全文获取类型
收费全文 | 22608篇 |
免费 | 3101篇 |
国内免费 | 4330篇 |
专业分类
测绘学 | 1139篇 |
大气科学 | 3740篇 |
地球物理 | 4920篇 |
地质学 | 11008篇 |
海洋学 | 3156篇 |
天文学 | 2030篇 |
综合类 | 1765篇 |
自然地理 | 2281篇 |
出版年
2024年 | 67篇 |
2023年 | 290篇 |
2022年 | 946篇 |
2021年 | 1161篇 |
2020年 | 1081篇 |
2019年 | 1060篇 |
2018年 | 1401篇 |
2017年 | 1307篇 |
2016年 | 1365篇 |
2015年 | 1013篇 |
2014年 | 1298篇 |
2013年 | 1372篇 |
2012年 | 1303篇 |
2011年 | 1417篇 |
2010年 | 1356篇 |
2009年 | 1275篇 |
2008年 | 1164篇 |
2007年 | 1218篇 |
2006年 | 1056篇 |
2005年 | 632篇 |
2004年 | 547篇 |
2003年 | 625篇 |
2002年 | 679篇 |
2001年 | 632篇 |
2000年 | 539篇 |
1999年 | 668篇 |
1998年 | 557篇 |
1997年 | 570篇 |
1996年 | 478篇 |
1995年 | 486篇 |
1994年 | 431篇 |
1993年 | 343篇 |
1992年 | 306篇 |
1991年 | 199篇 |
1990年 | 181篇 |
1989年 | 169篇 |
1988年 | 127篇 |
1987年 | 100篇 |
1986年 | 77篇 |
1985年 | 64篇 |
1984年 | 65篇 |
1983年 | 56篇 |
1982年 | 57篇 |
1981年 | 41篇 |
1980年 | 34篇 |
1979年 | 40篇 |
1978年 | 20篇 |
1977年 | 20篇 |
1975年 | 24篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
31.
ENVIRONMENTAL SUSTAINABILITY AND SCENARIOS OF URBANIZATION IN ARID AREA——A Case Study in Wuwei City of Gansu Province 总被引:1,自引:0,他引:1
YOUFei LIYu DONGSuo-cheng 《中国地理科学(英文版)》2005,15(2):120-130
1IN T R O D U C T IO N The western China isfacinggrowing problems of eco- logicaland economic development. The disparitiebse- tween the socio-economy of the western and eastern China were enlarging, and the major ecologicalprob- lems stilelvolve as past(H… 相似文献
32.
TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45
Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities. 相似文献
33.
本文论述了珠穆朗玛峯地区土壤中稀土元素的含量,以及它们在土壤中的分布模式,并发现土壤中稀土元素的含量水平在很大程度上受土壤母质的制约。 相似文献
34.
Methyl-galactosides were oxidized at room temperature by galactose oxidase in a one-step reaction and afforded methyl-galactoaldehyde
in excellent yield and high purity. The resulting galactoaldehyde as a useful intermediate can be directly used in glycopeptide
synthesis. 相似文献
35.
本文通过对1980年以来长江上游10次洪涝过程的500hpa环流形势分析,并用车比雪夫多项式对500hpa高度场进行展开,研究了各类洪涝过程的中期演变特征,发现代表不同洪涝过程环流形势变化的不同的车氏系数值都有明显的特征变化,结合欧洲中心中期数值预告96小时500hpa高度场的车氏系数分析,可为洪涝暴雨的中期预报提供一种新的思路。 相似文献
36.
Baolin Tan Haisheng Ji Guangli Huang Tuanhui Zhou Qiwu Song Yu Huang 《Solar physics》2006,239(1-2):137-148
Using one-minute cadence vector magnetograms from Big Bear Solar Observatory (BBSO), we analyze the temporal behavior of derived
longitudinal electric currents associated with two flares on July 26, 2002. One of the events is an M1.0 flare which occurred
in active region NOAA 10044, while the other is an M8.7 flare in the adjacent region 10039. Rapid changes of magnetic fields
in the form of flux emergence are found to be associated with both of these events. However, the temporal behavior of electric
currents are very different. For the M1.0 flare, the longitudinal electric current density drops rapidly near the flaring
neutral line; while for the M8.7 flare, the current density rapidly increases, confirming the picture of the current-carrying
flux emergence. We offer a possible explanation for such a difference: magnetic reconnection at different heights for the
two events, near the photosphere for the M1.0 flare, and higher up for the M8.7 flare. 相似文献
37.
Lu Sun 《国际地质力学数值与分析法杂志》2003,27(1):69-84
A closed‐form deflection response of a beam rest is presented in this paper using the integral transform method. The theory of linear partial differential equations is used to represent the deflection of beam subjected to a moving harmonic line load in integration form. The solution is finally carried out using the inverse Fourier transform. To evaluate the integration analytically, poles of the integrand are identified with the help of algebraic equation theory. Residue theorem is then utilized to represent the integration as a contour integral in the complex plane. Closed‐form deflections and numerical results are provided for different combinations of load frequency and velocity. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
38.
39.
40.
Byurakan Astrophysical Observatory. Translated from Astrofizika, Vol. 33, No. 2, pp. 271–281, September–October, 1990. 相似文献