全文获取类型
收费全文 | 1658篇 |
免费 | 80篇 |
国内免费 | 32篇 |
专业分类
测绘学 | 34篇 |
大气科学 | 111篇 |
地球物理 | 442篇 |
地质学 | 602篇 |
海洋学 | 157篇 |
天文学 | 247篇 |
综合类 | 6篇 |
自然地理 | 171篇 |
出版年
2024年 | 5篇 |
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 25篇 |
2020年 | 31篇 |
2019年 | 25篇 |
2018年 | 47篇 |
2017年 | 40篇 |
2016年 | 61篇 |
2015年 | 57篇 |
2014年 | 54篇 |
2013年 | 94篇 |
2012年 | 82篇 |
2011年 | 91篇 |
2010年 | 75篇 |
2009年 | 110篇 |
2008年 | 107篇 |
2007年 | 90篇 |
2006年 | 77篇 |
2005年 | 63篇 |
2004年 | 72篇 |
2003年 | 49篇 |
2002年 | 47篇 |
2001年 | 33篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 24篇 |
1997年 | 17篇 |
1996年 | 29篇 |
1995年 | 18篇 |
1994年 | 22篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 14篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 7篇 |
排序方式: 共有1770条查询结果,搜索用时 15 毫秒
201.
Richard P. Duncan Pavla Fenwick Jonathan G. Palmer Matt S. McGlone Chris S. M. Turney 《Climate Dynamics》2010,35(7-8):1429-1438
The warming trend over the last century in the northern hemisphere (NH) was interrupted by cooling from ad 1940 to 1975, a period during which the southern hemisphere experienced pronounced warming. The cause of these departures from steady warming at multidecadal timescales are unclear; the prevailing explanation is that they are driven by non-uniformity in external forcings but recent models suggest internal climate drivers may play a key role. Paleoclimate datasets can help provide a long-term perspective. Here we use tree-rings to reconstruct New Zealand mean annual temperature over the last 550 years and demonstrate that this has frequently cycled out-of-phase with NH mean annual temperature at a periodicity of around 30–60 years. Hence, observed multidecadal fluctuations around the recent warming trend have precedents in the past, strongly implicating natural climate variation as their cause. We consider the implications of these changes in understanding and modelling future climate change. 相似文献
202.
203.
D.G. Turner V.V. Kovtyukh D.J. Majaess D.J. Lane K.E. Moncrieff 《Astronomische Nachrichten》2009,330(8):807-815
New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small‐amplitude variability at a level of δV = 0.016 ± 0.002 is indicated, with a period of P = 123d.04 ± 0d.06. A weaker second signal may be present at P = 177d.84 ± 0d.18 with δV = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of EB–V = 1.02 ± 0.003, is associated with heavily‐reddened B‐type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ∼10′ to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of rn = 3.5′ and Rc = 14′, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid‐like pulsation, provided that it follows the semi‐period‐luminosity relation expected of such objects. Its inferred luminosity as a cluster member is MV = –7.76 ± 0.10, its age (9 ± 1) × 106 years, and its evolutionary mass ∼19 M⊙. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period‐luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
204.
205.
Calculations of the trapping of heavy noble gases within multiple guest clathrates under Mars-like conditions show that a substantial fraction of the martian Xe, perhaps even the vast majority, could be in clathrates. In addition, the Xe/Kr ratio in the clathrates would probably be much higher than in the atmosphere, so the formation or dissociation of a relatively small amount of clathrate could measurably change the atmospheric ratio. Relatively crude (factor of 2) measurements of the seasonal variability in that ratio by in situ spacecraft would be sensitive to ∼10% of the seasonal atmospheric CO2 variability being a result of clathrates, rather than pure CO2 frost. In addition, sequestration of Xe in clathrates remains a viable mechanism for explaining the variable Xe/Kr ratios seen in different suites of martian meteorites. 相似文献
206.
Thomas G. Müller Emmanuel Lellouch Hermann Böhnhardt John Stansberry Antonella Barucci Jacques Crovisier Audrey Delsanti Alain Doressoundiram Elisabetta Dotto René Duffard Sonia Fornasier Olivier Groussin Pedro J. Gutiérrez Olivier Hainaut Alan W. Harris Paul Hartogh Daniel Hestroffer Jonathan Horner Dave Jewitt Mark Kidger Csaba Kiss Pedro Lacerda Luisa Lara Tanya Lim Michael Mueller Raphael Moreno Jose-Luis Ortiz Miriam Rengel Pablo Santos-Sanz Bruce Swinyard Nicolas Thomas Audrey Thirouin David Trilling 《Earth, Moon, and Planets》2009,105(2-4):209-219
Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well. 相似文献
207.
