全文获取类型
收费全文 | 1150篇 |
免费 | 37篇 |
国内免费 | 12篇 |
专业分类
化学 | 658篇 |
晶体学 | 12篇 |
力学 | 29篇 |
数学 | 116篇 |
物理学 | 384篇 |
出版年
2024年 | 6篇 |
2023年 | 27篇 |
2022年 | 19篇 |
2021年 | 30篇 |
2020年 | 31篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 41篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 60篇 |
2012年 | 91篇 |
2011年 | 92篇 |
2010年 | 51篇 |
2009年 | 54篇 |
2008年 | 70篇 |
2007年 | 47篇 |
2006年 | 58篇 |
2005年 | 41篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 29篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有1199条查询结果,搜索用时 62 毫秒
41.
An expeditious synthesis of aryl substituted E‐homoallylic bromides has been accomplished by the cleavage of cyclopropylcarbinols with phosphorus tribromide. 相似文献
42.
Gakhyun Kim Dr. Ranjan Dutta Dr. Won-Young Cha Dr. Seong-Jin Hong Dr. Juwon Oh Dr. Dikhi Firmansyah Hongil Jo Prof. Dr. Kang Min Ok Prof. Dr. Chang-Hee Lee Prof. Dr. Dongho Kim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16434-16440
π–π Stacking is omnipresent not only in nature but in a wide variety of practical fields applied to our lives. Because of its importance in a performance of natural and artificial systems, such as light harvesting system and working layer in device, many researchers have put intensive effort into identifying its underlying nature. However, for the case of π–π stacked systems composed of antiaromatic units, the understanding of the fundamental mechanisms is still unclear. Herein, we synthesized a new type of planar β,β’-phenylene-bridged hexaphyrin (1.0.1.0.1.0), referred as naphthorosarin which possesses the 24π-electron conjugated pathway. Especially, the corresponding antiaromatic porphyrinoid shows the unique property to form dimeric species adopting the face-to-face geometry which is unprecedented in cases of known annulated naphthorosarins. In order to elucidate the intriguing properties derived from the stacked dimer, the current study focuses on the experimental support to rationalize the observed π–π interactions between the two subunits. 相似文献
43.
Ambarish Mondal Rajat K. Tripathy Parul Dutta Manas Kumar Santra Anvarhusein A. Isab Christopher W. Bielawski Hemanta K. Kisan Swapan K. Chandra Joydev Dinda 《应用有机金属化学》2019,33(1)
The syntheses, structures, and chemotherapeutic activities of Ag(I)‐, Au(I)‐, and Ru(II)‐complexes ligated to a novel N‐heterocyclic carbene ligand, 2‐(4‐nitrophenyl)imidazo[1,5‐a]pyridin‐2‐ylidene ( 1 ), are described. The corresponding complexes, [Ag( 1 )2][PF6], [Au( 1 )2][PF6] ( 3 ), and [Ru( 1 )(p‐cymene)Cl][PF6] ( 4 ), were prepared using convenient transmetallation chemistry and characterized using a range of spectroscopic and analytical techniques. X‐ray crystallography revealed that complexes 2 and 3 adopted linear structures whereas 4 exhibited a prototypical “piano‐stool”‐like geometry; the structural assignments were further supported by DFT calculations. A series of in vitro studies revealed that while the aforementioned Ag(I), Au(I) and Ru(II) complexes exhibited significant cytotoxicities against the human colon adenocarcinoma (HCT 116), lung cancer (A549), and breast cancer (MCF7) cell lines, the Ru derivative was most prominent. 相似文献
44.
45.
One‐pot protocol for the synthesis of novel class of triazole linked 2‐sugar and 2‐aryl substituted benzimidazoles has been developed. The rapid and simple method involves copper (I) catalyzed simultaneous formation of benzimidazole and triazole rings at room temperature and in high yield. 相似文献
46.
Dilip K. Dutta 《合成通讯》2013,43(13):1903-1906
Azoxy compounds have been prepared in good yields by reductive coupling of aromatic nitro compounds with manganese and a catalytic amount of acetic acid in aqueous conditions. 相似文献
47.
Solvent extraction and supported liquid membrane transport studies on Y(III) and Sr(II) were carried out using both nitric as well as hydrochloric acid feed conditions using N,N,N′,N′-tetra-octyldiglycolamide (TODGA) in several organic diluents. The solvent extraction studies indicated extremely large separation factor (SF) values with chloroform, carbon tetrachloride, 1-decanol and hexone when 6 M HNO3 was used as the feed. On the other hand, the SF values were 1–2 orders of magnitude lower when the nitric acid concentration was 3 M HNO3. Significantly large SF values were also obtained from 6 M HCl when xylene, carbon tetrachloride, n-dodecane and hexone were used as the diluent. Though mass transfer was not very promising in the supported liquid membrane studies with most of the diluent systems, quantitative Y(III) transport was observed with 0.1 M TODGA in xylene with negligible Sr(II) transport suggesting possibility of obtaining carrier free 90Y. The purity of the radiotracer was checked by half-life method. 相似文献
48.
