全文获取类型
收费全文 | 118106篇 |
免费 | 31954篇 |
国内免费 | 27315篇 |
专业分类
化学 | 62626篇 |
晶体学 | 1200篇 |
力学 | 6294篇 |
综合类 | 225篇 |
数学 | 12296篇 |
物理学 | 59263篇 |
无线电 | 35471篇 |
出版年
2024年 | 870篇 |
2023年 | 2040篇 |
2022年 | 2269篇 |
2021年 | 2332篇 |
2020年 | 2718篇 |
2019年 | 3837篇 |
2018年 | 3552篇 |
2017年 | 4245篇 |
2016年 | 5224篇 |
2015年 | 5956篇 |
2014年 | 5982篇 |
2013年 | 8211篇 |
2012年 | 8839篇 |
2011年 | 9466篇 |
2010年 | 11796篇 |
2009年 | 11494篇 |
2008年 | 5579篇 |
2007年 | 4920篇 |
2006年 | 4697篇 |
2005年 | 4493篇 |
2004年 | 5224篇 |
2003年 | 4319篇 |
2002年 | 4146篇 |
2001年 | 4151篇 |
2000年 | 3199篇 |
1999年 | 3263篇 |
1998年 | 2864篇 |
1997年 | 2620篇 |
1996年 | 2987篇 |
1995年 | 3212篇 |
1994年 | 3262篇 |
1993年 | 3305篇 |
1992年 | 2853篇 |
1991年 | 2476篇 |
1990年 | 2023篇 |
1989年 | 2092篇 |
1988年 | 1963篇 |
1987年 | 1193篇 |
1986年 | 1245篇 |
1985年 | 924篇 |
1984年 | 1035篇 |
1982年 | 916篇 |
1981年 | 760篇 |
1980年 | 803篇 |
1979年 | 543篇 |
1978年 | 555篇 |
1977年 | 647篇 |
1976年 | 1058篇 |
1973年 | 446篇 |
1972年 | 543篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
32.
33.
34.
Kinetics and Catalysis - A series of Cu-SSZ-13@CeO2 catalysts with surface modification with CeO2 was prepared by the modified self-resemble method based on the one-pot synthesized Cu-SSZ-13... 相似文献
35.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
36.
37.
Two new homosecoiridoids, named loniaceticiridoside (1) and lonimalondialiridoside (2), were isolated from an aqueous extract of the flower buds of Lonicera japonica. Their structures including the absolute configuration were determined by extensive spectroscopic studies, especially by 2D NMR and CD data analysis. A proposed biosynthetic pathway and preliminary investigations of the biological activity of compounds 1 and 2 are also discussed. 相似文献
38.
39.
40.
Thomas Wittmann Dr. Renée Siegel Nele Reimer Dr. Wolfgang Milius Prof. Dr. Norbert Stock Prof. Dr. Jürgen Senker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):314-323
The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH2 by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N2 and H2O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m2 g?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with 1H‐27Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking. 相似文献