全文获取类型
收费全文 | 6920篇 |
免费 | 251篇 |
国内免费 | 141篇 |
专业分类
测绘学 | 427篇 |
大气科学 | 547篇 |
地球物理 | 1607篇 |
地质学 | 2732篇 |
海洋学 | 503篇 |
天文学 | 1011篇 |
综合类 | 70篇 |
自然地理 | 415篇 |
出版年
2022年 | 80篇 |
2021年 | 105篇 |
2020年 | 107篇 |
2019年 | 128篇 |
2018年 | 326篇 |
2017年 | 333篇 |
2016年 | 330篇 |
2015年 | 235篇 |
2014年 | 321篇 |
2013年 | 507篇 |
2012年 | 284篇 |
2011年 | 380篇 |
2010年 | 292篇 |
2009年 | 353篇 |
2008年 | 349篇 |
2007年 | 279篇 |
2006年 | 255篇 |
2005年 | 216篇 |
2004年 | 172篇 |
2003年 | 192篇 |
2002年 | 157篇 |
2001年 | 100篇 |
2000年 | 113篇 |
1999年 | 79篇 |
1998年 | 83篇 |
1997年 | 71篇 |
1996年 | 74篇 |
1995年 | 60篇 |
1994年 | 73篇 |
1993年 | 55篇 |
1992年 | 54篇 |
1991年 | 65篇 |
1990年 | 53篇 |
1989年 | 51篇 |
1988年 | 47篇 |
1987年 | 57篇 |
1986年 | 58篇 |
1985年 | 72篇 |
1984年 | 58篇 |
1983年 | 54篇 |
1982年 | 58篇 |
1981年 | 61篇 |
1980年 | 53篇 |
1979年 | 47篇 |
1978年 | 51篇 |
1977年 | 31篇 |
1976年 | 32篇 |
1975年 | 30篇 |
1974年 | 42篇 |
1973年 | 34篇 |
排序方式: 共有7312条查询结果,搜索用时 31 毫秒
951.
Climate change and coastal flooding in Metro Boston: impacts and adaptation strategies 总被引:1,自引:0,他引:1
Sea level rise (SLR) due to climate change will increase storm surge height along the 825 km long coastline of Metro Boston,
USA. Land at risk consists of urban waterfront with piers and armoring, residential areas with and without seawalls and revetments,
and undeveloped land with either rock coasts or gently sloping beachfront and low-lying coastal marshes. Risk-based analysis
shows that the cumulative 100 year economic impacts on developed areas from increased storm surge flooding depend heavily
upon the adaptation response, location, and estimated sea level rise. Generally it is found that it is advantageous to use
expensive structural protection in areas that are highly developed and less structural approaches such as floodproofing and
limiting or removing development in less developed or environmentally sensitive areas. 相似文献
952.
Emilia K. Jin James L. Kinter III B. Wang C.-K. Park I.-S. Kang B. P. Kirtman J.-S. Kug A. Kumar J.-J. Luo J. Schemm J. Shukla T. Yamagata 《Climate Dynamics》2008,31(6):647-664
The overall skill of ENSO prediction in retrospective forecasts made with ten different coupled GCMs is investigated. The coupled GCM datasets of the APCC/CliPAS and DEMETER projects are used for four seasons in the common 22 years from 1980 to 2001. As a baseline, a dynamic-statistical SST forecast and persistence are compared. Our study focuses on the tropical Pacific SST, especially by analyzing the NINO34 index. In coupled models, the accuracy of the simulated variability is related to the accuracy of the simulated mean state. Almost all models have problems in simulating the mean and mean annual cycle of SST, in spite of the positive influence of realistic initial conditions. As a result, the simulation of the interannual SST variability is also far from perfect in most coupled models. With increasing lead time, this discrepancy gets worse. As one measure of forecast skill, the tier-1 multi-model ensemble (MME) forecasts of NINO3.4 SST have an anomaly correlation coefficient of 0.86 at the month 6. This is higher than that of any individual model as well as both forecasts based on persistence and those made with the dynamic-statistical model. The forecast skill of individual models and the MME depends strongly on season, ENSO phase, and ENSO intensity. A stronger El Niño is better predicted. The growth phases of both the warm and cold events are better predicted than the corresponding decaying phases. ENSO-neutral periods are far worse predicted than warm or cold events. The skill of forecasts that start in February or May drops faster than that of forecasts that start in August or November. This behavior, often termed the spring predictability barrier, is in part because predictions starting from February or May contain more events in the decaying phase of ENSO. 相似文献
953.
