全文获取类型
收费全文 | 596篇 |
免费 | 22篇 |
国内免费 | 3篇 |
专业分类
化学 | 464篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 25篇 |
物理学 | 120篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 10篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 20篇 |
2014年 | 28篇 |
2013年 | 42篇 |
2012年 | 32篇 |
2011年 | 36篇 |
2010年 | 19篇 |
2009年 | 18篇 |
2008年 | 27篇 |
2007年 | 28篇 |
2006年 | 30篇 |
2005年 | 35篇 |
2004年 | 19篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1988年 | 5篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1964年 | 2篇 |
1962年 | 2篇 |
1957年 | 2篇 |
1934年 | 3篇 |
排序方式: 共有621条查询结果,搜索用时 297 毫秒
61.
[reaction: see text] Commercially available 1-bromobenzocyclobutene is a potentially useful synthon particularly with the application of organometallic methodology. Here we show that it is readily converted into Cp(2)Zr(benzocyclobutadiene), which couples with alkynes or nitriles giving five-membered zirconacycles. Treatment of these alkyne- or nitrile-derived zirconacycles with CuCl yields substituted naphthalenes, isoquinolines, or in the presence of MeO(2)C-CC-CO(2)Me, a 3-benzazocine containing an eight-membered ring [corrected]. 相似文献
62.
Ajoy G Ramakrishna J Bahçeli S Klinowski J 《Solid state nuclear magnetic resonance》2000,16(4):63-338
We derive a complete analytical solution for the powder magic angle spinning (MAS) nuclear magnetic resonance (NMR) lineshape in the presence of second-order quadrupole interaction, considering a radiofrequency (rf) pulse of finite width, a finite MAS frequency, and a non-zero asymmetry parameter. Ix is calculated using two approaches. The first applies time-dependent perturbation theory in the presence of the rf pulse and stationary perturbation theory (SPT) in its absence. The second is based on the Magnus expansion of the density matrix in the interaction representation during the pulse and SPT in its absence. We solve the problem in the laboratory frame using the properties of the Fourier transform and spin operators. Diagonalisation is not required. Both approaches agree well with each other under all conditions and also with the transition probability approach for the central transition. The Magnus expansion exists at all times and the effect of the non-secular terms is negligible. We describe an analytical method of averaging Ix over the Euler angles and simulate the 11B MAS NMR lineshapes for crystalline and vitreous B2O3. A critical analysis is given of all earlier calculations of the MAS NMR lineshape. 相似文献
63.
P. Prathap N. Revathi Y.P.V. Subbaiah K.T. Ramakrishna Reddy R.W. Miles 《Solid State Sciences》2009,11(1):224-232
Al-doped ZnS films were deposited using close-spaced evaporation of the powders synthesized by chemical precipitation method. The films were prepared for different Al concentrations in the range 0–10 at.% on glass substrates kept at 300 °C. The effect of Al-doping on ZnS composition, microstructure and optoelectronic properties of as-grown ZnS layers was determined using appropriate techniques. The films were polycrystalline and showed (111) preferred orientation for all the doping concentrations in spite of an additional phase of Al2S3 observed at higher dopant levels. The surface morphological studies indicated that the Al incorporation had a considerable effect on the surface roughness of the films. The optical measurements indicated that the optical energy band gap decreased slightly with the increase of dopant concentration without affecting the optical transmittance characteristics significantly. The electrical analysis indicated that the resistivity of the layers changed significantly with the doping concentration in the layers. The change of photoluminescence behaviour of the as-grown ZnS:Al films with dopant concentration was also studied. 相似文献
64.
Swagata Chakraborty Susmitha A. L. Ramakrishna V. Hosur 《Magnetic resonance in chemistry : MRC》2012,50(9):587-591
Direct detection of 13C nucleus can be used as a valuable alternative where 1H detection poses a challenge due to relaxation effects, chemical exchange and poor chemical shift dispersion. In this context, we have designed a suite of 2D 13Cα‐detected hNCA experiments that provide sequential correlations of 13Cα with 15N on one hand and efficient spectroscopic labeling of certain groups of residues, namely, Gly, Ala, Ser and Thr, on the other. These residues act as checkpoints in the sequential walk, which in turn offer new possibilities of backbone assignment of small proteins from a set of 2D experiments, thereby providing great economy in terms of spectrometer time. The direct identification of peptide segments around Gly, Ala, Ser and Thr residues along a protein chain will be highly valuable for deriving important information on sites of ligand binding, phosphorylation, inhibitor/substrate binding, understanding protein folding pathways, comprehending local conformational dynamics etc. without having to obtain complete sequence‐specific assignments, which can be time consuming and at times formidable, especially in large proteins. We have illustratively demonstrated the multifaceted applications of these variants of 2D experiments on ubiquitin and M‐crystallin. We foresee that these 2D hNCA experiments will provide economic and efficient strategies for studying the structure and function of proteins. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
65.
66.
Ramakrishna Katakam Rajender Anugula Lingamurthy Macha Venkateswara Rao Batchu 《Tetrahedron letters》2017,58(6):559-562
A short and stereoselective synthesis of conduramine F-1 and ent-conduramine E-1 derivatives have been achieved starting from d-mannitol using nucleophilic vinylation on imine. A concise sequence of vinylation at both ends of d-mannitol and followed by RCM allowed us to prepare target compound. 相似文献
67.
A modular approach to 5-acylated naphtho[2,1-b]benzofurans was developed where Sonogashira cross-coupling and intramolecular alkyne carbonyl metathesis were sequentially employed to build the aromatic benzene C ring of naphtho[2,1-b]benzofuran with an acyl group at the C5 position. 相似文献
68.
69.
One-pot transition-metal-free synthesis of aromatic aldehydes and ketones via oxidative decarboxylation of arylacetic acids in water is developed. Protocol relies on the direct decarboxylation of sp3-hybridized carbon in water without any over oxidation into carboxylic acids with minimal waste. Reaction mechanism is investigated and application of this protocol is demonstrated on a gram scale. 相似文献
70.
Raimund J. Ober Viswanath Ramakrishna E. Sally Ward 《Journal of mathematical chemistry》1999,26(1-3):15-26
It is shown that the system theoretic concepts of reachability and observability are relevant to the analysis of NMR experiments.
Moreover, the sets of reachable states are examined and Lie theoretic criteria are given for the reachability of the system.
The question is investigated how the set of reachable states depends on the class of input functions that are allowed. Both
one‐dimensional and multi‐dimensional NMR experiments are considered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献