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131.
L. H. Klemm Jennifer J. Lu Diana S. Greene William Boisvert 《Journal of heterocyclic chemistry》1987,24(5):1467-1472
A comparison is made amongst the isosteric Systems quinoline, thieno[2,3,-b]pyridine, and thieno[3,2-b]-pyridine which bear the 1-carboethoxy-1-cyanomethyl substituent (R) alpha or gamma to the heterocyclic nitrogen atom. Treatment of thieno[3,2-b]pyridine 4-oxide with ethyl cyanoacetate and acetic anhydride at room temperature (Hamana reaction) gives the alpha R-derivative 6 (27%), formulated as an intramolecular H-bonded structure. Neither 6 nor its quinoline alpha analog reacts with refluxing acetic anhydride, while the quinoline gamma isomer 8 , existing as NH and CH tautomers, yields an N-acetyl derivative 10 (70%) under similar conditions. For each of 6 and 8 one can isolate two crystalline forms which differ considerably in color. Compound 10 and its gamma analog in the thieno[2,3-6]pyridine series (previously obtained directly from a Hamana reaction) serve as acetylating agents for aniline, 1-aminobutane, morpholine, and cholesterol. Correlations and contrasts in the three Systems are presented. 相似文献
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A method for detecting and quantifying uranium(VI) levels on building materials that include concrete, Plexiglas, glass and steel surfaces is presented. Uranium(VI) was extracted from building material surfaces using a pH 2.2 buffer rinse and, subsequently complexed by an organic chelating agent, arsenazo III. The application of a uranium-chelating molecule, arsenazo III, allows for concentration enhancement using C18 solid phase extraction and colorimetric detection of the uranium complex using ultraviolet-visible spectroscopy at 654 nm. The method has a detection limit (based on 3σ) of 40 ng/L (5 ng/cm2) and an overall extraction efficiency greater than 80% for each surface type (concrete, Plexiglas, glass, steel). Methods to prevent interference by metal ions commonly found on building materials are discussed. 相似文献
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L. J. Azevedo J. E. Schirber R. L. Greene E. M. Engler 《Molecular Crystals and Liquid Crystals》2013,570(1):479-484
Abstract The electron spin resonance of (TMTSF)2PF6 has been observed at low fields (Ho < 110 Oe) in the high pressure, metallic phase (p > 6.5 kbar) in the temperature range 1-4?K. The anisotropy in the g value is similar to that observed at ambient pressure above the metal-insulator transition. The linewidth is very narrow and the spin susceptibility strongly decreases as the superconducting transition is approached from above. We interpret this as evidence for singlet-paired superconductivity. Superconductivity is observed at 1.1 K and the critical field has angular dependence in the be plane. These observations lead us to conclude that (TMTSF)2PF6 is a singlet paired superconductor. 相似文献
137.
Fluorogenic analogues of α‐tocopherol developed by our group have been instrumental in monitoring reactive oxygen species (ROS) within lipid membranes. Prepared as two‐segment trap‐reporter (chromanol‐BODIPY) probes, photoinduced electron transfer (PeT) was utilized to provide these probes with an off/on switch mechanism warranting the necessary sensitivity. Herein, we rationalize within the context of Marcus theory of electron transfer how substituents on the BODIPY core and linker length joining the trap and reporter segments, tune PeT efficiency. DFT and electrochemical studies were used to estimate the thermodynamic driving force of PeT in our constructs. By tuning the redox potential over a 400 mV range, we observed over an order of magnitude increase in PeT efficiency. Increasing the linker length between the chromanol and BODIPY by 2.8 angstroms, in turn, decreased PeT efficiency 2.7‐fold. Our results illustrate how substituent and linker choice enable “darkening” the off state of fluorogenic probes based on BODIPY fluorophores, by favoring PeT over radiative emission from the singlet excited state manifold. Ultimately, our work brings light to the sensitivity ceiling one may achieve in developing fluorogenic antioxidant analogues of α‐tocopherol. The work provides general guidelines applicable to those developing fluorogenic probes based on PeT. 相似文献
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T. Tomiyama H. Suetomi W. Skorecki A. J. J. van de Velde J. Grant K. W. Brown P. A. Villaruz E. L. Breazeale R. A. Greene P. Hamer H. E. Evans L. Blanquet P. P. Tully N. M. Carter L. A. Kulski G. M. Mitilino M. P. Babkin J. C. Harral T v. Fellenberg W. Ohle R. E. Larson V. Bene E. Nolte H. J. Bandt G. Gad D. M. Taylor L. Urbányi und Käte Naumann 《Fresenius' Journal of Analytical Chemistry》1939,118(1-2):41-48
Ohne Zusammenfassung 相似文献
140.
Mid-infrared laser lines observed in hydrogen/rare gas discharges are assigned to three-body recombination processes involving an electron, a rare gas (He or Ne) atom, and the triatomic hydrogen ion (H(3)(+)). Calculations of radiative transitions between neutral H(3) Rydberg states support this interpretation, and link it to recent results for hydrogenic∕rare gas afterglow plasmas. A mechanism for the population inversion is proposed, and the potential generality and astrophysical implications of such molecular recombination laser systems are briefly discussed. 相似文献