全文获取类型
收费全文 | 1109篇 |
免费 | 101篇 |
国内免费 | 126篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 189篇 |
地球物理 | 239篇 |
地质学 | 431篇 |
海洋学 | 235篇 |
天文学 | 50篇 |
综合类 | 39篇 |
自然地理 | 88篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 35篇 |
2021年 | 42篇 |
2020年 | 39篇 |
2019年 | 42篇 |
2018年 | 59篇 |
2017年 | 75篇 |
2016年 | 81篇 |
2015年 | 76篇 |
2014年 | 84篇 |
2013年 | 80篇 |
2012年 | 67篇 |
2011年 | 95篇 |
2010年 | 78篇 |
2009年 | 64篇 |
2008年 | 50篇 |
2007年 | 60篇 |
2006年 | 48篇 |
2005年 | 37篇 |
2004年 | 28篇 |
2003年 | 32篇 |
2002年 | 29篇 |
2001年 | 29篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1336条查询结果,搜索用时 250 毫秒
831.
百年前的中国,百业凋敝、风雨如磐,地质工作在夹缝中艰难发展,在这样的时代背景下,26位中外地质学家齐聚北京地质调查所,共同发起创立了中国地质学会,使我国地质工作者有了自己的学术组织.在地质先驱们的共同努力下,学会以促成地质学及其关系科学之进步为宗旨,发挥了凝聚地质科学人才、加强国际学术交流的桥梁纽带作用.在1922年中... 相似文献
832.
Ki-Seon Choi Yu-Mi Cha Sung-Dae Kang Hae-Dong Kim Baek-Jo Kim 《Theoretical and Applied Climatology》2014,116(3-4):695-706
This study discovered that strong positive correlations exist between the frequency of tropical cyclones (TC) during the summer around Taiwan and the Arctic Oscillation (AO) during the preceding March to May period. In positive AO years, during the preceding spring to summer period, anomalous cyclone and anomalous anticyclone were strongly developed at low and middle latitudes, respectively. Because of such a distribution of pressure system, in Taiwan, Korea, and Japan during the positive AO years, anomalous southeasterlies, which play the role of anomalous steering flows in transferring TCs to these regions, were strengthened. On the other hand, in southern China and the Indochina Peninsula during the positive AO years, anomalous northwesterlies, which prevent the transfer of TCs to these regions, were strengthened. Moreover, such a distribution of pressure system strengthening during the positive AO years led TCs to occur, move, and recurve more eastward in the western North Pacific in positive AO years as compared with the negative AO years. Contrarily, during the negative AO years, TCs showed the tendency to pass over the South China Sea from the Philippines and move west toward southern China and the Indochina Peninsula. Eventually, the intensity of TCs in these years was lower than that of TCs in positive AO years due to the topographic effects from a high TC passage frequency in mainland China. 相似文献
833.
Yong-Sang Choi Heeje Cho Chang-Hoi Ho Richard S. Lindzen Seon Ki Park Xing Yu 《Theoretical and Applied Climatology》2014,115(1-2):355-364
Recent studies have estimated the magnitude of climate feedback based on the correlation between time variations in outgoing radiation flux and sea surface temperature (SST). This study investigates the influence of the natural non-feedback variation (noise) of the flux occurring independently of SST on the determination of climate feedback. The observed global monthly radiation flux is used from the Clouds and the Earth's Radiant Energy System (CERES) for the period 2000–2008. In the observations, the time lag correlation of radiation and SST shows a distorted curve with low statistical significance for shortwave radiation while a significant maximum at zero lag for longwave radiation over the tropics. This observational feature is explained by simulations with an idealized energy balance model where we see that the non-feedback variation plays the most significant role in distorting the curve in the lagged correlation graph, thus obscuring the exact value of climate feedback. We also demonstrate that the climate feedback from the tropical longwave radiation in the CERES data is not significantly affected by the noise. We further estimate the standard deviation of radiative forcings (mainly from the noise) relative to that of the non-radiative forcings, i.e., the noise level from the observations and atmosphere–ocean coupled climate model simulations in the framework of the simple model. The estimated noise levels in both CERES (>13 %) and climate models (11–28 %) are found to be far above the critical level (~5 %) that begins to misrepresent climate feedback. 相似文献
834.
Planulae of Aurelia aurita were exposed to 11 types of rocks (basalt, gabbro, granite, rhyolite, sandstone, limestone, conglomerate, gneiss, quartzite, marble and schist) to examine their attachment preference among rock material and position. Numbers of attached polyps was the highest on marble and the least on limestone. Their preference with regard to settling position was the same among the rocks, showing the highest density of polyps on the underside (88.5%) compared to upper (23.6%) and perpendicular sides (10.3%) of rock. The results showed that while position preference is more important than rock property, higher numbers of polyps were observed in rocks with a medium surface hardness. 相似文献
835.
