全文获取类型
收费全文 | 61篇 |
免费 | 4篇 |
专业分类
大气科学 | 1篇 |
地球物理 | 14篇 |
地质学 | 10篇 |
海洋学 | 25篇 |
天文学 | 15篇 |
出版年
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 10篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 1篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1981年 | 3篇 |
1978年 | 1篇 |
排序方式: 共有65条查询结果,搜索用时 0 毫秒
41.
Tu Binh Minh Mafumi Watanabe Haruhiko Nakata Shinsuke Tanabe Thomas A. Jefferson 《Marine pollution bulletin》1999,39(1-12):383-392
Blubber samples of 2 cetacean species, the Indo-Pacific hump-backed dolphin (Sousa chinensis) (n=11) and finless porpoise (Neophocaena phocaenoides) (n=9), collected from Hong Kong coastal waters were analysed for persistent organochlorines. Mean concentration in the blubber of DDTs was ranked first (46 μg/g wet wt.), followed by PCBs (24 μg/g wet wt.), HCHs (0.76 μg/g wet wt.), chlordane compounds (0.38 μg/g wet wt.) and HCB (0.07 μg/g wet wt.). The present cetacean species may potentially be faced with high risk due to the elevated level of DDTs and PCBs. Relatively high concentrations of PCBs and DDTs can be attributed to the continuous environmental input of these compounds in the Far East region including Hong Kong. Highly chlorinated PCBs such as IUPAC Nos. 138, 153, 180 were the prominent congeners, accounting for 39% of the total PCBs. Mean concentrations of 6 non- and mono-ortho coplanar congeners were 2.1 and 2.8 μg/g wet wt. in the hump-backed dolphin and finless porpoise, respectively. Among highly toxic coplanar PCBs, mono-ortho congener IUPAC No. 118 and non-ortho congener IUPAC No. 126 were estimated to have the greatest toxicity contribution. Tris(4-chlorophenyl) methane (TCPMe) and tris(4-chlorophenyl) methanol (TCPMeOH), which have been the most recently identified microcontaminants, were also detected with the highest concentration of 290 and 300 ng/g (wet wt. basis), respectively. The concentrations of TCPMe relative to TCPMeOH in cetaceans from Hong Kong coastal waters were significantly higher than those found in various seals collected from other parts of the world, suggesting the different metabolic system of these two compounds between seals and cetaceans. Correlations between the concentrations of tris-chlorophenyl compounds with other persistent organochlorines such as HCHs, CHLs, DDTs and PCBs were significant, suggesting their accumulation nature similar to these organochlorines. 相似文献
42.
Calcium and magnesium‐bearing sabugalite occurs as aggregations of yellowish platy crystals in veinlets or druses in conglomerate from the oxidized parts of the Tono uranium deposit, Central Japan. X‐ray powder diffractometry of this mineral has reflections consistent with previous powder diffraction data of sabugalite. It is included in the monoclinic system with space group C2/m and calculated cell parameters of a = 19.68Å, b = 9.89Å, c = 9.82Å α = γ = 90°, β‐96.93° and V = 1897.83Å3. Chemical analysis yields a formula of (Ca0.10 Mg0.09)Σ0.19Al0.53(UO2)2.04((PO4)1.99(AsO4)0.01)Σ2.00·11.22H2O. EMPA mapping shows that the mineral is compositionally uniform with no micron‐scale layering. Charge of cations including Ca and Mg in the cation‐H2O layer is 1.98 being identical to that of autunite group minerals. This suggests that the charge balance in the cation‐H2O layer of the mineral could be made by the alkaline earth or alkaline elements rather than by hydrogen ions. 相似文献
43.
Fumiaki Nakata Kazuhiro Shimasaku Mamoru Doi Nobunari Kashikawa Wataru Kawasaki Yutaka Komiyama Sadanori Okamura Maki Sekiguchi Masafumi Yagi Naoki Yasuda 《Monthly notices of the Royal Astronomical Society》1999,309(4):L25-L29
We investigate pure luminosity evolution models for early-type (elliptical and S0) galaxies (i.e. no number density change or morphological transition), and examine whether these models are consistent with observed number counts in the B , I and K bands, and redshift distributions of two samples of faint galaxies selected in the I and K bands. The models are characterized by the star formation time-scale τ SF and the time t gw when the galactic wind starts to blow, in addition to several other conventional parameters. We find that the single-burst model ( τ SF =0.1 Gyr and t gw =0.353 Gyr), which is known to reproduce the photometric properties of early-type galaxies in clusters, is inconsistent with the redshift distributions of early-type galaxies in the field environment, owing to overpredictions of the number of galaxies at z ≳1.4 even with strong extinction which is at work until t gw . In order for dust extinction to be more effective, we treat τ SF and t gw as free parameters, and find that models with τ SF ≳0.5 Gyr and t gw >1.0 Gyr can be made consistent with both the observed redshift distributions and the number counts, if we introduce strong extinction [ E ( B − V )≥1 as a peak value]. These results suggest that early-type galaxies in the field environment do not have the same evolutionary history as described by the single-burst model. 相似文献
44.
