全文获取类型
收费全文 | 990篇 |
免费 | 49篇 |
出版年
2023年 | 13篇 |
2022年 | 10篇 |
2021年 | 31篇 |
2020年 | 17篇 |
2019年 | 25篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 33篇 |
2015年 | 51篇 |
2014年 | 48篇 |
2013年 | 72篇 |
2012年 | 75篇 |
2011年 | 72篇 |
2010年 | 41篇 |
2009年 | 35篇 |
2008年 | 49篇 |
2007年 | 44篇 |
2006年 | 35篇 |
2005年 | 35篇 |
2004年 | 30篇 |
2003年 | 25篇 |
2002年 | 18篇 |
2001年 | 20篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 17篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有1039条查询结果,搜索用时 379 毫秒
951.
Tim S. Jessop Rita Chan Devi Stuart-Fox 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(7):619-630
In some species, females develop bright colouration to signal reproductive status and exhibit behavioural repertoires to incite
male courtship and/or reduce male harassment and forced copulation. Sex steroids, including progesterone and testosterone,
potentially mediate female reproductive colouration and reproductive behaviour. We measured associations among plasma profiles
of testosterone and progesterone with variation in colour expression and reproductive behaviour, including unique courtship
rejection behaviours, in female Lake Eyre dragon lizards, (Ctenophorus maculosus). At onset of breeding, progesterone and testosterone increased with vitellogenesis, coincident with colour intensification
and sexual receptivity, indicated by acceptance of copulations. As steroid levels peaked around the inferred ovulation time,
maximal colour development occurred and sexual receptivity declined. When females were gravid and exhibited maximal mate rejection
behaviours, progesterone levels remained consistently high, while testosterone exhibited a discrete second peak. At oviposition,
significant declines in plasma steroid levels, fading of colouration and a dramatic decrease in male rejection behaviours
co-occurred. Our results indicate a generally concordant association among steroid levels, colouration, behaviour and reproductive
events. However, the prolonged elevation in progesterone and a second peak of testosterone was unrelated to reproductive state
or further colour change, possibly suggesting selection on females to retain high steroid levels for inducing rejection behaviours. 相似文献
952.
953.
Haimanti Biswas Subhadra Devi Gadi V. Venkata Ramana M. Durga Bharathi R. Kesava Priyan D. Taruni Manjari M. Dileep Kumar 《Biodiversity and Conservation》2012,21(5):1309-1326
The role of microzooplankton (MZP) in the pelagic trophodynamics is highly significant, but the responses of marine MZP to
increasing CO2 levels are rather poorly understood. Hence the present study was undertaken to understand the responses of marine plankton
to increasing CO2 concentrations. Natural water samples from the coastal Bay of Bengal were incubated under the ambient condition and high
CO2 levels (703–711 μatm) for 5 days in May and June 2010. A significant negative correlation was obtained between phytoplankton
and MZP abundance which indicated that phytoplankton community structure can considerably be controlled by MZP in this region.
The average relative abundances of tintinnids under elevated CO2 levels were found to be significantly higher (68.65 ± 5.63% in May; 85.46 ± 9.56% in June) than observed in the ambient condition
(35.68 ± 6.83% in May; 79 ± 5.36% in June). The observed dominance of small chain forming diatom species probably played a
crucial role as they can be potentially grazed by tintinnids. This fact was strengthened by the observed high negative correlations
between the relative abundance of major phytoplankton and tintinnids. Moreover, particulate organic carbon and total bacterial
counts were also enhanced under elevated CO2 level and can serve as additional food source for ciliates. The observed responses of tintinnids to increasing CO2 might have multiple impacts on the energy transfer, nutrient and carbon cycling in the coastal water. The duration of the
present study was relatively short and therefore further investigation on longer time scale needs to be done and might give
us a better insight about phytoplankton and MZP species succession under elevated CO2 level. 相似文献
954.
A quick method based on chlorotetracycline induced fluorescence of the antherozoids is described. This method was found suitable for studying the number and duration of motility of antherozoids in toxicity studies where male fertility is a significant character. 相似文献
955.
956.
957.
