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1.
维生素D(VD)是一类具有抗佝偻病作用的类固醇激素,其中维生素D3(VD3)是VD在动物体内的主要存在形式。作为生命活动必不可少的一类物质,VD发挥着广泛且重要的生理学作用。VD在动物体内的代谢过程及相关的代谢酶具有较高的进化保守性,同时也受到多种因素的调控影响。由于鱼类在生活环境方面与陆生脊椎动物存在显著差异,VD在鱼类中的合成代谢及生理功能与高等动物也存在一定的区别。本文主要概述了鱼类VD3的主要来源以及需求量的研究,总结了近年来鱼类维生素D受体(VDR)、VD3代谢调控及其生理功能的研究进展,比较了鱼类和陆生高等动物在VD来源、代谢以及VDR等方面的差异,并对水生动物VD的未来研究方向进行了展望。  相似文献   
2.
Aquatic plants are essential for maintaining the diversity and stability of a lake ecosystem. Stable carbon isotopes (δ13C) of macrophytes have been widely used as a powerful tool to study ecological processes and paleoenvironmental evolution in lakes. Varying results are obtained when using the δ13C of macrophytes to study the changes in the lake environment at different spatio-temporal scales. Thus, sample preparation and subsequent laboratory analyses are crucial for studying environmental changes using the isotopic signal retained in the macrophytes, and are essential for the interpretation of isotope-environment relationships. This study analyzed the δ13C of different tissue components of macrophytes in three lakes of the lower Yangtze River basin, and a correlation analysis was performed on aquatic environments influencing the δ13C values in the different tissue components of macrophytes. The test results showed the difference between the δ13C values of the whole sample and cellulose. Relative analyses indicated that the major factors contributing to the δ13C variability in macrophytes were pH and the concentration of dissolved inorganic carbon (DIC). The δ13C of α-cellulose (δ13CAC) is more sensitive to environmental variables than that of the whole sample (δ13CW) and holocellulose (δ13CHC). The results of this study imply that extraction of α-cellulose is a prerequisite for research on the changes in lake environment using δ13C of macrophytes. This study aims to provide theoretical and data basis for further research on the environmental and ecological change using stable carbon isotopes of aquatic plants.  相似文献   
3.
从高硅含铝原料霓辉正长岩中提取氧化铝时,硅以水合硅酸钠钙的形式排出。实验研究了水合硅酸钠钙渣的高效利用技术。利用水合硅酸钠钙自身的水解作用和在NaOH溶液中使之分解两种方法来回收其中的Na2O,所得NaOH溶液经蒸发浓缩后可循环利用。回收碱后剩余的固体渣用来制备硅灰石粉体。实验得出回收碱的优化条件为温度180℃,起始溶液的Na2O浓度为20 g/L,液固比为4∶1,洗涤6~7次。在此条件下,碱回收率可达90%以上。对回收碱后所得固体渣进行差热-热重分析,确定制备硅灰石粉体的煅烧温度。在820℃下煅烧2 h,制得颗粒尺寸为50~100 nm的α-CaS iO3纳米粉体,对其反应机理进行了初步的探讨。  相似文献   
4.
利用中国太阳分光观测网的观测资料结合MODIS(中分辨率成像光谱仪)的气溶胶产品分析了北京、兰州、上海3个典型区域城市的气溶胶光学特性。结果表明:北京AOD(气溶胶光学厚度)年平均为0.41±0.35,春夏高,秋冬低,Angstrm波长指数α年平均为1.40±0.85表现为细模态粒子,MODIS的光学厚度为0.52±0.39与地面观测相关系数为0.91,存在系统性高估;兰州AOD年平均为0.55±0.21,夏季最低,秋冬较高,α年平均为0.95±0.20表现为粗模态粒子,MODIS光学厚度为0.43±0.21与地面观测相关系数仅为0.07,存在系统性低估;上海AOD年平均为0.55±0.21,无明显季节变化,α平均为1.03±0.25,MODIS光学厚度为0.74±0.30与地面观测相关系数为0.75,存在系统性高估。城市地理位置和复杂地表等原因造成反照率的不确定,MODIS气溶胶产品在这3个城市的反演效果仍有很大提升空间。  相似文献   
5.
任军博  杨思宇  苏涛  臧利斌  全成 《世界地质》2017,36(3):1001-1007
本文对云南先锋中新世木乃伊化木化石进行α-纤维素实验提取,以验证化石纤维素的可得性。实验利用有机溶剂分离、碱液分离、无机酸分离等方法分别对研究区5件木乃伊化化石样品进行处理,并采用红外光谱检测方法与现代木材α-纤维素和国际标准α-纤维素进行对比试验。实验结果显示,3种提取方法均可以从化石木材中提取出α-纤维素,但过程特征各有不同。其中,有机溶剂分离实验过程耗时最长,碱液分离方法样品损失最大。相比之下,无机酸分离方法对于木乃伊化木化石α-纤维素提取的效率最高。  相似文献   
6.
以液体石蜡为油相,以壳聚糖/α,β-甘油磷酸凝胶溶液为水相,用乳化法制备了壳聚糖/α,β-甘油磷酸凝胶微球,并对微球形态、粒径分布、溶胀性、蛋白吸附率、溶血率、体外降解率进行了分析。光学显微镜下显示,微球形态圆整,粒径主要分布在100~400μm;扫描电镜显示,微球内部为三维网络状结构,骨架清晰;pH=7.4的PBS缓冲液中干凝胶微球的溶胀率为218.08%,普通壳聚糖微球为70.98%;1和24h测得凝胶微球的蛋白吸附量分别为13.21和15.68μg/g,普通壳聚糖微球分别为3.71×103和4.83×103μg/g;微球的溶血率小于5%,血液相容性良好;体外降解实验显示,壳聚糖的脱乙酰度、黏度以及溶菌酶浓度对壳聚糖/α,β-甘油磷酸凝胶微球的降解性质产生影响。  相似文献   
7.
Abstract

