全文获取类型
收费全文 | 4849篇 |
免费 | 215篇 |
国内免费 | 32篇 |
专业分类
化学 | 3113篇 |
晶体学 | 25篇 |
力学 | 122篇 |
数学 | 1007篇 |
物理学 | 829篇 |
出版年
2023年 | 35篇 |
2022年 | 64篇 |
2021年 | 109篇 |
2020年 | 76篇 |
2019年 | 113篇 |
2018年 | 85篇 |
2017年 | 81篇 |
2016年 | 191篇 |
2015年 | 152篇 |
2014年 | 189篇 |
2013年 | 275篇 |
2012年 | 358篇 |
2011年 | 373篇 |
2010年 | 220篇 |
2009年 | 234篇 |
2008年 | 321篇 |
2007年 | 320篇 |
2006年 | 274篇 |
2005年 | 245篇 |
2004年 | 226篇 |
2003年 | 172篇 |
2002年 | 161篇 |
2001年 | 81篇 |
2000年 | 78篇 |
1999年 | 52篇 |
1998年 | 47篇 |
1997年 | 39篇 |
1996年 | 49篇 |
1995年 | 27篇 |
1994年 | 31篇 |
1993年 | 40篇 |
1992年 | 43篇 |
1991年 | 33篇 |
1990年 | 37篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 33篇 |
1983年 | 16篇 |
1982年 | 10篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1974年 | 10篇 |
1971年 | 6篇 |
1963年 | 5篇 |
排序方式: 共有5096条查询结果,搜索用时 31 毫秒
141.
Raymundo Cea-Olivares Jesús Wingartz Jorge Cárdenas Jesus Valdés-Martínez Thelma Alvarado 《Transition Metal Chemistry》1991,16(1):62-64
Summary The interaction of non-anhydrous solutions of the ligand 1,3-bis-(2-hydroxyphenyl)-1,3-propanedione (bhppH3) with hydrated rare earth chlorides resulted in the formation of anhydrous, non-solvated, complexes M(bhppH2)3 (M=Y, La, Nd, Pr, Sm or Yb). The complexes have been characterized by elemental analysis, t.g., i.r. and1H n.m.r. spectroscopy. The evidence suggests that the coordination is through the -diketone site. 相似文献
142.
143.
Jorge Bravo Jesús Castro Soledad García‐Fontn Elvira M. Lamas Pilar Rodríguez‐Seoane 《无机化学与普通化学杂志》2003,629(2):297-302
The manganese carbonyl complex [MnBr(CO)3 L ] ( 1 ), where L = Ph2POCH2CH2OPPh2, was prepared by reacting [MnBr(CO)5] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)2 LL ′], where L ′ = P(OMe)3 ( 2 ) or P(OEt)3 ( 3 ) and [MnBr(CO)3 L ′2], where L ′ =PPh(OEt)2 ( 4 ) or PPh2(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (1H, 13C and 31P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 . 相似文献
144.
Brown EC York JT Antholine WE Ruiz E Alvarez S Tolman WB 《Journal of the American Chemical Society》2005,127(40):13752-13753
By treating Cu(I) complexes of neutral, bidentate N-donor ligands with S8, clusters with novel delocalized mixed-valence [Cu3(mu-S)2]3+ cores have been isolated. X-ray crystal structures and UV-vis and resonance Raman spectral features of these clusters reveal similarities to the tetracopper-sulfide "CuZ" site in nitrous oxide reductase. A delocalized S = 1 ground state for the mixed-valent CuIIICu2II cores is supported by the observation of high symmetry in the X-ray structures and 10-line hyperfine features arising from coupling to three equivalent Cu ions in EPR spectra obtained at room temperature (shown) and 10 K. The delocalization we observe contrasts with the localization reported previously for a [Cu3(mu-O)2]3+ analogue (Root, D. E.; Henson, M. J.; Machonkin, T.; Mukherjee, P.; Stack, T. D. P.; Solomon, E. I. J. Am. Chem. Soc. 1998, 120, 4982), which we rationalized through DFT calculations. 相似文献
145.
Extraction of dry cured ham volatile compounds by solid-phase microextraction (SPME) was optimized. Different fiber coatings (carboxen/polydimethylsiloxane (CAR/PDMS), divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS), polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB)), times of extraction (15, 30, 60 min) and sample preparation (ground samples and homogenates with NaCl saturated solution) were assayed. CAR/PDMS and DVB/CAR/PDMS fiber coatings extracted more than 100 volatile compounds and showed the highest area counts for most volatile compounds. CAR/PDMS coating extracted better those compounds whose Kovats index (KI) was lower than 980 (on average) and DVB/CAR/PDMS those with higher KI. Fifteen minutes of extraction provided a volatile compound profile with lower area counts for most compounds and qualitatively different to that obtained with 30 and 60 min of extraction. Homogenates gave a different profile compared to ground samples, with lower total counts for most compounds but higher proportion of aldehydes, and presence of several compounds not found in ground samples. 相似文献
146.
