全文获取类型
收费全文 | 71508篇 |
免费 | 915篇 |
国内免费 | 1317篇 |
专业分类
测绘学 | 2500篇 |
大气科学 | 5212篇 |
地球物理 | 13577篇 |
地质学 | 29477篇 |
海洋学 | 5248篇 |
天文学 | 11827篇 |
综合类 | 2230篇 |
自然地理 | 3669篇 |
出版年
2021年 | 278篇 |
2020年 | 346篇 |
2019年 | 401篇 |
2018年 | 7174篇 |
2017年 | 6448篇 |
2016年 | 4419篇 |
2015年 | 869篇 |
2014年 | 958篇 |
2013年 | 1757篇 |
2012年 | 2681篇 |
2011年 | 5644篇 |
2010年 | 4978篇 |
2009年 | 5532篇 |
2008年 | 4562篇 |
2007年 | 5490篇 |
2006年 | 1514篇 |
2005年 | 1682篇 |
2004年 | 1784篇 |
2003年 | 1733篇 |
2002年 | 1378篇 |
2001年 | 832篇 |
2000年 | 874篇 |
1999年 | 709篇 |
1998年 | 709篇 |
1997年 | 619篇 |
1996年 | 501篇 |
1995年 | 503篇 |
1994年 | 528篇 |
1993年 | 416篇 |
1992年 | 414篇 |
1991年 | 361篇 |
1990年 | 403篇 |
1989年 | 349篇 |
1988年 | 334篇 |
1987年 | 395篇 |
1986年 | 331篇 |
1985年 | 467篇 |
1984年 | 509篇 |
1983年 | 464篇 |
1982年 | 424篇 |
1981年 | 387篇 |
1980年 | 385篇 |
1979年 | 338篇 |
1978年 | 318篇 |
1977年 | 308篇 |
1976年 | 272篇 |
1975年 | 273篇 |
1974年 | 239篇 |
1973年 | 245篇 |
1972年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Chris Yakymchuk Adrian Rehm Zhuoheng Liao John M. Cottle 《Journal of Metamorphic Geology》2019,37(6):839-862
Sapphirine–quartz granulites from the Cocachacra region of the Arequipa Massif in southern Peru record early Neoproterozoic ultrahigh‐temperature metamorphism. Phase equilibrium modelling and zircon petrochronology are used to quantify timing and pressure–temperature (P–T) conditions of metamorphism. Modelling of three magnetite‐bearing sapphirine–quartz samples indicates peak temperatures of >950°C at ~0.7 GPa and a clockwise P–T evolution. Elevated concentrations of Al in orthopyroxene are also consistent with ultrahigh‐temperature conditions. Neoblastic zircon records ages of c. 1.0–0.9 Ga that are interpreted to record protracted ultrahigh‐temperature metamorphism. Th/U ratios of zircon of up to 100 reflect U‐depleted whole‐rock compositions. Concentrations of heavy rare earth elements in zircon do not show systematic trends with U–Pb age but do correlate with variable whole‐rock compositions. Very large positive Ce anomalies in zircon from two samples probably relate to strongly oxidizing conditions during neoblastic zircon crystallization. Low concentrations of Ti‐in‐zircon (<10 ppm) are interpreted to result from reduced titania activities due to the strongly oxidized nature of the granulites and the sequestration of titanium‐rich minerals away from the reaction volume. Whole‐rock compositions and oxidation state have a strong influence on the trace element composition of metamorphic zircon, which has implications for interpreting the geological significance of ages retrieved from zircon in oxidized metamorphic rocks. 相似文献
3.
4.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
5.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
6.
The effects of natural fish oil,DHA oil and soybean lecithin in microparticulate diets on stress tolerance of larval gilthead seabream(Sparus aurata)were investigated after 15 days feeding trials.The tolerance of larval gilthead seabream to various stress factors such as exposure to air(lack of dissolved oxygen),changes in water temperature(low)and salinity(high) were determined.This study showed that microparticulate diet with natural fish oil and soybean lecithin was the most effective for in-creasing the tolerance of larval gilthead seabream to various stresses,and that microparticulate diet with natural fish oil and palmitic acid(16:0)was more effective than microparticulate diet with DHA oil and soybean lecithin. 相似文献
7.
8.
9.
10.
T.-C. Jim Yeh 《水文研究》1992,6(4):369-395
This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended. 相似文献