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991.
992.
人参挥发油的提取和分析 总被引:7,自引:0,他引:7
应用GC-MS-DS联机分析人参挥发油是当前较好的方法,但人参挥发油的提取方法和GC-MS条件的选择明显影响人参挥发油这一复杂天然混合物的分离和鉴定。本工作严格控制提取条件,提高了挥发油收率,达0.95%;选择最佳GC-MS条件,鉴定出76种化合物,该法稳定重现性好。 相似文献
993.
Zhixian Zhou Yuzhong Wang Jingchao Tao Yaoting Fan Yangjie Wu 《Journal of inclusion phenomena and macrocyclic chemistry》1998,32(1):69-80
A novel anion-selective electrode has been prepared by usingtetraazaporphyrinogen as the electroactive component and o-nitrophenyloctylether as the plasticizer. The electrode exhibits almost Nernstian responsecharacteristics for Pic-, ReO
4
-
,SCN-, ClO
4
-
and TPB-. The linearresponse ranges towards the above-mentioned anions are 10-6 10-2, 10-5 10-2,10-5 10-2, 10-5 10-1, and 10-5 10-2mol/Land the corresponding slopes are -56.8, -57.1, -56.3, -56.1, and -59.9mV/decade with correlation coefficients of -0.99978, -0.99987, -0.99999,-0.99998, and -0.99998, respectively. The electrode shows an anti-Hofmeisterselectivity sequence: Pic- > SCN- >ReO
4
-
> ClO
4
-
> I- >Br- > BF
4
-
> Sal->NO
3
-
> Cl-. The unusual responsemechanism of the novel anion-selective electrode was investigated byexperimental observations and calculation with the MNDO method. Theelectrode was used as a TPB- and a Pic-sensitiveelectrode, respectively, and applied to the assay of levamisolehydrochloride tablets by potentiometric titration and Gran's methods. Theresults obtained are in excellent agreement with that determined by thestandard pharmacopoeia method based on nonaqueous titration. 相似文献
994.
With the rapid development of human society, clean energy forms are imperative to sustain the normal operations of various mechanical and electrical facilities under a cozy environment. Hydrogen is considered among the most promising clean energy sources for the future. Recently, electrochemical water splitting has been considered as one of the most efficient approaches to harvest hydrogen energy, which generates only non-pollutant water on combustion. However, the sluggish anodic oxygen evolution reaction significantly restricts the efficiency of water splitting and requires a relatively high cell voltage to drive the electrolysis. Therefore, seeking a thermodynamically favorable anodic reaction to replace the sluggish oxygen evolution reaction by utilizing highly active bifunctional electrocatalysts for the anodic reaction and hydrogen evolution are crucial for achieving energy-efficient hydrogen production for industrial applications. Nevertheless, it is known that the oxygen evolution reaction can be replaced with other useful and thermodynamically favorable reactions to reduce the electrolysis voltage for realizing energy-efficient hydrogen production. Therefore, in this study, we present a bifunctional nickel nanoparticle-embedded carbon (Ni@C) prism-like microrod electrocatalyst synthesized via a two-step method involving the synthesis of a precursor metal-organic framework-74 and subsequent carbonization treatment for methanol oxidation and hydrogen evolution. The interfacial structure consisting of a nickel and carbon skeleton was realized via in situ carbonization. However, the dispersed nickel nanoparticles do not easily aggregate owing to the partition by the surrounding carbon as it would sufficiently expose the active Ni sites to the electrolytes, ensuring fast charge transfer between the catalyst and electrolytes by accelerating the electrochemical kinetics. In the anodic methanol oxidation, the products were detected as carbon dioxide and formate with faradaic efficiencies of 36.2% and 62.5%, respectively, at an applied potential of 1.55 V. Meanwhile, the Ni@C microrod catalyst demonstrated high activity and durability (2.7% current decay after 12 h of continuous operation) toward methanol oxidation, which demonstrates that methanol oxidation precedes oxidation under voltage forces. Notably, the bifunctional catalyst not only exhibits excellent performance toward methanol oxidation but also yields a low overpotential of 155 mV to drive 10 mA∙cm−2 toward hydrogen evolution in 1.0 mol∙L−1 KOH aqueous solution with 0.5 mol∙L−1 methanol at room temperature, which guarantees the hydrogen production efficiency. More importantly, the constructed two-electrode electrolyzer produced a current density of 10 mA∙cm−2 at a low cell voltage of 1.6 V, which decreased by 240 mV after replacing the oxygen evolution reaction with methanol oxidation. 相似文献
995.
