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891.
892.
893.
Lacustrine limestones were formerly identified by their faunistic (limnea, planorbis) and floristic (Charophytes) content. For 30 years, indications of pedogenesis have been found in many lacustrine deposits, and consequently the concept of palustrine limestone was defined.Lacustrine fabrics are not that numerous: varved, laminated, homogeneous, peloidal, brecciated, gravelly, bioturbated (burrows), bioclastic, algal, and stromatolitic. Detrital beds are sometimes present and are interpreted as bottomset deposits. Palustrine fabrics result from exposure and pedogenesis of lacustrine mud. The main processes involved in this evolution are: cracking, with planar, curved, craze and skew planes, colonization by plants resulting in root traces, marmorization (redistribution of iron due to water table fluctuation), and redistribution of carbonates (needles, subspherical or cylindrical vertical nodules, carbonate coatings, early and late diagenetic crystals, Microcodium). Carbonate palustrine features can be associated with other minerals: palygorskite, gypsum, or silica. Alternation of lacustrine sedimentation and exposure/pedogenesis leads to the pseudo-microkarst facies resulting from enlargement of the complex network of root traces and horizontal cracks. The voids in the pseudo-microkarst facies are infilled with a polyphased internal sediment composed of carbonate and vadose silt and phreatic and vadose cements. Traces of exposure and pedogenesis are less in evidence in lacustrine bioclastic sands and algal-stromatolitic limestones. Finally, under certain conditions, the surficial laminar horizon and its associated perlitic crust (ooids) develops on palustrine muds and form a desert stromatolite. 相似文献
894.
895.
Ernest S. GLADNEY Elizabeth A. JONES Eric J. NICKELL Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1992,16(2):111-300
Concentration data on up to 90 individual constituents in USGS AGV-1, GSP-1, and G-2 have been collected from 1270 journal articles and technical reports. These data are summarized in consensus (mean) values with uncertainties expressed as +/- one standard deviation. Mean values are also calculated as a function of analytical procedure and all raw data are given in the tables. Recommended values are proposed based upon data criteria used by NIST (National Institute of Standards and Technology, formerly the National Bureau of Standards or NBS). 相似文献
896.
Instrumental neutron activation in geoanalysis 总被引:1,自引:0,他引:1
Theoretical aspects of instrumental neutron activation analysis (INAA) are discussed. Various applications of INAA to exploration geochemistry are described demonstrating its capabilities and its limitations.Cost, turnaround time, high sensitivity for certain elements, the non-destructive nature of analysis and its precision and accuracy have combined to make INAA an indispensible method for multielement determination on virtually all geological matrices. Humus, vegetation, heavy minerals, lake bottom sediments as well as rocks and soils comprise the major sample types analyzed by INAA. As many as 50 elements can be determined routinely and easily by INAA. 相似文献
897.
Eric A. Crecelius John H. Trefry Margarete S. Steinhauer Paul D. Boehm 《Environmental Geology》1991,18(1):71-79
Increased development and changing climate have enhanced global interest in the Arctic Ocean and adjacent seas. Using a large, 3-yr data base, we have determined the distribution of trace metals in sediments from the inner shelf of the western Beaufort Sea. Metal concentrations in these sediments reflect pristine conditions, consistent with those for most coastal areas in the Arctic and with predictions based on average continental crust. Geographic variations in metal values are primarily related to sediment grainsize distribution. However, grain-size patterns are a complex function of several variables including source areas, ice and water movement, as well as physical and chemical weathering. Future identification of any metal contamination in Beaufort Sea sediments will be simplified by understanding the predictable natural patterns. 相似文献
898.
Dexter Perkins III Eric J. Essene Edgar F. Westrum Jr. Victor J. Wall 《Contributions to Mineralogy and Petrology》1977,64(2):137-147
Recent low temperature, adiabatic calorimetric heat capacity measurements for grossular have been combined with DSC measurements to give entropies up to 1000 K. In conjunction with enthalpy of solution values for grossular, these data have yielded H
f
o
(298.15K) and G
f
o
(298.15K) values of –1583.2 ± 3.5 and –1496.74 ± 3.7 kcal mol–1 respectively. For 15 reactions in the CaO-Al2O3-SiO2-H2O system, thermodynamically calculated P-T curves have been compared with experimental reversals and have shown good agreement in most cases. Calculations indicate that gehlenite is probably totally disordered. Estimates of zoisite and lawsonite entropies are consistent with the phase equilibrium and grossular data, but estimates of the entropies of pyrope and andradite show large discrepancies when compared with experimental reversals.Contribution no. 600 from the Mineralogical Laboratory, The Department of Geology and Mineralogy, The University of Michigan, Ann Arbor, Michigan 48109, USA 相似文献
899.
Charles P. Gerba Sagar M. Goyal Eric M. Smith Joseph L. Melnick 《Marine pollution bulletin》1977,8(12):279-282
Significant concentrations of human enteric viruses and bacteria were found to be present in the water and sediment of a coastal canal community into which secondarily treated sewage was being discharged. 相似文献
900.
We have calculated the total individual ion activity coefficients of carbonate and calcium, and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of and are and , respectively. These values of and are independent of liquid junction errors and internally consistent with the value . By defining and on a common scale (), the product is independent of the assigned value of and may be determined directly from thermodynamic measurements in seawater. Using the value and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978, Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data. 相似文献