In a previous paper, Bassom et al. (Proc. R. Soc. Lond. A, 455, 1443–1481, 1999) (BKS) investigated finite amplitude αΩ-dynamo wave trains in a thin turbulent, differentially rotating convective stellar shell; nonlinearity arose from α-quenching. There asymptotic solutions were developed based upon the small aspect ratio ε of the shell. Specifically, as a consequence of a prescribed latitudinally dependent α-effect and zonal shear flow, the wave trains have smooth amplitude modulation but are terminated abruptly across a front at some high latitude θF. Generally, the linear WKB-solution ahead of the front is characterised by the vanishing of the complex group velocity at a nearby point θf; this is essentially the Dee–Langer criterion, which determines both the wave frequency and front location.

Recently, Griffiths et al. (Geophys. Astrophys. Fluid Dynam. 94, 85–133, 2001) (GBSK) obtained solutions to the α2Ω-extension of the model by application of the Dee—Langer criterion. Its justification depends on the linear solution in a narrow layer ahead of the front on the short O(θf—θF) length scale; here conventional WKB-theory, used to describe the solution elsewhere, is inadequate because of mode coalescence. This becomes a highly sensitive issue, when considering the transition from the linear solution, which occurs when the dynamo number D takes its critical value D c corresponding to the onset of kinematic dynamo action, to the fully nonlinear solutions, for which the Dee—Langer criterion pertains.

In this paper we investigate the nature of the narrow layer for α2Ω-dynamos in the limit of relatively small but finite α-effect Reynolds numbers R α, explicitly ε½ ? R 2 α ? 1. Though there is a multiplicity of solutions, our results show that the space occupied by the corresponding wave train is generally maximised by a solution with θf—θF small; such solutions are preferred as evinced by numerical simulations. This feature justifies the application by GBSK of the Dee—Langer criterion for all D down to the minimum D min that the condition admits. Significantly, the frontal solutions are subcritical in the sense that |D min| ≤ |D c|; equality occurs as the α-effect Reynolds number tends to zero. We demonstrate that the critical linear solution is not connected by any parameter track to the preferred nonlinear solution associated with D min. By implication, a complicated bifurcation sequence is required to make the connection between the linear and nonlinear states. This feature is in stark contrast to the corresponding results for αΩ-dynamos obtained by BKS valid in the limit R 2 α ? ε½, which, though exhibiting a weak subcriticality, showed that the connection follows a clearly identifiable nonbifurcating track.  相似文献   
8.
9.
Abstract

Finite-difference numerical solutions were obtained to present the flow and temperature field details within the transient Ekman layer during spin-up of a thermally stratified fluid in a cylinder. This complements the earlier studies on stratified spin-up which examined the flows in the interior core region. As the stratification increases, the following changes in the flow field are noticeable. The radial velocity in the Ekman layer decreases in magnitude. The azimuthal flows adjust smoothly from the interior region to the endwall boundary, and the Ekman layer in the azimuthal flow field fades. Vertical motions are inhibited, resulting in a weakened Ekman pumping. The axial vorticity field behaves similarly to the azimuthal flows. The temperature deviation from the equilibrium profile decreases, and the heat transfer flux from the endwall to the fluid decreases. The thickness of the thermal layer is larger than the velocity layer thickness. Illustrative comparisons of the relative sizes of the terms in the governing equations are conducted in order to assess the stratification effect in the adjustment process of the fluid.  相似文献   
10.
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