全文获取类型
收费全文 | 724篇 |
免费 | 101篇 |
国内免费 | 82篇 |
专业分类
化学 | 551篇 |
晶体学 | 3篇 |
力学 | 41篇 |
综合类 | 14篇 |
数学 | 34篇 |
物理学 | 264篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 19篇 |
2021年 | 25篇 |
2020年 | 39篇 |
2019年 | 26篇 |
2018年 | 20篇 |
2017年 | 15篇 |
2016年 | 35篇 |
2015年 | 29篇 |
2014年 | 32篇 |
2013年 | 50篇 |
2012年 | 54篇 |
2011年 | 60篇 |
2010年 | 50篇 |
2009年 | 29篇 |
2008年 | 37篇 |
2007年 | 50篇 |
2006年 | 38篇 |
2005年 | 32篇 |
2004年 | 35篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 8篇 |
1997年 | 23篇 |
1996年 | 12篇 |
1995年 | 4篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有907条查询结果,搜索用时 15 毫秒
31.
Zhen-Su She 《中国科学:物理学 力学 天文学(英文版)》2018,(9)
正Newton’s gravitational law and its derived Kapler’s orbit of planetary motions are the very first triumph of science,which confirms that a purely human’s invention of mathematics is able to accurately describe observations in nature.For the 相似文献
32.
Cephalotanins A–D,Four Norditerpenoids Represent Three Highly Rigid Carbon Skeletons from Cephalotaxus sinensis 下载免费PDF全文
Dr. Jin‐Biao Xu Dr. Yao‐Yue Fan Prof. Dr. Li‐She Gan Dr. Yu‐Bo Zhou Prof. Dr. Jia Li Prof. Dr. Jian‐Min Yue 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(41):14648-14654
Four polycyclic norditerpenoids, cephalotanins A–D ( 1 – 4 ) representing three unprecedented carbon skeletons with highly rigid ring systems, were isolated from Cephalotaxus sinensis and structurally characterized by a combination of various methods. Compounds 1 and 2 are new skeletal norditerpenoid trilactones, while 3 and 4 are two norditerpenoids featuring different new carbon skeletons. Biosynthetic pathways for 1 – 4 were proposed by involving diverse and very fascinating chemical events with the coexisting cephalotane troponoids as the precursors. Compound 1 exhibited good NF‐κB inhibition with an IC50 value of 4.12±0.61 μΜ. 相似文献
33.
34.
35.
36.
Herein, we present three imidazo[1,2‐a]pyridin‐2(3 H)‐one derivatives that are diamagnetic in solution, but paramagnetic in the solid state, possibly owing to a stacking‐induced formation of phenoxide‐type radicals. Notably, a larger bathochromic shift of the absorption (even up to the near‐ infrared region) of these three compounds was observed in the solid state than in solution, which was attributable to the ordered columnar stacking arrangements or their single‐electron character as radicals in the solid state. Interestingly, compared to that in solution, (E)‐3‐(pyridin‐4′‐ylmethylene)imidazo[1,2‐a]pyridine 2(3 H)‐one displayed a largely red‐shifted emission (centered at 660 nm, with tailing above 800 nm) in the solid state. A larger bathochromic shift (260 nm) of the emission is an indication of better order and tight stacking in the solid state, which is brought about by the rigid and polar acceptor. These three compounds also reveal different magnetic susceptibilities at 300 K, thus implying that they possess various columnar stacking structures. Most interestingly, these three radicals exhibit unusual ferromagnetic‐to‐antiferromagnetic phase transitions, which can be attributed to anisotropic contraction and non‐uniform slippage of the columnar stacking chains. 相似文献
37.
Wei‐Syuan Lin Zih‐Jie Jian Hong‐Ming Lin Li‐Chung Lai Wen‐An Chiou Yeu‐Kuang Hwu She‐Huang Wu Wen‐Chang Chen Y. D. Yao 《中国化学会会志》2013,60(1):85-91
The iron nanowires can be fabricated via the process in which sodium borohydride reduces iron salts in external magnetic field. The iron nanowires are found to be covered by passivated layers of iron oxide which prevent the oxidation of iron nanowires. In this process, the boron will include in iron nanowires. The average length and diameter of iron nanowires is around 1.2 micrometers and 60 nanometers, respectively. According to ICP results, the contents of B and Fe are about 1.98 wt% and 87.04 wt%, respectively, in iron nanowires. A wide variety of equipment is used to investigate the morphological, microchemical, and structural characteristics of the newly synthesized iron nanowires ––– e.g., XRD, FE‐SEM, HR‐TEM, VSM and XANES. XANES analysis indicates the boron in iron nanowires exists in the form of B2O3. The saturation magnetization and the coercive force of iron nanowires are 157.93 emu/g and 9.74 Oe, respectively. In‐situ images of synthesized iron nanowires during reduction process in magnetic field are observed by NSRRC transmission X‐ray microscope. Thus, this study develop a novel process to produce iron nanowires with large quantitates and can control its length and diameter by various the concentration of precursors for various applications. 相似文献
38.
A general and practical one‐pot synthesis of naphthopyran derivatives using hexadecyltrimethylammonium bromide (HTMAB) as catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple workup procedure. The catalyst is low cost, facile, active, environmentally friendly, and reusable. In addition, water is chosen as a green solvent. 相似文献
39.
A concise asymmetric total synthesis of (+)-monocerin has been accomplished. The cis-fused furobenzopyranone of monocerin was efficiently constructed via a Lewis acid-mediated stereoselective cyclization of 1,2,4-triols intermediate. 相似文献
40.
Xiao‐Zhi He Bao‐Yan Zhang Corresponding author Jian‐She Hu Mei Tian 《Liquid crystals》2013,40(3):299-306
In this work we prepared a nematic monomer (4′‐allyloxybiphenyl 4′‐ethoxybenzoate, M1 ), a chiral crosslinking agent (isosorbide 4‐allyloxybenzoyl bisate, M2 ) and a series of new side chain cholesteric liquid crystalline elastomers derived from M1 and M2 . The chemical structures of the monomers and polymers were confirmed by FTIR and 1H NMR spectroscopy. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X‐ray diffraction. The effect of the content of the crosslinking unit on phase behaviour of the elastomers is discussed. Polymer P1 showed a nematic phase, P2 –P7 showed a cholesteric phase; P6 formed a blue Grandjean texture over a broad temperature range 145–209.6°C, with no changed on the cooling. Polymers P4 –P7 , with more than 6?mol?% of chiral crosslinking agent, gave rise to selective reflection. Elastomers containing less than 15?mol?% of the crosslinking units displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that, with increasing content of crosslinking agent, the glass transition temperatures first fell and then increased; the isotropization temperatures and mesophase temperature ranges decreased. 相似文献