全文获取类型
收费全文 | 922篇 |
免费 | 89篇 |
国内免费 | 1篇 |
专业分类
1012篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 26篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 33篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 55篇 |
2012年 | 80篇 |
2011年 | 71篇 |
2010年 | 42篇 |
2009年 | 35篇 |
2008年 | 65篇 |
2007年 | 61篇 |
2006年 | 40篇 |
2005年 | 38篇 |
2004年 | 52篇 |
2003年 | 46篇 |
2002年 | 30篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1984年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1962年 | 6篇 |
1960年 | 4篇 |
1958年 | 3篇 |
1942年 | 2篇 |
排序方式: 共有1012条查询结果,搜索用时 0 毫秒
921.
David P Fairlie Matthew Turner Karl A Byriel Josephine A McKeon W.Gregory Jackson 《Inorganica chimica acta》1999,290(2):4675-138
The complex [(NH3)5CoO3SCF3](CF3SO3)2 reacts with excess NaNCO in warm acetone solution to give, stereoselectively, a Schiff base complex (40%) which has been characterized by standard NMR techniques as one of the six isomers of [Co{NH2C(CH3)2CH2C(CH3)=NH}2(NH3)NCO](ClO4)2 · H2O, confirmed by a single crystal X-ray structural analysis. Schiff base formation in non-basic conditions for kinetically inert Co(III) complexes is unprecedented. Also, this is only the second cyanate complex of pentaaminecobalt(III) to be structurally characterized (CoNCO: Co–N, 1.908 Å; N–C, 1.152 Å; C–O, 1.206 Å; Co–N–C, 170°; N–C–O, 177°). 相似文献
922.
Hollamby S Afema-Azikuru J Sikarskie JG Kaneene JB Bowerman WW Fitzgerald SD Cameron K Gandolf AR Hui GN Dranzoa C Rumbeiha WK 《Journal of wildlife diseases》2004,40(3):501-514
The purpose of this research was to evaluate persistent organic pollutant (POP) and mercury concentrations in tissues of African fish eagles (Haliaeetus vocifer) and Nile tilapia (Oreochromis niloticus) from Lake Victoria near Entebbe and Lake Mburo, Uganda. Marabou stork (Leptoptilos crumeniferus) nestlings from urban Kampala (40 km from Entebbe) also were sampled for POPs and mercury. Total mercury was measured in the breast feathers of eight nestling and 10 adult African fish eagles from Lake Mburo, 10 nestling and five adult African fish eagles from Lake Victoria near Entebbe, and 20 nestling marabou storks from Kampala from June 2002 through January 2003. Mercury concentrations in all samples were below levels associated with adverse effects in similar species. Mercury concentrations were significantly higher in eagle adults and nestlings from Entebbe than in adults and nestlings from Lake Mburo (P< or =0.05). No significant differences (P> or =0.05) were found in mercury concentrations between sexes or between the entire fish eagle population sampled at Entebbe and marabou stork nestlings sampled at nearby Kampala. Plasma samples from the same birds were analyzed for 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, aldrin, hexachlorocyclohexane (alpha-HCH), dieldrin, endrin, heptachlor and their metabolites, as well as total polychlorinated biphenyls (PCBs). Nile tilapia whole-body cross sections collected from Lake Mburo (n=3) and Lake Victoria near Entebbe (n=8) also were analyzed for these POPs and mercury. No samples contained POPs or PCBs at the limits of detection except for 4,4'-1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene in five adult eagle plasma samples (0.0026+/-0.0015 ppm wet weight) and five Nile tilapia samples (0.002+/-0.001 ppm wet weight) from Entebbe. 相似文献
923.
Warman GR Pawley MD Bolton C Cheeseman JF Fernando AT Arendt J Wirz-Justice A 《PloS one》2011,6(7):e22073
Study Objectives
To determine the prevalence of self-reported circadian-related sleep disorders, sleep medication and melatonin use in the New Zealand blind population.Design
A telephone survey incorporating 62 questions on sleep habits and medication together with validated questionnaires on sleep quality, chronotype and seasonality.Participants
Participants were grouped into: (i) 157 with reduced conscious perception of light (RLP); (ii) 156 visually impaired with no reduction in light perception (LP) matched for age, sex and socioeconomic status, and (iii) 156 matched fully-sighted controls (FS).Sleep Habits and Disturbances
The incidence of sleep disorders, daytime somnolence, insomnia and sleep timing problems was significantly higher in RLP and LP compared to the FS controls (p<0.001). The RLP group had the highest incidence (55%) of sleep timing problems, and 26% showed drifting sleep patterns (vs. 4% FS). Odds ratios for unconventional sleep timing were 2.41 (RLP) and 1.63 (LP) compared to FS controls. For drifting sleep patterns, they were 7.3 (RLP) and 6.0 (LP).Medication Use
Zopiclone was the most frequently prescribed sleep medication. Melatonin was used by only 4% in the RLP group and 2% in the LP group.Conclusions
Extrapolations from the current study suggest that 3,000 blind and visually impaired New Zealanders may suffer from circadian-related sleep problems, and that of these, fewer than 15% have been prescribed melatonin. This may represent a therapeutic gap in the treatment of circadian-related sleep disorders in New Zealand, findings that may generalize to other countries. 相似文献924.
