全文获取类型
收费全文 | 615篇 |
免费 | 13篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 41篇 |
地球物理 | 123篇 |
地质学 | 192篇 |
海洋学 | 84篇 |
天文学 | 115篇 |
综合类 | 3篇 |
自然地理 | 64篇 |
出版年
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 11篇 |
2015年 | 16篇 |
2014年 | 7篇 |
2013年 | 32篇 |
2012年 | 9篇 |
2011年 | 24篇 |
2010年 | 21篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 15篇 |
2000年 | 27篇 |
1999年 | 21篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 7篇 |
1970年 | 4篇 |
排序方式: 共有636条查询结果,搜索用时 0 毫秒
91.
David J. Axon A. Marconi F.D. Macchetto A. Capetti Andrew Robinson 《Astrophysics and Space Science》1997,248(1-2):69-77
We have obtained HST FOC f/48 long-slit spectroscopy of the central 2 arcseconds of the Narrow Line Region of NGC 1068 between
3500-5400\OA with a spectral resolution of 1.78\OA/pixel. At a spatial scale of 0″.0287 per pixel these data provide an order
of magnitude improvement in resolution over previous ground based spectra and allow us to trace the interaction between the
radio jet and the gas in the NLR. Our results show that, within ±0″.5 of the radio-jet the emission lines are split into two
components whose velocity separation is 1500 km s-1. The emission line structure is reminiscent of that seen previously around
the jet of 3C120. Furthermore, this material enveloping the radio-jet is in a much higher ionization state than that of the
surrounding NLR gas. The highest excitation is coincident with the jet axis where emission in the coronal line of [FeVII]
λ3769\OA is detected but where [OII] λ3727 \OA is depressed. These results imply that we are witnessing a cocoon of hot gas
in expansion around the radio-jet created by its interaction with the gas, and that these shocks are sufficiently fast, at
least ± km s-1, that they are creating localized ionization effects.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
92.
The solar irradiante has been found to change by 0.1% over the recent solar cycle. A change of irradiante of about 0.5% is required to effect the Earth's climate. How frequently can a variation of this size be expected? We examine the question of the persistence of non-periodic variations in solar activity. The Hürst exponent, which characterizes the persistence of a time series (Mandelbrot and Wallis, 1969), is evaluated for the series of14 C data for the time interval from about 6000 BC to 1950 AD (Stuiver and Pearson, 1986). We find a constant Hürst exponent, suggesting that solar activity in the frequency range of from 100 to 3000 years includes an important continuum component in addition to the well-known periodic variations. The value we calculate,H ≈ 0.8, is significantly larger than the value of 0.5 that would correspond to variations produced by a white-noise process. This value is in good agreement with the results for the monthly sunspot data reported elsewhere, indicating that the physics that produces the continuum is a correlated random process (Ruzmaikin et al., 1992), and that it is the same type of process over a wide range of time interval lengths. We conclude that the time period over which an irradiance change of 0.5% can be expected to occur is significantly shorter than that which would be expected for variations produced by a white-noise process. The full paper has been submitted to Solar Physics. Part of the research decribed here was carried out by JPL, Caltech under a contract with NASA. 相似文献
93.
94.
R. D. Robinson R. T. Stewart N. R. Sheeley Jr. R. A. Howard J. Koomen D. J. Michels 《Solar physics》1986,105(1):149-171
An investigation is made to determine the relationship between a coronal mass ejection (CME) and the characteristics of associated metre-wave activity. It is found that (1) the CME width and leading edge velocity can be highly influential in determining the intensity, spectral complexity and frequency coverage of both type II and continuum bursts; (2) the presence of a CME is possibly a necessary condition for the production of a metric continuum event and (3) metric continuum bursts as well as intense, complex type II events are preferentially associated with strong, long lasting soft X-ray events. 相似文献
95.
XIONG Fahui YANG Jingsui Robinson T.PAUL XU Xiangzhen BA Dengzhu LI Yuan LIJinyang ZHANG Zhongming RONG He 《《地质学报》英文版》2015,89(Z2):99-100
<正>The first diamonds from ophiolite were found in peridotite of Luobusa ophiolite along Yarlung Zangbu suture zone in Tibet,China(IGCAGS,1981),and then more and more diamonds found in harzgurgite(Bai et al.,1993;Yang et al.,2007a;Robinson et al.,2014;Xu et al., 相似文献
96.
Global increase in record-breaking monthly-mean temperatures 总被引:2,自引:1,他引:1
The last decade has produced record-breaking heat waves in many parts of the world. At the same time, it was globally the warmest since sufficient measurements started in the 19th century. Here we show that, worldwide, the number of local record-breaking monthly temperature extremes is now on average five times larger than expected in a climate with no long-term warming. This implies that on average there is an 80 % chance that a new monthly heat record is due to climatic change. Large regional differences exist in the number of observed records. Summertime records, which are associated with prolonged heat waves, increased by more than a factor of ten in some continental regions including parts of Europe, Africa, southern Asia and Amazonia. Overall, these high record numbers are quantitatively consistent with those expected for the observed climatic warming trend with added stationary white noise. In addition, we find that the observed records cluster both in space and in time. Strong El Niño years see additional records superimposed on the expected long-term rise. Under a medium global warming scenario, by the 2040s we predict the number of monthly heat records globally to be more than 12 times as high as in a climate with no long-term warming. 相似文献
97.
