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61.
This paper presents a new computational approach for solving optimal control problems governed by impulsive switched systems. Such systems consist of multiple subsystems operating in succession, with possible instantaneous state jumps occurring when the system switches from one subsystem to another. The control variables are the subsystem durations and a set of system parameters influencing the state jumps. In contrast with most other papers on the control of impulsive switched systems, we do not require every potential subsystem to be active during the time horizon (it may be optimal to delete certain subsystems, especially when the optimal number of switches is unknown). However, any active subsystem must be active for a minimum non-negligible duration of time. This restriction leads to a disjoint feasible region for the subsystem durations. The problem of choosing the subsystem durations and the system parameters to minimize a given cost function is a non-standard optimal control problem that cannot be solved using conventional techniques. By combining a time-scaling transformation and an exact penalty method, we develop a computational algorithm for solving this problem. We then demonstrate the effectiveness of this algorithm by considering a numerical example on the optimization of shrimp harvesting operations. 相似文献
62.
The loss of stability of a flow resulting from the interaction of a transverse jet and a crossflow has been studied experimentally
by means of several nonintrusive optical methods (Laser-Induced Fluorescence, Particle Streak Velocimetry). In particular,
flow visualizations have allowed measurement of the characteristic velocity of rotation of a counter-rotating vortex pair,
which is the prevailing system of this complex flow. It is shown that the elliptical geometry of the cross sections of these
vortex structures can cause the loss of stability of the jet according to the theory of Landman and Saffman (1987). The unstable
jet state is characterized by the generation of transverse unsteady rotating structures on the jet boundaries. These transverse
eddies are clearly identifiable and their regularity of occurrence is satisfactorily explained by the theory of Landman and
Saffman. Therefore, this study shows for the first time that the longitudinal structures must be taken into account in the
mechanism of stability arising from the meeting of a jet and a cross stream.
Received: 7 May 1997/Accepted: 20 March 1998 相似文献
63.
Sebastien Graule Mark Rudolph Wenting Shen J. A. Gareth Williams Dr. Christophe Lescop Dr. Jochen Autschbach Prof. Jeanne Crassous Dr. Régis Réau Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(20):5976-6005
Aza[n]helicene phosphole derivatives have been prepared from aza[n]helicene diynes by the Fagan–Nugent route. Their photophysical properties (UV/Vis absorption and emission behavior) have been evaluated. Their behavior as P,N chelates towards coordination to PdII and CuI has been investigated: metal–bis(aza[n]helicene phosphole) assemblies are formed by a highly stereoselective coordination process, as demonstrated by X‐ray crystallography. An aza[6]helicene phosphole bearing an enantiopure helicene part has been obtained, which allows the preparation of enantiopure PdII and CuI complexes with original topologies and high molar rotation (MR) and circular dichroism (CD). The structure–property relationship established from the experimental data has been studied in detail by theoretical studies (TDDFT calculations of UV/Vis, CD, and MR). Aza[n]helicene phosphole derivatives show π conjugation extended over the entire molecule, and its influence on the MR of aza[6]helicene phosphole 5 c has been demonstrated. Finally, it has been shown that the nature of the metal (coordination geometry and electronic interaction) can have a great impact on the amplitude of the chiroptical properties in metal–bis(aza[n]helicene phosphole) assemblies. 相似文献
64.
Paul Blanchard 《Semigroup Forum》1991,43(1):218-246
We study some syntactic properties of languages obtained from rational languages through counting operations. These counting operations use the congruences-threshold p, modulo n—on the set of integers. We show that in some cases they preserve the properties of syntactic monoids: the structure of idempotent and commutative monoids is not modified, aperiodic monoids with central idempotents keep their central idempotents and their regular D-classes still are groups although not trivial, aperiodic left (right) nilsimple semigroups still have regular R (L)-classes which are (non trivial) groups. If possible results are expressed in terms of varieties of semigroups or monoids. 相似文献
65.
66.
We report on a mid-infrared (mid-IR) source consisting of an approximately 10 W average-power, linearly polarized 1.54 microm wavelength pulsed fiber source pumping an optical parametric oscillator. From this source, we obtained average power in excess of 1 W in the 3.8-4.0 microm wavelength range at a pulse repetition frequency of 100 kHz. With a slightly different setup, we also achieved an average power of 0.25 W at 4.5 microm wavelength. To our knowledge, these values represent the highest mid-IR power obtained through wavelength conversion of an eye-safe fiber source. 相似文献
67.
A non linear system modelling phase changes in metallic alloys is studied. Two existence, uniqueness and regularity results are established in the reversible or irreversible setting. The technique uses non linear semi-groups theory and a fixed point method. 相似文献
68.
Photoexcitation of fluorophores commonly used for biological imaging applications generates reactive oxygen species (ROS) which can cause bleaching of the fluorophore and damage to the biological system under investigation. In this study, we show that singlet oxygen contributes relatively little to Cy5 and ATTO 647N photobleaching at low concentrations in aqueous solution. We also show that Cy5 generates significantly less ROS when covalently linked to the protective agents, cyclooctatetraene (COT), nitrobenzyl alcohol (NBA) or Trolox. Such fluorophores exhibit enhanced photostability both in bulk solutions and in single‐molecule fluorescence measurements. While the fluorophores ATTO 647N and ATTO 655 showed greater photostability than Cy5 and the protective–agent‐linked Cy5 derivatives investigated here, both of ATTO 647N and ATTO 655 generated singlet oxygen and hydroxyl radicals at relatively rapid rates, suggesting that they may be substantially more phototoxic than Cy5 and its derivatives. 相似文献
69.
Shakya T Stogios PJ Waglechner N Evdokimova E Ejim L Blanchard JE McArthur AG Savchenko A Wright GD 《Chemistry & biology》2011,18(12):1591-1601
Kinase-mediated resistance to antibiotics is a significant clinical challenge. These enzymes share a common protein fold characteristic of Ser/Thr/Tyr protein kinases. We screened 14 antibiotic resistance kinases against 80 chemically diverse protein kinase inhibitors to map resistance kinase chemical space. The screens identified molecules with both broad and narrow inhibition profiles, proving that protein kinase inhibitors offer privileged chemical matter with the potential to block antibiotic resistance. One example is the flavonol quercetin, which inhibited a number of resistance kinases in vitro and in vivo. This activity was rationalized by determination of the crystal structure of the aminoglycoside kinase APH(2″)-IVa in complex with quercetin and its antibiotic substrate kanamycin. Our data demonstrate that protein kinase inhibitors offer chemical scaffolds that can block antibiotic resistance, providing leads for co-drug design. 相似文献
70.
Besson C Mirebeau JH Renaudineau S Roland S Blanchard S Vezin H Courillon C Proust A 《Inorganic chemistry》2011,50(6):2501-2506
The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW(11)O(39)Ru(VI)N](4-) has been extended to the N-heterocyclic carbene {CH(2)(Mes)N}(2)C and the coupling product {CH(2)(Mes)N}(2)CNH(2)(+) characterized by (1)H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW(11)O(39)Ru(III){NC{N(Mes)CH(2)}(2)}](5-) has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry. 相似文献