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211.
Hajsadeghi Saeid Asghari Omid Mirmohammadi Mirsaleh Meshkani Seyed Ahmad 《Natural Resources Research》2020,29(1):161-171
Natural Resources Research - Multivariate methods are useful for simplifying the interpretation of variables in geochemical data and are widely used to uncover relationships between elements that... 相似文献
212.
Ruhollah Taghizadeh Mehrjardi Shahla Mahmoodi Ahmad Heidari Ali Akbarzadeh 《山地科学学报》2009,6(2):162-172
The fact of, present is the key of the past, will help us to use paleosols properties as indicators of the ecological characteristics of past .time, particularly the paleoclimate. In this respect the micro- morphological properties showed to be a very good indicator. Therefore, for investigating of climate change in Ardakan-Yazd plain, Central Iran 9 pedons were digged and described. Yazd has an arid climate with less than 100 mm annual precipitation and more than 22℃ mean annual temperature (Aridic-hyper thermic soil moisture and temperature regions, respectively). Based on the morphological and physicochemical analysis Arglic, Calcic and Gypsic diagnostic horizons have been distinguished in these soils. Thin section studied showed that the illuviated form of clay includes, infillings on channel, coating on pendant, on nodules and on grains, at lower depths and also juxtaposed calcite needles on void argillan at upper part of the profiles. Mineralogical result showed fine clay in arglic horizon, too. Considering depth and forms of these pedofeatures, we concluded that, the observed illuviated clays at lower depth must be the result of the more humid climate of the past, where the carbonates have been removed completely as pendant, nodules or coating to considerable depth, following processes, clay has been dispersed and also trans located to these depths. In contrast to these features, the juxtaposed needle calcite at the shallower depth is probably the result of drier climate of today. 相似文献
213.
214.
A numerical algorithm based on the boundary element method (BEM) is presented for predicting the hydrodynamic characteristics of the various planing hull forms. The boundary integral equation is derived using Green's theorem on the wetted body surface and the free surface. The ventilation function at the transom is estimated with Doctor's empirical formula. This function is defined as the transom zone free surface boundary condition. The combined boundary integral equation and modified free surface boundary condition are simultaneously solved to determine the dipole on the wetted hull surface and the source on the free surface. The method is applied to investigate three examples of planing hulls, which include flat-plates, as well as wedge-shaped and variable deadrise planing hulls. Their hydrodynamic characteristics are calculated for different speeds. Computational results are presented and compared with existing theories and experiments. On the whole, the agreement between the present method and the selected experimental and numerical data is satisfactory. 相似文献
215.
216.
A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations
Nash'at Ahmad Zafer Boybeyi Rainald Löhner Ananthakrishna Sarma 《Pure and Applied Geophysics》2007,164(1):217-244
In recent years there has been a growing interest in using Godunov-type methods for atmospheric flow problems. Godunov's unique
approach to numerical modeling of fluid flow is characterized by introducing physical reasoning in the development of the
numerical scheme (van Leer, 1999). The construction of the scheme itself is based upon the physical phenomenon described by the equation sets. These
finite volume discretizations are conservative and have the ability to resolve regions of steep gradients accurately, thus
avoiding dispersion errors in the solution. Positivity of scalars (an important factor when considering the transport of microphysical
quantities) is also guaranteed by applying the total variation diminishing condition appropriately. This paper describes the implementation of a Godunov-type finite volume scheme based on unstructured
adaptive grids for simulating flows on the meso-, micro- and urban-scales. The Harten-Lax-van Leer-Contact (HLLC) approximate
Riemann solver used to calculate the Godunov fluxes is described in detail. The higher-order spatial accuracy is achieved
via gradient reconstruction techniques after van Leer and the total variation diminishing condition is enforced with the aid of slope-limiters. A multi-stage explicit Runge-Kutta time marching scheme is used for
maintaining higher-order accuracy in time. The scheme is conservative and exhibits minimal numerical dispersion and diffusion.
