全文获取类型
收费全文 | 1623篇 |
免费 | 68篇 |
出版年
2023年 | 8篇 |
2020年 | 15篇 |
2019年 | 27篇 |
2018年 | 33篇 |
2017年 | 34篇 |
2016年 | 48篇 |
2015年 | 31篇 |
2014年 | 40篇 |
2013年 | 519篇 |
2012年 | 66篇 |
2011年 | 59篇 |
2010年 | 56篇 |
2009年 | 61篇 |
2008年 | 33篇 |
2007年 | 52篇 |
2006年 | 57篇 |
2005年 | 24篇 |
2004年 | 30篇 |
2003年 | 24篇 |
2002年 | 21篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 17篇 |
1998年 | 17篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 12篇 |
1972年 | 8篇 |
1971年 | 11篇 |
1968年 | 13篇 |
1967年 | 8篇 |
1966年 | 7篇 |
排序方式: 共有1691条查询结果,搜索用时 15 毫秒
21.
22.
23.
Jase Sitton Christopher Stenzel Briggs Buchanan Metin I. Eren Brett Story 《Archaeometry》2023,65(3):463-479
Many factors governed the penetration efficacy of prehistoric projectile weaponry. Archaeologists broadly focus their efforts on understanding the effect of stone weapon tips because these specimens are often the only part of the weapon system that survives in the archaeological record. The tip cross-sectional area (TCSA) and perimeter (TCSP) of stone weapon tips have been shown to correlate with target penetration depth. Here, using results from both static and dynamic penetration testing, we compare TCSA and TCSP against other tip geometry metrics: lateral surface area (LSA) and volume (V). Our analyses broadly show that using a single-point geometry metric evaluated at multiple locations along the length of the point, or using multiple geometry metrics evaluated at a single location, better predicts required energy than using a single-point geometry metric evaluated at a single location. Our results also show that in the case where a single geometry metric evaluated at multiple locations is used LSA provided the most robust prediction models. Finally, our results show that for the case where all geometry metrics evaluated at a single location are used the location that provides the most robust prediction model is dependent on how far the point penetrated the target. 相似文献
24.
Policies concerning undocumented immigrants are inevitably ambivalent, creating uncertainty and confusion in the implementation process. We identify a clear example of this ambivalence —U.S. law setting standards for determining the credibility of asylum seekers—that resulted in an increase in asylum grants despite policymakers' intention to make it harder for individuals to obtain the status. We argue that this law, The REAL ID Act of 2005, sent mixed messages to immigration judges (IJs), street-level bureaucrats who implement immigration policy. It increased IJ discretion, but set vague limits. We theorize that IJs, behaving in a bounded rationality framework, use their professional legal training as a short-cut and look primarily to the courts for guidance. Our evidence supports our argument. After the passage of the REAL ID Act, IJ decision-making is more closely aligned with the preferences of their political and legal principals, and, in the final score, the federal circuit courts are the winners. 相似文献
25.
Angela I. Robledo 《Colonial Latin American Review》1994,3(1-2):245-251
Imaginación del Nuevo Mundo. Diez estudios sobre los inicios de la narrativa hispanoamericana. By JOSE JUAN ARROM. México: Siglo XXI Editores, 1991. Pp. 196.
Signs, Songs, and Memory in the Andes: Translating Quechua Language and Culture. By REGINA HARRISON. Austin: University of Texas Press, 1989. Pp. xvii, 233.
The Armature of Conquest: Spanish Accounts of the Discovery of America, 1492–1589. By BEATRIZ PASTOR. Translated by LYDIA LONGSTRETH HUNT. Stanford: Stanford University Press, 1992. Pp. x, 317.
Mil leguas por América. De Lima a Caracas 1740–1741. Diario de don Miguel de Santisteban. Preliminary study by DAVID J. ROBINSON. Bogotá: Banco de la República, 1992. Pp. 323. 相似文献
26.
27.
The flame atomic absorption spectroscopy method of analysis of trace elements (Mn, Sr, and Cu) in a mammoth's bone and the method of estimation of the data using regression analysis are described. The concentration fields of the single elements in a cross-section through the bone are well described by a fourth degree polynomial. The minimum values and their coordinates have been determined. A method of determination of the original concentrations of trace elements in fossil bones is described further. The approximating features of the regression exponential equations and of the diffusion functions of various shapes were determined and a method for calculating the concentrations and diffusion properties of the bones once deposited in the soil is suggested. The original trace element concentration can be estimated by extrapolation of a suitable exponential or diffusion function. 相似文献
28.
I.H. BURNLEY 《Geographical Research》1994,32(1):69-89
The paper examines the ancestry of Europeans in Sydney and that of the two largest non European groups. Spatial divergence occurs between the English, Scottish and Irish, and divergence from those of Australian ancestry. Residential persistence across generations occurs with persons of Greek, Italian, Maltese and Dutch origins, but not spatial segmentation. While there is greater language persistence in Greek and Italian second and third settlement concentrations, few third generation persons speak their ancestral language at home. The Chinese and Lebanese are compared with Greek and Italian ancestry in their areas of strongest representation. First generation Chinese are evident in areas of both low and high socioeconomic status, but without third generation language persistence. An evolving ethnic mix in Sydney is indicated. 相似文献
29.
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
30.