全文获取类型
收费全文 | 60340篇 |
免费 | 361篇 |
国内免费 | 338篇 |
专业分类
测绘学 | 1556篇 |
大气科学 | 3532篇 |
地球物理 | 10800篇 |
地质学 | 25160篇 |
海洋学 | 4997篇 |
天文学 | 12721篇 |
综合类 | 286篇 |
自然地理 | 1987篇 |
出版年
2022年 | 531篇 |
2021年 | 791篇 |
2020年 | 827篇 |
2019年 | 915篇 |
2018年 | 4064篇 |
2017年 | 3606篇 |
2016年 | 3014篇 |
2015年 | 847篇 |
2014年 | 1678篇 |
2013年 | 2438篇 |
2012年 | 2576篇 |
2011年 | 4140篇 |
2010年 | 3667篇 |
2009年 | 4120篇 |
2008年 | 3461篇 |
2007年 | 4083篇 |
2006年 | 2049篇 |
2005年 | 1382篇 |
2004年 | 1319篇 |
2003年 | 1342篇 |
2002年 | 1194篇 |
2001年 | 965篇 |
2000年 | 869篇 |
1999年 | 562篇 |
1998年 | 595篇 |
1997年 | 619篇 |
1996年 | 438篇 |
1995年 | 468篇 |
1994年 | 436篇 |
1993年 | 366篇 |
1992年 | 342篇 |
1991年 | 368篇 |
1990年 | 415篇 |
1989年 | 335篇 |
1988年 | 323篇 |
1987年 | 352篇 |
1986年 | 266篇 |
1985年 | 395篇 |
1984年 | 389篇 |
1983年 | 391篇 |
1982年 | 354篇 |
1981年 | 339篇 |
1980年 | 368篇 |
1979年 | 283篇 |
1978年 | 314篇 |
1977年 | 270篇 |
1976年 | 231篇 |
1975年 | 242篇 |
1974年 | 233篇 |
1973年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
This paper is devoted to Force-Free Electromagnetic Oscillations in a constant magnetic field. A correction is made in the derivation of the basic equation. The paper confirms the predicted spectrum of frequencies, namely
n
=
o
(n + 1)1/2;n = 0, 1, 2, .... In addition it is suggested that hybrid frequency
n
= (
n
2
+
H
2
)1/2 should be found in observational data. 相似文献
72.
The abundances of light elements (deuterium, helium and lithium) are calculated in unconventional cosmologies in which these elements are produced by interaction of fast -particles ejected by massive pregalactic stars with a purely hydrogenous cosmological substrate. The number density and energetics of such stars needed for suitable production of light elements are estimated. It is shown that the models always lead to overproduction of lithium. The intensity of ultraviolet, X-ray, and -ray emission caused by explosions of pregalactic massive stars is calculated. The distortions of cosmic background radiation by Compton losses of electrons heated by explosive stars are also calculated. 相似文献
73.
A simple self-consistent model of a high-temperature turbulent current sheet (HTCS) is considered. The anomalous character of plasma conductivity in a sheet is assumed to be due to gradient instabilities. The possibility of a low threshold of their excitation is demonstrated by an example of temperature-drift instability.Application of the HTCS model to the hot or main phase of a solar flare is discussed. The model consistently explains many observed properties of this phase. 相似文献
74.
The Culgoora radioheliograph has been modified for observing at 327.4 MHz, which is in addition to the three frequencies (43.25, 80, and 160 MHz) previously available. At the new frequency the array beamwidth is 56, which represents the highest resolution yet available for metre-wavelength solar mapping.At 327.4 MHz the sources of radio emission are mainly in the lowest layers of the corona. Some preliminary four-frequency observations have been made of type I storms. It is found that the source size generally decreases with increasing observing frequency. This result confirms earlier suggestions that the sources of both type I and type III emission are contained in structures whose boundaries diverge outwards in the corona. 相似文献
75.
V. N. Korzhnev 《Lithology and Mineral Resources》2008,43(6):596-602
In the Ordovician time, the transform margin of the Gornyi Altai region consisted of two bathymetric stages: (1) shelf and upper parts of continental slope; (2) foothills and lower parts of continental slope. The first stage includes the shallow-water facies complexes (terrigenous and terrigenous-carbonate schlieren and variegated flyschoid), while the second stage is composed of deep-water (black shale terrigenous) and subflysch gray (carbonate terrigenous) complexes. Model series of the facies complexes established in our work should be taken into account during the geodynamic analysis of fold zones. 相似文献
76.
77.
78.
The summer monsoon season of the year 2006 was highlighted by an unprecedented number of monsoon lows over the central and
the western parts of India, particularly giving widespread rainfall over Gujarat and Rajasthan. Ahmedabad had received 540.2mm
of rainfall in the month of August 2006 against the climatological mean of 219.8mm. The two spells of very heavy rainfall
of 108.4mm and 97.7mm were recorded on 8 and 12 August 2006 respectively. Due to meteorological complexities involved in replicating
the rainfall occurrences over a region, the Weather Research and Forecast (WRF-ARW version) modeling system with two different
cumulus schemes in a nested configuration is chosen for simulating these events. The spatial distributions of large-scale
circulation and moisture fields have been simulated reasonably well in this model, though there are some spatial biases in
the simulated rainfall pattern. The rainfall amount over Ahmedabad has been underestimated by both the cumulus parameterization
schemes. The quantitative validation of the simulated rainfall is done by calculating the categorical skill scores like frequency
bias, threat scores (TS) and equitable threat scores (ETS). In this case the KF scheme has outperformed the GD scheme for
the low precipitation threshold. 相似文献
79.
Doline probability map using logistic regression and GIS technology in the central Ebro Basin (Spain) 总被引:3,自引:0,他引:3
In the surroundings of Zaragoza, karstification processes are especially intense in covered karst areas where fluvial terraces
lie directly on Tertiary evaporites. Since the beginning of Quaternary, these processes have lead to the development of collapse
and subsidence dolines with a wide range of sizes, which have significant economic impacts. To reduce economic impact and
increase safety, a regional analysis of this phenomenon is needed for spatial management. Therefore, a probability map of
dolines was developed using logistic regression and geographic information system (GIS) techniques. This paper covers the
selection of input data, manipulation of data using the GIS technology, and the use of logistic regression to generate a doline
probability map. The primary variable in the doline development in this area is geomorphology, represented by the location
of endorheic areas and different terrace levels. Secondary variables are the presence of irrigation and the water table gradient. 相似文献
80.