全文获取类型
收费全文 | 361篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 38篇 |
地球物理 | 113篇 |
地质学 | 72篇 |
海洋学 | 49篇 |
天文学 | 69篇 |
综合类 | 1篇 |
自然地理 | 17篇 |
出版年
2020年 | 3篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 11篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 14篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1970年 | 4篇 |
1962年 | 3篇 |
1953年 | 3篇 |
1949年 | 3篇 |
排序方式: 共有377条查询结果,搜索用时 531 毫秒
61.
K. Nishiizumi J.R. Arnold M.W. Caffee J. Masarik 《Geochimica et cosmochimica acta》2009,73(7):2163-449
Cosmic ray produced 10Be (half-life = 1.36 × 106 yr), 26Al (7.05 × 105 yr), and 36Cl (3.01 × 105 yr) were measured in a depth profile of 19 carefully-ground samples from the glass-coated lunar surface rock 64455. The solar cosmic ray (SCR) produced 26Al and 36Cl in this rock are present in high concentrations, which in combination with the low observed erosion rate, <0.5 mm/Myr, provide well defined depth profiles characterizing the SCR component of the cosmic rays. In conjunction with new experimentally determined excitation functions, the 36Cl concentrations suggest a softer solar-proton spectral shape than that derived from most previous measurements. The fact that no SCR-produced 10Be activity could be detected in 64455 is in good agreement with observations in 68815 and also indicates a softer SCR spectrum. Comparison of observed SCR profiles in 64455 with theoretical calculations indicates that the average solar-proton spectrum over the past 2 Myr (based on 26Al) has an exponential rigidity parameter (R0) of about 90 MV with a proton flux (J) of 73 protons/cm2/s·4π above 10 MeV. Over the last ∼0.5 Myr (based on 36Cl) R0 is about 70 MV with a flux of ∼196 protons/cm2/s·4π above 10 MeV. These SCR fluxes are consistent with most previous work. 相似文献
62.
63.
Ohne Zusammenfassung 相似文献
64.
A broadband radio spectrometer has been put into operation at Bleien, Switzerland, to register the flare emission of the full
Sun. In the frequency range of operation, 0.1 to 4.0 GHz, both modes of circular polarization are recorded continuously. The
new system, Phoenix-2, has been developed from the experience with the previous Phoenix spectrometer. Improved, computer-controlled
focal hardware allows now a complete daily calibration, a more sophisticated calibration procedure, and monitoring of all
essential instrumental and environmental parameters. Calibrated data are now usually available the day after observation and
are accessible through the Internet. The scientific improvements include a larger frequency range of observation, a larger
number of completely recorded events due to full-day registration, more accurate measurements, particularly in circular polarization,
and more reliable operation. First observations are presented and quantitative results comparing the calibration with single
frequency instruments are reported.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005194314845 相似文献
65.
Gaboury Benoit Tim F. Rozan Peter C. Patton Chester L. Arnold 《Estuaries and Coasts》1999,22(1):65-80
Many small estuaries are influenced by flow restrictions resulting from transportation rights-of-way and other causes. The biogeochemical functioning and history of such systems can be evaluated through study of their sediments. Ten long and six short cores were collected from the length of Jordan Cove, Connecticut, a Long Island Sound subestuary, and analyzed for stratigraphy, radionuclides (14C, 210Pb, 226Ra, 137Cs, and 60Co), and metals (Ag, Cd, Cu, Pb, Zn, Fe, and Al). For at least 3,800 yr, rising sea level has gradually inundated Jordan Cove, filling it with mud similar to that currently being deposited there. Long-term sediment accumulation in the cove averaged close to 0.1 cm yr−1 over the last three millennia. Recent sediment accumulation rates decrease inland from 0.84 cm yr−1 to 0.40 cm yr−1, and are slightly faster than relative sea-level rise at this site (0.3 cm yr−1). Similarity of depth distributions of trace metals was used to confirm relative sediment accumulation rates. 60Co and Ag are derived from sources outside the cove and its watershed, presumably the Millstone nuclear power plant and regional contaminated sediments, respectively. The combined data suggest that Long Island Sound is an important source of sediment to the cove; a minor part of total sediment is supplied from the local watershed. Trace metal levels are strongly correlated with Fe but not with either organic matter or Al. Sediment quality has declined in the cove over the past 60 yr, but only slightly. Cu, Pb, and Zn data correlate strongly with Fe but not with either organic matter or aluminum. Ratios of Ag to Fe and to trace metals suggest that Ag in the cove is derived almost entirely from Long Island Sound. This result supports the notion that Fenormalized Ag can serve as a better tracer of some kinds of contamination than more common and abundant metals, like Cu, Pb, and Zn. *** DIRECT SUPPORT *** A01BY085 00008 相似文献
66.
