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161.
Combination of different space-geodetic observations for regional ionosphere modeling 总被引:2,自引:1,他引:1
Denise Dettmering Michael Schmidt Robert Heinkelmann Manuela Seitz 《Journal of Geodesy》2011,85(12):989-998
Most of the space-geodetic observation techniques can be used for modeling the distribution of free electrons in the Earth’s
ionosphere. By combining different techniques one can take advantage of their different spatial and temporal distributions
as well as their different observation characteristics and sensitivities concerning ionospheric parameter estimation. The
present publication introduces a procedure for multi-dimensional ionospheric modeling. The model consists of a given reference
part and an unknown correction part expanded in terms of B-spline functions. This approach is used to compute regional models
of Vertical Total Electron Content (VTEC) based on the International Reference Ionosphere (IRI 2007) and GPS observations
from terrestrial Global Navigation Satellite System (GNSS) reference stations, radio occultation data from Low Earth Orbiters
(LEOs), dual-frequency radar altimetry measurements, and data obtained by Very Long Baseline Interferometry (VLBI). The approach
overcomes deficiencies in the climatological IRI model and reaches the same level of accuracy than GNSS-based VTEC maps from
IGS. In areas without GNSS observations (e.g., over the oceans) radio occultations and altimetry provide valuable measurements
and further improve the VTEC maps. Moreover, the approach supplies information on the offsets between different observation
techniques as well as on their different sensitivity for ionosphere modeling. Altogether, the present procedure helps to derive
improved ionospheric corrections (e.g., for one-frequency radar altimeters) and at the same time it improves our knowledge
on the Earth’s ionosphere. 相似文献
162.
Can pharmaceuticals interfere with the synthesis of active androgens in male fish? An in vitro study 总被引:1,自引:0,他引:1
The in vitro interference of fibrate (gemfibrozil, clofibrate, clofibric acid), anti-inflammatory (ibuprofen, diclofenac), and anti-depressive (fluoxetine, fluvoxamine) drugs with key enzymatic activities—C17,20-lyase and CYP11β-involved in the synthesis of active androgens in gonads of male carp have been investigated. Among the tested compounds, fluvoxamine and fluoxetine were the strongest inhibitors of C17,20-lyase and CYP11β enzymes, with IC50s in the range of 321-335 μM and 244-550 μM, respectively. To our knowledge this is the first report on the interaction of pharmaceutical compounds with enzymatic systems involved in the synthesis of oxy-androgens. As oxy-androgens are known to influence spermatogenesis and stimulate reproductive behavior and secondary sexual characteristics in male fish, this work highlights the need for further investigating these endpoints when designing specific in vivo studies to assess the endocrine disruptive effect of pharmaceuticals in fish. 相似文献
163.
Ecosystem-based management (EBM) has been widely accepted as the new paradigm to manage marine ecosystems. Although various efforts have been made to define key components, guidelines, and principles, in support of its implementation, there is still a gap between theory and practice. To implement EBM, managers require a decision-making framework in which the values of constituents, objectives and performance measures are consistent and used to evaluate and choose between alternatives. Structured decision-making (SDM) is a systematic approach that can contribute to develop this framework for EBM. SDM was used for the on-going EBM process on the west coast of Vancouver Island, British Columbia, Canada. This case study provides insights into how SDM can be implemented for EBM, as well as some challenges and opportunities encountered during the process. 相似文献
164.
Juraj Majzlan Hannes Schlicht Maria Wierzbicka-Wieczorek Gerald Giester Herbert Pöllmann Beatrix Brömme Stephen Doyle Gernot Buth Christian Bender Koch 《Mineralogy and Petrology》2013,107(2):221-233
Voltaite is a mineral of fumaroles, solfatares, coal-fire gas vents, and acid-mine drainage systems. The nominal composition is K2Fe5 2+Fe3 3+Al(SO4)12·18H2O and the nominal symmetry is cubic, $Fd\overline{3}c$ . The tetragonal (I41/acd) superstructure of voltaite is known as the mineral pertlikite. In this study, we investigated 22 synthetic voltaite samples in which Fe2+ was partially or completely replaced by Mg, Zn, Mn, or Cd, by single-crystal and powder X-ray diffraction (both in-house and synchrotron). Two samples contained NH4 + instead of K+. The structure of voltaite is based on a framework defined by kröhnkite-like heteropolyhedral chains which host both M3+ and M2+ in octahedral coordination. Unit cell dimensions of the end-members scale almost linearly with the size of M2+. In the Fe2+-Mg-Zn solid solutions, the Fe2+-Mg and Fe2+-Zn solutions are linear (ideal) in terms of their lattice-parameter variations. The Mg-Zn solid solution, however, is strongly non-ideal. A detailed analysis of the topology of the chains showed that this behavior originates in expansion and contraction of individual M2+-O bonds within the chains. In the Mg-Zn solid solution, some of the M2+-O bonds expand while none contract. In the other solid solutions, expansion of some M2+-O bonds is always compensated by contraction of the other ones. Parts of the nominally cubic crystals are optically anisotropic and their symmetry is found to be tetragonal by single crystal X-ray diffraction measurements. The coexistence of cubic and tetragonal sectors within a single crystal without any detectable difference in their chemical composition is difficult to explain in terms of growth of such composite crystals. Mössbauer and infrared spectra collected on our synthetic crystals conform with previously published data. 相似文献
165.
Denise C. Gabuzda 《Astrophysics and Space Science》2003,288(1-2):39-50
The paper summarises the results to date of an ongoing multi-epoch, multi-frequency polarisation VLBI study of a complete sample of northern 1-Jy BL Lac objects. We discuss the physical origin of the characteristic polarisation properties of the core and jet structures as revealed by both general trends for the sample as a whole and more detailed observations of individual objects. It has been known for a decade that the distribution of the core polarisation position angles at moderate centimeter wavelengths is bimodal, with the corepolarisation angle being either aligned with or perpendicular to the direction of the inner VLBI jet. A preliminary analysis of the VLBI core spectral indices from 15–5 GHz suggests that this is the result of optical depth effects and that the two peaks in the distribution correspond to cores dominated by optically thin and thick regions of emission. This interpretation is supported by the results of quasi-simultaneous VLBI and optical polarisation observations, and also by VSOP polarisation observations of OJ287. Evidence for the presence of helical or toroidal magnetic fields associated with the VLBIjets is discussed. The collected results are discussed in the context of their possible implications for circular-polarisation studies of AGN. We are now beginning a search for parsec-scale circular polarisation in the complete sample BL Lac objects and hope to have our first results by June 2003. 相似文献
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