt %. When the MMT content was below 3 wt %, the PEI/MMT nanocomposites were strengthened and toughened at the same time. The nanocomposites also showed marked decreases in coefficient of thermal expansion and solvent uptake. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1857–1863, 2003 相似文献
189.
190.