全文获取类型
收费全文 | 871篇 |
免费 | 42篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 63篇 |
地球物理 | 219篇 |
地质学 | 292篇 |
海洋学 | 90篇 |
天文学 | 141篇 |
综合类 | 7篇 |
自然地理 | 88篇 |
出版年
2022年 | 4篇 |
2021年 | 23篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 27篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 48篇 |
2012年 | 32篇 |
2011年 | 52篇 |
2010年 | 39篇 |
2009年 | 54篇 |
2008年 | 34篇 |
2007年 | 44篇 |
2006年 | 37篇 |
2005年 | 27篇 |
2004年 | 19篇 |
2003年 | 25篇 |
2002年 | 17篇 |
2001年 | 21篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 13篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有918条查询结果,搜索用时 203 毫秒
1.
2.
Charles H. Nelson Douglas S. Hall Francis C. Fekel Robert E. Fried Richard E. Lines Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17
Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27d.07±0d.07, which is slightly different from the 27d.5384±0d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R
h=2.58R
,R
c=12.28R
,M
h=1.40M
,M
c=1.46M
,i=80o.61 and velocity semi-amplitudesK
c=48.36 km s–1±0.79 km s–1, andK
h=50.50 km s–1±0.33 km s–1. The apparent magnitudes areV
h=9
m
.73 andV
c=8
m
.48. The distance to HD 155638 was estimated to be 310 parsecs. 相似文献
3.
4.
The prevalence of dermal neoplasia among neotenic tiger salamanders (Ambystoma tigrinum) collected from the Reese Air Force Base sewage lagoon far exceeded that among salamanders from nearby uncontaminated lagoons. Perylene was the predominant pglycyclic aromatic hydrocarbon contaminant in this lagoon. Perylene was shown to be a substrate for monooxygenases in skin and liver homogenates and formed DNA-binding metabolites. Perylene exposure appeared to augment subsequent perylene metabolism by dermal enzymes but it was not a strong inducer of hepatic monooxygenases. Aroclor 1254 induced benzo(a)pyrene and perylene metabolism by both skin and liver enzymes. However, perylene apparently was not activated by salamander enzymes, as suggested by its lack of in vitro mutagenicity and failure to induce tumors. 相似文献
5.
6.
4-tert-octylphenol and 17beta-estradiol applied by feeding to flounder Platichthys flesus: induction of vitellogenin and accumulation in tissues 总被引:1,自引:0,他引:1
In order to simulate a possible natural administration route of xenoestrogens male flounder Platichthys flesus were exposed via the diet to the alkylphenol 4-tert-octylphenol. Treatment with 4-tert-octylphenol (10, 50 and 100 mg OP kg(-1) BW) or 17beta-estradiol (0.05 mg kg(-1) BW) every second day during a period of 11 days resulted in a significant increase in plasma vitellogenin (Vtg) concentrations. The induction of Vtg was greatest in the fish receiving 50 mg OP kg-' BW. A significant accumulation of 4-tert-octylphenol was found in liver and muscle tissue of the OP treated groups. The tissue concentrations of 4-tert-octylphenol and the plasma vitellogenin concentration were positively correlated. The results show that 4-tert-octylphenol accumulates in liver and muscles of flounder P. flesus, and exerts estrogenic effects such as vitellogenin induction. 相似文献
7.
8.
An extremely simple CFD tool is used to compare the calm-water drags of a series of hull forms and to define ‘optimized’ monohull ships for which the total (friction+wave) calm-water drag is minimized. The friction drag is estimated using the classical ITTC formula. The wave drag is predicted using the zeroth-order slender-ship approximation. Comparisons of theoretical predictions and experimental measurements for a series of eight hull forms show that—despite the extreme simplicity of the method that is used here to estimate the friction drag and the wave drag—the method is able to rank the drags of a series of hull forms roughly in accordance with experimental measurements. Thus, the method may be used, with appropriate caution, as a practical hull form design and optimization tool. For purposes of illustration, optimized hull forms that have the same displacement and waterplane transverse moment of inertia as the classical Wigley hull, taken as initial hull in the optimization process, are determined for three speeds and for a speed range. 相似文献
9.
We assess, based on fisheries and interview data collected on-site, whether Malthusian overfishing is occurring in Pulau Banggi, Sabah. Fisheries resources in Pulau Banggi have been perceived to be declining over the past 20 years, and characteristics of Malthusian overfishing are evident, although not at a magnitude comparable with other more heavily exploited artisanal fisheries in the Philippines. It appears that Pulau Banggi's reef fisheries are at an early stage of Malthusian overfishing, and this is therefore a critical time for addressing and mitigating drivers of overfishing to prevent inevitable and further decline of Pulau Banggi's reef fisheries. 相似文献