全文获取类型
收费全文 | 21123篇 |
免费 | 4072篇 |
国内免费 | 5200篇 |
专业分类
测绘学 | 1635篇 |
大气科学 | 4054篇 |
地球物理 | 5432篇 |
地质学 | 11088篇 |
海洋学 | 2686篇 |
天文学 | 753篇 |
综合类 | 2163篇 |
自然地理 | 2584篇 |
出版年
2024年 | 157篇 |
2023年 | 499篇 |
2022年 | 1137篇 |
2021年 | 1293篇 |
2020年 | 1100篇 |
2019年 | 1198篇 |
2018年 | 1348篇 |
2017年 | 1168篇 |
2016年 | 1287篇 |
2015年 | 1074篇 |
2014年 | 1337篇 |
2013年 | 1305篇 |
2012年 | 1225篇 |
2011年 | 1242篇 |
2010年 | 1269篇 |
2009年 | 1145篇 |
2008年 | 1044篇 |
2007年 | 957篇 |
2006年 | 779篇 |
2005年 | 744篇 |
2004年 | 611篇 |
2003年 | 566篇 |
2002年 | 608篇 |
2001年 | 666篇 |
2000年 | 656篇 |
1999年 | 866篇 |
1998年 | 732篇 |
1997年 | 658篇 |
1996年 | 626篇 |
1995年 | 510篇 |
1994年 | 499篇 |
1993年 | 423篇 |
1992年 | 383篇 |
1991年 | 260篇 |
1990年 | 214篇 |
1989年 | 181篇 |
1988年 | 139篇 |
1987年 | 103篇 |
1986年 | 75篇 |
1985年 | 68篇 |
1984年 | 47篇 |
1983年 | 46篇 |
1982年 | 33篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1958年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Tidal effects on temperature front in the Yellow Sea 总被引:5,自引:0,他引:5
Temperature front (TF) is one of the important features in the Yellow Sea, which forms in spring, thrives in summer, and fades
in autumn as thermocline declines. TF intensity ⋎S
T
⋎ is defined to describe the distribution of TF. Based on the MASNUM wave-tide-circulation coupled model, temperature distribution
in the Yellow Sea was simulated with and without tidal effects. Along 36°N, distribution of TF from the simulated results
are compared with the observations, and a quantitative analysis is introduced to evaluate the tidal effects on the forming
and maintaining processes of the TF. Tidal mixing and the circulation structure adapting to it are the main causes of the
TF.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
22.
采用PCR技术对2种亚洲龙鱼的mtDNAD_Loop全序列进行扩增和测序,序列结构分析和序列同源性比对结果表明,2种亚洲龙鱼的mtDNAD_Loop在靠近5’端有3个终止相关序列TAS(Ⅰ、Ⅱ、Ⅲ),靠近D_Loop的3’端有4个保守区域CSB1、CSB2、CSB3、CSB-D。在终止相关序列和保守区域之间是连续重复区域。经DNASP4.0软件分析,全序列中检测出多态位点数(S)为26,其中有17个转换,核苷酸多样性(Pi)为0.013,平均核苷酸差异数(K)为17.333。 相似文献
23.
CHEN Bing-lu ZHANG Yun-ni CHEN Xin-geng WANG Zhi-gang YANG Guang-xing 《中国地理科学(英文版)》2001,11(2):155-162
1 HYDROLOGIC FEATURES Lingdingyang Estuary, located at the middle south of Guangdong Province, is a bell-shaped estuary with a north-south direction. Its area is about 2100km2. The north of Qi′ao Island and Inner-Lingding Island, and the south of Humen are grouped as Neilingdingyang Estuary, having an area of 1041km2. Affected by topography, runoff and tide, its dynamic condition is very complicated. Different water areas have different hydrologic features. The topography under … 相似文献
24.
IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z… 相似文献
25.
基于拖带坐标法建立了岩层大变形的一维非线性微分方程,然后用解析与数值方法研究了变刚度、可伸缩岩层在侧向压力及自重作用下的分叉特性,初步揭示了褶皱岩层初始挠曲的形成机理。 相似文献
26.
Corrosion behavior of steel in the juncture area of sea clay and sand was studied. The results show that galvanic corrosion occurred between steel samples buried in sea clay and sand, and that the polarity of the galvanic cell reversed after some testing later. The cause of reversing of polarity is discussed. 相似文献
27.
卫星激光测距的新进展 总被引:6,自引:0,他引:6
扼要综述了近几年国际上卫星激光测距的进展,介绍了国内激光测距网的现状,展望了未来卫星激光测距的发展。 相似文献
28.
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
29.
30.
在20℃、4℃、-10℃、-20℃四种温度下贮藏马面卵巢,对其中磷脂含量的变化进行了测定,并利用薄层层析分析测定了不同温度下贮存3d后马面卵巢中磷脂各组分的相对百分比。结果表明马面卵巢中磷脂的损失率随贮藏温度的上升而增加;在不同温度下贮藏3d,磷脂各组分的相对百分比都发生了变化;随贮藏温度的升高磷脂酰胆碱的降解速度大大加快,所占的百分比快速下降,而溶血磷脂酰胆碱的比例有不同程度的增加。相对而言,-20℃下贮藏数天,磷脂的含量及组分的变化较小。 相似文献