全文获取类型
收费全文 | 1839篇 |
免费 | 60篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 81篇 |
大气科学 | 105篇 |
地球物理 | 376篇 |
地质学 | 638篇 |
海洋学 | 112篇 |
天文学 | 425篇 |
综合类 | 2篇 |
自然地理 | 165篇 |
出版年
2022年 | 13篇 |
2021年 | 26篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 44篇 |
2017年 | 46篇 |
2016年 | 74篇 |
2015年 | 29篇 |
2014年 | 57篇 |
2013年 | 104篇 |
2012年 | 50篇 |
2011年 | 58篇 |
2010年 | 68篇 |
2009年 | 73篇 |
2008年 | 82篇 |
2007年 | 87篇 |
2006年 | 78篇 |
2005年 | 58篇 |
2004年 | 57篇 |
2003年 | 52篇 |
2002年 | 43篇 |
2001年 | 43篇 |
2000年 | 40篇 |
1999年 | 36篇 |
1998年 | 51篇 |
1997年 | 28篇 |
1996年 | 22篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 24篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 26篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1973年 | 19篇 |
1972年 | 25篇 |
排序方式: 共有1904条查询结果,搜索用时 15 毫秒
71.
Giant gaseous layers(termed "superdisks") have been hypothesized in the past to account for the strip-like radio emission gap(or straight-edged central brightness depression) observed between twin radio lobes, in over a dozen relatively nearby powerful Fanaroff-Riley Class II radio galaxies. They could also provide a plausible alternative explanation for a range of observations. Although a number of explanations have been proposed for the origin of the superdisks, little is known about their material content. Some X-ray observations of superdisk candidates indicate the presence of hot gas, but a cool dusty medium also seems to be common. If they are entirely or partly composed of neutral gas, then it may be directly detectable and we report here a first attempt to detect/image any neutral hydrogen gas present in the superdisks that are inferred to be present in four nearby radio galaxies. We have not found a positive H I signal in any of the four sources, resulting in tight upper limits on the H I number density in the postulated superdisks,estimated directly from the central rms noise values of the final radio continuum subtracted image. The estimated ranges of the upper limit on neutral hydrogen number density and column density are 10-4-10-3 atoms per cm~3 and 10~(19)-10~(20) atoms per cm~2, respectively. No positive H I signal is detected even after combining all the four available H I images(with inverse variance weighting). This clearly rules out an H I dominated superdisk as a viable model to explain these structures, however, the possibility of a superdisk being composed of warm/hot gas still remains open. 相似文献
72.
Sea level rise threatens coastal communities throughout the United States, and South Florida is on the front line. The iconic and built-up city of Miami Beach, Florida, has a well-developed, high-value property market, and the municipality has been lauded for proactively taking action to adapt to anticipated sea level rise. Moving beyond hyperbole and piecemeal evidence, we compile a comprehensive inventory of adaptation and mitigation measures implemented by various municipal agencies. We employ these data sets to measure exposure and readiness for the entire city and make a preliminary effort to develop a city vulnerability index. Our findings reveal that exposure throughout the city is high and that readiness is concentrated near stormwater drainage systems, leading to high vulnerability along the coast. When we compare the spatial patterns of the vulnerability index and the residential property values, we find a mismatch. The most vulnerable regions are characterized by high income, transiency, and an apparent unresponsiveness to sea level rise. No doubt our findings illustrate a lag effect, but if sea level rise increases, the real estate market could reach a tipping point unless state and federal agencies also fund more comprehensive adaptation. 相似文献
73.
Remote sensing data and digital elevation models were utilized to extract the catchment hydrological parameters and to delineate storage areas for the Ugandan Equatorial Lakes region. Available rainfall/discharge data are integrated with these morphometric data to construct a hydrological model that simulates the water balance of the different interconnected basins and enables the impact of potential management options to be examined. The total annual discharges of the basins are generally very low (less than 7% of the total annual rainfall). The basin of the shallow (5 m deep) Lake Kioga makes only a minor hydrological contribution compared with other Equatorial Lakes, because most of the overflow from Lake Victoria basin into Lake Kioga is lost by evaporation and evapotranspiration. The discharge from Lake Kioga could be significantly increased by draining the swamps through dredging and deepening certain channel reaches. Development of hydropower dams on the Equatorial Lakes will have an adverse impact on the annual water discharge downstream, including the occasional reduction of flow required for filling up to designed storage capacities and permanently increasing the surface areas of water that is exposed to evaporation. On the basis of modelling studies, alternative sites are proposed for hydropower development and water storage schemes. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
74.
