全文获取类型
收费全文 | 7069篇 |
免费 | 286篇 |
国内免费 | 108篇 |
专业分类
测绘学 | 260篇 |
大气科学 | 625篇 |
地球物理 | 1698篇 |
地质学 | 2352篇 |
海洋学 | 692篇 |
天文学 | 1229篇 |
综合类 | 25篇 |
自然地理 | 582篇 |
出版年
2022年 | 40篇 |
2021年 | 78篇 |
2020年 | 89篇 |
2019年 | 107篇 |
2018年 | 167篇 |
2017年 | 162篇 |
2016年 | 228篇 |
2015年 | 173篇 |
2014年 | 217篇 |
2013年 | 396篇 |
2012年 | 250篇 |
2011年 | 387篇 |
2010年 | 291篇 |
2009年 | 411篇 |
2008年 | 405篇 |
2007年 | 361篇 |
2006年 | 321篇 |
2005年 | 279篇 |
2004年 | 250篇 |
2003年 | 267篇 |
2002年 | 229篇 |
2001年 | 159篇 |
2000年 | 170篇 |
1999年 | 128篇 |
1998年 | 150篇 |
1997年 | 101篇 |
1996年 | 109篇 |
1995年 | 84篇 |
1994年 | 79篇 |
1993年 | 74篇 |
1992年 | 69篇 |
1991年 | 73篇 |
1990年 | 48篇 |
1989年 | 53篇 |
1988年 | 42篇 |
1987年 | 54篇 |
1986年 | 54篇 |
1985年 | 75篇 |
1984年 | 72篇 |
1983年 | 68篇 |
1982年 | 63篇 |
1981年 | 63篇 |
1980年 | 55篇 |
1979年 | 47篇 |
1978年 | 56篇 |
1977年 | 38篇 |
1976年 | 42篇 |
1975年 | 37篇 |
1974年 | 35篇 |
1973年 | 37篇 |
排序方式: 共有7463条查询结果,搜索用时 46 毫秒
931.
Polybrominated diphenyl ethers (PBDEs) and organochlorines in small cetaceans from Hong Kong waters: levels, profiles and distribution 总被引:9,自引:0,他引:9
Polybrominated diphenyl ethers (PBDEs) and organochlorine compounds (OCs) were determined in the blubber, liver and kidney of Indo-Pacific humpback dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) stranded in Hong Kong coastal waters during 1995–2001. Among the organohalogen compounds analyzed, DDTs were the most dominant contaminants with concentrations ranging from 9.9 to 470 μg/g lipid wt. PBDEs in Hong Kong cetaceans, which are reported for the first time, were detected in all the samples with values ranging from 0.23 to 6.0 μg/g lipid wt., with a predominance of BDE-47. Results from this study suggest PBDEs should be classified as priority pollutants in Asia. Higher concentrations were found in humpback dolphins than in finless porpoises, and this was attributed mainly to differences in habitat. Elevated residues of PCBs and DDTs in some cetaceans suggest these species may be at risk. 相似文献
932.
Recent data on the Tully–Fisher relation for spiral galaxies are compatible with the traditional correlation for astrophysical
systems, where the angular momentum varies as the square of the mass. Such a correlation is consistent with standard gravitational
theory, but is not explained by it. We here show that the noted relation follows from currently popular accounts of extended
or higher-dimensional gravitational theory. The latter also predicts that the spins of spirals should decay as the universe
expands, which can be tested by extending the Tully–Fisher data to higher redshifts. 相似文献
933.
We have performed high-resolution spectral observations at mid-infrared wavelengths of C2H6 (12.16 μm), and C2H2 (13.45 μm) on Saturn. These emission features probe the stratosphere of the planet and provide information on the hydrocarbon photochemical processes taking place in that region of the atmosphere. The observations were performed using our cryogenic echelle spectrometer Celeste, in conjunction with the McMath-Pierce 1.5-m solar telescope in November and December 1994. We used Voyager IRIS CH4 observations (7.67 μm) to derive a temperature profile on the saturnian atmosphere for the region of the stratosphere. This profile was then used in conjunction with height-dependent volume mixing ratios of each hydrocarbon to determine global abundances for ethane and acetylene. Our ground-based measurements indicate abundances of for C2H6 (1.0 mbar pressure level), and for C2H2 (1.6 mbar pressure level). We also derived new mixing ratios from the Voyager mid-latitude IRIS observations; 8.6±0.9×10−6 for C2H6 (0.1-3.0 mbar pressure level), and 1.6±0.2×10−7 for C2H2 (2.0 mbar pressure level). 相似文献
934.
Ionospheric climatology derived from gps occultation observations made by the ionospheric occultation experiment 总被引:1,自引:1,他引:0
Paul Straus 《GPS Solutions》2005,9(2):164-173
The ionospheric occultation experiment (IOX) is a GPS occultation sensor with an ionospheric mission focus. IOX measurements of GPS L1 and L2 carrier phase during Earth limb views of setting GPS satellites are used together with the Abel transform to determine vertical profiles of electron density from which F-region peak parameters are determined. Data from a four and a half month period beginning in November 2001 are statistically binned and compared with a climatological model. To account for potential errors in interpretation that could arise from violation of the Abel transform assertion of spherical symmetry, the data are compared to both the climatology and to statistics of simulated ionospheric inversions using the climatological model. General characteristics of the climatology are reproduced by the occultation data. However, several significant discrepancies between the model and the data are observed during this near-solar maximum time period. In particular, average mid-latitude daytime densities are shown to be higher than the climatological prediction and the height of F2 layer in the post-sunset equatorial region is underestimated by up to 150 km.
