全文获取类型
收费全文 | 11620篇 |
免费 | 1039篇 |
国内免费 | 1篇 |
出版年
2023年 | 91篇 |
2022年 | 149篇 |
2021年 | 365篇 |
2020年 | 206篇 |
2019年 | 254篇 |
2018年 | 321篇 |
2017年 | 289篇 |
2016年 | 437篇 |
2015年 | 681篇 |
2014年 | 734篇 |
2013年 | 907篇 |
2012年 | 966篇 |
2011年 | 1009篇 |
2010年 | 597篇 |
2009年 | 471篇 |
2008年 | 700篇 |
2007年 | 681篇 |
2006年 | 557篇 |
2005年 | 503篇 |
2004年 | 486篇 |
2003年 | 377篇 |
2002年 | 359篇 |
2001年 | 131篇 |
2000年 | 110篇 |
1999年 | 104篇 |
1998年 | 74篇 |
1997年 | 65篇 |
1996年 | 58篇 |
1995年 | 69篇 |
1994年 | 55篇 |
1993年 | 40篇 |
1992年 | 55篇 |
1991年 | 53篇 |
1990年 | 50篇 |
1989年 | 43篇 |
1988年 | 39篇 |
1987年 | 45篇 |
1986年 | 37篇 |
1985年 | 31篇 |
1984年 | 52篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 33篇 |
1980年 | 20篇 |
1978年 | 19篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1975年 | 22篇 |
1974年 | 19篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
Jeremy D. Hogan Katharine M. Jack Fernando A. Campos Urs Kalbitzer Linda M. Fedigan 《American journal of primatology》2019,81(7)
Primates have long been used as indicator species for assessing overall ecosystem health. However, area‐wide census methods are time consuming, costly, and not always feasible under many field conditions. Therefore, it is important to establish whether monitoring a subset of a population accurately reflects demographic changes occurring in the population at large. Over the past 35 years, we have conducted 15 area‐wide censuses in Sector Santa Rosa, Costa Rica. These efforts have revealed important trends in population growth patterns of capuchin monkeys following the protection and subsequent regeneration of native forests. During this same period, we have also intensively studied a subset of the capuchin groups. Comparing these two datasets, we investigate whether the population structures of the closely monitored groups are reliable indicators of area‐wide demographic patterns. We compare the overall group size and the individual age/sex class compositions of study groups and nonstudy groups (i.e., those contacted during area‐wide censuses only). Our study groups contained more individuals overall with a larger proportion of infants, and there were indications that the proportion of adult and subadult males was lower. These differences can be ascribed either to sampling errors or real differences attributable to human presence and/or better habitat quality for the study groups. No other sex/age classes differed, and major demographic changes were simultaneously evident in both study and nonstudy groups. This study suggests that the Santa Rosa capuchin population is similarly impacted by large‐scale ecological patterns observable within our study groups. 相似文献
2.
Solange Faria Lua Figueiredo Norma Albarello Vera Regina Campos Viana 《In vitro cellular & developmental biology. Plant》2001,37(4):471-475
Summary A protocol for in vitro propagation of Rollinia mucosa, an important medicinal plant, was developed. The presence of 500 mg l−1 polyvinylpyrrolidone (PVP) during explant excision was important to avoid browning. Axillary buds, adventitious buds, and
shoot cluster proliferation were achieved from epicotyl and hypocotyl explants from nursery-grown seedlings. The highest direct
organogenesis percentage from hypocotyl explants was obtained upon culture of explants on Murashige and Skoog medium supplemented
with 2.2 μM benzyladenine (BA) plus 2.32 μM kinetin. Epicotyl explants display highest regeneration frequency on a medium containing 8.8 μM BA and 0.54 μM naphthaleneacetic acid. Gibberellic acid was necessary for shoot elongation. Root induction was observed when shoots were
pretreated with activated charcoal for 7 d in the dark before culture on Woody Plant Medium supplemented with 49.21 μM indolebutyric acid for 10 d. Root development was observed when 20 g l−1 sucrose was used. Rooted plantlets were acclimatized and grown in the greenhouse. 相似文献
3.
Zhaolin Wang Cara Fraley Adam R. Mezo 《Bioorganic & medicinal chemistry letters》2013,23(5):1253-1256
The neonatal Fc receptor, FcRn, prolongs the half-life of IgG in the serum and represents a potential therapeutic target for the treatment of autoimmune disease. Small molecules that block the protein–protein interactions of human IgG–human FcRn may lower pathogenic autoantibodies and provide effective treatment. A novel class of quinoxalines has been discovered as antagonists of the IgG:FcRn protein–protein interaction through optimization of a hit derived from a virtual ligand-based screen. 相似文献
4.
5.
Plant and Soil - Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research... 相似文献
6.
Francisco Gutirrez‐Corchero M. Victoria Arruga Lourdes Sanz Cristina García M. Angeles Hernndez Francisco Campos 《Molecular ecology resources》2002,2(1):75-77
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor. 相似文献
7.
8.
Hierarchy and monophyly 总被引:1,自引:0,他引:1
9.
Eliot C. Bush Anne E. Clark Chris M. DeBoever Lillian E. Haynes Sidra Hussain Singer Ma Matthew M. McDermott Adam M. Novak John S. Wentworth 《PloS one》2012,7(11)
A significant proportion of enzymes display cooperativity in binding ligand molecules, and such effects have an important impact on metabolic regulation. This is easiest to understand in the case of positive cooperativity. Sharp responses to changes in metabolite concentrations can allow organisms to better respond to environmental changes and maintain metabolic homeostasis. However, despite the fact that negative cooperativity is almost as common as positive, it has been harder to imagine what advantages it provides. Here we use computational models to explore the utility of negative cooperativity in one particular context: that of an inhibitor binding to an enzyme. We identify several factors which may contribute, and show that acting together they can make negative cooperativity advantageous. 相似文献
10.