全文获取类型
收费全文 | 1031篇 |
免费 | 51篇 |
国内免费 | 2篇 |
专业分类
化学 | 740篇 |
晶体学 | 13篇 |
力学 | 13篇 |
数学 | 61篇 |
物理学 | 257篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 31篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 52篇 |
2017年 | 34篇 |
2016年 | 57篇 |
2015年 | 41篇 |
2014年 | 100篇 |
2013年 | 108篇 |
2012年 | 68篇 |
2011年 | 71篇 |
2010年 | 38篇 |
2009年 | 29篇 |
2008年 | 41篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 17篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1084条查询结果,搜索用时 15 毫秒
101.
Kundan Tayade Amanpreet Kaur Sandesh Tetgure G. Krishana Chaitanya Narinder Singh Anil Kuwar 《Analytica chimica acta》2014
The (13E,19E)-N1′,N3′-bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide (L) has been developed for the detection of Th4+ ions using dual channel signalling system. The UV–vis absorbance and fluorescence spectroscopic data revealed the formation of L–Th4+ complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L–Th4+. The detection limit of L for Th4+ recognition is to a concentration down to 0.1 μM (0.023 μg g−1). The present sensing system is also successfully applied for the detection of Th4+ ion present in soil near nuclear atomic plants. 相似文献
102.
Expedient Protocols for the Installation of 1,5‐Benzoazepino‐Based Privileged Templates on the 2‐Position of 1,4‐Benzodiazepine Through a Phenoxyl Spacer 下载免费PDF全文
An efficient novel strategy for the hetero‐annulation of 2‐chloro‐1,4‐benzodiazepine ring, substituted on its 5‐position with a carboxamido group ( 5 ), has been developed to allow the incorporation of 1,5‐benzodiazepine, 1,5‐benzothiazepine, and 1,5‐benzoxazepine ( 8 , 9 , 10 , 11 , 12 , 13 ) rings through their dimethylaminomethylene ketone intermediate ( 7 ). 相似文献
103.
Navjeet Kaur 《合成通讯》2014,44(22):3229-3247
The development of new strategies for synthesis of five-membered O,N,N-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen and two nitrogen atoms containing five-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of five-membered O,N,N-heterocycles. 相似文献
104.
The development of new strategies for synthesis of six-membered O-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen-containing six-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of six membered O-heterocycles. 相似文献
105.
Solid-phase organic synthesis is a rapidly expanding area of synthetic chemistry that is being widely exploited in the search for new medicinally important compounds using combinatorial techniques. In recent decades, a large number of reports related to solid-phase synthesis of heterocycles have appeared because of the wide variety of their biological activity. In this review, we report the important role of solid-phase synthesis in the synthesis of nitrogen containing six-membered ring heterocycles. 相似文献
106.
107.
Fernandez FM Hostetler D Powell K Kaur H Green MD Mildenhall DC Newton PN 《The Analyst》2011,136(15):3073-3082
Throughout history, poor quality medicines have been a persistent problem, with periodical crises in the supply of antimicrobials, such as fake cinchona bark in the 1600s and fake quinine in the 1800s. Regrettably, this problem seems to have grown in the last decade, especially afflicting unsuspecting patients and those seeking medicines via on-line pharmacies. Here we discuss some of the challenges related to the fight against poor quality drugs, and counterfeits in particular, with an emphasis on the analytical tools available, their relative performance, and the necessary workflows needed for distinguishing between genuine, substandard, degraded and counterfeit medicines. 相似文献
108.
Indra Sandal Amita Bhattacharya Uksha Saini Devinder Kaur Shveta Sharma Ashu Gulati Jonnala K Kumar Neeraj Kumar Jyotsna Dayma Pralay Das Bikram Singh Paramvir S Ahuja 《BMC chemical biology》2011,11(1):1-13
Background
Accidental autoclaving of L-glutamine was found to facilitate the Agrobacterium infection of a non host plant like tea in an earlier study. In the present communication, we elucidate the structural changes in L-glutamine due to autoclaving and also confirm the role of heat transformed L-glutamine in Agrobacterium mediated genetic transformation of host/non host plants.Results
When autoclaved at 121°C and 15 psi for 20 or 40 min, L-glutamine was structurally modified into 5-oxo proline and 3-amino glutarimide (α-amino glutarimide), respectively. Of the two autoclaved products, only α-amino glutarimide facilitated Agrobacterium infection of a number of resistant to susceptible plants. However, the compound did not have any vir gene inducing property.Conclusions
We report a one pot autoclave process for the synthesis of 5-oxo proline and α-amino glutarimide from L-glutamine. Xenobiotic detoxifying property of α-amino glutarimide is also proposed. 相似文献109.
Dehydrotryptophan and its derivatives are non-proteinogenic amino acids commonly found in peptide-based natural products produced by microorganisms, marine organisms and plants. These non-proteinogenic amino acids are found in secondary metabolites and are formed by post translational modification processes. Although comprehensive reviews on the synthesis of dehydroamino acids are available, this perspective focuses solely on methods to synthesise the dehydrotryptophan-containing segment of naturally occurring peptides, amino acids and their derivatives. 相似文献
110.
A new multicomponent domino reaction for rapid and regioselective synthesis of highly functionalized benzo[h]pyrazolo[3,4-b]quinolines has been established. The reaction can be conducted by using readily available and inexpensive substrates under microwave irradiation within short periods of 10-26 min. Good to excellent chemical yields (61-91%) and complete regioselectivity have been achieved for 22 examples. Tedious work-up procedure can be avoided due to the direct precipitation of products from the reaction solution. The resulting benzoquinolines have been readily converted into quinoxaline-fused benzo[h]isoxazolo[5,4-b]quinoline analogues by treating with benzene-1,2-diamine under microwave irradiation. The structural assignment has been ambiguously confirmed by X-ray analysis. A new mechanism has been proposed for this new multicomponent domino process. 相似文献