Fondo M García-Deibe AM Corbella M Ruiz E Tercero J Sanmartín J Bermejo MR 《Inorganic chemistry》2005,44(14):5011-5020
The new tetranuclear carbonate complex [Cu2L)2(CO3)] x 8H2O (1 x 8H2O) (H3L = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) has been obtained by two different synthetic routes and fully characterized. Recrystallization of 1 x 8H2O in methanol yields single crystals of {[(Cu2L)2(CO3)]}2 x 12H2O (1 x 6H2O), suitable for X-ray diffraction studies. The crystal structure of 1 x 6H2O shows two crystallographically different tetranuclear molecules in the asymmetric unit, 1a and 1b. Both molecules can be understood as self-assembled from two dinuclear [Cu2L]+ cations, joined by a mu4-eta(2):eta(1):eta(1) carbonate ligand. The copper atoms of each crystallographically different [(Cu2L)2(CO3)] molecule present miscellaneous coordination polyhedra: in both 1a and 1b, two metal centers are in square pyramidal environments, one displays a square planar chromophore and the other one has a geometry that can be considered as an intermediate between square pyramid and trigonal bipyramid. Magnetic studies reveal net intramolecular ferromagnetic coupling between the metal atoms. Density functional calculations allow the assignment of the different magnetic coupling constants and explain the unexpected ferromagnetic behavior, because of the presence of an unusual NCN bridging moiety and countercomplementarity of the phenoxo (or carbonate) and NCN bridges. 相似文献
147.
Double exchange in polynuclear mixed-valence clusters. 1. General solution of the electronic problem
J. J. Borras-Almenar R. Jorge S. I. Klokishner E. Coronado S. M. Ostrovskii A. V. Palii B. S. Tsukerblat 《Journal of Structural Chemistry》1996,37(5):689-698
The problem of calculating the electronic energy spectra of mixed-valence clusters with one “extra” electron (dn-dn...dn+1) or hole (dn+1-dn+1...dn) delocalized in the paramagnetic cores of transition metals is solved. Unlike the available particular solutions, which are
restricted to small numbers of ions and electrons, the solution proposed in this work is general and is suitable for many-electron
systems of arbitrary numbers of nuclei and arbitrary symmetries. The new microscopic approach to the double exchange problem
is based on the combination of the sequential (“chain”) scheme of spin coupling and angular momentum method. In terms of this
approach, an analytical dependence of the matrix elements of the double exchange, Heisenberg exchange, and vibronic interaction
on all spin quantum numbers is obtained. The final equations contain only the 6j symbols and are free of the higher-order
nj symbols, which obstructed the solution of the double exchange problem in previous works.
Valencia University, Spain. Bordeaux University, France. Moldova State University. Institute of Chemistry, Academy of Sciences,
Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 805–815, September–October, 1996.
Translated by I. Izvekova 相似文献
148.
Fandos R Hernández C Otero A Rodríguez A Ruiz MJ Terreros P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(3):671-677
Titanium complexes with chelating alkoxide ligands [TiCp*(O(2)Bz)(OBzOH)] (1) and [TiCp*(Me)((OCH(2))(2)Py)] (2) were synthesised by reaction of [TiCp*Me(3)] (Cp*=eta(5)-C(5)Me(5)) with 2-hydroxybenzyl alcohol ((HO)(2)Bz) and 2,6-pyridinedimethanol ((HOCH(2))(2)Py), respectively. Complex 1 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) to yield the early-late heterobimetallic complexes [TiCp*(O(2)Bz)(2)M(cod)] [M=Rh (3), Ir (4)]. Carbon monoxide readily replaces the COD ligand in 3 to give the rhodium dicarbonyl derivative [TiCp*(O(2)Bz)(2)Rh(CO)(2)] (5). Compound 2 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) with protonolysis of a Tibond;Me bond to give [TiCp*((OCH(2))(2)Py)(mu-O)M(cod)] [M=Rh (6), Ir (7)]. The molecular structures of complexes 3, 5 and 7 were established by single-crystal X-ray diffraction studies. 相似文献
149.
Julio Belmar Claudio Jimnez C. Ruiz‐Prez F. S. Delgado Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):o599-o601
In the title compound, C15H20N2O, the bond distances and angles are consistent with the presence of the hydroxy tautomer. This tautomer was unambiguously determined by the clear presence of a H atom bonded to oxygen, as well as the total absence of any residual electron density around the N atom in the heterocycle, thus precluding any possibility of desmotropism. 相似文献
150.
In this work the effect of the basis set superposition error (BSSE) is explored with the counterpoise method on the occupied and unoccupied Hartree-Fock (HF) and Kohn-Sham (KS) orbitals. Three different systems linked by hydrogen bonds, H(2)O...FH, H(2)O...H(2)O, and H(2)O...CFH(3), were studied by using the basis set families cc-pVXZ and aug-cc-pVXZ (X = D, T, Q). The basis sets were tested with the HF method and two approximations for the exchange-correlation functional of KS: a generalized gradient approximation and a hybrid approach. In addition to these methods, the second-order M?ller-Plesset perturbation theory, MP2, was considered. It was found that the presence of the "ghost" basis set affects the orbitals in two ways: (1) The occupied KS orbitals are more sensitive to the presence of this "ghost" basis set than the occupied HF orbitals. For this reason the BSSE observed in HF is less than that obtained with KS. (2) The unoccupied HF orbitals are more sensitive to the presence of the "ghost" basis set than their corresponding occupied orbitals. Because the MP2 method uses both, occupied and unoccupied HF orbitals, to compute the total energy, the contribution of the BSSE is bigger than that obtained with HF or KS methodologies. 相似文献