全文获取类型
收费全文 | 42203篇 |
免费 | 824篇 |
国内免费 | 677篇 |
专业分类
测绘学 | 1065篇 |
大气科学 | 2410篇 |
地球物理 | 8358篇 |
地质学 | 16619篇 |
海洋学 | 4155篇 |
天文学 | 9213篇 |
综合类 | 269篇 |
自然地理 | 1615篇 |
出版年
2022年 | 595篇 |
2021年 | 889篇 |
2020年 | 910篇 |
2019年 | 1006篇 |
2018年 | 2116篇 |
2017年 | 1880篇 |
2016年 | 1920篇 |
2015年 | 855篇 |
2014年 | 1709篇 |
2013年 | 2386篇 |
2012年 | 1912篇 |
2011年 | 2435篇 |
2010年 | 2116篇 |
2009年 | 2351篇 |
2008年 | 2072篇 |
2007年 | 2216篇 |
2006年 | 1980篇 |
2005年 | 1099篇 |
2004年 | 981篇 |
2003年 | 963篇 |
2002年 | 847篇 |
2001年 | 847篇 |
2000年 | 707篇 |
1999年 | 467篇 |
1998年 | 486篇 |
1997年 | 513篇 |
1996年 | 381篇 |
1995年 | 374篇 |
1994年 | 347篇 |
1993年 | 293篇 |
1992年 | 297篇 |
1991年 | 312篇 |
1990年 | 340篇 |
1989年 | 267篇 |
1988年 | 262篇 |
1987年 | 265篇 |
1986年 | 201篇 |
1985年 | 309篇 |
1984年 | 305篇 |
1983年 | 307篇 |
1982年 | 276篇 |
1981年 | 258篇 |
1980年 | 274篇 |
1979年 | 205篇 |
1978年 | 246篇 |
1977年 | 208篇 |
1976年 | 181篇 |
1975年 | 189篇 |
1974年 | 179篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
31.
针对自然资源全要素调查工作中分类标准不同、调查口径不同、调查方法不同,造成的各部门调查软件平台重复开发建设和调查数据结果地理信息特征表达不清晰等问题,本文结合自然资源全要素野外调查工作的实际需要,以山水林田湖草生命共同体为统一对象,构建了自然资源语义化特征模型,提出了表征不同自然资源类型的自适应野外调查方法,实现了灵活性高、性能优异的自然资源调查技术平台,形成了统一的自然资源全要素野外调查框架,可以有效提升多门类自然资源基础调查、专业调查、动态调查的能力与水平,为自然资源治理能力现代化提供了可靠技术保障。 相似文献
32.
Izvestiya, Atmospheric and Oceanic Physics - The problem of atmospheric correction for shortwave channels of a multispectral low-resolution scanning radiometer onboard the Meteor-M No. 2 satellite... 相似文献
33.
为探究岩溶水库水文地球化学行为过程,对贵州普定夜郎湖表层水体进行了为期3 d的高分辨率昼夜监测。结果表明:1)多变的天气和水文条件叠加导致水体离子指标昼夜变化不显著,规律性较差。而水温、DO、pH值、SpC、SIc、pCO2等常规理化指标受水温变化和生物作用表现出明显的昼夜波动。2)利用亨利常数和主成分分析,得到温度变化、生物作用、人类活动、水库的蓄水与放水对夜郎湖水库水文地球化学特征变化的贡献率分别为21.66%、17.28%、14.08%和10.22%,说明作用于水库水文地球化学行为的因子具有多元性。3)δ 18O表现出与DO一致的波动趋势,即白天上升,晚上下降,反映在短时间尺度上,氢氧稳定同位素变化受控于生物过程(主要是呼吸作用过程);而对比水库水体和大气降水的d-excess(d值)发现,水库水体的d值(8.21‰)显著偏低于当地大气降水的d值(9.64‰),说明在长时间尺度上,主要受蒸发效应引起的不平衡分馏影响。 相似文献
34.
We present our observations of the galaxy UGS 5600 with a long-slit spectrograph (UAGS) and a multipupil field spectrograph (MPFS) attached to the 6-m Special Astrophysical Observatory telescope. Radial-velocity fields of the stellar and gaseous components were constructed for the central region and inner ring of the galaxy. We proved the existence of two nearly orthogonal kinematic subsystems and conclude that UGC 5600 is a galaxy with an inner polar ring. In the circumnuclear region, we detected noncircular stellar motions and suspected the existence of a minibar. The emission lines are shown to originate in H II regions. We estimated the metallicity from the intensity ratio of the [N II]λ6583 and Hα lines to be nearly solar, which rules out the possibility that the polar ring was produced by the accretion of gas from a dwarf companion. 相似文献
35.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
36.
37.
In the atmospheric Čerenkov technique γ-rays are detected against the abundant background produced by hadronic showers. In
order to improve the signal to noise ratio of theexperiment, it is necessary to reject a significant fraction of hadronic
showers. Traditional background rejection methods based on image shape parameters have been extensively used for the data
from imaging telescopes. However, non-imaging Čerenkov telescopes have to develop very different means of statistically identifying
and removing cosmic ray events. Some of the parameters, which could be potentially important for non-imaging arrays, are the
temporal and spectral differences, the lateral distributions and density fluctuations of Čerenkov photons generated by γ-ray
and hadron primaries. Here we study the differences in fluctuations of Čerenkov photon density in the light pool at the observation
level from showers initiated by photons and those initiated by protons or heavier nuclei. The database of simulated events
for the PACT array has been used to evaluate the efficiency of the new technique. Various types of density fluctuations like
the short range and medium range fluctuations as well as flatness parameter are studied. The estimated quality factors reflect
the efficiencies with which the hadrons can be rejected from the data. Since some of these parameters are independent, the
cuts may be applied in tandem and we demonstrate that the proton rejection efficiency of ∼90% can be achieved. Use of density
fluctuations is particularly suited for wavefront sampling observations and it seems to be a good technique to improve the
signal to noise ratio.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
38.
39.
40.
V. Delouille J. De Patoul J. F. Hochedez L. Jacques J. P. Antoine 《Solar physics》2005,228(1-2):301-321
The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in
temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution
during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum.
We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules
as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with
the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona
at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we
introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis. 相似文献