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31.
ZrIV and TaV Complexes with Methano‐Bridged Bis(aryloxy) Ligands The bis(aryloxy) ligand precursor compounds bis(2‐trimethylsiloxy‐5‐tbutylphenyl)methane (L–SiMe3) and its bromoderivative (2‐trimethylsiloxy‐3‐bromo‐5‐tbutylphenyl)(2′‐trimethylsiloxy‐5′‐tbutylphenyl)methane (LBr–SiMe3) are prepared in analogy to the corresponding calixarenes in excellent yields. X‐ray structure analysis for LBr–SiMe3: space group P21/c, a = 12.462(7), b = 10.466(6), c = 23.315(14) Å, β = 105.02(4)°, V = 2937(3) Å3, Z = 4. L–SiMe3 and LBr–SiMe3 react with ZrIV and TaV chlorides in very good yields forming di‐ and trinuclear complexes. From the reaction of CpZrCl3 with LBr–SiMe3 in the ratio of 3 : 2 a Zr3 complex ( 7 ) is obtained, with one LBr ligand only, which Zr atoms are bridged by a μ3‐oxygen. The X‐ray structure analysis of 7 (space group R 3, a = 33.23(6), c = 24.47(8) Å, V = 23405(128) Å3, Z = 18) additionally reveals that one phenolato oxygen atom of the LBr ligand is terminally bound to a distorted tetragonal‐pyramidal coordinated Zr atom, while the second phenolato oxygen atom of the LBr ligand forms a bridge to another Zr atom with a distorted octahedral coordination. The third Zr atom is also found in a distorted octahedral coordination mode. The reactions of L–SiMe3 and LBr–SiMe3 with CpTaCl4 and TaCl5 yield dinuclear Ta complexes with a bridging bis(aryloxy) ligand. NMR spectroscopic data point out that the coordination of the bis(aryloxy) ligands in the Ta complexes very much resembles that in the Zr3‐complex with one terminal and one bridging phenolato oxygen atom. The Zr3 and the Ta complexes LBrTa2Cp2Cl6 and LTa2Cl8 were tested with respect to their catalytic properties in olefin polymerisation reactions in the presence of MAO. 相似文献
32.
Eyal Ackerman Kevin Buchin Christian Knauer Rom Pinchasi Günter Rote 《Discrete and Computational Geometry》2008,39(1-3):3-16
A finite planar point set P is called a magic configuration if there is an assignment of positive weights to the points of P such that, for every line l determined by P, the sum of the weights of all points of P on l equals 1. We prove a conjecture of Murty from 1971 and show that if a set of n points P is a magic configuration, then P is in general position, or P contains n−1 collinear points, or P is a special configuration of 7 points.
The research by Rom Pinchasi was supported by a Grant from the G.I.F., the German-Israeli Foundation for Scientific Research
and Development. 相似文献
33.
Summary. We employ a data-sparse, recursive matrix representation, so-called -matrices, for the efficient treatment of discretized integral operators. We obtain this format using local tensor product interpolants of the kernel function and replacing high-order approximations with piecewise lower-order ones. The scheme has optimal, i.e., linear, complexity in the memory requirement and time for the matrix-vector multiplication. We present an error analysis for integral operators of order zero. In particular, we show that the optimal convergence (h) is retained for the classical double layer potential discretized with piecewise constant functions.Corrigendum This revised version was published online in February 2005 due to typesetting mistakes in the author correction process. 相似文献
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O-Acyl derivatives of 3-hydroxy-γ-butyrolactone are formed in up to 20% yield as by-products from 1-alkyl- and 1-phenyl-substituted 4-pentenols and tert-butyl hydroperoxide (TBHP) in vanadium-catalyzed synthesis of (tetrahydrofuran-2-yl)-methanols. The lactones are secondary products formed from (tetrahydrofuran-2-yl)-methanols via hydrogen atom abstraction in positions 4 and 5, as derived from experiments starting from deuterium-labeled alkenols. Stereocenters at tetrahydrofuran carbon 2 and the proximate hydroxyl carbon of the alkanol side chain retain configuration in the course of oxidative tetrahydrofuran conversion. In an atmosphere of nitrogen or argon, no γ-butyrolactone formation occurs, pointing to dioxygen as terminal oxidant for the secondary oxidation. Adding cyclohexa-1,4-diene or γ-terpinene to a solution of a 4-pentenol, TBHP, and a vanadium catalyst exposed to air inhibits formation of γ-butyrolactones. A third approach to prevent γ-butyrolactones from being formed in oxidative 4-pentenol cyclization uses cis-2,6-bis-(methanol)-piperidine instead of N-salicylidene-ortho-aminophenol as tridentate auxiliary for the vanadium catalyst. 相似文献
37.
