全文获取类型
收费全文 | 64453篇 |
免费 | 5454篇 |
国内免费 | 6417篇 |
专业分类
测绘学 | 2306篇 |
大气科学 | 7734篇 |
地球物理 | 14189篇 |
地质学 | 27180篇 |
海洋学 | 6657篇 |
天文学 | 9849篇 |
综合类 | 2963篇 |
自然地理 | 5446篇 |
出版年
2023年 | 564篇 |
2022年 | 1408篇 |
2021年 | 1813篇 |
2020年 | 1645篇 |
2019年 | 1812篇 |
2018年 | 2420篇 |
2017年 | 2327篇 |
2016年 | 2630篇 |
2015年 | 1758篇 |
2014年 | 2580篇 |
2013年 | 3321篇 |
2012年 | 2588篇 |
2011年 | 3104篇 |
2010年 | 2814篇 |
2009年 | 3152篇 |
2008年 | 2861篇 |
2007年 | 2901篇 |
2006年 | 2546篇 |
2005年 | 2063篇 |
2004年 | 1816篇 |
2003年 | 1884篇 |
2002年 | 1766篇 |
2001年 | 1573篇 |
2000年 | 1635篇 |
1999年 | 1933篇 |
1998年 | 1700篇 |
1997年 | 1789篇 |
1996年 | 1550篇 |
1995年 | 1418篇 |
1994年 | 1206篇 |
1993年 | 1078篇 |
1992年 | 886篇 |
1991年 | 789篇 |
1990年 | 728篇 |
1989年 | 628篇 |
1988年 | 576篇 |
1987年 | 548篇 |
1986年 | 554篇 |
1985年 | 601篇 |
1984年 | 605篇 |
1983年 | 597篇 |
1982年 | 542篇 |
1981年 | 496篇 |
1980年 | 477篇 |
1979年 | 445篇 |
1978年 | 393篇 |
1977年 | 394篇 |
1976年 | 356篇 |
1975年 | 366篇 |
1973年 | 373篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
Progress in the introduction of coulometry for the analysis of total carbon dioxide (TCO2) in marine waters is described. An extractor—stripper removes CO2 that is measured coulometrically by the quantity of electricity (coulombs) used to electrogenerate OH? ions for the titration of the acid formed by the reaction of CO2 and ethanolamine. The equivalence point is detected photometrically with thymolphthalein as the indicator, and Faraday's Law relates coulombs to equivalents of titrant generated and CO2 determined so that there are no standard curves needed or titrants to standardize or store. Accuracy was determined by adding gelatin capsules containing 100–1500 μg C of pure CaCO3 into the stripper, and accuracies of better than ± 1 μg C were achieved. The best precision for natural seawater (± 1 standard error) of ± 0.5 μmol l?1 was found for 17 samples of Bermuda coastal waters having a mean TCO2 of 2007.2 μmol l?1 (0.05% CV). Sources of error and precautions are discussed. This method, which has been used successfully at sea, can be used to study a variety of marine phenomena involving TCO2. 相似文献
62.
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
63.
64.
65.
The existence of prolonged periods of abnormally low solar activity (such as the Maunder minimum) is explained within the framework of Leighton's model of a solar cycle with a hypothetical internal magnetic field of the Sun taken into account. 相似文献
66.
67.
68.
G. Djurašević P. Rovithis H. Rovithis-Livaniou E. Fragoulopoulou 《Astrophysics and Space Science》2005,296(1-4):311-314
BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of
Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The
elements of the two components of the system are calculated and the spot characteristics are given. 相似文献
69.
The spectra of active galaxies and their nuclei are rich in emission and absorption line features. A major aim of present
research is the development of self-consistent hydrodynamic models for the production of the line-forming regions. We here
review such modelling and stress the central role played by shock phenomena induced by winds and explosions on scales ranging
from the circumstellar to the intergalactic. 相似文献
70.
在文献」1「4 基础上,根据近年文选址实践中提出的问题,先进一步讨论了大气相干直径和时间的的物理和意义,然后强调了自由大气湍流的天文成像效应及选址中进行研究和测量的重要性。最后对差分像运动方法测量视宁度的定标和系统误差等问题作了分析。 相似文献