全文获取类型
收费全文 | 36837篇 |
免费 | 18550篇 |
国内免费 | 43375篇 |
专业分类
测绘学 | 2909篇 |
大气科学 | 21856篇 |
地球物理 | 13338篇 |
地质学 | 35916篇 |
海洋学 | 16286篇 |
天文学 | 1195篇 |
综合类 | 4760篇 |
自然地理 | 2502篇 |
出版年
2024年 | 173篇 |
2023年 | 387篇 |
2022年 | 670篇 |
2021年 | 980篇 |
2020年 | 2094篇 |
2019年 | 5497篇 |
2018年 | 5754篇 |
2017年 | 5472篇 |
2016年 | 5540篇 |
2015年 | 4931篇 |
2014年 | 4409篇 |
2013年 | 4942篇 |
2012年 | 4651篇 |
2011年 | 4470篇 |
2010年 | 4367篇 |
2009年 | 3769篇 |
2008年 | 3055篇 |
2007年 | 3047篇 |
2006年 | 2633篇 |
2005年 | 2580篇 |
2004年 | 2848篇 |
2003年 | 2626篇 |
2002年 | 2361篇 |
2001年 | 2163篇 |
2000年 | 1754篇 |
1999年 | 1843篇 |
1998年 | 1879篇 |
1997年 | 1921篇 |
1996年 | 1528篇 |
1995年 | 1436篇 |
1994年 | 1303篇 |
1993年 | 1272篇 |
1992年 | 1060篇 |
1991年 | 785篇 |
1990年 | 741篇 |
1989年 | 624篇 |
1988年 | 533篇 |
1987年 | 415篇 |
1986年 | 340篇 |
1985年 | 256篇 |
1984年 | 293篇 |
1983年 | 174篇 |
1982年 | 211篇 |
1981年 | 151篇 |
1980年 | 114篇 |
1979年 | 112篇 |
1978年 | 53篇 |
1977年 | 49篇 |
1971年 | 56篇 |
1970年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
1 IntroductionBacteriaandtheiractivitiesplayanimportantroleintheelementalbiogeochemicalcyclesandenergytransformingintheocean (Zhenetal.1 997) .DortchandPackard(1 989) proposedthatfoodwebsintheeutrophicwatersaredominatedbythebiomassofprimaryproducerswhilefoodwebsintheoligotrophicwatersaredominatedbythebiomassofmicrobes.Heterotrophicbacteriahadbeenshowntoplayanimportantroleinthedecompositionoflarge ,rapidlysinkingorganicparticleswithinandbelowtheeuphot iczone ,andfurthertoaffecttheelementaldyn… 相似文献
12.
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
13.
14.
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
15.
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
16.
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
17.
18.
昆仑山8.1级地震前中国大陆的构造应变背景 总被引:10,自引:4,他引:6
利用“网络工程”1998~2001年累积的1181个测站的GPS重复观测资料,采用双三次样条函数模型建立中国大陆水平运动模型速度场,用大地坐标在椭球面上计算各类应变场,详细分析了2001年昆仑山8.1级地震前中国大陆水平构造应变场空间分布特征。各类构造应变场的最高值都出现在喜马拉雅构造带与昆仑山地块内(地震断裂带南侧),鲜水河—安宁河断裂带次之。分析表明,昆仑山8.1级地震正好发生在张性面膨胀应变率的高值区,第一、第二和最大剪应变率高值区边缘的突变区和最大、最小主应变率的高值区。 相似文献
19.
A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards 相似文献
20.
HU Xiaoke JIANG Xiaolu* GUAN Huashi Fishery College Ocean University of China Qingdao P..R.China 《中国海洋大学学报(英文版)》2003,2(1)
1 Introduction Protoplastsserveasabasicandversatiletoolforge neticengineeringandbiochemicalresearchforseveralreasons :theymayregeneratetheirwallsandprovideamodelsystemforstudyingwallbiogenesis ,theirlysisprovidesagentlemeansofpreparingsubcellularor ganelles ,andthemembraneexpositionallowsgeneticmanipulationsinvolvingfusionoruptakeofnucleicacidstobepossible .Theseadvantagesarelessachiev ablewhenusingintactcells (Liciaetal.,1999) .Incomparisonwithlandplantsandunicellularalgae ,on lylimitedrepo… 相似文献