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991.
Ramanan C Smeigh AL Anthony JE Marks TJ Wasielewski MR 《Journal of the American Chemical Society》2012,134(1):386-397
The photophysics and morphology of thin films of N,N-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-bis(dicarboximide) (1) and the 1,7-diphenyl (2) and 1,7-bis(3,5-di-tert-butylphenyl) (3) derivatives blended with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) were studied for their potential use as photoactive layers in organic photovoltaic (OPV) devices. Increasing the steric bulk of the 1,7-substituents of the perylene-3,4:9,10-bis(dicarboximide) (PDI) impedes aggregation in the solid state. Film characterization data using both atomic force microscopy and X-ray diffraction showed that decreasing the PDI aggregation by increasing the steric bulk in the order 1 < 2 < 3 correlates with a decrease in the density/size of crystalline TIPS-Pn domains. Transient absorption spectroscopy was performed on ~100 nm solution-processed TIPS-Pn:PDI blend films to characterize the charge separation dynamics. These results showed that selective excitation of the TIPS-Pn results in competition between ultrafast singlet fission ((1*)TIPS-Pn + TIPS-Pn → 2 (3*)TIPS-Pn) and charge transfer from (1*)TIPS-Pn to PDIs 1-3. As the blend films become more homogeneous across the series TIPS-Pn:PDI 1 → 2 → 3, charge separation becomes competitive with singlet fission. Ultrafast charge separation forms the geminate radical ion pair state (1)(TIPS-Pn(+?)-PDI(-?)) that undergoes radical pair intersystem crossing to form (3)(TIPS-Pn(+?)-PDI(-?)), which then undergoes charge recombination to yield either (3*)PDI or (3*)TIPS-Pn. Energy transfer from (3*)PDI to TIPS-Pn also yields (3*)TIPS-Pn. These results show that multiple pathways produce the (3*)TIPS-Pn state, so that OPV design strategies based on this system must utilize this triplet state for charge separation. 相似文献
992.
Fourier transform infrared (FTIR) smog chamber techniques were used to investigate the atmospheric chemistry of the isotopologues of methane. Relative rate measurements were performed to determine the kinetics of the reaction of the isotopologues of methane with OH radicals in cm3 molecule−1 s−1 units: k(CH3D + OH) = (5.19 ± 0.90) × 10−15, k(CH2D2 + OH) = (4.11 ± 0.74) × 10−15, k(CHD3 + OH) = (2.14 ± 0.43) × 10−15, and k(CD4 + OH) = (1.17 ± 0.19) × 10−15 in 700 Torr of air diluent at 296 ± 2 K. Using the determined OH rate coefficients, the atmospheric lifetimes for CH4–xDx (x = 1–4) were estimated to be 6.1, 7.7, 14.8, and 27.0 years, respectively. The results are discussed in relation to previous measurements of these rate coefficients. 相似文献
993.
Mn inclusion in the oxide based diluted magnetic semiconductor Zn1−x
Mn
x
O (x = 0.04, 0.06, 0.08, and 0.10) grown by standard high temperature solid state reaction technique has been studied. The local
and average structure of Zn1−x
Mn
x
O was characterized by the super resolution technique maximum entropy method and pair distribution function analysis using
the X-ray powder data. Magnetic studies on this material using a Vibrating Sample Magnetometer were also carried out to ascertain
the doping level in Zn1−x
Mn
x
O. 相似文献
994.
A series of ternary systems composed of cellulose acetate (CA), N,N-dimethylacetamide (DMA), and water were prepared by varying
the mixing temperature and order of component addition with increasing water content. The viscoelastic properties of the resulting
ternary systems were measured using steady state and dynamic rheology. The CA/DMA/H2O mixture formed physical gels at 17.5 and 19 wt% water concentrations after heating to 50 and 70/90 °C, respectively. Gel
formation was characterized by the loss of a Newtonian plateau in the steady state as well as the transition of the elastic
(G′) modulus becoming greater than the viscous (G″) modulus in the dynamic state. The order of component addition dramatically
affected phase behaviour. Adding CA to the DMA/water solution resulted in lower moduli gels and the formation of a two-phase
phase separated system at high nonsolvent contents in those prepared at low temperatures. The kinetics of phase separation
was improved by subjecting the gels to a thermal treatment of 90 °C. In this case, the gels previously heated at 50 and 70°
C showed a one-phase phase separated gel with higher viscous and elastic moduli. 相似文献
995.
