全文获取类型
收费全文 | 60285篇 |
免费 | 828篇 |
国内免费 | 472篇 |
专业分类
测绘学 | 1590篇 |
大气科学 | 4008篇 |
地球物理 | 12081篇 |
地质学 | 21061篇 |
海洋学 | 5446篇 |
天文学 | 14378篇 |
综合类 | 153篇 |
自然地理 | 2868篇 |
出版年
2022年 | 400篇 |
2021年 | 660篇 |
2020年 | 688篇 |
2019年 | 828篇 |
2018年 | 1734篇 |
2017年 | 1613篇 |
2016年 | 1860篇 |
2015年 | 961篇 |
2014年 | 1730篇 |
2013年 | 3072篇 |
2012年 | 1960篇 |
2011年 | 2487篇 |
2010年 | 2321篇 |
2009年 | 2974篇 |
2008年 | 2600篇 |
2007年 | 2773篇 |
2006年 | 2493篇 |
2005年 | 1710篇 |
2004年 | 1717篇 |
2003年 | 1610篇 |
2002年 | 1659篇 |
2001年 | 1478篇 |
2000年 | 1334篇 |
1999年 | 1147篇 |
1998年 | 1149篇 |
1997年 | 1157篇 |
1996年 | 917篇 |
1995年 | 884篇 |
1994年 | 826篇 |
1993年 | 694篇 |
1992年 | 643篇 |
1991年 | 645篇 |
1990年 | 635篇 |
1989年 | 649篇 |
1988年 | 571篇 |
1987年 | 663篇 |
1986年 | 596篇 |
1985年 | 709篇 |
1984年 | 817篇 |
1983年 | 745篇 |
1982年 | 719篇 |
1981年 | 653篇 |
1980年 | 579篇 |
1979年 | 579篇 |
1978年 | 580篇 |
1977年 | 506篇 |
1976年 | 455篇 |
1975年 | 458篇 |
1974年 | 440篇 |
1973年 | 509篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
K.A. MAASCH P.A. MAYEWSKI E.J. ROHLING J.C. STAGER W. KARLEN L.D. MEEKER E.A. MEYERSON 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):7-15
ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric 14 C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale. 相似文献
92.
93.
Data from the Pulkovo spectrophotometric data base on the absolute quasimonochromatic fluxes from oCet in the 320–1080 nm range are used to determine the physical parameters of this star in different phases of its light curve. The continuum emission layer is found to expand between the phases of the cycle corresponding to the rising and falling branches of the light curve. The average expansion velocity is 32 km/s. By the time the star’s brightness has fallen by roughly three magnitudes, its radius has increased by almost a factor of three. Over this same time the temperature of the layer has fallen from 3000 K to 2200 K. For this expansion velocity, the calculated mass rate loss is ⊙ M /year.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 175–189 (May 2005). 相似文献
94.
95.
96.
Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N2O to the atmosphere. Large and rapid increases in the concentrations of N2O, NO3?, and NO2? occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N2O in rivers. 相似文献
97.
98.
We present results of investigations into chromospheric velocity oscillations in sunspots, carried out at the Sayan Solar
Observatory. It is shown that the “chevron” structures in the space-time diagrams demonstrate wavetrain properties. Such structures
are indicators of a propagating wave process and they are typical of many sunspots. In the authors’ opinion, three-minute
umbral oscillations are not the source of running penumbral waves (RPW). It is very likely that umbral oscillations and RPW
initially propagate along different magnetic field lines. We explain the decrease in RPW propagation velocity and frequency
in the outer penumbra, as compared with the inner, by the combined action of different frequency modes. To better reveal the
properties of these modes, frequency filtering was used. Our measurements of the RPW (five-minute mode) wavelength and RPW
propagation velocity in different sunspots vary from 12″ to 30″ and from 28 to 60 – 70 km s−1 correspondingly. 相似文献
99.
Christopher P. McKay 《Planetary and Space Science》1985,33(7):761-771
To investigate the occurrence of low temperatures and the formation of noctilucent clouds in the summer mésosphere a one-dimensional time-dependent photochemical-thermal numerical model of the atmosphere between 50 and 120 km has been constructed. The model includes the important chemistry of the hydrogen and oxygen species and transport by eddy and molecular processes. The thermal balance incorporates: heating by solar ultraviolet radiation; transport of chemical potential energy; eddy diffusion and dissipation; molecular conduction; airglow emissions; and infrared cooling by carbon dioxide. A non- LTE parameterization is used to calculate 15 μm band cooling by carbon dioxide. The model self-consistently solves the coupled photochemical and thermal equations as perturbation equations from a reference state assumed to be in equilibrium and is used to consider the effect of variability in water vapor in the lower mesosphere on the temperature in the region of noctilucent cloud formation. It is found that change in water vapor from an equilibrium value of 5 ppm at 50 km to a value of 10 ppm, a variation consistent with observations, can produce a ~ 15 K drop in temperature at 82 km. It is suggested that this process may produce long periods (weeks) of cold temperatures and influence noctilucent cloud formation. 相似文献