全文获取类型
收费全文 | 953篇 |
免费 | 121篇 |
国内免费 | 137篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 96篇 |
地球物理 | 386篇 |
地质学 | 305篇 |
海洋学 | 163篇 |
天文学 | 112篇 |
综合类 | 22篇 |
自然地理 | 62篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 31篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 22篇 |
2015年 | 25篇 |
2014年 | 31篇 |
2013年 | 42篇 |
2012年 | 32篇 |
2011年 | 33篇 |
2010年 | 46篇 |
2009年 | 60篇 |
2008年 | 60篇 |
2007年 | 57篇 |
2006年 | 61篇 |
2005年 | 69篇 |
2004年 | 56篇 |
2003年 | 53篇 |
2002年 | 37篇 |
2001年 | 36篇 |
2000年 | 47篇 |
1999年 | 36篇 |
1998年 | 27篇 |
1997年 | 28篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1211条查询结果,搜索用时 15 毫秒
61.
This paper reports that vibrational spectroscopic analysis on hydrogen-bonding between acetone and water comprises both experimental Raman spectra and ab initio calculations on structures of various acetone/water complexes with changing water concentrations. The optimised geometries and wavenumbers of the neat acetone molecule and its complexes are calculated by using ab initio method at the MP2 level with 6-311+G(d,p) basis set. Changes in wavenumber position and linewidth (fullwidth at half maximum) have been explained for neat as well as binary mixtures with different mole fractions of the reference system, acetone, in terms of intermolecular hydrogen bonding. The combination of experimental Raman data with ab initio calculation leads to a better knowledge of the concentration dependent changes in the spectral features in terms of hydrogen bonding. 相似文献
62.
Dominant climate factors influencing the Arctic runoff and association between the Arctic runoff and sea ice 总被引:1,自引:0,他引:1
介绍了星载雷达波谱仪的观测原理及误差分析模型,并在Hauser等提出的SWIM(sea wave investigation and monitoring by satellite)的基础上分析了波谱仪反演海浪谱的波长分辨率和角度分辨率。为了减小反演调制谱的波动,在数据处理过程中时域和波数域相邻单元的平均个数分别为10和8个。系统在不同的模式下工作,为了获取20°的角度分辨率,对调制谱平均次数分别取3次(模式1)、7次(模式2)、10次(模式3)。使用解析法和仿真法分析了SWIM工作在模式2时海浪谱观测的能量误差,两种方法的结果一致。对于给定的海浪条件,能量误差小于20%。 相似文献
63.
An unstructured-grid procedure for SWAN is presented. It is a vertex-based, fully implicit, finite difference method which can accommodate unstructured meshes with a high variability in geographic resolution suitable for representing complicated bottom topography in shallow areas and irregular shoreline. The numerical solution is found by means of a point-to-point multi-directional Gauss–Seidel iteration method requiring a number of sweeps through the grid. The approach is stable for any time step while permitting local mesh refinements in areas of interest. A number of applications are shown to verify the correctness and numerical accuracy of the unstructured version of SWAN. 相似文献
64.
Based on the full water-wave equation, a second-order analytic solution for nonlinear interaction of short edge waves on a constant plane sloping bottom is presented in this paper. For special case of slope angle b=p/2, this solution can be reduced to the same order solution of deep water gravity surface waves traveling along parallel coastline. Interactions between two edge waves including progressive, standing and partially reflected standing waves were also discussed. The unified analytic expressions with transfer functions for kinematic-dynamic elements of edge waves were also discussed. The random model of the unified wave motion processes for linear and nonlinear irregular edge waves is formulated, and the corresponding theoretical autocorrelation and spectral density functions of the first and second orders are derived. The boundary conditions for the determining determination of the parameters of short edge wave are suggested, that may be seen as one special simple edge wave excitation mechanism and an extension to the sea wave refraction theory. Finally some computation results are demonstrated. 相似文献
65.
钨酸铅晶体是一种非化学计量化合物,缺陷丰富,蕴含着利用掺杂产生新效应和开发新功能的广泛可能性。探讨了不同浓度La3 掺杂对于钨酸铅晶体发光性能的影响,如热释光、X射线激发发光、光致发光等。La3 掺杂有效地抑制了陷阱中心,使发光受到强烈的抑制,在高浓度掺杂的钨酸铅中,激发机制有所改变,通过XPS测试的结果分析了不同浓度La3 掺杂机制。低浓度掺杂中,La3 取代Pb2 ,形成缺陷复合体[2(La3Pb ).-(VPb)″];高浓度掺杂晶体中,La3 离子不但占据Pb2 位置,而且也会占据W6 位置(La3W ),产生La3 的自补偿机制,形成La3 的自补偿对[(La3W )-(La3Pb ).]-(VO)..或缺陷聚集体[3(LaP3b ).-(La3W )]。 相似文献
66.
