全文获取类型
收费全文 | 42096篇 |
免费 | 2408篇 |
国内免费 | 3187篇 |
专业分类
测绘学 | 1412篇 |
大气科学 | 4402篇 |
地球物理 | 8419篇 |
地质学 | 17056篇 |
海洋学 | 4374篇 |
天文学 | 7747篇 |
综合类 | 1043篇 |
自然地理 | 3238篇 |
出版年
2023年 | 345篇 |
2022年 | 786篇 |
2021年 | 1050篇 |
2020年 | 998篇 |
2019年 | 1078篇 |
2018年 | 1560篇 |
2017年 | 1459篇 |
2016年 | 1565篇 |
2015年 | 1193篇 |
2014年 | 1569篇 |
2013年 | 2198篇 |
2012年 | 1693篇 |
2011年 | 2072篇 |
2010年 | 1823篇 |
2009年 | 2109篇 |
2008年 | 1890篇 |
2007年 | 1933篇 |
2006年 | 1774篇 |
2005年 | 1244篇 |
2004年 | 1202篇 |
2003年 | 1215篇 |
2002年 | 1218篇 |
2001年 | 1134篇 |
2000年 | 970篇 |
1999年 | 934篇 |
1998年 | 854篇 |
1997年 | 875篇 |
1996年 | 693篇 |
1995年 | 673篇 |
1994年 | 605篇 |
1993年 | 511篇 |
1992年 | 469篇 |
1991年 | 377篇 |
1990年 | 388篇 |
1989年 | 388篇 |
1988年 | 312篇 |
1987年 | 373篇 |
1986年 | 313篇 |
1985年 | 389篇 |
1984年 | 424篇 |
1983年 | 409篇 |
1982年 | 374篇 |
1981年 | 334篇 |
1980年 | 333篇 |
1979年 | 309篇 |
1978年 | 328篇 |
1977年 | 278篇 |
1976年 | 280篇 |
1975年 | 297篇 |
1973年 | 253篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
23.
The UBV photometric observations of RT Per, from Sanwal and Chaubey (1981), were analyzed by the Wilson and Devinney code (1971). The light curves include reflection effects that for the first time has been suggested by Dugan (1911). RT Per has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It has the characteristic of an Algol type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Lu, 1990). 相似文献
24.
25.
W. H. Jefferys G. F. Benedict P. D. Hemenway P. J. Shelus R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305
The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed. 相似文献
26.
Methyl-galactosides were oxidized at room temperature by galactose oxidase in a one-step reaction and afforded methyl-galactoaldehyde
in excellent yield and high purity. The resulting galactoaldehyde as a useful intermediate can be directly used in glycopeptide
synthesis. 相似文献
27.
Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR
1 =I(854.8 Å)/I(786.9 Å),R
2 =I(852.2 Å)/I(786.9 Å),R
3 =I(849.2 Å)/I(786.9 Å), andR
4 =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR
1, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed. 相似文献
28.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
29.
本文通过对1980年以来长江上游10次洪涝过程的500hpa环流形势分析,并用车比雪夫多项式对500hpa高度场进行展开,研究了各类洪涝过程的中期演变特征,发现代表不同洪涝过程环流形势变化的不同的车氏系数值都有明显的特征变化,结合欧洲中心中期数值预告96小时500hpa高度场的车氏系数分析,可为洪涝暴雨的中期预报提供一种新的思路。 相似文献
30.
Baolin Tan Haisheng Ji Guangli Huang Tuanhui Zhou Qiwu Song Yu Huang 《Solar physics》2006,239(1-2):137-148
Using one-minute cadence vector magnetograms from Big Bear Solar Observatory (BBSO), we analyze the temporal behavior of derived
longitudinal electric currents associated with two flares on July 26, 2002. One of the events is an M1.0 flare which occurred
in active region NOAA 10044, while the other is an M8.7 flare in the adjacent region 10039. Rapid changes of magnetic fields
in the form of flux emergence are found to be associated with both of these events. However, the temporal behavior of electric
currents are very different. For the M1.0 flare, the longitudinal electric current density drops rapidly near the flaring
neutral line; while for the M8.7 flare, the current density rapidly increases, confirming the picture of the current-carrying
flux emergence. We offer a possible explanation for such a difference: magnetic reconnection at different heights for the
two events, near the photosphere for the M1.0 flare, and higher up for the M8.7 flare. 相似文献