75.
76.
77.
Cloud — Aerosol interaction during lightning activity over land and ocean: Precipitation pattern assessment 总被引:1,自引:0,他引:1
Jayanti Pal Sutapa Chaudhuri Arumita Roy Chowdhury Tanuka Bandyopadhyay 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(3):251-261
The present study attempts to identify the land - ocean contrast in cloud - aerosol relation during lightning and non-lightning days and its effect on subsequent precipitation pattern. The thermal hypothesis in view of Convective Available Potential Energy (CAPE) behind the land - ocean contrast is observed to be insignificant in the present study region. The result shows that the lightning activities are significantly and positively correlated with aerosols over both land and ocean in case of low aerosol loading whereas for high aerosol loading the correlation is significant but, only over land. The study attempts to comprehend the mechanism through which the aerosol and lightning interact using the concept of aerosol indirect effect that includes the study of cloud effective radius, cloud fraction and precipitation rate. The result shows that the increase in lightning activity over ocean might have been caused due to the first aerosol indirect effect, while over land the aerosol indirect effect might have been suppressed due to lightning. Thus, depending on the region and relation between cloud parameters it is observed that the precipitation rate decreases (increases) over ocean during lightning (non-lightning) days. On the other hand during non-lightning days, the precipitation rate decreases over land. 相似文献
78.
Ananya Roy 《The Professional geographer》2016,68(2):313-321
Recently, in geography and related disciplines, there has been a call to generate conceptual frameworks from the Global South. Such a call does not imply cataloging the diversity and plurality of the world but rather requires new understandings of relationalities and transformations. In this article, I contribute to these ongoing endeavors by thinking from Asia. In doing so, I interpret Asia not as a bounded geographical location but instead as interconnected space. In particular, I pay attention to how such interconnections reference Asian models of development, thereby creating a politics of futurity. A study of the making of Asian futures allows a broader understanding of the renewal of development in a rearranged south–north world. 相似文献
79.
80.
Roy T. Churchwell Steve Kendall Stephen C. Brown Arny L. Blanchard Tuula E. Hollmen Abby N. Powell 《Estuaries and Coasts》2018,41(1):280-292
River deltas along Alaska’s Beaufort Sea coast are used by hatch-year semipalmated sandpipers (Calidris pusilla) after leaving their terrestrial natal sites, but the drivers of their use of these stopover sites on the first “hop” of fall migration are unknown. We quantified sandpiper temporal distribution and abundance as related to food resources at three river deltas during the beginning of their fall migration (post-breeding period) to compare the habitat quality among these deltas. We conducted population counts, sampled invertebrates, and captured birds to collect blood samples from individuals for triglyceride and stable isotope analyses to determine fattening rates and diet. Patterns of sandpiper and invertebrate abundance were complex and varied among deltas and within seasons. River deltas were used by sandpipers from late July to late August, and peak sandpiper counts ranged from 1000 to 4000 individuals, of which 98% were hatch-year semipalmated sandpipers. Isotopic signatures from blood plasma samples indicated that birds switched from a diet of upland tundra to delta invertebrate taxa as the migration season progressed, suggesting a dependence on delta invertebrates. Despite differences in diet among deltas, we found no differences in fattening rates of juvenile sandpipers as indicated by triglyceride levels. The number of sandpipers was positively associated with abundance of Amphipoda and Oligochaeta at the Jago and Okpilak-Hulahula deltas; an isotopic mixing model indicated that sandpipers consumed Amphipoda and Oligochaeta at Jago, mostly Chironomidae at Okpilak-Hulahula and Spionidae at Canning. Regardless of the difference in sandpiper diets at the Beaufort Sea deltas, their similar fattening rates throughout the season indicate that all of these stopover sites provide a critical food resource for hatch-year sandpipers beginning their first migration. 相似文献