全文获取类型
收费全文 | 96922篇 |
免费 | 1512篇 |
国内免费 | 961篇 |
专业分类
测绘学 | 2794篇 |
大气科学 | 7071篇 |
地球物理 | 19603篇 |
地质学 | 34529篇 |
海洋学 | 8057篇 |
天文学 | 21702篇 |
综合类 | 342篇 |
自然地理 | 5297篇 |
出版年
2022年 | 525篇 |
2021年 | 933篇 |
2020年 | 1009篇 |
2019年 | 1089篇 |
2018年 | 2553篇 |
2017年 | 2389篇 |
2016年 | 3080篇 |
2015年 | 1812篇 |
2014年 | 2986篇 |
2013年 | 5177篇 |
2012年 | 3029篇 |
2011年 | 4101篇 |
2010年 | 3455篇 |
2009年 | 4550篇 |
2008年 | 4127篇 |
2007年 | 3880篇 |
2006年 | 3711篇 |
2005年 | 3016篇 |
2004年 | 2842篇 |
2003年 | 2724篇 |
2002年 | 2551篇 |
2001年 | 2364篇 |
2000年 | 2255篇 |
1999年 | 1856篇 |
1998年 | 1923篇 |
1997年 | 1859篇 |
1996年 | 1570篇 |
1995年 | 1580篇 |
1994年 | 1371篇 |
1993年 | 1237篇 |
1992年 | 1178篇 |
1991年 | 1094篇 |
1990年 | 1180篇 |
1989年 | 1058篇 |
1988年 | 947篇 |
1987年 | 1175篇 |
1986年 | 973篇 |
1985年 | 1233篇 |
1984年 | 1347篇 |
1983年 | 1283篇 |
1982年 | 1228篇 |
1981年 | 1030篇 |
1980年 | 994篇 |
1979年 | 887篇 |
1978年 | 891篇 |
1977年 | 815篇 |
1976年 | 775篇 |
1975年 | 740篇 |
1974年 | 764篇 |
1973年 | 764篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Data are presented on some structure parameters of mesoscale turbulence mechanisms playing a significant role in the troposphere-stratosphere
exchange in the tropical tropopause layer and in the lower stratosphere. The data are obtained in the framework of the international
aircraft AMMA experiment in Burkina Faso (West Africa) in August 2006. 相似文献
993.
An analysis is made of the results from all repeated gravity measurements of the Fennoscandian land uplift gravity line 63°. The line is, thereby, divided into two separate parts: one part west of the land uplift maximum, and the other part east of the land uplift maximum. A statistically significant change of gravity is found both for the western part and the eastern one. Both parts give a relation between gravity change and land uplift of about ?0.22μgal/mm. 相似文献
994.
Abstract. The stomach contents of poor cod, Trisopterus minutus capelanus (Lacepède), were taken at monthly intervals off the eastern coast of the Gulf of Valencia (Spain). A total of 1276 were analyzed to determine diet according to fish size and season. The basic food consists of crustaceans (Mysidacea and Decapoda) and teleosts. Feeding habits varied with size: decapods and fishes were more abundant in the stomachs of larger specimens. Little seasonal variation in food habits was recorded. 相似文献
995.
V. M. Sergeeva L. S. Zhitina S. A. Mosharov A. A. Nedospasov A. A. Polukhin 《Oceanology》2018,58(5):700-709
Phytoplankton community and its distribution were investigated in the south part of the Polar Front in the eastern Barents Sea in October 2014. Analysis of the spatial differences in the phytoplankton structure was performed in connection with changes of the temperature, salinity and biogenic regime. At the end of the growing season in the phytoplankton community was dominated by destruction processes and the concentration of nutrients in the upper mixed layer was higher than the limiting level. Coccolithophores (Emiliania huxleyi and Discosphaera cf. tubifer) dominanted over investigated area. The maximum values of abundance and biomass of coccolithophores reached 90.4 mln.cell/m3 and 30.8 mgC/m3, drawing up 82% of the total number and 93% of the total biomass of phytoplankton. Influence of transformed the waters of Atlantic origin was observed in the western part of the investigated area. The number of species in the phytoplankton community here was 1.5–2 times lower than in the eastern part of the occupied mostly by Barents Sea water. In the eastern part of the presence of large dinoflagellates Neoceratium spp. (Ceratium spp.) and Dinophysis spp., lower values of chlorophyll a concentration, a higher proportion of pheophytin in the amount of pigment chlorophyll + pheophytin, the high content of ammonia in the upper mixed layer showed that in this area the phytoplankton was at a later seasonal succession stage than the western part. 相似文献
996.
