全文获取类型
收费全文 | 30833篇 |
免费 | 5223篇 |
国内免费 | 4348篇 |
专业分类
化学 | 23469篇 |
晶体学 | 422篇 |
力学 | 1512篇 |
综合类 | 277篇 |
数学 | 3342篇 |
物理学 | 11382篇 |
出版年
2024年 | 30篇 |
2023年 | 582篇 |
2022年 | 715篇 |
2021年 | 1010篇 |
2020年 | 1200篇 |
2019年 | 1242篇 |
2018年 | 1121篇 |
2017年 | 1022篇 |
2016年 | 1534篇 |
2015年 | 1465篇 |
2014年 | 1843篇 |
2013年 | 2468篇 |
2012年 | 2869篇 |
2011年 | 3008篇 |
2010年 | 2138篇 |
2009年 | 1984篇 |
2008年 | 2236篇 |
2007年 | 1997篇 |
2006年 | 1814篇 |
2005年 | 1472篇 |
2004年 | 1188篇 |
2003年 | 900篇 |
2002年 | 888篇 |
2001年 | 721篇 |
2000年 | 574篇 |
1999年 | 616篇 |
1998年 | 449篇 |
1997年 | 412篇 |
1996年 | 398篇 |
1995年 | 358篇 |
1994年 | 313篇 |
1993年 | 289篇 |
1992年 | 202篇 |
1991年 | 216篇 |
1990年 | 189篇 |
1989年 | 125篇 |
1988年 | 126篇 |
1987年 | 87篇 |
1986年 | 92篇 |
1985年 | 77篇 |
1984年 | 75篇 |
1983年 | 46篇 |
1982年 | 39篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1974年 | 14篇 |
1973年 | 18篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
101.
102.
A rigid supramolecular polymer was constructed in aqueous solution via cucurbit[8]uril(CB[8]) host recognition with a rigid monomer containing an azobenzene unit and two 4,4'-bipyridin-1-ium(BP)moieties in the two ends, which also exhibited photo-responsiveness owing to the photoinduced trans–cis isomerization of azobenzene group. 相似文献
103.
Analysis and pharmacokinetic study of polyphyllin H in beagle dog plasma after oral administration of Rhizoma Paridis Extracts by LC‐MS/MS 下载免费PDF全文
104.
105.
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones. 相似文献
106.
107.
JPC – Journal of Planar Chromatography – Modern TLC - A new high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous estimation of... 相似文献
108.
109.
110.
The Effect of Metal‐Ligand Affinity on Fe3O4_Supported Co–Rh Catalysts for Dicyclopentadiene Hydroformylation 下载免费PDF全文
Yubo Ma Shaojun Qing Nana Li Letao Zhang Shouzhu Li Zhixian Gao Hongyi Li Wumanjiang Eli Tianfu Wang 《国际化学动力学杂志》2015,47(10):621-628
The catalytic performances of Co‐Rh/Fe3O4 catalysts modified with phosphine ligands (PPh3) and its analogues on dicyclopentadiene hydroformylation were evaluated. Among these catalysts, Co‐Rh/Fe3O4 modified with tris(p‐trifluoromethylphenyl)phosphine was determined to be effective for monoformyltricyclodecanes production, whereas Co‐Rh/Fe3O4 modified with PPh3 or tri‐p‐tolylphosphine was effective for the diformyltricyclodecanes production. To investigate the ligand effects, the complex catalyst system (Co‐Rh/Fe3O4 and phosphine ligand) was subjected to pretreatment with syngas and then characterized by thermogravimetry and differential thermal analysis (TG‐DTA). It was determined that the threshold decomposition temperature reflected the corresponding Rh‐phosphine interaction strength, affecting the catalytic selectivity toward different products. A weak Rh‐phosphine interaction was desirable to produce monoformyltricyclodecanes with fast reaction kinetics, whereas a strong Rh‐phosphine complex was required for the synthesis of diformyltricyclodecanes. In addition to the selectivity rule shown in the PPh3 series, experiments with other ligands also demonstrated similar selectivity trends. 相似文献