全文获取类型
收费全文 | 101960篇 |
免费 | 1499篇 |
国内免费 | 898篇 |
专业分类
测绘学 | 2472篇 |
大气科学 | 7016篇 |
地球物理 | 20458篇 |
地质学 | 36187篇 |
海洋学 | 8790篇 |
天文学 | 23416篇 |
综合类 | 271篇 |
自然地理 | 5747篇 |
出版年
2022年 | 549篇 |
2021年 | 966篇 |
2020年 | 1059篇 |
2019年 | 1114篇 |
2018年 | 2565篇 |
2017年 | 2378篇 |
2016年 | 2956篇 |
2015年 | 1748篇 |
2014年 | 2919篇 |
2013年 | 5296篇 |
2012年 | 3104篇 |
2011年 | 4228篇 |
2010年 | 3655篇 |
2009年 | 4925篇 |
2008年 | 4414篇 |
2007年 | 4227篇 |
2006年 | 3987篇 |
2005年 | 3141篇 |
2004年 | 3081篇 |
2003年 | 2872篇 |
2002年 | 2678篇 |
2001年 | 2466篇 |
2000年 | 2340篇 |
1999年 | 1936篇 |
1998年 | 2031篇 |
1997年 | 1941篇 |
1996年 | 1596篇 |
1995年 | 1631篇 |
1994年 | 1389篇 |
1993年 | 1278篇 |
1992年 | 1241篇 |
1991年 | 1154篇 |
1990年 | 1300篇 |
1989年 | 1104篇 |
1988年 | 1016篇 |
1987年 | 1270篇 |
1986年 | 1039篇 |
1985年 | 1332篇 |
1984年 | 1456篇 |
1983年 | 1406篇 |
1982年 | 1272篇 |
1981年 | 1199篇 |
1980年 | 1058篇 |
1979年 | 986篇 |
1978年 | 1005篇 |
1977年 | 904篇 |
1976年 | 885篇 |
1975年 | 835篇 |
1974年 | 822篇 |
1973年 | 834篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Least-squares prediction using an empirically deduced local covariance function was performed to investigate the temporal
change in the rates of vertical crustal movements in the Tohoku district, Japan. Levelling data covering an area of approximately
450 × 275 km2 observed between 1966 and 1995 were used and the results shown in the form of contour maps. Firstly we derived a covariance
function of the rates of vertical crustal movement with a Gaussian form function. We used this function to estimate the spatial
distribution of the rates of vertical crustal movements. By the present method, a steady tilt of the Tohoku district to the
east, toward the Japan Trench and an areal uplift in the southwestern part were well reproduced. Moreover, a significant temporal
change in vertical movement rates is clearly seen.
Received: 15 July 1996 相似文献
993.
994.
P. K. Pal W. J. Prakash P. K. Thapliyal C. M. Kishtawal 《Meteorology and Atmospheric Physics》1999,71(3-4):157-168
Summary ?A methodology has been developed to assimilate satellite-measured rainfall during the initial phase of model integration
for extended range monsoon prediction. The vertical profiles of latent heating corresponding to different rain rates have
been derived from the model statistics. These heating rates have been assimilated through nudging in the thermodynamics equation
of the model. This procedure of assimilating observed heating has corrected the simulation of heating location in the model
and consequently removed the anomalous sinking motion over Indian landmass. With the correction of vertical circulation, both
mean July rainfall over India and the distribution have improved. Interannual variability has been brought out for the years
1987 and 1988. In view of the availability of rainfall profile from Tropical Rain Measuring Mission (TRMM) there is a scope
of adopting this method of assimilating observed rainfall, for extended range monsoon prediction.
Received February 12, 1999/Revised May 4, 1999 相似文献
995.
Single-crystal X-ray structure refinement of natural olivines equilibrated at high temperature under controlled oxygen fugacity (f
O2) conditions, coupled with a structure-energy model were used to establish the influence of T, f
O2 and bulk chemistry on intracrystalline disorder.The results are: 1) The k
D (k
D = [(Fe M1·Mg M2)/(Fe M2·Mg M1)]) factor describing site population on M1, M2 polyhedra increases from values lower than 1 at T below 400–600° C (depending on composition) to values higher than 1 at higher temperature. 2) The increase of k
D with T is quite regular. 3) At constant temperature and pressure, k
D increases with increasing fayalite content in the mixture; 4) Contrary to previous observations (Will and Nover 1979; Nover and Will 1981) varying f
O2, within the stability range of the substance, has a negligible influence on intracrystalline disorder. 5) As ancillary results, the model confirms the defect scheme of Nakamura and Schmalzried (1983) for the investigated solids. Moreover, it shows that cationic vacancies are always created on M 1 site at the expense of Mg ions, while trivalent iron is always stabilized on M2 site. This explains the marked anisotropies observed in Fe-Mg interdiffusion (Buening and Busek 1973; Misener 1974; Schock et al. 1989). 相似文献
996.
997.
998.
999.
Models for ground water flow (MODFLOW) and particle tracking (MODPATH) were used to determine ground water flow patterns, principal ground water discharge and recharge zones, and estimates of ground water travel times in an unconfined ground water system of an outer coastal plain watershed on the Delmarva Peninsula, Virginia. By coupling recharge and discharge zones within the watershed, flowpath analysis can provide a method to locate and implement specific management strategies within a watershed to reduce ground water nitrogen loading to surface water. A monitoring well network was installed in Eyreville Creek watershed, a first-order creek, to determine hydraulic conductivities and spatial and temporal variations in hydraulic heads for use in model calibration. Ground water flow patterns indicated the convergence of flow along the four surface water features of the watershed; primary discharge areas were in the nontidal portions of the watershed. Ground water recharge zones corresponded to the surface water features with minimal development of a regional ground water system. Predicted ground water velocities varied between < 0.01 to 0.24 m/day, with elevated values associated with discharge areas and areas of convergence along surface water features. Some ground water residence times exceeded 100 years, although average residence times ranged between 16 and 21 years; approximately 95% of the ground water resource would reflect land use activities within the last 50 years. 相似文献
1000.