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排序方式: 共有516条查询结果,搜索用时 156 毫秒
511.
512.
Walba DM Korblova E Huang CC Shao R Nakata M Clark NA 《Journal of the American Chemical Society》2006,128(16):5318-5319
The SmC phase of 4'-octyloxyphenyl-4-octyloxybenzoate has been examined in light of recent reports that this phase is chiral. The results suggest that two varieties of chiral domains in LC cells of the phenylbenzoate are indeed formed, driven by interactions with surfaces. Application of sensitive probes for chirality and polarity in the absence of such interfacial influences failed to find any. Currently, there is no evidence that the subject SmC phase is chiral. 相似文献
513.
Lee S Dyer JA Sparks DL Scrivner NC Elzinga EJ 《Journal of colloid and interface science》2006,298(1):20-30
Macroscopic sorption studies indicated that Pb sorption capacity was independent of pH over the pH range 5-7, while sorption as a function of reaction time up to two weeks for systems with no bulk precipitate phases showed continuous Pb uptake on dolomite. This could be due to diffusion of Pb into the micropores of dolomite as well as an increase in surface sites caused by particle size reduction during suspension mixing. Normalized XANES spectra for systems undersaturated with respect to Pb carbonate precipitates resembled the spectrum of Pb4(OH)4(4+), suggesting that Pb is mainly coordinated to dolomite as an inner-sphere surface complex. On the other hand, the XANES spectrum for 10(-3) M Pb at 1 atm CO2(g) in a 2 M Mg(NO3)2 background electrolyte solution resembled that of cerussite, while a sample at 5 x 10(-4) M Pb in equilibrium with air and 2 M Mg(NO3)2 resembled that of hydrocerussite. EXAFS analyses of sorption samples in chloride solutions showed that there were only first-shell contributions under 1 atm CO2(g), while higher shell contributions from Ca/Mg were seen at 10(-3.42) atm CO2(g). On the other hand, EXAFS samples prepared in nitrate solutions showed noticeable differences in speciation under different reaction conditions-from outer-sphere surface complexes at low Pb concentrations and pH, to inner-sphere surface complexes at moderate Pb concentrations and neutral pH, to the formation of Pb carbonate precipitates at the highest Pb loadings. 相似文献
514.
Noel P. McLaughlin Paul Evans Nigel P. Brunton Anastasios Koidis Dilip K. Rai 《Tetrahedron》2010,66(51):9681-9687
A short, practical synthesis of the bis-acetylenic natural product falcarinol 1 is reported. This method relies on the alternate functionalisation of bis-trimethylsilylbutadiyne 10. This may be achieved in one-pot, however, better yields were obtained more conventionally. Lipase mediated enzymatic kinetic resolution of the racemic adduct in an organic solvent afforded (+)-1 in 97% enantiomeric excess. The analogous process performed with racemic 3-acetoxy falcarinol 11 under aqueous conditions gave (−)-1. Oxidation of 1 with Dess-Martin periodinane gave falcarinone 2. 相似文献
515.
Noel A. Powell Timothy J. Hagen Cuiman Cai Daniele Leonard Jeremy J. Edmunds 《Tetrahedron letters》2010,51(33):4441-4544
We have optimized the Pd-catalyzed intramolecular α-arylation of 2-(2-halo-benzyl)-cyclohexanones and found that the use of 2-(dicyclohexylphosphino)-2′,4′,6′-tri-i-propyl-1,1′-biphenyl (X-Phos) as an added ligand led to a reproducible, efficient, and scalable synthesis of tricycle-[7.3.1.02,7]-trideca-2,4,6-trien-13-ones. 相似文献
516.
Kathleen Fuchs Dr. Samara Medina Rivero Anna Weidlich Dr. Frank Rominger Noel Israel Dr. Alexey A. Popov Prof. Dr. Andreas Dreuw Dr. Jan Freudenberg Prof. Juan Casado Prof. Dr. Uwe H. F. Bunz 《Angewandte Chemie (International ed. in English)》2023,62(32):e202305712
Two series of regioisomeric dicyanomethylene substituted dithienodiazatetracenes with formal para- or ortho-quinodimethane subunits were synthesized and characterized. Whereas the para-isomers (p-n, diradical index y0=0.01) are stable and isolable, the ortho-isomer (y0=0.98) dimerizes into a covalent azaacene cage. Four elongated σ-CC bonds are formed and the former triisopropylsilyl(TIPS) -ethynylene groups transformed into cumulene units. The azaacene cage dimer (o-1)2 was characterized by X-ray single crystal structure analysis and temperature-dependent infrared (IR), electron paramagnetic resonance (EPR, solid-state), nuclear magnetic resonance (NMR) and ultraviolet-visible (UV/Vis) spectroscopies (solution) indicating reformation of o-1. 相似文献