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排序方式: 共有491条查询结果,搜索用时 15 毫秒
251.
We study the partition function ZG(nk,k)(Q,v) of the Q -state Potts model on the family of (non-planar) generalized Petersen graphs G(nk,k). We study its zeros in the plane (Q,v) for 1?k?7. We also consider two specializations of ZG(nk,k), namely the chromatic polynomial PG(nk,k)(Q) (corresponding to v=−1), and the flow polynomial ΦG(nk,k)(Q) (corresponding to v=−Q). In these two cases, we study their zeros in the complex Q -plane for 1?k?7. We pay special attention to the accumulation loci of the corresponding zeros when n→∞. We observe that the Berker–Kadanoff phase that is present in two-dimensional Potts models, also exists for non-planar recursive graphs. Their qualitative features are the same; but the main difference is that the role played by the Beraha numbers for planar graphs is now played by the non-negative integers for non-planar graphs. At these integer values of Q, there are massive eigenvalue cancellations, in the same way as the eigenvalue cancellations that happen at the Beraha numbers for planar graphs. 相似文献
252.
Jesper Funch Thomsen 《Transformation Groups》2013,18(1):263-286
Let X denote a flag variety of type A or type C. We construct a canonical Frobenius splitting of X × X which vanishes with maximal multiplicity along the diagonal. This way we verify a conjecture by Lakshmibai, Mehta and Parameswaran [4] in type C, and obtain a new proof in type A. In particular, we obtain a proof of Wahl's conjecture in type C, and a new proof in type A. We also present certain cohomological consequences. 相似文献
253.
Anders Egede Daugaard Katja Jankova Jose Manuel Roman Marín Jesper Bøgelund Søren Hvilsted 《European Polymer Journal》2012,48(4):743-750
A novel functionalized multi walled carbon nanotube (MWCNT) was prepared through grafting with α-azido-poly(ethylene-co-butylene) (PEB-N3). The PEB-N3 was prepared through a two step procedure and grafted onto an industrial grade multi walled carbon nanotube (MWCNT) through a highly efficient nitrene addition. This novel nano filler was melt mixed into polypropylene (PP) and the composite was characterized by FT-IR spectroscopy, Raman spectroscopy, Scanning Electron Microscopy (SEM), Rheology and Dielectric Relaxation Spectroscopy (DRS). The analyses showed that composites with the novel filler had a high degree of discharge from the surface and higher conductivity compared to the pristine filler, illustrating an efficient conductive network in the composites. The composites showed low percolation thresholds of 0.3 wt.% (0.15 vol.%) as well as improved stability at a range of temperatures from 25–135 °C. 相似文献
254.
255.
Longfei Yu Eliza Harris Dominika Lewicka-Szczebak Matti Barthel Margareta R.A. Blomberg Stephen J. Harris Matthew S. Johnson Moritz F. Lehmann Jesper Liisberg Christoph Müller Nathaniel E. Ostrom Johan Six Sakae Toyoda Naohiro Yoshida Joachim Mohn 《Rapid communications in mass spectrometry : RCM》2020,34(20):e8858
The isotopic composition of nitrous oxide (N2O) provides useful information for evaluating N2O sources and budgets. Due to the co-occurrence of multiple N2O transformation pathways, it is, however, challenging to use isotopic information to quantify the contribution of distinct processes across variable spatiotemporal scales. Here, we present an overview of recent progress in N2O isotopic studies and provide suggestions for future research, mainly focusing on: analytical techniques; production and consumption processes; and interpretation and modelling approaches. Comparing isotope-ratio mass spectrometry (IRMS) with laser absorption spectroscopy (LAS), we conclude that IRMS is a precise technique for laboratory analysis of N2O isotopes, while LAS is more suitable for in situ/inline studies and offers advantages for site-specific analyses. When reviewing the link between the N2O isotopic composition and underlying mechanisms/processes, we find that, at the molecular scale, the specific enzymes and mechanisms involved determine isotopic fractionation effects. In contrast, at plot-to-global scales, mixing of N2O derived from different processes and their isotopic variability must be considered. We also find that dual isotope plots are effective for semi-quantitative attribution of co-occurring N2O production and reduction processes. More recently, process-based N2O isotopic models have been developed for natural abundance and 15N-tracing studies, and have been shown to be effective, particularly for data with adequate temporal resolution. Despite the significant progress made over the last decade, there is still great need and potential for future work, including development of analytical techniques, reference materials and inter-laboratory comparisons, further exploration of N2O formation and destruction mechanisms, more observations across scales, and design and validation of interpretation and modelling approaches. Synthesizing all these efforts, we are confident that the N2O isotope community will continue to advance our understanding of N2O transformation processes in all spheres of the Earth, and in turn to gain improved constraints on regional and global budgets. 相似文献
256.