Vulnerability and adaptation to climate variability and water stress in Uttarakhand State, India 总被引:1,自引:0,他引:1
Ulka Kelkar Kapil Kumar Narula Ved Prakash Sharma Usha Chandna 《Global Environmental Change》2008,18(4):564
This paper presents a participatory approach to investigate vulnerability and adaptive capacity to climate variability and water stress in the Lakhwar watershed in Uttarakhand State, India. Highly water stressed microwatersheds were identified by modelling surface runoff, soil moisture development, lateral runoff, and groundwater recharge. The modelling results were shared with communities in two villages, and timeline exercises were carried out to allow them to trace past developments that have impacted their lives and livelihoods, and stimulate discussion about future changes and possible adaptation interventions. 相似文献
954.
Kirsty J. Rhook Paul M. Geil J. Stuart B. Wyithe 《Monthly notices of the Royal Astronomical Society》2009,392(4):1388-1396
It has recently been suggested that the power spectrum of redshifted 21 cm fluctuations could be used to measure the scale of baryonic acoustic oscillations (BAOs) during the reionization era. The resulting measurements are potentially as precise as those offered by the next generation of galaxy redshift surveys at lower redshift. However, unlike galaxy redshift surveys, which in the linear regime are subject to a scale-independent galaxy bias, the growth of ionized regions during reionization is thought to introduce a strongly scale-dependent relationship between the 21 cm and mass power spectra. We use a seminumerical model for reionization to assess the impact of ionized regions on the precision and accuracy with which the BAO scale could be measured using redshifted 21 cm observations. For a model in which reionization is completed at z ∼ 6 , we find that the constraints on the BAO scale are not systematically biased at z ≳ 6.5 . In this scenario, and assuming the sensitivity attainable with a low-frequency array comprising 10 times the collecting area of the Murchison Widefield Array, the BAO scale could be measured to within 1.5 per cent in the range 6.5 ≲ z ≲ 7.5 . 相似文献
955.
Timothy Garn David A. Green Julia M. Riley Paul Alexander 《Monthly notices of the Royal Astronomical Society》2009,397(2):1101-1112
We probe the relationship between star formation rate (SFR) and radio synchrotron luminosity in galaxies at 0 < z < 2 within the northern Spitzer Wide-area Infrared Extragalactic survey (SWIRE) fields, in order to investigate some of the assumptions that go into calculating the star formation history of the Universe from deep radio observations. We present new 610-MHz Giant Metrewave Radio Telescope (GMRT) observations of the European Large-Area ISO Survey-North 2 (ELAIS-N2) field, and using this data, along with previous GMRT surveys carried out in the ELAIS-N1 (North 1) and Lockman Hole regions, we construct a sample of galaxies which have redshift and SFR information available from the SWIRE survey. We test whether the local relationship between SFR and radio luminosity is applicable to z = 2 galaxies, and look for evolution in this relationship with both redshift and SFR in order to examine whether the physical processes which lead to synchrotron radiation have remained the same since the peak of star formation in the Universe. We find that the local calibration between radio luminosity and star formation can be successfully applied to radio-selected high-redshift, high-SFR galaxies, although we identify a small number of sources where this may not be the case; these sources show evidence for inaccurate estimations of their SFR, but there may also be some contribution from physical effects such as the recent onset of starburst activity, or suppression of the radio luminosity within these galaxies. 相似文献
956.
