全文获取类型
收费全文 | 35641篇 |
免费 | 2754篇 |
国内免费 | 1803篇 |
专业分类
电工技术 | 1201篇 |
综合类 | 2049篇 |
化学工业 | 11720篇 |
金属工艺 | 5244篇 |
机械仪表 | 2644篇 |
建筑科学 | 1231篇 |
矿业工程 | 817篇 |
能源动力 | 1905篇 |
轻工业 | 3401篇 |
水利工程 | 329篇 |
石油天然气 | 1672篇 |
武器工业 | 210篇 |
无线电 | 1448篇 |
一般工业技术 | 3950篇 |
冶金工业 | 1574篇 |
原子能技术 | 303篇 |
自动化技术 | 500篇 |
出版年
2024年 | 154篇 |
2023年 | 692篇 |
2022年 | 920篇 |
2021年 | 1117篇 |
2020年 | 1216篇 |
2019年 | 1120篇 |
2018年 | 1046篇 |
2017年 | 1162篇 |
2016年 | 1117篇 |
2015年 | 1124篇 |
2014年 | 1754篇 |
2013年 | 2139篇 |
2012年 | 2054篇 |
2011年 | 2469篇 |
2010年 | 1798篇 |
2009年 | 2115篇 |
2008年 | 1822篇 |
2007年 | 2299篇 |
2006年 | 2077篇 |
2005年 | 1741篇 |
2004年 | 1480篇 |
2003年 | 1299篇 |
2002年 | 1110篇 |
2001年 | 1017篇 |
2000年 | 889篇 |
1999年 | 614篇 |
1998年 | 604篇 |
1997年 | 500篇 |
1996年 | 485篇 |
1995年 | 336篇 |
1994年 | 309篇 |
1993年 | 261篇 |
1992年 | 248篇 |
1991年 | 205篇 |
1990年 | 182篇 |
1989年 | 106篇 |
1988年 | 82篇 |
1987年 | 71篇 |
1986年 | 59篇 |
1985年 | 60篇 |
1984年 | 62篇 |
1983年 | 24篇 |
1982年 | 51篇 |
1981年 | 37篇 |
1980年 | 33篇 |
1979年 | 25篇 |
1978年 | 25篇 |
1977年 | 22篇 |
1976年 | 17篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
异丙苯在Cu-HMS分子筛上的催化氧化 总被引:3,自引:2,他引:1
以含Cu的中孔分子筛(Cu-HMS)为催化剂,研究异丙苯的催化氧化。研究发现,Cu-HMS催化剂的加入使异丙苯氧化的诱导期显著缩短。在75℃下,以Cu-HMS为催化剂,O2为氧化剂的纯异丙苯氧化反应,苯乙酮为主要副产物,反应的选择性和转化率都很高。当催化剂用量为1 5×10-4mol/ml时,反应8h后,异丙苯转化率为32 7%,目的产物的累积浓度(质量分数)为37 7%,选择性为99%;反应12h后,异丙苯转化率为42 4%,目的产物的累积浓度为46 3%,选择性为95 6%。 相似文献
62.
Two commercial Pt modified aluminide coatings (RT22 and MDC150L) on the same single crystal Ni-based superalloy (CMSX-4) were studied by: scanning electron microscopy; transmission electron microscopy; energy dispersive X-ray spectrometry; and gravimetry. The RT22 coating is an inward grown coating (high activity), while MDC150L is produced by outward growth (low activity). Samples were oxidised in still laboratory air at 1050 °C for various times up to 2000 h. It was found that the outward grown coating produced a slower growing oxide that was more spallation resistant. Several possible reasons for this were identified including: coating purity; coating surface topography; and ductile to brittle transition temperature. The microstructural differences between the two coatings in the as-coated condition were investigated and the development of their microstructure during heat treatment was described. A model for coating growth during heat treatment was proposed. 相似文献
63.
重载齿轮齿面疲劳损坏及预防 总被引:1,自引:0,他引:1
丁守祥 《兵器材料科学与工程》2002,25(1):49-52
点蚀和剥落是重载齿轮齿面疲劳损坏最普遍的形式.根据齿轮失效分析实例,对齿面初始点蚀、破坏性点蚀和齿面剥落等三种主要疲劳损坏的特征、发生部位及破损危害程度进行了分析研究,较系统地论述了齿轮接触疲劳破坏机理,影响因素及其产生原因,并对有关的齿面破坏提出了相应的预防措施. 相似文献
64.
65.
提出了一种具有特殊运转方式的新型RBC系统--回转升降生物接触工艺,对回转升降生物接触工艺的工作原理和工艺特征进行了论述。并通过动态实验,对回转升降生物接触工艺小型实验装置的性能和效果进行了初步考察。 相似文献
66.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献
67.
In order to enhance product yields in selective oxidation reactions, numerous reaction engineering concepts are being studied worldwide. Periodic operation has been investigated for decades, yet its application is limited to a few examples, such as the butane oxidation after DuPont or reverse-flow reactors for VOC removal. The use of microchannel reactors is a younger field, but it has already yielded promising results for process optimization. Catalytic wall reactors have proved to be a helpful tool for kinetic studies. On the laboratory scale, membrane reactors have displayed favorable behavior in selective oxidation. The Na vapor-catalyzed dehydrogenation of methanol to formaldehyde is a final example of an unusual new concept for selective oxidation. 相似文献
68.
69.
PENGLiming MAOXiemin XUKuangdi DINGWenjiang 《稀有金属(英文版)》2002,21(1):62-66
In order to develop a new type of contact cable with high strength and high electrical conductivity, Cu-Cr alloy series were selected as materials and Cu-Cr alloy castings were produced by means of directional solidification continuous casting (DSCC) process. The results show that the fibrillar strengthening phase, 13-Cr, orderly arranges among the copper matrix phase along the wire direction; and a microstructure of in-situ composite forms, which retains the basic property of good conductivity of the copper matrix and meanwhile obtains the strengthening effect of [3-Cr phase. The production technology as well as the mechanical property, electrical property, and synthetic property of the in-situ composite contact cables was discussed. 相似文献
70.
Behaviour of a series of lubricant oils and the effect of a non stoichiometric inorganic compound, as solid extreme pressure additive, on rolling fatigue life are studied using the rolling four-ball accelerated service simulation test proposed by Barwell and Scott. The results show, in all tested cases, the remarkable efficacy of this type of additive. The Total Acidity Number (tan) was found to increase with performance time for the case of the base lubricant, while for the oils with additives, it remained at its constant low value. This led to a proposal of a possible mechanism of the additive performance in the rolling process. 相似文献