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901.
Astaxanthin is a potential high-value coproduct in an ethanol biorefinery. Three mutant strains of the astaxanthin-producing
yeast Phaffia rhodozyma, which were derived from the parent strain ATCC 24202 (UCD 67-210) and designated JTM166, JTM185, and SSM19, were tested
for their capability of utilizing the major sugars that can be generated from cellulosic biomass, including glucose, xylose,
and arabinose, for astaxanthin production. While all three strains were capable of metabolizing these sugars, individually
and in mixtures, JTM185 demonstrated the greatest sugar utilization and astaxanthin production. Astaxanthin yield by this
strain (milligrams astaxanthin per gram of sugar consumed) was highest for xylose, followed by arabinose and then glucose.
The kinetics of sugar utilization by strain JTM185 was studied in fermenters using mixtures of glucose, xylose, and arabinose
at varied concentrations. It was found that glucose was utilized preferentially, followed by xylose, and lastly, arabinose.
Astaxanthin yield was significantly affected by sugar concentrations. Highest yields were observed with sugar mixtures containing
the highest concentrations of xylose and arabinose. Hydrolysates produced from sugarcane bagasse and barley straw pretreated
by the soaking in aqueous ammonia method and hydrolyzed with the commercial cellulase preparation, Accellerase™ 1000, were
used for astaxanthin production by the mutant strain JTM185. The organism was capable of metabolizing all of the sugars present
in the hydrolysates from both biomass sources and produced similar amounts of astaxanthin from both hydrolysates, although
these amounts were lower when compared to yields obtained with reagent grade sugars. 相似文献
902.
Duclos RI Johnston M Vadivel SK Makriyannis A Glaser ST Gatley SJ 《The Journal of organic chemistry》2011,76(7):2049-2055
The metabolic intermediate and endocannabinoid signaling lipid 2-arachidonoylglycerol (2-AG) has not been readily labeled, primarily because of its instability toward rearrangement. We now detail a synthetic method that easily gives tritiated 2-AG from [5,6,8,9,11,12,14,15-(3)H(N)]arachidonic acid in two steps. We utilized a short chain 1,3-diacylglycerol and proceeded through the "structured lipid" [5',6',8',9',11',12',14',15'-(3)H(N)]2-arachidonoyl-1,3-dibutyrylglycerol, a triacylglycerol that was conveniently deprotected in ethanol with acrylic beads containing Candida antarctica lipase B to give [5',6',8',9',11',12',14',15'-(3)H(N)]2-arachidonoylglycerol ([(3)H]2-AG). The flash chromatographic separation necessary to isolate the labeled 2-acylglycerol [(3)H]2-AG resulted in only 4% of the rearrangement byproducts that have been a particular problem with previous methodologies. This reliable "kit" method to prepare the radiolabeled endocannabinoid as needed gave tritiated 2-arachidonoylglycerol [(3)H]2-AG with a specific activity of 200 Ci/mmol for enzyme assays, metabolic studies, and tissue imaging. It has been run on unlabeled materials on over 10 mg scales and should be generally applicable to other 2-acylglycerols. 相似文献
903.
Strachan DR Johnston DE Guiton BS Datta SS Davies PK Bonnell DA Johnson AT 《Physical review letters》2008,100(5):056805
We present real-time transmission electron microscopy of nanogap formation by feedback controlled electromigration that reveals a remarkable degree of crystalline order. Crystal facets appear during feedback controlled electromigration indicating a layer-by-layer, highly reproducible electromigration process avoiding thermal runaway and melting. These measurements provide insight into the electromigration induced failure mechanism in sub-20 nm size interconnects, indicating that the current density at failure increases as the width decreases to approximately 1 nm. 相似文献
904.
T. E. M?lholt R. Mantovan H. P. Gunnlaugsson D. Naidoo S. ólafsson K. Bharuth-Ram M. Fanciulli K. Johnston Y. Kobayashi G. Langouche H. Masenda R. Sielemann G. Weyer H. P. Gíslason 《Hyperfine Interactions》2010,197(1-3):89-94
We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe3?+? in MgO single crystals, obtained after implantation of 57Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ ???1 as a parameter. The temperature dependent spin relaxation rate of Fe3?+? in MgO is found to increase to ~108 s???1 at 647 K by assuming a relaxation rate of τ ???1?< 106 s???1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe3?+? from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides. 相似文献
905.
Josafat Guerrero-Jordan José Luis Cabellos Roy L. Johnston Alvaro Posada-Amarillas 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(6):123
A genetic algorithm has been used to perform a global sampling of the potential energy surface in the search for the lowest-energy structures of unsupported 38-atom Cu–Pt clusters. Structural details of bimetallic Cu–Pt nanoparticles are analyzed as a function of their chemical composition and the parameters of the Gupta potential, which is used to mimic the interatomic interactions. The symmetrical weighting of all parameters used in this work strongly influences the chemical ordering patterns and, consequently, cluster morphologies. The most stable structures are those corresponding to potentials weighted toward Pt characteristics, leading to Cu–Pt mixing for a weighting factor of 0.7. This reproduces density functional theory (DFT) results for Cu–Pt clusters of this size. For several weighting factor values, the Cu30Pt8 cluster exhibits slightly higher relative stability. The copper-rich Cu32Pt6 cluster was reoptimized at the DFT level to validate the reliability of the empirical approach, which predicts a Pt@Cu core-shell segregated cluster. A general increase of interatomic distances is observed in the DFT calculations, which is greater in the Pt core. After cluster relaxation, structural changes are identified through the pair distribution function. For the majority of weighting factors and compositions, the truncated octahedron geometry is energetically preferred at the Gupta potential level of theory. 相似文献
906.
Mikail Aslan Roy L. Johnston 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(6):120
Anionic CoPt-ethynyl metal-organic clusters have been investigated comprehensively. The lowest energetic of anionic Co n Pt m (ethynyl) clusters have been generally found as 3D structure but with low symmetrical point groups. Our results indicate that the most preferred dissociation channel of the studied clusters is Co atom ejection and the favorable dissociation channel is independent of cluster size. The anionic Pt5C2H cluster shows the highest chemical stability according to the HOMO-LUMO Gap analysis. The C2H generally prefers to bind on a bridge site with a few exceptions. The Co4?5 nanoparticles have a lengthening effect on the C≡C bond of the ethynyl molecule, which may be valuable for C≡C bond activation. In addition, the lowest and the highest vibrational frequencies are reported to guide further experimental studies. 相似文献
907.
Despite the rapid growth of enantioselective halolactonization reactions in recent years, most are effective only when forming smaller (6,5,4-membered) rings. Seven-membered ε-lactones, are rarely formed with high selectivity, and never without conformational bias. We describe the first highly enantioselective 7-exo-trig iodolactonizations of conformationally unbiased ε-unsaturated carboxylic acids, effected by an unusual combination of a bifunctional BAM catalyst, I2, and I(iii) reagent (PhI(OAc)2:PIDA).We describe the first highly enantioselective 7-exo-trig iodolactonizations of conformationally unbiased ε-unsaturated carboxylic acids, effected by an unusual combination of a bifunctional BAM catalyst, I2, and I(iii) reagent (PhI(OAc)2:PIDA). 相似文献
908.