Gerald G. Miller Kevin Brown Ronald B. Moore Malcolm S. McPhee Zhenjun J. Diwu Jixiang Liu Liren Huang J. William Lown David A. Begg Vera Chlumecky John Tulip 《Photochemistry and photobiology》1995,61(6):632-638
Hypocrellins are naturally occurring compounds with photosensitizing properties in biological systems. We have prepared synthetic derivatives of hypocrellin B, which have promise as photosensitizers in the clinical application of photodynamic therapy. The intracellular localization and uptake kinetics of hypocrellin B and several selected hypocrellin congeners were determined semiquantitatively by fluorescence confocal microscopy in monolayer cultures of EMT6/Ed murine tumor cells. Each compound had unique uptake kinetics. Although no compound tested to date has demonstrated nuclear labeling, most could be detected in lysosomes, Golgi, endoplasmic reticulum and, to a minor extent, in cellular membranes. No two compounds gave identical labeling distributions. The differences are assumed to originate in physicochemical properties characteristic of each compound, which may ultimately impact upon the primary modality of phototoxicity. 相似文献
996.
Kommareddi Nagesh S. Tata Murthy Karayigitoglu Cigdem John Vijay T. McPherson Gary L. Herman Michael F. O'Connor Charles J. Lee Young-Sook Akkara Joseph A. Kaplan David L. 《Applied biochemistry and biotechnology》1995,51(1):241-252
Applied Biochemistry and Biotechnology - Horseradish peroxidase has been used as a biocatalyst to synthesize a polymeric material from alkyl-substituted phenols. The synthesis is carried out in a... 相似文献
997.
998.
Ye?Mei Caiyi?Wei Yew?Mun?Yip Chun?Ying?Ho John?Z.?H.?Zhang Dawei?ZhangEmail author 《Theoretical chemistry accounts》2012,131(3):1168
Two replica exchange molecular dynamics (REMD) simulations were carried out to study the thermodynamics of a 20-residue Trp-cage
folding based on a newly developed polarized protein-specific charge (PPC). Starting from a fully extended conformation, Trp-cage
native conformation was successfully sampled using REMD based on a 3-step PPC update. Next, the obtained Trp-cage folded conformation
was then used to calculate the PPC in which another REMD was performed to explore the thermodynamic stability of Trp-cage.
The theoretical melting temperature T
m of ≈325 K was found to be in close agreement with experimental melting temperature, T
m of 315 K. This indicates that the PPC was correctly predicting the temperature dependence. The current study provides a direct
proof of how electrostatic polarization affects protein folding. 相似文献
999.
Libby Yoerg M. Ellen Matthews Lakshmi Kaza Naullage Indika Perera David W. Ball John Moran Alan T. Riga 《Journal of Thermal Analysis and Calorimetry》2012,108(1):19-24
Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts.
Phase transitions, including glass transition (T
g) and melting temperature (T
m), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced
dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each
of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles
were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and
solid–liquid transitions. 相似文献
1000.
John A. Mikroyannidis 《Journal of polymer science. Part A, Polymer chemistry》1995,33(3):381-387
3,5-Dinitrobenzoyl chloide was condensed with malononitrile in the presence of sodium hydroxide under phase-transfer conditions to afford 1-(2,2-dicyano-1-hydroxyvinyl)-3,5-dinitrobenzene, sodium salt, which was catalytically hydrogenated to the corresponding diamine. The latter was used as starting material for the preparation of unsaturated cyanosubstituted polyamides and polyimides. The polymers were soluble in polar aprotic solvents, dilute sodium hydroxide, and certain strong inorganic and organic acids. Upon curing at 300°C for 65 h, crosslinked polymers were obtained that were stable up to 392–404°C in N2 or air and afforded an anaerobic char yield of 60–71% at 800°C. Their glass transition temperatures as determined by thermal mechanical analysis (TMA) were 221–275°C. © 1995 John Wiley & Sons, Inc. 相似文献