Astam K. Patra Arghya Dutta Prof. Dr. Asim Bhaumik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12388-12395
Mesoporous nanoparticles composed of γ‐Al2O3 cores and α‐Fe2O3 shells were synthesized in aqueous medium. The surface charge of γ‐Al2O3 helps to form the core–shell nanocrystals. The core–shell structure and formation mechanism have been investigated by wide‐angle XRD, energy‐dispersive X‐ray spectroscopy, and elemental mapping by ultrahigh‐resolution (UHR) TEM and X‐ray photoelectron spectroscopy. The N2 adsorption–desorption isotherm of this core–shell materials, which is of type IV, is characteristic of a mesoporous material having a BET surface area of 385 m2 g?1 and an average pore size of about 3.2 nm. The SEM images revealed that the mesoporosity in this core–shell material is due to self‐aggregation of tiny spherical nanocrystals with sizes of about 15–20 nm. Diffuse‐reflectance UV/Vis spectra, elemental mapping by UHRTEM, and wide‐angle XRD patterns indicate that the materials are composed of aluminum oxide cores and iron oxide shells. These Al2O3@Fe2O3 core–shell nanoparticles act as a heterogeneous Fenton nanocatalyst in the presence of hydrogen peroxide, and show high catalytic efficiency for the one‐pot conversion of cyclohexanone to adipic acid in water. The heterogeneous nature of the catalyst was confirmed by a hot filtration test and analysis of the reaction mixture by atomic absorption spectroscopy. The kinetics of the reaction was monitored by gas chromatography and 1H NMR spectroscopy. The new core–shell catalyst remained in a separate solid phase, which could easily be removed from the reaction mixture by simple filtration and the catalyst reused efficiently. 相似文献
49.
Dr. Dipanwita Das Hemlata Agarwala Dr. Abhishek Dutta Chowdhury Tuhin Patra Dr. Shaikh M. Mobin Prof. Dr. Biprajit Sarkar Prof. Dr. Wolfgang Kaim Prof. Dr. Goutam Kumar Lahiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7384-7394
The complex series [Ru(pap)(Q)2]n ([ 1 ]n–[ 4 ]n; n=+2, +1, 0, ?1, ?2) contains four redox non‐innocent entities: one ruthenium ion, 2‐phenylazopyridine (pap), and two o‐iminoquinone moieties, Q=3,5‐di‐tert‐butyl‐N‐aryl‐1,2‐benzoquinonemonoimine (aryl=C6H5 ( 1+ ); m‐(Cl)2C6H3 ( 2+ ); m‐(OCH3)2C6H3 ( 3+ ); m‐(tBu)2C6H3 ( 4 +)). A crystal structure determination of the representative compound, [ 1 ]ClO4, established the crystallization of the ctt‐isomeric form, that is, cis and trans with respect to the mutual orientations of O and N donors of two Q ligands, and the coordinating azo N atom trans to the O donor of Q. The sensitive C? O (average: 1.299(3) Å), C? N (average: 1.346(4) Å) and intra‐ring C? C (meta; average: 1.373(4) Å) bond lengths of the coordinated iminoquinone moieties in corroboration with the N?N length (1.292(3) Å) of pap in 1 + establish [RuIII(pap0)(Q.?)2]+ as the most appropriate electronic structural form. The coupling of three spins from one low‐spin ruthenium(III) (t2g5) and two Q.? radicals in 1 +– 4 + gives a ground state with one unpaired electron on Q.?, as evident from g=1.995 radical‐type EPR signals for 1 +– 4 +. Accordingly, the DFT‐calculated Mulliken spin densities of 1 + (1.152 for two Q, Ru: ?0.179, pap: 0.031) confirm Q‐based spin. Complex ions 1 +– 4 + exhibit two near‐IR absorption bands at about λ=2000 and 920 nm in addition to intense multiple transitions covering the visible to UV regions; compounds [ 1 ]ClO4–[ 4 ]ClO4 undergo one oxidation and three separate reduction processes within ±2.0 V versus SCE. The crystal structure of the neutral (one‐electron reduced) state ( 2 ) was determined to show metal‐based reduction and an EPR signal at g=1.996. The electronic transitions of the complexes 1 n– 4 n (n=+2, +1, 0, ?1, ?2) in the UV, visible, and NIR regions, as determined by using spectroelectrochemistry, have been analyzed by TD‐DFT calculations and reveal significant low‐energy absorbance (λmax>1000 nm) for cations, anions, and neutral forms. The experimental studies in combination with DFT calculations suggest the dominant valence configurations of 1 n– 4 n in the accessible redox states to be [RuIII(pap0)(Q.?)(Q0)]2+ ( 1 2+– 4 2+)→[RuIII(pap0)(Q.?)2]+ ( 1 +– 4 +)→[RuII(pap0)(Q.?)2] ( 1 – 4 )→[RuII(pap.?)(Q.?)2]? ( 1 ?– 4 ?)→[RuIII(pap.?)(Q2?)2]2? ( 1 2?– 4 2?). 相似文献
50.
R. K. Dutta U. C. Bind J. B. M. Krishna A. K. Sinha G. S. Taki 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(2):819-824
ZnS nanoparticles implanted with 45 keV O5+ ion beam exhibited 83.6 % degradation of methyl blue in 2 h. This idea was utilized to fabricate nanocomposite system of ZnS and PMMA where ZnS nanoparticles were immobilized in PMMA film and irradiated with 45 keV O5+ ion beam at particle fluence of 2.5 × 1015, 1 × 1016 and 4 × 1016 particles/cm2. These irradiated batches of ZnS nanoparticle immobilized in PMMA batches revealed formation of porous structure characterized by scanning electron microscopy and these batches exhibited 54 % photocatalytic degradation of methyl blue in 80 min which was higher as compared to the pristine ZnS nanoparticles. 相似文献