全文获取类型
收费全文 | 9670篇 |
免费 | 327篇 |
国内免费 | 151篇 |
专业分类
测绘学 | 187篇 |
大气科学 | 783篇 |
地球物理 | 2329篇 |
地质学 | 3396篇 |
海洋学 | 885篇 |
天文学 | 1382篇 |
综合类 | 43篇 |
自然地理 | 1143篇 |
出版年
2022年 | 37篇 |
2021年 | 136篇 |
2020年 | 178篇 |
2019年 | 174篇 |
2018年 | 242篇 |
2017年 | 226篇 |
2016年 | 285篇 |
2015年 | 247篇 |
2014年 | 296篇 |
2013年 | 540篇 |
2012年 | 342篇 |
2011年 | 471篇 |
2010年 | 431篇 |
2009年 | 547篇 |
2008年 | 470篇 |
2007年 | 469篇 |
2006年 | 397篇 |
2005年 | 338篇 |
2004年 | 332篇 |
2003年 | 334篇 |
2002年 | 269篇 |
2001年 | 219篇 |
2000年 | 234篇 |
1999年 | 174篇 |
1998年 | 167篇 |
1997年 | 143篇 |
1996年 | 155篇 |
1995年 | 142篇 |
1994年 | 132篇 |
1993年 | 112篇 |
1992年 | 114篇 |
1991年 | 72篇 |
1990年 | 100篇 |
1989年 | 82篇 |
1988年 | 90篇 |
1987年 | 100篇 |
1986年 | 91篇 |
1985年 | 123篇 |
1984年 | 136篇 |
1983年 | 132篇 |
1982年 | 111篇 |
1981年 | 82篇 |
1980年 | 62篇 |
1979年 | 73篇 |
1978年 | 70篇 |
1977年 | 62篇 |
1976年 | 61篇 |
1975年 | 69篇 |
1974年 | 55篇 |
1973年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
This article argues that the material incentives associated with climate policies such as the Clean Development Mechanism (CDM) may contribute to the socialization of emerging economies such as Vietnam in economic-oriented climate change norms. In current academic research, the CDM has both been extolled as a cost-effective and vilified as an environmentally inadequate instrument. Few studies so far, however, have looked into the CDM's potential contribution to socialization-related phenomena such as raising climate change awareness. This article aims to fill that gap by studying the CDM in EU–Vietnam relations in four periods, namely initiation (2001–2007), improvement (2008–2010), consolidation (2010–2012), and potential habit formation (2012 and beyond), with both the EU and Vietnam being important players in the market for CDM credits (Certified Emission Reductions or CERs). We argue that there is at least a strong potential for habit formation resulting from the CDM's material incentives, and that the underlying causal mechanism involves the emergence and activities of norm entrepreneurs and habit formation through a process of legal institutionalization.Policy relevanceNormative transformation or change is increasingly attracting the attention of both climate policy makers and scholars alike, certainly in view of the failures of ‘standard’ economic or technological solutions to tackle climate change. There is a need, however, to apply insights from social theory to specific policies and cases. The policy relevance of this article lies here: does the CDM (a specific policy) affect climate concerns (norms) in Vietnam (a specific case)? And, if so, to what extent and why? Based on previous research regarding the Chinese case, it is expected that the CDM's material incentives result in a mild effect in Vietnam, probably less pronounced than in China in view of the latter's relative level of economic development, and the strength of its political and legal-institutional system and (human) capacity to develop CDM projects. This article's research findings point out that whether and how ‘deep’ these new shared ideas will succeed in becoming standards of appropriate behaviour in Vietnam might to some extent depend on whether the international community is able to offer a material incentive structure that fosters such a normative transformation. 相似文献
992.
