全文获取类型
收费全文 | 4992篇 |
免费 | 186篇 |
国内免费 | 53篇 |
专业分类
测绘学 | 125篇 |
大气科学 | 424篇 |
地球物理 | 1136篇 |
地质学 | 1845篇 |
海洋学 | 357篇 |
天文学 | 876篇 |
综合类 | 17篇 |
自然地理 | 451篇 |
出版年
2022年 | 28篇 |
2021年 | 64篇 |
2020年 | 67篇 |
2019年 | 90篇 |
2018年 | 144篇 |
2017年 | 151篇 |
2016年 | 154篇 |
2015年 | 137篇 |
2014年 | 190篇 |
2013年 | 260篇 |
2012年 | 204篇 |
2011年 | 267篇 |
2010年 | 209篇 |
2009年 | 268篇 |
2008年 | 215篇 |
2007年 | 192篇 |
2006年 | 181篇 |
2005年 | 175篇 |
2004年 | 185篇 |
2003年 | 161篇 |
2002年 | 162篇 |
2001年 | 82篇 |
2000年 | 91篇 |
1999年 | 75篇 |
1998年 | 91篇 |
1997年 | 68篇 |
1996年 | 66篇 |
1995年 | 65篇 |
1994年 | 55篇 |
1993年 | 63篇 |
1992年 | 47篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 50篇 |
1986年 | 47篇 |
1985年 | 58篇 |
1984年 | 72篇 |
1983年 | 54篇 |
1982年 | 58篇 |
1981年 | 50篇 |
1980年 | 50篇 |
1979年 | 49篇 |
1978年 | 47篇 |
1977年 | 40篇 |
1976年 | 35篇 |
1975年 | 34篇 |
1974年 | 36篇 |
1973年 | 35篇 |
排序方式: 共有5231条查询结果,搜索用时 27 毫秒
171.
Thomas Koellner Joachim Sell Manuela Ghwiler Roland W. Scholz 《Global Environmental Change》2008,18(4):746
Global environmental change leads to degradation of tropical forests in many countries. In response to this pressure, programs for payments for ecosystem services (PES) are developing and organizations are emerging which manage forests in order to supply ecosystem services, rather than only harvest timber. Typically such services are carbon sequestration, biodiversity conservation, pollination, and watershed protection. Public or private actors interested to invest in or donate money for the provisioning of such services are faced with the problem of choosing the appropriate organization supplying ecosystem services. The goal of this paper was to develop an assessment framework based on the balanced scorecard concept including drivers, impact, performance and context variables. Results of a survey of international market actors were used to determine assessment criteria and their weights. Putting the focus of this paper on drivers and impacts, we assessed Latin American organizations that “sell” ecosystem services from tropical forests in terms of their general management, marketing, forest management, client and stakeholder satisfaction, and forest ecosystem status. We found that supplying organizations vary widely with respect to their achievements in these areas. However, the variance of assessment results is influenced even more by the variance in weights the international market actors allocate to the assessment criteria. The insights of this study can contribute to the continuous improvement of management processes in supplying organizations and can support investors and donors in their decision-making with respect to organization supplying ecosystem services. 相似文献
172.
Thomas Foken Jan Pretel Reviewer J. Bednář Reviewer Z. Jaňour 《Studia Geophysica et Geodaetica》1988,32(3):318-328
In the present paper the first results of the international KOPEX-86 experiment are presented. The experiment took place at the Kopisty Atmospheric Observatory of the Institute of Physics of the Atmosphere in Prague as part of a special project of the Commission of the Academy of Sciences in Planetary Geophysics (KAPG) in June and July 1986. Using 4 ultrasonic anemometers at 4 levels up to 80 m, Doppler-SODAR and wind-, temperature- and radiation balance gradients from 2 to 80 m, a complex investigation of the atmospheric boundary layer in an industrial area was made. The authors present the first results of
am n mam ¶rt;a¶rt; numa -86. num n¶rt;u mu u u u 1986. a num mu amuu mumma uuu am aa nma . u nu 4 amuu am a 4 ma ¶rt; 80 , ¶rt;nn ¶rt;aa u uua¶rt;um mu ma, mnam u a¶rt;uauu 2 ¶rt; 80 n¶rt;uu n u¶rt;au nau am. m n¶rt;aam n mam, aau
相似文献
| the anthropogenic influence on the energy exchange in the atmospheric boundary layer. |
| the influence of a complex terrain on the turbulent characteristics and their vertical distribution. |
| u¶rt;au amn ¶rt;mu a muu na am, |
| uu n mmu a aamumuu mmmu u a u mua an¶rt;u. |
173.
