全文获取类型
收费全文 | 32534篇 |
免费 | 6946篇 |
国内免费 | 9570篇 |
专业分类
测绘学 | 3126篇 |
大气科学 | 6019篇 |
地球物理 | 7451篇 |
地质学 | 18271篇 |
海洋学 | 5426篇 |
天文学 | 1051篇 |
综合类 | 3496篇 |
自然地理 | 4210篇 |
出版年
2024年 | 177篇 |
2023年 | 594篇 |
2022年 | 1623篇 |
2021年 | 1983篇 |
2020年 | 1655篇 |
2019年 | 1906篇 |
2018年 | 2048篇 |
2017年 | 1805篇 |
2016年 | 2028篇 |
2015年 | 1863篇 |
2014年 | 2101篇 |
2013年 | 2314篇 |
2012年 | 2325篇 |
2011年 | 2381篇 |
2010年 | 2274篇 |
2009年 | 2180篇 |
2008年 | 2083篇 |
2007年 | 2002篇 |
2006年 | 1674篇 |
2005年 | 1557篇 |
2004年 | 1142篇 |
2003年 | 948篇 |
2002年 | 973篇 |
2001年 | 925篇 |
2000年 | 972篇 |
1999年 | 1151篇 |
1998年 | 852篇 |
1997年 | 909篇 |
1996年 | 841篇 |
1995年 | 703篇 |
1994年 | 569篇 |
1993年 | 515篇 |
1992年 | 406篇 |
1991年 | 295篇 |
1990年 | 240篇 |
1989年 | 178篇 |
1988年 | 178篇 |
1987年 | 137篇 |
1986年 | 110篇 |
1985年 | 75篇 |
1984年 | 51篇 |
1983年 | 47篇 |
1982年 | 38篇 |
1981年 | 29篇 |
1980年 | 36篇 |
1979年 | 32篇 |
1978年 | 15篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
孙世春 《中国海洋湖沼学报》1995,(2)
Two nemerteans of the Zhoushan Islands, Paranemertes sinensis sp. nov. and P. peregrina, are reportedin this paper. P. sinensis sp. nov. has the body wall longitudinal musculature anteriorly divided,numerous eyes grouped into four clusters, two pairs of cephalic furrows, rhynchocoel 1/3 to 1/2 of fullbody length, cephalic glands well developed and posteriorly extending beyond the cerebral ganglia.precerebral septum absent, cerebral sense organs situated in front of brain, three pairs of nephridiopores,and 17-18 proboscis nerves. 相似文献
72.
A component (s-factor) with obvious promoting effect on hydrogen evolution of hydrogenase has beenisolated and extracted from a Cell=free preparation of Spirulina platensis.The effect of the s-factor in the re-action system is similar to that of Na_2S_2O_4, but is coupled with ligh. The s-factor has the maximumabsorption peak at 620 nm in the oxidized state, at 590 nm in the reduced state. The partially purifieds-factor showed two bands by SDS-PAGE and is distinctly different from phycocyanin,which has nochange of oxidized state and reduced state absorption spectra, and also has no promoting effect onhydrogenase of Spirulina platensis under the light. 相似文献
73.
黑色高岭石粘土岩,是铜川王石凹煤矿石炭纪煤系地层顶部,五号煤层的上部一层稳定的煤矸石。经偏光显微镜及费氏台测试光性特征、化学试验及分析鉴定表明,这是一种由高岭石组成的,成分很纯、颗粒大、结晶良好的高岭石粘土岩。据微量元素含量分析,此高岭石系淡水沉积物。 相似文献
74.
原子钟噪声的蒙特卡络模拟方法 总被引:1,自引:0,他引:1
讨论了原子钟噪声的蒙特卡络模拟方法.具体过程是:先产生模拟所需的正态分布随机数,从实际钟的阿仑方差估算出噪声电平,然后用1组递点函数产生高质量的模拟钟时差的随机序列.在对1台商品铯钟进行具体模拟后,给出了真实数据与模拟值的阿仑方差之问的相符程度,最后对实际问题进行了分析. 相似文献
75.
The characteristics of red karst weathering crust in the research region can be divided into three subtypes. The first one includes the silicon to aluminum ratio, the composition of the clay minerals, etc., and reflects the weak action of de-silicon and aluminum enrichment. The second one, for example the granularity, shows that the viscous action is strong. The third one, such as the CaCO3 content and pH value, has regional difference in a large scale, which is consistent with the condition of modern scenery, so it is not important as for the ancient environment.
相似文献76.
1 INTRODUCTION Active oxygen free radicals can damage cell structure, even kill the cells, causing aging and cer- tain serious diseases (Bors et al., 1989). Usually, the production and scavenging of active oxygen free radicals are in balance in healthy hu… 相似文献
77.
G. Z. Xie F. K. Liu Y. Y. Zhu J. H. Fan R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F
obs = 3 +
F
intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem
v
must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem
v
corr
and logZ have a good correlation. 相似文献
78.
We found that the structure of the Universe can be characterized by a set of actions
s
. This means that some discontinuous phenomena in the Universe can be considered as large-scale quantum effects. The behaviour of matter on a typical scale is determined by the behaviour of matter on other scales through the interactions. 相似文献
79.
Deng Zu-Gan Zhou You-Yuan Liu Yong-Zhen Dai He-Jun 《Astrophysics and Space Science》1986,126(2):301-312
In former works (Zhouet al., 1983, 1985), a quantitative method have been developed to take the selection effects in the identification of emission lines of quasars into account. It was proved that these selection effects may be the cause of the unevenness in the redshift distribution of quasars. The present work is a continuation and development of former works. We use results given by the surveys with same limit-apparent magnitude and choose the quasars whose absolute magnitudes are within a specific range as the analysing samples. Using the method given in the former papers we may find out the evolutionary parameter in an evolutionary law with form of (1+z)
y
from the best fitting between the calculative and observational redshift distribution. The result of analysis shows that the evolutionary law of quasars selected by slitless technique isp =p
0(1 + z)6.5 ± 1 up toz=2.8. This result coincides with and generalizes the earlier result given by other authors. 相似文献
80.