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941.
942.
Stanis?aw Krompiec Mateusz Penkala Ewelina Kowalska Robert Penczek Piotr Bujak Witold Danikiewicz Grzegorz Spólnik Andrzej Kita Iwona Grudzka 《Monatshefte für Chemie / Chemical Monthly》2011,33(7):1241-1247
Abstract
Ru-catalyzed synthesis of mixed alkyl–alkyl acetals via addition of primary alcohols to allyl ethers has been extended to include long-chain and/or functionalized substrates. The catalytic systems for these reactions were generated from RuCl2(PPh3)3 and [RuCl2(1,5-COD)]x and phosphines [PPh3 or P(p-chlorophenyl)3] or SbPh3. Of particular importance is the almost quantitative elimination of transacetalization. The addition proceeds through allyl complexes, not via isomerization of allyl ethers––subsequent addition of ROH to vinyl ethers. 相似文献943.
Pawe? Niedzia?kowski Tadeusz Ossowski Rados?aw Majewski Zdzis?awa Nowakowska Grzegorz Schroeder 《Monatshefte für Chemie / Chemical Monthly》2011,89(3):1121-1129
Abstract
In this work, the synthesis of various thiol-functionalized anthraquinone compounds is presented. The studied compounds were characterized by mass spectrometry and the main fragmentation pathways are discussed. The compounds studied formed stable self-assembled monolayers (SAMs) in the gold surface. The parameters for the reduction processes in the gold surface of the studied new anthraquinones were determined by cyclic voltamperometry tests. 相似文献944.
A new multiresidue method for the efficient screening, identification and quantification of over 160 pesticides belonging to different chemical classes in red, rose and white wines have been developed. The analysis was based on gas chromatographic-tandem quadrupole mass spectrometric determination (GC-QqQ-MS/MS). An optimization strategy involved the selection of buffering conditions and sorbents for dispersive-solid phase extraction (dispersive-SPE) in order to achieve acceptably high recoveries and reduce co-extractives in the final extracts. As a result, the optimized procedure allowed us to obtain consistent recoveries of the target pesticides including problematic ones such as captan, chlorothalonil, dichlofluanid, folpet and tolylfluanid. The attained recoveries were typically between 80 and 110% (89% on average) with RSD values typically lower than 10% (8% on average) at three spiking levels of 0.01, 0.05 and 0.2 mg kg−1. Linearity was studied in the range between 0.005 and 0.2 mg kg−1 using pesticide standards prepared both in pure solvent and in the presence of matrix, showing coefficients of determination (R2) higher than 0.99 for all the pesticides except for desmedipham, thiabendazole and thiamethoxam in pure solvent. The study of the ratio of the slopes obtained in solvent and in matrix provided information about the matrix effects, which was <10%, 10-20% and >20% for 33, 36 and 31% of the studied pesticides, respectively. To improve accuracy, matrix matched standards were always used for calculation of the quantification results. The expanded uncertainties were estimated by using a “top-down” approach as being 17% on average (coverage factor k = 2, confidence level 95%). Finally, the method was used with success to detect and quantify pesticide residues in commercial wines. 相似文献
945.