Gérard Thuillier Michel Hersé Paul C. Simon Dietrich Labs Holger Mandel Didier Gillotay Thomas Foujols 《Solar physics》1998,177(1-2):41-61
The SOLSPEC instrument has been built to carry out solar spectral irradiance measurements from 200 to 3000 nm. It consists of three spectrometers designed to measure the solar spectral irradiance in ultraviolet, visible, and infrared domains. It flew with the ATLAS I mission in March 1992. This paper is dedicated to the visible part of the solar spectrum. Comparisons with recent data are shown and differences below 450 nm are discussed. 相似文献
174.
Comparison of the observed solar far ultraviolet irradiance and the observed solar sector structure during 1969 through 1972 shows a tendency for EUV maxima to be located near sector boundaries. 相似文献
175.
Shanti Priya Devarapalli Rukmini Jagirdar M. Parthasarathy D. K. Sahu Vijay Mohan B. C. Bhatt Vineet S. Thomas 《Astrophysics and Space Science》2018,363(4):69
The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand presence of mass transfer, a disk or circumstellar matter and chromospheric emission. We also present first spectroscopic and period study for few Algols and conclude that high resolution spectra within and outside the primary minimum are needed for better understanding of these Algol type close binaries. 相似文献
176.
Raymond F. Smith K. Thomas Lorenz Darwin Ho Bruce A. Remington Alex Hamza John Rogers Stephen Pollaine Seokwoo Jeon Yun-Suk Nam J. Kilkenny 《Astrophysics and Space Science》2007,307(1-3):269-272
In recently developed laser-driven shockless compression experiments an ablatively driven shock in a primary target is transformed
into a ramp compression wave in a secondary target via unloading followed by stagnation across an intermediate vacuum gap.
Current limitations on the achievable peak longitudinal stresses are limited by the ability of shaping the temporal profile
of the ramp compression pulse. We report on new techniques using graded density reservoirs for shaping the loading profile
and extending these techniques to high peak pressures. 相似文献
177.
Thomas E. Kiess 《Astrophysics and Space Science》2012,339(2):329-338
We derive an exact Maxwell-Einstein metric for a spherically symmetric static perfect fluid with mass and charge (Q), that electrifies the Tolman-VII metric and meets applicable physical boundary conditions. We show that there is more than one way to electrify any Q=0 metric, depending on whether metric component g tt , g rr , or neither, is independent of Q. We illustrate an approach not yet in the literature in which g rr is independent of Q. When applied to a baryonic stellar model, this metric is versatile, capable of producing a range of values for radius, mass, Q, and far-field mass due to the presence of charge. 相似文献
178.
The present paper deals with the inhibition of the specific activity of the acid and alkaline phosphatases in the kidney tissue of mudskipper Boleophthalmus dentatus, exposed to different sublethal concentrations of mercuric chloride. There was a more or less linear inhibition of the specific activity of both the enzymes with increasing concentration of mercuric chloride as well as exposure time. The inhibition of acid phosphatase could be due to the rupture of lysosomal membrane in the presence of mercury compound, which acts as a labilizing agent. The inhibition of alkaline phosphatase probably caused a breakdown of the membrane transport system. 相似文献
179.
Serge H. Zbaz Togouet Thomas Njine Norbert Kemka Moise Nola Samuel Foto Menbohan Walter Koste Claude Boutin Rick Hochberg 《Limnologica》2007,37(4):311-322
Studies on the biodiversity and population dynamics of freshwater planktonic Gastrotricha have been carried out in conjunction with a physical–chemical analysis of the water in the Yaounde Municipal Lake (Cameroon, Central Africa) over a 14 months period (November 1996–December 1997). The results obtained allow to consider the Yaounde Municipal Lake as an eutrophic lake. It harbours eight species of Gastrotricha belonging to four genera (Chaetonotus, Dasydytes, Neogossea and Polymerurus) of the order Chaetonotida. This community was characterized by high abundances of populations, and was dominated by the genus Neogossea and Chaetonotusreaching up to 2000 ind. L−1. Polymerurus was mostly abundant at the almost anoxic bottom layers. The highest abundances were found mostly during the rainy season, when there is an important sedimentation process of organic matter, and were influenced by several different environmental factors such as dissolved oxygen, temperature and pH of the water.
Finally this community which may play an important role in the water bodies, is a potential water quality indicator. 相似文献
180.