全文获取类型
收费全文 | 69647篇 |
免费 | 25169篇 |
国内免费 | 51725篇 |
专业分类
测绘学 | 9978篇 |
大气科学 | 24448篇 |
地球物理 | 18785篇 |
地质学 | 55356篇 |
海洋学 | 22154篇 |
天文学 | 1164篇 |
综合类 | 6860篇 |
自然地理 | 7796篇 |
出版年
2024年 | 654篇 |
2023年 | 1662篇 |
2022年 | 2962篇 |
2021年 | 3767篇 |
2020年 | 4037篇 |
2019年 | 7151篇 |
2018年 | 7018篇 |
2017年 | 6645篇 |
2016年 | 6781篇 |
2015年 | 6773篇 |
2014年 | 6206篇 |
2013年 | 7201篇 |
2012年 | 7533篇 |
2011年 | 7403篇 |
2010年 | 7436篇 |
2009年 | 6620篇 |
2008年 | 6132篇 |
2007年 | 5893篇 |
2006年 | 5546篇 |
2005年 | 4883篇 |
2004年 | 4337篇 |
2003年 | 3661篇 |
2002年 | 3390篇 |
2001年 | 3064篇 |
2000年 | 2556篇 |
1999年 | 1983篇 |
1998年 | 1791篇 |
1997年 | 1850篇 |
1996年 | 1441篇 |
1995年 | 1324篇 |
1994年 | 1196篇 |
1993年 | 1171篇 |
1992年 | 1030篇 |
1991年 | 754篇 |
1990年 | 740篇 |
1989年 | 600篇 |
1988年 | 515篇 |
1987年 | 408篇 |
1986年 | 339篇 |
1985年 | 294篇 |
1984年 | 299篇 |
1983年 | 194篇 |
1982年 | 222篇 |
1981年 | 157篇 |
1980年 | 113篇 |
1979年 | 137篇 |
1978年 | 56篇 |
1977年 | 48篇 |
1976年 | 47篇 |
1971年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
根据印度洋西北部鸢乌贼(Sym plectoteuthis oualaniensis)作业渔场的现场调查数据.分析了作业水深、作业时段、摄食等级和月相等因子对手钓上钩率的影响。统计表明.晚上、午夜和凌晨3个不同时段和不同作业水深对手钓上钩率均有显著性影响。3个时段中,其摄食等级呈先低后高再低的现象。午夜和凌展,上钩率的变化趋势与摄食等级的变化趋势呈显著的负相关。在月相的影响下.离朔日三四天之前,手钓产量呈上升趋势;离望日五六天之前。手钓产量呈明显的下降趋势。 相似文献
2.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
3.
4.
5.
本文使用红外天文卫星(IRAS)巡天数据的最新版本IRAS天空巡天图(ISSA),经过进一步处理,得到了S140S141和S142SharplessHII区-分子云复合体的红外发射强度、温度及其光深的分布.在此基础上对各HII区的一些物理参量进行了统计分析,得到了分子云复合体的红外发射总光度以及复合体中尘埃的分布情况,对小尺度尘埃(VSG)的丰度进行了分析.并对各恒星形成区中的致密团块进行了研究,揭示出其中一些可能的恒星形成区域.同时,对S140区中的有关红外点源作出了能谱分析,并对S141区的激发星进行了讨论. 相似文献
6.
A new species,Clathrocorys gracilis nov. spec. of Tripocyrtidae (Radiolarians: Nassellaria) from surface water in northern South China Sea, is described in this
paper. The new species has four radial beams arising from the cephalic base centre, each foot with cup-shaped structure and
ramified bar in the proximal section (near cephalic base), and each wing with a large mesh in the middle, a medium mesh and
a small mesh on each side respectively.
Project supported by the NSFC (No. 40276044) and the Chinese Academy of Sciences (No. KSCX2-SW-101B). 相似文献
7.
1 INTRODUCTIONIn the previous paper (on et al. 1999, hereafter Paper I), we investigated the wavelength-dependence of four colltribution functions (CFs) derived from dmerent formal solutions andreferring to different emergellt quantities in the unpolarized case. Because one cannot generallyassign a single formation region to the whole line band in a real stellar atmosphere, e.g., the solaratmosphere, instead, the line formation region can be defined as the layers deviating farthestfrom t… 相似文献
8.
9.
Formation of saline groundwaters in the Baltic region through freezing of seawater during glacial periods 总被引:1,自引:0,他引:1
Typical Ca---Cl brines occur in crystalline and metamorphic rocks below freshwater horizons at various localities in Sweden and Finland. Total dissolved solids (TDS) range in concentration between 2 and 120 gl−1 and have long been thought to derive from water-rock interactions. The relationships between Na, Cl and Br in these brines suggest, however, that they were derived from freezing of seawater during glacial periods. The brines were subsequently diluted by meteoric waters and their Ca/Mg ratio was increased through water-rock interactions in the subsurface. The hydrogeological model for both the formation of freeze-derived marine brines and their lateral intrusion involves restricted inland marine basins in recent and subrecent polar climatic belts. Seawater in such basins gradually freezes in response to glaciation. The solutes which concentrate in the remaining water body are residual after precipitation of a sequence of minerals which include carbonates, mirabilite and hydrohalite. Hydraulic pressure of the growing ice sheet over the frozen seas is gradually added to the ambient hydrostatic pressure exerted on the brines. This, together with their increased density, increases the intrusional potential of the brines. As the land ice cannot exert hydraulic pressure on continental groundwater in the aquifers, the balance of pressure favours deep landward intrusion of brines. Post-glacial processes cause the subsurface dilution and replacement of the brines both by seawater and fresh waters. The presence of such brines also far from present-day coastal settings reflects the shifting of coastlines as a result of isostatic movements and eustatic sea-level changes associated with glaciation and deglaciation. 相似文献
10.
Shi Zhi-dong Li Zhong-yuanUniversity of Science Technology of China Hefei PRC Advanced Centre for Earth Science Astronomy Third World Academy of Science 《紫金山天文台台刊》1996,(2)
Areview about K-H instability related to comet tail is presented.The effect of dust graing on KHI is theoretically analysed and relations of critical shear to excit KHI with the properties of dust grains both for sheared ion flow and for sheared dust flow re put out.Their possible application in comet tail is suggested. 相似文献