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71.
Flotation modelling to date has concentrated either on macroscale processes or on ideal microscale processes — there has been no attempt to integrate detailed models at different scales. In this paper, bubble-particle collision efficiency with mobile bubble surfaces in a turbulent flow is investigated from a multiscale modelling viewpoint and a general methodology for modelling is present. Comparisons are carried out to illustrate the method. Turbulence effects on bubble-particle collision efficiency are systematically studied using a 3D k–ε turbulence model. 相似文献
72.
Natalia Hauser Wolf Uwe Reimold Aaron J. Cavosie Alvaro P. Crsta Winfried H. Schwarz Mario Trieloff Carolinna Da Silva Maia de Souza Luciana A. Pereira Eduardo N. Rodrigues Matthews Brown 《Meteoritics & planetary science》2019,54(10):2286-2311
A silicious impact melt rock from polymict impact breccia of the northern part of the alkali granite core of the Araguainha impact structure, central Brazil, has been investigated. The melt rock is thought to represent a large mass of impact‐generated melt in suevite. In particular, a diverse population of zircon grains, with different impact‐induced microstructures, has been analyzed for U‐Pb isotopic systematics. Backscattered electron and cathodoluminescence images reveal heterogeneous intragrain domains with vesicular, granular, vesicular plus granular, and vesicular plus (presumably) baddeleyite textures, among others. The small likely baddeleyite inclusions are not only preferentially located along grain margins but also occur locally within grain interiors. LA‐ICP‐MS U‐Pb data from different domains yield lower intercept ages of 220, 240, and 260 Ma, a result difficult to reconcile with the previous “best age” estimate for the impact event at 254.7 ± 2.7 Ma. SIMS U‐Pb data, too, show a relatively large range of ages from 245 to 262 Ma. A subset of granular grains that yielded concordant SIMS ages were analyzed for crystallographic orientation by EBSD. Orientation mapping shows that this population consists of approximately micrometer‐sized neoblasts that preserve systematic orientation evidence for the former presence of the high‐pressure polymorph reidite. In one partially granular grain (#36), the neoblasts occur in linear arrays that likely represent former reidite lamellae. Such grains are referred to as FRIGN zircon. The best estimate for the age of the Araguainha impact event from our data set from a previously not analyzed type of impact melt rock is based on concordant SIMS data from FRIGN zircon grains. This age is 251.5 ± 2.9 Ma (2σ, MSWD = 0.45, p = 0.50, n = 4 analyses on three grains), indistinguishable from previous estimates based on zircon and monazite from other impact melt lithologies at Araguainha. Our work provides a new example of how FRIGN zircon can be combined with in situ U‐Pb geochronology to extract an accurate age for an impact event. 相似文献
73.
Filippo Giadrossich Denis Cohen Massimiliano Schwarz Antonio Ganga Roberto Marrosu Mario Pirastru Gian Franco Capra 《地球表面变化过程与地形》2019,44(8):1602-1609
Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks – for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. We therefore designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pull out roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field-measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots, which hold much more force than small roots. © 2019 John Wiley & Sons, Ltd. 相似文献
74.
OPUS-RS is a rapid static form of the National Geodetic Survey’s On-line Positioning User Service (OPUS). Like OPUS, OPUS-RS
accepts a user’s GPS tracking data and uses corresponding data from the U.S. Continuously Operating Reference Station (CORS)
network to compute the 3-D positional coordinates of the user’s data-collection point called the rover. OPUS-RS uses a new
processing engine, called RSGPS, which can generate coordinates with an accuracy of a few centimeters for data sets spanning
as little as 15 min of time. OPUS-RS achieves such results by interpolating (or extrapolating) the atmospheric delays, measured
at several CORS located within 250 km of the rover, to predict the atmospheric delays experienced at the rover. Consequently,
standard errors of computed coordinates depend highly on the local geometry of the CORS network and on the distances between
the rover and the local CORS. We introduce a unitless parameter called the interpolative dilution of precision (IDOP) to quantify
the local geometry of the CORS network relative to the rover, and we quantify the standard errors of the coordinates, obtained
via OPUS-RS, by using functions of the form
here α and β are empirically determined constants, and RMSD is the root-mean-square distance between the rover and the individual
CORS involved in the OPUS-RS computations. We found that α = 6.7 ± 0.7 cm and β = 0.15 ± 0.03 ppm in the vertical dimension
and α = 1.8 ± 0.2 cm and β = 0.05 ± 0.01 ppm in either the east–west or north–south dimension. 相似文献
75.
