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61.
Michael J.S. Belton Karen J. Meech Steven Chesley Jana Pittichová Brian Carcich Michal Drahus Alan Harris Stephen Gillam Joseph Veverka Nicholas Mastrodemos William Owen Michael F. A’Hearn S. Bagnulo J. Bai L. Barrera Fabienne Bastien James M. Bauer J. Bedient B.C. Bhatt Hermann Boehnhardt H. Zhao 《Icarus》2011,213(1):345-368
The evolution of the spin rate of Comet 9P/Tempel 1 through two perihelion passages (in 2000 and 2005) is determined from 1922 Earth-based observations taken over a period of 13 year as part of a World-Wide observing campaign and from 2888 observations taken over a period of 50 days from the Deep Impact spacecraft. We determine the following sidereal spin rates (periods): 209.023 ± 0.025°/dy (41.335 ± 0.005 h) prior to the 2000 perihelion passage, 210.448 ± 0.016°/dy (41.055 ± 0.003 h) for the interval between the 2000 and 2005 perihelion passages, 211.856 ± 0.030°/dy (40.783 ± 0.006 h) from Deep Impact photometry just prior to the 2005 perihelion passage, and 211.625 ± 0.012°/dy (40.827 ± 0.002 h) in the interval 2006–2010 following the 2005 perihelion passage. The period decreased by 16.8 ± 0.3 min during the 2000 passage and by 13.7 ± 0.2 min during the 2005 passage suggesting a secular decrease in the net torque. The change in spin rate is asymmetric with respect to perihelion with the maximum net torque being applied on approach to perihelion. The Deep Impact data alone show that the spin rate was increasing at a rate of 0.024 ± 0.003°/dy/dy at JD2453530.60510 (i.e., 25.134 dy before impact), which provides independent confirmation of the change seen in the Earth-based observations.The rotational phase of the nucleus at times before and after each perihelion and at the Deep Impact encounter is estimated based on the Thomas et al. (Thomas et al. [2007]. Icarus 187, 4–15) pole and longitude system. The possibility of a 180° error in the rotational phase is assessed and found to be significant. Analytical and physical modeling of the behavior of the spin rate through of each perihelion is presented and used as a basis to predict the rotational state of the nucleus at the time of the nominal (i.e., prior to February 2010) Stardust-NExT encounter on 2011 February 14 at 20:42.We find that a net torque in the range of 0.3–2.5 × 107 kg m2 s?2 acts on the nucleus during perihelion passage. The spin rate initially slows down on approach to perihelion and then passes through a minimum. It then accelerates rapidly as it passes through perihelion eventually reaching a maximum post-perihelion. It then decreases to a stable value as the nucleus moves away from the Sun. We find that the pole direction is unlikely to precess by more than ~1° per perihelion passage. The trend of the period with time and the fact that the modeled peak torque occurs before perihelion are in agreement with published accounts of trends in water production rate and suggests that widespread H2O out-gassing from the surface is largely responsible for the observed spin-up. 相似文献
62.
J.J. Bhatt 《Sedimentary Geology》1976,15(3):173-191
This preliminary petrographic study of a Paleozoic carbonate section (Upper Ordovician to Silurian) in the Lone Mountain district in east-central Nevada provides new information on its microfacies and dolomitization. The occurrence of diversified microfacies in rocks from this section reveals the complex nature of their depositional history, as well as the subsequent diagenesis. Most microfacies from these rocks fall into two general groups: (1) dolomite facies which predominates in the Hanson Creek Formation (Upper Ordovician to Lowest Silurian) and the Lone Mountain Unit 1; and (2) dolomitized limestone facies which is common in the Lone Mountain Formation (Upper Silurian).The dolomite in the mid-Paleozoic carbonate section of the Lone Mountain is overwhelmingly diagenetic in origin. The early diagenetic dolomite is characterized by its homogeneous texture, uniform medium-to-coarse grain size and poorly preserved fossil impressions. The fossil content in this type of dolomite indicates its original calcareous nature. On the other hand, the late-diagenetic dolomite is characterized by its heterogeneous texture, non-uniform grain-size, detrital-quartz content and the presence of partly or incompletely altered fossil structures. 相似文献
63.
Himali Bhatt J. C. Pandey K. P. Singh Ram Sagar Brijesh Kumar 《Journal of Astrophysics and Astronomy》2014,35(1):39-54
We present, for the first time, an analysis of seven intense X-ray flares observed from six stars (LAV 796, LAV 1174, SHM2002 3734, 2MASS 02191082+5707324, V553 Car, V557 Car). These stars are located in the region of young open star clusters NGC 869 and IC 2602. These flares detected in the XMM-Newton data show a rapid rise (10–40 min) and a slow decay (20–90 min). The X-ray luminosities during the flares in the energy band 0.3–7.5 keV are in the range of 1029.9 to 1031.7 erg s?1. The strongest flare was observed with the ratio ~13 for count rates at peak of the flare to the quiescent intensity. The maximum temperature during the flares has been found to be ~100 MK. The semi-loop lengths for the flaring loops are estimated to be of the order of 1010 cm. The physical parameters of the flaring structure, the peak density, pressure and minimum magnetic field required to confine the plasma have been derived and found to be consistent with flares from pre-main sequence stars in the Orion and the Taurus-Auriga-Perseus region. 相似文献
64.
