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181.
In this summary of the 10 November 2006 RAS Specialist Discussion Meeting, organizers Paul Crowther and Steve Smartt consider aspects of massive stellar evolution, their dependence upon stellar winds, progenitor models and explosion mechanisms. In addition, observations of core-collapse supernovae were discussed alongside the question of whether supernovae form significant quantities of dust, of relevance to the detection of dust in star-forming galaxies in the early universe. 相似文献
182.
Hwa-Lung Yu Alexander Kolovos George Christakos Jiu-Chiuan Chen Steve Warmerdam Boris Dev 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):647-572
This paper describes the spatiotemporal epistematics knowledge synthesis and graphical user interface (SEKS–GUI) framework
and its application in medical geography problems. Based on sound theoretical reasoning, the interactive software library
of SEKS–GUI explores heterogeneous (spatially non-homogeneous and temporally non-stationary) health attribute distributions
(disease incidence, mortality, human exposure, epidemic propagation etc.); expresses the health system’s dependence structure
using (ordinary and generalized) spatiotemporal covariance models; synthesizes core knowledge bases, empirical evidence and
multi-sourced system uncertainty; and generates a meaningful picture of the real-world system using space–time dependent probability
functions and associated maps of health attributes. The implementation stages of the SEKS–GUI library are described in considerable
detail using appropriate screens. The wide applicability of SEKS–GUI is demonstrated by reviewing a selection of real-world
case studies.
An erratum to this article can be found at 相似文献
183.
184.
Chris J. Willott Steve Rawlings Katherine M. Blundell 《Monthly notices of the Royal Astronomical Society》2001,324(1):1-17
We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models that constrain their redshifts. Six of these seven galaxies have extremely red colours ( R − K >5.5) and we find that almost all of them lie in the redshift range 1< z <2. We also present near-infrared spectroscopy of these galaxies which demonstrate that their SEDs are not dominated by emission lines, although tentative lines, consistent with H α at z =1.45 and z =1.61, are found in two objects. Although the red colours of the 7CRS galaxies can formally be explained by stellar populations that are either very old or young and heavily reddened, independent evidence favours the former hypothesis. At z ∼1.5 at least 1/4 of powerful radio jets are triggered in massive (> L *) galaxies, which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z ≳5. If a similar fraction of all z ∼1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10 and 100 per cent of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 1< z <2. An ERO found serendipitously in the field of one of the 7CRS radio sources appears to be a radio-quiet analogue of the 7CRS EROs with an emission line likely to be [O ii ] at z =1.20. The implication is that some of the most massive elliptical galaxies formed the bulk of their stars at z ≳5 and these objects probably undergo at least two periods of active galactic nucleus activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z ∼1.5. 相似文献
185.
Steve Holland 《Experimental Astronomy》2002,14(2):83-89
Fully depleted, back-illuminated charge-coupled devices fabricated at Lawrence Berkeley National Laboratory on high-resistivity
silicon are described. Device operation and technology are discussed, as well as the results on telescopes and future plans.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
186.
McMahon K Bengtson Nash S Eaglesham G Müller JF Duke NC Winderlich S 《Marine pollution bulletin》2005,51(1-4):325-334
Low concentrations of herbicides (up to 70 ng l(-1)), chiefly diuron (up to 50 ng l(-1)) were detected in surface waters associated with inter-tidal seagrass meadows of Zostera muelleri in Hervey Bay, south-east Queensland, Australia. Diuron and atrazine (up to 1.1 ng g(-1) dry weight of sediment) were detected in the sediments of these seagrass meadows. Concentration of the herbicides diuron, simazine and atrazine increased in surface waters associated with seagrass meadows during moderate river flow events indicating herbicides were washed from the catchment to the marine environment. Maximum herbicide concentration (sum of eight herbicides) in the Mary River during a moderate river flow event was 4260 ng l(-1). No photosynthetic stress was detected in seagrass in this study during low river flow. However, with moderate river flow events, nearshore seagrasses are at risk of being exposed to concentrations of herbicides that are known to inhibit photosynthesis. 相似文献
187.
Will J. Percival Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Stephen Moody Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,327(4):1297-1306
The 2dF Galaxy Redshift Survey has now measured in excess of 160 000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct Fourier transform based technique. We argue that, within the k -space region , the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analysed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the Universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68 per cent confidence limits on the total matter density times the Hubble parameter , and the baryon fraction , assuming scale-invariant primordial fluctuations. 相似文献
188.
