全文获取类型
收费全文 | 1025篇 |
免费 | 42篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 109篇 |
地球物理 | 295篇 |
地质学 | 246篇 |
海洋学 | 109篇 |
天文学 | 177篇 |
自然地理 | 111篇 |
出版年
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 54篇 |
2012年 | 26篇 |
2011年 | 47篇 |
2010年 | 43篇 |
2009年 | 53篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 52篇 |
2005年 | 47篇 |
2004年 | 49篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 35篇 |
2000年 | 26篇 |
1999年 | 18篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 23篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有1073条查询结果,搜索用时 477 毫秒
591.
A parameter-estimation technique based on existing hydrological, geophysical, and geological data was developed to approximate transmissivity values for use in a ground-water flow model of the Animas Valley, southwest New Mexico. Complete Bouguer gravity anomaly maps together with seismic-refraction profiles, geologic maps, geologic, geophysical, and drillers' logs, water levels, and pumping-test data provide insight into the transmissivity of bolson deposits throughout the basin. The transmissivity distribution was primarily based on reported pumping and specific-capacity tests in conjunction with complete Bouguer gravity anomaly maps and well log data. Reported transmissivity values were characterized by gravity values and well log data. In grid blocks lacking pumping and specific-capacity tests, transmissivity values were assigned based on the relationship of gravity values and well log data within the grid block to gravity values and well log data within other grid blocks for which transmissivity values are available. A two-dimensional, finite-difference, ground-water flow computer code was used to evaluate the effectiveness of the parameter-estimation technique. Although the trial-and-error method of calibration was employed, the actual computer time necessary for model calibration was minimal. The conceptually straightforward approach for parameter estimation utilizing existing hydrological, geophysical, and geological data provides realistic parameter estimates. 相似文献
592.
Keith Chapman 《Geoforum》1983,14(1):37-44
Most analyses of agglomeration in manufacturing evaluate the merits of clustered and dispersed spatial arrangements of plants in terms of their effects upon the profitability of individual enterprises. However, the problem of defining optimal levels of agglomeration becomes very much more acute if the costs and benefits are considered with reference to society as a whole. Examples of air and water pollution from petrochemical plants in Texas and Louisiana are used to illustrate these difficulties. It is argued that the technology and economics of pollution control have tended to reinforce the cost advantages to industry of agglomeration in large complexes despite the fact that major concentrations of polluting industries may be regarded, from a broader environmental perspective, as intrinsically undesirable. 相似文献
593.
It is physically possible to capture CO2 directly from the air and immobilize it in geological structures. Air capture differs from conventional mitigation in three key aspects. First, it removes emissions from any part of the economy with equal ease or difficulty, so its cost provides an absolute cap on the cost of mitigation. Second, it permits reduction in concentrations faster than the natural carbon cycle: the effects of irreversibility are thus partly alleviated. Third, because it is weakly coupled to existing energy infrastructure, air capture may offer stronger economies of scale and smaller adjustment costs than the more conventional mitigation technologies. We assess the ultimate physical limits on the amount of energy and land required for air capture and describe two systems that might achieve air capture at prices under 200 and 500 $/tC using current technology. Like geoengineering, air capture limits the cost of a worst-case climate scenario. In an optimal sequential decision framework with uncertainty, existence of air capture decreases the need for near-term precautionary abatement. The long-term effect is the opposite; assuming that marginal costs of mitigation decrease with time while marginal climate change damages increase, then air capture increases long-run abatement. Air capture produces an environmental Kuznets curve, in which concentrations are returned to preindustrial levels. 相似文献
594.
Glyn Williams-Jones Keith A. Horton Tamar Elias Harold Garbeil Peter J. Mouginis-Mark A. Jeff Sutton Andrew J. L. Harris 《Bulletin of Volcanology》2006,68(4):328-332
A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately
measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual
plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least
two time-synchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the
time varying structure of SO2 concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on
Kīlauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s−1. Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer
method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic
or industrial gas flux measurements.
Editorial responsibility: A. Woods 相似文献
595.
Etienne Balan Michele Lazzeri Simon Delattre Merlin Méheut Keith Refson Bjoern Winkler 《Physics and Chemistry of Minerals》2007,34(9):621-625
The theoretical anharmonicity of the inner-OH stretching modes of kaolinite and lizardite is determined using a frozen-phonon
approach. The anharmonicity parameter, defined as the difference between half the first overtone frequency and the frequency
of the fundamental transition, is −95 and −92 cm−1 for kaolinite and lizardite, respectively. These values are consistent with the experimental measurements. The very good
agreement usually observed between harmonic calculations of vibrational frequencies at the density functional theory (DFT)
level, using the generalized gradient approximation (GGA), and experimental positions of vibrational bands results from the
fortuitous, but almost exact, cancelation of two types of errors. One is related to the GGA approximation and the other to
the neglect of anharmonicity. 相似文献
596.
597.
Cosmogenic 10Be concentrations in exposed bedrock surfaces and alluvial sediment in the northern Flinders Ranges reveal surprisingly high erosion rates for a supposedly ancient and stable landscape. Bedrock erosion rates increase with decreasing elevation in the Yudnamutana Catchment, from summit surfaces (13·96 ± 1·29 and 14·38 ± 1·40 m Myr?1), to hillslopes (17·61 ± 2·21 to 29·24 ± 4·38 m Myr?1), to valley bottoms (53·19 ± 7·26 to 227·95 ± 21·39 m Myr?1), indicating late Quaternary increases to topographic relief. Minimum cliff retreat rates (9·30 ± 3·60 to 24·54 ± 8·53 m Myr?1) indicate that even the most resistant parts of cliff faces have undergone significant late Quaternary erosion. However, erosion rates from visibly weathered and varnished tors protruding from steep bedrock hillslopes (4·17 ± 0·42 to 14·00 ± 1·97 m Myr?1) indicate that bedrock may locally weather at rates equivalent to, or even slower than, summit surfaces. 10Be concentrations in contemporary alluvial sediment indicate catchment‐averaged erosion at a rate dominated by more rapid erosion (22·79 ± 2·78 m Myr?1), consistent with an average rate from individual hillslope point measurements. Late Cenozoic relief production in the Yudnamutana Catchment resulted from (1) tectonic uplift at rates of 30–160 m Myr?1 due to range‐front reverse faulting, which maintained steep river gradients and uplifted summit surfaces, and (2) climate change, which episodically increased both in situ bedrock weathering rates and frequency–magnitude distributions of large magnitude floods, leading to increased incision rates. These results provide quantitative evidence that the Australian landscape is, in places, considerably more dynamic than commonly perceived. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
598.
599.
Keith E. Schilling 《水文研究》2007,21(18):2415-2424
600.
Compositional data of orthopyroxene crystals obtained by the electron microprobe may be biased unless zoning morphologies are taken into account in the sampling design. Statistical models (predictive or interpretative) based on such data are open to question because the input data, such as correlations, are spurious. In an attempt to propose sampling designs two established crystal zoning morphologies are considered which are (a) the concentric shell-type and (b) sectoral zonations. These zonational types lend themselves well to statistical population modeling and graphical interpretation provided assumptions of chemical invariance hold or are approximated by a stratified sampling design. The statistical designs may be regarded as limiting cases in the sense that relaxations of certain assumptions lead to other population models. Hypersthene crystals from a central portion of the mafic norite formation at the Strathcona Mine, Sudbury irruptive, are examined for zonation. It appears that the trace elements have a different zoning morphology than the major elements of hypersthene. 相似文献