全文获取类型
收费全文 | 41808篇 |
免费 | 8593篇 |
国内免费 | 12985篇 |
专业分类
测绘学 | 4306篇 |
大气科学 | 7765篇 |
地球物理 | 9784篇 |
地质学 | 24893篇 |
海洋学 | 5528篇 |
天文学 | 1635篇 |
综合类 | 4426篇 |
自然地理 | 5049篇 |
出版年
2024年 | 252篇 |
2023年 | 729篇 |
2022年 | 2031篇 |
2021年 | 2377篇 |
2020年 | 1857篇 |
2019年 | 2301篇 |
2018年 | 2316篇 |
2017年 | 2119篇 |
2016年 | 2387篇 |
2015年 | 2373篇 |
2014年 | 2533篇 |
2013年 | 2668篇 |
2012年 | 2775篇 |
2011年 | 3146篇 |
2010年 | 3007篇 |
2009年 | 2826篇 |
2008年 | 2304篇 |
2007年 | 2306篇 |
2006年 | 2170篇 |
2005年 | 1998篇 |
2004年 | 2134篇 |
2003年 | 1662篇 |
2002年 | 1464篇 |
2001年 | 1381篇 |
2000年 | 1240篇 |
1999年 | 1508篇 |
1998年 | 1343篇 |
1997年 | 1243篇 |
1996年 | 1057篇 |
1995年 | 912篇 |
1994年 | 838篇 |
1993年 | 898篇 |
1992年 | 767篇 |
1991年 | 522篇 |
1990年 | 330篇 |
1989年 | 318篇 |
1988年 | 279篇 |
1987年 | 193篇 |
1986年 | 145篇 |
1985年 | 99篇 |
1984年 | 73篇 |
1983年 | 56篇 |
1982年 | 74篇 |
1981年 | 50篇 |
1980年 | 42篇 |
1979年 | 45篇 |
1978年 | 17篇 |
1977年 | 21篇 |
1976年 | 21篇 |
1958年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
92.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
93.
94.
我们于1989年11月30日晚对PG0027+260进行了时间分辨率为108秒的高速CCD测光,得到了一条完整的光变曲线,从而确认其为激变食变星系统,轨道周期0.146~d 相似文献
95.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
96.
Vertical profiles of chl-a and primary productivity in the middle continental shelf area and eddy area of the East China Sea
were studied using data from a cruise in the East China Sea in February to March, 1997 and a cruise in July, 1998. The results
showed that chl-a vertical distribution closely related to in situ hydrological and nutrient conditions. Chla-a concentration
ranged from 0.22 to 0.35 mg/m3 and 0.93–1.09 mg/m3 in the eddy area and in the middle continental shelf area, respectively. In both areas, chl-a concentrations in deep layers
were slightly higher than those in shallow layers, but was of the same order of magnitude. In summer, when a thermocline existed
in the water column, highest chl-a concentrations appeared at the base of the thermocline layers in both areas. In the eddy
area, chl-a concentration maximized at 31.743 mg/m3, and averaged 1.143 mg/m3 below 30 m depth. In the middle continental shelf area, the highest chl-a concentration was 2.120 mg/m3, the average was 1.168 mg/m3. The primary productivity reached 1418.76 mgC/(m2·d) in summer and 1360.69 mgC/(m2·d) in winter. In the eddy area, the primary productivity was 787.50 mgC/(m2·d) in summer and 159.04 mgC/(m2·d) in winter. Vertical carbon sinking rate from the deep layer to the bottom in both areas is also discussed in this paper.
Contribution NO. 4183 from the Institute of Oceanology, Chinese Academy of Sciences.
Project No. 49636210 supported by NSFC. 相似文献
97.
98.
OQ208 is used ore and more frequently as a VLBI calibrator of flux density. A VLBI image of OQ208 at 5 GHz is firstly provided in this paper. Its structure consists of a compact core and a component. The angular distance between the core and the component is about 7 milli-arcsecond; the position angle is −125 degrees. In principle, OQ208 is not an ideal VLBI calibrator of flux density. This paper provides the structural information for correcting the structure effect when OQ208 is to be used as a calibrator. 相似文献
99.
100.