Knobloch B Mucha A Operschall BP Sigel H Jeżowska-Bojczuk M Kozłowski H Sigel RK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(19):5393-5403
With a view on protein–nucleic acid interactions in the presence of metal ions we studied the “simple” mixed‐ligand model systems containing histamine (Ha), the metal ions Ni2+, Cu2+, or Zn2+ (M2+), and the nucleotides adenosine 5′‐triphosphate (ATP4?) or uridine 5′‐triphosphate (UTP4?), which will both be referred to as nucleoside 5′‐triphosphate (NTP4?) . The stability constants of the ternary M(NTP)(Ha)2? complexes were determined in aqueous solution by potentiometric pH titrations. We show for both ternary‐complex types, M(ATP)(Ha)2? and M(UTP)(Ha)2?, that intramolecular stacking between the nucleobase and the imidazole residue occurs and that the stacking intensity is approximately the same for a given M2+ in both types of complexes: The formation degree of the intramolecular stacks is estimated to be 20 to 50 %. Consequently, in protein–nucleic acid interactions imidazole–nucleobase stacks may well be of relevance. Furthermore, the well‐known formation of macrochelates in binary M2+ complexes of purine nucleotides, that is, the phosphate‐coordinated M2+ interacts with N7, is confirmed for the M(ATP)2? complexes. It is concluded that upon formation of the mixed‐ligand complexes the M2+? N7 bond is broken and the energy needed for this process corresponds to the stability differences determined for the M(UTP)(Ha)2? and M(ATP)(Ha)2? complexes. It is, therefore, possible to calculate from these stability differences of the ternary complexes the formation degrees of the binary macrochelates: The closed forms amount to (65±10) %, (75±8) %, and (31±14) % for Ni(ATP)2?, Cu(ATP)2?, and Zn(ATP)2?, respectively, and these percentages agree excellently with previous results obtained by different methods, confirming thus the internal validity of the data and the arguments used in the evaluation processes. Based on the overall results it is suggested that M(ATP)2? species, when bound to an enzyme, may exist in a closed macrochelated form only, if no enzyme groups coordinate directly to the metal ion. 相似文献
946.
947.
Urszula Domańska Kamil Paduszyński Zuzanna Żołek-Tryznowska 《The Journal of chemical thermodynamics》2011,43(2):167-171
(Liquid + liquid) phase equilibria (LLE) of binary mixtures containing hyperbranched polymer Boltorn® H2004 and n-alkanes (n-hexane, n-heptane, n-octane, and n-decane) were studied over the temperature range from about (260 up to 360) K. The polymer is partially miscible with n-alkanes and the solubility decreases with an increase of the chain length of the solvent. Corresponding LLE phase diagrams including spinodal and binodal (liquid + liquid) coexistence curves were calculated in terms of the statistical mechanics – based on the lattice-cluster theory, based only on the upper critical solution temperature, and the polymer chain architecture. The results show semi-qualitative agreement of predicted and experimental equilibrium compositions and temperatures. Boltorn® H2004 reveals complete miscibility in the liquid phase with alcohols (C1–C8), aromatic hydrocarbons (benzene, toluene, and thiophene), and ethers (methyl tetra-butyl ether, ethyl tetra-butyl ether, and tetrahydrofurane). 相似文献
948.
O. V. Reshetnyak E. P. Koval’chuk J. Błażejowski 《Russian Journal of Electrochemistry》2011,47(10):1111-1118
A short review is dedicated to the role of molecular oxygen and its active forms in generation of electrochemiluminescence
(ECL). It is shown at the example of such widely used luminogens as luminol, lucigenin, acridine esters, acridane, and indoles
that the role of O2 and its active forms, such as hydrogen peroxide, superoxide and hydroperoxide radicals in generation of ECL by organic compounds
is largely reduced to oxidation of the initial luminogen or intermediates of its partial electrochemical preoxidation/prereduction.
Such intermediates are most often particles in the doublet state (radical-cation, radical-anion, or free radicals) that form
unstable emitter precursors of peroxide (dioxetanone) type under interaction with O2, hydrogen peroxide, or other active oxygen forms. It is also shown that the product of secondary transformations of active
oxygen forms is singlet oxygen that may also be a radiation source as a result of cooperative transitions. 相似文献
949.
A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium
iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with
the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV
+) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was
obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 104 L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard. 相似文献
950.
Maślanka A Krzek J Stolarczyk M Walczak M Głogowska A 《Journal of AOAC International》2011,94(6):1791-1799
Stability of clonazepam, diazepam, haloperidol, and doxepin was determined in acidic solutions. In addition, determination of the kinetic and thermodynamic properties of this stability was carried out. Reaction rate constants (k), half-life times (t(0.1) and t(0.5)), and activation energy (Ea) were estimated for the drugs, which differed in polarity expressed with log P values. It was observed that estimated Ea values increased from 42.13 to 125.03 kJ/mol with an increase of lipophilicity (log P) beginning from the most hydrophilic drug (clonazepam, 2.70 log P) to the most lipophilic drug (doxepin, 4.10 log P). All degradation products were studied using an HPLC/electrospray ionization-MS technique in the positive ionization mode. 相似文献