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81.
Sven Rau 《Journal of organometallic chemistry》2004,689(22):3582-3592
The binuclear complex [(acac)Pd(oxam)Pd(acac)] 1 (oxam: tetraphenyl oxalic amidinate) has been prepared from H2oxam and Pd(acac)2 in excellent yield. The complex was characterized by elemental analyses, mass spectroscopy, 1H NMR, 13C NMR spectroscopy and in the solid state by X-ray single crystal diffraction analyses. 1 consists of a bimetallic centrosymmetric unit in which the planar oxam ligand acts in a bis-chelating fashion. Each palladium center is in a planar environment.The complex 1 acts as highly selective pre-catalyst in the copper-free Sonogashira reaction between 4-bromoacetophenone and phenylacetylene. Its long-time catalytic activity is higher than that of the related binuclear complex 2 (oxam: tetra-p-tolyl oxalic amidinate) or that of the trinuclear compound [(acac)Pd(oxam)Zn(oxam)Pd(acac)] (3), the solid-state structure of which was also determined by an X-ray structural analysis of single crystals. In addition, 2 is an active and extremely selective pre-catalyst for the Negishi reaction between 3,5,6,8-tetrabromophenanthroline and R-CC-ZnCl (R: Ph, (iprop)3Si) to form tetra-alkyne-substituted derivatives. 相似文献
82.
Zusammenfassung Durch Hinzunahme von Magnesiumoxid zur Verbrennungsrohrfüllung wird der Anwendungsbereich des CHN-Automaten auf fluor- und phosphorhaltige Proben erweitert. Diese beiden Elemente werden im wesentlichen in der Magnesiumoxidzone der Füllung gebunden. Bei manchen phosphorhaltigen Verbindungen macht die geringe Pyrolysegeschwindigkeit einen längeren Analysezyklus notwendig. Die längere Verbrennungszeit wird durch eine Reduzierung des Gasstromes ermöglicht. Bei metallhaltigen Proben geben alle Verbindungen, deren Metalle unter den herrschenden Bedingungen definierte Rückstände bilden, ohne besondere Maßnahmen gute Werte. Die Bildung carbonathaltiger Rückstände bei Alkali und Erdalkali wird meistens von der Apparatur als solche registriert.
Die Firma Technicon hat uns für diese Untersuchungen dankenswerterweise einen CHN-Analyzer zur Verfügung gestellt. 相似文献
Summary The field of application of the CHN-automatic combustion devices is extended to samples containing fluorine and phosphorus by including magnesium oxide in the filling of the combustion tube. These two elements are essentially bound in the magnesium oxide zone. Many compounds containing phosphorus make it necessary to reduce the speed of the gas stream because of the low pyrolysis velocity. When samples containing metals are being analyzed, excellent results are obtained with all compounds whose metals yield definite residues under the prevailing conditions. The formation of residues containing carbonate in the case of alkali and alkaline earths is usually registered as such by the apparatus.
Die Firma Technicon hat uns für diese Untersuchungen dankenswerterweise einen CHN-Analyzer zur Verfügung gestellt. 相似文献
83.
Mechanism of Thermal Dehydration of Sodium Dihydrogenphosphate The thermal dehydration of sodium dihydrogenphosphate (P1) to sodium cyclotriphosphate (CP3) and sodium polyphosphate, the so-called Maddrell's salt (MS), is controlled by nucleation and crystallization of CP3 and MS, respectively. The wellknown influence of various formation conditions on the CP3:MS product ratio is caused by amorphous and crystalline intermediate phases and their ability to form CP3 or MS nuclei. On seeding P1 with CP3 or MS the dehydration proceeds structure-controlled via dihydrogendiphosphate to pure CP3 or pure MS. The particularities of thermal dehydration of crystalline sodium dihydrogendiphosphate, and also the dehydration and reorganization of sodium phosphate glasses (Na:P = 1:1) with different mean chain lengths, under formation of CP3 or MS are described. 相似文献
84.
