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971.
《Chemphyschem》2003,4(1):79-83
We present Monte Carlo simulations of the self‐assembly of bivalent bis‐biotinylated DNA molecules with the tetravalent biotin‐binding protein streptavidin (STV). By fitting the STV binding probabilities for the four possible valencies, the modelling correctly reproduces the dependencies of various network parameters experimentally observed in an earlier study. The combined results from the experimental and theoretical studies suggest that the binding probability for divalent STV formation is about 50 times larger than for the formation of trivalent and about 200 times larger than for tetravalent STV. In accordance with the experimental results, the modelling also indicates that the mixture of an equimolar ratio of DNA and STV leads to a maximum in size of the oligomeric DNA–STV clusters formed. Furthermore, we found a percolation transition in which the DNA cluster size increases rapidly with increasing DNA concentration resulting in the formation of a single supercluster at elevated concentrations. This behaviour coincides with the occurrence of an immobile band previously observed in electrophoretic experiments, indicating the formation of extremely large DNA–STV aggregate networks. 相似文献
972.
Sr3(BS3)2 and Sr3(B3S6)2: Two Novel Non‐oxidic Chalcogenoborates with Boron in a Trigonal‐Planar Coordination The thioborates Sr3(BS3)2 and Sr3(B3S6)2 were prepared from strontium sulfide, amorphous boron and sulfur in solid state reactions at a temperature of 1123 K. In a systematic study on the structural cation influence on this type of ternary compounds, the crystal structures were determined by single crystal X‐ray diffraction. Sr3(BS3)2 crystallizes in the monoclinic spacegroup C2/c (No. 15) with a = 10.187(4) Å, b = 6.610(2) Å, c = 15.411(7) Å, β = 102.24(3)° and Z = 4. The crystal structure of Sr3(B3S6)2 is trigonal, spacegroup R3¯ (Nr. 148), with a = 8.605(1) Å, c = 21.542(4) Å and Z = 3. Sr3(BS3)2 contains isolated [BS3]3— anions with boron in a trigonal‐planar coordination. The strontium cations are found between the layers of orthothioborate anions. Sr3(B3S6)2 consists of cyclic [B3S6]3— anions and strontium cations, respectively. 相似文献
973.
974.
975.
Crystal Structures of KNdTe4, RbPrTe4, and RbNdTe4 — Investigations concerning the Thermal Stability of KNdTe4 as well as some Remarks concerning Additional Representatives of the Composition ALnTe4 (A = K, Rb, Cs and Ln = Rare Earth Metal) Of the compounds ALnQ4 (A = Na, K, Rb, Cs; Ln = Lanthanoid; Q = S, Se and Te) the crystal structures of the three new tellurides KNdTe4, RbPrTe4 and RbNdTe4 were determined by X‐ray single‐crystal structure analysis and of the three additional new ones KCeTe4, KPrTe4 and CsNdTe4 by X‐ray powder diffraction experiments. All six new compounds are isotypic with KCeSe4. Characteristic for the crystal structure of the compounds mentioned above are layers built from (Q2)2— dumbbells in form of 4.32.4.3 nets with embedded cations A+ and Ln3+ between them, which are coordinated eightfold in form of square‐shaped antiprisms by Q ions. The distances Te‐Te within the dumbbells were found to be 277.8(2) pm for all investigated tellurides. By combination of X‐ray diffraction and DTA measurements it was shown that the compound KNdTe4 is metastable at ambient temperature with a limited existence range between the temperatures 260 and 498 °C. 相似文献
976.
