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   1392篇
  免费   70篇
  2023年   8篇
  2020年   12篇
  2019年   22篇
  2018年   34篇
  2017年   28篇
  2016年   41篇
  2015年   32篇
  2014年   30篇
  2013年   446篇
  2012年   60篇
  2011年   55篇
  2010年   52篇
  2009年   56篇
  2008年   26篇
  2007年   47篇
  2006年   55篇
  2005年   19篇
  2004年   23篇
  2003年   22篇
  2002年   20篇
  2001年   24篇
  2000年   18篇
  1999年   11篇
  1998年   15篇
  1997年   8篇
  1996年   12篇
  1995年   15篇
  1994年   13篇
  1993年   12篇
  1992年   9篇
  1989年   12篇
  1988年   9篇
  1987年   8篇
  1986年   8篇
  1985年   9篇
  1984年   9篇
  1983年   13篇
  1982年   8篇
  1981年   8篇
  1980年   14篇
  1979年   12篇
  1978年   9篇
  1977年   7篇
  1976年   7篇
  1974年   12篇
  1972年   6篇
  1971年   8篇
  1968年   10篇
  1967年   6篇
  1966年   7篇
排序方式: 共有1462条查询结果,搜索用时 31 毫秒
81.
Why does a state build institutional capacity in certain sectors rather than others? Despite having gained leverage explaining the emergence of institutions in the developmental states of East Asia, we have comparatively weak accounts for sub‐national variation in institutional strength, a much more common phenomenon. Investigating the surprising achievements of the Philippines’ National Irrigation Administration, this article advances a theory of sectoral success in the face of a generally poor developmental record. The author demonstrates that executives will only construct institutional capacity when facing strong political pressure combined with resource scarcity. Such vulnerability permits politicians to exercise discretion in choosing which policies to pursue, allowing them to avoid upsetting their coalitions. Once a politician achieves some degree of policy success, he or she is then able to avoid engaging in similar reforms in other fields. Thus we see pockets of institutional capacity in states that otherwise struggle with developmental tasks.  相似文献   
82.
The aim of this study was to present classic bone lesions caused by tuberculosis, as seen in a Late Neolithic–Early Copper Age osteoarchaeological sample deriving from the site of Alsónyék‐Bátaszék (the western part of Hungary from the 5th millennium bc ). In one particular case of an adult male skeleton, vertebral bodies' destruction, collapse, ankylosis and marked angulation in the lower thoracic and the upper lumbal region of the vertebral column were observed. The collapse resulted in a severe gibbus formation. The paleopathological analysis was carried out using morphological observation supported by radiological analyses. The results from this study increase our knowledge of the early occurrence of skeletal tuberculosis in past populations. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
83.
84.
A polyphasic tectonic‐fluid system of a fault that involves crystalline and carbonate rocks (Hospital fault, Barcelona Plain) has been inferred from regional to thin section scale observations combined with geochemical analyses. Cathodoluminescence, microprobe analyses and stable isotopy in fracture‐related cements record the circulation of successive alternations of hydrothermal and low‐temperature meteoric fluids linked with three main regional tectonic events. The first event corresponds to the Mesozoic extension, which had two rifting stages, and it is characterized by the independent tectonic activity of two fault segments, namely southern and northern Hospital fault segments. During the Late Permian‐Middle Jurassic rifting, these segments controlled the thickness and distribution of the Triassic sediments. Also, dolomitization was produced in an early stage by Triassic seawater at shallow conditions. During increasing burial, formation of fractures and their dolomite‐related cements took place. Fault activity during the Middle Jurassic–Late Cretaceous rifting was localized in the southern segment, and it was characterized by hydrothermal brines, with temperatures over 180°C, which ascended through this fault segment precipitating quartz, chlorite, and calcite. The second event corresponds to the Paleogene compression (Chattian), which produced exhumation, folding and erosion, favouring the percolation of low‐temperature meteoric fluids which produced the calcitization of the dolostones and of the dolomite cements. The third event is linked with the Neogene extension, where three stages have been identified. During the syn‐rift stage, the southern segment of the Hospital fault grew by tip propagation. In the relay zone, hydrothermal brines with temperature around 140°C upflowed. During the late postrift, the Hospital fault acted as a unique segment and deformation occurred at shallow conditions and under a low‐temperature meteoric regime. Finally, and possibly during the Messinian compression, NW‐SE strike‐slip faults offset the Hospital fault to its current configuration.  相似文献   
85.