Kim Greis Dr. Eike Mucha Maike Lettow Dr. Daniel A. Thomas Carla Kirschbaum Sooyeon Moon Alonso Pardo-Vargas Prof. Dr. Gert von Helden Prof. Dr. Gerard Meijer Dr. Kerry Gilmore Prof. Dr. Peter H. Seeberger Prof. Dr. Kevin Pagel 《Chemphyschem》2020,21(17):1905-1907
It has been reported that fragments produced by glycosidic bond breakage in mass spectrometry-based experiments can retain a memory of their anomeric configuration, which has major implications for glycan sequencing. Herein, we use cryogenic vibrational spectroscopy and ion mobility-mass spectrometry to study the structure of B-type fragments of protected galactosides. Cationic fragments were generated from glycosyl donors carrying trichloroacetimidate or thioethyl leaving groups of different anomeric configuration. The obtained infrared signatures indicate that the investigated fragments exhibit an identical structure, which suggests that there is no anomeric memory in B-type ions of fully protected monosaccharides. 相似文献
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39.
Maike Schwarz Cornelia Sauer Hans Daduna Rafal Kulik Ryszard Szekli 《Queueing Systems》2006,54(1):55-78
We derive stationary distributions of joint queue length and inventory processes in explicit product form for various M/M/1-systems
with inventory under continuous review and different inventory management policies, and with lost sales. Demand is Poisson,
service times and lead times are exponentially distributed. These distributions are used to calculate performance measures
of the respective systems. In case of infinite waiting room the key result is that the limiting distributions of the queue
length processes are the same as in the classical M/M/1/∞-system.
All authors were supported by DAAD/KBN grant number D/02/32206. 相似文献
40.
Day JG Iorenz M Wilding TA Friedl T Harding K Pröschold T Brennan D Müller J Santos LM Santos MF Osório HC Amaral R Lukesova A Hrouzek P Lukes M Elster J Lukavsky J Probert I Ryan MJ Benson EE 《Cryo letters》2007,28(5):359-376
Two cryopreservation methods, colligative cryoprotection coupled with controlled cooling and vitrification-based, encapsulation-dehydration were validated by five members of the EU research infrastructure consortium, COBRA, and two independent external validators. The test strain Chlorella vulgaris SAG 211-11b was successfully cryopreserved using two-step cooling employing passive (Mr Frosty) and Controlled Rate Freezers (CRF) attaining the desired recovery target within 15% of the median viability level (94%). Significant differences (p < 0.05) between cooling regimes were observed where Mr Frosty was more variable (Inter-Quartile Range being 21.5%, versus 13.0% for CRF samples). Viability assessment using fluorescein diacetate gave significantly (P < 0.0001) higher survival than growth in agar with median values being 96% and 89%, respectively. On employing encapsulation-dehydration, greater variability between some validators was observed, with six labs observing recovery in 100% of the beads (84-95% of cells surviving) and one lab observing survival in 80% of the treated beads. Bead disruption followed by algal growth in agar was considered the most reliable and accurate method of assessing cell survival for encapsulation-dehydration. 相似文献