全文获取类型
收费全文 | 30112篇 |
免费 | 3732篇 |
国内免费 | 3312篇 |
专业分类
化学 | 21901篇 |
晶体学 | 375篇 |
力学 | 1469篇 |
综合类 | 249篇 |
数学 | 3623篇 |
物理学 | 9539篇 |
出版年
2024年 | 89篇 |
2023年 | 497篇 |
2022年 | 894篇 |
2021年 | 935篇 |
2020年 | 1007篇 |
2019年 | 1024篇 |
2018年 | 865篇 |
2017年 | 820篇 |
2016年 | 1228篇 |
2015年 | 1248篇 |
2014年 | 1476篇 |
2013年 | 2020篇 |
2012年 | 2405篇 |
2011年 | 2621篇 |
2010年 | 1815篇 |
2009年 | 1773篇 |
2008年 | 1952篇 |
2007年 | 1771篇 |
2006年 | 1592篇 |
2005年 | 1405篇 |
2004年 | 1117篇 |
2003年 | 907篇 |
2002年 | 882篇 |
2001年 | 741篇 |
2000年 | 626篇 |
1999年 | 580篇 |
1998年 | 504篇 |
1997年 | 444篇 |
1996年 | 474篇 |
1995年 | 386篇 |
1994年 | 373篇 |
1993年 | 342篇 |
1992年 | 325篇 |
1991年 | 277篇 |
1990年 | 233篇 |
1989年 | 191篇 |
1988年 | 167篇 |
1987年 | 129篇 |
1986年 | 142篇 |
1985年 | 156篇 |
1984年 | 101篇 |
1983年 | 65篇 |
1982年 | 71篇 |
1981年 | 53篇 |
1980年 | 52篇 |
1979年 | 58篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 40篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
自动化流动注射停流动力学分析仪的研制及其性能测试 总被引:1,自引:0,他引:1
本文研制了一套自动化流动注射停流动力学分析仪,该仪器由苹果Ⅱ型微机通过12位AD/DA卡,流动注射停流控制仪及用BASIC语言编制的软件控制泵的起动和停止,试样的输送和混合,数据采集和处理,结果显示和打印,通过以铁(Ⅲ)与硫氰酸盐的反应体系采用固定时间法和以钒(V)的胶束催化反庆体系采用安始速法的现场测试证明,该仪器具有结构简单,操作方便,恒温性能好,通用性强等特点。 相似文献
153.
In the present paper, on the basis of our work. advances in study of the catalysts of polyacid-type hydrotalcite-like are reported and reviewed. Using polyoxometalates (POM) as pillaring species and layered double hydroxides (LDH) as host matter, a new class of catalytic materials, LDHPOM, has been synthesized by five different methods. Their acidic and oxidative catalytic properties have been investigated by several research groups. The above mentioned information is given in this review. 相似文献
154.
Guan X Lin X Kwok WM Du Y Li YL Zhao C Wang D Phillips DL 《The journal of physical chemistry. A》2005,109(6):1247-1256
Ultraviolet photolysis of low concentrations of CH2I2 in methanol solution found that CH2I2 is converted into dimethoxymethane and some H+ and I- products. Picosecond time-resolved resonance Raman (ps-TR3) experiments observed that the isodiiodomethane (CH2I-I) photoproduct decayed faster as the concentration of methanol increases, suggesting that isodiiodomethane is reacting with methanol. Ab initio calculations indicate isodiiodomethane is able to react with methanol via an O-H insertion/HI elimination to form an iodoether (ICH2-O-CH3) and HI products. The iodoether can then further react via another O-H insertion/HI elimination reaction to form the dimethoxymethane (CH3-O-CH2-O-CH3) observed in the photochemistry experiments. A reaction mechanism consistent with these experimental and theoretical observations is proposed. 相似文献
155.
Recently the hydrogen-bond activated reactions have attracted much attention.1 Takemoto2 reported a highly enantioselective Michael addition of manolate to nitroolefins catalyzed by a bifunctional organocatalyst with tertiary amine and thiourea moiety. As we known,stereoselective conjugate additions of thiols are interesting due to the standpoint of biological and synthetic importance, however, only very limited good results have been obtained except for the works of Shibasaki3, Kanemasa4 and Deng5 et al.In this letter, we report an efficient catalytic asymmetric Michael reactions of thiols to a,a-unsaturated carbonyl compounds promoted by bifunctional organocatalysts. A series of organocatalysts with chiral amine and thiourea structures were designed and synthesized and have been successfully applied in the conjugated additions of thiols to a,a-unsaturated imides and enones.The reactions got quantitative yields and the ee values were up to 84%. It is noteworthy that the a-asymmetric protonation (up to 43% ee) also could be achieved.The Michael addition between aromatic thiols and a,a-unsaturated carbonyl compounds isdescribed as follows:Works to further increase the enantioselectivity is under investigation in our laboratory. 相似文献
156.
157.
有机金属络合物用于高分子富氧膜的研究进展 总被引:2,自引:0,他引:2
本文介绍了能够可逆吸附分子氧的有机金属络合物用于高分子富氧膜的研究进展,以及以双重吸附理论进行的膜的促进输送机理。 相似文献
158.
159.
160.
Shuang‐Jun Lin Chang‐Heng Tan Shan‐Hao Jiang Yi‐Ming Li Da‐Yuan Zhu 《Helvetica chimica acta》2006,89(11):2789-2793
Four new iridoids, buergerinins B–E ( 1 – 4 ), along with three known iridoids, were isolated from the roots of Scrophularia buergeriana. Their structures were identified on the basis of spectroscopic analysis. 相似文献