全文获取类型
收费全文 | 57181篇 |
免费 | 984篇 |
国内免费 | 580篇 |
专业分类
测绘学 | 1614篇 |
大气科学 | 4307篇 |
地球物理 | 10792篇 |
地质学 | 20793篇 |
海洋学 | 5048篇 |
天文学 | 13328篇 |
综合类 | 206篇 |
自然地理 | 2657篇 |
出版年
2022年 | 382篇 |
2021年 | 688篇 |
2020年 | 716篇 |
2019年 | 752篇 |
2018年 | 1713篇 |
2017年 | 1647篇 |
2016年 | 2061篇 |
2015年 | 1103篇 |
2014年 | 1924篇 |
2013年 | 3083篇 |
2012年 | 1939篇 |
2011年 | 2507篇 |
2010年 | 2207篇 |
2009年 | 2858篇 |
2008年 | 2415篇 |
2007年 | 2439篇 |
2006年 | 2279篇 |
2005年 | 1691篇 |
2004年 | 1687篇 |
2003年 | 1598篇 |
2002年 | 1546篇 |
2001年 | 1362篇 |
2000年 | 1275篇 |
1999年 | 1050篇 |
1998年 | 1104篇 |
1997年 | 998篇 |
1996年 | 859篇 |
1995年 | 845篇 |
1994年 | 749篇 |
1993年 | 636篇 |
1992年 | 621篇 |
1991年 | 622篇 |
1990年 | 660篇 |
1989年 | 527篇 |
1988年 | 532篇 |
1987年 | 560篇 |
1986年 | 509篇 |
1985年 | 653篇 |
1984年 | 715篇 |
1983年 | 643篇 |
1982年 | 605篇 |
1981年 | 539篇 |
1980年 | 504篇 |
1979年 | 506篇 |
1978年 | 508篇 |
1977年 | 397篇 |
1976年 | 375篇 |
1975年 | 399篇 |
1974年 | 357篇 |
1973年 | 386篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Mussels, Mytilus edulis L., were exposed to elevated concentrations of copper or cadmium in the laboratory, then placed in cages in the sea (salinity 7‰). One year later maximum lengths of the mussels were measured and shells screened for deformities. Growth was 0·6 cm year?1 in the control cages and retarded in cages of exposed mussels. A total of 63% of cadmium-exposed and 46% of copper-exposed mussels had shell deformities. In the control cages 26% were deformed while in a natural population only 3% were deformed. The proportion of deformities to growth was inversely related. Low concentrations showed their injuriousness in this long-term test, probably due to the closing of the valves during exposure to high concentrations. 相似文献
122.
An analysis previously developed for rough surface scattering with narrow-beam reception is extended to wide-beam or omnidirectional reception. The source is considered to be a pulsed electric dipole. The analysis includes multipathing effects on the received signal. The results are used to develop a model for the backscattered radar cross section of the ocean surface, up to a second-order approximation. 相似文献
123.
124.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
125.
P.S. Rainbow 《Estuarine, Coastal and Shelf Science》1985,21(5):669-686
The crab Carcinus maenas (L.) and the barnacle Elminius modestus Darwin were exposed to a range of dissolved concentrations of Zn, Cu and Cd for 21 days in artificial seawater. Accumulation of Zn and Cu by crabs has been interpreted in terms of the presence of a regulation mechanism to maintain constant body concentrations (83·2 ± 19·4 μg Zn g?1 dry wt.; 39·8 ± 9·8 μg Cu g?1 dry wt.) under varying external dissolved metal levels, until a threshold dissolved metal concentration (c. 400 μg Zn l?1; c. 170 μg Cu l?1) beyond which net accumulation of metal begins. Cadium appears to be accumulated by C. maenas at all exposures with no evidence for regulation of body cadmium concentrations. Exposure of E. modestus to Zn, Cu or Cd caused net accumulation of the respective metal in the bodies of the barnacles, with no evidence for regulation of body metal concentrations. 相似文献
126.
S. Casertano M. G. Lattanzi M. A. C. Perryman A. Spagna 《Astrophysics and Space Science》1996,241(1):89-104
The proposed baseline GAIA mission will be able to detect the astrometric signature of Jupiter-size planets around of the order of a million stars, using either global or narrow-angle astrometry. If the mission can realize the higher astrometric accuracy that photon statistics allows for bright stars, lower-mass planets (from Earth size to ten times larger) can be found around ten to a few hundred stars. 相似文献
127.
The main analytical properties of the generalized Shkarofsky function and a numerical code for its computation are discussed. The results of a numerical analysis are compared with the results of an asymptotic analysis for parameter values relevant to the problem of whistler-mode propagation in the Earth's magnetosphere. This comparison allows us to specify the range of applicability of different approximations to the generalized Shkarofsky function, which have been used for the analysis of relativistic effects on whistler-mode propagation and instability. 相似文献
128.
129.
S. Torres 《Earth, Moon, and Planets》1993,63(2):163-170
Observations and recommendations of the second un/esa workshop on basic space science 相似文献
130.