全文获取类型
收费全文 | 1196篇 |
免费 | 165篇 |
国内免费 | 210篇 |
专业分类
测绘学 | 34篇 |
大气科学 | 221篇 |
地球物理 | 243篇 |
地质学 | 369篇 |
海洋学 | 354篇 |
天文学 | 42篇 |
综合类 | 56篇 |
自然地理 | 252篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 29篇 |
2021年 | 29篇 |
2020年 | 54篇 |
2019年 | 40篇 |
2018年 | 39篇 |
2017年 | 37篇 |
2016年 | 36篇 |
2015年 | 51篇 |
2014年 | 59篇 |
2013年 | 79篇 |
2012年 | 42篇 |
2011年 | 56篇 |
2010年 | 37篇 |
2009年 | 97篇 |
2008年 | 82篇 |
2007年 | 88篇 |
2006年 | 79篇 |
2005年 | 69篇 |
2004年 | 45篇 |
2003年 | 47篇 |
2002年 | 40篇 |
2001年 | 30篇 |
2000年 | 34篇 |
1999年 | 46篇 |
1998年 | 35篇 |
1997年 | 25篇 |
1996年 | 34篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有1571条查询结果,搜索用时 93 毫秒
121.
122.
《中国科学D辑(英文版)》2006,(Z2)
The study by the eddy covariance technique in the alpine shrub meadow of the Qing-hai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO2 emission of the shrub ecosystem culminated in April and September while the CO2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO2·m-2 respectively, yielding an average of 253.1 gCO2·m-2 per year: that accounts for a large proportion of absorbed CO2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g Cm"2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m-2 in 2003 and 74.9 g C·m-2 in 2004) in the corresponding plant growing season. 相似文献
123.
We review the historical, geological, tide-gauge, GPS and gravimetric evidence advanced in favour of, or against, continuing
land uplift around Hudson Bay, Canada. We also reanalyse the tide-gauge and GPS data for Churchill using longer time series
than those available to previous investigators. The dependence of the mean rate of relative sea-level change obtained from
the tide-gauge record on the length and mid-epoch of the observation interval considered is investigated by means of a newly
developed linear-trend analysis diagram. For studying the shorter-period variability of the tide-gauge record, the wavelet
transform is used. The mean rate of land uplift obtained from GPS is based on a new analysis using IGS solutions of GFZ. To
include the post-glacial land uplift, sea-level indicators from the Churchill region representing the relative sea-level history
during the past 8000 years are also used. Finally, the values of the four observables are jointly inverted in terms of mantle
viscosity. The optimum values are ~3.2 × 1020 Pa s and ~1.6 × 1022 Pa s for the upper- and lower-mantle viscosities, respectively. 相似文献
124.
The diagenesis of modern and ancient carbonatesedi ments has been widely studied and systematicallyreviewed since the 1960s (e .g. Moore ,2001 ,1989 ;Wang et al ., 1994 , 1991 ; McIlreath and Morrow,1990 ; Tucker and Bathurst , 1990 ; Schneidermannand Harris , 1985 ; Longman, 1980 ; Bathurst ,1975) . With the development of sequence stratigra-phy and its more widespread application, discussionabout the relationship between diagenesis and se-quence stratigraphy/sea-level changes ,as well as… 相似文献
125.
对商丘国家观象台1954--2005年月报表中挑取的符合暴雨日条件的142个样本分析,结果表明:商丘暴雨日具有明显的季节性,频发于7、8月份;暴雨日年平均2.73个;日暴雨量最大(193.3mm)不超过200mm;最长连续暴雨日数不超过2日;连续暴雨日降水量累计(223.9mm)不超过250mm;1h最大降水量不超过70mm。暴雨目的年代际变化特征明显,20世纪80年代后暴雨日出现较晚,60--90年代的暴雨日数递减,90年代后有增加趋势;大暴雨日数自60年代起有逐步增加趋势。暴雨日对月、年降水量有显著贡献,4—9月暴雨日对月降水量的贡献很大,且从4月到7月暴雨目的贡献呈递增趋势。一年内暴雨日出现5次时,当年的年雨量为偏多年份。 相似文献
126.
Interdecadal variations in the frequency of typhoon affecting China (TAC) during 1951-2004 were investigated in this study. The yearly frequency of TACs showed a slightly increasing trend from the 1950s to the early 1970s and a significant decreasing trend afterwards. There were more TACs during the 1960s while the most inactive period was observed in recent 10 years. A decreasing trend was observed in the monthly frequency of TACs in June, August and September throughout the 54 years. Large interannual variabilities were apparent in yearly and monthly frequencies of TACs. 相似文献
127.
The ionospheric effect is one of the major errors in GPS data processing over long baselines. As a dispersive medium, it is
possible to compute its influence on the GPS signal with the ionosphere-free linear combination of L1 and L2 observables,
requiring dual-frequency receivers. In the case of single-frequency receivers, ionospheric effects are either neglected or
reduced by using a model. In this paper, an alternative for single-frequency users is proposed. It involves multiresolution
analysis (MRA) using a wavelet analysis of the double-difference observations to remove the short- and medium-scale ionosphere
variations and disturbances, as well as some minor tropospheric effects. Experiments were carried out over three baseline
lengths from 50 to 450 km, and the results provided by the proposed method were better than those from dual-frequency receivers.
The horizontal root mean square was of about 0.28 m (1σ). 相似文献
128.
概述辽、金、元三代有关测绘的管理和机构,职官设置,各类测绘状况及成果,着重介绍了元代的测绘技术,发明创造及著述。 相似文献
129.
CHEN Hao-Wen 《冰川冻土》1998,(4)
The outdoor air borne microbial content over Great Wall Station, Antarctica has been monitored, including its diurnal variations and states in fair or foul weather conditions.The results obtained show: the concentration averaged 161. 9 CFU. m-3. When the weather condition was fair, its range of variation is 0~1 336. 2 CFU. m-3, the average value was 1488. 3 CFU. m-3,when the weather was foul, the range of variation was 471. 4-4 296. 8 CFU. m-3. The average value of air borne microbial number in either fair or foul weather was 383. 0 CFU. m-3. This value is over than 21 times that obtained during 1986/1987.The results seem to show that the influence of human activities have been increasing on Antarctic ecosystem. The diurnal variation of the outdoor air borne microbes shows that the peak of content appeared at about 01: 00, and the trough at about 13: 00 in a whole day. Analyses were made of the relationships between the microbial concentration with its related indexes, i. e. relevant air temperature relative humidity or wind force.The results showed some particularities as compared with those from the areas outside Antarctica. 相似文献
130.
Matthew T. DeLand Richard P. Cebula Ernest Hilsenrath 《Studia Geophysica et Geodaetica》1998,42(2):83-91
The Shuttle SBUV (SSBUV) and NOAA-11 SBUV/2 instruments measured solar spectral UV irradiance during the maximum and declining phase of solar cycle 22. The SSBUV data accurately represent the absolute solar UV irradiance between 200–405 nm, and also show the long-term variations during eight flights between October 1989 and January 1996. These data have been used to correct long-term sensitivity changes in the NOAA-11 SBUV/2 data, which provide a near-daily record of solar UV variations over the 170–400 nm region between December 1988 and October 1994. The NOAA-11 data demonstrate the evolution of short-term solar UV activity during solar cycle 22. 相似文献