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71.
The photochromism of [3H]-naphthopyran derivatives can be switched from T-type to inverse- or P-type through the manipulation of relative thermodynamic stabilities of open isomers with intramolecular CH-π bonds. 相似文献
72.
Castro L Labouille S Kindra DR Ziller JW Nief F Evans WJ Maron L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(25):7886-7895
Reaction mechanisms for the oxidative reactions of CO(2) and COS with [(C(5)Me(5))(2)Sm] have been investigated by means of DFT methods. The experimental formation of oxalate and dithiocarbonate complexes is explained. Their formation involve the samarium(III) bimetallic complexes [(C(5)Me(5))(2)Sm-CO(2)-Sm(C(5)Me(5))(2)] and [(C(5)Me(5))(2)Sm-COS-Sm(C(5)Me(5))(2)] as intermediates, respectively, ruling out radical coupling for the formation of the oxalate complex. 相似文献
73.
Anke Dierckx Dr. Francois‐Alexandre Miannay Dr. Nouha Ben Gaied Søren Preus Markus Björck Prof. Dr. Tom Brown Prof. Dr. L. Marcus Wilhelmsson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):5987-5997
Fluorescent‐base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base‐pairing properties of a new environment‐sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid‐phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B‐form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2‐aminopurine, and the recently developed triazole adenine, qA shows highly specific base‐pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300 nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8 % with an emission maximum at 456 nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2‐aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid‐containing systems. 相似文献
74.
Guo Q Brodzeli Z Pozhidaev EP Fan F Chigrinov VG Kwok HS Silvestri L Ladouceur F 《Optics letters》2012,37(12):2343-2345
The electro-optical behavior of deformed helix ferroelectric liquid crystal in reflective mode is described in this paper. The electrically controlled reflectance has been measured at subkilohertz driving voltage frequency for different polarizations of the incident light and compared quite successfully with the simulation results. 相似文献
75.
The yielding of several reversible yield stress fluids is studied during scissometric-like creep experiments. The temporal evolution of the apparent deformation is recorded for applied stresses close and below the usual yield stress. Similarly to solids, three main creep regimes are observed. First, a primary creep regime displaying a temporal power law evolution of the deformation rate occurs, followed by a temporal minimum, which leads to an apparent flow of the material. This local minimum, defined as the “transition time,” and the subsequent fluidization can be observed at long times. The evolution of this time as a function of the applied stress appears to follow a universal law reminiscent of fracture behavior in hard solids. 相似文献
76.
Various methods used to determine the shock Hugoniot of condensed phase multi-component mixtures are reviewed and compared
to available experimental data. The assumptions inherent in the different models are presented in this overview and their
implications are discussed. The comparisons of the various models demonstrate that the predicted shock Hugoniots are in good
agreement with published data despite the simplifying assumptions that are associated with the models. Averaging models are
shown to be among the simplest methods to implement and result in the closest agreement with experimental data. 相似文献
77.
A closure approximation for nematic liquid crystals based on the canonical distribution subspace theory 总被引:2,自引:0,他引:2
A closure approximation for nematic polymers is presented. It approximates the fourth rank order tensor in terms of lower
rank tensors, and is derived in the framework of the canonical distribution subspace theory. This approach requires a choice
of the class of distributions: Here the set of Bingham distributions is chosen, as already introduced by Chaubal and Leal
(1998). The closure is written in a generic frame of reference, and in an explicit form, so that it can be easily implemented.
Such formulation also permits studying the closure approximation with continuation tools, which rather completely describe
the system dynamics. The predictions can then be compared with those obtained with the exact model. The shear flow is considered
as a test, since this flow condition appears to be the most demanding for closure approximations for nematic polymers.
Received: 30 November 1999/Accepted: 30 November 1999 相似文献
78.
Yahya S. Alqahtani Sunil S. More Keerthana R. Ibrahim Ahmed Shaikh Anusha K. J. Veena S. More Francois N. Niyonzima Uday M. Muddapur Aejaz A. Khan 《Molecules (Basel, Switzerland)》2022,27(13)
Enzymes that degrade pectin are called pectinases. Pectinases of microbial origin are used in juice clarification as the process is cost-effective. This study screened a pectinase-producing bacterium isolated from soil and identified as Bacillus subtilis 15A B-92 based on the 16S rRNA molecular technique. The purified pectinase from the isolate showed 99.6 U/mg specific activity and 11.6-fold purity. The molecular weight of the purified bacterial pectinase was 14.41 ± 1 kD. Optimum pectinase activity was found at pH 4.5 and 50 °C, and the enzyme was 100% stable for 3.5 h in these conditions. No enzymatic inhibition or activation effect was seen with Fe2+, Ca2+, or Mg2+. However, a slight inhibition was seen with Cu2+, Mn2+, and Zn2+. Tween 20 and 80 slightly inhibited the pectinase, whereas iodoacetic acid (IAA), ethylenediaminetetraacetate (EDTA), urea, and sodium dodecyl sulfate (SDS) showed potent inhibition. The bacterial pectinase degraded citrus pectin (100%); however, it was inactive in the presence of galactose. With citrus pectin as the substrate, the Km and Vmax were calculated as 1.72 mg/mL and 1609 U/g, respectively. The high affinity of pectinase for its substrate makes the process cost-effective when utilized in food industries. The obtained pectinase was able to clarify orange and apple juices, justifying its application in the food industry. 相似文献
79.
Delduc Francois Lacroix Sylvain Magro Marc Vicedo Benoît 《Letters in Mathematical Physics》2020,110(7):1645-1687
Letters in Mathematical Physics - In the approach recently proposed by K. Costello and M. Yamazaki, which is based on a four-dimensional variant of Chern–Simons theory, we derive a simple and... 相似文献
80.
Rachna AggarwalAnthony A. Birkbeck Charles B. de KoningRobin G.F. Giles Ivan R. GreenShuk-Hui Li Francois J. Oosthuizen 《Tetrahedron letters》2003,44(24):4535-4538
peri-Interactions are important in determining both the conformation of the dihydropyran ring of 2-benzopyrans as well as the stereochemistry of its substituents. 相似文献