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981.
The rate constant of the reaction OH + HCl → H2O + Cl was measured in a flow tube over the temperature range 224 to 460°K using resonance fluorescence detection of OH. An Arrhenius expression k1 = (2.0 ± 0.1) × 10?12 exp [?(620 ± 20 cal/mole)/RT] was obtained. Stratospheric and reaction kinetic implications are discussed briefly. 相似文献
982.
[reaction: see text] Stereo-controlled syntheses of two possible C1-C25 diastereomers of spirastrellolide A containing the cis-disubstituted tetrahydropyran and [6,6]-spiroacetal are reported, exploiting boron-mediated asymmetric aldol and allylation methodology. 相似文献
983.
Z. B. Güvenç M. A. Anderson B. H. Choi 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,35(1):51-55
A detailed evaluation of the structural and dynamical properties of isolated water dimers and tetramers using the Lemberg, Stillinger and Rahman potential energy surface and microcanonical molecular dynamics simulations are reported. The lowest-energy configurations of these clusters were obtained by simulated thermal quenching. Relative root-mean-square bond length fluctuations were used to characterize phase transitions. Solid-like, pre-melting, liquid-like, and dissociated states were identified. Global-local minimum transitions and the minimum energy path to dissociation of the dimer were also characterized. 相似文献
984.
A group of dissolved-bioavailable organochlorine (OC) pesticides and inorganic anions in water and total OC pesticides in sediments were measured in the Malheur Watershed, a semi-arid region in the western United States, over a 2-year period. OC pesticide levels were compared with those from a 1990 study of the lower section of the river, the most recent data available. After calculating the dissolved fraction from the 1990, study it seems that DDD and dieldrin levels have decreased in the water by 50-70%, while DDE and DDT have changed little. Although banned nearly 30 years ago, DDT is still persistent throughout the Malheur River basin/watershed because it was found in all water samples tested. All of the OC pesticides tested during the 2-year study are well below the criterion continuous concentration for aquatic community exposure as defined by the U.S. Environmental Protection Agency (EPA). OC pesticides appear to be decreasing, however, at lower Ontario there remains a human health risk (EPA Human Health Risk Water Quality Criteria) for DDT, because this criteria includes daily consumption of water and fish from the river. Overall, although the upper forest watershed sites have lower OC pesticide concentrations, they represent an important contribution to the total DDT load to this watershed, a source not previously acknowledged. The large increase in DDT and sigmaDDT between the Ontario sites may indicate a possible historical point source of contamination or historical preferential deposition of contamination. Normalized sediment (sigmaDDT/organic carbon) strongly correlates with dissolved water sigmaDDT. 相似文献
985.
James L. Anderson 《General Relativity and Gravitation》1984,16(6):595-601
The method of calculating radiation damping effects by means of energy balance is applied to a simple model problem. The balance equation is derived from the conservation law for energy that is a consequence of the equations of motion for the system by integrating over a four-dimensional space-time region bounded in the wave zone by two future-directed null cones and in the near zone by twot=const surfaces. It is assumed that the sources are in slow motion and the fields are calculated by the method of matched asymptotic expansions. Our principle conclusion is that even though the damping isO(
3) where is an expansion parameter the fields need only be determined toO(1) to calculate the effects of damping by this method.Work supported in part by NSF Grant No. 79-11664-01. 相似文献
986.