67.
Masao SAKAMOTO Arnold GUCSIK Hirotsugu NISHIDO Kiyotaka NINAGAWA Tasuku OKUMURA Shin TOYODA 《Meteoritics & planetary science》2010,45(1):32-42
Abstract– Planar deformation features (PDFs) and planar fractures (PFs) have been found and confirmed by optical microscope observations and microRaman spectroscopy in quartz grains from Mt. Oikeyama (Akaishi Mountains, Central Japan), for which the semicircular topographic feature of the ridge suggests a crater formed by an impact event. According to the optical microscope observations, a low shock pressure (8–10 GPa) is estimated by the occurrence of basal or ω PDFs leading to lack of multiple sets of PDFs. In addition, a new type of planar microstructure was found in several quartz grains. The microRaman characteristics of PDFs in quartz from Mt. Oikeyama show the amorphous state indicating the presence of weak broad bands at 400 and 800 cm?1 peak positions. These characteristics are indicative of PDFs that are limited to shocked quartz. This indicates an impact origin for distinct planar microstructures in quartz from Mt. Oikeyama. 相似文献
68.
Do landslides follow landslides? Insights in path dependency from a multi-temporal landslide inventory 总被引:1,自引:0,他引:1
Jalal Samia Arnaud Temme Arnold Bregt Jakob Wallinga Fausto Guzzetti Francesca Ardizzone Mauro Rossi 《Landslides》2017,14(2):547-558
Landslides are a major category of natural disasters, causing loss of lives, livelihoods and property. The critical roles played by triggering (such as extreme rainfall and earthquakes), and intrinsic factors (such as slope steepness, soil properties and lithology) have previously successfully been recognized and quantified using a variety of qualitative, quantitative and hybrid methods in a wide range of study sites. However, available data typically do not allow to investigate the effect that earlier landslides have on intrinsic factors and hence on follow-up landslides. Therefore, existing methods cannot account for the potentially complex susceptibility changes caused by landslide events. In this study, we used a substantially different alternative approach to shed light on the potential effect of earlier landslides using a multi-temporal dataset of landslide occurrence containing 17 time slices. Spatial overlap and the time interval between landslides play key roles in our work. We quantified the degree to which landslides preferentially occur in locations where landslides occurred previously, how long such an effect is noticeable, and how landslides are spatially associated over time. We also investigated whether overlap with previous landslides causes differences in landslide geometric properties. We found that overlap among landslides demonstrates a clear legacy effect (path dependency) that has influence on the landslide affected area. Landslides appear to cause greater susceptibility for follow-up landslides over a period of about 10 years. Follow-up landslides are on average larger and rounder than landslides that do not follow earlier slides. The effect of earlier landslides on follow-up landslides has implications for understanding of the landslides evolution and the assessment of landslide susceptibility. 相似文献
69.
70.
Research on gas hydrate has increased recently as an alternative to fossil fuel. This study of marine controlled source electromagnetics (CSEM) is motivated by this increase, particularly in deep waters, and examines representative models. We present 2D models and test their efficacy in detection and characterization of gas hydrates. Earlier modeling studies used a horizontal transmitter to study the CSEM response??two electrical and one magnetic component??for resistive subsurface layers. Here we use six components??three electrical and three magnetic??and show that the proposed method reduces ambiguity in interpretation. Additionally, we show results utilizing the transmitter dipole in a borehole and receivers at the sea bottom. We found that CSEM response from a vertical transmitter helps us characterize resistive layers more confidently than from a transmitter moving horizontally at sea bottom. We conclude that in a complex environment, combining horizontal and vertical movements of the transmitter with sea-bottom receivers helps us delineate the subsurface structure more clearly and may help reduce drilling costs. Our models closely match the gas hydrate region in the Gulf of Mexico??Walker Ridge Block-313. Although this study examines gas hydrate, the methodology is applicable to other areas??for example, in monitoring gas diffusion at subsurface depths, which may help in CO2 sequestration. 相似文献