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121.
L. Morales A. Caneiro D. VegaR. Zysler H. LanzaR.C. Mercader 《Journal of solid state chemistry》2002,168(1):100-109
The incorporation of Sn into LaMnO3 perovskite and its influence on magnetotransport properties were studied in samples synthesized at low temperature. Single-phase materials for two series of samples with La/(Sn+Mn)=1 and La/(Sn+Mn)<1 ratios were obtained by substitution of up to 10% of the Mn ions by Sn4+. The effect of Sn substitution was monitored through measurements of thermal, “M(T)”, and magnetic field, “M(H)”, dependences of magnetization, as well as of resistivity, “ρ(T)”, at 0 and 70 kOe. These showed that this effect depends strongly on the perovskite cation site ratio (A/B). For La/(Sn+Mn)=1, M and TC were depressed as Sn content was increased. The magnetization data suggest the presence of magnetic clusters with superparamagnetic behavior. No evidence of magnetoresistance (MR) was found. For La/(Sn+Mn)<1 ratio, the samples showed ferromagnetic behavior and MR and both M and TC raised as Sn content increased. The results are discussed in terms of A site vacancies. 相似文献
122.
Zhen‐Yi Jiang Xiao‐Hong Xu Hai‐Shun Wu Fu‐Qiang Zhang Zhi‐Hao Jin 《International journal of quantum chemistry》2004,97(4):876-882
Geometric and electronic properties of CmN2 (m = 1–14) clusters have been investigated by density functional theory using the hybrid B3LYP functional and the 6‐311G(d) basis set. Harmonic frequencies for these clusters are given to aid in the characterization of the ground states. These results show that CmN2 (m = 1–14) clusters form linear structures with D∞h symmetry. Two N atoms favor to bond at ends in linear isomers. The chains with odd m have triplet ground states whereas the ones with even m have singlet ground states. The calculated HOMO–LUMO gaps and ionization potentials all show that the CmN2 (m = 1–14) clusters with even m are more stable than those with odd m, which is consistent with the observed even–odd alternation of the time‐of‐flight signal intensities. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
123.
We discuss the impact of density functional electronic structure calculations for understanding the organometallic chemistry of transition metal (TM) surface complexes and clusters. Examples will cover three types of systems, mainly of interest in the context of heterogeneous catalysis: (i) supported carbonyl complexes of rhenium on MgO and of rhodium in zeolites, (ii) TM clusters with CO ligands and adsorbates, and (iii) metal clusters exhibiting chemical bonds with atomic carbon. The first group of case studies promotes the concept that surface groups of oxide supports are bonded to TM complexes in the same way as common (poly-dentate) ligands are bonded in coordination compounds. The second group of examples demonstrates various “ligand effects” of TM clusters. Finally, we illustrate how carbido centers stabilize TM clusters and modify the propensity for adsorption at the surface of such clusters. 相似文献
124.
19F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo6Br Cl )F ]2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo6BrCl)4+ is formed by exchange of innersphere bound Cli against outersphere bound Bra on tempering the solid [(Mo6Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H3O)2[(Mo6BrCl)Cl] and precipitation of the outer Cla with AgBF4 in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)2 [(Mo6BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 19F nmr signals are expected, which are really observed in the high resolution 1D-19F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-19F/19F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers. 相似文献
125.
