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   71558篇
  免费   1133篇
  国内免费   663篇
测绘学   1718篇
大气科学   5058篇
地球物理   14286篇
地质学   25373篇
海洋学   6191篇
天文学   16379篇
综合类   210篇
自然地理   4139篇
  2022年   397篇
  2021年   705篇
  2020年   787篇
  2019年   827篇
  2018年   1899篇
  2017年   1763篇
  2016年   2241篇
  2015年   1324篇
  2014年   2189篇
  2013年   3793篇
  2012年   2293篇
  2011年   3136篇
  2010年   2618篇
  2009年   3539篇
  2008年   3271篇
  2007年   3062篇
  2006年   2902篇
  2005年   2367篇
  2004年   2264篇
  2003年   2116篇
  2002年   1942篇
  2001年   1808篇
  2000年   1722篇
  1999年   1381篇
  1998年   1474篇
  1997年   1391篇
  1996年   1105篇
  1995年   1145篇
  1994年   970篇
  1993年   874篇
  1992年   858篇
  1991年   760篇
  1990年   856篇
  1989年   720篇
  1988年   650篇
  1987年   818篇
  1986年   664篇
  1985年   857篇
  1984年   924篇
  1983年   864篇
  1982年   833篇
  1981年   707篇
  1980年   664篇
  1979年   606篇
  1978年   603篇
  1977年   552篇
  1976年   539篇
  1975年   501篇
  1974年   506篇
  1973年   469篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The addition of Fe and Cr to the simple system MgO-SiO2-Al2O3 markedly affects the activities of phases involved in the equilibrium
\textMg\text2 \textSiO\text4 \text + MgAl\text2 \textSiO\text6 \text = MgAl\text2 \textO\text4 \text + Mg\text2 \textSi\text2 \textO\text6 \textOlivine + Opx\textsolid solution \text = Spinel + Opx\textsolid solution \begin{gathered} {\text{Mg}}_{\text{2}} {\text{SiO}}_{\text{4}} {\text{ + MgAl}}_{\text{2}} {\text{SiO}}_{\text{6}} {\text{ = MgAl}}_{\text{2}} {\text{O}}_{\text{4}} {\text{ + Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} \hfill \\ {\text{Olivine + Opx}}_{{\text{solid solution}}} {\text{ = Spinel + Opx}}_{{\text{solid solution}}} \hfill \\ \end{gathered}  相似文献   
132.
133.
134.
135.
The transition 111 ? 110 at 4.829 GHz of formaldehyde (H2CO) was the first one showing the anomalous absorption, i.e., the absorption against the cosmic microwave background. Anomalous absorption is an unusual phenomena. Structure of H2CC is very similar to that of H2CO and H2CS. Both H2CO and H2CS have already been identified in a number of cosmic objects. Though H2CC is not yet identified in the cosmic objects, we propose that H2CC may be identified in cool cosmic objects through its transition 111 ? 110 at 4.85 GHz in anomalous absorption.  相似文献   
136.
Manufactured and tested in his work is a photoelectric device that makes it possible to automatically determine the relative angular position of the beam of a miniature torsion balance, angular readings being discretized with various time step values and stored in a computer. Measurements were taken with this device that captured the occurrence of the partial solar eclipse on September 11, 2007, and confirmed the fact, established previously through visual observation, that the position of torsion balance beams changed at the instant an eclipse took place.  相似文献   
137.
The area of sea subjected to heated effluent discharged from the power station at Piombino is very suitable for the study of problems connected with thermal pollution of the nearshore environment. Construction of the power station is planned to go ahead by successive operational stages, producing correspondingly increased amounts of heat discharged into the marine environment. At present it produces 640 MW and discharges 190 Mcal s?1 into the sea.This paper studies the benthic communities after the power station had been operating for about 1 yr. Comparison of these data with those about subsequent operational stages will presumably allow to establish to what extent the environment can receive, without damage, increasing amounts of heat.  相似文献   
138.
An analysis is made of the results from all repeated gravity measurements of the Fennoscandian land uplift gravity line 63°. The line is, thereby, divided into two separate parts: one part west of the land uplift maximum, and the other part east of the land uplift maximum. A statistically significant change of gravity is found both for the western part and the eastern one. Both parts give a relation between gravity change and land uplift of about ?0.22μgal/mm.  相似文献   
139.
The history of the joint use of maps and air photos/space imagery in geographic problem solving is examined, as are general problems which must be addressed before more complete consolidation of map use and image interpretation methods will be possible. The relatively new field of geoiconics, encompassing image theory, processing, and interpretation, is proposed as a branch of knowledge promoting the integration of cartography and remote sensing rather than a megafield that will ultimately replace them. Translated from: Geografiya i prirodnyye resursy, 1985, No. 4, pp. 11-22.  相似文献   
140.
Evaluation of higher derivatives (gradients) of potential fields plays an important role in geophysical interpretation (qualitative and/or quantitative), as has been demonstrated in many approaches and methods. On the other hand, numerical evaluation of higher derivatives is an unstable process – it has the tendency to enlarge the noise content in the original data (to degrade the signal-to-noise ratio). One way to stabilize higher derivative evaluation is the utilization of the Tikhonov regularization. In the submitted contribution we present the derivation of the regularized derivative filter in the Fourier domain as a minimization task by means of using the classical calculus of variations. A very important part of the presented approach is the selection of the optimum regularization parameter – we are using the analysis of the C-norm function (constructed from the difference between two adjacent solutions, obtained for different values of regularization parameter). We show the influence of regularized derivatives on the properties of the classical 3D Euler deconvolution algorithm and apply it to high-sensitivity magnetometry data obtained from an unexploded ordnance detection survey. The solution obtained with regularized derivatives gives better focused depth-estimates, which are closer to the real position of sources (verified by excavation of unexploded projectiles).  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