Nishith Y. Bhatt Satish J. Patel Dipal A. Patel Hardik P. Patel 《Journal of the Geological Society of India》2009,74(4):515-530
Behavioural activities of the goby fish-Periophthalmodon septemradiatus were observed in the intertidal zone around Navinal coast in the Gulf of Kachchh, western India. Intertidal zone is broad,
and comprise of creeks, which are muddy and vegetated by mangrove on eastern side and ridge runnel systems on western side
of the study area which are hospitable for the goby fish. Different types of biogenic activities are observed such as crawling,
pellet making, grazing and burrowing. The crawling activity is part of movement of the goby fish from one burrow to another
burrow and pellet making activity is part of burrow modification. The grazing activity is feeding on the surface mud after
receding of tide and exposure of the tidal flat by left and right movement of the front part of the body. The most conspicuous
activity is burrowing, they construct unlined, vertical to incline ‘I’, ‘J’ and ‘Y’ shaped branched, circular to oval burrows
with varying diameter and depth. In the muddy sediments goby fish produced circular to oval rimmed muddy lumps as surfacial
expression around the burrows and further produced funnel shape depression and downward extended cylindrical holes, while
in the runnels burrows are usually small and simple. The trail is consisting of fin marking on either side of the tail marks
(grooves) which are radiate around the burrows. Occasionally burrows are interconnected in more than one burrow system which
is nested within single funnel structure on the surface.
The burrow systems of the goby fish in the intertidal sediments serves for protection and dwelling purpose and most importantly
these burrows are irrigated by water which supply the oxygen and keep body surface wet. The overall dimensions of the burrow
decrease towards the lower intertidal zone. In all, behavioural structure produced by the goby fish marks the combined activity
of dwelling, feeding and grazing. The complex behavioural mechanisms have helped the goby fish to survive and flourish in
the harsh intertidal environments along the Navinal Coast, in the Gulf of Kachchh. 相似文献
65.
C. M. Bhatt Rajiv Chopra P. K. Sharma 《Journal of the Indian Society of Remote Sensing》2007,35(2):129-139
Anandpur Sahib area of Rupnagar district (Punjab) was investigated using an integrated multi-disciplinary approach of geomorphological,
structural, drainage and morphotectonic analysis through satellite data and GIS. Most commonly used geomorphic indices viz.,
channel sinuosity, drainage basin asymmetry, basin elongation ratio, mountain front sinuosity and valley floor to valley width
ratio index have been used to identify the geomorphic indicators of active tectonics in the area. Existence of fluvial anomalies
viz., abrupt changes in flow direction, flow against gradient, beheaded streams and river terraces reflect the strong structural
control on the fluvial features. Asymmetric nature of drainage basin, elongated nature of the sub-watersheds, straight to
curvilinear mountain fronts and narrow incised valley floors further substantiate the role of active tectonics in the region. 相似文献
66.
The capacity spectrum method (CSM) has established itself as one of the most used Nonlinear Static Procedures for the seismic assessment of structures, since its introduction in 1975, when it was first presented by Freeman. More recently, this procedure was implemented in the ATC40 guidelines and lately improved in the FEMA‐440 report. The first step of work addressed by this paper relates to the comparison between the two features of the CSM. In the second part, an extension of the FEMA‐440CSM version is proposed for plan‐asymmetric real RC building structures. The case studies under analysis are the SPEAR building—an irregular 3D structure representing typical old three‐storey buildings in the Mediterranean region, from the early 1970s—and two real Turkish buildings with five and eight storeys. The CSM‐ATC40, the CSM‐FEMA440 and the proposed extended CSM‐FEMA440 method are applied and the results obtained duly compared with nonlinear dynamicit timehistory analyses. For the latter, semi‐artificial ground motions are used to define the seismic action. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
67.
68.
Prizomwala S. P. Gandhi Drasti Ukey Vishal M. Bhatt Nilesh Rastogi B. K. 《Natural Hazards》2015,75(2):1187-1203
Natural Hazards - The coastal segment of Diu Island from west coast of India has been studied for its boulder deposits. The dimensions, morphology and characteristics of these boulders were studied... 相似文献
69.
70.
Angelica glauca is one of the important medicinal plants and it is widely used by indigenous communities for different purposes. The present study analyzes variability in reproductive characters of A. glauca. The reproductive parts were found having significant positive correlation with altitude (e.g.,number of umbellets /umber r= 0.857,p〈0.05; umbel diameter r=0.735,p〈0.05). 相似文献