全文获取类型
收费全文 | 779篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 363篇 |
晶体学 | 4篇 |
力学 | 25篇 |
数学 | 39篇 |
物理学 | 363篇 |
出版年
2023年 | 7篇 |
2021年 | 5篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 19篇 |
2017年 | 7篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 22篇 |
2011年 | 40篇 |
2010年 | 19篇 |
2009年 | 24篇 |
2008年 | 47篇 |
2007年 | 43篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 12篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 14篇 |
2000年 | 18篇 |
1999年 | 5篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 14篇 |
1972年 | 5篇 |
1955年 | 4篇 |
排序方式: 共有794条查询结果,搜索用时 31 毫秒
121.
122.
Metal-acteylacetonates are important sublimable metal-organic precursors for metal-oxide thin film formation over solid preforms by MOCVD (Metal Organic Chemical Vapour Deposition) technique. Mixed-metal-acetylacetonates (MMAA) are suitable starting materials for mixed metal nano-oxidic thin film formation through such facile routes. Layered Double Hydroxides (LDH) of suitable metal ion combination can perform as appropriate starting base for neutralisation by enol form of 2,4-pentanedione or acteylacetonate tautomer ligands to obtain such MMAA. In this paper synthesis of composite crystals of Cu(II)/Cr(III) acetylacetonates (CCAA) is reported by the reaction of Cu–Cr-LDH with acetylacetone. The products were characterized by various different techniques. The surface area and pore volume analysis of the crystals showed the formation of nanopores in the compound. TEM analysis confirmed that the inner core of the nanoporous crystals of Cu(acac)2 was covered by coating of poorly crystallised Cr(acac)3 and they together form the composite crystals, and they together form the composite crystals. Due to eutectic mixture formation the melting point of CCAA lies in between the melting points of individual components Cu(acac)2 and Cr(acac)3 and shows sublimability, a property important for the formation of MOCVD films. The composite was used for CuCr2O4 spinel mixed oxide films formation over solid ceramic honeycomb monolithic substrates. Application prospects of the route in the field of catalysis is high as it can directly combine the benefits of mixed metal oxide catalysis and structured supports without the involvement of a third component. In this work the performance of such a catalytic device has been tested for low temperature decomposition of high Global Warming Potential (GWP) gas N2O to N2 and O2. 相似文献
123.
124.
Ruthenium(II)‐Catalyzed Synthesis of Spirobenzofuranones by a Decarbonylative Annulation Reaction
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Partha P. Kaishap Gauri Duarah Dr. Bipul Sarma Prof. Dr. Dipak Chetia Dr. Sanjib Gogoi 《Angewandte Chemie (International ed. in English)》2018,57(2):456-460
The first decarbonylative insertion of an alkyne through C?H/C?C activation of six‐membered compounds is reported. The Ru‐catalyzed reaction of 3‐hydroxy‐2‐phenyl‐chromones with alkynes works most efficiently in the presence of the ligand PPh3 to provide spiro‐indenebenzofuranones. Unlike previously reported metal‐catalyzed decarbonylative annulation reactions, in the present decarbonylative annulation reaction, the annulation occurs before extrusion of carbon monoxide. 相似文献
125.
U. Pandey A. Mukherjee G. Samuel S. Banerjee H. D. Sarma M. Venkatesh 《Journal of Radioanalytical and Nuclear Chemistry》2008,275(2):243-246
Lanreotide, a somatostatin analogue, was radioiodinated with 125I to explore the possibility of using 123I labeled lanreotide as a diagnostic radiopharmaceutical for tumors overexpressing somatostatin (SST) receptors. Radioiodination
was carried out with 125I using chloramine T as the oxidant. The labeling yield was >90%. Characterization of 125I-Lanreotide was carried out by paper electrophoresis as well as HPLC. 125I-Lanreotide was purified by chromatography using a C18 Sep-Pak column. Radiochemical purity of the purified 125I-Lanreotide thus obtained was >99%. Significant tumor uptake of 125I-Lanreotide was observed in C57BL/6 mice bearing melanoma. 相似文献
126.
