全文获取类型
收费全文 | 9836篇 |
免费 | 1953篇 |
国内免费 | 2949篇 |
专业分类
测绘学 | 978篇 |
大气科学 | 1941篇 |
地球物理 | 2419篇 |
地质学 | 5262篇 |
海洋学 | 1520篇 |
天文学 | 320篇 |
综合类 | 943篇 |
自然地理 | 1355篇 |
出版年
2024年 | 51篇 |
2023年 | 162篇 |
2022年 | 464篇 |
2021年 | 583篇 |
2020年 | 450篇 |
2019年 | 576篇 |
2018年 | 594篇 |
2017年 | 583篇 |
2016年 | 638篇 |
2015年 | 565篇 |
2014年 | 653篇 |
2013年 | 692篇 |
2012年 | 713篇 |
2011年 | 741篇 |
2010年 | 792篇 |
2009年 | 654篇 |
2008年 | 649篇 |
2007年 | 585篇 |
2006年 | 500篇 |
2005年 | 406篇 |
2004年 | 342篇 |
2003年 | 318篇 |
2002年 | 298篇 |
2001年 | 307篇 |
2000年 | 275篇 |
1999年 | 358篇 |
1998年 | 244篇 |
1997年 | 257篇 |
1996年 | 199篇 |
1995年 | 190篇 |
1994年 | 180篇 |
1993年 | 154篇 |
1992年 | 103篇 |
1991年 | 84篇 |
1990年 | 64篇 |
1989年 | 59篇 |
1988年 | 59篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1976年 | 5篇 |
1966年 | 3篇 |
1958年 | 7篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Preliminary Study on Applicability of Microsatellite DNA Primers from Parasite Protozoa Trypanosoma cruzi in Free-living Protozoa 总被引:1,自引:0,他引:1
1 Introduction Generallyknownasacodominantgeneticmarker ,microsatellitehasbeenwidelyusedinstudiesonpopu lationgenetics,high resolutiongenotyping ,genemap ping ,evolution ,linkageanalysis ,conservationbiology ,behaviouralecology ,relationsbetweenparasite… 相似文献
992.
A quantitative analysis of the spatial pattern of rural settlements in the upper reaches of the Minjiang River was made with
the major data sources being the relevant ETM image and the national geographical database of China (including contour line,
river and road) at the scale of 1:250 000, and using image interpretation and field investigation to obtain spatial information
on rural settlements. The results of the spatial analysis technique of GIS and correlation analysis showed that most settlements
(78.2 %) were located in the mountain area at 1500 ∼ 2700 m altitude, and almost half in the arid valley area. More than 80.0
% of settlements had their slopes above 15°. Most settlements had good access to water resources, roads and communications,
and tended to cluster close to the road network rather than the river. About half of the rural settlements in the study area
were relatively concentrated, while the others were decentralized. Those with higher altitude usually had land with steep
slope, inconvenient water and road accesses, and were located far apart from each other. In view of such a situation, further
research should be done to make reasonable countermeasures on these settlements for better living conditions and ecosystem
stability. 相似文献
993.
A double discontinuity is a rarely observed compound structure composed of a slow shock layer and an adjoining rotational
discontinuity layer in the downstream region. In this paper, we report the observations of a double discontinuity detected
by Wind on May 15, 1997. This double discontinuity is found to be the front boundary of a magnetic cloud boundary layer. We
strictly identify the shock layer and the rotational discontinuity layer by using the high-resolution plasma and magnetic
field data from Wind. The observed jump conditions of the upstream and downstream region of the slow shock layer are in good
agreement with the Rankine – Hugoniot relations. The flow speeds in the shock frame U
n
<V
Acos θ
Bn
on both sides of the slow shock layer. In the upstream region, the slow Mach number M
s1=U
n1/V
s1 is 1.95 (above unity), and in the downstream region, the slow Mach number M
s2=U
n2/V
s2 is 0.31 (below unity). Here V
A and V
s represent the Alfvén speed and the local slow magnetosonic speed, respectively, and θ
Bn
is the angle between the direction of the magnetic field and the shock normal. The magnetic cloud boundary layer observed
by Wind was also detected by Geotail 48 min later when the spacecraft was located outside the bow shock of the magnetosphere.
However, Geotail observations showed that its front boundary was no longer a double discontinuity and the rotational discontinuity
layer disappeared, indicating that this double discontinuity was unstable when propagating from Wind to Geotail. 相似文献
994.
���������ֽ�ؿ��α������о� 总被引:1,自引:1,他引:0
?????????????????????У???????????????????????????????о????????????α????????????????????????????????λ???????????С?????????????????????????????????????????У??????????λ??????????????????????????????????????????????????????????????????????????????????????????????????????????????Ч??????????????????????????????????????????????????????е????????С??????????????????????????α????????????????????????????????????????????Ш???????????? 相似文献
995.
黑洞吸积理论及其天体物理学应用的近期发展(Ⅱ) 总被引:1,自引:0,他引:1
黑洞吸积理论是天体物理学的一个基础理论,是认识许多高能天体系统如活动星系核、黑洞X射线双星,以及伽马暴等的重要物理基础.该文评述近年来黑洞吸积理论尤其是径移主导吸积流模型(advection-dominated accretion flow)及其变种的主要发展,并介绍该理论在银河系中心、低光度活动星系核、黑洞X射线双星等方面的应用.共分为两篇,该文是第2篇,内容是关于黑洞热吸积流理论在低光度活动星系核以及黑洞X射线双星方面的应用. 相似文献
996.
任基 《成都信息工程学院学报》1990,(1)
本文介绍了一种新的标定流气式正比计数管的方法。此方法的特点是把正比管作为吸收体,利用He气对光子较为透明的原理,标定正比管的探测效率。方法简便实用,并对P-10(90%Ar+10%CH_4)为工作气体的正比管进行了标定。 相似文献
997.
WANGLiming FENGRenguo YANGYanfeng GUANQingfeng 《山地科学学报》2004,1(1):89-95
As an important measure of ecoenvironmental construction, the process of de-farming in slope farmland is being undertaken gradually in the whole China. Meanwhile, the problem of reducing in food yield in de-farming areas can not be neglected any more. It is especially the case in areas with concentrated slope farmland and inconvenient transportation. In this paper, we analyze the causes of hidden troubles in food security, and the spatial relationship between farmland and slope farmland in the reservoir area of Three Gorges, and unveil the spatial disparity of contradictions between food supply and demand. Finally, combining the accessibility of areas, three different spatial types of food security, food security area, food alert area, and food crisis area, are divided. 相似文献
998.
Félix Darve Stein Sture René de Borst Andrew J. Whittle Ian M. Smith 《国际地质力学数值与分析法杂志》2009,33(3):n\a-n\a
999.
1000.