The subgrid scale diffusion in the model is parameterized via the Smagorinsky-Lilly turbulence closure. The scheme uses a non-staggered mesh arrangement of variables (all quantities are
cell-centered) and requires no explicit filtering for stability. A comparison with exact solutions shows that the scheme can
resolve the different types of wave structures admitted by the atmospheric flow equation set. A qualitative evaluation for
an idealized test case of convection in a neutral atmosphere is also presented. The scheme was able to simulate the onset
of Kelvin-Helmholtz type instability and shows promise in simulating atmospheric flows characterized by sharp gradients without
using explicit filtering for numerical stability. 相似文献
217.
Masayuki Ehiro Satoru Kojima Tadashi Sato Talat Ahmad Tomoyuki Ohtani 《Island Arc》2007,16(1):124-132
Abstract Callovian (late Middle Jurassic) ammonoids Macrocephalites and Jeanneticeras were recovered from the Shyok suture zone, northeast of Chang La Pass, Ladakh, northwest India. They are the first reliable Jurassic fossils and the oldest chronologic data from the Shyok suture zone. The ammonoid-bearing Jurassic strata, newly defined as the Tsoltak Formation, consist largely of terrigenous mudstone with thin sandstone beds and were probably a part of the continental basement to the Cretaceous Ladakh Arc. 相似文献
218.
Afaq Ahmad 《Astrophysics and Space Science》1974,27(2):343-350
A class of equilibrium solutions of the Vlasov equation for self-gravitating systems is discussed. The density and the potential are derived in form of Jacobi polynomials, which in a special case give rise to a model with uniform density. 相似文献
219.
Agusa T Kunito T Yasunaga G Iwata H Subramanian A Ismail A Tanabe S 《Marine pollution bulletin》2005,51(8-12):896-911
Concentrations of trace elements (V, Cr, Mn, Co, Cu, Zn, Ga, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Cs, Ba, Hg, Tl, Pb and Bi) were determined in muscle and liver of 12 species of marine fish collected from coastal areas in Malaysia. Levels of V, Cr, Mn, Co, Cu, Zn, Ga, Sr, Mo, Ag, Cd, Sn, Ba and Pb in liver were higher than those in muscle, whereas Rb and Cs concentrations showed the opposite trend. Positive correlations between concentrations in liver and muscle were observed for all the trace elements except Cu and Sn. Copper, Zn, Se, Ag, Cd, Cs and Hg concentrations in bigeye scads from the east coast of the Peninsular Malaysia were higher than those from the west, whereas V showed the opposite trend. The high concentration of V in the west coast might indicate oil contamination in the Strait of Malacca. To evaluate the health risk to Malaysian population through consumption of fish, intake rates of trace elements were estimated on the basis of the concentrations of trace elements in muscle of fish and daily fish consumption. Some specimens of the marine fish had Hg levels higher than the guideline value by US Environmental Protection Agency (EPA), indicating that consumption of these fish at the present rate may be hazardous to Malaysian people. To our knowledge, this is the first study on multielemental accumulation in marine fish from the Malaysian coast. 相似文献
220.
Groundwater quality in parts of Central Ganga Basin, India 总被引:1,自引:0,他引:1
This paper deals with the drinking water quality of the Ganga-Kali sub-basin which occupies 1300 km2 over parts of Aligarh and Etah districts. Water samples were collected from shallow and deep aquifers and were analyzed for
major ions and trace elements. The analytical data were interpreted according to published guidelines. Chemical analysis shows
that the groundwater in the basin is alkali bicarbonate type. Trace element studies of water from the shallow aquifer show
that the concentration of toxic metals Fe, Mn, Cd, Pb, and Cr+6 are above permissible limits which may present a health hazard. The water from the deep aquifer is comparatively free from
contamination. The aquifers are subject to contamination due to sewage effluents and excessive use of fertilizers and pesticides
in agriculture.
Received: 7 December 1998 · Accepted: 2 March 1999 相似文献