全文获取类型
收费全文 | 106942篇 |
免费 | 1457篇 |
国内免费 | 844篇 |
专业分类
测绘学 | 2664篇 |
大气科学 | 7270篇 |
地球物理 | 20754篇 |
地质学 | 38328篇 |
海洋学 | 9472篇 |
天文学 | 24653篇 |
综合类 | 339篇 |
自然地理 | 5763篇 |
出版年
2022年 | 701篇 |
2021年 | 1201篇 |
2020年 | 1265篇 |
2019年 | 1408篇 |
2018年 | 3004篇 |
2017年 | 2803篇 |
2016年 | 3336篇 |
2015年 | 1745篇 |
2014年 | 3220篇 |
2013年 | 5577篇 |
2012年 | 3490篇 |
2011年 | 4492篇 |
2010年 | 4017篇 |
2009年 | 5101篇 |
2008年 | 4477篇 |
2007年 | 4545篇 |
2006年 | 4274篇 |
2005年 | 3136篇 |
2004年 | 3019篇 |
2003年 | 2864篇 |
2002年 | 2823篇 |
2001年 | 2482篇 |
2000年 | 2425篇 |
1999年 | 1978篇 |
1998年 | 2018篇 |
1997年 | 1901篇 |
1996年 | 1670篇 |
1995年 | 1650篇 |
1994年 | 1421篇 |
1993年 | 1320篇 |
1992年 | 1220篇 |
1991年 | 1262篇 |
1990年 | 1236篇 |
1989年 | 1113篇 |
1988年 | 1035篇 |
1987年 | 1219篇 |
1986年 | 1067篇 |
1985年 | 1298篇 |
1984年 | 1426篇 |
1983年 | 1386篇 |
1982年 | 1291篇 |
1981年 | 1167篇 |
1980年 | 1076篇 |
1979年 | 998篇 |
1978年 | 957篇 |
1977年 | 857篇 |
1976年 | 833篇 |
1975年 | 814篇 |
1974年 | 822篇 |
1973年 | 894篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
We investigate a dynamical model of prominence formation in a current sheet at the boundary between two regions of opposite magnetic polarity. Coupled nonlinear equations describing the temporal compression and condensation of plasma in the current sheet are set up as a natural extension of the usual equations for current sheet collapse (Imshennik and Syrovatskii, 1967). It is shown that under certain conditions the current sheet undergoes a nonlinear oscillation during the compression. The thermal instability with cooling is driven by a density enhancement produced during the current sheet formation stage. 相似文献
882.
The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. 相似文献
883.
Victor A. Avdyushev 《Celestial Mechanics and Dynamical Astronomy》2003,87(4):383-409
Mainly, the author focuses on Baumgarte's method and its applications in satellite, asteroid, stellar and planetary problems. In the paper arguments are given for the use of energy relations for stabilization in the elliptical two-body problem. Stabilizing properties of Baumgarte's equations and others are discussed. A simple approach is proposed for stabilizing the equations of almost circular motion. By using Baumgarte's technique, the author derives stabilized equations of perturbed restricted three-body problem. It is shown experimentally that stabilization in the problems mentioned above can raise the accuracy of numerical integration by several orders. 相似文献
884.
Martin A. Lee 《Astrophysics and Space Science》1998,264(1-4):497-508
The interaction of interstellar pickup ions with the solar wind termination shock is reviewed and assessed. The pickup ions
mass and momentum load the wind and increase its pressure, effects which decrease the strength of the shock and its distance
from the Sun. The pickup hydrogen may contribute substantially to the "reflected" ion population, which should provide most
of the dissipation at the supercritical quasi-perpendicular shock. A fraction of the pickup ions impinging on the shock is
"injected" into the process of diffusive shock acceleration to form the anomalous cosmic ray component. An injection mechanism
which accounts for the apparent absence of solar wind ions in the anomalous component is "shock surfing", in which pickup
ions which approach the shock slowly may be trapped between the upstream Lorentz force and the shock potential and accelerated
in the motional electric field beyond the energy threshold for diffusive shock acceleration. However, the simplest interpretation
of shock surfing would favor less massive pickup ion species, in contradiction with Voyager observations of anomalous component
composition. A possible extension of the shock surfing mechanism is considered, as well as other injection mechanisms. Finally,
the pressure of the anomalous component may modify the structure of the termination shock, which in turn may influence injection
rates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
885.
E. K. Semenov N. N. Sokolikhina E. V. Sokolikhina 《Russian Meteorology and Hydrology》2013,38(10):661-668
The genetic and synoptic classifications of the Novorossiysk Bora are created using the data of daily observations at the Novorossiysk meteorological station and other available synoptic information. Obtained are the quantitative criteria of these classifications, and on this base worked out are the basic scenarios of the generation and evolution of this dangerous phenomenon on the Black Sea coast of Russia. According to the genetic classification, the Bora was divided into four types: frontal, air-mass, monsoon, and gravity. Quantitative criteria worked out for each type can be used for the more accurate forecast of this destructive phenomenon near Novorossiysk. According to the synoptic classification, four classes were distinguished: Azores, North Atlantic, Siberian, and Arctic. 相似文献
886.
