全文获取类型
收费全文 | 17109篇 |
免费 | 3369篇 |
国内免费 | 4716篇 |
专业分类
测绘学 | 1383篇 |
大气科学 | 4001篇 |
地球物理 | 4043篇 |
地质学 | 8832篇 |
海洋学 | 2331篇 |
天文学 | 722篇 |
综合类 | 1656篇 |
自然地理 | 2226篇 |
出版年
2024年 | 76篇 |
2023年 | 289篇 |
2022年 | 816篇 |
2021年 | 930篇 |
2020年 | 762篇 |
2019年 | 872篇 |
2018年 | 954篇 |
2017年 | 889篇 |
2016年 | 1022篇 |
2015年 | 891篇 |
2014年 | 1072篇 |
2013年 | 1183篇 |
2012年 | 1094篇 |
2011年 | 1133篇 |
2010年 | 1143篇 |
2009年 | 1088篇 |
2008年 | 1092篇 |
2007年 | 988篇 |
2006年 | 869篇 |
2005年 | 755篇 |
2004年 | 566篇 |
2003年 | 571篇 |
2002年 | 589篇 |
2001年 | 541篇 |
2000年 | 522篇 |
1999年 | 679篇 |
1998年 | 555篇 |
1997年 | 553篇 |
1996年 | 499篇 |
1995年 | 424篇 |
1994年 | 359篇 |
1993年 | 290篇 |
1992年 | 243篇 |
1991年 | 174篇 |
1990年 | 125篇 |
1989年 | 138篇 |
1988年 | 108篇 |
1987年 | 72篇 |
1986年 | 56篇 |
1985年 | 47篇 |
1984年 | 27篇 |
1983年 | 33篇 |
1982年 | 14篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1958年 | 13篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
形变大地测量学的进展、问题与地震预报 总被引:12,自引:7,他引:5
简要概括了形变大地测量学的革命性进展,研讨了它的科学特色、功能和定义以及对地球科学和防灾减灾的推动。形变大地测量学有助于从根本上击破多年来制约地震预报的“瓶颈”,但也存在不少急待解决的问题。着重研讨了在21世纪前10年,形变大地测量学如何依托多年的学科积累并充分受益于人造卫星和数字化等新技术,开展创新性研究和试验以推进地震预报。为此,对当前的研究工作提出了12条科学技术途径。最后对学科名称提出了建议。 相似文献
22.
In this paper, we reconstruct the finite energy force-free magnetic field of the active region NOAA 8100 on 4 November 1997
above the photosphere. In particular, the 3-D magnetic field structures before and after a 2B/X2 flare at 05:58 UT in this
region are analyzed. The magnetic field lines were extrapolated in close coincidence with the Yohkoh soft X-ray (SXR) loops accordingly. It is found that the active region is composed of an emerging flux loop, a complex loop
system with differential magnetic field shear, and large-scale, or open field lines. Similar magnetic connectivity has been
obtained for both instants but apparent changes of the twisting situations of the calculated magnetic field lines can be observed
that properly align with the corresponding SXR coronal loops. We conclude that this flare was triggered by the interaction
of an emerging flux loop and a large loop system with differential magnetic field shear, as well as large-scale, or open field
lines. The onset of the flare was at the common footpoints of several interacting magnetic loops and confined near the footpoints
of the emerging flux loop. The sheared configuration remained even after the energetic flare, as demonstrated by calculated
values of the twist for the loop system, which means that the active region was relaxed to a lower energy state but not completely
to the minimum energy state (two days later another X-class flare occurred in this region). 相似文献
23.
LUO Kai-li LI Bao-sheng ZHU Yi-zhi JIN He-ling ZHANG David Dian YAN Man-cun LI Hou-xin YAO Chun-xia ZHANG Yu-hongf . Department of Geography South China Normal University Guangzhou P. R. China . State Key Labor 《中国地理科学(英文版)》2001,11(4):336-342
About 70years ago,Frenc卜卜alaeohdoglst回LL sc卜dars al卜ome and a卜road卜ave successively con-HARD de Chardin P.et al.Initiated the Quaternary ducted large amount ofwork on the Later Quaternarygeologlcal research In the >alawusu River Basin of strata(TEILHARD,1924; YUAN,1978; LI,1987;desert region of Northern China and established th,ZHENG,1989; SUN et al,1996; LI et al,1993),Salawusu Formation门EILHARD,1924).Sine,then,palaeobiology… 相似文献
24.
25.
The energy flow ofBranchiura sowerbyi was studied for the first time in China in a shallow macrophytic lake, Biandantang Lake, Hubei Province. The energy flow
was calculated from the measurement of flesh production (12.5241kJ/m2a), egestion (517.7302kJ/m2a), metabolism (38.3273 kJ/m2a), and excretion (4.3798kJ/m2a). The net growth efficiency of the species is about 22.7%, which accords well with the generally reported value for oligochaetes.
In addition, the relationship between starvation respiration (R, mgO2/ind·d), wet weight (Ww, mg) and temperature (T, °C) were also measured, with the regression function beingR=0.008Ww0.736 e0.050T.
Project supported by NSFC (30270278, 3960019), the foundation of the government of Hubei Province (No. 2000J109), and the
foundation of Ecological Station, CAS in the Institute of Hydrobiology. 相似文献
26.
27.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
28.
The energy budget ofBellamya earuginosa in a shallow algal lake, Houhu Lake (Wuhan, China) was investigated by the measurement of flesh production (32.8 kJ/(m2·a)), egestion (337.7 kJ/(m2·a)), metabolism (246.7 kJ/(m2·a)), and estimation of excretion (21.4kJ/(m2·a)). The net growth efficiency of the species is about 10.9%, which accords with the generally reported value for gastropods.
In addition, the relationships between starvation respiration (R, mgO2/(Ind·d)), body weight (Wd, mg in dry wt) and temperature (T, °C) were also determined. The regression equationR=0.044Wd
0.537
e
0.061T
was obtained by the least square method, The measured SDA of the species is 26.51% of its gross metabolism.
Project No. 3960019 and 39430101 supported by NSFC and also a granted for the East Lake Ecological Experimental Station, CAS,
Wuhan. 相似文献
29.
30.
Chun-sheng Li Qi-jun Fu Yu-hua Yan Shu-ying Jiang Hong-wei Li 《Chinese Astronomy and Astrophysics》1985,9(2):128-133
We propose a model of two acceleration regions, which can explain, on the basis of microwave maser caused by a “hollow-beam” distribution of electrons, the presence of millisecond spikes in the event of 1981 May 16 and their absence in the event of 1981 October 12, and the enhanced continuous emission in the latter. We have also uncovered relations among the features, e.g. the Type IIIG, Type IVDCIM and hard x-ray bursts, that accompany the microwave millisecond spikes during the impulsive phase of a large flare. 相似文献