A. Mangalam Gopal-Krishna Paul J. Wiita 《Monthly notices of the Royal Astronomical Society》2009,397(4):2216-2224
The recently discovered apparent dramatic expansion in the effective radii of massive elliptical galaxies from z ≃ 2 to ≃0.1 has been interpreted in terms of either galaxy mergers or the rapid loss of cold gas due to active galactic nuclei (AGN) feedback. In examining the latter case, we have quantified the extent of the expansion, which is uncertain observationally, in terms of the star formation parameters and time of the expulsion of the cold gas. In either case, the large global decrease in stellar density should translate into a major drop in the interstellar medium density and pressure with cosmic epoch. These cosmological changes are expected to have a major influence on the gas accretion mode, which will shift from 'cold' thin disc accretion at high redshifts towards 'hot' Bondi fed Advection Dominated Accretion Flow (ADAF) accretion at low redshifts. The decline of angular momentum inflow would then lead to a spin down of the black hole, for which we have calculated more precise time-scales; a value of about 0.2 Gyr is typical for a 109 M⊙ central black hole. These results have implications for the different cosmological evolutionary patterns found for the luminosity functions of powerful and weak radio galaxies. 相似文献
957.
Sagar Godambe C. Konar D. J. Saikia Paul J. Wiita 《Monthly notices of the Royal Astronomical Society》2009,396(2):860-869
We present low-frequency observations with the Giant Metrewave Radio Telescope of three giant radio sources (GRSs: J0139+3957, J0200+4049 and J0807+7400) with relaxed diffuse lobes which show no hotspots and no evidence of jets. The largest of these three, J0200+4049, exhibits a depression in the centre of the western lobe, while J0139+3957 and J0807+7400 have been suggested earlier by Klein et al. and Lara et al., respectively, to be relic radio sources. We estimate the ages of the lobes. We also present Very Large Array observations of the core of J0807+7400, and determine the core radio spectra for all three sources. Although the radio cores suggest that the sources are currently active, we explore the possibility that the lobes in these sources are due to an earlier cycle of activity. 相似文献
958.
Thomas G. Müller Emmanuel Lellouch Hermann Böhnhardt John Stansberry Antonella Barucci Jacques Crovisier Audrey Delsanti Alain Doressoundiram Elisabetta Dotto René Duffard Sonia Fornasier Olivier Groussin Pedro J. Gutiérrez Olivier Hainaut Alan W. Harris Paul Hartogh Daniel Hestroffer Jonathan Horner Dave Jewitt Mark Kidger Csaba Kiss Pedro Lacerda Luisa Lara Tanya Lim Michael Mueller Raphael Moreno Jose-Luis Ortiz Miriam Rengel Pablo Santos-Sanz Bruce Swinyard Nicolas Thomas Audrey Thirouin David Trilling 《Earth, Moon, and Planets》2009,105(2-4):209-219
Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well. 相似文献
959.
Gabriel Grigorescu Paul Alexander Rosie C. Bolton Roshene McCool 《Experimental Astronomy》2009,27(1-2):95-107
The future Square Kilometre Array (SKA) radio telescope is an interferometer array that will use a variety of collector types, including approximately 2500 dishes distributed with separations up to a few thousand kilometres, and about 250 aperture array (AA) stations located within 200 km of the core. The data rates associated with each individual collector are vast: around 10 GBytes/s for each dish and 2 TBytes/s for an AA station. As each of these must be connected directly to a central correlator, designing a cost-effective cabling and trenching infrastructure presents a great engineering challenge. In this paper we discuss approaches to performing this optimisation. In graph theory, the concept of a minimum spanning tree (MST) is equivalent to finding the minimum total trench length joining a set of n arbitrary points in the plane. We have developed a set of algorithms which optimise the infrastructure of any given telescope layout iteratively, taking into consideration not only trenching but also cabling and jointing costs as well. Solutions for few example configurations of telescope layout are presented. We have found that these solutions depend significantly on the collectors’ output data rates. When compared to a “traditional” MST-based approach which minimises trenching costs only, our algorithms can further reduce total costs by up to 15–20%. This can influence greatly the SKA infrastructure related costs. 相似文献
960.