Adaptive Kalman Filtering for INS/GPS 总被引:69,自引:0,他引:69
After reviewing the two main approaches of adaptive Kalman filtering, namely, innovation-based adaptive estimation (IAE)
and multiple-model-based adaptive estimation (MMAE), the detailed development of an innovation-based adaptive Kalman filter
for an integrated inertial navigation system/global positioning system (INS/GPS) is given. The developed adaptive Kalman filter
is based on the maximum likelihood criterion for the proper choice of the filter weight and hence the filter gain factors.
Results from two kinematic field tests in which the INS/GPS was compared to highly precise reference data are presented. Results
show that the adaptive Kalman filter outperforms the conventional Kalman filter by tuning either the system noise variance–covariance
(V–C) matrix `Q' or the update measurement noise V–C matrix `R' or both of them.
Received: 14 September 1998 / Accepted: 21 December 1998 相似文献
76.
77.
The radial optical depth profile of the Encke ringlet obtained by the occultation experiment of the Voyager photopolarimeter (PPS data) is explained to be caused by the gravitational action of the recently discovered stallite 1981 S13 and a second smaller moonlet orbiting near one of its either libration points — L4 or L5. To this aim the results of previous and new numerical particle simulations as well as an extension of the scattering theory concerning a single moonlet to a pair of satellites have been used leading to a triple-peaked ringlet near the orbits of the moonlets. The width and the shape of that ringlet and its separate peaks depend on the mass ratio of both moonlets and on their orbital eccentricites. The best resemblance between the PPS data and the theoretical profile is obtained if the mass ratio of the either moonlets takes M2/M1981S13 ≈ (0.8 … 3.0) × 10−2 and the eccentricities hold: e1981S13 < h1981S13; e2 ≈ h2 (the values h are the Hill scales of either moonlets defined by h1981S13/2 ≈ (M1981S13/2/3Mh)1/3, Mh = Saturn mass). Furthermore, our results yield a size of 1981 S13 of < 15 km in diameter. 相似文献
78.
79.
Oxygen isotope systematics of emerald: relevance for its origin and geological significance 总被引:2,自引:0,他引:2
G. Giuliani C. France-Lanord P. Coget D. Schwarz A. Cheilletz Y. Branquet D. Giard A. Martin-Izard P. Alexandrov D. H. Piat 《Mineralium Deposita》1998,33(5):513-519
Oxygen isotopic composition of emerald from 62 occurrences and deposits in the world reveals a wide range in δ18O (SMOW) between +6.2 and +24.7‰. The δ18O-values for each deposit are restricted and can be used to determine the origin of emerald from the world's most important
producers. The δ18O-value of emerald appears to be a fingerprint of its origin, especially for gems of exceptional quality from Colombia (eastern
emerald zone, δ18O = +16.8 ± 0.1‰; western emerald zone, δ18O = +21.2 ± 0.5‰), Afghanistan (δ18O = +13.5 ± 0.1‰), Pakistan (Swat-Mingora districts, δ18O = +15.7 ± 0.1‰), Brazil (Santa Terezinha de Goiás, δ18O = +12.2 ± 0.1‰; Quadrilatero Ferrifero, δ18O = +6.9 ± 0.4‰) and Zimbabwe (Sandawana, δ18O = +7.5 ± 0.5‰). Furthermore, the 18O-composition of emerald appears to be a good marker of its geological environment because the data suggest that host-rock-buffering
of fluid δ18O is considerable during fluid-rock interaction.
Received: 29 January 1998 / Accepted: 25 March 1998 相似文献
80.
Greg J. Schwarz Peter H. Hauschildt S. Starrfield P. A. Whitelock E. Baron & G. Sonneborn 《Monthly notices of the Royal Astronomical Society》1998,300(3):931-944
We study star-formation-inducing mechanisms in galaxies through multiwavelength measurements of a sample of dwarf galaxies in the Virgo cluster described in Paper I. Our main goal is to test how star-formation-inducing mechanisms depend on several parameters of the galaxies, such as morphological type and hydrogen content. We derive the star formation rate and star formation histories of the galaxies, and check their dependence on other parameters. Comparison of the sample galaxies with population synthesis models shows that these objects have significantly lower metallicity than the solar value. The colours can generally be explained as a combination of two different stellar populations: a young (3–20 Myr) metal-poor population which represents the stars currently forming presumably in a starburst, and an older (0.1–1 Gyr) population of previous stellar generations. There is evidence that the older stellar population was also formed in a starburst. This is consistent with the explanation that star formation in this type of objects takes place in short bursts followed by long quiescent periods. No significant correlation is found between the star formation properties of the sample galaxies and their hydrogen content. Apparently, when star formation occurs in bursts, other parameters influence the star formation properties more significantly than the amount of atomic hydrogen. No correlation is found between the projected Virgocentric distance and the rate of star formation in the galaxies, suggesting that tidal interactions are not significant in triggering star formation in cluster dwarf galaxies. 相似文献