Chloro ethane dimethyl sulfoxide,C_2H_5Cl·DMSO(ECI·DMSO)was prepared by interaction of acrylic acid with conc.Hydrochloric acid in dimethyl sulfoxide(DMSO)and subsequent decarboxylation with H_2O_2 solution.The formation of the compound was confirmed by spectral and analytical methods;the molecular weight was determined by cryoscopic method.The solubility of poly(vinyl alcohol)(PVA)in different solvents or mixed solvents at 40℃,50℃and 60℃temperature in the presence of 0.01% of EC1·-DMSO was determined.It... 相似文献
127.
Prewetting transition is studied for the square-well fluid of attractive-well diameter lambda(ff)sigma(ff)=1.5 in the presence of a homogeneous surface modeled by the square-well potential of attractive well from 0.8sigma(ff) to 1.8sigma(ff). We investigate surface phase coexistence of thin-thick film transition using grand-canonical transition matrix Monte Carlo (GC-TMMC) and histogram reweighting techniques. Molecular dynamics (MD) and GC-TMMC are utilized to predict the properties of the fluid for various surface fluid affinities. Occurrences of prewetting transition with the variation of surface affinity are observed for a domain of reduced temperature from T(*)=0.62 to 0.75. We have used MD and GC-TMMC+finite size scaling (FSS) simulations to calculate the boundary tension as a function of temperature as well as surface affinity. Boundary tensions via MD and GC-TMMC+FSS methods are in good agreement. The boundary tension increases with the decrease of wall-fluid affinity. Prewetting critical properties are calculated using rectilinear diameter approach and scaling analysis. We found that critical temperature and density increase with the decrease of wall-fluid affinity. 相似文献
128.
Papu Kalita Biman Medhi Haobam Kisan Singh Himangshu Pratim Bhattacharyya Nikhil Gupt Dr. Manabendra Sarma 《Chemphyschem》2023,24(3):e202200727
The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (−F) and donating (−CH3) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multi-reference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and non-adiabatic dynamics suggest that the −CH3 substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to −F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with −F or −CH3, the conversion proceeds via the conrotatory pathway. 相似文献
129.
Jagadeesh B Prabhakar A Sarma GD Chandrasekhar S Chandrashekar G Reddy MS Jagannadh B 《Chemical communications (Cambridge, England)》2007,(4):371-373
Residue based control of specific helical folding is explored in hybrid peptide oligomers consisting of alternating L-Ala and cis-beta-furanoid sugar amino acid (FSAA) residues as building blocks; two series of these hybrid oligomers are designed, synthesized and extensively characterized by using NMR, CD, FT-IR and MD simulation studies; results show the co-existence of left-handed 11- and 14/15-helical conformations in these short oligomers of Boc-(alpha/beta) and Boc-(beta/alpha) series. 相似文献
130.
Vibrational excitation (nu(f)<--nu(i)) cross-sections sigma(nu(f)<--nu(i) )(E) in resonant e-N(2) and e-H(2) scattering are calculated from transition matrix elements T(nu(f),nu(i) )(E) obtained using Fourier transform of the cross correlation function , where psi(nu(i))(R,t) approximately =e(-iH(A(2))-(R)t/h phi(nu(i))(R) with time evolution under the influence of the resonance anionic Hamiltonian H(A(2) (-))(A(2) (-)=N(2)(-)/H(2) (-)) implemented using Lanczos and fast Fourier transforms. The target (A(2)) vibrational eigenfunctions phi(nu(i))(R) and phi(nu(f))(R) are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curves of the neutral target. Application of this simple systematization to calculate vibrational structure in e-N(2) and e-H(2) scattering cross-sections provides mechanistic insights into features underlying presence/absence of structure in e-N(2) and e-H(2) scattering cross-sections. The results obtained with approximate PE curves are in reasonable agreement with experimental/calculated cross-section profiles, and cross correlation functions provide a simple demarcation between the boomerang and impulse models. 相似文献