全文获取类型
收费全文 | 524篇 |
免费 | 68篇 |
国内免费 | 74篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 21篇 |
地球物理 | 215篇 |
地质学 | 169篇 |
海洋学 | 115篇 |
天文学 | 112篇 |
综合类 | 10篇 |
自然地理 | 16篇 |
出版年
2024年 | 4篇 |
2023年 | 3篇 |
2022年 | 24篇 |
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 28篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 22篇 |
2013年 | 19篇 |
2012年 | 19篇 |
2011年 | 32篇 |
2010年 | 20篇 |
2009年 | 20篇 |
2008年 | 20篇 |
2007年 | 26篇 |
2006年 | 27篇 |
2005年 | 29篇 |
2004年 | 22篇 |
2003年 | 31篇 |
2002年 | 22篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 13篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有666条查询结果,搜索用时 46 毫秒
251.
Interpretation of magnetic resonance soundings in rocks with high electrical conductivity 总被引:1,自引:0,他引:1
A. Legchenko M. Ezersky J.-F. Girard J.-M. Baltassat M. Boucher C. Camerlynck A. Al-Zoubi 《Journal of Applied Geophysics》2008,66(3-4):118
Magnetic resonance sounding (MRS) is an electromagnetic method designed for groundwater investigations. MRS can be applied not only for studying fresh-water aquifers, but also in areas where intrusion of saline water is rendering the subsurface electrically conductive. In the presence of rocks with a high electrical-conductivity attenuation and a phase shift of the MRS signal may influence the efficiency of the MRS method. We investigated the performance of MRS for allowing us to propose a procedure for interpreting MRS data under these conditions. For numerical modeling, we considered a subsurface with a resistivity between 0.5 and 10 Ω m. The results show that the depth of investigation with MRS depends upon the electrical conductivity of groundwater and surrounding rocks, on the depth of the saline water layer, and on the amount of fresh water above the saline water. For interpreting MRS measurements, the electrical conductivity of the subsurface is routinely measured with an electrical or electromagnetic method. However, due to the equivalence problem, the result obtained with these methods may be not unique. Hence, we investigated the influence of the uncertainty in conductivity distribution provided by transient electromagnetic measurements (TEM) on MRS results. It was found that the uncertainty in TEM results has an insignificant effect on MRS. 相似文献
252.
地面核磁共振(NMR)方法是地球物理上采用的探测地下水的最新方法,能够探测地下含水层中的自由水.但是有时会出现对地下含水层的出水量判断失误的现象,这种失误发生的主要原因是由于IRIS仪器设计时假设利用NMR信号的弛豫时问就能够区分地下含水层中的自由水和束缚水,实际上弛豫时间取决于以下几个参数即:孔隙度、渗透率和导水率.地层孔隙水中氢质子弛豫时间不仅与其本身的弛豫特点有关,还与岩石孔隙结构、成份密切相关.为了更好的理解以上这些参数对地下含水层涌水量的影响,本文讨论了含水多孔介质的弛豫特性,研究有效孔隙度与含水量之间的关系,给出计算渗透率和导水率的方法,利用几个实测地点数据资料分析地下含水层岩性对涌水量的影响,结果表明地层中平均含水量大而且含水地层弛豫时间较长的地点才能获得较大的涌水量. 相似文献
253.
Sea-bottom pressure gauges were used to measure sea levels at two points on the shelf off the southern coast of Satsuma Peninsula,
Kyushu, Japan. Spectral analysis of the observed records and the tide-gauge record of Makurazaki Harbor revealed several predominant
common peaks. At the same time, the eigenmodes for the trapped waves on the shelf and inside Makurazaki Bay were obtained
numerically using a two-dimensional model, and the periods and the spatial distribution of amplitudes of the proper modes
were obtained. A comparison of the calculated modes with the periods and phase patterns of the observed peaks clarified that
peaks with periods of 19.5, 16, 13.3, and 12.2 minutes in the shelf region were the modes of standing-edge waves, and the
peak with the period of 16 minutes in Makurazaki Harbor was the fundamental mode of the harbor. Among the modes of standing-edge
waves, the mode of the period 16 minutes on the shelf had nearly the same period as that of the fundamental mode of Makurazaki
Harbor. An analysis of changes of spectral densities of these two modes confirmed that the fundamental mode of the Makurazaki
Harbor was induced by this standing-wave mode. 相似文献
254.
山东蓝宝石的宝石矿物学特征 总被引:6,自引:0,他引:6
对山东蓝宝石进行了系统的宝石矿物学研究,描述了山东蓝宝石的形态,大小,结构及包裹体特征,运用电子探针,粉晶X射线分析,顺磁共振光谱及化学全分析等测试手段,揭示了山东蓝宝石的成分,结构和物性之间的相互关系。 相似文献
255.