Sarah Gilbert Leonid Danyushevsky Philip Robinson Cora Wohlgemuth‐Ueberwasser Norman Pearson Dany Savard Marc Norman Jacob Hanley 《Geostandards and Geoanalytical Research》2013,37(1):51-64
A range of independently characterised reference materials (RMs) for LA‐ICP‐MS, used for the determination of the platinum‐group elements (PGE) and Au in a sulfide matrix, were analysed and compared: 8b, PGE‐A, NiS‐3, Po727‐T1, Po724‐T and the Lombard meteorite. The newly developed RM NiS‐3 was used as the RM for the calibration of all LA‐ICP‐MS analyses and the measured concentrations of the other RMs compared against their published concentrations. This data were also used to assess the consistency of concentrations calibrated against the different RMs. It was found that Po727‐T1 and 8b produced results that were comparable, within uncertainty, for all elements. Po727‐T1 also produced consistent results with NiS‐3 for all elements. All other RMs showed differences for some elements, especially Ru in Po724‐T, and Os, Ir and Au in PGE‐A. The homogeneity of the PGE and Au in each RM was assessed, by comparing the precision of multiple LA‐ICP‐MS spot analyses with the average uncertainty of the signal. Po724‐T, Po727‐T1 and the Lombard meteorite were found to be homogeneous for all elements, but 8b, PGE‐A and NiS‐3 were heterogeneous for some elements. This is the first direct comparison between a range of independently characterised PGE and Au LA‐ICP‐MS RMs. 相似文献
98.
Pesticide use by farmers on Santa Cruz Island, Galapagos—a perceived adaptation to changing ecological and economic dynamics—has the potential to lead to environmental degradation in an area that is known and valued worldwide for its biodiversity. We survey Santa Cruz farmers to understand motivations for and concerns about pesticide use on the island. Results from farmer surveys are supplemented with interview data to develop the case study of pesticide use on Santa Cruz Island. We then apply a “complex trade-off” framework to explore and navigate the tensions between conservation and livelihoods. We conclude by elaborating the implementation of a participatory certification system, the Participatory Guarantee System, as a possible path for reconciling trade-offs in Santa Cruz, Galapagos. 相似文献
99.
Chunhui Lu Adrian D. Werner Craig T. Simmons Neville I. Robinson Jian Luo 《Ground water》2013,51(2):219-228
In this study, we examine the maximum net extraction rate from the novel arrangement of an injection‐extraction well pair in a coastal aquifer, where fresh groundwater is reinjected through the injection well located between the interface toe and extraction well. Complex potential theory is employed to derive a new analytical solution for the maximum net extraction rate and corresponding stagnation‐point locations and recirculation ratio, assuming steady‐state, sharp‐interface conditions. The injection‐extraction well‐pair system outperforms a traditional single extraction well in terms of net extraction rate for a broad range of well placement and pumping rates, which is up to 50% higher for an aquifer with a thickness of 20 m, hydraulic conductivity of 10 m/d, and fresh water influx of 0.24 m2/d. Sensitivity analyses show that for a given fresh water discharge from an inland aquifer, a larger maximum net extraction is expected in cases with a smaller hydraulic conductivity or a smaller aquifer thickness, notwithstanding physical limits to drawdown at the pumping well that are not considered here. For an extraction well with a fixed location, the optimal net extraction rate linearly increases with the distance between the injection well and the sea, and the corresponding injection rate and recirculation ratio also increase. The analytical analysis in this study provides initial guidance for the design of well‐pair systems in coastal aquifers, and is therefore an extension beyond previous applications of analytical solutions of coastal pumping that apply only to extraction or injection wells. 相似文献
100.
Type III solar radio bursts are investigated by modelling the propagation of the electron beam and the generation and subsequent propagation of waves to the observer. Predictions from this model are compared in detail with particle, Langmuir wave, and radio data from the ISEE-3 spacecraft and with other observations to clarify the roles of fundamental and harmonic emission in type III radio bursts. Langmuir waves are seen only after the arrival of the beam, in accord with the standard theory. These waves persist after a positive beam slope is last resolved, implying that sporadic positive slopes persist for some time, unresolved but in accord with the predictions of stochastic growth theory. Local electromagnetic emission sets in only after Langmuir waves are seen, in accord with the standard theory, which relies on nonlinear processes involving Langmuir waves. In the events investigated here, fundamental radiation appears to dominate early in the event, followed and/or accompanied by harmonic radiation after the peak, with a long-lived tail of multiply scattered fundamental or harmonic emission extending long afterwards. These results are largely independent of, but generally consistent with, the conclusions of earlier works. 相似文献