全文获取类型
收费全文 | 719篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 546篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 31篇 |
物理学 | 168篇 |
出版年
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 29篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 25篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 21篇 |
2013年 | 44篇 |
2012年 | 59篇 |
2011年 | 58篇 |
2010年 | 37篇 |
2009年 | 33篇 |
2008年 | 35篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有753条查询结果,搜索用时 46 毫秒
131.
132.
133.
Sumanta Bhattacharya Sandip K Nayak Subrata Chattopadhyay Manas Banerjee Asok K Mukherjee 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(2):289-298
[70]fullerene has been shown to form 1:1 EDA complex with anthracene, naphthalene, phenanthrene, pyrene and acenaphthene in CCl4 medium. Charge transfer (CT) bands have been detected in all the cases. Isosbestic points have been observed in the cases of phenanthrene and acenaphthene complexes. Ionisation potentials of the donors and CT transition energies have been found to correlate in accordance with Mulliken equation and from this correlation the electron affinity of C70 has been found to be 2.59 eV. Enthalpies and entropies of formation of the complexes have been estimated from the formation constants of the complexes determined spectrophotometrically at three different temperatures. 相似文献
134.
A spectrophotometric method for the detection of tyrosinase activity is developed by utilizing the product-triggered aggregation of boronic acid-functionalized gold nanoparticles. Based on the changes of absorbance in UV-visible spectra, the assay shows extremely high sensitivity and lowered limit of detection of 1 × 10(-10) u mL(-1). 相似文献
135.
Simone Giombi Shiraz Minwalla Shiroman Prakash Sandip P. Trivedi Spenta R. Wadia Xi Yin 《The European Physical Journal C - Particles and Fields》2012,72(8):1-65
We study three-dimensional conformal field theories described by U(N) Chern?CSimons theory at level k coupled to massless fermions in the fundamental representation. By solving a Schwinger?CDyson equation in light-cone gauge, we compute the exact planar free energy of the theory at finite temperature on ?2 as a function of the ??t?Hooft coupling ??=N/k. Employing a dimensional reduction regularization scheme, we find that the free energy vanishes at |??|=1; the conformal theory does not exist for |??|>1. We analyze the operator spectrum via the anomalous conservation relation for higher spin currents, and in particular show that the higher spin currents do not develop anomalous dimensions at leading order in 1/N. We present an integral equation whose solution in principle determines all correlators of these currents at leading order in 1/N and present explicit perturbative results for all three-point functions up to two loops. We also discuss a light-cone Hamiltonian formulation of this theory where a W ?? algebra arises. The maximally supersymmetric version of our theory is ABJ model with one gauge group taken to be U(1), demonstrating that a pure higher spin gauge theory arises as a limit of string theory. 相似文献
136.
A novel, ultrafast, mild and scalable amide bond formation strategy in methanol using simple thioacids and amines is described. The mechanism suggests that the coupling reactions are initially mediated by CuSO(4)·5H(2)O and subsequently catalyzed by in situ generated copper sulfide. The pure peptides were isolated in satisfactory yields in less than 5 minutes. 相似文献
137.
Amal Halder Sandip K. Nayak Subrata Chattopadhyay Sumanta Bhattacharya 《Journal of solution chemistry》2012,41(2):223-240
The present article reports the host-guest complexation of a calix[4]arene derivative, namely 4-iso-propyl-calix[4]arene (1), with fullerenes (both C60 and C70) in toluene and benzonitrile solutions. It is observed that the charge-transfer (CT) absorption bands are located in the
ground state for the C60 and C70 complexes of 1. By utilizing the CT absorption bands, various important physicochemical parameters like the oscillator strength, resonance
energy, transition dipole moment, electronic coupling element and solvent reorganization energies have been estimated for
the C60-1 and C70-1 complexes. The CT transition energy is very helpful for determining the vertical ionization potential of 1 in solution. Jobs method of continuous variation was used to establish 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds C70 preferentially compared to C60 as obtained from binding constant (K) data. The effect of solvent on the complexation of fullerenes (C60 and C70) with 1 is clearly observed from the trend in the K values: in toluene and whereas in benzonitrile, and . Molecular mechanics force field (MMMF) calculations reveal fascinating features regarding the binding pattern of fullerenes
towards 1 in vacuo in terms of enthalpy of formation. MMMF calculations establish that during C70-1 complexation, C70 is directed in an end-on manner rather than the traditional side-on pattern. 相似文献
138.
Highly efficient regioselective protocol for the synthesis of hitherto unreported 4H-benzo[f]chromenes has been developed by one-pot four-component coupling of aromatic aldehydes, β-naphthol, β-oxodithioesters, and primary alcohols in the presence of InCl3. This transformation presumably proceeds via domino Knoevenagel condensation/Michael addition/intramolecular cyclodehydration/transesterification sequence creating four new bonds and one stereocenter in a single operation. Further, alcohol plays dual role as a reactant as well as reaction medium. 相似文献
139.
Shabber Mohammed Anil K. Padala Bashir A. Dar Baldev Singh B. Sreedhar Ram A. Vishwakarma Sandip B. Bharate 《Tetrahedron》2012,68(39):8156-8162
Montmorillonite KSF clay supported CuO nanoparticles efficiently catalyzes one-pot aromatic azidonation of aryl boronic acids followed by regioselective azide–alkyne 1,3-dipolar cycloaddition (CuAAC) reaction producing corresponding 1-aryl-1,2,3-triazole derivatives at room temperature in excellent yields without use of any additives. Investigations on mechanism of CuAAC revealed that sodium azide, which is used as azidonating reagent in one-pot protocol reduces Cu(II) to click-active Cu(I). The catalytic efficiency of another Cu(II) source CuSO4 in combination with NaN3 for this one-pot CuAAC protocol, further supported our mechanism. This is the first report for use of Cu(II)/NaN3 catalytic system for CuAAC protocol. The clay–Cu(II) catalyst being ligand-free, leaching-free, easy to synthesize from inexpensive commercially available precursors, recyclable, and environmentally friendly will be highly useful for economical synthesis of 1,4-disubstituted 1,2,3-triazoles. 相似文献
140.
J.S. Yadav Sandip Sengupta Nagendra Nath Yadav D. Narasimha Chary Ahmad Alkhazim Al Ghamdi 《Tetrahedron letters》2012,53(44):5952-5954
(−)-Lardolure and (2R,4R,6R,8R)-2,4,6,8-tetramethylundecanoic acid have been synthesized via lipase catalyzed desymmetrization strategy to create two methyl chiral centers. Other key steps involved in the synthesis are Wittig reaction, Evan’s asymmetric alkylation, Grignard reaction, Pd-catalyzed isomerization of primary allylic alcohol to corresponding saturated aldehyde, and PhNO/proline catalyzed MacMillan α-hydroxylation. 相似文献