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641.
Yuhua CaoChanggang Lou Xin ZhangQingcui Chu Yuzhi FangJiannong Ye 《Analytica chimica acta》2002,452(1):123-128
The use of micellar electrokinetic capillary chromatography (MECC) with electrochemical detection is described for the determination of puerarin and daidzein in Puerariae radix and its medicinal preparations. Operated in a wall-jet configuration, a 300 μm diameter carbon-disk electrode was used as the working electrode, which exhibits good responses at +900 mV (versus SCE) for the two analytes. Under the optimum conditions, the analytes were base-line separated within 11 min in a sodium dodecyl sulphate—borax (pH 7.8) running buffer, and excellent linearity was obtained in the concentration range from 5.0×10−4 to 5.0×10−6 mol/l. The detection limit (S/N=3) was 6×10−7 and 1.1×10−6 mol/l for puerarin and daidzein, respectively. This work provides a useful method for the analysis of traditional Chinese medicines. 相似文献
642.
线性低密度聚乙烯/乙烯醋酸乙烯共聚物共混体系的相容性及性能杨毓华*白春霞花荣于李三喜(中国科学院长春应用化学研究所长春130022)(沈阳化工学院高分子科学与工程系沈阳)关键词线性低密度聚乙烯,乙烯醋酸乙烯共聚物,共混,相容性,DSC,WAXD,力... 相似文献
643.
The decomposition of methoxy on Cu(111), Ag(111), Au(111), Ni(111), Pt(111), Pd(111), and Rh(111) has been studied in detail by the density functional theory calculations. The calculated activation barriers were successfully correlated with the coupling matrix element V 2 ad and the d-band center (ε d ) for the group IB metals and group VIII metals, respectively. By comparison of the activation energy barriers of the methoxy decomposition on different metals, it was found that Pt is the best catalyst for methoxy decomposition. The possible reason why the metallic Pt is the best catalyst has been analyzed from both the energetic data and the electronic structure information, that is, methoxy decomposition on Pt(111) has the largest exothermic behavior due to the closest p-band center of the CH 3 O among all metals after the adsorption. 相似文献
644.
Guoqing Chang Caiyun Lou Yuhua Li Yizhi Gao Bingkun Zhou 《International Journal of Infrared and Millimeter Waves》1999,20(12):2063-2074
The time-domain ABCD matrix formalism is based on the propagation of a Gaussian pulse which is characterized by the pulsewidth and chirp. In this paper, we will perfect this method and derive time-domain ABCD matrices for more optical devices. Especially, we extend this perfected theory to analyze the principle of passive mode-locking by reasonable approximation though, as we know, the output pulse generated from passive mode-locking fiber laser is of sech-shape. It is attractive because it can present a fairly apparent view to understand the mechanism of fiber lasers as well as analytic results to understand the pulse characteristics. 相似文献
645.
646.
Yuhua Shen Chuanhao Li Xuemei Zhu Anjian Xie Lingguang Qiu Jinmiao Zhu 《Journal of Chemical Sciences》2007,119(4):319-324
This paper reports a simple method to prepare barium sulphate nanoparticles by use of tetradecanoic acid, hexadecanoic acid
and stearic acid as modifier. The barium sulphate nanoparticles obtained are characterized by using Fourier transform infra-red
spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic laser light scatter
(DLLS) and thermogravimetric analysis (TGA), respectively. The results show that the BaSO4 particles are all spherical and in the nano-scale. Our method has a better dispersion and controllable diameter dependent
on the length of the chain of organic acid and the pH value of the system. A possible mechanism is also discussed. 相似文献
647.
Yuhua Long 《Journal of Mathematical Analysis and Applications》2008,342(1):726-741
By making use of Clark duality, perturbation technique and dual least action principle, some results on the existence of subharmonic solutions with minimal period to second-order subquadratic discrete Hamiltonian systems are obtained. 相似文献
648.
649.
建立了一种高效液相色谱同时测定尿液中4种肾脏病常用药物依那普利、氨苯蝶啶、呋塞米及缬沙坦含量的方法。色谱分离选用WondaSil C18-WR (150 mm×4.6 mm, 5 μ m);以10.0 mmol/L乙酸铵溶液(pH 3.90)和乙腈为流动相进行梯度洗脱,流速为1.0 mL/min,于254 nm波长下检测,18 min内实现了4种药物的分离分析。结果表明依那普利、氨苯蝶啶、呋塞米、缬沙坦分别在0.15~300 mg/L、0.05~100 mg/L、0.75~750 mg/L、0.05~100 mg/L范围内线性良好,检出限依次为1.38×10-2、7.67×10-3、3.69×10-2、1.16×10-2mg/L,平均加标回收率在89.49%~99.20%之间,相对标准偏差(RSD, n=3)在4.12%~9.44%之间。结果表明该方法样品处理简便、快速,结果准确可靠,为肾脏病患者尿液中的治疗药物浓度监测提供了一种新方法。 相似文献
650.
A simple and rapid sample preparation method of dispersive liquid-liquid microextraction(DLLME) was applied in the simultaneous determination of six parabens in the aqueous cosmetics. The analysis was performed on gas chromatography coupled with a flame ionization detection(GC-FID). The mixed solution containing 30 μL of chloroform(extraction solvent) and 300 μL of tetrahydrofuran(dispersive solvent) was rapidly injected into the sample solution for the purpose of microextraction. After that, the solution mentioned above was centrifuged at 4000 r/min for 10 min, and then the organic sediment phase was detected by GC-FID. The effects of experimental parameters, such as the extraction solvent and the volume of it, and the dispersive solvent and the volume of it, on the yield of the extraction were studied in detail. Under the optimum conditions, the enrichment factors of the target analytes range from 87 to 214. Linearity ranges are 0.05-10.0μg/mL for methylparaben and 0.025--5.0 μg/mL for the other five parabens. The relative standard deviations(RSDs) are lower than 8.2%(n=6). The proposed method was applied to the analysis of six parabens in eleven aqueous cosmetics. The recoveries of the target analytes in the spiked real samples are in the range of 81.0%-103%. 相似文献