全文获取类型
收费全文 | 979篇 |
免费 | 15篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 135篇 |
大气科学 | 56篇 |
地球物理 | 168篇 |
地质学 | 382篇 |
海洋学 | 45篇 |
天文学 | 176篇 |
综合类 | 12篇 |
自然地理 | 28篇 |
出版年
2022年 | 20篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 24篇 |
2018年 | 47篇 |
2017年 | 40篇 |
2016年 | 60篇 |
2015年 | 36篇 |
2014年 | 46篇 |
2013年 | 78篇 |
2012年 | 47篇 |
2011年 | 33篇 |
2010年 | 44篇 |
2009年 | 33篇 |
2008年 | 31篇 |
2007年 | 30篇 |
2006年 | 21篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 13篇 |
2000年 | 26篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 3篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 25篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有1002条查询结果,搜索用时 0 毫秒
981.
Monthly mesoscale eddy kinetic energy (EKE) per unit mass has been computed for four years, 1993-1996, from TOPEX altimeter data in the Indian Ocean. It ranges from 50 cm2/s2 to 2,700 cm2/s2 (about 4,000 cm2/s2 near the Somali region in a few months). In the Arabian Sea and the Bay of Bengal, regions of high energies associated with various current systems under the influence of monsoonal winds have been delineated. Monthly variation of EKE near the Somali region has been studied. In this region the maximum EKE per unit mass has been observed during August every year, with variations in magnitude from year to year. The mesoscale eddy kinetic energy computed from TOPEX altimeter-derived SSH during 1993-1996 is highest near the Somali region during the SW monsoon, due to formation of mesoscale eddies and also because of upwelling. In the Bay of Bengal, high eddy kinetic energy is seen toward the western side during nonmonsoonal months due to the western boundary current. In the South Indian Ocean, it is high at a few places in some of the months. A large part of the Indian Ocean exhibits low eddy kinetic energy (less than 300 cm2/s2) year-round. 相似文献
982.
This paper presents the model equations governing the nonlinear interaction between dispersive Alfvén wave (DAW) and magnetosonic
wave in the low-β plasmas (β≪m
e/m
i; known as inertial Alfvén waves (IAWs); here
\upbeta = 8pn0T /B02\upbeta = 8\pi n_{0}T /B_{0}^{2} is thermal to magnetic pressure, n
0 is unperturbed plasma number density, T(=T
e≈T
i) represents the plasma temperature, and m
e(m
i) is the mass of electron (ion)). This nonlinear dynamical system may be considered as the modified Zakharov system of equations
(MZSE). These model equations are solved numerically by using a pseudo-spectral method to study the nonlinear evolution of
density cavities driven by IAW. We observed the nonlinear evolution of IAW magnetic field structures having chaotic behavior
accompanied by density cavities associated with the magnetosonic wave. The relevance of these investigations to low-β plasmas
in solar corona and auroral ionospheric plasmas has been pointed out. For the auroral ionosphere, we observed the density
fluctuations of ∼ 0.07n
0, consistent with the FAST observation reported by Chaston et al. (Phys. Scr.
T84, 64, 2000). The heating of the solar corona observed by Yohkoh and SOHO may be produced by the coupling of IAW and magnetosonic wave via filamentation process as discussed here. 相似文献
983.
Landslide susceptibility zonation of the Chamoli region, Garhwal Himalayas, using logistic regression model 总被引:5,自引:2,他引:3
A remote sensing and Geographic Information System-based study has been carried out for landslide susceptibility zonation in the Chamoli region, part of Garhwal Himalayas. Logistic regression has been applied to correlate the presence of landslides with independent physical factors including slope, aspect, relative relief, land use/cover, lithology, lineament, and drainage density. Coefficients of the categories of each factor have been obtained and used to assess the landslide probability value to ultimately categorize the area into various landslide susceptibility zones; very low, low, moderate, high, and very high. The results show that 71.13% of observed landslides fall in 21.96% of predicted very high and high susceptibility zone, which in fact should be the case. Furthermore, lineament first buffer category (0–500 m) and the east and south aspects are the most influential in causing landslides in the region. 相似文献
984.
Numerical model and flume experiments of single- and two-layered hillslope flow related to slope failure 总被引:1,自引:0,他引:1
A hillslope flow model is developed considering 3D saturated and unsaturated flow of water during rainfall events. A finite difference-based numerical model of hillslope flow processes is developed. Four different experiments are done to see the effects of a single- and double-layered soil in pore-water pressure dynamics and slope failure. Results from the numerical model are verified with experimental results. The numerical and experimental values of the pore-water pressure and moisture contents are in good agreement. The results show that the hillslope heterogeneity caused by multiple layers of soil has greater influence on hillslope pore-pressure dynamics and slope failure patterns. The depth of slope failure shows high dependency on layering characteristics of the soil slope and pattern of rainfall. The proposed model provides a perspective on failure mechanism of a single- or double-layered slope under rainfall infiltration. 相似文献
985.
Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to
heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required
to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of
the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide
are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust
passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important
to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of
slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can
be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta
Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available
worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this high-altitude mountainous terrain.
VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was
delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient
resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the
slide parallel to the geological gneiss–schist contact within the Lanta Khola slide. This indicates that the conductive feature
correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive
structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out
water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide. 相似文献
986.
Ram Krishan Sharma 《Astrophysics and Space Science》1987,135(2):271-281
This paper deals with the stationary solutions of the planar restricted three-body problem when the more massive primary is a source of radiation and the smaller primary is an oblate spheroid with its equatorial plane coincident with the plane of motion. The collinear equilibria have conditional retrograde elliptical periodic orbits around them in the linear sense, while the triangular points have long- or short-periodic retrograde elliptical orbits for the mass parameter 0 < crit, the critical mass parameter, which decreases with the increase in oblateness and radiation force. Through special choice of initial conditions, retrograde elliptical periodic orbits exist for the case = crit, whose eccentricity increases with oblateness and decreases with radiation force for non-zero oblateness. 相似文献
987.
Pasquale Crea Concetta De Stefano Frank J. Millero Silvio Sammartano Virender K. Sharma 《Aquatic Geochemistry》2010,16(3):447-466
Oxidized glutathione (GSSG), which has four carboxylic and two amino groups, interacts with metal ions and may affect the
bioavailability and geochemistry of metals in natural waters. In the present paper, six stepwise protonation constants
K\textHi K^{\text{H}}_{i} for GSSG were measured as a function of salinity, S = 5–35‰ at t = 25°C (and in NaCl/MgCl2 mixtures at different ionic strengths), in order to provide thermodynamic data for their acid base properties, which are
useful for studying the interaction with metals in these media. The protonation enthalpies (ΔH
i
/kJ mol−1) were also determined at t = 25°C. The results were interpreted using the SIT model and Pitzer equations. The seawater model with the interaction parameters
accounts for the differences between the values in NaCl and seawater. The results suggest that it is important to consider
all of the ionic interactions in natural waters in examining the proton dissociation of GSSG. 相似文献
988.
ABSTRACT Use of granular pile as a ground improvement technique in case of soft soils is one of the reliable and economic options. Analysis of a partially stiffened group of granular floating piles has been numerically assessed and presented here. Partial stiffening simply means that instead of using conventional material for making the granular pile (GP) in its full length, top region is replaced partially by some suitable material, having better mechanical properties, i.e. higher deformation modulus. Various normalised parameters like settlement influence factor for top of GP, settlement interaction factor, settlement reduction factor, percentage load shared by the base and shear stress distribution along the length of the granular pile are evaluated. The settlement influence factor for top of GP is found to decrease with the increase in the values of the stiffening parameters. The interfacial shear stresses get redistributed along the length of the granular pile. 相似文献
989.
M. Ahmad M. K. Ansari Rajesh Singh L. K. Sharma T. N. Singh 《Geotechnical and Geological Engineering》2017,35(2):827-842
Weathering and durability are the key factors of the rock in the suitability and usefulness of different construction materials, building materials and engineering structures. A single test never predicts the entire factor for suitability of rock stone and aggregate in different uses. Thus, variety of physical, mechanical and chemical tests and indices of rocks are widely used to estimate and evaluate the rocks for the suitability of the required purpose. In all the cases, knowledge of durability and weathering properties are the most important along with the strength of the rock. Micropetrographic index and rock durability indicators (dynamic and static) are the one of the best methods to evaluate the rock for weathering and durability. To estimate these indices, variety of tests are performed such as petrographic examination test, point load index, sulfate soundness test, water absorption test, modified aggregate impact value test and test for specific gravity. Slake durability index and impact strength index tests were also performed for correlation with static and dynamic rock durability indicators due to its application and usefulness in the durability and strength of the rock materials. Micropetrographic index was obtained by petrographic examination test and correlated with all the physical and mechanical properties used for find out the durability indicators. The present study is to express the usefulness of these three indices in the classification of weathering and durability classes and estimation of durability indices by slake durability index, impact strength index and micropetrographic index. 相似文献
990.
A simulation based on a pseudo-spectral method has been performed in order to study particle acceleration. A model for the acceleration of charged particles by field localization is developed for the low-\(\upbeta\) plasma. For this purpose, a fractional diffusion approach has been employed. The nonlinear interaction between a 3D inertial Alfvén wave and a slow magnetosonic wave has been examined, and the dynamical equations of these two waves in the presence of ponderomotive nonlinearity have been solved numerically. The nonlinear evolution of the inertial Alfvén wave in the presence of slow magnetosonic wave undergoes a filamentation instability and results in field intensity localization. The results obtained show the localization and power spectrum of inertial Alfvén wave due to nonlinear coupling. The scaling obtained after the first break point of the magnetic power spectrum has been used to calculate the formation of the thermal tail of energetic particles in the solar corona. 相似文献