全文获取类型
收费全文 | 4367篇 |
免费 | 152篇 |
专业分类
4519篇 |
出版年
2020年 | 64篇 |
2019年 | 74篇 |
2018年 | 108篇 |
2017年 | 113篇 |
2016年 | 143篇 |
2015年 | 104篇 |
2014年 | 98篇 |
2013年 | 1161篇 |
2012年 | 120篇 |
2011年 | 144篇 |
2010年 | 131篇 |
2009年 | 101篇 |
2008年 | 118篇 |
2007年 | 93篇 |
2006年 | 74篇 |
2005年 | 92篇 |
2004年 | 75篇 |
2003年 | 39篇 |
2002年 | 51篇 |
2001年 | 70篇 |
2000年 | 54篇 |
1999年 | 65篇 |
1998年 | 44篇 |
1997年 | 48篇 |
1996年 | 41篇 |
1995年 | 32篇 |
1994年 | 41篇 |
1993年 | 45篇 |
1992年 | 44篇 |
1991年 | 36篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 36篇 |
1987年 | 48篇 |
1986年 | 33篇 |
1985年 | 51篇 |
1984年 | 38篇 |
1983年 | 66篇 |
1982年 | 48篇 |
1981年 | 56篇 |
1980年 | 55篇 |
1979年 | 39篇 |
1978年 | 40篇 |
1977年 | 59篇 |
1976年 | 42篇 |
1975年 | 45篇 |
1974年 | 32篇 |
1973年 | 31篇 |
1972年 | 30篇 |
1971年 | 35篇 |
排序方式: 共有4519条查询结果,搜索用时 0 毫秒
21.
AAS, FE and OES are each used in the analysis of thirteen samples of fragments of window glasses from three Catalan Gothic churches: Sta. Maria del Mar (Barcelona, Spain), Pedralbes Monastery (Barcelona, Spain) and Girona Cathedral (Spain). Two kinds of stained window glass are found. Special attention is paid to Co/Cu, Co/Ni and Cu/Ni ratios for blue glasses and Mn/Cu and Fe/Cu ratios for red glasses. 相似文献
22.
23.
Nearshore water circulation and bar patterns at Coledale, New South Wales, were surveyed daily over thirty-six consecutive days, from 3 November to 8 December 1978, to identify sequences of changes that might occur in response to spring-to-spring tide cycles of fourteen days, changing barometric and wind conditions associated with the passage of anticyclonic weather systems across the coast, and day to day variation in the nearshore wave regime. During the survey the bar patterns tended to vary from transverse bars, through a composite arrangement incorporating longshore and transverse bars, to a longshore bar pattern as the tide changed from its spring to neap tide phase. However, this sequence was too brief to unequivocally establish variations in nearshore bar pattern that might be attributed to the fourteen day, spring-to-spring tide cycle. Nevertheless, morphologic changes occurring in response to wave regime fluctuation at Coledale were broadly in accord with studies from elsewhere by Dolan et al. (1979, 1982), and Clarke and Eliot (1982, 1983) in that bars and rips were systematically distributed along the beach. At Coledale, bars tended to relocate approximately 0.4 and 0.75 of the distance along the beach from its southern end. The preferred bar spacing closely matches hypothetical standing waves trapped between the headlands of the Coledale embayment. Temporally, the nearshore morphology is highly responsive to wave regime changes such that, as primary breaker heights decrease and remain below Hmax=1.0m, the bar pattern changes from longshore through mixed to transverse bar patterns within three to five days. On one occasion the bar pattern switched from a longshore to a transverse bar pattern within twenty-four hours. 相似文献
24.
Using data describing the historical distribution of county seats in the United States, we (1) replicate the traditional ratio-variable test of the size-density law, (2) test a new multivariate, nonratio form of the law, and (3) introduce an alternative method of testing, one which avoids three possible problems in traditional analyses: ratio-variables, multicollinearity, and logarithmic transformation. 相似文献
25.
26.
ABSTRACT This paper develops a model of regional financial markets which can encompass different degrees of spatial financial integration. The behavior of the system is analyzed under alternative assumptions about the time frame of analysis and the extent of the flexibility of interest rates. It is argued that links may exist between regional real and financial sectors even in the short run and that such links must, through the regional balance of payments, exist in the long run, even where there is perfect financial spatial integration. It is observed that these relationships have generally been ignored by regional economic model builders. 相似文献
27.
The history of Alzheimer's disease: three debates 总被引:2,自引:0,他引:2
T G Beach 《Journal of the history of medicine and allied sciences》1987,42(3):327-349
28.
29.
THE PALEOLITHIC CAVE ART OF VASCO-CANTABRIAN SPAIN 总被引:1,自引:0,他引:1
LAWRENCE G. STRAUS 《Oxford Journal of Archaeology》1987,6(2):149-163
Summary. This article explores the relationship between cave art and Upper Paleolithic archeology in northern Spain (and extreme southwestern France). Among the 83 known art sanctuaries, only three can probably be terminus ante quem dated to the early Upper Paleolithic (c. 35,000-20,000 BP). Other types of evidence (virtual absence of ornaments and mobile art objects before the Solutrean, stylistic similarities between works of late Upper Paleolithic mobile art and parietal art, overwhelming association of Solutrean and/or Magdalenian cultural deposits with art sanctuaries) clearly suggest that most of the cave art was done in the period between c. 20,000-10,000 BP. Cave art sanctuaries are distributed in non-random fashion. The clusters of sanctuaries usually correspond with dense clusters of habitation sites. The clusters are separated by substantial geographical gaps. These chronological and geographical facts coincide with contemporaneous subsistence intensification, all of which tends to support the hypothesis of increased territorialism in the late Last Glacial. 相似文献
30.