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31.
催化裂化USY/ZnO/Al2O3脱硫添加剂的高温水热失活 总被引:3,自引:0,他引:3
对USY/ZnO/Al2O3汽油催化裂化脱硫添加剂经高温水热老化处理前后的脱硫性能进行了考察,发现老化后添加剂的脱硫性能大幅度下降.采用XRD和IR等技术对USY/ZnO/Al2O3添加剂在高温和高温水热条件下失活的原因进行了研究.结果表明,在高温下,ZnO可与USY沸石中的铝发生固相反应生成ZnAl2O4尖晶石,从而造成USY晶体结构崩塌,转变成无定形状态.在ZnO含量较高的条件下,ZnO可继续与USY晶体结构崩塌后生成的无定形的硅和铝的氧化物反应,生成Zn2SiO4硅锌矿和ZnAl2O4尖晶石结构.这一方面使添加剂失去了可形成硫化物吸附中心的ZnO,另一方面破坏了硫化物的裂化活性组分USY,从而造成添加剂脱硫性能下降甚至失去脱硫活性.ZnO对USY的破坏作用主要与温度有关.在USY/ZnO/Al2O3体系中,ZnO被ZnO与Al2O3之间形成的锌铝尖晶石膜固定并与USY隔离,单纯的高温条件对添加剂的破坏不显著,而水蒸气可以促进ZnO的移动,有利于ZnO与USY的接触,因此在高温和有水蒸气存
在的条件下添加剂的结构易遭到破坏. 相似文献
32.
The performance of single-drop microextraction (SDME), coupled with gas chromatography/mass spectrometry, was assessed for the determination of tributyltin compounds in water and solid samples. Experimental parameters impacting the performance of SDME, such as microextraction solvent and sampling and stirring time, were investigated. Analytical results obtained by SDME were compared with those generated by conventional solid phase microextraction (SPME) and liquid-liquid extraction (LLE) for the determination of TBT in PACS-2 sediment certified reference material (CRM). 相似文献
33.
34.
The solubility of glycine,
-alanine,
-valine,
-leucine, and
-isoleucine in water was measured at 298.15 K and pressures up to 400 MPa. The standard deviation of the logarithm of the solubility is 0.001–0.003, equal to or better than the accuracy of atmospheric pressure measurement in the literature (0.001–0.05). A variety of solubility phenomena were observed. The solubility of glycine decreased with increasing pressure, whereas that of
-alanine increased. The
-valine and
-isoleucine have a solubility maximum at around 100 MPa, and
-leucine seems to exhibit a solid-phase phase transition at around 200 MPa. Pressure coefficient of the solubilities at 0.10 MPa is compared with that thermodynamically estimated in reference to aqueous density measurements of glycine and
-alanine at 298.15 K and 0.10 MPa, supporting a reliability of our high-pressure measurements. 相似文献
35.
A method combining the techniques of liquid – solid disk extraction (LSDE) and supercritical fluid elution (SFE) has been developed for the phenols regulated by the Clean Water Act. LSDE uses a disk or membrane made of polytetrafluoroethylene (PTFE) fibrils impregnated with small particles, e.g. styrene divinylbenzene (SDB) resin, to extract phenols from water. After disk extraction the retained analytes are eluted from the disk using SFE. SFE is used as an alternative to liquid solvent elution with an organic solvent. Analytes are separated, identified, and quantified using gas chromatography – ion trap detector mass spectrometry (GC-ITDMS). The method is capable of sub parts per billion detection limits, and precision of 5–28% RSD. Evaluation of various disks or membranes, such as C18-silica disks, SDB disks, and ion exchange membranes, has also been performed for the extraction of phenols from water. The results obtained from the in-situ aqueous acetylation of phenols and extraction of their acetates are quantitative. The utilization of LSDE and SFE techniques has proven to be a more effective approach than liquid – liquid extraction in minimizing air pollution and solvent waste. 相似文献
36.