Surfaces designed for charge reversal 总被引:2,自引:0,他引:2
Matthews JR Tuncel D Jacobs RM Bain CD Anderson HL 《Journal of the American Chemical Society》2003,125(21):6428-6433
We have created surfaces which switch from cationic at pH < 3 to anionic at pH > 5, by attaching aminodicarboxylic acid units to silica and gold substrates. Charge reversal was demonstrated by monitoring the adsorption of cationic dyes (methylene blue and a tetracationic porphyrin) and an anionic sulfonated porphyrin, at a range of pH using UV-vis absorption and reflection spectroscopy. The cationic dyes bind under neutral conditions (pH 5-7) and are released at pH 1-4, whereas the anionic dye binds under acidic conditions (pH 1-4) and is released at pH 5-7. Gold surfaces were functionalized with two different amphoteric disulfides with short (CH(2))(2) and long (CH(2))(10)CONH(CH(2))(6) linkers; the longer disulfide gave surfaces exhibiting charge reversal in a narrower pH range. Adsorption is much faster on the functionalized gold (t(1/2) = 62 s) than on functionalized silica (t(1/2) = 6900 s), but the final extents of coverage on both surface are similar, for a given dye at a given pH, with maximal coverages of around 2 molecules nm(-)(2). These charge-reversal processes are reversible and can be repeatedly cycled by changing the pH. We have also created surfaces which undergo irreversible proton-triggered charge switching, using a carbamate-linked thiol carboxylic acid which cleaves in acid. These surfaces are versatile new tools for controlling electrostatic self-assembly at surfaces. 相似文献
987.
The rate constant of the reaction OH (v = 0) + O3 HO2 + O2 was measured over the temperature range from 220 to 450°K at total pressures between 2 and 5 torr using ultraviolet fluorescent scattering for the detection of OH radicals. An Arrhenius expression, k1 = 1.3 × 10?12 exp(?1900/RT) cm3/sec was obtained and the rate constant for the reaction HO2 + O3OH + 2O2 was inferred to be less than 0.1 k1 over the entire temperature interval. 相似文献
988.
Maximilian Wolf Dominik Lungerich Stefan Bauroth Maximilian Popp Benedikt Platzer Timothy Clark Harry L. Anderson Norbert Jux Dirk M. Guldi 《Chemical science》2020,11(27):7123
Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. In short, a unidirectional flow of excited state energy from the HBC termini to the (metallo)porphyrin focal points enables concentrating light at the latter. Control over excitonic interactions within, for example, the electron-donating porphyrin dimers was realized by complexation of bidentate ligands to set up panchromatic absorption that extends all the way into the near-infrared range. The bidentate binding motif was then exploited to create a supramolecular electron donor–acceptor assembly based on a HBC-ethynyl-porphyrin dimer and an electron accepting bis(aminoalkyl)-substituted fullerene. Of great relevance is the fact that charge separation from the photoexcited HBC-ethynyl-porphyrin dimer to the bis(aminoalkyl)-substituted fullerene is activated not only upon photoexciting the HBCs in the UV as well as the (metallo)porphyrins in the visible but also in the NIR. Implicit is the synergetic interplay of energy and charge transfer in a photosynthetic mimicking manner. The dimer and bis-HBC-ethynyl-porphyrin monomers, which serve as references, were probed by means of steady-state as well as time-resolved optical spectroscopies, including global target analyses of the time-resolved transient absorption data.Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. 相似文献
989.
Kroll JH Donahue NM Cee VJ Demerjian KL Anderson JG 《Journal of the American Chemical Society》2002,124(29):8518-8519
Gas-phase ozone-alkene reactions are known to produce the hydroxyl radical (OH) in high yields. Most mechanistic studies to date have focused on the role of syn carbonyl oxides; however, OH production from ethene ozonolysis indicates a second, poorly understood OH-forming channel, which may contribute to OH production in the ozonolysis of substituted alkenes as well. Using laser-induced fluorescence, we have measured OH and OD yields from the ozonolysis of two partially deuterated alkenes, cis- and trans-3-hexene-3,4-d2. OD is formed from both alkenes, indicating a pathway of hydroxyl-radical formation involving vinylic hydrogens, accounting for one-third of total OH formation from cis-3-hexene. The lack of a significant kinetic isotope effect suggests this pathway is the "hot acid" channel, arising from rearrangement of anti carbonyl oxides. Measured yields also allow for the estimation of syn:anti carbonyl oxide ratios, approximately 50:50 for trans-3-hexene and approximately 20:80 for cis-3-hexene, qualitatively consistent with our understanding of ozonide decomposition pathways. 相似文献
990.
The Galileo solar redshift experiment 总被引:2,自引:0,他引:2