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81.
Excimer Formation in a Confined Space: Photophysics of Ladderphanes with Tetraarylethylene Linkers 下载免费PDF全文
Dr. Chih‐Hsien Chen Kamani Satyanarayana Yi‐Hung Liu Shou‐Ling Huang Prof. Tsong‐Shin Lim Prof. Tien‐Yau Luh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):800-807
Communication between chromophores is vital for both natural and non‐natural photophysical processes. Spatial confinements offer unique conditions to scrutinize such interactions. Polynorbornene‐ and polycyclobutene‐based ladderphanes are ideal model compounds in which all tetraarylethylene (TAE) linkers are aligned coherently. The spans for each of the monomeric units in these ladderphanes are 4.5–5.5 Å. Monomers do not exhibit emission, because bond rotation in TAE can quench the excited‐state energy. However, polymers emit at 493 nm (Φ=0.015) with large Stokes shift under ambient conditions and exhibit dual emission at 450 and 493 nm at 150 K. When the temperature is lowered, the emission intensity at 450 nm increases, whereas that at 493 nm decreases. At 100 K, both monomers and polymers emit only at 450 nm. This shorter‐wavelength emission arises from the intrinsic emission of TAE chromophore, and the emission at 493 nm could be attributed to the excimer emission in the confined space of ladderphanes. The fast kinetics suggest diffusion‐controlled formation of the excimer. 相似文献
82.
A simple and new synthetic approach to various analogues of Irbesartan is described. 相似文献
83.
Ravi Kiran Kaja K. V. Surendranath P. Radhakrishnanand J. Satish P. V. V. Satyanarayana 《Chromatographia》2010,72(5-6):441-446
A novel, sensitive, stability indicating RP-LC method has been developed for the quantitative determination of deferasirox, its related impurities in both bulk drugs and pharmaceutical dosage forms. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination delivered in an isocratic mode and quantitation was by ultraviolet detection at 245 nm. The mobile phase consisted of buffer, acetonitrile and methanol (50:45:5, v/v) delivered at a flow rate of 1.0 mL min?1. Buffer consisted of 10 mM potassium dihydrogen orthophosphate monohydrate, pH adjusted to 3.0 by using orthophosphoric acid. In the developed LC method the resolution (R s ) between deferasirox and its four potential impurities was found to be greater than 2.0. Regression analysis showed an r value (correlation coefficient) greater than 0.999 for deferasirox and its four impurities. This method was capable to detect all four impurities of deferasirox at a level of 0.002% with respect to test concentration of 0.5 mg mL?1 for a 10 μL injection volume. The inter- and intra-day precision values for all four impurities and for deferasirox was found to be within 2.0% RSD. The method showed good and consistent recoveries for deferasirox in bulk drugs (98.3–101.1%), pharmaceutical dosage forms (100.2–103.1%) and for its all the four impurities (99.7–102.1%). The test solution was found to be stable in methanol for 48 h. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in acid stress hydrolysis. The stress samples were assayed against a qualified reference standard and the mass balance was found close to 99.95%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness. 相似文献
84.
T. Satyanarayana 《Journal of luminescence》2010,130(3):498-506
The glasses of the composition (39−x)BaO-xAl2O3-60P2O5:1.0Ho2O3 (in mol%) with x value ranging from 1.0 to 4.0 have been synthesized. The IR spectral studies of these glasses have indicated that there is a gradual transformation of Al3+ ions from tetrahedral to octahedral with increase in the concentration of Al2O3 up to 3.0 mol%. Optical absorption and fluorescence spectra (in the visible and NIR regions) of these glasses have been recorded at room temperature. The Judd-Ofelt theory could successfully be applied to characterize the absorption and luminescence spectra of Ho3+ ions in these glasses. From the luminescence spectra, various radiative properties like transition probability A, branching ratio βr, the radiative lifetime τr and emission cross-section σE for various emission levels of these glasses have been evaluated. The radiative lifetime of the 5S2→5I8 (green emission) transition has also been measured. The variations observed in these parameters have been discussed in the light of varying co-ordinations (tetrahedral and octahedral positions) of Al3+ ions in the glass network. The influence of hydroxyl groups on the luminescence efficiency of the transition 5S2→5I8 has also been discussed. Finally the optimum concentration of Al2O3 for getting maximum luminescence output has also been identified and reported. 相似文献
85.
