全文获取类型
收费全文 | 30448篇 |
免费 | 1370篇 |
国内免费 | 2622篇 |
专业分类
测绘学 | 1916篇 |
大气科学 | 3477篇 |
地球物理 | 5898篇 |
地质学 | 14773篇 |
海洋学 | 1749篇 |
天文学 | 1912篇 |
综合类 | 2720篇 |
自然地理 | 1995篇 |
出版年
2024年 | 51篇 |
2023年 | 125篇 |
2022年 | 296篇 |
2021年 | 359篇 |
2020年 | 275篇 |
2019年 | 302篇 |
2018年 | 4956篇 |
2017年 | 4244篇 |
2016年 | 2867篇 |
2015年 | 534篇 |
2014年 | 430篇 |
2013年 | 376篇 |
2012年 | 1298篇 |
2011年 | 3043篇 |
2010年 | 2342篇 |
2009年 | 2603篇 |
2008年 | 2153篇 |
2007年 | 2606篇 |
2006年 | 283篇 |
2005年 | 415篇 |
2004年 | 560篇 |
2003年 | 587篇 |
2002年 | 456篇 |
2001年 | 256篇 |
2000年 | 277篇 |
1999年 | 358篇 |
1998年 | 360篇 |
1997年 | 336篇 |
1996年 | 252篇 |
1995年 | 230篇 |
1994年 | 219篇 |
1993年 | 187篇 |
1992年 | 141篇 |
1991年 | 131篇 |
1990年 | 82篇 |
1989年 | 79篇 |
1988年 | 79篇 |
1987年 | 43篇 |
1986年 | 46篇 |
1985年 | 33篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 22篇 |
1981年 | 32篇 |
1980年 | 34篇 |
1979年 | 11篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1958年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Using analytic signal method, interpretation of pole-pole secondary electric potentials due to 2D conductive/resistive prisms
is presented. The estimated parameters are the location, lateral extent or width and depth to top surface of the prism. Forward
modelling is attempted by 2D-Finite Difference method. The proposed stabilised analytic signal algorithm (RES2AS) uses Tikhonov’s
regularization scheme and FFT routines. The algorithm is tested on three theoretical examples and field data from the campus
of Roorkee University. The stability of RES2AS is also tested on synthetic error prone secondary pole-pole potential data. 相似文献
43.
44.
45.
46.
47.
锶,硼和氟联合作用的亚急性毒理实验及环境意义 总被引:1,自引:0,他引:1
本文以自由饮水给药方式进行了锶、硼和氟联合作用的亚急性实验,以探讨锶、硼对氟的拮抗作用。实验结果,给予小鼠200×l0^-6 F 六个月后,可使其骨氟含量显著升高(P<0.01),肾碱性磷酸酶活力(ALP)显著增高(P<0.01),4、5个月后血清碱性磷酸酶(ALP)活力亦显著增高(P<0.O1),同时给予80×l0^-1 B3+、100×l0^-6Sr2+ 时,可以显著降低骨氟含量,抑制血清、肾碱性磷酸酶的活力,表明锶与硼对氟存在拮抗作用。 相似文献
48.
49.
The major gold deposits in east China are characterized by their occurrence in pre-Cambrian host metamorphic rocks,restriction in some specific stratigraphic-structural terranes,tendentious localization in ductile or ductile-brittle shear zones,association with the syntexis type granitoids,and significant remobilization,superimposition and enrichment by the later stage Mesozoic tectono-magmatic activities. 相似文献
50.
Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning 总被引:1,自引:0,他引:1
Shufeng Yang Hanlin Chen Jishuang Jiang Guoqiang Zhu Hongshen Xie Wei Hou Yueming Zhang Huigang Xu 《中国科学D辑(英文版)》1997,40(5):470-476
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure
and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity
change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed
during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth
of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km
approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately
and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening”
of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting,
these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting
of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related
to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type
granitoid. 相似文献