Tabasum Kawoosa Harsharan Singh Amit Kumar Sunil Kumar Sharma Kiran Devi Som Dutt Surender Kumar Vats Madhu Sharma Paramvir Singh Ahuja Sanjay Kumar 《Functional & integrative genomics》2010,10(3):393-404
Picrorhiza (Picrorhiza kurrooa) is an endangered medicinal plant with well-known hepatoprotective activity attributed to monoterpenoid picrosides. The present
article details on regulatory genes of terpenoid metabolism, 3-hydroxy-3-methylglutaryl coenzyme A reductase (pkhmgr) and 1-deoxy-D-xylulose-5-phosphate synthase (pkdxs) from picrorhiza. Since no molecular information was available, these genes were cloned to full-length by degenerate primers
and rapid amplification of cDNA ends, followed by cloning of the upstream sequences that showed the presence of core sequences
for light and temperature responsiveness. Electrophoretic mobility shift assay confirmed binding of protein to these motifs.
Expression of pkhmgr and pkdxs was up-regulated at 15°C as compared to at 25°C as well as under light as compared to dark conditions. Picrosides content
exhibited the trend similar to gene expression. To rule out the possible limitation of carbon pool under dark condition, plantlets
of picrorhiza were raised in vitro in Murashige and Skoog medium supplemented with 3% sucrose. Results showed similar up-regulation
of both the genes and the higher picrosides content in in vitro raised plantlets in the presence of light. Data suggested
the important roles played by light and temperature in regulating pkhmgr and pkdxs, and the picrosides level in picrorhiza. 相似文献
958.
959.
Jalisa H. Ferguson Zeus De Los Santos Saroja N. Devi Stefan Kaluz Erwin G. Van Meir 《Journal of enzyme inhibition and medicinal chemistry》2017,32(1):992-1001
While progress has been made in treating cancer, cytotoxic chemotherapeutic agents are still the most widely used drugs and are associated with severe side-effects. Drugs that target unique molecular signalling pathways are needed for treating cancer with low or no intrinsic toxicity to normal cells. Our goal is to target hypoxic tumours and specifically the hypoxia inducible factor (HIF) pathway for the development of new cancer therapies. To this end, we have previously developed benzopyran-based HIF-1 inhibitors such as arylsulfonamide KCN1. However, KCN1 and its earlier analogs have poor water solubility, which hamper their applications. Herein, we describe a series of KCN1 analogs that incorporate a morpholine moiety at various positions. We found that replacing the benzopyran group of KCN1 with a phenyl group with a morpholinomethyl moiety at the para positions had minimal effect on potency and improved the water solubility of two new compounds by more than 10-fold compared to KCN1, the lead compound. 相似文献
960.
Prenatal maternal psychological distress increases risk for adverse infant outcomes. However, the biological mechanisms underlying this association remain unclear. Prenatal stress can impact fetal epigenetic regulation that could underlie changes in infant stress responses. It has been suggested that maternal glucocorticoids may mediate this epigenetic effect. We examined this hypothesis by determining the impact of maternal cortisol and depressive symptoms during pregnancy on infant NR3C1 and BDNF DNA methylation. Fifty-seven pregnant women were recruited during the second or third trimester. Participants self-reported depressive symptoms and salivary cortisol samples were collected diurnally and in response to a stressor. Buccal swabs for DNA extraction and DNA methylation analysis were collected from each infant at 2 months of age, and mothers were assessed for postnatal depressive symptoms. Prenatal depressive symptoms significantly predicted increased NR3C1 1F DNA methylation in male infants (β = 2.147, P = 0.044). Prenatal depressive symptoms also significantly predicted decreased BDNF IV DNA methylation in both male and female infants (β = −3.244, P = 0.013). No measure of maternal cortisol during pregnancy predicted infant NR3C1 1F or BDNF promoter IV DNA methylation. Our findings highlight the susceptibility of males to changes in NR3C1 DNA methylation and present novel evidence for altered BDNF IV DNA methylation in response to maternal depression during pregnancy. The lack of association between maternal cortisol and infant DNA methylation suggests that effects of maternal depression may not be mediated directly by glucocorticoids. Future studies should consider other potential mediating mechanisms in the link between maternal mood and infant outcomes. 相似文献