The varying -bonding contributions in the title compounds caused by the different electronic and molecular structure of the chelate rings are used for explaining the large band splittings in the absorption spectra by trigonal symmetry. It is shown that usual ligand field theory and the angular overlap model are not able to account for the trigonal level splitting of Cr(acac)3 for which the coordination sphere of oxygen atoms is nearly octahedrally arranged. The experimental finding can, however, be rationalized by an extended angular overlap model which considers the phase coupling of -orbitals in the ligands leading to non-additive contributions to the metal-ligand bond energy.On leave of absence from the Bulgarian Academy of Sciences, Sofia, Bulgaria 相似文献
85.
The theory of chirality functions described in a previous publication is generalized to allow for chiral ligands. In the earlier theory, all symmetry operations of the molecular frame could be thought of as permutations of the ligands among the sites; in the present work, improper rotations not only permute the ligands, but convert them into mirror images. The group that generates all isomers from a given ordered molecule belonging to a frame with n sites is now the hyperoctahedral group of order 2n
n! consisting of all possible combinations of permutations and site reflections. The representation theory of these groups is described, and applied to the problem of constructing qualitatively complete chirality functions, and of deciding which ligand partitions, and which isomer mixtures, are chiral. It is found useful to classify chiral representations of the covering group as ligand specific and class specific. The ligand specific representations describe chiral properties which are common to all frames and arise purely from the chirality of the ligands, while the class specific representations describe the chiral properties of the frame. A number of examples are explicitly worked out. 相似文献
86.
F. Asinger W. Schäfer H. Meisel H. Kersten A. Saus 《Monatshefte für Chemie / Chemical Monthly》1967,98(2):338-352
Zusammenfassung 2,2,5-Trisubstituierte Imidazolidin-thione-(4) lassen sich mittels Schwefels mit guten Ausbeuten zu Imidazolin-(3)-thionen-(5) dehydrieren. Hierüber sowie über einige Verbesserungen der bisher bekannten Synthesen für insbesondere 2,2,5-trisubstituierte Imidazolidin-thione-(4) wird berichtet.
Mitt.:F. Asinger, W. Schäfer undH. Triem, Mh. Chem.97, 1510 (1966).
Teil der Dissertation vonH. Meisel, Techn. Hochschule Aachen, 1963.
Teil der Dipl.-Arbeit vonHilde Kersten, Techn. Hochschule Aachen, 1963, und Teil der Dissertation vonHilde Kersten, Techn. Hochschule Aachen, 1965. 相似文献
Dehydration of 2.2.5-trisubstituted imidazolidine-(4)-thiones with elementary sulfur gives in good yields 3-imidazoline-(5)-thiones. This reaction and improved methods of the well known syntheses of especially 2.2.5-trisubstituted imidazolidine-(4)-thiones are described.
Mitt.:F. Asinger, W. Schäfer undH. Triem, Mh. Chem.97, 1510 (1966).
Teil der Dissertation vonH. Meisel, Techn. Hochschule Aachen, 1963.
Teil der Dipl.-Arbeit vonHilde Kersten, Techn. Hochschule Aachen, 1963, und Teil der Dissertation vonHilde Kersten, Techn. Hochschule Aachen, 1965. 相似文献
87.
The systems AeAl(2-x)Mgx (Ae = Ca, Sr, Ba) display electron concentration induced Laves phase structural changes. However, the complete sequence MgCu2 --> MgNi2 --> MgZn2 with increasing x (decreasing electron count) is only observed for Ae = Ca. Compounds SrAl(2-x)Mgx (0 < x < or = 2) and BaAl(2-x)Mgx (x = 0.85 and 2.0) were synthesized and structurally characterized by X-ray diffraction experiments. For the Sr system the structural sequence CeCu2 --> MgNi2 --> MgZn2 occurs with increasing Mg content x. Thus, larger Sr does not allow the realization of the MgCu2 structure at low x. For Ae = Ba a binary compound BaAl2 does not exist, but more Ba-rich Ba7Al13 forms. The reinvestigation of the crystal structure of Ba7Al13 by selected area and convergent beam electron diffraction in a transmission electron microscope revealed a superstructure, which subsequently could be refined from single X-ray diffraction data. The formula unit of the superstructure is Ba21Al40 (space group P31m, Z = 1, a = 10.568(1) angstroms, c = 17.205(6) angstroms). In Ba21Al40 a size match problem between Ba and Al present in Ba7Al13 is resolved. The structure of Ba7Al13 (Ba21Al40) can be considered as a Ba excess variant of the hexagonal MgNi2 Laves phase type structure. An incommensurately modulated variant of the MgNi2 structure is obtained for phases BaAl(2-x)Mgx with x = 0.8-1. At even higher Mg concentrations a structural change to the proper MgZn2 type structure takes place. 相似文献
88.
