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141.
The results presented in this paper shows that high concentrations of sodium hydroxide causes abnormal changes on the volume
change behaviour of illite–smectite (interstratified mineral) soil due to mineralogical changes. The higher swell that occurs
is shown in the form of a new second stage of swelling. Increase in negative charges on soil particles and mineralogical changes
after interaction with soil, respectively, are responsible for the swelling in these two stages. However, potassium hydroxide
does not induce such high swelling in soils. This is mainly due to the fixation of potassium ions. Hence an attempt has been
made to control the swelling induced by sodium hydroxide by making used of potassium chloride as an additive. Potassium fixation
which is not substantial at neutral pH is favoured at higher pH Addition of potassium chloride salt solution (as 2 and 5%
solution) can reduce only the first stage of swelling by linking the unit layers of mineral by reducing development diffuse
double layer near clay surface. Potassium chloride is unable to prevent the formation of mineralogical alteration due to soil
alkali interaction and hence the swelling associated with mineralogical changes. X-ray diffraction studies have revealed that
mineralogical changes leading to formation of zeolite by soil alkali interaction is not inhibited by potassium ions. Morphological
changes studied by scanning electron microscope corroborate these observations. Also the compressibility of soil which is
increased in alkali solution is reduced in the presence of potassium salts. This reduction is due to reduction in the first
stage of swelling. 相似文献
142.
M. Bala Krishna Prasad Mathew R. P. Sapiano Clarissa R. Anderson Wen Long Raghu Murtugudde 《Estuaries and Coasts》2010,33(5):1128-1143
A retrospective analysis of freshwater discharge, riverine dissolved nutrient loads, dissolved nutrients, and chlorophyll in the Chesapeake Bay from 1985 to 2008 is presented. It is evident that each field displays an interannual variability averaged over the Bay. The N and P loads peaked in 1997 and have fluctuated with a decreasing trend since early 2004. Dissolved nutrient concentrations in the Bay appear to be largely controlled by riverine nutrient loads. The temporal variability of chlorophyll is positively correlated with nutrient loads and concentrations. Over the study period, N:P (DIN:DIP) molar ratios were consistently higher than the Redfield ratio (N:P?=?16:1) and strongly correlated with river discharge (R 2?=?0.68, p?0.05) with high discharge periods corresponding to high DIN levels. The N:P stoichiometric analysis indicates that P is the limiting nutrient in spring (N:P?>?16:1), and N is the limiting nutrient in summer and early autumn (N:P?16:1), pointing to an uptake of dissolved nitrogen by the phytoplankton and the release of PO4 from anoxic sediments. Long-term climate indices, such as El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), appear to exert only a moderate control over the riverine discharge to the Bay or over the ecosystem response in terms of chlorophyll in the Bay. While not all related mechanisms can be inferred from available data, this analysis should help in determining future data needs for monitoring water quality and human and climate influence on the health of the Bay. 相似文献
143.
The laminated lacustrine sediments deposited in the last glacial Lake Lisan represent annual deposits of primary aragonite and silty detritus that reflect the annual supply of bicarbonate‐bearing freshwater to the lake. A varve‐counting curve was constructed for the time interval of ca. 17.4–22 cal. ka BP based on aragonite U/Th, and atmospheric radiocarbon ages of organic debris recovered from the studied section. Radiocarbon in the primary (evaporitic) aragonite comprises both atmospheric and old carbon (reflecting the reservoir age). The aragonite reservoir ages were determined by comparing the aragonite radiocarbon dates to the varve counting curve, and are found to lie in the range 1900–600 a and display a continuous decline. This opens the possibility for high (annual) resolution monitoring of the reservoir age, similar in quality to tree ring counting, during the upper part of Marine Isotope Stage (MIS) 2. Our work also demonstrates that a ‘uniform’ reservoir age correction is inappropriate when determining the chronology of short‐term climate events in lacustrine environments. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
144.
145.
Expressions for the effective cluster formation rates
are written in terms of neutral densities and recent laboratory data on reaction rate coefficients. At D-region heights these parameters show seasonal variations due to mesospheric temperature changes. Reduction in cluster formation rates for winter months would result in a decrease in the concentration of hydrated ions and hence reduced effective recombination coefficient for electrons. The results show latitude and seasonal variations which are similar to that of a normal winter anomaly in radio wave absorption. 相似文献
146.
The paper deals with an application of a stochastic model to the frequency and duration of precipitation events. With the aid of the model, the magnitudes ofmth highest rainfall amount in 24 hours' duration with 97.5% probability are obtained for various climatic regimes over a tropical monsoon region. There is good agreement between them-day minimum rainfall estimated through the model and the observed value. The model satisfactorily explains the frequency of the extreme rainfall event. 相似文献
147.
148.
B. Gururaj J.P. Sharma A. Baldawa S.C.D. Arora N. Prasad A.K. Biswas 《International Journal of Mineral Processing》1983,11(4):285-302
Studies have been made on the separability of clay minerals such as kaolinite, illite and montmorillonite from hematite in dispersant-starch flocculant systems. The grossly different dispersibility of hematite from that of clay minerals aided separation by selective dispersion and flocculation. Moderate success has been achieved with a selectivity index nearing 4.0 (average recovery values around 80%).The studies have been extended to hematite recovery and clay rejection from the slimes of the Barsua iron ore washing plant owned by Rourkela Steel Plant, India. Limited success achieved in the starch selective flocculation method has been attributed to the difficulties associated with fine grain size, clay mineraloty and liberation.The ore exhibits the phenomenon of differential grinding. Hematite-rich coarser particles in the slime can be separated by differential settling in dispersant systems followed by selective flocculation in low-starch systems. 相似文献
149.
The empirical orthogonal functions have been obtained for the individual summer monsoon (June through September) months using
the grid point values of monthly 700 mb geopotential heights over Indian region. The data for 21 summer monsoon months for
the years 1958 to 1978 have been used in the present computation.
The major variance reduction is due to the first three dominant functions accounting over 80% of the total variance in each
month. The variance reduction only due to the first function ranges from 45 to 65%.
The first function has in-pbase oscillation throughout the area indicating that the area under study is homogeneous and the
centre of the oscillation lies over northwest India. The amplitudes of the first function also show generally quasipers stence
in their sign within a season. The second function has two centres of action over the region of monsoon trough which are in
phase. The third function has also two centres oriented in the east-west direction but they are in the opposite phase.
Fairly large values of correlation coefficients between the patterns of the different monsoon months suggest that the patterns
for these months corresponding to the first and the second functions respectively are quite similar. The patterns for these
months also evolve with time in a related way. The spectrum analysis to the time series of amplitudes indicates the presence
of the quasi-periodicity of 3 years during these monsoon months. The amplitudes corresponding to the dominant functions are
found to be significantly related with the rainfall of central and western parts of India 相似文献
150.
We use a generic stochastic acceleration formalism to examine the power Lin (erg s-1) input to non-thermal electrons that cause noise-storm continuum emission. The analytical approach includes the derivation of the Greens function for a general second-order Fermi process, and its application to obtain the particular solution for the non-thermal electron distribution resulting from the acceleration of a Maxwellian source in the corona. We compare Lin with the power Lout observed in noise-storm radiation. Using typical values for the various parameters, we find that Lin 1023–1026 erg s-1, yielding an efficiency estimate Lout/Lin in the range 10-10 10-6 for this non-thermal acceleration/radiation process. These results reflect the efficiency of the overall process, starting from electron acceleration and culminating in the observed noise-storm emission. 相似文献