全文获取类型
收费全文 | 3991篇 |
免费 | 465篇 |
国内免费 | 1篇 |
出版年
2023年 | 32篇 |
2022年 | 42篇 |
2021年 | 99篇 |
2020年 | 63篇 |
2019年 | 70篇 |
2018年 | 86篇 |
2017年 | 72篇 |
2016年 | 101篇 |
2015年 | 181篇 |
2014年 | 186篇 |
2013年 | 212篇 |
2012年 | 283篇 |
2011年 | 260篇 |
2010年 | 144篇 |
2009年 | 130篇 |
2008年 | 167篇 |
2007年 | 188篇 |
2006年 | 171篇 |
2005年 | 172篇 |
2004年 | 138篇 |
2003年 | 132篇 |
2002年 | 120篇 |
2001年 | 58篇 |
2000年 | 53篇 |
1999年 | 68篇 |
1998年 | 45篇 |
1997年 | 33篇 |
1996年 | 49篇 |
1995年 | 38篇 |
1993年 | 26篇 |
1992年 | 43篇 |
1991年 | 45篇 |
1990年 | 47篇 |
1989年 | 44篇 |
1988年 | 46篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 50篇 |
1983年 | 31篇 |
1982年 | 27篇 |
1979年 | 47篇 |
1976年 | 28篇 |
1975年 | 28篇 |
1974年 | 30篇 |
1973年 | 34篇 |
1972年 | 31篇 |
1971年 | 27篇 |
1970年 | 36篇 |
1969年 | 28篇 |
排序方式: 共有4457条查询结果,搜索用时 15 毫秒
1.
Marvin J. Allison Guillermo Focacci Calogero Santoro 《American journal of physical anthropology》1982,59(3):299-304
Burials and mummies of dogs from the Arica, Chile, area are described. It is concluded that these dogs were brought to this area 2500 years ago by shepherds from the highlands and are still present, relatively unchanged. 相似文献
2.
The cost of mutualism in a fly-fungus interaction 总被引:2,自引:0,他引:2
The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study,
I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous
stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions
to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure
and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s
ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure
on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management.
Received: 14 July 1999 / Accepted: 23 March 2000 相似文献
3.
4.
Ryan P. Bourbour Breanna L. Martinico Megan M. Crane Angus C. Hull Joshua M. Hull 《Ecology and evolution》2019,9(3):1452-1457
Complex coevolutionary relationships among competitors, predators, and prey have shaped taxa diversity, life history strategies, and even the avian migratory patterns we see today. Consequently, accurate documentation of prey selection is often critical for understanding these ecological and evolutionary processes. Conventional diet study methods lack the ability to document the diet of inconspicuous or difficult‐to‐study predators, such as those with large home ranges and those that move vast distances over short amounts of time, leaving gaps in our knowledge of trophic interactions in many systems. Migratory raptors represent one such group of predators where detailed diet studies have been logistically challenging. To address knowledge gaps in the foraging ecology of migrant raptors and provide a broadly applicable tool for the study of enigmatic predators, we developed a minimally invasive method to collect dietary information by swabbing beaks and talons of raptors to collect trace prey DNA. Using previously published COI primers, we were able to isolate and reference gene sequences in an open‐access barcode database to identify prey to species. This method creates a novel avenue to use trace molecular evidence to study prey selection of migrating raptors and will ultimately lead to a better understanding of raptor migration ecology. In addition, this technique has broad applicability and can be used with any wildlife species where even trace amounts of prey debris remain on the exterior of the predator after feeding. 相似文献
5.
Social justice issues remain some of the most pressing problems in the United States. One aspect of social justice involves the differential treatment of demographic groups in the criminal justice system. While data consistently show that Blacks and Hispanics are often treated differently than Whites, one understudied aspect of these disparities is how police officers'' assessments of suspects'' size affects their decisions. Using over 3 million cases from the New York Police Department (NYPD) Stop, Question, and Frisk (SQF) Database, 2006–2013, this study is the first to explore suspects'' race, perceived size, and police treatment. Results indicate that tall and heavy black and Hispanic men are at the greatest risk for frisk or search. Tall and heavy suspects are at increased risk for experiencing police force, with black and Hispanic men being more likely to experience force than white men across size categories. 相似文献
6.
7.
B Zisman E F Wheelock A C Allison 《Journal of immunology (Baltimore, Md. : 1950)》1971,107(1):236-243
8.
9.
Although diabetes has been identified as a major risk factor for atrial fibrillation, little is known about glucose metabolism in the healthy and diabetic atria. Glucose transport into the cell, the rate-limiting step of glucose utilization, is regulated by the Glucose Transporters (GLUTs). Although GLUT4 is the major isoform in the heart, GLUT8 has recently emerged as a novel cardiac isoform. We hypothesized that GLUT-4 and -8 translocation to the atrial cell surface will be regulated by insulin and impaired during insulin-dependent diabetes. GLUT protein content was measured by Western blotting in healthy cardiac myocytes and type 1 (streptozotocin-induced, T1Dx) diabetic rodents. Active cell surface GLUT content was measured using a biotinylated photolabeled assay in the perfused heart. In the healthy atria, insulin stimulation increased both GLUT-4 and -8 translocation to the cell surface (by 100% and 240%, respectively, P<0.05). Upon insulin stimulation, we reported an increase in Akt (Th308 and s473 sites) and AS160 phosphorylation, which was positively (P<0.05) correlated with GLUT4 protein content in the healthy atria. During diabetes, active cell surface GLUT-4 and -8 content was downregulated in the atria (by 70% and 90%, respectively, P<0.05). Akt and AS160 phosphorylation was not impaired in the diabetic atria, suggesting the presence of an intact insulin signaling pathway. This was confirmed by the rescued translocation of GLUT-4 and -8 to the atrial cell surface upon insulin stimulation in the atria of type 1 diabetic subjects. In conclusion, our data suggest that: 1) both GLUT-4 and -8 are insulin-sensitive in the healthy atria through an Akt/AS160 dependent pathway; 2) GLUT-4 and -8 trafficking is impaired in the diabetic atria and rescued by insulin treatment. Alterations in atrial glucose transport may induce perturbations in energy production, which may provide a metabolic substrate for atrial fibrillation during diabetes. 相似文献
10.