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901.
Jesse A. Myhill Liang Zhang Gabriel J. Lovinger Prof. James P. Morken 《Angewandte Chemie (International ed. in English)》2018,57(39):12799-12803
Catalytic enantioselective conjunctive cross‐coupling has been developed to construct tertiary alkylboronic esters. These reactions occur with good yield and enantioselectivity for a range of substrates. Mechanistic experiments reveal aspects of the catalytic cycle that allow hindered substrates to react without significant complicating side reactions. 相似文献
902.
Experimental values for 1H and 19F nuclear shielding anisotropies obtained from solid state, nematic phase, and molecular beam measurements are reviewed. Certain discrepancies are pointed out. An anisotropy operator is defined as a sum of two operators corresponding to the Lamb and high frequency terms. Approximations to the high frequency operator are given. Scales of absolute shielding constants are obtained, so that the magnitudes of the anisotropies can be discussed on the basis of non-empirical and semi-empirical calculations, and of the experimental results. The hypothesis due to Ramsey that the potential is constant for a given nucleus in different molecules is used to obtain approximate values for the Lamb term in the nuclear shielding constant. The distinction between shielding in large and small molecules is stressed. For the fluoromethanes and fluorobenzene the results of CNDO/2 molecular orbital calculations are used for a qualitative discussion of the anisotropies. 相似文献
903.
Tram Dang Richard Ramsaran Sayak Roy Jesse Froehlich Joseph Wang Clifford P. Kubiak 《Electroanalysis》2011,23(10):2335-2342
A combinatorial approach is described for screening homogeneous CO2 reduction electrocatalysts by means of a high‐throughput 25‐well parallel electrolyzer. Active catalysts were then screened by three methods: (1) the presence of CO gas in the electrolyzer head space; (2) a pH change for the individual solutions before and after bulk electrolysis due to proton consumption during CO2 reduction; and (3) other physical attributes. Based on these screening methods, two solutions out of the 25 were selected for further study. One out of two selected solutions, nickel cyclam, a well‐known CO2 reduction electrocatalyst, was correctly identified to be the most active. 相似文献
904.
Dr. Monica Vasiliu Dr. John K. Gibson Prof. Dr. Kirk A. Peterson Prof. Dr. David A. Dixon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(17):4245-4254
Gas-phase bimolecular reactions of metal cations with water provide insights into intrinsic characteristics of hydrolysis. For the actinide dioxide cations, actinyl(V) AnO2+, melding of experiment and computation provides insights into trends for hydrolysis, as well as for oxo-exchange between actinyls and water that proceeds by a hydrolysis pathway. Here this line of inquiry is further extended into the actinide series with CCSD(T) computations of potential energy surfaces, for the reaction pathway for oxo-exchange through hydrolysis of nine actinyl(V) ions, from PaO2+ to EsO2+. The computed surfaces are in accord with previous experimental results for oxo-exchange, and furthermore predict spontaneous exchange for CmO2+, BkO2+, CfO2+ and EsO2+, but not for AmO2+. Natural Bond Order analysis of the species involved in both hydrolysis and oxo-exchange reveals an inverse correlation between the barrier to hydrolysis and the charge on the actinide centre, q(An). Based on this correlation, it can be concluded that hydrolysis, and related phenomena such as oxo-exchange, become less favourable as the charge on the metal centre decreases. The new results provide a straightforward rationalization of trends across a wide swathe of the actinide series. 相似文献
905.
Robinson Troy A. Peterson John P. Hague Robert K. 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(7):3015-3023
Journal of Radioanalytical and Nuclear Chemistry - Gamma attenuation attributable to xenon and carbon dioxide carrier gas in radioactive xenon assay samples has been calculated using Monte Carlo... 相似文献
906.