Density of supercritical CO_2-tetrahydrofuran binary mixture and the partial molar volume of the cosolvent 总被引:1,自引:0,他引:1
The densities of supercritical CO2-tetrahydrofuran (cosolvent) binary mixture weremeasured at temperatures in range of 308.15 to 323.15 K and at pressure up to 16.5 MPa.The concentrations of tetrahydrofuran were from 0 to 0.57 mol/L.The partial molar volume of tetrahydrofuran was calculated based on the relationship between the density of the mixture and the concentration of the cosolvent.It is observed that the partial molar volume of the cosolvent is negative and the absolute value decreases with increasing pressure and the concentration of the cosolvent. 相似文献
37.
Addition of a small amount of polar solvent (i.e., modifier) to CO2 in packed column supercritical fluid chromatography (SFC) has shown major improvements in both polar analyte solubility and interaction of the polar analyte with the stationary phase. Recently, the addition of an ionic component (i.e., additive) to the primary modifier by one of us has been shown to extend even further the application of SFC to polar analytes. In this work, the effect of various ionic additives on the elution of ionic compounds, such as sodium 4-dodecylbenzene sulfonate and sodium 4-octylbenene sulfonate, has been studied. The additives were lithium acetate, ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, and ammonium chloride dissolved in methanol. Three stationary phases with different degrees of deactivation were considered: conventional cyanopropyl, deltabond cyanopropyl, and bare silica. The effect of additive concentration and additive functionality on analyte retention was investigated. Sodium 4-dodecylbenzene sulfonate was successfully eluted using all the additives with good peak shape under isocratic/isobaric/isothermal conditions. Different additives, however, yielded different retention times and in some cases different peak shapes. 相似文献
38.
Hans-Gerd Janssen Henri M. J. Snijders Jacques A. Rijks Carel A. Crarners Peter J. Schoenmakers 《Journal of separation science》1991,14(7):438-445
The effects of the pressure drop across the column on retention and efficiency in SFC have been studied. Numerical methods are described which enable the prediction of hold-up time and pressure drop in both packed and open tubular columns. Predictions of both hold-up time and pressure drop are in good agreement with experimental data. The density gradient along the column can be calculated using the numerical methods and a procedure is described which enables the calculation of the overall capacity factors of the solutes from the density profile in the column. Significant variations of the capacity factor are observed along the column. The effect of the density gradient along the column on local diffusivity and dispersion is studied. The column efficiency in systems with significant pressure drops is affected by changes in: the linear velocity of the mobile phase; the diffusion coefficients; and the capacity factors of the solutes along the column. The overall efficiency of the chromatographic system can be calculated if, as is the case for open tubular columns, adequate plate height equations are available. 相似文献
39.
由聚苯胺粒子组成的电流变液的研究 总被引:6,自引:1,他引:6
由经碱处理的掺杂态聚苯胺(PAn)制得高介电常数的半导体PAn粒子,将其悬浮于电绝缘油可组成电流变液,讨论了电流变(ER)液的静态屈服应力(τ_s),电流密度等性能与PAn的介电常数(ε_p),导电率(σ),体积分数和应用电场强度的关系。对导电率相同的PAn粒子,用氨水处理的PAn粒子ε_p较用NaOH液处理的高,前者在σ足够低如σ≤1.0×10 ̄(-7)/cm时,ER液的τ_s随偶极系数的平方(β ̄2)的增大而呈现非线性增加;后者ER液的τ_s随β ̄2的增大出现一最大值.结果表明:由聚苯胺粒子可组成高电流变活性的无水ER液. 相似文献
40.
de Toledo RA Santos MC Cavalheiro ET Mazo LH 《Analytical and bioanalytical chemistry》2005,381(6):1161-1166
This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite–polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L–1; pH 7.4). Analytical curves were constructed under optimized conditions (f=60s–1, Ea=50 mV, EI=2 mV) and detection and quantification limits of 6.4×10–8 mol L–1 (12.1 g L–1) and 5.2×10–6 mol L–1 (0.9 mg L–1), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9×10–6 mol L–1 dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine. 相似文献