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258.
Torben Birk Henning Osholm Srensen Jesper Bendix 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(5):m231-m233
Two new chromium(V)–nitride complexes with a coordination sphere completed by bidentate ligands have been synthesized and structurally characterized. Bis(2‐methylquinolin‐8‐olato)nitridochromium(V), [Cr(C10H8NO)2(N)], has the coordination sphere completed by an equatorial N2O2 set of ligators. The compound crystallizes with the five‐coordinate complexes at sites with twofold rotational symmetry and all Cr—N bond directions aligned with the crystallographic b axis. Nitridobis(2‐sulfidopyridine N‐oxide)chromium(V), [Cr(C5H4NOS)2(N)], crystallizes with the molecules on general positions and has an equatorial S2O2 coordination environment, which is unprecedented among nitride complexes of the first‐row transition metals. In both systems, Cr[triple‐bond]N bonds are short at ca 1.56 Å. 相似文献
259.
Anders Hammershi Magnus Schau‐Magnussen Jesper Bendix Anne Mlgaard 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(11):m319-m322
The structures of the diastereoisomers Λ(+)578‐, (I), and Δ(−)578‐bis(ethane‐1,2‐diamine)[β‐ethyl (S)‐aspartato‐κ2N,O1]cobalt(III) bis(perchlorate) monohydrate, (II), both [Co(C6H10N2O4)(C2H8N2)2](ClO4)2·H2O, are compared. In both structures, the ester group of the amino acid side chain is engaged only in intramolecular hydrogen bonding to coordinated amine groups. This interaction is stronger in (I) and correlates with previously observed diastereoisomeric equilibrium ratios for related metal complex systems in aqueous media. The two perchlorate anions of (II) are located on twofold axes. Both perchlorates in (I) and one of the perchlorates in (II) are affected by disorder. Both structures exhibit extensive three‐dimensional hydrogen‐bonding networks. 相似文献
260.
Lijing Xue Denka G. Hristova-Bogaerds Jesper G. van Berkel Guy Verbist Piet J. Lemstra 《Polymer Degradation and Stability》2010,95(2):126-131
A non-destructive analysis is performed of thermally unstable sulfur-styrene reaction products, combining preparative size exclusion chromatography (P-SEC), ultraviolet-visible (UV-vis) and nuclear magnetic resonance (NMR). The crystallizing compounds are identified as be 2,4-diphenylthiophanes with short sulfur bridge (x ∼ 2) contrary to earlier suggestions which were based on destructive analysis. A new cyclic structure (styrene polysulfide x = 1 up to 8) was assigned to the amorphous species containing a single styrene repeating unit. Comparison with the amorphous fractions suggests that the rigid ring of styrene repeating units in adjacent sequences is the characteristic feature for the crystallisability. The melting and crystallization behaviour of this crystalline component was observed, by optical microscopy (OM) and differential scanning calorimetry (DSC), to be step-wise as well as broad, due to the variation in the length of the sulfur bridge. 相似文献