全文获取类型
收费全文 | 175篇 |
免费 | 17篇 |
国内免费 | 23篇 |
专业分类
化学 | 129篇 |
晶体学 | 1篇 |
力学 | 9篇 |
综合类 | 2篇 |
数学 | 21篇 |
物理学 | 53篇 |
出版年
2023年 | 1篇 |
2022年 | 11篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 11篇 |
2012年 | 18篇 |
2011年 | 24篇 |
2010年 | 16篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
排序方式: 共有215条查询结果,搜索用时 15 毫秒
91.
Transition‐Metal‐Free Synthesis of N‐Hydroxy Oxindoles by an Aza‐Nazarov‐Type Reaction Involving Azaoxyallyl Cations 下载免费PDF全文
Wenzhi Ji Dr. Yahu A. Liu Prof. Dr. Xuebin Liao 《Angewandte Chemie (International ed. in English)》2016,55(42):13286-13289
A novel transition‐metal‐free method to construct N‐hydroxy oxindoles by an aza‐Nazarov‐type reaction involving azaoxyallyl cation intermediates is described. A variety of functional groups were tolerated under the weak basic reaction conditions and at room temperature. A one‐pot process was also developed to make the reaction even more practical. This method provides alternative access to oxindoles and their biologically active derivatives. 相似文献
92.
93.
Dr. Weiwei Sun Xiaowei Chen Dr. Qinfen Gu Kia S. Wallwork Yingbin Tan Ziwei Tang Prof. Xuebin Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6825-6834
A new ammine dual‐cation borohydride, LiMg(BH4)3(NH3)2, has been successfully synthesized simply by ball‐milling of Mg(BH4)2 and LiBH4 ? NH3. Structure analysis of the synthesized LiMg(BH4)3(NH3)2 revealed that it crystallized in the space group P63 (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three‐dimensional architecture is built up through corner‐connecting BH4 units. Strong N? H???H? B dihydrogen bonds exist between the NH3 and BH4 units, enabling LiMg(BH4)3(NH3)2 to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH4)3(NH3)2/LiBH4 composite is able to release over 8 wt % hydrogen below 200 °C, which is comparable to that released by Mg(BH4)3(NH3)2. More importantly, it was found that release of the byproduct NH3 in this system can be completely suppressed by adjusting the ratio of Mg(BH4)2 and LiBH4 ? NH3. This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems. 相似文献
94.
[reaction: see text] The enantiospecific synthesis of 7-methoxy-d-tryptophan was completed by combination of the Larock heteroannulation process with a Sch?llkopf-based chiral auxiliary in good yield. This ester was then employed in the first total synthesis of (+)-12-methoxy-Na-methylvellosimine, (+)-12-methoxyaffinisine, and (-)-fuchsiaefoline in regiospecific, stereospecific fashion in excellent overall yield. The asymmetric Pictet-Spengler reaction and enolate-driven palladium-catalyzed cross coupling processes served as key steps. 相似文献
95.
分期付款期权在基于教育基金保险的期权中的应用 总被引:1,自引:0,他引:1
文献[1]提出了一种基于教育基金保险的欧式看涨期权,它赋予合约持有人在约定时间以约定价格购买连续支付固定年限的教育年金保险的权利,本文在[1]的基础上进一步提出基于教育基金保险的分期付款期权,该期权进一步改进了基于教育基金保险的欧式看涨期权,它赋予期权持有人分期支付期权费的权利,而不是一次性支付期权费,经过首期期权费的支付,期权持有人可以在继续支付期权费以持有期权和中断期权费的支付让期权作废之间选择,这样就可以使投资者在必要的时候取消期权,从而避免无效成本支出.该期权更加方便于低收入家庭和欲将资本用于其它高回报的投资的家庭进行教育投资.本文用后向递推和二叉树方法的方法给出期权定价公式,并确定分期支付的期权费的范围. 相似文献
96.
New Synthesis of 3,6‐Dibromophthalonitrile and Phthalocyanine Having Eight Thienyl Substituents at Peripheral α‐Positions 下载免费PDF全文
Rongrong Wang Yan Zhao Chunli Zhu Xuebin Huang 《Journal of heterocyclic chemistry》2015,52(4):1230-1233
3,6‐Dibromophthalonitrile was successfully synthesized from 3,6‐dihydroxyphthalonitrile using triphenylphosphine dibromide as bromation reagent. Starting from 3,6‐dibromophthalonitrile, synthesis of 1,4,8,11,15,18,22,25‐octakis(4‐dodecylthiophen‐2‐yl)phthalocyaninatozinc(II) (ZnPc) was described. TGA demonstrated the perfect stability of ZnPc. The newly prepared ZnPc that was symmetrically substituted with thienyl substituents results in an intensively red‐shifted Q‐band. The HOMO and LUMO values of ZnPc were acquired by CV. 相似文献
97.
Graphene oxide based recyclable dehydrogenation of ammonia borane within a hybrid nanostructure 总被引:1,自引:0,他引:1
The recyclable dehydrogenation of ammonia borane (AB) is achievable within a graphene oxide (GO)-based hybrid nanostructure, in which a combined modification strategy of acid activation and nanoconfinement by GO allows AB to release more than 2 equiv of pure H(2) at temperatures below 100 °C. This process yields polyborazylene (PB) as a single product and, thus, promotes the chemical regeneration of AB via reaction of PB with hydrazine in liquid ammonia. 相似文献
98.
Xingguang Zhang Dr. Xuebin Ke Prof. Dr. Huaiyong Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(26):8048-8056
With new photocatalysts of gold nanoparticles supported on zeolite supports (Au/zeolite), oxidation of benzyl alcohol and its derivatives into the corresponding aldehydes can proceed well with a high selectivity (99 %) under visible‐light irradiation at ambient temperature. Au/zeolite photocatalysts were characterised by UV/Vis, X‐ray photoelectron spectroscopy (XPS), TEM, XRD, energy‐dispersive spectroscopy (EDS), Brauner–Emmet–Teller (BET) analyses, IR and Raman techniques. The surface plasmon resonance (SPR) effect of gold nanoparticles, the adsorption capability of zeolite supports and the molecular polarities of aromatic alcohols were demonstrated to have an essential correlation with the photocatalytic performances. In addition, the effects of light intensity, wavelength range and the role of molecular oxygen were investigated in detail. The kinetic study indicated that the visible‐light irradiation required much less apparent activation energy for photooxidation compared with thermal reaction. Based on the characterisation data and the photocatalytic performances, we proposed a possible photooxidation mechanism. 相似文献
99.
本文利用Riemann-Liouville分数积分算子的半群性质以及分数Lévy过程的Wie-ner积分,给出由同一平方可积Lévy过程定义的不同分数Lévy过程之间的积分变换公式. 相似文献
100.
Regenerable hydrogen storage of lithium amidoborane is firstly achieved through the routes of direct thermal dehydrogenation and subsequent chemical hydrogenation of its dehydrogenated products by treatment with hydrazine in liquid ammonia. 相似文献