全文获取类型
收费全文 | 631篇 |
免费 | 15篇 |
国内免费 | 6篇 |
专业分类
化学 | 393篇 |
晶体学 | 19篇 |
力学 | 7篇 |
数学 | 31篇 |
物理学 | 202篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 27篇 |
2021年 | 23篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 14篇 |
2014年 | 33篇 |
2013年 | 54篇 |
2012年 | 45篇 |
2011年 | 54篇 |
2010年 | 33篇 |
2009年 | 16篇 |
2008年 | 18篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 12篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1944年 | 1篇 |
排序方式: 共有652条查询结果,搜索用时 46 毫秒
21.
Navjeet Kaur Pooja Grewal Pranshu Bhardwaj Meenu Devi Neha Ahlawat Yamini Verma 《合成通讯》2013,43(22):3058-3100
The heterocyclic chemistry field has been revolutionized using transition metal catalyst in recent years. Various research groups have focused on the development of general protocols to achieve better functional group compatibilities and greater levels of molecular complexity under mild reaction conditions using easily available starting substrates. These methods afford many advantages as compared to alternative pathways involved in the synthesis of heterocyclic compounds. In this review article, we have concentrated on the synthesis of nitrogen-containing five-membered heterocylces in the presence of silver catalyst. 相似文献
22.
AbstractA simple and facile method for the denitrosation of cyclic N-nitrosamines using HN3 (concentrated H2SO4 + NaN3) is reported. In this method, limited usage of this reagent does not affect the carbonyl group. 相似文献
23.
The first total synthesis of triumfettamide (1) is described. The asymmetric syntheses of two highly functionalized units—α-hydroxylated C17 monounsaturated fatty acid unit (2) and C26 phytosphingosine (3) have been accomplished involving Sharpless asymmetric dihydroxylation, Sharpless kinetic resolution, regioselective epoxide opening, regioselective DIBAL-H reduction of acetal, Wittig olefination as the key steps. Finally N-acylation of phytosphingosine 3 with (2R,6Z)-2-hydroxy-6-heptadecenoic acid 2 followed by DDQ deprotection of PMB, provided target compound 1. 相似文献
24.
在303 K恒温条件下,以NaCl为电解质保持离子强度为0.16 mol·L-1,用pH滴定法研究了M(Ⅱ)-Dopa(多巴)二元配合物在0~60%(V/V)的丙二醇(PG)-水体系中的生成平衡。在PG-水体系中,Ca(Ⅱ)和Mg(Ⅱ)的典型配合物为MLH,ML2,ML2H和ML2H2,而Zn(Ⅱ)的典型配合物为ML,MLH,ML2,ML2H和ML2H2。根据静电和非静电力解释了稳定常数随介质的介电常数而变化的倾向。还讨论了在不同组成的丙二醇(PG)-水体系中配合物物种随pH值变化的情况。 相似文献
25.
P. Lakshmi Reddy D. Ashok Kumar M. Lakshmi Devi T. Veera Reddy B.V. Subba Reddy R. Narender 《Tetrahedron letters》2014
A three-component, four center Ugi reaction of 3-(1-(2-aminophenyl)-5-phenyl-1H-pyrrol-2-yl)propanoic acid with aromatic aldehyde and t-butyl isocyanide has been achieved to produce a novel class of N-tert-butyl-2-(6-oxo-11-phenyl-7,8-dihydrobenzo[b]pyrrolo[1,2-d][1,4]diazacine-5(6H)-yl)-2-phenylacetamides in moderate to good yields. 相似文献
26.
Fe(Cp)2BF4 is an efficient catalyst for the alcoholysis of aromatic, aliphatic, and cyclic epoxides giving excellent yields of the corresponding β-alkoxy alcohols under ambient conditions. The methanolysis of styrene oxide using Fe(Cp)2BF4 as a catalyst (5 mol %) gave excellent yield of 2-methoxy-2-phenylethanol with complete regio-selectivity. The ring opening of cyclic epoxides gave 77–97% yields of trans-β-methoxy alcohols, in 0.5–6 h. The use of 1,2-epoxyhexane and 1,2-epoxydodecane as substrates gave both regioisomers in excellent yields. The first order rate of reaction with respect to catalyst was observed for the kinetics of ring opening of 1,2-epoxyhexane with methanol. 相似文献
27.
Indirect electrochemical synthesis of quinone derivatives of a series of substituted anthracene and naphthalene by the electrolysis of aqueous solution of potassium bromide (3.0 M) using Pt anode at constant current density (40 mA/cm2) has been carried out. These reactions resulted in good to excellent yields of the corresponding para-quinones as confirmed by physical and spectral data. 相似文献
28.
Durga Charan Panigrahi Patitapaban Sahu Devi Prasad Mishra Vivekanand Jha R. Lokeswara Patnaik 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):433-439
This paper presents the assessment of inhalation exposure potential of broken uranium ore piles in different stopes of Jaduguda uranium mines of India. 222Rn emanation coefficient of broken uranium ore was measured in laboratory by collecting air sample from airtight glass jar containing ore sample. An attempt was also made to correlate the emanation coefficient with 226Ra content of the ore. The 222Rn progeny doses estimated based on radon activity concentration of broken ore, occupancy period and equilibrium ratio in different stopes were well below the prescribed limit of International Commission on Radiological Protection. The maximum 222Rn progeny dose contribution from broken ore piles was worked out to be 0.22 mSv year?1. This suggests that the broken ore piles are not the significant contributor of inhalation exposure under the existing ventilation condition of Jaduguda uranium mine. 相似文献
29.
Dr. Srivari Chandrasekhar Kakita Veera Mohana Rao Mallikanti Seenaiah Police Naresh Ambure Sharada Devi Dr. Bharatam Jagadeesh 《化学:亚洲杂志》2014,9(2):457-461
Hybrid peptidic oligomers comprising natural and unnatural amino acid residues that can exhibit biomolecular folding and hydrogen‐bonding mimicry have attracted considerable interest in recent years. While a variety of hybrid peptidic helices have been reported in the literature, other secondary structural patterns such as γ‐turns and ribbons have not been well explored so far. The present work reports the design of novel periodic γ‐turns in the oligomers of 1:1 natural‐α/unnatural trans‐β‐norborenene (TNAA) amino acid residues. Through DFT, NMR, and MD studies, it is convincingly shown that, in the mixed conformational pool, the heterogeneous backbone of the hybrid peptides preferentially adopt periodic 8‐membered (pseudo γ‐turn)/7‐membered (inverse γ‐turn) hydrogen bonds in both polar and non‐polar solvent media. It is observed that the stereochemistry and local conformational preference of the β‐amino acid building blocks have a profound influence on accessing the specific secondary fold. These findings may be of significant relevance for the development of molecular scaffolds that facilitate desired positioning of functional side‐chains. 相似文献
30.
Borah Preetismita Chetan Sharma Vaishali Malakar Arindam Bhinder Surinder Singh Kansal Sushil Kumar Devi Pooja 《Chromatographia》2022,85(2):213-218
Chromatographia - In this work, we present a new method for the determination and speciation of selenium in water with ion chromatography (IC) using a conductometric detector. Chromatographic... 相似文献