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901.
Robert C. Anderson Gregory H. Peters Louise Jandura Kenneth Manatt Erik Pounders Dan Sunshine 《Icarus》2009,204(2):545-7971
We report on the nature of fine particle (<150 μm) transport under simulated martian conditions, in order to better understand the Mars Science Laboratory’s (MSL) sample acquisition, processing and handling subsystem (SA/SPaH). We find that triboelectric charging due to particle movement may have to be controlled in order for successful transport of fines that are created within the drill, processed through the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample handing system, and delivered to the Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. These fines will be transferred from the surface material to the portioner, a 3 mm diameter, 8 mm deep distribution center where they will drop ∼2 cm to the instrument inlet funnels. In our experiments, movement of different material including terrestrial analogs and martian soil simulants (Mars Mojave Simulant - MMS) resulted in 1-7 nanocoulombs of charge to build up for several different experimental configurations. When this charging phenomenon occurs, several different results are observed including particle clumping, adherence of material on conductive surfaces, or electrostatic repulsion, which causes like-charged particles to move away from each other. This electrostatic repulsion can sort samples based upon differing size fractions, while adhesion causes particles of different sizes to bind into clods. Identifying these electrostatic effects can help us understand potential bias in the analytical instruments and to define the best operational protocols to collect samples on the surface of Mars. 相似文献
902.
Pascal J. Elahi Robert J. Thacker Lawrence M. Widrow Evan Scannapieco 《Monthly notices of the Royal Astronomical Society》2009,395(4):1950-1962
We explore the dependence of the subhalo mass function on the spectral index n of the linear matter power spectrum using scale-free Einstein-de Sitter simulations with n =−1 and −2.5. We carefully consider finite volume effects that may call into question previous simulations of n < −2 power spectra. Subhaloes are found using a 6D friends-of-friends algorithm in all haloes originating from high-σ peaks. For n =−1 , we find that the cumulative subhalo mass function is independent of the parameters used in the subhalo finding algorithm and is consistent with the subhalo mass function found in Λ cold dark matter (ΛCDM) simulations. In particular, the subhalo mass function is well fit by a power-law with an index of α=−0.9 , that is the mass function has roughly equal mass in subhaloes per logarithmic interval in subhalo mass. Conversely, for n =−2.5 , the algorithm parameters affect the subhalo mass function since subhaloes are more triaxial with less well-defined boundaries. We find that the index α is generally larger with α≳−0.75 . We infer that although the subhalo mass function appears to be independent of n so long as n ≳−2 , it begins to flatten as n →−3 . Thus, the common practice of using α≈−1.0 may greatly overestimate the number of subhaloes at the smallest scales in the CDM hierarchy. 相似文献
903.
Robert Chapman Robert S. Priddey Nial R. Tanvir 《Monthly notices of the Royal Astronomical Society》2009,395(3):1515-1522
There is increasing evidence of a local population of short duration gamma-ray bursts (sGRB), but it remains to be seen whether this is a separate population to higher redshift bursts. Here we choose plausible luminosity functions (LFs) for both neutron star binary mergers and giant flares from soft gamma repeaters (SGR), and combined with theoretical and observed Galactic intrinsic rates we examine whether a single progenitor model can reproduce both the overall Burst and Transient Source Experiment (BATSE) sGRB number counts and a local population, or whether a dual progenitor population is required. Though there are large uncertainties in the intrinsic rates, we find that at least a bimodal LF consisting of lower and higher luminosity populations is required to reproduce both the overall BATSE sGRB number counts and a local burst distribution. Furthermore, the best-fitting parameters of the lower luminosity population agree well with the known properties of SGR giant flares, and the predicted numbers are sufficient to account for previous estimates of the local sGRB population. 相似文献
904.
Louise O. V. Edwards † Carmelle Robert Mercedes Mollá Sean L. McGee 《Monthly notices of the Royal Astronomical Society》2009,396(4):1953-1971
We present integral field spectroscopy of the nebular line emission in a sample of nine brightest cluster galaxies (BCGs). The sample was chosen to probe both cooling flow and non-cooling flow clusters, as well as a range of cluster X-ray luminosities. The line emission morphology and velocity gradients suggest a great diversity in the properties of the line emitting gas. While some BCGs show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and MKW 3s), others have extended emission (Abell 1204, Abell 2199), while still others have centrally concentrated emission (Abell 2052). We examine diagnostic line ratios to determine the dominant ionization mechanisms in each galaxy. Most of the galaxies show regions with active galactic nucleus like spectra, however, for two BCGs, Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which can be described by the emission from young stellar populations. The diversity of emission-line properties in our sample of BCGs suggests that the emission mechanism is not universal, with different ionization processes dominating different systems. Given this diversity, there is no evidence for a clear distinction of the emission-line properties between cooling flow and non-cooling flow BCGs. It is not always cooling flow BCGs which show emission (or young stellar populations), and non-cooling flow BCGs which do not. 相似文献
905.
906.
907.