长白山地区近代火山岩的ESR测年研究 总被引:3,自引:0,他引:3
在对火山灾害和潜在危险性评价中火山活动的时代起着极其重要的作用,但是,目前还没有成熟的测年方法能够对年轻火山岩直接定年。本文采用电子自旋共振(ESR)测年方法对年轻火山岩直接测年进行了尝试。所测年轻火山岩石英矿物中没有E信号,有较弱的Ge中心信号,根据Ge中心信号获得了长白山三期近代火山岩的年龄,其中,气象站碱性流纹岩的ESR年龄约3930 a BP,而气象站碱性流纹岩之下粗面岩的ESR年龄约为17500~20900 a BP。 相似文献
256.
257.
John D. Hadjidemetriou 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):65-76
We present a 3-D symplectic mapping model that is valid at the 2:1 mean motion resonance in the asteroid motion, in the Sun-Jupiter-asteroid
model. This model is used to study the dynamics inside this resonance and several features of the system have been made clear.
The introduction of the third dimension, through the inclination of the asteroid orbit, plays an important role in the evolution
of the asteroid and the appearance of chaotic motion. Also, the existence of the secondary resonances is clearly shown and
their role in the appearance of chaotic motion and the slow diffusion of the elements of the orbit is demonstrated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
258.
Otávio de Oliveira Costa Filho Wagner Sessin 《Celestial Mechanics and Dynamical Astronomy》1999,74(1):1-17
This paper is concerned with the extended Delaunay method as well as the method of integration of the equations, applied to
first order resonance. The equations of the transformation of the extended Delaunay method are analyzed in the (p + 1)/p type resonance in order to build formal, analytical solutions for the resonant problem with more than one degree of freedom.
With this it is possible to gain a better insight into the method, opening the possibility for more generalized applications.
A first order resonance in the first approximation is carried out, giving a better comprehension of the method, including
showing how to eliminate the ‘Poincaré singularity’ in the higher orders.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
259.
Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS 总被引:1,自引:0,他引:1
Boris P. Koch Kai-Uwe Ludwichowski Gerhard Kattner Thorsten Dittmar Matthias Witt 《Marine Chemistry》2008,111(3-4):233-241
Marine dissolved organic matter (DOM) was separated by reversed-phase (RP) liquid chromatography method and analyzed with fluorescence/absorption detection and Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). The three key characteristics of the RP method are: (a) The C18-RP column chosen provides enhanced separation when the aqueous phase is 100% buffer-free water, and it does not degrade over time; (b) the water eluent adjusted to pH 7 significantly improves the resolution of water soluble compounds; (c) the initial flow maintained at low levels improves the separation of polar compounds. In samples, containing “fresh” DOM, specific peaks were detected, which were absent in “old” DOM samples. The combination with size exclusion chromatography (SEC) also demonstrated the relation between polarity and molecular size of DOM. FT-ICR-MS was applied to evaluate the quality of separation on a molecular scale demonstrating that physico-chemical characteristics of DOM can be related to molecular formulas. Sample extracts were separated into 4 preparative fractions, and a large suite of the identified molecular formulas only occurred in specific fractions. This is an important basis for the application of further analytical techniques in order to perform a more target-oriented analysis aiming at the determination of source and process biomarkers for DOM. 相似文献
260.
A combination of a three-dimensional hydrodynamic model and in-situ measurements provides the structures of barotropic tides,
tidal circulation and their relationship with turbulent mixing in the Java Sea, which allow us to understand the impact of
the tides on material distribution. The model retains high horizontal and vertical resolutions and is forced by the boundary
conditions taken from a global model. The measurements are composed of the sea level at coastal stations and currents at moorings
embedded in Seawatch buoys, in addition to hydrographic data. The simulated tidal elevations are in good agreement with the
data for the K1 and M2 constituents. The K1 tide clearly shows the lowest mode resonance in the Java Sea with intensification around the nodal point in the central region.
The M2 tide is secondary and propagates westward from the eastern open boundary, along with a counterclockwise amphidromic point
in the western part. The K1 tide produces a major component of tidal energy, which flows westward and dissipates through the node region near the Karimata
Strait. Meanwhile, the M2 tide dissipates in the entire Java Sea. However, the residual currents are mainly induced by the M2 tide, which flows westward following the M2 tidal wave propagation. The tidal mixing is mainly caused by K1 tide which peaks at the central region and is consistent with the uniform temperature and salinity along the vertical dimension.
This mixing is expected to play an important role in the vertical exchange of nutrients and control of biological productivity. 相似文献