Abstract We have studied the behavior of nonlinear waves in isothermal atmospheres using an improved beam scheme method. It is shown that although the magnitude of the mass leakage due to side beams is significant, nevertheless in a motion close to hydrostatic equilibrium it can be suppressed, if special density distributions and/or suitable mesh intervals are selected. We adopt as the parameters for our model of the atmospheres M=1 M[odot], R=50 R[odot] and T=4864 K. The time variation of the physical quantities in each cell is found for several oscillation periods. The critical frequency for the model atmosphere in the case of waves with a weak nonlinearity seems to be consistent with that in the linear theory. 相似文献
45.
H.Shirai Y.Kamide E.A.Kihn B.Hausman M.Shinohara H.Nakata M.Isowa T.K.Takada Y.Watanabe S.Masuda 《中国天文和天体物理学报》2003,3(4):375-380
This paper presents the recent progress in our project of estimating near real-time electric fields and currents in the ionosphere through our computer system called the Geospace Environment Data Analysis System (GEDAS). We show a new technique in which data from ground magnetometers are collected by the system and used as input for the KRM and AMIE programs to calculate the distribution of ionospheric electric fields and currents, as well as of other ionospheric parameters, such as electric potential patterns. One of the goals of this project is to specify ionospheric processes. Examples of the near real-time calculation and the data flow of our scheme are presented. 相似文献
46.
47.
H. G. Wilshire J. K. Nakata Susan Shipley Karen Prestegaard 《Environmental Geology》1978,2(5):295-319
The impacts of off-road vehicles on vegetation and soil were investigated at seven representative sites in the San Francisco
Bay area. Plant cover of grass and chaparral (with shrubs to 4 m tall) have been stripped by the two- and four-wheel vehicles
in use. Impacts on loamy soils include increased surface strength (as much as 275 bars), increased bulk density (averaging
18%) to depths of 90 cm or more, reduction of soil moisture by an average 43% to 30 cm depths, greatly reduced infiltration,
extension of the diurnal temperature range by as much as 12°C, and reduction of organic carbon by an average 33% in exposed
soils. Very sandy soils respond similarly to vehicular use except that moisture is increased and surface strength of beach
sand is decreased.
These physical and chemical impacts reduce the land's capability of restoring its vegetative cover, which in turn adversely
affects animal populations. Both the loss of plant cover and the physical changes caused by vehicles promote erosion. Measured
soil and substrate losses from vehicular use zones range from 7 to 1180 kg/m2. The estimated erosion rate of the Chabot Park site exceeds the rate of erosion considered a serious problem by a factor
30, it exceeds United States Soil Conservation Service tolerance values by a factor of 46, and it exceeds average San Francisco
Bay area erosion rates by a factor of 17. The resulting soil losses are effectively permanent. Neither the increased sediment
yield nor the increased runoff is accomodated on the sites of use, and both are causing adverse effects to neighboring properties. 相似文献
48.
This study proposes a new substructure shake table test method that allows for experimental investigation of the lower portion of structures while the upper part is numerically analyzed. Compatibility conditions are derived to ensure that the dynamic characteristics of the substructured system are equivalent to the reference entire structure. This method utilizes controlled masses to incorporate interface forces from the computational substructure to the experimental substructure. A feasible implementation procedure for the interface force compatibility is developed using a series of conversions and signal processing. For validation of the capabilities and limitations of the proposed substructure method, numerical simulations are performed using detailed models including dynamics of the controlled mass systems. Results from the numerical simulations showed that the proposed substructure method produced comparable results to the reference entire simulations. The average error between top floor displacements produced by substructured and entire responses for earthquake inputs was 7.1%. Numerical studies showed that the substructure method has potential to serve as an alternative to shaking table tests of entire structures. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
49.
Experimental implementation and verification of multi‐degrees‐of‐freedom effective force testing 下载免费PDF全文
This paper presents an experimental implementation and verification of multi‐degrees‐of‐freedom effective force testing (MDOF‐EFT). An experimental setup that consists of a two‐degrees‐of‐freedom structural system and two hydraulic actuators at the Johns Hopkins University was utilized in this study. First, experimental system identification was performed to develop compatible analytical models for the multi‐input and multi‐output systems. Dynamics of the control plant, that is, the valve‐to‐force relations, were modeled with a rational polynomial transfer function matrix and delay components. By using the analytical model, a centralized decoupling loop‐shaping force feedback controller was designed such that the forces are uncoupled and the loop transfer functions have desirable dynamic characteristics in the frequency domain. Then, a series of harmonic force and earthquake simulation tests were performed to assess capabilities and limitations of MDOF‐EFT. Experimental results showed that the dynamic forces in the two actuators were accurately controlled to provide tracking while the system was stable and robust for the entire period of the experiment. Furthermore, earthquake simulation tests with increased levels of the reference forces demonstrated the feasibility of MDOF‐EFT with highly nonlinear test structures. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
50.
Masahisa Yanagisawa Satoshi Tanaka Tatsuaki Okada Tatsuo Konno 《Earth, Moon, and Planets》1996,73(2):117-124
We monitored Jupiter with a video movie camera attached to a 1.3 m reflector during the impact event of the K fragment of D/Shoemaker-Levy 9. The camera was sensitive to visible radiation. A plume, which was generated by the impact and prominent in infrared wavelength, was not detected. Jovian images with hypothetical plumes were synthesized to examine how luminous the plume should have been to be recognized. It has been revealed that the plume was no more than twice as bright as Io in visible wavelength. 相似文献