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81.
Maffei AV Budd PM McKeown NB 《Langmuir : the ACS journal of surfaces and colloids》2006,22(9):4225-4229
The adsorption/desorption of N2 at 77 K and the adsorption from aqueous solution at 298 K of four organic probe molecules of different sizes (phenol, 4-nitrophenol, orange II, naphthol green B) were studied for a phthalocyanine network polymer of intrinsic microporosity (PIM) and for an activated carbon (Darco 20-40 mesh). N2 sorption analysis gave similar surface areas for the PIM and the carbon (610 and 545 m2 g(-1), respectively) but showed differences in pore size distribution, the PIM being essentially microporous (pore size < 2 nm), with a high proportion of ultramicropores (<0.7 nm), while the carbon had a broader pore size distribution, extending into the mesopore region. The carbon acted as an adsorbent for all the organic probe molecules studied, while the PIM was more selective, adsorbing the smaller molecules but rejecting the large dye naphthol green B. The PIM offers selectivity combined with a well-defined chemical structure incorporating catalytic sites. 相似文献
82.
Becker E Stingl V Dazinger G Puchberger M Mereiter K Kirchner K 《Journal of the American Chemical Society》2006,128(20):6572-6573
The reaction of [RuCp(IPri)(CH3CN)2]PF6 (IPri = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with HCCR (R = COOMe, COOEt, COMe) yields the allyl carbene complexes [RuCp(=C(R)-eta3-CHC(R)CH-IPri)]PF6. This conversion involves selective head-to-tail coupling of two alkynes and an unusual migratory insertion of the N-heterocyclic carbene into the ruthenium-carbon double bond of a ruthenacyclopentatriene intermediate. 相似文献
83.
Although potassium, rubidium, and cesium uranyl nitrate have been characterized a long time ago, the crystal structure and properties of the homologous sodium compounds has not been reported yet. Na[UO2(NO3)3] crystallizes in a unique structure [Pearson code cP72, cubic, P213, no. 198, Z = 4, a = 10.6324(14) Å, 938 unique reflections with Io > 2σ(Io), R1 = 0.0379, wR2 = 0.0947, GooF = 1.092, T = 293 K]. The structure is characterized by an open framework built by interconnected helical chains formed by {UO8} and {NaO6} units. The vibrational and optical (UV/Vis absorption and luminescence) spectra match well with those of the higher alkali metal uranyl nitrates. 相似文献
84.
85.
Verena Jung Vadim Ksenofontov Maria-Louisa Aigner Thomas Pfeiffer Dirk Sprenger Claudia Felser 《Hyperfine Interactions》2008,183(1-3):215-220
In this work Mössbauer spectroscopy is used to investigate the oxidation states and structures of tin in silicate glasses. Thermal treatment of the glasses in atmospheres with varying oxygen partial pressure leads to the simultaneous appearance of reduction and diffusion. Experiments with varying treatment time give the opportunity to study diffusion and reduction processes in detail. Comparison of the hyperfine parameters of reference materials with measured parameter provides information about the local surroundings of the tin atoms. An octahedral surrounding for Sn4?+? is presumed, while Sn2?+? and three oxygen atoms form a tetrahedral coordination. 相似文献
86.
Claudia Bartels Martin Wegrzyn Anne Wiedl Verena Ackermann Hannelore Ehrenreich 《BMC neuroscience》2010,11(1):118
Background
Cognitive deterioration is a core symptom of many neuropsychiatric disorders and target of increasing significance for novel treatment strategies. Hence, its reliable capture in long-term follow-up studies is prerequisite for recording the natural course of diseases and for estimating potential benefits of therapeutic interventions. Since repeated neuropsychological testing is required for respective longitudinal study designs, occurrence, time pattern and magnitude of practice effects on cognition have to be understood first under healthy good-performance conditions to enable design optimization and result interpretation in disease trials. 相似文献87.
88.
Krebs A Ludwig V Pfizer J Dürner G Göbel MW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(2):544-553
We present two complementary methods for the stereoselective synthesis of non-natural alpha-amino acids with aromatic or heteroaromatic side chains. One approach is based on the chemical transformation of methionine, whereas the other applies the stereoselective Myers alkylation of glycine. The resulting product types differ in the linker length between glycine and the aromatic substituent. Since methionine and pseudoephedrine are available in both absolute configurations, R- or S-configured enantiopure amino acids with either C(2) or C(3) linkers can be obtained on gram scales. In each case the key step of the synthesis is hydroboration of the unsaturated building blocks 9 and 17, followed by palladium-catalyzed Suzuki cross-coupling with aryl halides. Attention must in certain cases be paid to the stereochemical integrity when basic Suzuki conditions are applied. Our initial difficulties are reported as well as the final "racemization-proof" procedures. The protecting groups chosen for the alpha-amino acids should be compatible with solid-phase peptide synthesis. This was confirmed by the successful synthesis of a series of tripeptides. 相似文献
89.
The biosynthesis of caulerpenyne 1 was studied in the invasive green alga Caulerpa taxifolia. The investigation was performed on intact algae with stable-isotope-labeled precursors administered under mixotrophic growth conditions. According to the labeling pattern, after incorporation of 1-(13)C-acetate and (13)CO(2), respectively, the biosynthesis of the sesquiterpene backbone occurs in the chloroplast and follows the methyl-erythritol-4-phosphate (MEP) pathway. In contrast, the acetyl residues of caulerpenyne 1 are derived from a cytosolic resource. [structure: see text] 相似文献
90.
The synthesis of a novel hybrid pyrazolate/phosphine anionic ligand [CH2=CHCH2B(CH2PPh2)(pz)2]- is described. Coordination of this ligand to metals in a fac tridentate fashion occurs in the complexes [CH2=CHCH2B(CH2PPh2)(pz)2M(cod)], prepared by reactions of the lithium salt of the ligand with [M(mu-Cl)(cod)]2 (M=Rh, Ir). They are pentacoordinated, with the rhodium complex showing a distorted trigonal-bipyramidal structure in the solid state, as determined by X-ray diffraction methods. Furthermore, the ligand has been linked to the periphery of a carbosilane dendrimer, resulting in the polyanionic dendrimer [Li(TMED)]4[Si{(CH2)3SiMe2(CH2)3B(CH2PPh2)(pz)2}4], which leads further to the corresponding metallodendrimer with four rhodium atoms. 相似文献