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   1609篇
  免费   35篇
  国内免费   4篇
测绘学   53篇
大气科学   37篇
地球物理   718篇
地质学   372篇
海洋学   17篇
天文学   363篇
综合类   3篇
自然地理   85篇
  2020年   16篇
  2019年   17篇
  2018年   37篇
  2017年   33篇
  2016年   56篇
  2015年   38篇
  2014年   37篇
  2013年   58篇
  2012年   59篇
  2011年   51篇
  2010年   54篇
  2009年   47篇
  2008年   43篇
  2007年   58篇
  2006年   40篇
  2005年   35篇
  2004年   39篇
  2003年   41篇
  2002年   38篇
  2001年   27篇
  2000年   29篇
  1999年   20篇
  1998年   17篇
  1997年   19篇
  1996年   23篇
  1995年   20篇
  1994年   22篇
  1993年   23篇
  1992年   18篇
  1989年   22篇
  1988年   19篇
  1987年   24篇
  1986年   27篇
  1985年   25篇
  1984年   28篇
  1983年   29篇
  1982年   28篇
  1981年   26篇
  1980年   26篇
  1979年   26篇
  1978年   29篇
  1977年   21篇
  1976年   19篇
  1975年   24篇
  1973年   20篇
  1972年   21篇
  1971年   36篇
  1970年   16篇
  1969年   16篇
  1968年   20篇
排序方式: 共有1648条查询结果,搜索用时 31 毫秒
121.
Zusammenfassung Es wird eine Methode für experimentelle Untersuchung der Frequenzkennlinien von Induktionsvariometern mit Aufnahmeschleifen nichttraditioneller Ausmasse beschrieben. Die Grundlage des beschriebenen Verfahrens bildet eine genaue Bestimmung jenes Teils des magnetischen Kraftflusses, der durch die Aufnahmeschleife durchgeht.  相似文献   
122.
123.
Zusammenfassung Bei dem Versuch, die Kristallstruktur von Bonchevit zu bestimmen, stellte sich heraus, daß dieses Mineral—bis dahin PbBi4S7—aus zwei Phasen besteht. Der Hauptanteil wurde eindeutig als Galenobismutit identifiziert. Der Rest wies nach den Gitterkonstanten (a0=13,58±0,02 Å, b0=20,51±0,07 Å, c0=4,09±0,07 Å) auf ein bisher unbekanntes Mineral hin. Die Raumgruppe ist Bbmm. Ein indiziertes Pulverdiagramm und die dazugehörigen d-Werte werden angegeben.Die Emissionsspektralanalyse zeigt Pb und Bi als Hauptkomponenten, Cu und Ag als Nebenkomponenten und Spuren von Zn und Sn. Die Strukturanalyse führte zu der Formel Me5S6, wobei die Me-Atome etwa gleich schwer sind, so daß als chemischo Formel nur Pb3Bi2S6 mit Z=4 in Frage kommt.Strukturell gehört das Mineral in die Gruppe Andorit-Ramdohrit-Fizelyit. Die Verwandtschaft bzw. Identität des Minerals mit anderen Mineralen und synthetischen Verbindungen wird diskutiert.
Mineralogical data on a sulphosalt from the Rhodope mountains, Bulgaria
Summary During an attempt to determine the crystal structure of bonchevite, this mineral was found to consist of two phases. Previously it was thought to have the composition PbBi4S7. The main constituent could unambiguously be identified as galenobismutite. For the rest the lattice constants (a0=13.58±0,02 Å, b0=20.51±0,07 Å, c0=4.09±0.07 Å), indicated a new mineral. Space group is Bbmm. An indexed powder diagram (with d-values) is given.The emission spectrographic analysis shows Pb and Bi to be main components, Cu and Ag to be minor components, and traces only of Zn and Sn. The structure analysis has led to the formula Me5S6, with Me-atoms of approximately the same atomic number; therefore, the chemical formula has to be Pb3Bi2S6, with Z=4.In a structural classification the mineral belongs to the andoriteramdohrite-fizelyite-group. The relationships to or the identity with other minerals and synthetic compounds are discussed.
