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11.
P.A. Bates E.J. Ditzel M.P. Hartshorn Huong Tuong Ing K.E. Richards W.T. Robinson 《Tetrahedron letters》1981,22(24):2325-2328
Dinitration of 2,4,5-tribromo-3,6-dimethylphenol(1) gives either the tribromodinitro-compound(2) or its acyloin rearrangement product(3), depending on the reaction conditions: X-ray crystal structure analyses are reported for compounds (2) and (3). 相似文献
12.
Journal of Global Optimization - Improperly efficient solutions in the sense of Geoffrion in linear fractional vector optimization problems with unbounded constraint sets are studied systematically... 相似文献
13.
A family of homochiral metal carboxylate coordination polymers have been synthesized by treating 2,2'-dihydroxy-1,1'-binaphthalene-6,6'-dicarboxylic acid (H(2)BDA) with metal salts at elevated temperatures. BDA ligands link adjacent metal centers to form 1D coordination polymeric chains using the carboxylate functionality, while the hydroxyl groups of BDA ligands form H-bonds with carboxylate oxygen atoms to link 1D coordination polymeric chains into open frameworks of higher dimensionality. We also present evidence for the important role played by H-bonds in the stabilization of open framework structures which allows for the hierarchical assembly of chiral porous solids. 相似文献
14.
A rapid and sensitive flow-injection method is described for the fluorimetric determination of the proteolytic activity of a number of enzymes. The substrate, fluorescein-labelled bovine serum albumin coupled to a 2-fluoro 1-methylpyridinium salt-activated Fractogel support, is packed in a small reactor (35 × 2 mm i.d.) and inserted into a flow manifold. Under the reaction conditions the amount of fluorescein released from enzymatic cleavage of the substrate is found to be directly proportional to the activity of the proteolytic enzyme. Sample throughput is 30–35 h?1. The calibration range for trypsin is linear up to at least 0.35 μg ml?1. Linear responses were also obtained for otherproteolytic enzymes such as papain, chymotrypsin, ficin and bromelain. 相似文献
15.
James D. Korp Ivan Bernal Nikolaus H. Fischer Charles Leonard Ihl-Young Lee Ngo LeVan 《Journal of heterocyclic chemistry》1982,19(1):181-187
The isolation and structure determination of two new guaianolides, pumilin and its 2,3-epoxide, from Berlandiera pumila and B. texana are reported. The structure of pumilin was determined from nmr and mass spectral data, and from an X-ray single crystal study; the structure of the epoxide was found by comparison of nmr spectra. Pumilin is shown to be a Δ1(10)-cis-guaianolide with a cyclopentenone ring attached to C1 and C5, and an α-methylene-γ-lactone ring trans-fused to C6 and C7. The absolute configuration was inferred from spectral considerations and knowledge of previous structural determinations. The cd spectrum of pumilin exhibits a negative Cotton effect, and the lactone chromophore has left-handed chirality. The cyclo-heptene ring is in the chair configuration, with the lactone a half-chair and the cyclopentenone essentially planar. Crystals are orthorhombic, a = 7.065, b = 13.652, c = 19.586 Å, space group P212121, Z = 4, and the final R value is 3.9%. The crystal structure is strengthened by an O···O hydrogen bond linking the molecules into infinite chains. 相似文献
16.
Pierre Thuéry Nelly Keller Monique Lance Julien-Daniel Vigner Martine Nierlich 《Journal of inclusion phenomena and macrocyclic chemistry》1994,20(1):89-96
The doubly deprotonated form of calix[6]arene, with two protonated triethylamines as counter-ions, crystallizes in the monoclinic system: space groupP21/n,a=8.465(4),b=17.822(8),c=15.182(6) Å,=90.18(4)°,V=2291(2) Å3,Z=2. Refinement led to a final conventionalR value of 0.063 for 1046 reflections. The macrocycle conformation is not apinched cone, usual for freeR-calix[6]arene, but a distorted 1,2,3-alternate cone, since the molecule lies on a symmetry center. Furthermore, one of the torsion angles defined by the methylene bridges is near to zero, which is unusual in calixarene structures.
Supplementary Data relating to this article (atomic coordinates for hydrogen atoms, anisotropic displacement parameters for oxygen and nitrogen atoms, and observed and calculated structure factors) are deposited with the British Library as Supplementary Publication No. SUP 82182 (7 pages). 相似文献
17.