Fluctuations in US Freezing Rain Days 总被引:1,自引:0,他引:1
Freezing rain occurrences during a 50-year period, 1949/1950–1998/1999, derived from carefully examined records of 161 first-order stations distributed across the United States, were assessed for temporal fluctuations and trends. Classification of station fluctuations based on five 10-year periods revealed five unique distribution types in areas east of the Rockies. One of these five distributions, for stations located in the western Great Plains, experienced its greatest 10-year value at the end of the 50-year period. The other four regional distributions experienced their highest 10-year value in either of the first two 10-year periods. Nationally, the 10-year period when the greatest number of stations experienced their maximum value was 1949/1950–1958/1959, while the period when the greatest number of stations experienced their minimum value fell near the end of the 50-year record (1979/1980–1988/1989). The 50-year linear trends defined one region, the western Great Plains, with increasing values, while three areas of decreasing trend were identified; the Great Lakes, the eastern Ohio River valley, and southern New England. These analyses also indicate the need to examine and consider such time–space changes in the frequency of climate variables at various spatial scales when assessing weather risks and developing climate change scenarios. 相似文献
993.
David P. Rowell 《Climate Dynamics》2005,25(7-8):837-849
A scenario of European climate change for the late twenty-first century is described, using a high-resolution state-of-the-art
model. A time-slice approach is used, whereby the atmospheric general circulation model, HadAM3P, was integrated for two periods,
1960–1990 and 2070–2100, using the SRES A2 scenario. For the first time an ensemble of such experiments was produced, along
with appropriate statistical tests for assessing significance. The focus is on changes to the statistics of seasonal means,
and includes analysis of both multi-year means and interannual variance. All four seasons are assessed, and anomalies are
mapped for surface air temperature, precipitation and snow mass. Mechanisms are proposed where these are dominated by straightforward
local processes. In winter, the largest warming occurs over eastern Europe, up to 7°C, mean snow mass is reduced by at least
80% except over Scandinavia, and precipitation increases over all but the southernmost parts of Europe. In summer, temperatures
rise by 6–9°C south of about 50°N, and mean rainfall is substantially reduced over the same area. In spring and autumn, anomalies
tend to be weaker, but often display patterns similar to the preceding season, reflecting the inertia of the land surface
component of the climate system. Changes in interannual variance are substantial in the solsticial seasons for many regions
(note that for precipitation, variance estimates are scaled by the square of the mean). In winter, interannual variability
of near-surface air temperature is considerably reduced over much of Europe, and the relative variability of precipitation
is reduced north of about 50°N. In summer, the (relative) interannual variance of both variables increases over much of the
continent. 相似文献
994.
W. David Rust Donald R. MacGorman Eric C. Bruning Stephanie A. Weiss Paul R. Krehbiel Ronald J. Thomas William Rison Timothy Hamlin Jeremiah Harlin 《Atmospheric Research》2005,76(1-4):247
Balloon-borne electric field soundings and lightning mapping data have been analyzed for three of the storms that occurred in the Severe Thunderstorm Electrification and Precipitation Study field program in 2000 to determine if the storms had inverted-polarity electrical structures. The polarities of all or some of the vertically stacked charge regions in such storms are opposite to the polarities observed at comparable heights in normal storms. Analyses compared the charge structures inferred from electric field soundings in the storms with charges inferred from three-dimensional lightning mapping data. Charge structures were inferred from electric field profiles by combining the one-dimensional approximation of Gauss's law with additional information from three-dimensional patterns in the electric field vectors. The three different ways of inferring the charge structure in the storms were found to complement each other and to be consistent overall. Charge deposition by lightning possibly occurred and increased the charge complexity of one of the storms.Many of the cloud flashes in each case were inverted-polarity flashes. Two storms produced ground flash activity comprised predominantly of positive ground flashes. One storm, which was an isolated thunderstorm, produced inverted-polarity cloud flashes, but no flashes to ground. The positive and negative thunderstorm charge regions were found at altitudes where, respectively, negative and positive charge would be found in normal-polarity storms. Thus, we conclude that these storms had anomalous and inverted-polarity electrical structures. Collectively, these three cases (along with the limited cases in the refereed literature) provide additional evidence that thunderstorms can have inverted-polarity electrical structures. 相似文献
995.