Koridze A. A. Zdanovich V. I. Lagunova V. Yu. Petukhova I. I. Dolgushin F. M. Starikova Z. A. Ezernitskaya M. G. Petrovskii P. V. 《Russian Chemical Bulletin》2002,51(5):876-886
The thermal reaction of Ru3(CO)10(-Ph2PCH2PPh2) (1) with enyne PhCH=CHCCPh afforded the trinuclear ruthenium clusters Ru3(CO)6{3-P(Ph)CH2PPh2}{3-C(Ph)=CHCC(Ph)(1,2-C6H4)C(=0)} (2), Ru3(-H)(CO)5{3-P(Ph)CH2PPh2}{3-C(Ph)=CHCC(Ph)(1,2-C6H4)C(—0)} (3), and Ru3(CO)6(-CO){3-P(Ph)CH2PPh2}{3-C(C=CPh2)CH=C(H)Ph} (4) and also two isomers of Ru3(CO)5(-CO)(-Ph2PCH2PPh2){3-C4Ph2(CH=CHPh)2} (5a and 5b). Clusters 2, 3, and 4 were characterized by IR spectroscopy, 1H and 31P NMR spectroscopy, and X-ray diffraction analysis. The reaction of complex 1 with enyne FcCH=CHCCFc gave rise to the Ru3(CO)6{3-P(Ph)CH2PPh2}{3-C(Fc)=CHCC(Fc)(1,2-C6H4)C(=0)} (6) and Ru3(-H)(CO)5{3-P(Ph)CH2PPh2}{3-C(Fc)=CHCC(Fc)(1,2-C6H4)C(—0)} (7) clusters. According to the spectral data, the latter compounds are isostructural to complexes 2 and 3, respectively. 相似文献
126.
127.
Preparation and characterization of the first derivatives of the fused macropolyhedral anion [B22H22]2− are reported. The species [B22H21OH]2− (1) and [B22H21OEt]2− (2) are obtained from workup of the products of the reaction between HgBr2 and [NBzlEt3]2[B22H22]; a cluster involving the conjoining of a closo-B12 icosahedron with a nido-B10 cluster. Washing the products with ethanol followed by thin-layer chromatography allows the isolation of 1 and 2, reproducibly, in yields of 27 and 20%, respectively. The species were characterized by NMR spectroscopy, elemental analysis and X-ray diffraction studies. The crystal structure determinations of the two species identify novel features. Apparently the influence of the O atoms in the ions [B22H21OH]2− and [B22H21OEt]2− results in the lengthening of what was a gunwale B---B connection adjacent to the junction of the two cages such that the distances are 2.180 and 2.230 Å, respectively. These latter are longer than the corresponding distance in the parent species [B22H22]2−, which is 2.09 Å; quite long for a normal B---B distance. Thus it is assumed that these B atoms, in 1 and 2, one of which bears the substituent, are not bonded to each other. 相似文献
128.
The LiHe+
n
, the NaHe+
n
, and the MgHe+
n
complexes with n=1, 2, 3, 4 were studied using ab initio calculations with the MP2/6-311+G(3df, 3pd) method. The complexes are found to be stable. For the n=1 complexes, previous results were available and the calculations performed are in good agreement with those results. This lends credibility to the results obtained for the complexes with higher n. 相似文献
129.
《Angewandte Chemie (International ed. in English)》2017,56(43):13249-13252
The reaction of [(DippForm)2Ln(thf)2] with an excess of elemental sulfur in toluene resulted in the formation of the trinuclear polysulfide coordination clusters [(DippForm)3Ln3S12] (Ln=Sm, Yb; DippForm=N,N′‐bis(2,6‐diisopropylphenyl)formamidinate). These are the first f element coordination clusters (LnnSx) with a larger polysulfide unit (n and x>2). The formation of the coordination clusters can be rationalized by the reductive cleavage of S8 with divalent lanthanides. 相似文献
130.
Michał Terlecki Dr. Szymon Sobczak Dr. Michał K. Leszczyński Prof. Andrzej Katrusiak Prof. Janusz Lewiński 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(55):13757-13764
Understanding the factors governing the formation of supramolecular structures and phase transitions between various forms of molecular crystals is pivotal for developing dynamic, stimuli-responsive materials and polymorph-controlled syntheses. Here, we investigate the pressure-induced dynamic of both the intrinsic molecular structure and the supramolecular network of a predesigned polyhedral oxo-centered zinc cluster incorporating monoanionic N,N’-diphenylformamidinate and featuring N-bonded phenyl groups in close proximity to the primary coordination sphere. We demonstrate that the model oxo cluster is prone to undergoing pressure-induced conformational transformations of the secondary coordination sphere and simultaneous stepwise (initially every second polyhedral molecule undergoes the conformational transformations) and reversible transitions from an ambient phase α to high-pressure phases β and γ, as single-crystal-to-single-crystal events. The observed phase transitions illustrate the key role of an interplay between the low-energy conformation perturbations and cooperative intra- and intermolecular noncovalent interactions. 相似文献