全文获取类型
收费全文 | 4894篇 |
免费 | 223篇 |
专业分类
5117篇 |
出版年
2023年 | 40篇 |
2020年 | 93篇 |
2019年 | 112篇 |
2018年 | 197篇 |
2017年 | 166篇 |
2016年 | 199篇 |
2015年 | 136篇 |
2014年 | 133篇 |
2013年 | 1413篇 |
2012年 | 159篇 |
2011年 | 180篇 |
2010年 | 167篇 |
2009年 | 138篇 |
2008年 | 111篇 |
2007年 | 116篇 |
2006年 | 106篇 |
2005年 | 69篇 |
2004年 | 53篇 |
2003年 | 57篇 |
2002年 | 61篇 |
2001年 | 74篇 |
2000年 | 62篇 |
1999年 | 75篇 |
1998年 | 51篇 |
1997年 | 41篇 |
1996年 | 33篇 |
1995年 | 50篇 |
1994年 | 32篇 |
1993年 | 42篇 |
1992年 | 29篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 37篇 |
1988年 | 28篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 45篇 |
1984年 | 52篇 |
1983年 | 47篇 |
1982年 | 39篇 |
1981年 | 44篇 |
1980年 | 42篇 |
1979年 | 40篇 |
1978年 | 36篇 |
1977年 | 35篇 |
1975年 | 27篇 |
1974年 | 27篇 |
1973年 | 29篇 |
1972年 | 29篇 |
1970年 | 27篇 |
排序方式: 共有5117条查询结果,搜索用时 0 毫秒
61.
An important line of research concerning historical fertility patterns in currently developed countries of Europe has concluded that, prior to the fertility transition, marital fertility was essentially constant over time, and deliberate fertility control was virtually unknown. It has been argued that variations over time in overall fertility were largely the consequence of variations in nuptiality. Other researchers have challenged these views and present evidence for the existence of a significant minority of fertility controllers in pretransition populations. In this article, we find support for this second view and argue that (1) there was significant, non-random variation in marital fertility over time, prior to the transition; (2) in many cases, this variation in marital fertility was large relative to contemporaneous variations in nuptiality; and (3) in a substantial minority of the cases, the variation over time in pretransition marital fertility was so large that it is suggestive of deliberate fertility control. Thus, our findings question the view of fertility transition as an innovation in deliberate marital fertility control. While most of our evidence is based on data from England and Wales, we find corroboration of our key results in other European data. 相似文献
62.
Blue glass trade beads from well-dated late seventeenth- to early twentieth-century sites and collections have been analysed non-destructively by instrumental neutron activation analysis. The beads display enough variations in their elemental contents to allow us to characterize the different chemistries. The implication of these results is that similar chemical analyses of blue beads from undated archaeological sites may be used to help date the sites, since each bead chemistry has a specific earliest period. 相似文献
63.
D. E. NELSON G. CHALOUPKA C. CHIPPINDALE M. S. ALDERSON J. R. SOUTHON 《Archaeometry》1995,37(1):151-156
Accelerator mass spectrometry radiocarbon ages have been taken for a test suite of small samples of material removed from some of the ‘beeswax’art figures found in rock shelters in northern Australia. The results indicate that we can reliably date this unique form of rock art with no noticeable damage. We had not expected to find figures of any great antiquity, and so we were surprised to find that the ages obtained spanned the time period from the recent past to about 4000 BP. 相似文献
64.
Random Time Sampling is an innovative data collection method which has potential for adaptation and use by geographers. Individual pocket-sized programmable beepers were used in a pilot study of the uses of time by older households and older people's attitudes to different activities. Random beeps were used to prompt individuals living in eleven Melbourne suburbs to record time use data in diaries over a period of a week. The method proved extremely effective and reliable, and many participants reporting that they enjoyed the exercise. 相似文献
65.
66.
“JINNAH: CREATOR OF PAKISTAN.” by Hector Bolitho. John Murray. London, 7954. Pp. x and 244, illus.
“WANTED: AN ASIAN POLICY,” by Edwin O. Reisehauer. New York: Knopf, 7955. Pp. 256. 相似文献
67.
68.
69.
Richard S. Davis 《Journal of Archaeological Research》1998,6(2):169-194
Recent Paleolithic work along the middle Enisei River of central Siberia has revealed a long history of occupation that almost certainly begins in the Middle Pleistocene. Although the evidence for the Lower Paleolithic is somewhat tentative, there is good reason to believe that hunter-gatherers had periodically occupied the middle Enisei before the last interglacial. The steppe environment of the region during the Upper Pleistocene was relatively bountiful; more than 200 Upper Paleolithic sites, both before and after the Last Glacial Maximum, have been located. The region appears to have been abandoned during the Last Glacial Maximum. Most of Soviet and Russian archaeological work has been guided by a cultural–historical orientation, but recently there has been increased interest in developing adaptationist and ecological research strategies. The middle Enisei and the wider central Siberian region are key to understanding early adaptations to the north and the dimensions of Paleolithic population movements. 相似文献
70.
S.L. BRIAN CEH 《The Canadian geographer》1996,40(4):319-337
Inventing is an important prerequisite for industrial economies to remain technologically competitive. Yet it is not well known how inventive companies of domestic or foreign ownership can affect a nation's technological base and, ultimately, its spatial-economic system. The present study examines this relationship in Canada by investigating the performance of its indigenous and foreign-owned inventive companies at the national, subnational, and urban levels. The results indicate that: (1) Canada's indigenous inventive companies are distinct from their foreign-owned counterparts in that they are generally smaller, are more apt to have teams of inventors, are more likely to develop product inventions, have come to manage a greater share of this nation's inventions, and are increasing their role in key Canadian industries; and (2) geographically, Canada's two largest cities and its core region were adversely affected by the declining inventiveness of American-controlled companies during the 1980s. L'esprit ?invention est une nécessité pour que les économies industrielles restent en conditions de concurrence technologique. Cependant, on connaît très peu de la manière que les entreprises inventives de propriété domestique ou étrangère affectent la base technologique ?un pays et, enfin, affectent son système spatio-écono-mique. La présente étude considère ces rapports au Canada au niveau national, sous-national et local, en exminant les performances des entreprises inventives indigènes et étrangères. Les résultats indiquent (1) qu'au Canada les entreprises indigènes et inventives diffèrent de leurs analogues étrangers: en général elles sont plus petites, ont plus tendance à consister en équipes ?inven-teurs, sont plus susceptibles de développer les inventions produites, produisent une plus grande part des inventions canadiennes, et sont en train ?augmenter leur rôle dans les industries canadiennes; et (2) que le déclin de ?esprit ?invention dans les entreprises dirigées par les américains a affecté défavorablement les deux villes les plus grandes au Canada, ainsi que la partie centrale du pays, pendant les années 1980. Mots-clés: invention, Canada, propriétéétrangère, technologie, produit 相似文献