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991.
992.
Milton Rogério Pereira Pedro Augusto Arroyo Maria Angélica Simões Dornellas de Barros Viviane Monteiro Sanches Edson Antonio da Silva Isabel Maria Fonseca Rafael García Lovera 《Adsorption》2006,12(2):155-162
In this work, Cr(III) adsorption on activated carbon obtained from olive stones in an upflow fixed-bed column at 30∘C was studied. The flow rate influence on the breakthrough curves at a feed concentration of 0.87 meq/L was investigated in
an attempt to minimize the diffusional resistances. Breakthrough curves for a flow range of 2–8 mL/min were obtained at 10.5
cm bed height and inlet diameter of 0.9 cm. The mass transfer parameters indicated that the bed minimal resistance was attained
at 2 mL/min. Therefore, the data equilibrium was carried out until the bed was saturated at 2 mL/min. The dynamic system generated
a favorable isotherm with a maximum chromium uptake of 0.45 meq/g. A column sorption mathematical model was created considering
the axial dispersion in the column and the intraparticle diffusion rate-controlling steps. The isotherm was successfully modeled
by the Langmuir equation and the mathematical model described the experimental dynamic data adequately for feed concentrations
from 0.26 to 3.29 meq/L. 相似文献
993.
α,α-二乙酰基二苄硫缩烯酮的碱催化脱乙酰基反应及缩合反应机理研究 总被引:2,自引:0,他引:2
α-羰基二硫缩烯酮是一类极其重要的有机合成中间体,烷硫基对该类具有推-拉电子效应的共轭体系的性质影响很大。据此,我们率先提出了烷硫基对α-羰基二硫缩烯酮类化合物的化学行为具有调控作用的观点,并将其归因于空间电子因素的作用,α-乙酰基-α′-羰基二苄硫缩烯酮(1)具有多反应性特征。近来,我们利用该特征在氢氧化钠催化下通过化合物1的环合合成了多取代噻吩类化合物;在乙醇钠-醋酸铅作用下经乙氧基对化合物1的苄硫基的取代实现了α-羰基-O,O-缩烯酮的合成。 相似文献
994.
Novozyme-435催化10-羟基癸酸进行自缩聚反应得到线性聚酯, 端基分别是羟基(—OH)和羧基(—COOH), 在三乙胺催化下, 分别用α-溴代丙酰溴和三甲基氯硅烷(TMSCL)进行端基官能化生成一个单官能度的大分子引发剂, 在CuCl/2,2'-联吡啶(bpy)催化体系中, 引发甲基丙烯酸环氧丙酯(GMA)的原子转移自由基反应(ATRP), 得到聚(10-羟基癸酸酯)/聚甲基丙烯酸环氧丙酯(PHDA-b-PGMA) AB 型两亲性嵌段共聚物, 其结构及分子量(分布)通过核磁共振和凝胶渗透色谱(GPC)确证. 此AB型两亲性嵌段共聚物在水溶液中能自组装形成纳米粒子, 用原子力显微镜(AFM)观察粒子的形状和大小. 相似文献
995.
R.M. Almeida M.I. de Barros Marques Xavier Orignac 《Journal of Sol-Gel Science and Technology》1997,8(1-3):293-297
A series of SiO2-TiO2 sol-gel films with and without heat treatment were analyzed by EXAFS and XANES spectroscopies. Both techniques indicate that essentially all Ti4+ ions remain four-fold coordinated, with a Ti–O bond distance between 1.82–1.85 Å. In the glassy films produced by heat treatment at 900° C, a gradual phase separation may occur at the nanoscale, as the TiO2 concentration of the films increases. 相似文献
996.
HongYingDUAN FangCHEN XinPingAI ZhiKeHE 《中国化学快报》2005,16(7):947-950
The addition of propranolol induced the aggregation of gold nanoparticles, and increased Rayleigh light scattering (RLS) intensity greatly. The interaction between them was studied by RLS spectrum, UV-Vis spectrum and transmission electron microscopy (TEM). Based on these results, a novel method was proposed for propranolol assay. With the combination of solid phase microextraction (SPME), the proposed method was successfully applied to determine propranolol in urine. 相似文献
997.
In this paper we explore the relations between the standard dual problem of a convex generalized fractional programming problem and the partial dual problem proposed by Barros et al. (1994). Taking into account the similarities between these dual problems and using basic duality results we propose a new algorithm to directly solve the standard dual of a convex generalized fractional programming problem, and hence the original primal problem, if strong duality holds. This new algorithm works in a similar way as the algorithm proposed in Barros et al. (1994) to solve the partial dual problem. Although the convergence rates of both algorithms are similar, the new algorithm requires slightly more restrictive assumptions to ensure a superlinear convergence rate. An important characteristic of the new algorithm is that it extends to the nonlinear case the Dinkelbach-type algorithm of Crouzeix et al. (1985) applied to the standard dual problem of a generalized linear fractional program. Moreover, the general duality results derived for the nonlinear case, yield an alternative way to derive the standard dual of a generalized linear fractional program. The numerical results, in case of quadratic-linear ratios and linear constraints, show that solving the standard dual via the new algorithm is in most cases more efficient than applying directly the Dinkelbach-type algorithm to the original generalized fractional programming problem. However, the numerical results also indicate that solving the alternative dual (Barros et al., 1994) is in general more efficient than solving the standard dual.This research was carried out at the Econometric Institute, Erasmus University Rotterdam, the Netherlands and was supported by the Tinbergen Institute Rotterdam 相似文献
998.
J. Acacio de Barros N. Pinto-Neto M. A. Sagioro-Leal 《General Relativity and Gravitation》2000,32(1):15-39
We apply the causal interpretation of quantum mechanics to homogeneous and isotropic quantum cosmology, where the source of the gravitational field is a conformally coupled scalar field, and the maximally symmetric hypersurfaces have positive curvature. In order to simplify the system of coupled equations studied and study the quantum behavior near the singularity, we restricted ourselves to the cases where the scale factor is small. In this case, the general solution of the Wheeler–DeWitt equation is a discrete superposition of Hermitian polynomials multiplied by complex exponentials. Superpositions with up to two parcels are studied, and the phase diagrams of their corresponding Bohmian trajectories are analyzed in detail. Nonsingular periodic quantum solutions are found. We also find that singular quantum solutions present an inflationary era in the begining of the Universe. Numerical calculations indicates that these results remain valid for general superpositions. 相似文献
999.
1000.