全文获取类型
收费全文 | 15377篇 |
免费 | 3548篇 |
国内免费 | 4533篇 |
专业分类
测绘学 | 1586篇 |
大气科学 | 2759篇 |
地球物理 | 3958篇 |
地质学 | 8701篇 |
海洋学 | 2360篇 |
天文学 | 553篇 |
综合类 | 1387篇 |
自然地理 | 2154篇 |
出版年
2024年 | 82篇 |
2023年 | 264篇 |
2022年 | 818篇 |
2021年 | 902篇 |
2020年 | 777篇 |
2019年 | 882篇 |
2018年 | 967篇 |
2017年 | 826篇 |
2016年 | 904篇 |
2015年 | 911篇 |
2014年 | 970篇 |
2013年 | 1067篇 |
2012年 | 1132篇 |
2011年 | 1178篇 |
2010年 | 1151篇 |
2009年 | 1069篇 |
2008年 | 1083篇 |
2007年 | 1062篇 |
2006年 | 882篇 |
2005年 | 747篇 |
2004年 | 607篇 |
2003年 | 481篇 |
2002年 | 530篇 |
2001年 | 500篇 |
2000年 | 489篇 |
1999年 | 474篇 |
1998年 | 350篇 |
1997年 | 353篇 |
1996年 | 288篇 |
1995年 | 250篇 |
1994年 | 292篇 |
1993年 | 217篇 |
1992年 | 180篇 |
1991年 | 130篇 |
1990年 | 111篇 |
1989年 | 79篇 |
1988年 | 102篇 |
1987年 | 55篇 |
1986年 | 46篇 |
1985年 | 40篇 |
1984年 | 42篇 |
1983年 | 35篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1975年 | 4篇 |
1958年 | 7篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
21.
对边界层理论新结果中出现的一类奇异积分方程w(t)=∫1 t(1-s)(λ+λs+s)/w(s)ds+(1-t)∫t 0s/w(s)ds,t∈(0,1)进行讨论,并得出了上述方程在λ∈(-1/2,0)上正解存在性的新结果。 相似文献
22.
利用Logisitic曲线模型和扩展支撑模型对居民可支配收入预测和单项消费预测,以河北省居民的收入及其消费支出为实例,研究了城镇居民和农民的可支配收入分配和单项边际消费倾向,合理建立了预测模型,并理论计算了1999~2003年的通信消费方面的边际消费倾向、预测了2004~2008年通信消费情况。最后,根据预测结果对通信网络建设提出了一些有价值的建议。 相似文献
23.
CARBON DYNAMICS OF WETLAND IN THE SANJIANG PLAIN 总被引:2,自引:0,他引:2
SONG Chang-chun WANG Yi-yong WANG Yue-si YAN Bai-xing WANG De-xuan ZHAO Zhi-chun LOU Yan-jing 《中国地理科学(英文版)》2003,13(3):228-231
1INTRODUCTIONWetlandsplayanimportant roleintheprocessofcar-bonstorage.Thetotalcarbonstoredindifferentkindsofwetlandsisabout15%-35%ofthetotalcarboninthegloballandsoils(POSTetal.,1982;GORHAM,1991).Inaddition,wetlandsaresignificantnaturalsources fortheatmospheric CH4 (MOORE,1994).It isestimatedthatabout110×1012gCH4 originates fromanaerobicdecompositioninthenaturalwetlands,CH4 emission fromthenaturalwetlandsis15%-30%oftheglobalCH4 emission andtheCH4 emission from thepeat land at hi… 相似文献
24.
The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions (MTF) of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic (e.m.) wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle for HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%-60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization. 相似文献
25.
Jianhua FAN Bingfei SHI 《东北亚地学研究》2006,9(2):217-219
Kunming Basin locates middle of Yunnan altiplano and has a particularity in geography,topographic and geological environment.With the urban dilation quickly,add the reason of the unreasonable city layout,conflicts between environment and urban resources consumption become shrill increasingly.It is human being activities that lead to vulnerability and depravation of geological environment in local.Take a few examples on geological environment to expatiate relationship between urban construction and geological environment carrying capacity,and find a way how to make a better plan for urban sustainable development to achieve new balance between man and nature in local. 相似文献
26.
疏散星团在天文学和天体物理学研究中有着多方面的重要性。近年来在观测和理论工作上都取得了显著的进展。综述了疏散星团的研究现状,对成员判别、基本参数确定、团与恒星的演化、团的结构和动力学进行了详细评述。 相似文献
27.
本文提出了一个普适的衡量成团天体系统成员概率计算结果的有效性指数:E=1-NΣ{P(i)[1-P(i)]}/ΣP(i)Σ[1-P(i)]},并以此对以Sanders方法为基础的各种成员确定模型的有效性进行了分析.从总体上说,运动学资料(自行、视向速度等)是一类有效的观测判据. 相似文献
28.
Based on the CN and C2 comae isophotes for two comets (1961 IX and 1970 16) given by Rahe et al. and the relevant theory of physical chemistry, we have deduced the distributions of the CN and C2 modecules in the coma, their scale heights and mean lifetimes. The results favour the viewpoint that HCN is the parent of CN, and that C2H2 is the parent of C2. 相似文献
29.
Method for evaluating the degrees of land use sustainability of mountainous county and its application in Yunnan Province,China 总被引:4,自引:1,他引:3
The evaluation of sustainable land use is the key issue in the field of studying the sustainable land utilization. In general analysis, the sustainable land use is evaluated respectively from its ecological sustainability, economic sustainability and social sustainability in China and other countries in recent years. Although this evaluation is an important work, it seems insufficient and hard to comprehensively reflect the whole degree of land use sustainability. Thus, to make up this deficiency, this paper brings forward the evaluation indexes, which make it possible to quantitatively reflect the whole degree of land use sustainability, namely, the concept of "degrees of overall land use sustainability" (Dos), and research and measurement development of the method of and calculation in Dos. Taking the evaluation of the degree of land use sustainability in county regions of Yunnan Province as the actual example for analysis, results are basically as follows:
1) The degree of land use sustainability (Dos) is the ration index to organically and systematically integrate the degree of ecological friendliness (DeF), the degree of economic viability (Dev) and the degree of social acceptability (Dsa), able to comprehensively reflect the whole sustainability degree of regional land use
2) Based on the value of Dos, the grading system and standard for the sustainability of land use may be established and totally divided into five grades, namely, the high-degree sustainability, middle-degree sustainability, low-degree sustainability, conditional sustainability and non-sustainability. Meanwhile, the standard for distinguishing sustainability grades has also been confirmed so as to determine the nature of sustainability degrees in different grades. This makes the possibility for the combination of nature determination with ration in research result and provides with the scientific guideline and decision-making gist for better implementation of sustainable land use strategy.
3) The pract 相似文献
1) The degree of land use sustainability (Dos) is the ration index to organically and systematically integrate the degree of ecological friendliness (DeF), the degree of economic viability (Dev) and the degree of social acceptability (Dsa), able to comprehensively reflect the whole sustainability degree of regional land use
2) Based on the value of Dos, the grading system and standard for the sustainability of land use may be established and totally divided into five grades, namely, the high-degree sustainability, middle-degree sustainability, low-degree sustainability, conditional sustainability and non-sustainability. Meanwhile, the standard for distinguishing sustainability grades has also been confirmed so as to determine the nature of sustainability degrees in different grades. This makes the possibility for the combination of nature determination with ration in research result and provides with the scientific guideline and decision-making gist for better implementation of sustainable land use strategy.
3) The pract 相似文献
30.