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991.
The separation of four water soluble nucleobases (thymine, uracil, adenine, and cytosine) via supercritical fluid chromatography with a CO2‐based mobile phase containing an alcohol modifier and additive is described. Methanol, ethanol, 1‐propanol, and 1‐butanol were examined in conjunction with water as a neutral additive. Packed column stationary phases included silica bonded diol, cyanopropyl, and 2‐ethyl pyridine. Thymine and uracil eluted with good peak shapes without additive, while adenine and cytosine yielded late eluting, severely tailing peaks. The addition of up to 5% water to each of the five alcohols gave rise to much sharper peaks that eluted under gradient conditions in less than 10 min with no baseline noise. Results with water under identical chromatographic conditions were compared with formic acid and ammonium acetate as additives. Water proved to be much superior to formic acid, and it was comparable to ammonium acetate. The role of water was speculated to not only enhance the solvating power of the binary mobile phase for water soluble analytes, but the common elution pattern exhibited by each of the three stationary phases suggested that water had altered the surface chemistry of the packed phase. 相似文献
992.
Two new cobalt(III) complexes of the Schiff base N,N′-disalicylidene-1,2-phenylendiimine dianion (salophen), trans- [CoIII(salophen)(ta)2]ClO4, (ta = thioacetamide) (1) and trans-[CoIII(salophen)(tb)2]ClO4, (tb = thiobenzamide) (2) were synthesized and characterized using single-crystal X-ray diffraction and spectroscopic techniques. Both complexes show solvatochromism in a variety of solvents. Complex (1) crystallized from CHCl3 as a solvate of orthorhombic symmetry, space group Pca21 with a = 17.3480(10) Å, b = 18.7522(10) Å, c = 18.8128(11) Å, α = β = γ = 90°, and Z = 8. The cobalt(III) center lies in a distorted octahedral environment. The crystal structure of (1) consists of two independent [CoIII(salophen)(ta)2]+ cations and ClO4 - anions held together essentially via hydrogen bonds and π-π stacking interactions. Complex (2), forming also a CHCl3 solvate, crystallized in the monoclinic space group P21/n with a = 14.710(3) Å, b = 13.506(3) Å, c = 18.595(4) Å, β = 100.295(4)°, and Z = 4. The geometry around cobalt(III) center is a distorted octahedron. The crystal structure of (2) contains a [CoIII(salophen)(tb)2]+ complex with a remarkably twisted salophen ligand. Both complexes, (1) and (2), contain approximately one disordered CHCl3 molecule per Co in the solid state. 相似文献
993.
Alternative supply chain production-sales policies for new product diffusion: An agent-based modeling and simulation approach 总被引:3,自引:0,他引:3
Applying agent-based modeling and simulation (ABMS) methodology, this paper analyzes the impact of alternative production-sales policies on the diffusion of a new generic product and the generated NPV of profit. The key features of the ABMS model, that captures the marketplace as a complex adaptive system, are: (i) supply chain capacity is constrained; (ii) consumers’ new product adoption decisions are influenced by marketing activities as well as positive and negative word-of-mouth (WOM) between consumers; (iii) interactions among consumers taking place in the context of their social network are captured at the individual level; and (iv) the new product adoption process is adaptive. Conducting over 1 million simulation experiments, we determined the “best” production-sales policies under various parameter combinations based on the NPV of profit generated over the diffusion process. The key findings are as follows: (1) on average, the build-up policy with delayed marketing is the preferred policy in the case of only positive WOM as well as the case of positive and negative WOM. This policy provides the highest expected NPV of profit on average and it also performs very smoothly with respect to changes in build-up periods. (2) It is critical to consider the significant impact of negative word-of-mouth in choosing production-sales policies. Neglecting the effect of negative word-of-mouth can lead to poor policy recommendations, incorrect conclusions concerning the impact of operational parameters on the policy choice, and suboptimal choice of build-up periods. 相似文献
994.
995.
Mehrdad Lakestani Mehdi Dehghan Safar Irandoust-pakchin 《Communications in Nonlinear Science & Numerical Simulation》2012,17(3):1149-1162
Fractional calculus has been used to model physical and engineering processes that are found to be best described by fractional differential equations. For that reason we need a reliable and efficient technique for the solution of fractional differential equations. Here we construct the operational matrix of fractional derivative of order α in the Caputo sense using the linear B-spline functions. The main characteristic behind the approach using this technique is that it reduces such problems to those of solving a system of algebraic equations thus we can solve directly the problem. The method is applied to solve two types of fractional differential equations, linear and nonlinear. Illustrative examples are included to demonstrate the validity and applicability of the new technique presented in the current paper. 相似文献
996.