887.
V. V. Aristov I. I. Babarina A. V. Grigor’eva V. Yu. Alekseev V. Yu. Prokof’ev A. A. Uzyunkoyan O. V. Zabolotskaya S. G. Titov 《Geology of Ore Deposits》2017,59(1):68-101
Gold deposits and occurrences small in reserves and high in Au grade conventionally determine the line of prospecting in terrigenous sequences of the Verkhoyansk–Kolyma region. In this paper, the geological structure of such gold objects is considered with the example of the deposits and prospects making up the Zhdaninsky ore–placer cluster in the Republic of Sakha (Yakuia). From lithological, structural, and mineralogical–geochemical data, the formation conditions of ore-bearing complexes are specified, the geological evolution history of the northern Ol’chan Zone of the Kular–Nera Belt is reconstructed, and the zonal distribution of mineralization within the ore–placer cluster is revealed. The structural–compositional complexes were formed in the following succession: (1) sedimentation at the shelf of the passive margin accompanied by synsedimentation deformations; (2) metagenesis of sediments and the development of bedding-plane intraformational detachments of collision stage D1 under conditions of tangential compression and accompanied by the formation of carbon dioxide–aqueous metamorphic fluid at a temperature of 300°C and under a pressure of 1.4 kbar; (3) folding and faulting of orogenic stage D2 with the formation of synkinematic magmatic bodies, metasomatic alteration, and Au-bearig mineral assemblages. Small Au-bearing objects with veined mineralization and high Au grade are localized in structures of stage D2 transverse to bedding-plane schistosity S1. They form at the collision stage above intraformational detachment surfaces and are controlled by shear structures of the orogenic stage with misalignment of these deformations. The ore zoning is determined by the distribution of Co and Ni minerals and by variations in the anionic composition of ore (S, As, Sb). 相似文献
888.
R. L. Karale K. K. Narula V. Dayal K. M. Saini 《Journal of the Indian Society of Remote Sensing》1989,17(1):23-31
In order to check the premature siltation of the reservoirs and guard against the drop in the irrigation potential, the Government of India has launched the schemes of soil conservation and integrated watershed management in the catchments of RVPs and Flood Prone rivers. Owing to the large financial and manpower commitments needed to implement and execute soil conservation measures over vast catchment areas, a priority approach for treatment was identified. The methodology developed for prioritization of watersheds of a catchment area conceptualizes sedimentation of the reservoirs as a multiplicative function of erosivity value and the delivery ratio. This paper deals with the development of a computerized data base software module ‘WEIGHT’ for determination of erosivity values for the mapping units comprising assemblages of the varying combinations of climate, physiography and slope, land use and cover conditions, soil characteristics (texture, solumn thickness, permeability and pH) and the existing erosion and soil conservation measures. The WEIGHT software package is coded in FORTRON-4 for PDP 11/83 operating system. the data base comprises storage of the attributes of the different erosivity determinants of the mapping units with predetermined erosivity values sequentially on a disk and comparing the attributes of a new mapping unit to get the most probabilities erosivity value. The objective has been to eliminate the personal bias and bring about the objectivity in the process of assigning erosivity values to the different mapping units. The data base design, design logic and operational sequence of the data base are discussed in the paper. 相似文献
889.
Whistler data recorded during a 14 h period on 10–11 July 1973 at Siple (L = 4.17) and Sanae (L = 3.98) have been used to compare the apparent plasma convection patterns observed from these Antarctic stations. Two distinct bulges in the plasmasphere are seen at both stations, each bulge corresponding to an apparent outflowed followed by in flow of plasma. These structures do not coincide in U.T. or M.L.T. The first bulge is seen at Siple almost 1 h earlier in M.L.T. than at Sanae and the second bulge almost 3 h earlier. This is interpreted in terms of a fairly rapid westward and inward movement of the plasmasphere structure. 相似文献
890.
A. A. Galal H. A. Deebes Maha S. Quassim Shahinaz Yousef 《Earth, Moon, and Planets》1995,70(1-3):151-162
TheK
p-indices measured at Misallat station [ø = 29°45 N; = 30°54 E] during the period 1958–1989, have been compared with the data of two geomagnetic stations; one of them has similar longitude as Misallat and the second has almost similar latitude. The spectra of daily and hourly data of the three stations are compared together to define the latitude and longitude-effects on the detected periodicities. Daily periodicities ofK
p-index activities at the values 32.7, 21.2, 12.9, 11.6 and 9.2 days have been obtained to be common in the spectra of the three stations. The existence of 5-days periodicity in these stations has also been detected. 相似文献