Total dissolvable metals (Co, Ni, Cu, Cd, and Pb) in both surface waters and the water columns were acquired in the southern East/Japan Sea during a cruise around the Ulleung Basin in June 2001 to understand the spatial distributions of the metals. Concentrations in offshore surface waters were found to be Co 60 ± 12 pM, Ni 2.16 ± 0.25 nM, Cu 1.85 ± 0.55 nM, Cd 0.134 ± 0.018 nM, and Pb 155 ± 40 pM. Spatial distributions in surface waters showed that metal levels were generally enhanced at coastal sites in both Korea and Japan, where the metal distributions indicated complex patterns due to inputs, biogeochemical processes, and physical factors including upwelling. The Co distributions in the water columns seemed to be influenced predominantly by surface and bottom inputs, scavenged rather than regenerated at depth. For Cd, there was generally good agreement between the Cd and PO4 depth distributions, in agreement with the literature. The Cd/PO4 ratio from the water columns was found to be 0.133–0.203, lower than that in other marginal seas (e.g. the East/South China Seas and the Philippine Sea) of the western Pacific Ocean; this might be a result of the fast ventilation rate in this sea. The vertical Pb profile showed typical scavenged-type behavior with a surface maximum and deep minimum. From a comparison of inputs from the atmosphere and the Tsushima Warm Current, atmospheric deposition is substantial enough that it cannot be ignored, and its role in metal cycling is more significant in the offshore zone. 相似文献
836.
837.
This paper is concerned with the robust control synthesis of autonomous underwater vehicle(AUV) for general path following maneuvers.First,we present maneuvering kinematics and vehicle dynamics in a unified framework.Based on H∞ loop-shaping procedure,the 2-DOF autopilot controller has been presented to enhance stability and path tracking.By use of model reduction,the high-order control system is reduced to one with reasonable order,and further the scaled low-order controller has been analyzed in both the frequency and the time domains.Finally,it is shown that the autopilot control system provides robust performance and stability against prescribed levels of uncertainty. 相似文献
838.
Like any other coal, the highly heterogeneous nature of brown coal can sometimes make it difficult to interpret the results
of laboratory experiments. More homogeneous samples with properties reproducible in the laboratory would provide significant
advantage, especially in understanding the effects of various factors in the properties of coal. An attempt was made to develop
reconstituted coal (RC) samples in the laboratory through an extensive material development and laboratory testing programme.
The latter consisted of mainly uniaxial compression tests. The main objective in developing the RC material is to use it in
future research on CO2 sequestration in unmineable coal seams. A highly homogeneous coal sample would make it much easier to identify, for example,
the effect of CO2 sorption on the mechanical, flow and transport properties of coal. Uniaxial compression tests were conducted on some brown
coal samples to determine the approximate mechanical properties. The results revealed an average uniaxial compressive strength
of 1.46 MPa, an average elastic modulus of 77.43 MPa and a Poisson’s ratio of 0.16. The measured properties were used as a
reference for the development of RC samples. An extensive laboratory experimental programme was conducted to develop RC samples
with the desirable mechanical properties. Portland cement was used as the cementing agent for the RC. Different variables
such as percentage of cement, water content, compaction load and curing time were taken into account when developing RC samples.
Uniaxial compression tests were carried out to ensure that the RC samples were reasonably homogeneous and the properties were
similar to those of natural coal. Percentages of cement by weight of coal such as 4, 6 and 8% were attempted and a 4% cement
mix with 50% water was considered most suitable for the RC samples. Average compressive strength of 0.8 MPa (28-day strength)
and an average elastic modulus of 34 MPa were achieved for the RC samples. Further efforts at improvement would involve better
matching of the uniaxial compressive strength and elastic modulus of RC samples with the natural coal samples. 相似文献
839.
基于光纤光栅应变传感理论,开发以光纤光栅振动传感器为核心的周界入侵报警系统。由理论出发,建立了光纤光栅振动传感器设计框架。通过对不同尺寸质量块的实验研究,提出使用规格为4.5×20(mm×mm)的质量块;通过对不同光栅拉伸量的实验研究,提出0.8~1.0nm之间光栅拉伸量的光纤光栅振动传感器;通过对不同封装材料的对比实验,采用石英玻璃材料封装的方法。最后,将周界入侵报警系统进行了现场试验,波长检测范围是1 280~1 580nm,响应时间在3s以内,报警定位准确无误。 相似文献
840.
Fugacity of CO2 (fCO2), temperature, salinity, nutrients, and chlorophyll-a were measured in the surface waters of southwestern East Sea/Japan Sea in July 2005. Surface waters were divided into three
waters based on hydrographic characteristics: the water with moderate sea surface temperature (SST) and high sea surface salinity
(SSS) located east of the front (East water); the water with high SST and moderate SSS located west of the front (West water);
and the water with low SST and SSS located in the middle part of the study area (Middle water). High fCO2 larger than 420 μatm were found in the West water. In the Middle water, CO2 was undersaturated with respect to the atmosphere, with values between 246 and 380 μatm. Moderate fCO2 values ranging from 370 to 420 μatm were observed in the East water. For the East and West waters, estimates of temperature
dependency of fCO2 (12.6 and 15.1 μatm °C−1, respectively) were rather similar to a theoretical value, indicating that SST is likely to be a major factor controlling
the surface fCO2 distribution in these two regions. In the Middle water, however, the estimated temperature dependence was somewhat lower
than the theoretical value, and relatively high concentrations of surface chlorophyll-a coincided with the low surface fCO2, implying that biological uptake may considerably affect the fCO2 distribution. The net sea-to-air CO2 flux of the study area was estimated to be 0.30±4.81 mmol m−2 day−1 in summer, 2005. 相似文献