Hamelin O Pécaut J Fontecave M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(10):2548-2554
Recently, we observed that the enantiopure Lambda form of the tributylammonium salt of the chiral anion tris[tetrachlorobenzene-1,2-bis(olato)]phosphate, also named Trisphat, was able to induce an efficient resolution of a Delta,Lambda racemic mixture of cis-[Ru(dmp)2(NCCH3)2](PF6)2 (dmp=2,9-dimethyl-1,10-phenanthroline) due to the spontaneous and selective precipitation of the heterochiral pair [Delta-Ru(dmp)2(CH3CN)2][Lambda-Trisphat]2. We report here that the combination of such a stereoselective precipitation process and irradiation results in the quantitative conversion of the initial [Ru(dmp)2(NCCH3)2]2+ racemate into only one of the two enantiomers. This is the first example in inorganic chemistry of an asymmetric transformation that leads to a chiral complex with no chiral ligand. Finally, three new racemic ruthenium bis(diimine) complexes, namely [Ru(dmp)2(NCCH3)Py](PF6)2 (Py=pyridine), [Ru(dmp)2(1,3-diaminopropane)](PF6)2, and [Ru(dmp)2(ethylenediamine)](PF6)2 were synthesized. For all of them, crystallization-induced asymmetric transformation proved to be an efficient way of obtaining the corresponding optically active chiral-at-metal complexes in high yields and with excellent stereoselectivities. 相似文献
977.
Chiral terpyridine ligands have been synthesized and characterized. By applying Ru(III)/Ru(II) chemistry, symmetrical as well as asymmetrical bis-terpyridine ruthenium(II) complexes were obtained. These materials were fully characterized and their optical properties investigated. While the chiral metal complexes revealed no Cotton effect in good solvents such as chloroform, CD-measurements in dodecane showed an effect in both ligand and MLCT regions, suggesting chirality transfer from the lateral alkyl chains to the complex core. This behavior points to the formation of supramolecular aggregates in dodecane. Furthermore, the analogous achiral ligand and its corresponding ruthenium(II) complexes were prepared. 相似文献
978.
Two new esters, methyl 4‐(prenyloxy)dihydrocinnamate and methyl 4‐(geranyloxy)dihydrocinnamate, together with fourteen known compounds have been isolated from the stem bark of Zanthoxylum pistaciiflorum. The structures of two new compounds were determined through spectral analyses. Among the isolates, four compounds exhibited effective cytotoxicities against P‐388 and HT‐29 cell lines in vitro. 相似文献
979.
A novel hyperbranched polyester acrylate (HPEA) was synthesized based upon ethylenediamine tetraacetic acid as a “core” molecule, 5‐hydroxyisophthalic acid as an AB2 monomer, and 2‐hydroxyethyl acrylate as an endcapping reagent. The obtained oligomer has an unsaturation concentration of 4.10 mmolC?C g?1 measured by nuclear magnetic resonance and a wide molecular weight distribution of 1.64 measured by gel permeation chromatography. The two‐photon absorption (TPA) photopolymerization of HPEA under the exposure of a Ti : sapphire femtosecond laser with a wavelength of 800 nm was investigated through laser exposure dose‐dependant spatial resolutions of its resins. The TPA photopolymerization thresholds at the range 1.6–4.3 × 107 mJ cm?2, and exposure dose windows at the range 3.4–4.3 for three formulations were determined. A spatial resolution of 0.85 μm was obtained through the TPA photopolymerization of the formulation containing 1 wt% photoinitiator and 0.3 wt% photoinhibitor. A diffraction grating and real three‐dimensional coupled gear wheel created by TPA photopolymerization were described to demonstrate the unique capability of HPEA in microfabrications. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
980.
R. Demchyna J. P. F. Jemetio Yu. Prots Th. Doert L. G. Akselrud W. Schnelle Yu. Kuz'ma Yu. Grin 《无机化学与普通化学杂志》2004,630(5):635-641
Single crystals of CeAgAs2 have been obtained by chemical transport reactions starting from a pre‐reacted powder sample. The crystal structure was solved using X‐ray diffraction (space group Pmca, No. 57, a = 5.7586(4) Å, b = 5.7852(4) Å, c = 21.066(3) Å, Z = 8) and refined to a residual of R(F) = 0.029 for 46 refined parameters and 1020 reflections. The structure of CeAgAs2 represents a new distorted and ordered variant of the HfCuSi2 type. The characteristic feature of this structure are infinite cis‐trans chains of As atoms with As—As distances of 2.563(1) Å and 2.601(1) Å. CeAgAs2 is paramagnetic (μeff = 2.37 μB, θ = —10.5(2) K), with antiferromagnetic ordering at 5.5(2) K and exhibits a metamagnetic transition starting at 4.6 kOe and T = 1.8 K. 相似文献