全文获取类型
收费全文 | 8735篇 |
免费 | 1445篇 |
国内免费 | 1226篇 |
专业分类
化学 | 6959篇 |
晶体学 | 98篇 |
力学 | 414篇 |
综合类 | 119篇 |
数学 | 917篇 |
物理学 | 2899篇 |
出版年
2024年 | 34篇 |
2023年 | 162篇 |
2022年 | 307篇 |
2021年 | 333篇 |
2020年 | 348篇 |
2019年 | 384篇 |
2018年 | 324篇 |
2017年 | 294篇 |
2016年 | 410篇 |
2015年 | 428篇 |
2014年 | 477篇 |
2013年 | 575篇 |
2012年 | 744篇 |
2011年 | 794篇 |
2010年 | 552篇 |
2009年 | 500篇 |
2008年 | 632篇 |
2007年 | 503篇 |
2006年 | 461篇 |
2005年 | 439篇 |
2004年 | 368篇 |
2003年 | 296篇 |
2002年 | 360篇 |
2001年 | 292篇 |
2000年 | 216篇 |
1999年 | 175篇 |
1998年 | 125篇 |
1997年 | 93篇 |
1996年 | 143篇 |
1995年 | 124篇 |
1994年 | 87篇 |
1993年 | 55篇 |
1992年 | 53篇 |
1991年 | 69篇 |
1990年 | 53篇 |
1989年 | 36篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 4篇 |
1983年 | 16篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1957年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
34.
草酸锰分解过程的机理函数判别和动力学研究 总被引:6,自引:1,他引:6
用等温热重和线性升温热重分析法研究了草酸锰热分解过程,提出了判断其机理函数的3步判别法。经实验和理论分析证明,该反应受随机成核和晶核随后生长的过程(A_3a机理)支配,其活化能E=103.95 kJ/mol,频率因子A=4.448×10~8min~(-1).动力学补偿效应为IgA=0.09661E-1.2856 相似文献
35.
Bao Liu Ling Huang Juntao Liu Yao Zhong Xingshu Li Albert S.C. Chan 《Tetrahedron: Asymmetry》2007,18(24):2901-2904
Chiral tridentate N-tosylated aminoimine ligands were used in the Cu(II)-catalyzed enantioselective addition of phenylacetylene to N-aryl arylimines, affording products up to 92% ee. 相似文献
36.
Bakhtar Ullah Yuli Zhou Jingwen Chen Zongbi Bao Yiwen Yang Qiwei Yang Qilong Ren Zhiguo Zhang 《Tetrahedron letters》2019,60(4):348-351
Thiourea itself has been introduced as a mild and efficient organocatalyst for the oxidative α -cyanation of N-aryltetrahydroisoquinolines (THIQs) with trimethylsilyl cyanide (TMSCN), giving the corresponding products in good to excellent yields. Experimental investigations demonstrated that thiourea acts as a radical initiator by abstracting hydroxyl radical (OH) from tert-butyl hydroperoxide (TBHP) directly instead of non-covalent hydrogen bondings (H-bondings) activation. The use of thiourea as a radical initiator offers a new avenue for innovative chemical transformations in organocatalyzed radical chemistry. 相似文献
37.
S. Maruyama M. Y. Lee R. E. Haufler Y. Chai R. E. Smalley 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,18(4):409-412
The kinetics of cluster formation in supersonic jets is examined by numerical integration of the master equation system. Some general characteristics of cluster kinetics could be formulated. Excellent agreement between experimental curves of p-cresol (H2O)0, 1, 2, 3 formation as function of H2O pressure and the corresponding calculated curves were obtained assuming successive cluster formation. From the kinetic curves, an unambiguous assignment of cluster size was possible which agreed with mass-resolved REMPI measurements. The fit of the rate coefficients shows the formation of p-cresol (H2O)1 to be faster than p-cresol (H2O)2 and p-cresol (H2O)3. 相似文献
38.
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
39.
A New Asterosaponin from the Starfish Culcita novaeguineae 总被引:1,自引:0,他引:1
HaiFengTANG YangHuaYI LingLI PengSUN DaZhengZHOU BaoShuLIU 《中国化学快报》2005,16(5):619-622
A new asterosaponin named novaeguinoside A, along with a known saponin, asteronyl pentaglycoside sulfate, was isolated from the starfish Culcita novaeguineae. The new compound was identitied to be sodium 6α-O-{β-D-fucopyranosyl-(1→2)-β-D-fucopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-xylopyranosyl-(1→3)-[β-D-quinovopyranosyl}-5α-pregn-9(11)-en-20-one-3β-yl-sulfate by extensive spectral analysis and chemical evidence. 相似文献
40.
Determination of Gossypol in Trace Level by Flow Injection Analysis with Chemiluminescence Detection
Bing Chun XUE Er Bao LIU College of Chemistry Life Sciences Tianjin Normal University Tianjin 《中国化学快报》2006,17(1):57-60
Gossypol, [1, 1′, 6, 6′, 7,7′-hexahydroxyl-5,5′-diisopropyl-3,3′-dimethyl-(2,2′-binaphtha- lene)-8,8′-dicarboxaldehyde] is a polyphenolic yellow compound naturally occurring in various parts of cotton plants1. The compound has been associated with 相似文献