全文获取类型
收费全文 | 991篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 777篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 135篇 |
物理学 | 86篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2017年 | 13篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 19篇 |
2012年 | 31篇 |
2011年 | 47篇 |
2010年 | 22篇 |
2009年 | 16篇 |
2008年 | 30篇 |
2007年 | 43篇 |
2006年 | 36篇 |
2005年 | 34篇 |
2004年 | 43篇 |
2003年 | 28篇 |
2002年 | 32篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1990年 | 7篇 |
1932年 | 10篇 |
1930年 | 14篇 |
1927年 | 12篇 |
1926年 | 10篇 |
1925年 | 8篇 |
1920年 | 8篇 |
1914年 | 8篇 |
1913年 | 8篇 |
1911年 | 9篇 |
1909年 | 7篇 |
1908年 | 7篇 |
1906年 | 16篇 |
1905年 | 12篇 |
1904年 | 11篇 |
1903年 | 10篇 |
1900年 | 7篇 |
1886年 | 6篇 |
1885年 | 10篇 |
1884年 | 12篇 |
1883年 | 8篇 |
1881年 | 10篇 |
1880年 | 6篇 |
1875年 | 6篇 |
排序方式: 共有1011条查询结果,搜索用时 0 毫秒
31.
Meyer WH Deetlefs M Pohlmann M Scholz R Esterhuysen MW Julius GR Raubenheimer HG 《Dalton transactions (Cambridge, England : 2003)》2004,(3):413-420
A series of palladium, platinum and manganese di(organo)carbene complexes have been prepared from 4-chloro-N-methylquinolinone by processes that involve alkylation before or after attachment to the metal unit; the nucleophilic heteroatoms are separated from the C-donor atom by three bonds. 相似文献
32.
Yang VX Munce N Pekar J Gordon ML Lo S Marcon NE Wilson BC Vitkin IA 《Optics letters》2004,29(15):1754-1756
High-resolution optical coherence tomography demands a large detector bandwidth and a high numerical aperture for real-time imaging, which is difficult to achieve over a large imaging depth. To resolve these conflicting requirements we propose a novel multifocus fiber-based optical coherence tomography system with a micromachined array tip. We demonstrate the fabrication of a prototype four-channel tip that maintains a 9-14-microm spot diameter with more than 500 microm of imaging depth. Images of a resolution target and a human tooth were obtained with this tip by use of a four-channel cascaded Michelson fiber-optic interferometer, scanned simultaneously at 8 kHz with geometric power distribution across the four channels. 相似文献
33.
The finite-difference time-domain method is a simple but powerful numerical method for simulating full-wave acoustic propagation and scattering. However, the method can demand a large amount of computational resources. Traditionally, continuously curved boundaries are represented in a stair-step fashion and thus accurately modeling scattering from a boundary will require a finer discretization than would otherwise be necessary for modeling propagation in a homogeneous medium. However, a fine discretization might not be practical due to limited computational resources. A locally conformal technique is presented here for modeling acoustic scattering from continuously curved rigid boundaries. This technique is low cost, simple to implement, and gives better results for the same grid discretization than the traditional stair-step representation. These improvements can be traded for a coarser discretization which reduces the computational burden. The improved accuracy of this technique is demonstrated for a spherical scatterer. 相似文献
34.
In DMF-d7 tetrabenzimidazole cavitands 2 exist as monomeric species and vase-like conformers. Several possible arrangements of the four benzimidazole NHs are indicated by 1H NMR spectroscopy. The cavitands form 1:1 inclusion complexes with tetraethyl ammonium and phosphonium cations only when strong hydrogen bonding anions like chloride or acetate are present. These complexes are stable on the NMR time scale at 295 K feature a C2V-symmetrical arrangement of benzimidazole functions. The stability of the C2V-symmetrical tetramethylammonium acetate complex is independent of the temperature. In contrast, tetramethylammonium and phosphonium chloride complexes exist at 233 K as several isomers. This complicated behavior is, in part, attributed to the hydrogen bonding interactions between the anions and the NH groups of benzimidazole functions. 相似文献
35.
36.
37.
38.
39.
Ohne Zusammenfassung 相似文献
40.