Jayeon Hong Sangsub Kim Gyurim Park Yongmoon Lee Hyungchae Kim Sungjin Kim Tae-Woo Lee Changsoon Kim Youngmin You 《Chemical science》2021,12(25):8668
Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (gabs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (gPL) of the order of 10−3 were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of gabs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (gEL) of 1.09 × 10−4 and −1.02 × 10−4 at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. 相似文献
996.
α,β-Unsaturated ketones are important synthetic intermediates because of their versatile reactivities and many syn-thetic applications of them have been reported in the literature.[1] However, only a few methods for the synthesis of (Z)-α,β-unsaturated ketones are available. The palladium catalyzed coupling reactions of alkenyl copper reagents with acid chlorides afforded (Z)-α,β-unsaturated ketones.[2] The phase transfer catalyzed hydroacylation of allenes with carbon monoxide, decacarbonyldimanganese and methyl iodide gave (Z)-α,β-unsaturated ketones in a stereospecific process. 相似文献
997.
Syntheses of quaternary 1-alkyl-3-perfluoroalkyl-4,5-dimethyl-1,2,4-triazolium iodides have led to a variety of new quaternary salts via metathesis reactions. 1,4,5-Trimethyl-3-trifluoro-methyl-1,2,4-triazolium iodide (6) with LiN(SO(2)CF(3))(2), KSO(3)CF(3), AgClO(4), AgBF(4); 1-(3-fluoropropyl)-3-trifluoromethyl-4,5-dimethyl-1,2,4-triazolium iodide (7) with LiN(SO(2)CF(3))(2); and 1,4,5-trimethyl-3-perfluorooctyl-1,2,4-triazolium iodide (8) with LiN(SO(2)CF(3))(2), AgClO(4), AgBF(4) gave excellent yields of new thermally stable and relatively low melting quaternary salts. The structure of 1,4,5-trimethyl-3-perfluorooctyl-1,2,4-triazolium tetrafluoroborate (11c) was confirmed by single-crystal X-ray analysis. Although the molecular weight of 11c (cation) is 3-fold greater than that of the 3-trifluoromethyl derivative 9d, its melting point is 32 degrees C lower. 相似文献
998.
Yao‐Cheng Shi Su‐Hua Zhang Hong‐Jian Cheng Wei‐Ping Sun 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):m407-m410
The title compounds, both [Fe(C5H5)(C15H14NO2)], crystallize with Z′ = 2 in the centrosymmetric space group P. In each compound, there is an intramolecular N—H⋯O=C hydrogen bond, and pairs of intermolecular O—H⋯O=C hydrogen bonds link the molecules into chains, parallel to [10] in the 3‐hydroxy compound and parallel to [10] in the 4‐hydroxy compound. 相似文献
999.
The adsorption of Am(III) (total concentration 10(-9) mol/l) on alumina, silica, and hematite was studied by a batch technique. The effects of pH, ionic strength, and humic substances on the adsorption of Am(III) on alumina and silica were investigated, and the adsorption isotherms of Am(III) on alumina and silica at different pH values were determined. It was found that compared with the adsorption of Am(III) on alumina, the adsorbability of silica on the basis of mass is less, the relative adsorption rate on silica is slower, the sensitivity of adsorption on silica to ionic strength is less, the dependence of adsorption on silica on pH is gentler, and consequently that the adsorption characteristics of Am(III) on alumina and silica are distinctly different. The negative effect of fulvic acid on the adsorption on silica and the positive effect of humic acid on the adsorption on alumina were found. In contrast to the Am(III) adsorption on alumina and silica, a tremendously high adsorbability of Am(III) on hematite was found. The sequence of adsorbabilities of Am(III) on the basis of mass is Fe2O3 > Al2O3 > SiO2. 相似文献
1000.
A2Ca[B4O5(OH)4]2·8H2O(A=Rb,Cs)硼氧酸盐复盐的合成与表征 总被引:5,自引:0,他引:5
硼氧酸盐晶体结构复杂,因此出现了许多具有特殊物理性能的晶体功能材料犤1,2犦,尤其是重稀碱金属硼氧酸盐(或复盐),如CsLiB6O10犤3犦、LiRbB4O7犤4犦和CsB3O5(CBO)犤5犦都是非线性光学材料。一些学者对铷、铯的偏硼氧酸盐、四硼氧酸盐和五硼氧酸盐的合成、性质及晶体结构等进行过研究犤6~9犦。硼氧酸盐复盐,大多为碱金属和碱土金属、碱金属和碱金属及碱土金属和碱土金属的硼氧酸盐犤10犦,如自然界存在的钠硼解石狖NaCa犤B5O6(OH)6犦·5H2O狚、硼钠镁石狖Na2Mg犤B6O8(OH)4犦2·6H2O… 相似文献