全文获取类型
收费全文 | 43529篇 |
免费 | 2851篇 |
国内免费 | 1721篇 |
专业分类
电工技术 | 2186篇 |
综合类 | 3722篇 |
化学工业 | 13452篇 |
金属工艺 | 2526篇 |
机械仪表 | 2324篇 |
建筑科学 | 1556篇 |
矿业工程 | 1282篇 |
能源动力 | 1070篇 |
轻工业 | 2402篇 |
水利工程 | 388篇 |
石油天然气 | 4053篇 |
武器工业 | 305篇 |
无线电 | 3440篇 |
一般工业技术 | 2526篇 |
冶金工业 | 2430篇 |
原子能技术 | 672篇 |
自动化技术 | 3767篇 |
出版年
2024年 | 140篇 |
2023年 | 524篇 |
2022年 | 1198篇 |
2021年 | 1401篇 |
2020年 | 1082篇 |
2019年 | 728篇 |
2018年 | 780篇 |
2017年 | 1010篇 |
2016年 | 1034篇 |
2015年 | 1007篇 |
2014年 | 2378篇 |
2013年 | 2172篇 |
2012年 | 2825篇 |
2011年 | 2524篇 |
2010年 | 2075篇 |
2009年 | 2467篇 |
2008年 | 2451篇 |
2007年 | 3478篇 |
2006年 | 3685篇 |
2005年 | 2753篇 |
2004年 | 1636篇 |
2003年 | 1835篇 |
2002年 | 1423篇 |
2001年 | 1274篇 |
2000年 | 1177篇 |
1999年 | 1055篇 |
1998年 | 771篇 |
1997年 | 596篇 |
1996年 | 485篇 |
1995年 | 397篇 |
1994年 | 328篇 |
1993年 | 260篇 |
1992年 | 222篇 |
1991年 | 166篇 |
1990年 | 130篇 |
1989年 | 80篇 |
1988年 | 81篇 |
1987年 | 73篇 |
1986年 | 53篇 |
1985年 | 77篇 |
1984年 | 61篇 |
1983年 | 28篇 |
1982年 | 35篇 |
1981年 | 23篇 |
1980年 | 32篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
莫达非尼的绿色化学合成 总被引:1,自引:0,他引:1
采用[bm im]BF4离子液体作为反应溶剂,以二苯甲硫醇为原料,经醚化、氨解、氧化得到新型提神醒脑药物莫达非尼。讨论了不同的氯乙酸酯和反应温度对醚化反应收率的影响,讨论了不同的二苯甲硫乙酸酯对氨解反应收率的影响,及离子液体的回收使用。研究表明,采用氯乙酸甲酯作为醚化试剂,反应时间4 h,反应温度100℃,二苯甲硫醇∶氯乙酸甲酯=1∶1.5(摩尔比),室温下氨解反应20 h,二苯甲硫乙酰胺收率76%;采用过氧化氢作为氧化试剂,反应时间3 h,反应温度60℃,过氧化氢∶二苯甲硫乙酰胺=1∶1(摩尔比),莫达非尼收率79%,反应总收率可达48%。 相似文献
43.
44.
The pheromone system of the summer fruit tortrix mothAdoxophyes orana (Fischer von Röslerstamm) consists of a mixture ofcis-9- andcis-11-tetradecen-1-ol acetate (cis-9- andcis-11-TDA, respectively) in a ratio of 9:1. Substitution of one or both of these compounds by related unsaturated acetates reduced the attractancy. Onlycis-11-TDA could be replaced bycis-11-tridecen-1-ol acetate (cis-11-TriDA), although the 9:1 mixture ofcis-9-TDA andcis-11-TriDA was less attractive in the field than the pheromone system itself. The major component of the pheromone system of the leaf rollerClepsis spectrana (Treitschke)(cis-9-TDA:cis-11-TDA=1:9) could also be replaced bycis-11-TriDA, again with some reduction in attractancy. 相似文献
45.