Monte G. Bateman Kenneth B. Eack W. David Rust Thomas C. Marshall 《Atmospheric Research》1999,51(3-4)
We have designed a new instrument to measure the current flowing along balloon rigging line during flights through thunderstorms. This instrument was tested in a high voltage facility and used to collect line current data during one balloon flight into a thunderstorm. Using these data, worst-case calculations are made; as such, we claim that they are the upper limits of any alteration (to the measured electric field or particle charge) that may occur, and the real number is likely much less. It is postulated the rigging-line current could have two separate effects on the measured electric field: (1) reduction of the field due to emission of corona ions, and (2) enhancement of the field due to the insertion of a long thin ‘conductor.' Even with current as high as 1 μA (the largest measured was around 50–100 nA), these two effects were found to be about −1% and +1%, respectively. Also, the calculated worst-case alteration to charged precipitation measurements is about 0.1 pC. Thus, with proper efforts to make the rigging line as poor a conductor as possible, it seems that we are justified in stating that these effects are negligible. 相似文献
996.
Climatic Change - Recent water resources planning studies have proposed climate adaptation strategies in which infrastructure and policy actions are triggered by observed thresholds or... 相似文献
997.
998.
Leena Järvi Ari-Juhani Punkka David M. Schultz Tuukka Petäjä Harri Hohti Janne Rinne Toivo Pohja Markku Kulmala Pertti Hari Timo Vesala 《Boundary-Layer Meteorology》2007,125(2):343-359
On the afternoon of 3 July 2004 in Hyytiälä (Juupajoki, Finland), convective cells produced a strong downburst causing forest damage. The SMEAR II field station, situated near the damage site, enabled a unique micrometeorological analysis of a microburst with differences above and inside the canopy. At the time of the event, a squall line associated with a cold front was crossing Hyytiälä with a reflectivity maximum in the middle of the squall line. A bow echo, rear-inflow notch, and probable mesovortex were observed in radar data. The bow echo moved west-north-west, and its apex travelled just north of Hyytiälä. The turbulence data were analysed at two locations above the forest canopy and at one location at sub-canopy. At 1412 EET (Eastern European Time, UTC+2), the horizontal and vertical wind speed increased and the wind veered, reflecting the arrival of a gust front. At the same time, the carbon dioxide concentration increased due to turbulent mixing, the temperature decreased due to cold air flow from aloft and aerosol particle concentration decreased due to rain scavenging. An increase in the number concentration of ultra-fine particles (< 10 nm) was detected, supporting the new particle formation either from cloud outflow or due to rain. Five minutes after the gust front (1417 EET), strong horizontal and downward vertical wind speed gusts occurred with maxima of 22 and 15 m s?1, respectively, reflecting the microburst. The turbulence spectra before, during and after the event were consistent with traditional turbulence spectral theory. 相似文献
999.
For the 1980–2003 period, we analyzed the relationship between crop yield and three climatic variables (minimum temperature,
maximum temperature, and precipitation) for 12 major Californian crops: wine grapes, lettuce, almonds, strawberries, table
grapes, hay, oranges, cotton, tomatoes, walnuts, avocados, and pistachios. The months and climatic variables of greatest importance
to each crop were used to develop regressions relating yield to climatic conditions. For most crops, fairly simple equations
using only 2–3 variables explained more than two-thirds of observed yield variance. The types of variables and months identified
suggest that relatively poorly understood processes such as crop infection, pollination, and dormancy may be important mechanisms
by which climate influences crop yield. Recent climatic trends have had mixed effects on crop yields, with orange and walnut
yields aided, avocado yields hurt, and most crops little affected by recent climatic trends. Yield-climate relationships can
provide a foundation for forecasting crop production within a year and for projecting the impact of future climate changes. 相似文献
1000.
Henry P. Huntington Michelle Boyle Gwenn E. Flowers John W. Weatherly Lawrence C. Hamilton Larry Hinzman Craig Gerlach Rommel Zulueta Craig Nicolson Jonathan Overpeck 《Climatic change》2007,82(1-2):77-92
Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the
more complicated but more likely possibility that human activities themselves can interact with climate or environmental change
in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed
to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously
thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities
in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend.
Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in
the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence
the trajectory of arctic system change. 相似文献