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   85590篇
  免费   1459篇
  国内免费   1181篇
测绘学   2288篇
大气科学   5928篇
地球物理   16471篇
地质学   34112篇
海洋学   7113篇
天文学   17969篇
综合类   468篇
自然地理   3881篇
  2022年   702篇
  2021年   1089篇
  2020年   1112篇
  2019年   1199篇
  2018年   4395篇
  2017年   3996篇
  2016年   3622篇
  2015年   1428篇
  2014年   2398篇
  2013年   3751篇
  2012年   3372篇
  2011年   5194篇
  2010年   4597篇
  2009年   5342篇
  2008年   4484篇
  2007年   5051篇
  2006年   3249篇
  2005年   2252篇
  2004年   2088篇
  2003年   2049篇
  2002年   1898篇
  2001年   1592篇
  2000年   1445篇
  1999年   1079篇
  1998年   1129篇
  1997年   1138篇
  1996年   907篇
  1995年   913篇
  1994年   838篇
  1993年   700篇
  1992年   686篇
  1991年   655篇
  1990年   764篇
  1989年   649篇
  1988年   602篇
  1987年   693篇
  1986年   535篇
  1985年   724篇
  1984年   830篇
  1983年   754篇
  1982年   723篇
  1981年   666篇
  1980年   682篇
  1979年   547篇
  1978年   612篇
  1977年   546篇
  1976年   496篇
  1975年   494篇
  1974年   503篇
  1973年   561篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing.  相似文献   
52.
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
53.
Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990.  相似文献   
54.
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements of selected lines in the spectra  相似文献   
55.
Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents.  相似文献   
56.
57.
In this paper we analyse error-removing techniques used without sufficient theoretical support in a previous paper, where Chandrasekhar's higher-order perturbation theories were developed for either uniformly or differentially-rotating polytropic stars.  相似文献   
58.
Solutions of field equations of the generalized theory of gravitation for neutral and charged point masses are found. The problem is formulated so that the solution may be expressed in harmonic, isotropic, Schwarzschild and, if necessary, any other coordinates. A method for the solution of the static axisymmetric problem (an analogue of a well-known Weyl's solution) is also proposed.  相似文献   
59.
60.
Laser-induced plasmas in various gas mixtures were used to simulate lightning in other planetary atmospheres. This method of simulation has the advantage of producing short-duration, high-temperature plasmas free from electrode contamination. The laser-induced plasma discharges in air are shown to accurately simulate terrestrial lightning and can be expected to simulate lightning spectra in other planetary atmospheres. Spectra from 240 to 880 nm are presented for simulated lightning in the atmospheres of Venus, Earth, Jupiter, and Titan. The spectra of lightning on the other giant planets are expected to be similar to that of Jupiter because the atmospheres of these planets are composed mainly of hydrogen and helium. The spectra of Venus and Titan show substantial amounts of radiation due to the presence of carbon atoms and ions and show CN Violet radiation. Although small amounts of CH4 and NH3 are present in the Jovian atmosphere, only emission from hydrogen and helium is observed. Most differences in the spectra can be understood in terms of the elemental ratios of the gas mixtures. Consequently, observations of the spectra of lightning on other planets should provide in situ estimates of the atmospheric and aerosol composition in the cloud layers in which lightning is occuring. In particular, the detection of inert gases such as helium should be possible and the relative abundance of these gases compared to major constituents might be determined.  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