全文获取类型
收费全文 | 51431篇 |
免费 | 8339篇 |
国内免费 | 11350篇 |
专业分类
测绘学 | 2960篇 |
大气科学 | 10206篇 |
地球物理 | 11799篇 |
地质学 | 25599篇 |
海洋学 | 6478篇 |
天文学 | 3536篇 |
综合类 | 4759篇 |
自然地理 | 5783篇 |
出版年
2024年 | 163篇 |
2023年 | 680篇 |
2022年 | 1996篇 |
2021年 | 2445篇 |
2020年 | 2143篇 |
2019年 | 2352篇 |
2018年 | 2892篇 |
2017年 | 2667篇 |
2016年 | 2860篇 |
2015年 | 2260篇 |
2014年 | 2996篇 |
2013年 | 3027篇 |
2012年 | 2847篇 |
2011年 | 3014篇 |
2010年 | 3103篇 |
2009年 | 3039篇 |
2008年 | 2720篇 |
2007年 | 2756篇 |
2006年 | 2363篇 |
2005年 | 1808篇 |
2004年 | 1467篇 |
2003年 | 1478篇 |
2002年 | 1571篇 |
2001年 | 1517篇 |
2000年 | 1573篇 |
1999年 | 2085篇 |
1998年 | 1688篇 |
1997年 | 1763篇 |
1996年 | 1523篇 |
1995年 | 1403篇 |
1994年 | 1268篇 |
1993年 | 1098篇 |
1992年 | 908篇 |
1991年 | 638篇 |
1990年 | 469篇 |
1989年 | 493篇 |
1988年 | 416篇 |
1987年 | 290篇 |
1986年 | 256篇 |
1985年 | 184篇 |
1984年 | 161篇 |
1983年 | 130篇 |
1982年 | 131篇 |
1981年 | 87篇 |
1980年 | 71篇 |
1979年 | 62篇 |
1978年 | 35篇 |
1977年 | 27篇 |
1975年 | 26篇 |
1958年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
81.
PALEOSOLSOFSANDYLANDSANDENVIRONMENTALCHANGESINTHEWESTERNPARTOFNORTHEASTPLAINOFCHINAWESTERNDURINGHOLOCENE¥QiuShanwen(裘善文)LiQus... 相似文献
82.
THE SIMULATED STORAGE CAPACITY OF FLOOD AND WATERLOGGING IN THE TYPICAL AGRICULTURAL REGION IN JIANGHAN PLAIN 总被引:2,自引:0,他引:2
1INTRODUCTIONJianghanPlainisoneoftheimportantbasesofChina′sagriculturalproductivitylocatedinthemiddleChangjiangRivervalleyofcentralChina.TheJianghanplainapproximately6.6×104km2inareaandover30millioninpopulationistherenowned“countryoffishandrice"in… 相似文献
83.
从ROSAT巡天和定点观测结果的对比出发,发现了几个低银纬的巡天源表中的X射线源在定点观测中没有出现.本文计算了在这些位置的定点观测中出现点源的流强上限,发现比巡天源表中这些源的流强值低很多,这表明它们的流强变化很大,可能是X射线双星系统中的一类———X射线暂现源. 相似文献
84.
In this paper, we idealize the actual solar atmosphere as a multi-isothermal-layer system so as to obtain the energy transmittance of the linear Alfvén wave that propagates through such a system in presence of a uniform oblique magnetic filed. The results indicate that the two-layer model is essentially different to the three-layer one. In the two-layer model, the temperature jump acts as a high pass filter. In the three-layer model, resonant transfer will take place and the transmittance undergoes oscillation as the trigonometric function terms dominate its behavior. For actual solar atmosphere, the result reveals that the lower parts of solar atmosphere are more suitable for those Alfvén waves with period of seconds to transfer their energy. 相似文献
85.
Boli basin, between Yishu fracture belt and Dunmi fracture belt, is the biggest Mesozoic coal basin in the east of Heilongjiang Province. Now it is a fault - fold remnant basin. The basin' s shape is generally consistent with the whole distribution of the cover folds, an arc protruding southwards. The basement of the basin can be divided into three fault blocks or structural units. The formation and evoluation of the basin in Mesozoic was determined by the basement fault blocks' displacement features rusulted from by the movement of the edge faults and the main basement faults. 相似文献
86.
In this paper, two factors — the redistribution of the density and the variation in the angular velocity of the Earth rotation, that affect the adopted value of the flattening for equidensity surface within the Earth, are discussed. The computational results show that the contribution of the redistribution of the density in the Earth interior (especially in the core) on the change of the flattening at the core-mantle boundary (CMB) is marginal, and that the calculated value of the flattening at the CMB can be in good agreement with the VLBI observed value so long as the fact that the angular velocity of the Earth rotation has undergone the tidal evolution is taken into account. As a result, this paper presents a set of recommended values of the dynamical parameters of the Earth (see Table III) for computing Earth's forced nutation series. 相似文献
87.
88.
本文分析了国外用于测定度盘分划改正的几种方法,并分析了固定角距法的优点和不足之处;详细叙述了组合固定角距法测定对径改正的原理和计算公式;并且讨论了两对显微镜之间夹角变化以及显微镜比例尺变化对对径改正的影响,给出了相应的修正方法。用固定角距法所测的对径改正精度可达±0″.009。 相似文献
89.
The effect of light intensity ( 1500 Ix and 5000 Ix) on the total lipid and fatty acid composition of six strains of marine diatoms Cylindrotheca fusiformis (B211 ), Phaeodactylum tricornutum (Bl14, Bl18 and B221) Nitzschia closterium (B222) and Chaetoceros gracilis (B13) was investigated.The total lipids of B13, Bl14, and B211 grown at 5000 Ix were lower than those grown at 1500 Ix. No evident changes were observed in Bl18, B221 and B222. Fatty acid composition changed considerably at different light intensity although no consistent correlation between the relative proportion of a single FA and light intensity. The major fatty acids of the 6 strains were 14:0, 16:0, 16:l(n- 7) and 20:5(n-3) . Cylindrothecafusiformis had high percentage of 20:4n - 6 (9.2 - 10.9% ) . The total polyunsaturated fatty acid /rl all 6 strains decreased with increasing light intensity. The percentage of the highly unsaturated fatty acid eicosapentaenoic acid (EPA) decreased with increasing light intensity in all strains except Chaetoceros gracilis. 相似文献
90.