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81.
Hans R. Kricheldorf Bettina Weegen-Schulz 《Journal of polymer science. Part A, Polymer chemistry》1995,33(13):2193-2201
Numerous BuSnCl, Bu2SnCl, and Bu3SnCl-initiated polymerizations of cyclo(tri-methylene carbonate) (TMC) were conducted in bulk. In addition to the initiator, reaction time, temperature, and monomer/initiator (M/I) ratio were varied. Yields above 90% were obtained with all three initiators, but their reactivities decrease in the order BuSnCl3 > Bu2SnCl2 > Bu3SnCl. The maximum molecular weights decrease in the same order. With BuSnCl3 Mws up to 250,000 were obtained. These molecular weights were determined by GPC on the basis of the universal calibration method. In this connection Mark-Houwink equations for two solvents, tetrahydrofuran (THF) and CH2Cl2 were determined and compared with literature data. Furthermore, mechanistic aspects were studied. 1H- and 13C- NMR spectra revealed that BuSnCl3 forms complexes with the CO-group of TMC, whereas Bu2SnCl3 do not cause NMR spectroscopic effects. Kinetic studies in chloroform and nitrobenzene and a comparison with Bu3SnOMe suggest that at least BuSnCl3 initiates a cationic mechanism. However, in contrast to SnCl4 (or SnBr4), BuSnCl3 does not cause decarboxylation. Regardless of the initiator 1H-NMR spectroscopy revealed CH2OH and CH2CI endgroups in all cases. © 1995 John Wiley & Sons, Inc. 相似文献
82.
A novel method is proposed for the detection and quantification of protein-protein interactions in solution. In this approach, one protein binding partner is tagged with a ligand binding domain, and protein-protein interaction is monitored via changes in the NMR relaxation of a reporter ligand which reversibly binds to the ligand binding domain. The particular benefit of the method is that only minute amounts of protein material and no isotope labeling are required. Its ease of implementation and the high-throughput capabilities make the method an attractive complement to existing proteomic methodology. 相似文献
83.
Cyril A. Grob Bettina Günther Reinhard Hanreich Adrian Waldner 《Tetrahedron letters》1981,22(9):835-838
Solvolysis of 6-exo- and 6-endo-substituted 2-exo-norbornyl tosylates and , respectively, yields identical or different product mixtures depending on the inductive effect of the substituent, indicating that induction involves graded σ-participation. 相似文献
84.
The impact of particle geometry on the phase behavior of hard colloidal tetragonal parallelepipeds (TPs) was studied by using Monte Carlo simulations in continuum space. TPs or "cuboids" of aspect ratios varying from 0.25 to 8 were simulated by approximating their shapes with multisite objects, i.e., via rigid clusters of hard spheres. Using equation of state curves, order parameters, radial distribution functions, particle distribution functions along three directions, and visual analysis of configurations, an approximate phase diagram for the TPs was mapped out as a function of aspect ratio (r) and volume fraction. For r > 3 and intermediate concentrations, the behavior of the TPs was similar to that of spherocylinders, exhibiting similar liquid crystalline mesophases (e.g., nematic and smectic phases). For r = 1, a cubatic phase occurs with orientational order along the three axes but with little translational order. For 1 < r < 4, the TPs exhibit a cubatic-like mesophase with a high degree of order along three axes where the major axes of the particles are not all aligned in the same direction. For r < 1, the TPs exhibit a smectic-like phase where the particles have rotational freedom in each layer but form stacks with tetratic order. The equation of state for perfect hard cubes (r = 1) was also simulated and found to be consistent with that of the rounded-edge r = 1 TPs, except for its lack of discontinuity at the cubatic-solid transition. 相似文献
85.
Phillips ST Piersanti G Rüth M Gubernator N van Lengerich B Bartlett PA 《Organic letters》2004,6(24):4483-4485
The synthesis of @-tide beta-strand peptidomimetics has been improved such that oligomers now can be obtained from solution- and solid-phase synthesis protocols approaching the efficiency and flexibility of peptide chemistry. These methods enable the synthesis of @-tide oligomers with a variety of amino acids and with lengths up to 13 units. [reaction: see text] 相似文献
86.
Rainer E. Burkard Karin Dlaska Bettina Klinz 《Mathematical Methods of Operations Research》1993,37(1):31-58
Consider a network
=(G, c, ) whereG=(N, A) is a directed graph andc
ij
and
ij
, respectively, denote the capacity and the transmission time of arc (i, j) A. The quickest flow problem is then to determine for a given value the minimum numberT() of time units that are necessary to transmit (send) units of flow in
from a given sources to a given sinks.In this paper we show that the quickest flow problem is closely related to the maximum dynamic flow problem and to linear fractional programming problems. Based on these relationships we develop several polynomial algorithms and a strongly polynomial algorithm for the quickest flow problem.Finally we report computational results on the practical behaviour of our metholds. It turns out that some of them are practically very efficient and well-suited for solving large problem instances.Partial financial support by the Air Force Office of Scientific Research under grants AFOSR-89-0512 and AFOSR-90-0008 is gratefully acknowledged by the first author. 相似文献
87.
88.
Oswin Aichholzer Franz Aurenhammer Thomas Hackl Bettina Speckmann 《Computational Geometry》2009,42(6-7):627-631
In this note we discuss some structural properties of minimum weight pseudo-triangulations of point sets. 相似文献
89.
90.
Mihály Hujter Bettina Klinz Gerhard J. Woeginger 《Mathematical Methods of Operations Research》1999,50(1):9-16
In this note we investigate the computational complexity of the transportation problem with a permutable demand vector, TP-PD for short. In the TP-PD, the goal is to permute the elements of the given integer demand vector b=(b1,
,bn) in order to minimize the overall transportation costs. Meusel and Burkard [6] recently proved that the TP-PD is strongly NP-hard. In their NP-hardness reduction, the used demand values bj, j=1,
,n, are large integers. In this note we show that the TP-PD remains strongly NP-hard even for the case where bj]{0,3} for j=1,
,n. As a positive result, we show that the TP-PD becomes strongly polynomial time solvable if bj] {0,1,2} holds for j=1,
,n. This result can be extended to the case where bj]{3,3+1,3+2} for an integer 3. 相似文献