As technology matures, Real Time Kinematic (RTK) global positioning system (GPS) receivers are providing increased performance
in accuracy, on-the-fly (OTF) initialization times, measurement speed, and latency. Leica's Dozer 2000 machine guidance system
combines an MC1000 GPS sensor, graphic intensive guidance software, a digital terrain model, and a digital site plan. Figure
1 shows the operator's view of the system. The end results is a highly accurate, extremely responsive local navigation system.
Engineers can easily upload design information onto a touch-screen machine guidance personal computer (PC) and greatly reduce
earthmoving costs while simultaneously recording “as-built” inspection data.
The Leica MC1000 machine control sensor is a true 10-Hz, centimeter-level-accuracy, open-architecture GPS sensor specifically
designed for machine guidance and control. At the heart of the MC1000's performance are a very stable oven-controlled oscillator
(3 × 10−11/s short-term stability), a low-power Intel 486-DX4-80 processor, and four user-configurable input/output (I7O) ports. Special
algorithms mitigate the effects of multipath and Selective Availability (SA) while providing centimeter accuracy up to 10
times per second with only 30 milliseconds' latency. The high update rate and low latency are essential for machine guidance
and control.
The MC1000 GPS reference station is capable of outputting RTK and Differential GPS (DGPS) data simultaneously, providing and
entire site with GPS information for machine guidance and control, tracking and dispatching of vehicles, and support of survey
crews.
This article describes how recent advances in technology have combined to produce the Leica Dozer 2000 – a machine guidance
system that is ideal for a wide range of earthmoving and inspection applications. ? 2000 John Wiley & Sons, Inc. 相似文献
189.
The caldera-forming eruption of Volcán Ceboruco, Mexico 总被引:1,自引:1,他引:0
3 of magma erupted, ∼95% of which was deposited as fall layers. During most of the deposition of P1, eruptive intensity (mass
flux) was almost constant at 4–8×107 kg s−1, producing a Plinian column 25–30 km in height. Size grading at the top of P1 indicates, however, that mass flux waned dramatically,
and possibly that there was a brief pause in the eruption. During the post-P1 phase of the eruption, a much smaller volume
of magma erupted, although mass flux varied by more than an order of magnitude. We suggest that caldera collapse began at
the end of the P1 phase of the eruption, because along with the large differences in mass flux behavior between P1 and post-P1
layers, there were also dramatic changes in lithic content (P1 contains ∼8% lithics; post-P1 layers contain 30–60%) and magma
composition (P1 is 98% rhyodacite; post-P1 layers are 60–90% rhyodacite). However, the total volume of magma erupted during
the Jala pumice event is close to that estimated for the caldera. These observations appear to conflict with models which
envision that, after an eruption is initiated by overpressure in the magma chamber, caldera collapse begins when the reservoir
becomes underpressurized as a result of the removal of magma. The conflict arises because firstly, the P1 layer makes up too
large a proportion (∼75%) of the total volume erupted to correspond to an overpressurized phase, and secondly, the caldera
volume exceeds the post-P1 volume of magma by at least a factor of three. The mismatches between model and observations could
be reconciled if collapse began near the beginning of the eruption, but no record of such early collapse is evident in the
tephra sequence. The apparent inability to place the Jala pumice eruptive sequence into existing models of caldera collapse,
which were constructed to explain the formation of calderas much greater in volume than that at Ceboruco, may indicate that
differences in caldera mechanics exist that depend on size or that a more general model for caldera formation is needed.
Received: 18 November 1998 / Accepted: 23 October 1999 相似文献
190.
Ren Bødker William Kisinza Robert Malima Hamisi Msangeni Steve Lindsay 《Global Change & Human Health》2000,1(2):134-153
The recent spread of malaria in the Usambara Mountains in Tanzania has been blamed on climatic changes experienced during the 20th century. Here we suggest that recent changes in the pattern of malaria does not result so much from these changes as from changes in the use and efficacy of antimalarial drugs. The recent resurgence of malaria in this area corresponds with the rapid evolution of parasite strains resistant to chloroquine. The ineffectiveness of anti-malarial drugs may have left the people of the Usambaras at the same high risk of infection as they were before the introduction of modern medicine. 相似文献