全文获取类型
收费全文 | 75194篇 |
免费 | 19122篇 |
国内免费 | 43140篇 |
专业分类
测绘学 | 3804篇 |
大气科学 | 24507篇 |
地球物理 | 20562篇 |
地质学 | 48602篇 |
海洋学 | 19772篇 |
天文学 | 10614篇 |
综合类 | 4572篇 |
自然地理 | 5023篇 |
出版年
2022年 | 701篇 |
2021年 | 1202篇 |
2020年 | 2377篇 |
2019年 | 5839篇 |
2018年 | 6570篇 |
2017年 | 6197篇 |
2016年 | 6553篇 |
2015年 | 5392篇 |
2014年 | 5258篇 |
2013年 | 6903篇 |
2012年 | 5661篇 |
2011年 | 5917篇 |
2010年 | 5750篇 |
2009年 | 5580篇 |
2008年 | 4548篇 |
2007年 | 4582篇 |
2006年 | 4075篇 |
2005年 | 3750篇 |
2004年 | 4017篇 |
2003年 | 3731篇 |
2002年 | 3412篇 |
2001年 | 3081篇 |
2000年 | 2664篇 |
1999年 | 2607篇 |
1998年 | 2683篇 |
1997年 | 2747篇 |
1996年 | 2170篇 |
1995年 | 2078篇 |
1994年 | 1914篇 |
1993年 | 1797篇 |
1992年 | 1559篇 |
1991年 | 1287篇 |
1990年 | 1224篇 |
1989年 | 1108篇 |
1988年 | 996篇 |
1987年 | 952篇 |
1986年 | 814篇 |
1985年 | 856篇 |
1984年 | 940篇 |
1983年 | 764篇 |
1982年 | 736篇 |
1981年 | 720篇 |
1980年 | 577篇 |
1979年 | 568篇 |
1978年 | 478篇 |
1977年 | 469篇 |
1976年 | 408篇 |
1975年 | 385篇 |
1974年 | 389篇 |
1973年 | 398篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Histological study on the ontogeny of the lymphoid organs, kidney, thymus and spleen of Japanese flounder, Paralichthys olivaceus, from hatching to 40 d was carried out. The pronephric kidney duct appeared early in hatching although the primordial haemopoietic
stem cells were observed within a week after hatching. The spleen was first seen after 8d of hatching. The thymus appeared
after 15d, situated near the pronephric kidney. Small lymphoid cells appeared during the later phase of the post-larval stage
in the sequence of thymus, kidney and spleen. During the 40d of observations, there were no distinct inner or outer zones
in thymus and no red or white pulp in spleen. These results suggest that the nonspecific defense immune system plays a very
important role in the early larval stage of Japanese flounder. 相似文献
32.
33.
We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during
1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal
that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles.
The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease
of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles
of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed. 相似文献
34.
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
35.
36.
37.
38.
地壳对海洋潮汐的响应 总被引:2,自引:2,他引:0
应用三维动态有限元方法研究了中国北部地区的地壳对邻近的渤海与黄海海平面变化的响应。虽然此应力场过于微弱不足以引发地震,但发现应力集中的位置及应力场变化较大的位置恰好与某些现代地震的震中一致。这一结果表明研究地壳对广泛分布的载荷的响应对研究区域地震构造是有帮助的。 相似文献
39.
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
40.
青藏块体东北缘断层形变与中强地震 总被引:7,自引:4,他引:3
对祁连山-海原断裂带近期断层形变特征进行了初步研究,发现多场地,大范围的断层活动异常是中等强度地震发生的显著背景,并且往往与大陆地震活动的阶段性总体状况相呼应;区域形变存在明显的特征量,包括特征形态和特征时间,同一场地在不同地震前的异常特征具有重复性,但会受到背景差异显著的不同地震的影响,目前形变状况表明研究区仍具有发生中强地震的地壳运动背景。 相似文献