全文获取类型
收费全文 | 70359篇 |
免费 | 18269篇 |
国内免费 | 42378篇 |
专业分类
测绘学 | 3669篇 |
大气科学 | 23754篇 |
地球物理 | 19897篇 |
地质学 | 45623篇 |
海洋学 | 19090篇 |
天文学 | 10927篇 |
综合类 | 4046篇 |
自然地理 | 4000篇 |
出版年
2022年 | 466篇 |
2021年 | 857篇 |
2020年 | 2131篇 |
2019年 | 5658篇 |
2018年 | 6392篇 |
2017年 | 6059篇 |
2016年 | 6359篇 |
2015年 | 5229篇 |
2014年 | 5124篇 |
2013年 | 6581篇 |
2012年 | 5504篇 |
2011年 | 5588篇 |
2010年 | 5464篇 |
2009年 | 5363篇 |
2008年 | 4433篇 |
2007年 | 4408篇 |
2006年 | 3954篇 |
2005年 | 3523篇 |
2004年 | 3933篇 |
2003年 | 3567篇 |
2002年 | 3312篇 |
2001年 | 2955篇 |
2000年 | 2508篇 |
1999年 | 2389篇 |
1998年 | 2504篇 |
1997年 | 2589篇 |
1996年 | 2027篇 |
1995年 | 1923篇 |
1994年 | 1767篇 |
1993年 | 1648篇 |
1992年 | 1413篇 |
1991年 | 1192篇 |
1990年 | 1136篇 |
1989年 | 1044篇 |
1988年 | 905篇 |
1987年 | 878篇 |
1986年 | 759篇 |
1985年 | 769篇 |
1984年 | 930篇 |
1983年 | 734篇 |
1982年 | 760篇 |
1981年 | 651篇 |
1980年 | 548篇 |
1979年 | 536篇 |
1978年 | 494篇 |
1977年 | 425篇 |
1976年 | 378篇 |
1975年 | 365篇 |
1974年 | 346篇 |
1973年 | 383篇 |
排序方式: 共有10000条查询结果,搜索用时 336 毫秒
951.
Semidiurnal and diurnal tidal waves in the Taiwan Strait are computed simultaneously by using finite difference method with two-dimensional nonlinear hydrodynamic equations. The agreement between the computed and observed results is considered satisfactory. 相似文献
952.
Two new species (Nitzschia sinensis Liu, sp. nov. and Podosira granulata Liu, sp. nov.) and one new variety (Xanthiopyxis microspinosa var. ellipticus Liu, var. nov.) collected from the urface sediments off the southern Huanghai Sea and the East China Sea are described and a list of diatoms from the surface sediments in the survey area and some new records in China are attached. 相似文献
953.
Harpacticoida taxocen diversity in the silty-sandy littoral zone of Kandalaksha Bay of the White Sea
E. S. Chertoprud M. V. Chertoprud D. V. Kondar P. N. Kornev A. A. Udalov 《Oceanology》2006,46(4):492-500
The fauna composition, ecological groups, and life forms of Harpacticoids of soft littoral grounds from 15 sites off the Karelian coast in Kandalaksha Bay of the White Sea were studied. Six types of harpacticoid taxocens with different sets of dominating species are described. On silty sands with clear signs of desalination, the Stenchelia palustris taxocen is common; medium-grained sands are characterized by the Heterolaophonte minuta, Paraleptastacus kliei — Huntemannia jadensis, and Amphiascoides nanus — Scottopsyllus minor taxocens; while on coarse sands, the Ameira parvula and Ameira scotti — Mesochra lilljeborgi taxocens have developed. The diversity of the taxocens is partly explained by the differences in the grain-size composition and salinity at different sites. In addition, groups of various taxocens dwelling on the same type of the sediments were found in different minor bights of the coastline. 相似文献
954.
In 1979, we found many small colorless transparent and light yellow-green glassy spherules in the surface layer and core sediment samples taken from the west of the Central Pacific Occan, which are considered to be microtektites. This finding is worthy of further determination of the range of strewn field and origin of tektites. 相似文献
955.
Santos MM ten Hallers-Tjabbes CC Vieira N Boon JP Porte C 《Marine environmental research》2002,54(3-5):661-665
Normal and imposex-affected female Buccinum undatum were sampled from the open North Sea at three locations, one with low, and two with high shipping densities. Cytochrome P450 components and P450 aromatase activity were determined in the microsomal fractions isolated from pooled digestive gland/gonads. Cytochrome P450 aromatase activity was significantly higher (P < 0.05) in normal females collected in the low shipping density area (1,325 +/- 295 fmol/h/mg protein) than levels from imposex animals from a high shipping density area (620 +/- 287 fmol/h/mg protein). A negative correlation was found between aromatase activity and organotin body burden (r = -0.99). Levels of CYP450, cytochrome b5 and NADPH cytochrome c reductase activity did not show differences among groups. This is the first field evidence of depressed aromatase activity in imposex affected females, although additional research under laboratory controlled conditions is required to fully understand the mechanisms underlying the development of imposex in this species. 相似文献
956.
This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system. 相似文献
957.
958.
Donald J. Walter Douglas N. Lambert David C. Young Kevin P. Stephens 《Geo-Marine Letters》1997,17(4):260-267
Real-time trackline plots of surficial sediment acoustic impedance delineate several sedimentary facies off Garden Key in
the Dry Tortugas. The sea floor within a 6×6 km surveyed area consists of carbonate muds (silts), sands and shell, rock, and
live corals. The 4-kHz acoustic data supports this finding by providing a pictographic representation of the distribution
and structure of several sediment facies types. Plotting the gridded acoustic data with commercial mapping software (Surfer)
provides a three-dimensional (3D) perspective of the bottom topography with a color contour map of surficial sediment impedance
(upper 0.4 m) draped over the 3D surface. 相似文献
959.
Zhang Changkuan Wang Zhen Zhang Dongsheng
Associate Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing
Lecturer Dept. of Navigation Ocean Engineering Hohai University Nanjing
Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing 《中国海洋工程》1995,(2)
A numerical model of shoreline change of sand beaches based on long-term field wave data is proposed, the explicit and implicit finite difference forms of the model are described, and an application of the model is presented. Results of the application indicate that the model is sensitive to the order of the input wave data, and that the effects of long-term wave series and the effects of the mean annual wave conditions on the model are different. Instead of a single wave condition, the wave series will make the calibration and the verification of the model more practical and the results of the model more reasonable. 相似文献
960.
The expansion of the temperature anomaly field in the North Atlantic is considered using natural orthogonal functions of depth. It is shown that the first few components of this expansion describe the field both at the surface and in the upper 1000 m layer accurately enough. The relation between the water temperature anomaly at some levels and the above components is estimated for various regions of the ocean.Translated by Mikhail M. Trufanov. 相似文献