全文获取类型
收费全文 | 309篇 |
免费 | 26篇 |
专业分类
335篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 8篇 |
2012年 | 11篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 11篇 |
2005年 | 15篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1995年 | 3篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1986年 | 9篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 11篇 |
1977年 | 3篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1962年 | 3篇 |
1959年 | 4篇 |
1958年 | 2篇 |
1950年 | 2篇 |
1925年 | 2篇 |
1920年 | 2篇 |
排序方式: 共有335条查询结果,搜索用时 15 毫秒
181.
S. L. Goldson M. R. McNeill J. R. Proffitt G. M. Barker P. J. Addison B. I. P. Barratt C. M. Ferguson 《BioControl》1993,38(4):527-536
The method whereby equal numbers of seven ecotypes of the parasitoidMicroctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae) were reared and released is described along with the reasons for doing so. This was achieved by variably intense rearing effort depending on the number of founder females in that particular ecotype. The parasitoid was released in three regions of New Zealand as a control agent of theListronotus bonariensis Kuschel (Col.: Curculionidae), a severe pest of New Zealand pastures. It was later recovered from all three regions. 相似文献
182.
PJ?Baker H?Johnston M?Abel HM?Charlton PJ?O'ShaughnessyEmail author 《Reproductive biology and endocrinology : RB&E》2003,1(1):4
During mammalian testis development distinct generations of fetal and adult Leydig cells arise. Luteinising hormone (LH) is
required for normal adult Leydig cell function and for the establishment of normal adult Leydig cell number but its role in
the process of adult Leydig cell differentiation has remained uncertain. In this study we have examined adult Leydig cell
differentiation in gonadotrophin-releasing hormone (GnRH)-null mice which are deficient in circulating gonadotrophins. Adult
Leydig cell differentiation was assessed by measuring expression of mRNA species encoding four specific markers of adult Leydig
cell differentiation in the mouse. Each of these markers (3β-hydroxysteroid dehydrogenase type VI (3βHSD VI), 17β-hydroxysteroid
dehydrogenase type III (17βHSD III), prostaglandin D (PGD)-synthetase and oestrogen sulphotransferase (EST)) is expressed
only in the adult Leydig cell lineage in the normal adult animal. Real-time PCR studies showed that all four markers are expressed
in adult GnRH-null mice. Localisation of 3βHSD VI and PGD-synthetase expression by in situ hybridisation confirmed that these genes are expressed in the interstitial tissue of the GnRH-null mouse. Treatment of animals
with human chorionic gonadotrophin increased expression of 3βHSD VI and 17βHSD III within 12 hours further indicating that
differentiated, but unstimulated cells already exist in the GnRH-null mouse. Thus, while previous studies have shown that
LH is required for adult Leydig cell proliferation and activity, results from the present study show that adult Leydig cell
differentiation will take place in animals deficient in LH. 相似文献
183.
Courtney Addison 《The journal of the Royal Anthropological Institute》2022,28(1):260-278
Science and medicine have been cast as disenchanted arenas of modernity, even as scholars have illustrated the many enchantments of everyday life. Taking these conversations into the context of experimental paediatric medicine, I explore the dis/enchantments produced through the research ethics systems that govern interactions between medical practitioners and patients’ families. Research ethics enact forms of disenchantment, aiming to produce the informed patient-subject who can knowingly submit to the unknowns of experimental medicine. However, by following one young patient's emotive disruption of the consent process, I suggest that we instead consider an ethics of enchantment: one that recognizes the affective logics of patienthood alongside the informatic. Elaborating how ethical practice is both institutionally structured and interpersonally improvised, I develop key conversations from the anthropology of ethics, and highlight the interplay of enchantment and disenchantment that constitutes modern medical subjects. 相似文献
184.
185.
Philip Addison 《BMJ (Clinical research ed.)》1971,1(5750):667-668
186.
187.
188.
Xavier Bailly Elisa Giuntini M Connor Sexton Ryan PJ Lower Peter W Harrison Nitin Kumar J Peter W Young 《The ISME journal》2011,5(11):1722-1734
We investigated the genomic diversity of a local population of the symbiotic bacterium Sinorhizobium medicae, isolated from the roots of wild Medicago lupulina plants, in order to assess genomic diversity, to identify genomic regions influenced by duplication, deletion or strong selection, and to explore the composition of the pan-genome. Partial genome sequences of 12 isolates were obtained by Roche 454 shotgun sequencing (average 5.3 Mb per isolate) and compared with the published sequence of S. medicae WSM 419. Homologous recombination appears to have less impact on the polymorphism patterns of the chromosome than on the chromid pSMED01 and megaplasmid pSMED02. Moreover, pSMED02 is a hot spot of insertions and deletions. The whole chromosome is characterized by low sequence polymorphism, consistent with the high density of housekeeping genes. Similarly, the level of polymorphism of symbiosis genes (low) and of genes involved in polysaccharide synthesis (high) may reflect different selection. Finally, some isolates carry genes that may confer adaptations that S. medicae WSM 419 lacks, including homologues of genes encoding rhizobitoxine synthesis, iron uptake, response to autoinducer-2, and synthesis of distinct polysaccharides. The presence or absence of these genes was confirmed by PCR in each of these 12 isolates and a further 27 isolates from the same population. All isolates had rhizobitoxine genes, while the other genes were co-distributed, suggesting that they may be on the same mobile element. These results are discussed in relation to the ecology of Medicago symbionts and in the perspective of population genomics studies. 相似文献
189.
190.
The South American curculionid Listronotus bonariensis (Kuschel) is an important pest of pastures in New Zealand. Population census data were gathered for L. bonariensis in northern New Zealand pastures during 1980-1983 in the absence of parasitism and again in 1991-1996 after the introduction and establishment of the braconid parasitoid Microctonus hyperodae Loan as a biological control agent. M. hyperodae achieved high rates of parasitism, with 75-90% of overwintering L. bonariensis parasitized within 3 yr of the parasitoid establishing at a site. Multistratum analysis of variance (ANOVA), with allowance for variation in host plant resource (numbers of Neotyphodium-free grass tillers), indicated reduction in the abundance of L. bonariensis life stages in the early part of life cycle. Although providing evidence for suppression of L. bonariensis, these analyses indicated the regulatory role of M. hyperodae was weak because L. bonariensis populations continued to exhibit marked intergenerational variability in abundance. Analyses of life tables indicated larval + pupal survival contributed most to intergenerational changes in abundance, irrespective of presence or absence of M. hyperodae. However, the density dependence of the stage survivals was modified in the presence of the parasitoid, with loss of density-dependent mortality in overwintering adults and increased density dependence in population natality. Regression analyses indicated dual contribution of parasitism and host plant resource to regulation of population natality and population trend in L. bonariensis. We conclude that M. hyperodae is a useful adjunct to host plant resistance in reducing the economic status of L. bonariensis populations in northern New Zealand pastures. 相似文献