Structure‐ and tectonic‐related gas migration into Ordovician sandstone reservoirs and its impact on diagenesis history were reconstructed in two gas fields in the Sbaa Basin, in SW Algeria. This was accomplished by petrographical observations, fluid inclusion microthermometry and stable isotope geochemistry on quartz, dickite and carbonate cements and veins. Two successive phases of quartz cementation (CQ1 and CQ2) occurred in the reservoirs. Two phase aqueous inclusions show an increase in temperatures and salinities from the first CQ1 diagenetic phase toward CQ2 in both fields. Microthermometric data on gas inclusions in quartz veins reveal the presence of an average of 92 ± 5 mole% of CH4 considering a CH4‐CO2 system, which is similar to the present‐day gas composition in the reservoirs. The presence of primary methane inclusions in early quartz overgrowths and in quartz and calcite veins suggests that hydrocarbon migration into the reservoir occurred synchronically with early quartz cementation in the sandstones located near the contact with the Silurian gas source rock at 100–140°C during the Late Carboniferous period and the late Hercynian episode fracturing at temperatures between 117 and 185°C, which increased in the NW‐direction of the basin. During the fracture filling, three main types of fluids were identified with different salinities and formation temperatures. A supplementary phase of higher fluid temperature (up to 226°C) recorded in late quartz, and calcite veins is related to a Jurassic thermal event. The occurrence of dickite cements close to the Silurian base near the main fault areas in both fields is mainly correlated with the sandstones where the early gas was charged. It implies that dickite precipitation is related to acidic influx. Late carbonate cements and veins (calcite – siderite – ankerite and strontianite) occurred at the same depths resulting from the same groundwater precipitation. The absence of methane inclusions in calcite cements result from methane flushing by saline waters.  相似文献   
86.
This paper continues the characterization of the lead isotopic fingerprint of ancient copper mines in the north‐west of Spain. In this work, the lead isotopic compositions found in copper ores from the La Profunda mine are presented. Azurites and malachites sampled from this deposit were subjected to lead isotope analysis by multicollector ICP–MS. The results showed a clear radiogenic lead signature compatible with the presence of uranium‐rich minerals (such as zeunerite) in the same mining complex. Moreover, a rare copper artefact, found in the galleries of the mine during its modern exploitation, was also analysed and showed that local mineral was used for its manufacturing.  相似文献   
87.
Though the evolution of prisons and the prison system in medieval Europe is a well-developed field in the history of law, little attention has been paid to prisons and incarceration on the frontiers of Latin Christendom. The present study makes use of archival and literary sources in order to examine how prisons functioned in Venice's most important colony, the island of Crete. As there has been no previous study of prisons and incarceration in medieval Greece, the article's first aim is to establish some basic facts about the prisons of Crete, such as their locations, their organization and their system of administration. More importantly, however, the study investigates the role that incarceration played in the legal system of the Venetian colony and attempts to set this role within the context of the juridical developments of the Late Middle Ages. Of particular interest is the question of how closely the legal system of the Venetian colony followed the judicial practice of the metropolis and whether it was influenced by the pre-existing legal institutions of Byzantium. Finally, the study also examines how the jurisprudence of the colonial regime dealt with offenders of different ethnic background and legal status.  相似文献   
88.
The approaches of comparative studies and profile measurements, often used in order to detect post‐depositional alterations of ceramics, have been applied simultaneously to two sets of Roman pottery, both of which include altered individuals. As analytical techniques, Neutron Activation Analysis and X‐Ray Diffraction have been used. Both approaches lead to substantially different results. This shows that they detect different levels of alteration and should complement each other rather than being used exclusively. For the special process of a glassy phase decomposition followed by a crystallization of the Na‐zeolite analcime, the results suggest that it changes high‐fired calcareous pottery rapidly, and so fundamentally that the results of various archaeometric techniques can be severely disturbed.  相似文献   
89.
The ability to make rapid measurements on small samples using laser fluorination enhances the potential of oxygen isotopes in the investigation of early inorganic materials and technologies. δ18O and 87Sr/86Sr values are presented for glass from two primary production sites, four secondary production sites and a consumer site in the Near East, dating from Late Antiquity to the medieval period. δ18O is in general slightly less effective than 87Sr/86Sr in discriminating between sources, as the spread of measured values from a single source is somewhat broader relative to the available range. However, while 87Sr/86Sr is derived predominantly from either the lime‐bearing fraction of the glass‐making sand or the plant ash used as a source of alkali, δ18O derives mainly from the silica. Thus the two measurements can provide complementary information. A comparison of δ18O for late Roman – Islamic glasses made on the coast of Syria–Palestine with those of previously analysed glasses from Roman Europe suggests that the European glasses are relatively enriched in 18O. This appears to contradict the view that most Roman glass was made using Levantine sand and possible interpretations are discussed.  相似文献   
90.
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