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161.
We present a study at HST-like spatial resolution of the gas kinematics in the innermost part of NGC 1068. This work is based
on observations with the integral field spectrograph TIGER mounted on the CFH Telescope. We first derived the final spatial
PSF of our data and checked its photometric integrity by comparison with two independent [OIII] HST images (FOC and WFPC2).
We then performed a spatial deconvolution of the data-cube constraining the sum of the deconvolved velocity-slices to be as
close as possible to the HST image. The resulting deconvolved data-cube has then a resolution similar to the HST image. It
shows that the velocity distribution of the inner clouds detected with the HST differs strongly from a simple NE-SW ejection
flow. We thus show that the previous interpretations of the double-peaked lines NE of the nucleus must be revisited.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
162.
The Portneuf–Mauricie Domain (PMD), located in the south-central part of the Grenville province, contains Mesoproterozoic
Ni–Cu ± platinum-group element (PGE) prospects hosted in a variety of plutonic intrusions (layered, with simple structures,
or zoned) and emplaced in a mature island arc setting. A two-stage model is envisaged to explain the formation of magmatic
sulfides. An early loss of a small amount of sulfides in the conduits of primitive, hydrous mantle-derived melts under high
fO2, resulted in depletion of the magmas in chalcophile and precious metals (Cu/Pd ratios vary from initial mantle values up
to 1.6 × 106). Then, nearer the mineralized zones, the magmas interacted with sulfide-bearing country rocks, resulting in felsification
of the magmas, assimilation of crustal sulfur (δ
34S values up to +5.5‰), and the formation of an immiscible sulfide liquid. Liquid-sulfide formation was followed by variable
interactions between the silicate and sulfide magmas, which were responsible for the enrichment of sulfides in Ni, Cu, and,
locally, PGE. Indeed, low R factors are found for prospects hosted in intrusions with a simple internal structure and in layered intrusions whereas high
R factors are found for prospects hosted in zoned intrusions. Finally, sulfide melt may have been partly incorporated into
later pulses of magma and injected into shallow magma chambers to form the PMD prospects. The PMD prospects share common characteristics
with other well-known deposits (Aguablanca, Vammala, Stormyrplunen, and deposits in Alaskan/Ural-type intrusions), attesting
to the Ni, Cu, and PGE potential of deposits associated with subduction-zone settings. 相似文献
163.
An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cádiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB–), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higher-energy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management. Figure
GSTA model for Camposoto Beach, Cádiz, with FB– (finer, better sorted, more negatively skewed) and FB+ (finer, better sorted, less negatively/more positively skewed) textural trends dominating the lower and upper foreshore respectively 相似文献
164.
M. Hénon 《Celestial Mechanics and Dynamical Astronomy》1977,15(1):99-105
We show the existence of a general relation between the parameters of periodic solutions in dynamical systems with ignorable coordinates. In particular, for time-independent systems with an axis of symmetry, the relation takes the form T/A=–/E, whereT is the period,A is the angular momentum, is the angle through which the system has rotated after one period, andE is the energy. 相似文献
165.
M. Hénon 《Celestial Mechanics and Dynamical Astronomy》1977,15(2):243-261
A family of rectilinear periodic solutions of the three-body problem, in which the central body collides alternately with each of the two other bodies, is investigated numerically for all values of the three masses. It is found that for every mass combination there exists just one solution of this kind. The linear stability of the orbits with respect to arbitrary three-dimensional perturbations is also investigated. Domains of stability and instability are displayed in a triangular mass diagram. Their boundaries form one-parameter families of critical orbits, which are tabulated. Limiting cases where one or two masses vanish are studied in detail. The domains of stability cover nearly one half of the total area in the mass diagram: this reinforces the conclusion that real triple stars might have motions of a kind entirely different from the usual hierarchical arrangement. 相似文献
166.
The north-south incidence has been studied of 31 white-light flares observed since 1859 and of 1669 events meeting the criteria for major flares of Dodson and Hedeman (1971) for the period 1955–1974. The asymmetry in favor of the northern hemisphere increases strikingly with the importance of the events. Similarly, magnetically complex sunspot groups (Mt. Wilson classes, and) display a more pronounced asymmetry in favor of the north than non-complex groups for 1962–1970. Contrary to the flare asymmetry, the spottedness asymmetry is independent of the size of sunspots. 相似文献
167.
Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance
of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The
sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km2 year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or
catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This
requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology
(precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from
an alluvial evaporite karst area (0.81 km2) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features
attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability
of occurrence of 0.14 sinkholes/km2 year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule
out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km2 year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter
may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes
allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse
structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence.
Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions
with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial
karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes. 相似文献
168.
Summary TheIAU Symposium No. 61 (Perth, 1973, “New Problems in Astrometry’) makes clear that radiosources will play an important role for astrometry
in view of the linkage of reference systems.
The purposes developed later were to link the various systems from the earth and the solar system to the most inertial possible
one.
Extragalactic radiosources are the most reliable objects but they are faint. So, intermediate objects are needed. Among them
the radiostars, optical objects having radioemission at a certain level and for given frequencies have a fundamental and key
position.
Most of such radiostars are double or multiple ‘binaries’ as it can be seen from the list of reference stars issued by the
Working Group of Commission 24, Working Group created in 1978. The last issue of the core list of radiostars was presented
by Ch. de Vegt (Chairman of the WG) on the occasion of the last General Assembly of the IAU (November 1985).
A recent study of the system α Scorpii (Antares) has shown that the data concerning the magnitude and the spectral type are
not accurate enough, according to the accuracy obtained for the astrometric position (±0
.
s
003 for an astrolabe campaign in right ascension).
There is also a need for better knowledge about the orbits. In the case of the astrolabe observations, if the distance between
the components in <3″ the astrometric position concerns the photocenter and accurate physical properties are needed for comparison
with the radio position.
Better astrophysical properties are strongly needed for all radiostars to be used as references, during the time the astrometrists
have to improve the accuracy of their measurements both in optical and radio fields.
Presented by S. Débarbat. 相似文献
169.
Exploration of remotely sensed forest structure and ultrasonic range sensor metrics to improve empirical snow models 下载免费PDF全文
Current methods to estimate snow accumulation and ablation at the plot and watershed levels can be improved as new technologies offer alternative approaches to more accurately monitor snow dynamics and their drivers. Here we conduct a meta‐analysis of snow and vegetation data collected in British Columbia to explore the relationships between a wide range of forest structure variables – obtained from Light Detection and Ranging (LiDAR), hemispherical photography (HP) and Landsat Thematic Mapper – and several indicators of snow accumulation and ablation estimated from manual snow surveys and ultrasonic range sensors. By merging and standardizing all the ground plot information available in the study area, we demonstrate how LiDAR‐derived forest cover above 0.5 m was the variable explaining the highest percentage of absolute peak snow water equivalent (SWE) (33%), while HP‐derived leaf area index and gap fraction (45° angle of view) were the best potential predictors of snow ablation rate (explaining 57% of variance). This study reveals how continuous SWE data from ultrasonic sensors are fundamental to obtain statistically significant relationships between snow indicators and structural metrics by increasing mean r2 by 20% when compared to manual surveys. The relationships between vegetation and spectral indices from Landsat and snow indicators, not explored before, were almost as high as those shown by LiDAR or HP and thus point towards a new line of research with important practical implications. While the use of different data sources from two snow seasons prevented us from developing models with predictive capacity, a large sample size helped to identify outliers that weakened the relationships and suggest improvements for future research. A concise overview of the limitations of this and previous studies is provided along with propositions to consistently improve experimental designs to take advantage of remote sensing technologies, and better represent spatial and temporal variations of snow. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
170.
Dr. C. C. Wallén 《Pure and Applied Geophysics》1950,18(1):175-178
Summary A review is given of the investigations on variations in the general circulation in middle latitudes made byWillett andPetterssen. According toWillett a «high-index» type of circulation pattern with a strong zonal flow has probably caused the recent climatic improvement in the northern latitudes while the «low-index» type with meridional flow would create a cooling off in the same areas. According toPetterssen an other type of «low-index» pattern with a weak zonal flow and strong meridional exchange of air has been the essential cause of the warming up of the northern latitudes in Europe. This implies that the definition of the «low-index» type is not clear and gives rise to misunderstanding. Making use of our experience on glacier retreat in northern Scandinavia it is concluded that thePetterssen type of circulation more probably than the «high-index» type has caused the warming-up in the North Atlantic area from which the retreat of the glaciers has followed. 相似文献