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991.
We explore flat ΛCDM models with bulk viscosity, and study the role of the bulk viscosity in the evolution of these universe
models. The dynamical equations for these models are obtained and solved for some cases of bulk viscosity. We obtain differential
equations for the Hubble parameter H and the energy density of dark matter ρ
m
, for which we give analytical solutions for some cases and for the general case we give a numerical solution. Also we calculate
the statefinder parameters for these models and display them in the s–r-plane. 相似文献
992.
Near-Earth asteroid (99942) Apophis currently resides among the top positions on the list of objects with small, yet non-zero impact probability with the Earth. For that reason an unusual observational and theoretical effort has been dedicated to precisely characterize its future orbit. Here we discuss orbital perturbation of Apophis due to incident and reflected solar radiation pressure (SRP). We both revisit recent analytical estimate of the SRP effects for this body and also formulate a numerical approach allowing us to compute the SRP orbital perturbation under general assumptions. Contrary to some previous results, we show that SRP has a much smaller effect on the Apophis trajectory than does the thermal re-radiation force which produces the Yarkovsky effect. When the Yarkovsky effect becomes constrained enough in the future, our approach may be used to improve the orbit determination for this asteroid. 相似文献
993.
?uk et al. (?uk, M. Gladman, B.J., Stewart, S.T. [2010]. Icarus 207 590-594) concluded that the the lunar cataclysm (late heavy bombardment) was recorded in lunar Imbrian era craters, and that their size distribution is different from that of main belt asteroids (which may have been the dominant pre-Imbrian impactors). This result would likely preclude the asteroid belt as the direct source of lunar cataclysm impactors. Malhotra and Strom (Malhotra, R., Strom, R.G. [2011]. Icarus) maintain that the lunar impactor population in the Imbrian era was the same as in Nectarian and pre-Nectarian periods, and this population had a size distribution identical to that of main belt asteroids. In support of this claim, they present an Imbrian size distribution made from two data sets published by Wilhelms et al. (Wilhelms, D.E., Oberbeck, V.R., Aggarwal, H.R. [1978]. Proc. Lunar Sci. Conf. 9, 3735-3762). However, these two data sets cannot be simply combined as they represent areas of different ages and therefore crater densities. Malhotra and Strom (Malhotra, R., Strom, R.G. [2011]. Icarus) differ with the main conclusion of Wilhelms et al. (Wilhelms, D.E., Oberbeck, V.R., Aggarwal, H.R. [1978]. Proc. Lunar Sci. Conf. 9, 3735-3762) that the Nectarian and Imbrian crater size distributions were different. We conclude that the available data indicate that the lunar Imbrian-era impactors had a different size distribution from the older ones, with the Imbrian impactor distribution being significantly richer in small impactors than that of older lunar impactors or current main-belt asteroids. 相似文献
994.
995.
Handbook of Hydrogeology is a professional reference book guiding the work and re-search of hydrogeology and providing enlightenment to hydrogeologists and those working in re-lated fields. This paper introduces the revision and enlargement of Handbook of Hydro-geology (2nd edition) on the basis of its first edition. It gives a brief account of the background, principles, and necessity of revising the handbook. The content, features and application of the handbook are also addressed. 相似文献
996.
Stable cosmogenic isotopes such as 3He and 21Ne are useful for dating of diverse lithologies, quantifying erosion rates and ages of ancient surfaces and sediments, and for assessing complex burial histories. Although many minerals are potentially suitable targets for 3He and 21Ne dating, complex production systematics require calibration of each mineral–isotope pair. We present new results from a drill core in a high-elevation ignimbrite surface, which demonstrates that cosmogenic 3He and 21Ne can be readily measured in biotite and hornblende. 21Ne production rates in hornblende and biotite are similar, and are higher than that in quartz due to production from light elements such as Mg and Al. We measure 21Nehbl/21Neqtz = 1.35 ± 0.03 and 21Nebio/21Neqtz = 1.3 ± 0.02, which yield production rates of 25.6 ± 3.0 and 24.7 ± 2.9 at g? 1 yr? 1 relative to a 21Neqtz production rate of 19.0 ± 1.8 at g? 1 yr? 1. We show that nucleogenic 21Ne concentrations produced via the reaction 18O(α,n)21Ne are manageably small in this setting, and we present a new approach to deconvolve nucleogenic 21Ne by comparison to nucleogenic 22Ne produced from the reaction 19F(α,n)22Ne in F-rich phases such as biotite. Our results show that hornblende is a suitable target phase for cosmogenic 3He dating, but that 3He is lost from biotite at Earth surface temperatures. Comparison of 3He concentrations in hornblende with previously measured mineral phases such as apatite and zircon provides unambiguous evidence for 3He production via the reaction 6Li(n,α)3H → 3He. Due to the atypically high Li content in the hornblende (~ 160 ppm) we estimate that Li-produced 3He represents ~ 40% of total 3He production in our samples, and must be considered on a sample-specific basis if 3He dating in hornblende is to be widely implemented. 相似文献
997.
Naifang?Bei Fuqing?ZhangEmail author John?W.?Nielsen-Gammon 《Pure and Applied Geophysics》2012,169(3):539-554
This study examines the effectiveness of targeted meteorological observations for improving ozone prediction in Houston and
the surrounding area based on perfect-model simulation experiments. Supplementary observations are targeted for the location
that has the highest impact factor (maximum Kalman gain) estimated from an ensemble and is expected to minimize ozone forecast
uncertainty at the verification time. It is found that the observational impact factor field varies with time and is sensitive
to ensemble resolutions and physics parameterizations. The efficiency of observation targeting is further examined through
assimilating observations in areas with different impact factors using an ensemble Kalman filter. It is found that the ensemble
sensitivity analysis is capable of locating supplementary observations that may reduce meteorological and ozone forecast error,
but not as effectively as expected. 相似文献
998.
999.
Jacek?StankiewiczEmail author Michael?H.?Weber Ayman?Mohsen Rami?Hofstetter 《Pure and Applied Geophysics》2012,169(4):615-623
In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region
of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007
to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term
recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range
from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify
the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean
Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured
between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four
such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving
an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead
Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure
of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of
the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth
of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests. 相似文献
1000.
While it is obvious that large-scale gravity studies should account for the sphericity of the Earth, each case should be examined.
If a geometry model is very large for the 3D-gravity calculation, it cannot be correctly defined in Cartesian coordinates.
Because of the Earth’s curvature it is necessary to use spherical coordinates, the importance of which is shown in this paper.
The calculation of the gravity for a cylinder reveals, 1 m above the center of the cylinder, a relative difference of 13%
between the models with Cartesian and spherical coordinates. 相似文献