  相似文献   
124.
Summary It has been shown that it is necessary to combine several methods to be able to describe and explain recent movements of the Earth's crust.Presented at the XVth General Assembly of the IUGG, Moscow 1971.  相似文献   
125.
Summary According to the results of the adjustments of eight trigonometric and three-dimensional networks, the a priori variance m2() of the measured vertical angle is expressed by the formula: m2() = m2(a) + [C 1/2 m(k)]2, where m(a) represents accidental observation errors; the constant C is estimated in the interval 0.5–1.5 according to the number of repreated observations and the variation of their changes with time; is the angle between the normals to the ellipsoid at the initial and final point of the line of sight, and m(k) is the mean square error of the coefficient of refraction which can be estimated for a given network from Tab. 1.Dedicated to 90th Birthday of Professor Frantiek Fiala  相似文献   
126.
Summary The paper deals with the results of DSS measurements along international profile VII, carried out by Czechoslovak and Polish geophysicists in 1970 – 71. The profile situation is shown in Fig. 1. By 1971 part of the profile in the region of the Bohemian Massif between points 1 and 3 and in Poland between points 5 and 7 had been surveyed (Fig. 2). The seismograms were used to construct the travel-time curves of the fundamental types of waves PK, PM, Pn (Fig. 4). The mean velocities were computed from the travel-time curves of the reflected waves (PM and PK) and the refracted waves (Pg). Isolines of the mean velocities could be constructed for the region of the Bohemian Massif (Fig. 6). The velocity data found were used for the depth interpretation of the travel-time curves of the principal types of waves and to construct a seismic section (Fig. 8). In the region of the Pre-Sudeten block the thickness of the crust was found to be 34–37 km, and in the Sudeten it increased to 40 km. Towards the south the thickness of the crust gradually reduces to 30 km in the system of the Luice faults. In the Bohemian Cretaceous the thickness of the crust is about 30 km. Further to the south, in the region of the Moldanubicum, the thickness of the Earth's crust increases rapidly, and at the southern border of the Central Bohemian pluton it reaches values of about 42 km.  相似文献   
127.
128.
FárnÍk  F.  Karlický  M.  Švestka  Z. 《Solar physics》1999,187(1):33-44
We study two long transequatorial loops connecting high-latitude regions of the new solar cycle. These loops (with lengths of 47 and 61 heliographic degrees) provide evidence that the upper length limit of 37° found by Chase et al. (1976) from Skylab data was determined simply by the typical distances between northern and southern active regions during the period of Skylab observations. We find strong support for the idea that these long interconnecting loops originate through reconnection of field lines extending from the two active regions towards and beyond the equator, and confirm the earlier finding by Canfield, Pevtsov, and McClymont (1996) that only field lines from active regions with the same chirality reconnect. As we are not aware of any longitudinal (E–W) loops of comparable lengths, we suggest that it is mainly the solar differential rotation which drives the reconnection of latitudinal (N–S) field lines.  相似文献   
129.
Accurate temperature–depth profiles may help to assess the temperature variations associated with the climate changes in the past. Ninety-eight ground surface temperature histories inverted from the temperature–depth borehole logs drilled on the territory of the Czech Republic [Bodri, L., ermák, V., 1995. Climate changes of the last millennium inferred from borehole temperatures: results from the Czech Republic — Part I. Global Planet. Change 11, pp. 111–125; Bodri, L., ermák, V., 1997. Climate changes of the last two millennia inferred from borehole temperatures: results from the Czech Republic — Part II. Global Planet. Change 14, pp. 163–173.] are used to reconstruct the regional patterns of the respective climate change. The climate was mapped for the following periods: 1100–1300 A.D. (Little Climatic Optimum), 1400–1500 A.D., 1600–1700 A.D. (main phase of the Little Ice Age), and for the most recent climate trend after year 1960. Comparison of the obtained maps with the meteorological observations and proxy climatic reconstructions confirmed good applicability of the “geothermal” paleoclimatic reconstructions for the regional studies.  相似文献   
130.
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