全文获取类型
收费全文 | 21974篇 |
免费 | 3490篇 |
国内免费 | 3116篇 |
专业分类
化学 | 17323篇 |
晶体学 | 284篇 |
力学 | 1124篇 |
综合类 | 296篇 |
数学 | 2450篇 |
物理学 | 7103篇 |
出版年
2024年 | 59篇 |
2023年 | 415篇 |
2022年 | 730篇 |
2021年 | 745篇 |
2020年 | 938篇 |
2019年 | 988篇 |
2018年 | 744篇 |
2017年 | 638篇 |
2016年 | 1116篇 |
2015年 | 1132篇 |
2014年 | 1301篇 |
2013年 | 1587篇 |
2012年 | 1902篇 |
2011年 | 1922篇 |
2010年 | 1462篇 |
2009年 | 1317篇 |
2008年 | 1486篇 |
2007年 | 1391篇 |
2006年 | 1223篇 |
2005年 | 1024篇 |
2004年 | 936篇 |
2003年 | 838篇 |
2002年 | 969篇 |
2001年 | 836篇 |
2000年 | 535篇 |
1999年 | 461篇 |
1998年 | 293篇 |
1997年 | 252篇 |
1996年 | 218篇 |
1995年 | 178篇 |
1994年 | 130篇 |
1993年 | 123篇 |
1992年 | 123篇 |
1991年 | 120篇 |
1990年 | 111篇 |
1989年 | 60篇 |
1988年 | 50篇 |
1987年 | 36篇 |
1986年 | 40篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1978年 | 6篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1936年 | 4篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Benefiting from the environmental friendliness of organic electrodes and the high security of aqueous electrolyte,an all-organic aqueous potassium dual-ion full... 相似文献
72.
73.
74.
A highly convenient method for N-formylation of amines via treatment by formic acid in the presence of melamine trisulfonic acid as a catalyst has been developed. This method showed improvements over previous reports in terms of yield, reaction time and chemoselectivity. 相似文献
75.
Hcp-icosahedron structural transformation induced by the change in Ag concentration during the freezing of (CoAg)561 clusters 下载免费PDF全文
The synergy effect of alloy elements in bimetallic clusters can be used to tune the chemical and physical properties. Research on the influences of alloy concentration and distribution on the frozen structure of bimetallic clusters plays a key rolc in exploring new structural materials. In this paper, we study the influence of Ag concentration on the frozen structure of the (AgCo)561 cluster by using molecular dynamics simulation with a general embedded atom method. The results indicate that tt~e structure and chemical ordering of the (AgCo)561 cluster are strongly related to Ag concentration. Hcp-icosahedron structural transformation in the frozen (CoAg)561 cluster can be induced by changing Ag concentration. The chemical ordering also transforms to Janus-like Co Ag from core-shell Co-Ag. 相似文献
76.
Coral reef-like PANI nanotubes composed of nanopaticles were successfully synthesized by a reactive template of manganese oxide.The structure was characterized by using SEM,TEM,and FT-IR,and the supercapacitive behaviors of these nanotubes were investigated with cyclic voltammetry(CV),and charge-discharge tests,respectively.A maximum specific capacitance of 533 F/g could be achieved in 1mol/L aqueous H2SO4 with the potential range of -0.2 to 0.8 V(vs.the saturated calomel electrode) in a half-cell setup configuration for PANI electrode,suggesting its potential application in the electrode material for electrochemical capacitors. 相似文献
77.
78.
Pei Tang Qi-Feng Chen Ling Wang Qiao-Hong Chen Xi-Xian Jian Feng-Peng Wang 《Tetrahedron》2012,68(27-28):5668-5676
O-Demethylation at C-1 in the C19-diterpenoid alkaloids is very challenging. In this paper, it was firstly observed that 10-OH group in deltaline (1) is a determining factor for the O-demethylation reaction. After removal of this hydroxyl group, 1-O-methyl group in the corresponding deltaline analogs can be readily removed by treatment with HBr–HOAc. Meanwhile, the C-14 atom in bromides 18 or 20 can be extruded under basic condition probably via a sequence, including Grob fragmentation, aerobic oxidation, deformylation, and SN2 nucleophilic substitution, to give enone 21 (70%) and oxetane 22 (14%). The structure of compound 22 was confirmed by X-ray crystallographic analysis of its derivative 21. 相似文献
79.
80.