相似文献
Paul StrausEmail: Phone: +1-310-3365328Fax: +1-310-3361636 |
935.
The Summer Surface Energy Balance of the High Antarctic Plateau 总被引:1,自引:0,他引:1
Dirk?van?AsEmail author Michiel?van?den?Broeke Carleen?Reijmer Roderik?van?de?Wal 《Boundary-Layer Meteorology》2005,115(2):289-317
The summertime surface energy balance (SEB) at Kohnen station, situated on the high Antarctic plateau (75°00′ S, 0°04′ E,
2892m above sea level) is presented for the period of 8 January to 9 February 2002. Shortwave and longwave radiation fluxes
were measured directly; the former was corrected for problems associated with the cosine response of the instrument. Sensible
and latent heat fluxes were calculated using the bulk method, and eddy-correlation measurements and the modified Bowen ratio
method were used to verify these calculated fluxes. The calculated sub-surface heat flux was checked by comparing calculated
to measured snow temperatures. Uncertainties in the measurements and energy-balance calculations are discussed.
The general meteorological conditions were not extraordinary during the period of the experiment, with a mean 2-m air temperature
of −27.5°C, specific humidity of 0.52×10−3kg kg−1 and wind speed of 4.1ms−1. The experiment covered the transition period from Antarctic summer (positive net radiation) to winter (negative net radiation),
and as a result the period mean net radiation, sensible heat, latent heat and sub-surface heat fluxes were small with values
of −1.1, 0.0, −1.0 and 0.7 Wm−2, respectively. Daily mean net radiation peaked on cloudy days (16 Wm−2) and was negative on clear-sky days (minimum of −19 W m−2). Daily mean sensible heat flux ranged from −8 to +10 Wm−2, latent heat flux from −4 to 0 Wm−2 and sub-surface heat flux from −8 to +7 Wm−2. 相似文献
936.
937.
A novel scenario for Maunder minimum-like grand minima epochs of reduced solar activity is proposed, based on diffusive coupling
between both solar hemispheres, each susceptible to stochastically-driven intermittent behavior. After introducing cross-hemispheric
coupling into a well-validated reduced model of the solar cycle based on the Babcock–Leighton mechanism for poloidal field
regeneration, simulations are presented demonstrating that even weak coupling can lead to a high degree of synchronicity between
the two hemispheres. This is in qualitative agreement with the similar onset and recovery times of sunspot activity at and
around the Maunder minimum. Moreover, even weak coupling manages to greatly reduce the frequency and duration of quiescent
episodes, again in qualitative agreement with the relative paucity of grand minima in the sunspot and radioisotope records. 相似文献
938.
J. C. van der Ha 《Celestial Mechanics and Dynamical Astronomy》1982,26(3):285-309
The three-dimensional relative motion of a subsatellite with respect to a reference station in an elliptical orbit is studied. A general theory based on the variation of the relative elements, i.e. the instantaneous differences between the orbital parameters of the subsatellite and those of the station, is formulated in order to incorporate arbitrary perturbing forces acting on both satellites. The loss of precision inherent in the subtraction of almost identical quantities is avoided by the consistent use of difference variables. In the absence of perturbations exact analytical representations can be obtained for the relative state parameters. The influences of air drag and Earth's oblateness on the relative motion trajectories are investigated and illustrated graphically for a number of cases. 相似文献
939.
Wave-tank studies were conducted on the measurement of the drift velocity at the breaking point under different types of breaking waves on a rigid, plane beach. The drift velocity has onshore direction near the surface and close to the bottom; in the main flow column, the drift velocity is always offshore. The offshore drift velocity shows a more uniform vertical distribution than that in the offshore region. The experimental data are compared with theoretical values of three different second-order constant-depth wave theories. Comparisons with data from other sources are also made. 相似文献
940.
J. van Kuilenburg 《Mathematical Geology》1986,18(1):75-92
Design of a system which accepts geological maps or soil maps, together with corresponding well logs and produces interpretation maps, is described. The major aim was to get a processing program that would be useful at an operational scale that avoids the use of special purpose graphics hardware. This was achieved by using segment encoding of lines and by treatment of mapped units as basic graphical units (atoms). The system operation was split into an input phase and a processed phase. Input- and file-building require some technical experience, but are a one-time affair, whereas subsequent processing requires less (graphical) resources and experience, but is of a repetitive nature. When writing processing programs, emphasis was placed on ease of adding options. Clever improvements of efficiency (e.g., disk traffic) were not deemed worthwhile or even wise. Two driving forces behind the project required the programs reported here. First was the observation that digital data can be used only if appropriate programs are readily available to produce required results without need for large investments in hardware. Second was the idea that digital tools could be most effective if they allow the end-user (customer) to interact directly with the full base of data without recourse to technical experts. The resulting system is operational and running on a VAX 11/750, coded in FORTRAN. 相似文献