L. N. Berdnikov A. Yu. Kniazev V. V. Kravtsov E. N. Pastukhova D. G. Turner 《Astronomy Letters》2009,35(1):39-44
Cepheids, the principal distance indicators, point to the existence of two inner Galactic spiral arms in the immediate solar neighborhood (within 5 kpc). However, the available Cepheids are clearly insufficient for a detailed study of the structure of these arms. Fortunately, southern-sky monitoring (the ASAS project) has led to the discovery of many new variable stars, more than one thousand of which have been identified as possible Cepheids. To improve the classification and to construct reliable light curves for new Cepheids, we have begun their regular photometric observations. Here, we present the first results: 1192 photoelectricBV I c observations were performed for 33 classical Cepheidswith the 76-cm telescope of the South-African Astronomical Observatory (SAAO, the South-African Republic) from December 2006 to January 2008. We provide tables of observations and V light and B-V and V-I c color curves. The new observations together with ASAS-3 data have been used to improve the elements of the light variations. 相似文献
208.
Kai-Uwe Ulrich Eugene S. Ilton Jonathan O. Sharp Rizlan Bernier-Latmani John R. Bargar 《Geochimica et cosmochimica acta》2009,73(20):6065-7290
The long-term stability of biogenic uraninite with respect to oxidative dissolution is pivotal to the success of in situ bioreduction strategies for the subsurface remediation of uranium legacies. Batch and flow-through dissolution experiments were conducted along with spectroscopic analyses to compare biogenic uraninite nanoparticles obtained from Shewanella oneidensis MR-1 and chemogenic UO2.00 with respect to their equilibrium solubility, dissolution mechanisms, and dissolution kinetics in water of varied oxygen and carbonate concentrations. Both materials exhibited a similar intrinsic solubility of ∼10−8 M under reducing conditions. The two materials had comparable dissolution rates under anoxic as well as oxidizing conditions, consistent with structural bulk homology of biogenic and stoichiometric uraninite. Carbonate reversibly promoted uraninite dissolution under both moderately oxidizing and reducing conditions, and the biogenic material yielded higher surface area-normalized dissolution rates than the chemogenic. This difference is in accordance with the higher proportion of U(V) detected on the biogenic uraninite surface by means of X-ray photoelectron spectroscopy. Reasonable sources of a stable U(V)-bearing intermediate phase are discussed. The observed increase of the dissolution rates can be explained by carbonate complexation of U(V) facilitating the detachment of U(V) from the uraninite surface. The fraction of surface-associated U(VI) increased with dissolved oxygen concentration. Simultaneously, X-ray absorption spectra showed conversion of the bulk from UO2.0 to UO2+x. In equilibrium with air, combined spectroscopic results support the formation of a near-surface layer of approximate composition UO2.25 (U4O9) coated by an outer layer of U(VI). This result is in accordance with flow-through dissolution experiments that indicate control of the dissolution rate of surface-oxidized uraninite by the solubility of metaschoepite under the tested conditions. Although U(V) has been observed in electrochemical studies on the dissolution of spent nuclear fuel, this is the first investigation that demonstrates the formation of a stable U(V) intermediate phase on the surface of submicron-sized uraninite particles suspended in aqueous solutions. 相似文献
209.
Jonathan P. WILLIAMS 《Meteoritics & planetary science》2012,47(12):1915-1921
Abstract– I summarize recent surveys of protoplanetary disks at millimeter wavelengths and show that the distribution of luminosity, equivalent to the mass in small dust grains, declines rapidly. This contrasts with statistics on the lifetime of disks from infrared observations and the high occurrence of planets from radial velocity and transit surveys. I suggest that these disparate results can be reconciled if most of the dust in a disk is locked up in millimeter and larger‐sized particles within about 2 Myr. This statistical result on disk evolution agrees with detailed modeling of a small number of individual disks and with cosmochemical measurements of rapid planetesimal formation. 相似文献
210.
Jonathan Horner Olivier Mousis Jonathan I. Lunine 《Planetary and Space Science》2008,56(12):1585-1595
We consider the role of deuterium as a potential marker of location and ambient conditions during the formation of small bodies in our Solar system. We concentrate in particular on the formation of the regular icy satellites of Jupiter and the other giant planets, but include a discussion of the implications for the Trojan asteroids and the irregular satellites. We examine in detail the formation of regular planetary satellites within the paradigm of a circum-Jovian subnebula. Particular attention is paid to the two extreme potential subnebulae—“hot” and “cold”. In particular, we show that, for the case of the “hot” subnebula model, the D:H ratio in water ice measured from the regular satellites would be expected to be near-Solar. In contrast, satellites which formed in a “cold” subnebula would be expected to display a D:H ratio that is distinctly over-Solar. We then compare the results obtained with the enrichment regimes which could be expected for other families of icy small bodies in the outer Solar system—the Trojan asteroids and the irregular satellites. In doing so, we demonstrate how measurements by Laplace, the James Webb Space Telescope, HERSCHEL and ALMA will play an important role in determining the true formation locations and mechanisms of these objects. 相似文献