C. Hinnen C. Nguyen Van Huong A. Rousseau J.P. Dalbera 《Journal of Electroanalytical Chemistry》1979,95(2):131-146
The admittance and differential reflectivity of an electrode of polycrystalline gold in contact with aqueous 0.02 M NaF, KClO4, 0.01 M Na2SO4 and KCl have been measured in the range of potential where the electrode is ideally polarized (?0.7 V to 0.8 V NHE). In NaF and KClO4 evidence was obtained for the compression of the adsorbed layer of water. The increase of the number of water molecules, with respect to the number in the least original state (at?4μC cm?2), is 3% at +8 μC cm?2 and at?17 μC cm?2. At the potential of zero charge the water dipoles are oriented preferentially with the oxygen towards the metal. In KCl the optical measurements confirm the existence of two types of Au?Cl? interaction and the covalent character of the bond at the most positive charges. 相似文献
18.
P. Thuéry M. Nierlich C. Bressot V. Lamare J. F. Dozol Z. Asfari J. Vicens 《Journal of inclusion phenomena and macrocyclic chemistry》1995,23(4):305-312
The crystal structures of two binuclear complexes between caesium and 1,3-calix[4]-bis-crowns have been determined. Cs2
Bis-benzoC6(NO3)2. 3CHCl3 (1) in whichBis-benzoC6 is 1,3-calix[4]-bis-benzo-crown-6, crystallizes in the orthorhombic system: space groupPca2
1 a=19.513(10),b=15.382(5),c=23.708(9) Å,V=7116(5) Å3,Z=4. Refinement led to a final conventionalR value of 0.065 for 2321 reflections. The structure of (1) is analogous to those already reported withBis-C6, (in whichBis-C6 is, 1,3-calix[4]-bis-crown-6) and NO
3
–
as a counter-ion. Cs2
Bis-C6(NCS)2 (2) crystallizes in the monoclinic system: space, groupC2 a=36.57(2),b=11.47(1),c=13.65(1) Å, =109.03(5)°.,V=5415(6) Å3,Z=4. Refinement led to a final conventionalR value of 0.063 for 2227 reflections. Compound (2) is made of dimers bridged by a disordered NCS– ion. The crown ether chain conformations are discussed.
Supplementary data relating to this article (atomic coordinates, anisotropic displacement parameters, bond distances and angles and observed and calculated structure factors) are deposited with the British Library as Supplementary Publication No. SUP 82199 (52 pages). 相似文献
19.
Preparation of Ammonium Rare Earth Halides totally free of Water Ammonium rare earth halides totally free of traces of water were prepared in an one step synthesis from metal, ammonium halide, and halogen in a two step temperature regime. 相似文献
20.
Analysis of organotin compounds by grignard derivatization and gas chromatography-ion trap tandem mass spectrometry 总被引:1,自引:0,他引:1
Tsunoi S Matoba T Shioji H Giang le TH Harino H Tanaka M 《Journal of chromatography. A》2002,962(1-2):197-206
The determination of organotin compounds in water using gas chromatography-tandem mass spectrometry (GC-MS-MS) is described. Several organotin derivatives were synthesized by the reaction of organotin chlorides with Grignard reagents such as methyl-, propyl- and pentylmagnesium halides. After the optimization of the GC-MS-MS conditions, several derivatizations with the Grignard reagents were compared by evaluating the molar responses and volatilities of the derivatives and derivatization yields. As a result, the derivatizing reagent of choice is pentylmagnesium bromide. Calibration curves for the mono-, di- and tributyltins and mono-, di- and triphenyltins with pentylmagnesium bromide were linear in the range of 0.5-100 pg of Sn. The instrumental detection limits of six organotins ranged from 0.20 to 0.35 pg of Sn. The recovery tests from water samples (500 ml) were performed by using sodium diethyldithiocarbamate (DDTC) as a complexing reagent. Except for monophenyltin, the absolute recoveries of organotins from pure water at 200 ng of Sn/l were satisfactory. The recoveries calibrated by surrogate compounds (perdeuterated organotin chlorides) ranged from 71 to 109%. The method detection limits ranged from 0.26 to 0.84 pg of Sn (500-ml sample). This method was applied to the recovery of organotins from river water and seawater. The calibrated recoveries were between 90 and 122%. 相似文献