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排序方式: 共有462条查询结果,搜索用时 31 毫秒
41.
I. Sreedhar Harini Kantamneni K. Suresh Kumar Reddy K. V. Raghavan 《Kinetics and Catalysis》2014,55(2):229-232
Acylation of anisole is a commercially important reaction in the production of various fine chemicals, agrochemicals, pharmaceuticals and fragrances. Conventionally, it is carried out using the catalysts like AlCl3, FeCl3, ZnCl3, HF, which suffer from major drawbacks such as larger consumption, corrosion and safety issues, waste disposal and the material handling. Hence the conventional catalysts are being replaced with solid acid catalysts like H-Beta, H-ZSM5 to overcome the above drawbacks. In this work, liquid phase acylation of anisole has been carried out employing H Beta, H ZSM-5 and HY catalysts and the process standardization at a macrolevel has been done with reference to parameters like temperature, reaction time, molar ratio of reactants, catalyst nature, Si/Al ratio of catalyst and the catalyst quantity. In addition, catalyst stability was investigated. 相似文献
42.
Iron doped semiconducting nanoparticles Sn1−xFexO2 with x=0, 0.001, 0.002, 0.003, 0.004, 0.01 and 0.03 were prepared by a sol-gel method. The X-ray diffraction, Transmission Electron Microscopy measurements confirm the rutile structure with no impurity phase. The three characteristic lines of electron spin resonance (ESR) are observed in the doped samples for all compositions, which is a clear evidence for rhombic Fe3+ in rutile phase. The line width of ESR increases with increase in Fe concentration due to induced disorder. The spin-pumping effect is observed at temperatures below 250 K for the samples with x=0.01 and 0.03. However, based on the Curie-Weiss susceptibility, iron is in paramagnetic state and is subject to weak antiferromagnetic interaction. Blue shift in the optical band gap is observed with increase in the Fe content. 相似文献
43.
Wan S Wu F Rech JC Green ME Balachandran R Horne WS Day BW Floreancig PE 《Journal of the American Chemical Society》2011,133(41):16668-16679
The potent cytotoxins pederin and psymberin have been prepared through concise synthetic routes (10 and 14 steps in the longest linear sequences, respectively) that proceed via a late-stage multicomponent approach to construct the N-acyl aminal linkages. This route allowed for the facile preparation of a number of analogs that were designed to explore the importance of the alkoxy group in the N-acyl aminal and functional groups in the two major subunits on biological activity. These analogs, including a pederin/psymberin chimera, were analyzed for their growth inhibitory effects, revealing several new potent cytotoxins and leading to postulates regarding the molecular conformational and hydrogen bonding patterns that are required for biological activity. Second generation analogs have been prepared based on the results of the initial assays and a structure-based model for the binding of these compounds to the ribosome. The growth inhibitory properties of these compounds are reported. These studies show the profound role that organic chemistry in general and specifically late-stage multicomponent reactions can play in the development of unique and potent effectors for biological responses. 相似文献
44.
Pathik Sahoo Dr. D. Krishna Kumar Dr. Srinivasa R. Raghavan Dr. Parthasarathi Dastidar 《化学:亚洲杂志》2011,6(4):1038-1047
Easy access to a class of chiral gelators has been achieved by exploiting primary ammonium monocarboxylate ( PAM ), a supramolecular synthon. A combinatorial library comprising of 16 salts, derived from 5 l ‐amino acid methyl esters and 4 cinnamic acid derivatives, has been prepared and scanned for gelation. Remarkably, 14 out of 16 salts prepared (87.5 % of the salts) show moderate to good gelation abilities with various solvents, including commercial fuels, such as petrol. Anti‐solvent induced instant gelation at room temperature has been achieved in all the gelator salts, indicating that the gelation process is indeed an aborted crystallization phenomenon. Rheology, optical and scanning electron microscopy, small angle neutron scattering, and X‐ray powder diffraction have been used to characterize the gels. A structure‐property correlation has been attempted, based on these data, in addition to the single‐crystal structures of 5 gelator salts. Analysis of the FT‐IR and 1H NMR spectroscopy data reveals that some of these salts can be used as supramolecular containers for the slow release of certain pest sex pheromones. The present study clearly demonstrates the merit of crystal engineering and the supramolecular synthon approach in designing new materials with multiple properties. 相似文献
45.
The set of correlated equilibria for a bimatrix game is a closed, bounded, convex set containing the set of Nash equilibria. We show that every extreme point of a maximal Nash set is an extreme point of the above convex set. We also give an example to show that this result is not true in the payoff space, i.e. there are games where no Nash equilibrium payoff is an extreme point of the set of correlated equilibrium payoffs. 相似文献
46.