Gunther KLETETSCHKA Robert J. LILLIS Norman F. NESS Mario H. ACUÑA Jack E. P. CONNERNEY Peter J. WASILEWSKI 《Meteoritics & planetary science》2009,44(1):131-140
Abstract— Intense magnetic anomalies over Martian surface suggest preservation of large volumes of very old crust (>3 Gyr) that formed in the presence of a global magnetic field. The global distribution of the magnetic intensities observed above the Martian crust suggests a division into three zones. Zone 1 is where the magnetic signature is negligible or of relatively low intensity at Mars Global Surveyor (MGS) satellite mapping altitude (400 km). Zone 2 is the region of intermediate crustal magnetic amplitudes and zone 3 is where the highest magnetic intensities are measured. Crater demagnetization near zone 3 reveals the presence of rocks with both high magnetic intensity and coercivity. Magnetic analyses of terrestrial rocks show that compositional banding in orogenic zones significantly enhances both magnetic coercivity and thermal remanent magnetization (TRM) efficiency. Such enhancement offers a novel explanation for the anomalously large intensities inferred of magnetic sources on Mars. We propose that both large magnetic coercivity and intensity near the South Pole is indicative of the presence of a large degree of deformation. Associated compositional zoning creates conditions for large scale magnetic anisotropy allowing magnetic minerals to acquire magnetization more efficiently, thereby causing the distinct magnetic signatures in zone 3, expressed by intense magnetic anomalies. We use a simple model to verify the magnetic enhancement. We hypothesize that magnetically enhanced zone would reside over the down welling plume at the time of magnetization acquisition. 相似文献
908.
We use reactive transport modeling to better understand the kinetics of chemical weathering in the Cretaceous Middendorf aquifer of South Carolina, USA, and the relationship of this process to subsurface microbial activity. We constructed a model accounting for the kinetics of mineral dissolution and precipitation, ion exchange, and the CO2 and bicarbonate produced by iron reducing and sulfate reducing bacteria in the aquifer. We then fit the model to observed trends in the chemical composition of groundwater along the aquifer by adjusting the rate constants for the kinetic reactions considered. The modeling portrays weathering in the Middendorf as a slow process by which groundwater gradually reacts toward equilibrium with minerals in the aquifer. The rate constants predicted are 6 to 7 orders of magnitude smaller than measured in laboratory experiments and 3 to 4 orders of magnitude less than those inferred from weathering rates in soils. The rate constants are smaller even than expected by projecting observed trends with the duration of weathering to the geologic age of the Middendorf. Weathering is driven largely by biological activity: about half the acid consumed is CO2 derived from the recharge area, and about half is supplied by iron reducing bacteria in the aquifer; only about 1% of the acid is of atmospheric origin, from CO2 dissolved in rainwater. 相似文献
909.
The activity of silica in kimberlites,revisited 总被引:1,自引:1,他引:0
Robert W. Luth 《Contributions to Mineralogy and Petrology》2009,158(2):283-294
The activity of silica in a silicate liquid in equilibrium with olivine and orthopyroxene decreases with increasing pressure. In contrast, the activity of silica in
an unbuffered silicate liquid changes little with pressure. Although the implications of these pressure dependencies have
been considered by previous authors in terms of inferring pressures of origin of magmas, less consideration has been given
to the implications of these dependencies on the evolution of the magma en route to the surface, or to the mantle through
which the magma passes. In this paper, a combination of Schreinemakers’ analysis in isothermal section and calculated reactions in space is used to (a) rationalize the absence of orthopyroxene xenocrysts in kimberlites and the relative abundance of olivine
“megacrysts” therein, (b) propose another reason for the paucity of xenocrystic mantle-derived carbonates in kimberlites,
(c) explain why clinopyroxene is much less reactive in the kimberlite melt than is orthopyroxene, and (d) explore the implications
of the relative stabilities of olivine, orthopyroxene, and clinopyroxene in kimberlitic magma for the mantle through which
the magma transits.
相似文献
Robert W. LuthEmail: |
910.
Ying Wang Alex L. Sessions Robert J. Nielsen William A. Goddard III 《Geochimica et cosmochimica acta》2009,73(23):7060-7075
Carbon-bound hydrogen in sedimentary organic matter can undergo exchange over geologic timescales, altering its isotopic composition. Studies investigating the natural abundance distribution of 1H and 2H in such molecules must account for this exchange, which in turn requires quantitative knowledge regarding the endpoint of exchange, i.e., the equilibrium isotopic fractionation factor (αeq). To date, relevant data have been lacking for molecules larger than methane. Here we describe an experimental method to measure αeq for C-bound H positions adjacent to carbonyl group (Hα) in ketones. H at these positions equilibrates on a timescale of days as a result of keto-enol tautomerism, allowing equilibrium 2H/1H distributions to be indirectly measured. Molecular vibrations for the same ketone molecules are then computed using Density Functional Theory at the B3LYP/6-311G** level and used to calculate αeq values for Hα. Comparison of experimental and computational results for six different straight and branched ketones yields a temperature-dependent linear calibration curve with slope = 1.081−0.00376T and intercept = 8.404−0.387T, where T is temperature in degrees Celsius. Since the dominant systematic error in the calculation (omission of anharmonicity) is of the same size for ketones and C-bound H in most other linear compounds, we propose that this calibration can be applied to analogous calculations for a wide variety of organic molecules with linear carbon skeletons for temperatures below 100 °C. In a companion paper (Wang et al., 2009) we use this new calibration dataset to calculate the temperature-dependent equilibrium isotopic fractionation factors for a range of linear hydrocarbons, alcohols, ethers, ketones, esters and acids. 相似文献