Jesse O. Omamogho Elaine M. Stack Apichai Santalad Supalax Srijaranai Jeremy D. Glennon Helen Yamen Klaus Albert 《Analytical and bioanalytical chemistry》2010,397(6):2513-2524
This study describes the use of stationary phases with polar functionality suitable for the chemical analysis of carbamates
pesticides and comparing with conventional alkyl C8 and C18 phases. The emphasis of this study was to compare the selectivity
and retention of the pesticides on different stationary phases, bonded onto 1.7 μm partially porous silica particles under
isocratic separation condition. Four stationary phases including: phenylaminopropyl (PAP) phase, bidentate propylurea-C18
(BPUC18), C8 and C18, were successfully bonded on the partially porous silica spheres as evidenced by 29Si and 13C solid-state NMR analysis. The phenylaminopropyl phase exhibited smaller retentivity and enhanced selectivity compared to
the alkyl C8 phase; the analysis time to run separation of the six carbamate pesticides (i.e., methomyl, propoxur, carbofuran,
carbaryl, isoprocarb, and promecarb) on the PAP phase was threefold faster than alkyl C8 phase. In a similar manner, the BPUC18 phase shows similar selectivity to that of the PAP phase, but with longer retentivity; although the BPUC18 phase is characterized with a lesser degree of retentivity for the carbamate pesticides than the conventional alkyl C18 phase.
We propose that π–π and weak polar interactions between the carbamate pesticides and the PAP phase dominates the separation
mechanism and providing a superior selectivity; faster separation time was also achieved as a result of smaller retentivity.
Whereas the C8 and C18 bonded phases exhibits only hydrophobic interactions with the pesticides, leading to larger retentivity.
The BPUC18 phase is shown to interact via polar–polar interactions in addition to hydrophobic interactions with the pesticides, providing
similar selectivity with the PAP phase but with larger retentivity. 相似文献
907.
Yongmei Wang Aaron MasurYutian Zhu Jesse Ziebarth 《Journal of chromatography. A》2010,1217(39):6102-6109
The partitioning of star branched polymers into a slit pore at three different chromatography conditions, namely, size exclusion chromatography (SEC), liquid chromatography at the critical condition (LCCC), and liquid adsorption chromatography (LAC) have been investigated with lattice Monte Carlo simulations. Two different chain models are used: random walks (RW) that have no excluded volume interaction and self-avoiding walks (SAW) that have excluded volume interaction. The simulation data obtained for the two chain models are compared to illustrate the effect of excluded volume interactions on the partitioning of star branched polymers. The two most outstanding effects observed due to the introduction of excluded volume interactions are: (i) stars with a high number of arms can be excluded from the pore at condition corresponding to the LCCC of the linear polymers; (ii) the partition coefficient of stars in LAC mode is not dependent only on the total number of monomers on the chain. These effects illustrated by the current study should be taken into account when interpreting experimental chromatography data for branched polymers. 相似文献
908.
Ivan Pedrosa Long Ngo Jesse Wei Michael Schuster Houman Mahallati Martin Smith Neil M. Rofsky 《Magnetic resonance imaging》2009
Objective
The objective of this study was to retrospectively analyze the value of dynamic half-Fourier single-shot turbo spin echo (HASTE) imaging in patients with suspected deep venous thrombosis (DVT).Materials and Methods
Fifty-five veins in 24 patients were interrogated using a HASTE sequence with the patients relaxed and in various degrees of Valsalva. Veins were analyzed for changes in caliber (+CAL) and signal intensity (+SI) or in their absence (−CAL and −SI, respectively) and compared with the presence of thrombus on gadolinium-enhanced magnetic resonance imaging.Results
There was no thrombus in veins with the +CAL, +SI pattern (n=40) (P<.01). Five of seven veins (71.4%) with the −CAL, −SI pattern had thrombus (P<.01). A qualitative change in CAL had a sensitivity of 100% and a specificity of 91% for the presence of thrombus. An increase of 1.5 mm in CAL had a sensitivity of 100% and a specificity of 93% for this diagnosis.Conclusion
Dynamic HASTE imaging offers a physiological method to evaluate veins for deep venous thrombosis. 相似文献909.
910.
Reactions of nucleophiles with metal-bound hydrocarbyl pi-ligands bound in an eta3-fashion are key steps in a variety of carbon-carbon and carbon-heteroatom bond-forming reactions. To reveal factors that control the rates of reaction of nucleophiles with this type of ligand, the rates of reactions of an aromatic and an aliphatic amine with a series of eta3-allyl, eta3-benzyl, and eta3-phenethyl palladium complexes ligated by the bisphosphine (R)-BINAP to form allylic and benzylic amines were measured. These data showed that the less common addition to an eta3-benzyl complex is faster than the more common addition to an eta3-allyl complex. The relative rates of reaction followed the trend naphthylmethyl > naphthylethyl > benzyl > 1,1-dimethylallyl > allyl. Computational studies suggest that there is a correlation between the amount of positive charge at the site of nucleophilic attack and the rate of C-N bond formation. 相似文献