D. Labat C. T. Hoang J. Masbou A. Mangin I. Tchiguirinskaia S. Lovejoy D. Schertzer 《水文研究》2013,27(25):3708-3717
Karstic watersheds are highly complex hydrogeological systems that are characterized by a multiscale behaviour corresponding to the different pathways of water in these systems. The main issue of karstic spring discharge fluctuations consists in the presence and the identification of characteristic time scales in the discharge time series. To identify and characterize these dynamics, we acquired, for many years at the outlet of two karstic watersheds in South of France, discharge data at 3‐mn, 30‐mn and daily sampling rate. These hydrological records constitute to our knowledge the longest uninterrupted discharge time series available at these sampling rates. The analysis of the hydrological records at different levels of detail leads to a natural scale analysis of these time series in a multifractal framework. From a universal class of multifractal models based on cascade multiplicative processes, the time series first highlights two cut‐off scales around 1 and 16 h that correspond to distinct responses of the aquifer drainage system. Then we provide estimates of the multifractal parameters α and C1 and the moment of divergence qD corresponding to the behaviour of karstic systems. These results constitute the first estimates of the multifractal characteristics of karstic spingflows based on 10 years of high‐resolution discharge time series and should lead to several improvements in rainfall‐karstic springflow simulation models. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
67.
迁安紫苏花岗岩的~(40)Ar/~(39)Ar年龄谱 总被引:1,自引:1,他引:1
对采自河北省迁安县水厂地区的紫苏花岗岩中的黑云母和紫苏辉石进行了~(40)Ar/~(39)Ar年龄测定,分别给出了18.7亿年和19.6亿年的~(40)Ar保存年龄。这两种矿物的年龄谱的视年龄的梯度变化表明,紫苏花岗岩形成后是缓慢冷却的。3.9亿年左右的一次热事件,造成了放射成因~(40)Ar的丢失。根据热历史和封闭温度的研究,从27亿年(侵入到该区紫花岗岩中的花岗闪长岩的锆石U-Pb年龄)到19.6亿年,紫苏花岗岩岩体的抬升速率为6.5m/Ma,但从19.6亿年到18.7亿年,其抬升速率高达111m/Ma,具有明显的构造抬升作用。 相似文献
68.
69.
本文解释热剩磁和粘滞剩磁的阻挡过程。较慢冷却伴随较低的阻挡温度。一组同一的磁颗粒,其实验室解阻温度不一定等于其磁化成分的阻挡温度。冷却速率不同,重排剩磁量会不同,两者的关系与磁畴状态有关。距烘烤体不同距离采集磁颗粒分布相同的围岩样品,在一定场合下,根据其剩磁-实验室解阻温度谱所示的重排剩磁量的差别,可讨论冷却速度及模型。本文列举苏格兰某些围岩的不同重排剩磁量,讨论有关问题。 相似文献
70.
Transient and stationary spectra of kinetic energy (KE), available potential energy (APE) and enstrophy (EN), and their spectral fluxes as a function of the two-dimensional wavenumbern were computed for July 1979. Triangular truncation at zonal wavenumber 42 was used for computation. The slopes of various
spectra in the wavenumber range 14≤n≤25 were obtained by fitting a straight line in log-log scale by the least square method. The transientKE, APE andEN spectra in the lower (upper) troposphere had slopes −2·21 (−2·30), −2·65 (−2·64) and −0·36 (−0·46), respectively. The effect
of stationary and divergent motion on the slope values was investigated. The possible correlation between the slope and percentage
of transient component in the combined energy and enstrophy was examined to identify the transient motion of the atmosphere
with the two-dimensional homogeneous isotropic turbulence. The vertically averaged slope of kinetic energy and enstrophy in
the lower (upper) troposphere was close to the value at 700 (200) hPa level.
The spectral fluxes of kinetic energy and enstrophy in the wavenumber range 14≤n≤25 satisfied, to a very rough approximation, the criteria of inertial subrange. The stationary fluxes were small. The estimated
stationary-transient component of flux was larger, comparable and less than the corresponding transient flux of APE, KE and
EN.
Representative levels for computation of energy and enstrophy spectra and their fluxes in the lower and upper troposphere
were identified. 相似文献