全文获取类型
收费全文 | 6935篇 |
免费 | 97篇 |
专业分类
7032篇 |
出版年
2020年 | 111篇 |
2019年 | 149篇 |
2018年 | 165篇 |
2017年 | 184篇 |
2016年 | 226篇 |
2015年 | 160篇 |
2014年 | 154篇 |
2013年 | 1859篇 |
2012年 | 187篇 |
2011年 | 243篇 |
2010年 | 243篇 |
2009年 | 198篇 |
2008年 | 163篇 |
2007年 | 173篇 |
2006年 | 161篇 |
2005年 | 97篇 |
2004年 | 87篇 |
2003年 | 86篇 |
2002年 | 98篇 |
2001年 | 115篇 |
2000年 | 89篇 |
1999年 | 106篇 |
1998年 | 75篇 |
1997年 | 61篇 |
1996年 | 53篇 |
1995年 | 67篇 |
1994年 | 54篇 |
1993年 | 71篇 |
1992年 | 50篇 |
1991年 | 55篇 |
1990年 | 63篇 |
1989年 | 48篇 |
1988年 | 58篇 |
1987年 | 65篇 |
1986年 | 62篇 |
1985年 | 67篇 |
1984年 | 89篇 |
1983年 | 68篇 |
1982年 | 68篇 |
1981年 | 73篇 |
1980年 | 73篇 |
1979年 | 58篇 |
1978年 | 58篇 |
1977年 | 59篇 |
1976年 | 55篇 |
1975年 | 40篇 |
1974年 | 49篇 |
1973年 | 49篇 |
1972年 | 54篇 |
1970年 | 44篇 |
排序方式: 共有7032条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
By 1980, the Brasilian steel industry had grown to be the eighth largest among the market economies. It is a largely state-owned industry, much of the expansion of which has been funded by international capital. The pattern of development has not been externally imposed, however, but rather reflects the changing balance of class forces within Brasil as policies oscillate between nationalist, populist limits on foreign investment and open, pro-development strategies that rely on foreign investment. Both policies develop their own contradictions, that are reflected in frequent military interventions. 相似文献
85.
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
86.
Several samples of geological stones from statuary pedestals found in various archaeological sites in Cyprus have been characterized using non-contact laser infrared photothermal radiometry. Thermal diffusivities and effective optical absorption coefficients were calculated using a one-dimensional thermal-wave model. The mean values and standard deviations were tabulated and comparisons were made with lithographic and petrographic studies of the samples. Good correlations were found, thus demonstrating that laser photothermal archaeometry is a promising methodology for the accurate, potentially non-destructive and convenient characterization of the origins of ancient stones in Cyprus and other geological and archaeological sites. 相似文献
87.
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
88.
89.
The localization or representation of mental abilities in the brain have always been considered as key questions for understanding the organization of the human nervous system. Particularly with the advent of modern electrophysiological and imaging techniques that provide maps of electromagnetic fields and metabolic processes on the living central nervous system, the representation theory is experiencing a scientific renaissance in neurology, but is only one theory, however, in the succession of a long philosophical tradition dealing with the possible identification of mental phenomena and brain processes. This dichotomy was formulated at the latest in the Cartesian dualism of res cogitans and res extensa of the mind-body problem. Nowadays philosophical discussion, on the contrary, is dominated by monistic concepts that attempt to explain the mental realm on an organic foundation in order not to succumb to the problem of a psychophysical dualism. Of these, the identity theory offers a philosophically plausible concept postulating that the identity of brain conditions and mental phenomena is based on organic foundations. In this theory, the efforts of brain research converge on the representations of mental phenomena in the human nervous system. In a comprehensive approach, both concepts could complement each other. 相似文献
90.
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