A kinetic study for the one-step conversion of synthesis gas to gasoline on a ZnO–Cr2O3–ZSM-5 catalyst is described. On this catalyst, three reactions are involved in the overall transformation of synthesis gas: the methanol synthesis, the conversion of methanol to hydrocarbons and the water–gas shift reaction. Under the operating conditions selected for the study, it was found that the water–gas shift was at equilibrium and the methanol was completely converted to hydrocarbons. Consequently, it was postulated that the kinetics of the limiting reaction step, the methanol synthesis on the ZnO–Cr2O3 component, was the one that controls the overall reaction rate. Three kinetic model equations describing the rate of synthesis gas conversion on the bifunctional catalyst, were considered to fit the data of the experimental runs performed in a Berty well-mixed reactor. Those equations were derived under very special conditions where the methanol decomposition term could be neglected. It was also observed that in the kinetic equations a term involving the fugacity of CO2 was required to predict the rate properly. The catalyst deactivation was also taken into account in the analysis. 相似文献
46.
水杨醛型腙类试剂测定铝的研究 总被引:4,自引:0,他引:4
合成了以水杨醛为母体的4种腙类新荧光试剂,并对其与铝的荧光反应性能进行了比较研究,结果表明,5-溴-水杨醛水杨酰腙是一种优良试剂。它与铝在pH5.4醋酸-醋酸铵缓冲溶液中形成13型荧光配合物,其λex=370nm,λem=460nm。建立的分析方法检测下限为1.1ng/mL,相对标准偏差为1.45%。考察了30余种共存离子的干扰情况。直接应用于葡萄糖注射液及常见饮料中微量铝的测定,结果满意。 相似文献
47.
Ion exchange of HZSM-5 samples with alkali metal cations, using metal chloride solutions, results in partially exchanged zeolites, MHZSM-5, M = Li, Na, K or Cs. The degree of exchange is found to increase with increasing ionic radius of the cations. The catalytic properties of the alkalized zeolites were evaluated using the reaction conditions under which the catalytic activity of the HZSM-5 samples in terms of n-hexane cracking is proportional to the aluminium content. From the residual catalytic activity exhibited by the Na-, K- and CsHZSM-5 samples it is concluded that each of the larger Na+, K+ and Cs+ ions is influencing more than one AlO
4
–
tetrahedron, implying that the aluminium sites in ZSM-5 are not isolated. The ion-exchange results are then interpreted in terms of non-isolated aluminium sites. The ion-exchange and catalytic properties of the zeolites as a function of aluminium content are also discussed. 相似文献
48.
MaleArchips argyrospilus (Walker) were maximally attracted to a 60404200 admixture of (Z)-11-tetradecenyl, (E)-11-tetradecenyl, (Z)-9-tetradecenyl and dodecyl acetates. The identification of (Z)-9-tetradecenyl acetate, in addition to the other 3 components reported previously, is the first report of a 4-component pheromone system in moths.Archips mortuanus Kearfoot, a sibling species, was maximally attracted to a blend of the same components, but in a 90101 mix of the tetradecenyl acetates. Among a number of tortricine moths that co-occur on apples and other hosts in New York, British Columbia, and elsewhere, differences in diel rhythms of attraction and seasonal distribution are insufficient to maintain reproductive isolation. Although the attractant systems of these species often possess components in common, males are maximally attracted to a speciesspecific blend. In tortricine moths attraction specificity appears to be a paramount mechanism for species partitioning. 相似文献
49.
Consuelo Montes de Correa H. Ai´da Luz Villa 《Applied catalysis. B, Environmental》1996,10(4):313-323
The effect of Pd-loading on Pd-NaZSM-5 and Pd-NaMordenite catalysts prepared by ion exchange was studied for methane combustion with excess oxygen (1% CH4, 18% O2, balance N2) in the temperature range 40–500°C. Fresh and calcined samples (3 h, 450°C) showed methane conversions proportional to Pd-loading on Pd-NaZSM-5 catalysts, while conversions decreased with Pd-loading on calcined Pd-NaMordenite catalysts. TOF (number of methane molecules converted per second per Pd2+ ion) for over exchanged Pd-NaZSM5-116 was low as compared to under exchanged Pd-NaZSM5-80 and Pd-NaZSM5-58 samples. Close TOF's were found for the last two samples at 330°C. TOF differences in Pd-NaMordenite catalysts demonstrate the heterogeneity of Pd+2 sites due to structurally nonidentical locations of cations. TOF's appear to be related to Na/Pd ratios in both catalyst types. Apparent activation energies for Pd-NaZSM-5 materials are higher than those for Pd-NaMordenite catalysts. 相似文献
50.