A detailed investigation has been made on the possibility of synthesizing LiNiO2 through different methods using a variety of precursors and varying heat treating conditions with a view to identify a suitable
method to synthesize LiNiO2 and to understand the influence of synthesis method and the nature of the precursors towards the performance characteristics
of LiNiO2. In this regard, four different methods,viz., solid-state, organic precursors, solution combustion and microwave methods were adopted involving suitable combinations
of lithium and nickel precursors. All the synthesized compounds were characterized for their phase purity (PXRD), local cation
environment (FTIR), particle size, surface area, and electrochemical behavior (charge-discharge). Based on the results obtained
especially from PXRD and charge-discharge studies, the “all-hydroxide” precursors of Li and Ni were found to be effective
in yielding battery active LiNiO2 as far as the solid-state and microwave-assisted methods are concerned. With regard to solution synthesis methods, citrate
precursor and the combustion method involving hydrazine hydrate fuel were found to yield better performing LiNiO2, compared to the rest of the combinations attempted in both categories. However, among the wet chemistry based solution methods
the present study recommends solution combustion method with hydrazine hydrate as fuel to synthesize electrochemically active
LiNiO2 as it was found to exhibit a stable discharge capacity of 177 mAh/g at least up to 20 cycles. 相似文献
47.
48.
Shin Y Fournier JH Brückner A Madiraju C Balachandran R Raccor BS Edler MC Hamel E Sikorski RP Vogt A Day BW Curran DP 《Tetrahedron》2007,63(35):8537-8562
Total syntheses of (−)-dictyostatin, 6,16-bis-epi-dictyostatin, 6,14,19-tris-epi-dictyostatin, and a number of other isomers and analogs are reported. Three main fragments—top, middle, and bottom—were first assembled and then joined by olefination or anionic addition reactions. After appending the two dienes at either end of the molecule, macrolactonization and deprotection completed the syntheses. The work proves both the relative and absolute configurations of (−)-dictyostatin. The compounds were evaluated by cell-based measurements of increased microtubule mass and antiproliferative activity, and in vitro tubulin polymerization assays as well as competitive assays with paclitaxel for its binding site on microtubules. These assays showed dictyostatin to be the most potent of the agents and further showed that the structural alterations caused from 20- to >1000-fold decreases in activity. 相似文献
49.
N. Kalaiselvi M. Ashok Kumar M. S. Prasath N. G. Renganathan M. Raghavan N. Muniyandi 《Ionics》2002,8(5-6):447-452
Li2CoMn3O8, a 5 V cathode material used in rechargeable lithium batteries, has been synthesized by adopting a novel technique of using
fuels along with the nitrate reactants. The effect of the fuel on the synthesis of Li2CoMn3O8 has been analyzed in terms of the physical and electrochemical properties of the final product formed by various methods
such as solid-state carbonate fusion and the solution route using acetate and nitrate precursors. Powder X-ray diffraction
FT IR spectrum, particle size, surface area and SEM analysis were carried out. The combustion method, also known as selfpropagating
high temperature (SPHT) method, has been employed in the present study by using nitrate mixtures of the respective salts and
a nitrogeneous fuel (urea or glycine) at a temperature of 300 °C for 3 hrs. The nitrate reactants without the addition of
fuel gave only a deliquescent product even at elevated temperature (600 °C) thus indicating the necessity of fuels. Similar
attempts using acetate reactants with and without the addition of nitrogeneous fuels were made separately in order to find
out the necessity of fuel also in this case. The characterization of the product in terms of purity, single-phase formation
and surface morphology suggested that the fuel played no role in the case of the acetate precursors. A comparative study was
made on the products obtained by the acetate precursor, combustion method and the conventional carbonate method. Among the
three methods, the combustion method with glycine as fuel yielded the spinel phase with high purity Li2CoMn3O8 with superior electrochemical behavior both in terms of high cell voltage and good cycle life behavior. 相似文献
50.
V. Raghunathan P. S. Raghavan K. Vaidyanathan V. S. Srinivasan 《Journal of Chemical Sciences》1982,91(3):241-246
The chlorination of acetophenone by chloramine-T cat has been catalysed by anionic micelle, sodium lauryl sulphate (NaLS).
Though the order in cat is one, the order in acetophenone is fractional at lower concentration and becomes zero at higher
concentration in the presence and absence of NaLS. This is probably due to the change in rate-determining step. At lower acetophenone
concentration, the decomposition of enol-chlorinating species complex is rate-determining whereas at higher concentration,
the formation of chlorinating species is rate determining. The graph ofk
2 versus detergent concentration is sigmoidal and the positive co-operativityversus log[D] graph is 1.11, indicating possible interaction between micelle and substrate. 相似文献