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81.
Internal calibration in modified hydrodynamic chromatography has been realized by the approach of Prieve and Hoysan, i.e. the use of polystyrene monodisperse latexes to evaluate the equivalent capillary radius, R. The value obtained has been used to estimate the average sizes of a variety of liposome samples from egg yolk lecithin.  相似文献   
82.
Ultrasonic technology has been intensively studied recently due to its special features. In this paper, an ultrasonic crystallization method was introduced for the preparation of ZnAl-Hydrotalcite-Like compounds (ZnAl-HTLcs). Samples with high crystallinity, small particle size and narrow particle size distribution were obtained and fully characterized using conventional techniques of XRD, FT-IR and TGDTA. The results prove that both ultrasonic frequency and ultrasonic power have effects on the sizes of the product particles. By varying the ultrasonic power from 250 W to 88 W, with the ultrasonic frequency fixed at 59 kHz, the median particle size of the samples increased from 0.37 μm to 0.82 μm. By altering the hydrothermal treatment time from 1 h to 5 h at 110℃, the median particle size of ZnAl-HTLcs synthesized via ultrasonic crystallization increased from 0.88 μm to 1.11 μm.  相似文献   
83.
The dialysis potentials of different collodion membranes with graded pore sizes and electrochemical activities have been measured in dilute aqueous KCl solutions as functions of concentration. It is possible to predict the value of the diffusion potential within a few millivolts on the basis of electrical conductivity data obtained with the same membranes. In general, the measured values are lower than those calculated. It is assumed that this difference is caused by the membranes having a distribution of pore sizes.  相似文献   
84.
 Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering (QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle morphology information were inferred for discussion of the polymerization mechanism of this system. Received: 21 August 1997 Accepted: 22 October 1997  相似文献   
85.
对用溶胶凝胶法制备的CdS/SiO2复合材料进行低频Raman散射研究,结果表明可从其低频Raman散射峰位计算出CdS微晶的粒径,两种不同的低频振动模式由激发光的两种偏振方向加以区分,低频Raman散射射的二级散射峰根据实验结果加以指认,所得平均粒径结果与透射电镜观察结果有较好的对应关系,复合材料吸收光谱吸收边蓝移与CdS纳米子粒径之间存在着密切的关系,实验证明,样品吸收边能量与CdS平均粒径的  相似文献   
86.
Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.Presented in part at the Cellulose '91 meeting in New Orleans.  相似文献   
87.
A need for an elaboration of the methods for synthesis and characterization of activated carbons with a requisite porous structure has existed for a long time. One of the methods giving possibility for creating controlled mesopore and micropore structures deals with the steam gasification of various carbon materials. In this work the effects of calcium catalyst on the catalytic steam gasification of active carbons from plum stones and porous polymers are presented. Determination of micropores capacity and specific adsorption in mesopores have been performed by means of the s method, but adsorption on the heterogeneous solids was described by the integral equation with various local isotherms. This equation has been solved by the regularization method. Based on this method the changes in structural parameters of active carbons depending on the amount of calcium catalyst were estimated.Nomenclature d width of slit-like micropore - F(x) distribution function of the half-width - p vapor pressure of sorbate - p/p N relative pressure - PSAC Plum Stone Active Carbon - average pore radius, nm - S 1 relative limit of the validity of experimental point on the adsorption isotherm in the computations by means of regularization method - SAC Synthetic Active Carbon - S BET specific surface area calculated by means of BET method, m2/g - S mes mesopore surface area, m2/g - S mic micropore surface area, m2/g - T absolute temperature, K - V mes sorption capacity of mesopores, cm3/g - V mic sorption capacity of micropores, cm3/g - V p sorption capacity of pores, cm3/g - w/w weight in weight concentration - x half-width of slit-like micropore, nm - x 1 maximum of half-width of micropore slit, nm - average half-width of slit-like micropore, nm - X min-X max integration limits of thex Greek Letters Greek Letters variance of average half-width of slit-like micropore, nm2 - local relative filling of micropores - total relative filling of micropores  相似文献   
88.
用定量体积排除色谱方法研究了过渡金属Fe(Ⅲ)、Co(Ⅲ)、Cu(Ⅱ)、Ni(Ⅱ)的乙酰丙酮螯合物在四氢呋喃溶液中的加合和缔合行为。在溶液中乙酰丙酮钴(Ⅲ)以单个螯合物分子的形式存在,乙酰丙酮铜(Ⅱ)和乙酰丙酮铁(Ⅲ)与溶剂加合生成加合物,乙酰丙酮铁(Ⅲ)除加合物外还存在缔合度为2-10的多分散缔合物,乙酰丙酮镍(Ⅱ)水合物在四氢呋喃中产生了加合交换作用,同时存在缔合度为6左右的缔合物。色谱数据给出了螯合物、加合物及缔合物  相似文献   
89.
对非绝热波聚合体系进行了数学模拟, 将反应器尺寸与聚合波关联, 建立了非绝热条件下蔓延聚合波波速和最大波温的数学模型; 利用所建模型计算不同引发剂浓度、 不同环境温度、 不同试管直径下淀粉接枝聚合波的波速和波温, 并与实验测定值进行了比较. 结果表明, 非绝热聚合波的数学模型对无相变体系的拟合结果令人满意, 对聚合波的发生条件及反应器尺寸的影响有很好的预见性; 另一方面, 对于存在相变及与环境有质量交换的波聚合体系, 所建模型的预测性受到了限制.  相似文献   
90.
Monodisperse, thermosensitive poly(N‐ethyl methacrylamide) microgel particles were prepared by the batch precipitation/emulsion polymerization of water‐soluble N‐ethyl methacrylamide and the hydrophobic crosslinker ethylene glycol dimethacrylate initiated by potassium persulfate. Particular attention was paid to the effect of the crosslinker agent on the polymerization process (kinetics, conversion, and water‐soluble oligomer content). Particles were characterized in terms of their size distribution and swelling capacity. A polymerization mechanism for the water‐soluble monomer and non‐water‐soluble crosslinker is proposed and discussed on the basis of a combination of both emulsion and precipitation polymerization processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1808–1817, 2002  相似文献   
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