The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov. 相似文献
997.
The effect of ambient currents on nearshore nonlinear wave–wave energy transfer in random waves is studied with the use of a nonlinear frequency domain wave–current interaction model. We focus on the phenomenon of wave recurrence as a classical nonlinear phenomenon whose characteristics are well established for systems truncated to small numbers of frequency modes. The model used for this study is first extended to enhance accuracy; comparisons of permanent form solutions to analytical forms confirm the model accuracy. Application of the model to a highly truncated system confirmed the model’s consistency with published results for both positive (following) and negative (adverse) currents. Propagation of random wave spectra over a flat bottom was performed with the model, with the intent of determining the prevalence of recurrence between the spectral peak and its harmonics. For spectra of moderate Ursell number, it was found that positive currents extended the length scale of recurrence relative to the case with no currents; conversely, negative currents reduced the recurrence lengths. However, beyond a propagation distance of ≈40 wavelengths of the spectral peak, recurrence becomes almost completely damped as the spectra becomes broad and the spectral energies equilibrate. For spectra of high Ursell number, in contrast, recurrence is almost immediately damped, suggesting that the nonlinearity is sufficient to allow immediate spectral broadening and equilibration and overwhelming any preferential interactions among the spectral peak and its harmonics, regardless of current magnitude or direction. 相似文献
998.
H. Tissoux H. Valladas P. Voinchet J.L. Reyss N. Mercier C. Falguères J.-J. Bahain L. Zöller P. Antoine 《Quaternary Geochronology》2010,5(2-3):131-136
As part of a chronological study of the famous Upper Pleistocene Nussloch (Germany) loess sequence, three samples were collected to check the applicability of palaeodosimetric dating methods (OSL and ESR) to quartz grains. The ESR-multicentre method showed a partial bleaching of the ESR centers in aeolian sands. This partial bleaching was also observed by OSL. Laminated loess seemed to be sufficiently bleached but showed a large scatter of the doses, which we ascribed to heterogeneous responses of the luminescent grains to the SAR protocol. Ages could nevertheless be calculated for the three samples and were found to be somewhat older than the IRSL and 14C ages obtained for the same layers of the laminated loess. 相似文献
999.
C. G. Campbell & P. M. Heptinstall 《Monthly notices of the Royal Astronomical Society》1998,301(2):558-568
A full numerical solution is found for the effect of a strongly magnetic star on its accretion disc, for the case of magnetic buoyancy diffusion. As in the previously considered case of turbulent diffusion, the disc becomes disrupted when magnetic and viscous stresses become comparable. A magnetically induced temperature elevation leads to electron scattering opacity and radiation pressure becoming significant far from the stellar surface, with consequent viscous instability and vertical disruption of the disc. This, together with the previous turbulent case, suggests that such a disruption mechanism owing to strongly magnetic accretors is generally operable. 相似文献
1000.
An upper limit has been calculated on the effective aperture separation or detector thickness of ion drift meters of two fundamental types. The limit applies to meters which compare currents collected by detectors with different view directions at the same retarding potential and to meters which measure the entire thermal ion distribution function. For both types, a single scanned detector may be employed instead of multiple detectors, in which case the limit applies to twice the radius of curvature of the path followed by the detector aperture during a scan, (i.e. the diameter of a spinning payload). The limit was found to be important in two cases. First, in the F region on spacecraft with stringent electrostatic cleanliness requirements, the 10% error limit was found to be 40 cm. Second, in the E region, the limit was found to be 1 cm.Originally submitted to the journalSpace Science Instrumentation.Deceased. 相似文献