首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   139260篇
  免费   2137篇
  国内免费   1884篇
测绘学   4078篇
大气科学   9814篇
地球物理   26935篇
地质学   52033篇
海洋学   11686篇
天文学   28664篇
综合类   2456篇
自然地理   7615篇
  2022年   770篇
  2021年   1303篇
  2020年   1401篇
  2019年   1570篇
  2018年   7542篇
  2017年   6631篇
  2016年   6040篇
  2015年   2169篇
  2014年   3684篇
  2013年   6219篇
  2012年   4664篇
  2011年   7319篇
  2010年   6281篇
  2009年   7758篇
  2008年   6721篇
  2007年   7183篇
  2006年   4800篇
  2005年   3670篇
  2004年   3845篇
  2003年   3660篇
  2002年   3428篇
  2001年   2831篇
  2000年   2736篇
  1999年   2186篇
  1998年   2275篇
  1997年   2060篇
  1996年   1819篇
  1995年   1782篇
  1994年   1532篇
  1993年   1421篇
  1992年   1364篇
  1991年   1395篇
  1990年   1386篇
  1989年   1173篇
  1988年   1123篇
  1987年   1273篇
  1986年   1152篇
  1985年   1409篇
  1984年   1584篇
  1983年   1470篇
  1982年   1377篇
  1981年   1288篇
  1980年   1181篇
  1979年   1133篇
  1978年   1079篇
  1977年   915篇
  1976年   898篇
  1975年   882篇
  1974年   844篇
  1973年   913篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
In this paper, the problem of the motion of n gyrostats in a central field, with relative momenta k r (k=1, 2, ..., n) functions of the time, is considered.In these conditions, the existence of the linear and angular momentum integrals is established.Moreover, a sufficient condition for the existence of the Jacobi's Integral is given. This study generalizes the results given by Duboshin for n rigid bodies.  相似文献   
842.
This paper reviews labor planning and population policies in Noril'sk, a mining and metallurgical settlement in northern Siberia. When the settlement was established in 1935, planners were lacking in ideas about how to recruit workers to staff the mines and smelters and how to retain the labor force once it was in place. From 1935-79, planners followed a forced labor policy dependent upon the labor of prisoners. However, this solution was not adequate for meeting the manpower needs of an economy undergoing rapid technological sophistication. Northern wage increments were introduced after 1945 to recruit skilled workers from other regions. These increments built up over a 4-year period to a maximum of 80% of base pay. A special cost of living bonus was also awarded. Although these inducements facilitated labor recruitment, labor retention remained a major problem. Surveys indicated that workers would prefer improvements in housing and social services to further wage increases. Thus, policy was directed at the housing shortages, poor medical care, and inadequate child care facilities in Noril'sk. Such improvements facilitated labor retention but also contributed to overpopulation. The population doubled between 1956-80, exceeding 180,000 in the latter year. In the early 1980s, selective measures toward population control were implemented to ensure maintenance of living standards (e.g., encouragement of older workers to leave the area upon retirement, more careful screening of recruits). The goal is to stabilize city size at around 250,000. The Noril'sk case illustrates that quality of life investments can alleviate labor retention problems even in the harshest physical environments. Recent policies have advocated productivity-enriching technologies that do not require increments in the labor force.  相似文献   
843.
"The paper reports the use of Australian Resources Information System to calculate two proximate populations (people living within (i) 150 and (ii) 500 km) for the centroids of each of 3,000 half by half degree geodetic grid cells covering Australia. The use of proximate population data is exemplified by computing a map of the eighteen regions collectively containing a maximum fraction of the Australian population." The data used are from the 1981 census.  相似文献   
844.
The continuum energy distribution of the emission line star X Per (O9.5III-V) has been obtained in the wavelength range 340–710 nm and has been compared with the energy distribution of Cam in the same wavelength range. The continuum of the star is found to be modified by the circumstellar envelope. A number density of the order of 1011 in the envelope has been obtained from the observations of H in emission.  相似文献   
845.
We respond to comments made in a recent letter by Karimet al. (1984), and show that the examples of interstellar absorption at2800 Å that they have presented so far can all be attributed to overexposure of the IUE detectors.  相似文献   
846.
The size distribution of dark clouds and of H II regions were used to derive a distance of 440±22 kpc for M31. Some galactic H II regions and dark clouds were combined with the same ingredients in M31 to study the mass spectrum of both phenomena. A gas to dust ratio of 10001 has been derived for M31. Radii of the classical H II regions as derived in this work using distance of 440 kpc agrees with the galactic classical H II region radii.  相似文献   
847.
Hugh S. Hudson 《Solar physics》1985,100(1-2):515-535
Solar flares emit line and continuum -radiation as well as neutrons and charged particles. These high-energy emissions require the presence of energetic ions within the magnetic structures of the flare proper. We have already learned a great deal about the location and mode of particle acceleration. The observations have now become extensive enough so that we can begin to study the dynamics of the energetic ions within the flare structures themselves. This paper reviews the -ray and neutron observations and the theory of their emission, and discusses on this basis the presence of energetic ions deep within the flaring atmosphere.  相似文献   
848.
S. N. Osipov 《Solar physics》1985,102(1-2):29-32
The blanketing effect for the solar disc center and its value near the limb (cos = 0.23) are obtained for the rocket ultraviolet region using the Harvard center and limb spectra. The value of for the disc center appears to be 0.67 (on average) relative to the quasicontinuum. The essential decrease of towards the limb is also revealed.  相似文献   
849.
We consider the collision probability for comets with the Sun under the suppositions of different velocity distributions and various initial conditions. We solve the problem applying Laplace's method and using Schiaparelli's hyperboloid of visibility. The probabilities obtained in this manner are given separately for elliptic and hyperbolic orbits.  相似文献   
850.
Elemental abundances of the VH group of cosmic radiation have been measured in the energy interval 250–550 MeV nucl–1 in a balloon exposure at Sioux Falls (South Dakota) of a plastic detector LeXAN stack. The so obtained abundances have been extrapolated to the sources in the frame of the homogeneous model correcting for energy loss. After taking into account solar modulation, the best fit to model values has led to a escape mean free path e = 5E –0.4 g cm–2, whereE is the energy in GeV nucl–1, forE>1 GeV nucl–1, and a constant e = 5 g cm–2 forE1 GeV nucl–1. When turning to the diffusion model, also including an energy loss term, a diffusion coefficientD=3×1028 cm2 s–1 has been estimated.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号