Hausner SH Striley CA Krause-Bauer JA Zimmer H 《The Journal of organic chemistry》2005,70(15):5804-5817
Dibenzotetraaza (DBTA) crown ethers possess two o-phenylenediamine moieties. They are homologues of dibenzo crown ether phase-transfer catalysts and were prepared from the condensation of benzimidazoles with oligo(ethyleneglycol) dichlorides and oligo(ethyleneglycol) ditosylates. Compounds with ring sizes ranging from 18-crown-6 to 42-crown-14 were prepared. In addition, various altered benzimidizoles were used to produce DBTA crown ethers with modified substituents and ether bridges, as well as benzimidazolidine crown ethers. The synthetic approach presented here proved to be a convenient route to a new family of crown ethers with overall yields of up to 48% based on the benzimidazole. Yields for the ring-closing step were generally high, ranging from 51% to 94%, without the need for high-dilution conditions. Reaction of the DBTA crown ethers with alkyl and benzyl halides was found to be a facile way to obtain the corresponding tetra(N-organyl) compounds. Picrate extraction studies were carried out to determine phase-transfer catalytic capabilities. Extraction efficiencies for alkali-metal ions were lower than those for dibenzo-18-crown-6. Efficiencies were higher for other metal ions, with some selectivity for Pb(2+). Tetra(N-methyl) DBTA-18-crown-6 generally exhibited higher extraction efficiencies than its N-H analogue, but the selectivity was lower. 相似文献
89.
Mass spectrometric identification and characterization of steroids using electrospray ionization and tandem mass spectrometry has advantages in drug testing and doping control analysis attributable to limitations of gas chromatography followed by electron ionization mass spectrometry. Steroids with an androstadiene-17beta-ol-3-one nucleus and double bonds located either at C-1 and C-4, C-4 and C-9, or C-4 and C-6 were used to determine characteristic fragmentation pathways. Diagnostic dissociation routes are proposed using deuterium labeling, MS3 experiments, and analyses of structurally closely related compounds. Steroids such as boldenone (androst-1,4-diene-17beta-ol-3-one) produced characteristic product ions at m/z 121, 135, and 147. Compounds with double bonds at C-4 and C-9 generated abundant product ions at m/z 145 and 147. Conjugated double bonds at C-4 and C-6 gave rise to an intense and characteristic signal at m/z 133. Stereochemical differentiation between 5alpha- and 5beta-isomers of androstan-17beta-ol-3-ones was possible because of significant differences in relative abundance of product ions generated by elimination of acetone from alpha,beta-saturated 3-keto steroids. 相似文献
90.
Ansgar Schäfer Christian Huber Jürgen Gauss Reinhart Ahlrichs 《Theoretical chemistry accounts》1993,87(1-2):29-40
Summary Experimentally known copper selenium clusters show extraordinary geometrical features, especially short Cu-Cu distances. We report the first theoretical investigation of Cu2Se and Cu4Se2. Various quantum chemical methods (SCF, MP2, CPF, CCSD, CCSD(T), LDF) are applied to determine the importance of dynamic electron correlation. We find that inclusion of correlation does not essentially change the electronic structure of the clusters but has a strong influence on geometries. To reduce the computational effort we apply effective core potentials (ECPs) in combination with small, but carefully optimized basis sets. The applicability of simple modellings of correlation energies for approximate inclusion of correlation effects in SCF geometry optimizations is tested. 相似文献