M. Ravikumar M. Satish Varma T. Satyanarayana Raju P. Suchitra P. Yadagiri Swamy 《Chromatographia》2009,69(1-2):85-89
A new stereospecific LC method for the separation and quantification of moxifloxacin and its (R,R)-enantiomer in bulk drug was developed and validated by ligand-exchange liquid chromatography on a reversed phase column using aqueous mobile phase containing the chiral reagent l-isoleucine-Cu(II). The UV detector was operated at 293 nm. The flow rate of mobile phase was set at 0.9 mL min?1. The achiral ODS column offers good separation of the two enantiomers in less than 20 min. The test concentration was 1,000 μg mL?1 in the mobile phase. This method was capable of detecting the (R,R)-enantiomer of moxifloxacin up to 0.1 μg mL?1 for a 20 μL injection volume. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. There was no interference of degradants with the (R,R)-enantiomer in the developed method. The developed chiral RP-LC method was validated with respect to linearity, accuracy, precision and robustness. The percentage recovery for the (R,R)-enantiomer in bulk drug samples ranged from 98.1 to 104.4%. The test solution was found to be stable in the mobile phase for 48 h after preparation. 相似文献
86.
The phytase production by Sporotrichum thermophile TLR50 was recorded on all the commonly used animal feed ingredients tested to varying degrees in solid-state fermentation. Enzyme production increased to 180 U/g of dry moldy residue (DMR) in sesame oil cake at 120 h and 45 degrees C at the initial substrate-to-moisture ratio of 1:2.5 and aw of 0.95. Supplementation of sesame oil cake with glucose and ammonium sulfate further enhanced phytase titer (282 U/g of DMR). An overall 76% enhancement in phytase production was achieved owing to optimization. The mold secreted acid phosphatase, amylase, xylanase, and lipase along with phytase. By the action of phytase, inorganic phosphate was liberated efficiently, leading to dephytinization of sesame oil cake. 相似文献
87.
Asymmetric amplification by kinetic resolution using a racemic reagent: example in amine acetylation
The reaction of a racemic reagent on a mixture of enantiomers with small ee (ee=enantiomeric excess) has been studied for amine acylation. A substantial asymmetric amplification could be realized, for example, from 67 to >95.5 ee. The combination of asymmetric amplifications is subsequently discussed. Two sequential asymmetric amplifications, one using a racemic reagent and another using a positive nonlinear effect allowed us to start from 1.5 % ee and end with a large amount of a product of 97 % ee. 相似文献
88.
Kinetics and equilibria of the axial ligation of alkyl(aquo)cobaloximes by imidazole and cyanide have been measured spectrophotometrically
in aqueous solutions of ionic strength 1.0 M at 25°C as a function of pH. Comparison of KIMD and KCN- of CH3, C2H5 and BrCH2cobaloximes indicates that their stability is in the order BrCH2>CH3>C2H2. As the electron-withdrawing capacity of the alkyl grouptrans to water increases, the electron density of the cobalt(III) decreases and thus it becomes a stronger Lewis acid and binds
more strongly to imidazole and cyanide. The association and dissociation rate constants are better correlated to the relative
softness of the ligand showing that cyanide binds 30 times faster than imidazole. These complexes are isolated and are characterized
by IR and1H NMR spectra. 相似文献
89.
The first enantiospecific total synthesis of the tricyclic sesquiterpene (+)-seychellene, starting from (R)-carvone via (S)-3-methylcarvone, has been accomplished employing a combination of an intermolecular Michael addition-intramolecular Michael addition sequence and an intramolecular alkylation reaction for the generation of the two vicinal quaternary carbon atoms. 相似文献
90.
Summary 0.02 g/0.2 ml of potassium ferricyanide can be detected on a spot plate by utilising its catalytic effect on the reaction of cerium (III) with sulphosalicylic acid. A probable mechanism is discussed.
Zusammenfassung Die katalytische Wirkung von Hexacyanoferrat(III) auf die Reaktion zwischen Cer(III) und Sulfosalicylsäure wird zur einem empfindlichen Tüpfelnachweis für [Fe(CN)6]3– benutzt. Noch 0,02 g/0,2 ml können nachgewiesen werden. Der Reaktionsmechanismus wird diskutiert.相似文献