The chemical composition of the essential oil of Haussknechtia elymaitica Boiss. was investigated by capillary GC and GC/MS for the first time. Twelve components were identified which accounting for 99.7% of the oil composition. The major compounds were trans-asarone (59.9%), trans-methyl isoeugenol (22.4%), α-zingiberene (7.96%), β-sesquiphellandrene (4.7%) and β-bisabolene (4.3%). The first three compounds considered as the main components of the essential oil were isolated and characterised by spectroscopic techniques. 相似文献
997.
Hammoud L Seghiri R Benayache S Mosset P Lobstein A Chaabi M León F Brouard I Bermejo J Benayache F 《Natural product research》2012,26(3):203-208
A new flavone glucoside, apigenin 4'-(6″-methylglucuronide) (1), together with six known compounds, cirsilineol, jaceosidin, melitensin, apigenin, apigenin 7-(6″-methylglucuronide) and prunasin, were isolated from the ethanolic extract of the aerial parts of Centaurea nicaeensis All. var. walliana M. (Asteraceae) collected from Souk-Ahras, eastern Algeria. The structures were established by spectral analysis, mainly HRESI-MS, UV and 2D-NMR experiments (COSY, HSQC and HMBC). 相似文献
998.
Sayed Mehdi Ghoreishi Mohsen Behpour Mona Delshad Asma Khoobi 《Central European Journal of Chemistry》2012,10(6):1824-1829
Tyrosine (Tyr) was quantitated with high sensitivity and selectivity in the presence of uric acid (UA) using a carbon paste electrode modified with multi-walled carbon nanotubes. Tyr and UA were catalytically oxidized with diffusion-controlled characteristics. They were determined simultaneously by differential pulse voltammetry with a potential difference of 350 mV. The electrocatalytic currents increase linearly with Tyr and UA concentrations 4×10?7?1×10?4 M and 3×10?7?2×10?4 M. Their detection limits were 1×10?7 and 5.1×10?8 M respectively. In the presence of sodium dodecyl sulfate the Tyr detection limit improved from 1×10?7 to 6.9×10?8 M. The electrode was successfully used to quantitate Tyr and UA in serum. 相似文献
999.
Soraia Meghdadi Vratislav Langer Hossein Farrokhpour Alshimaá A. Massoud Mehdi Amirnasr 《Journal of the Iranian Chemical Society》2012,9(1):85-92
The title complex [Pd(Me2bqb)] (1), [Me2bqb2?C?=?1,2-bis(quinoline-2-carboxamide)-4,5-dimethyl-benzene dianion], has been synthesized and characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structure of [Pd(Me2bqb)] has been determined by X-ray crystallography. The complex exhibits distorted square-planar PdN4 coordination geometry with two short and two long Pd?CN bonds (Pd?CN ~1.957 and ~2.095 ?, respectively). In addition to the molecular geometry from X-ray experiment, theoretical studies have been carried out on the structure of the complex at the density functional theory (DFT-B3LYP) level in conjunction with effective core potential basis set (LANL2DZ) for Pd atom and 6-311++G(d,p) basis set for N, O, C and H atoms. Electrochemical studies in CH2Cl2 solution revealed A reversible redox process corresponding to the PdII/PdIII couple with E 1/2 at 0.924?V (vs. SCE). 相似文献
1000.
Ali NA Sharopov FS Alhaj M Hill GM Porzel A Arnold N Setzer WN Schmidt J Wessjohann L 《Natural product communications》2012,7(2):257-260
The chemical composition of the essential oil obtained from the leaves of Pulicaria undulata Gamal Ed Din (syn P. orientalis sensu Schwartz and P. jaubertii Gamal Ed Din) was analyzed by GC-MS. Major compounds of P. undulata oil were the oxygenated monoterpenenes, carvotanacetone (91.4%) and 2,5-dimethoxy-p-cymene (2.6.%). The antimicrobial activity of the essential oil was evaluated against six microorganisms, Escherichia coli Pseudomonas aeruginosa, Staphylococcus aureus, methicillin-resistant S. aureus, Bacillus subtilis, and Candida albicans, using disc diffusion and broth microdilution methods. The oil showed the strongest bactericidal activity against Staphylococcus aureus and methicillin-resistant S. aureus, as well as Candida albicans. The essential oil showed moderate cytotoxic activity against MCF-7 breast tumor cells, with an IC50 of 64.6 +/- 13.7 microg/mL. Bioautographic assays were used to evaluate the acetylcholinesterase inhibitory effect as well as antifungal activity of the oil against Cladosporium cucumerinum. 相似文献