Camillo Bérénos Philip A. Ellis Jill G. Pilkington Josephine M. Pemberton 《Molecular ecology》2016,25(13):3152-3168
There is ample evidence for inbreeding depression manifested as a reduction in fitness or fitness‐related traits in the focal individual. In many organisms, fitness is not only affected by genes carried by the individual, but also by genes carried by their parents, for example if receiving parental care. While maternal effects have been described in many systems, the extent to which inbreeding affects fitness directly through the focal individual, or indirectly through the inbreeding coefficients of its parents, has rarely been examined jointly. The Soay sheep study population is an excellent system in which to test for both effects, as lambs receive extended maternal care. Here, we tested for both maternal and individual inbreeding depression in three fitness‐related traits (birthweight and weight and hindleg length at 4 months of age) and three fitness components (first‐year survival, adult annual survival and annual breeding success), using either pedigree‐derived inbreeding or genomic estimators calculated using ~37 000 SNP markers. We found evidence for inbreeding depression in 4‐month hindleg and weight, first‐year survival in males, and annual survival and breeding success in adults. Maternal inbreeding was found to depress both birthweight and 4‐month weight. We detected more instances of significant inbreeding depression using genomic estimators than the pedigree, which is partly explained through the increased sample sizes available. In conclusion, our results highlight that cross‐generational inbreeding effects warrant further exploration in species with parental care and that modern genomic tools can be used successfully instead of, or alongside, pedigrees in natural populations. 相似文献
925.
Christian Akem Dimala Julius Atashili Josephine C. Mbuagbaw Akam Wilfred Gottlieb L. Monekosso 《PloS one》2016,11(2)
Background
Highly active antiretroviral therapy (HAART) has greatly reduced the morbidity and mortality of HIV/AIDS patients but has also been associated with increased metabolic complications and cardiovascular diseases. Data on the association between HAART and hypertension (HTN) in Africa are scarce.Objectives
Primarily to compare the prevalence of HTN in HIV/AIDS patients on HAART and HAART-naïve patients in Limbe, Cameroon; and secondarily to assess other socio-demographic and clinical factors associated with HTN in this population.Methods
A cross-sectional study was conducted at the Limbe Regional Hospital HIV treatment center between April and June 2013, involving 200 HIV/AIDS patients (100 on first-line HAART regimens for at least 12 months matched by age and sex to 100 HAART-naïve patients). HTN was defined as a systolic blood pressure (BP) ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg.Results
The prevalence of HTN in patients on HAART was twice (38%; 95% CI: 28.5–48.3) that of the HAART-naïve patients (19%; 95% CI, 11.8–28.1), p = 0.003. In multivariate analyses adjusted for age, gender, smoking, family history of HTN, and BMI-defined overweight, HAART was associated with HTN, the adjusted odds ratio of the HAART-treated versus HAART-naïve group was 2.20 (95% CI: 1.07–4.52), p = 0.032. HTN was associated with older age and male gender, in the HAART group and with BMI-defined overweight in the HAART-naïve group.Conclusion
The prevalence of hypertension in HIV/AIDS patients in Limbe stands out to be elevated, higher in patients on HAART compared to those not on treatment. Blood pressure and cardiovascular risk factors should be routinely monitored. Other factors such as diet, weight control and physical exercise should also be considered. 相似文献926.
Lee T. Gettler Patty X. Kuo Stacy Rosenbaum Josephine L. Avila Thomas W. McDade Christopher W. Kuzawa 《Evolution and human behavior》2019,40(2):249-258
Sociosexuality is defined as an individual's interest in uncommitted sexual activity and can be measured in terms of both psychological orientations and behavioral expression. In socio-ecological contexts in which adults monogamously partner and cooperate to raise children, individuals with unrestricted sociosexuality are likely to prioritize mating/competition over committed partnering and parenting. Given the importance of mother-father cooperation in the evolutionary past, humans may have the capacity to facultatively and opportunistically downregulate sociosexuality to focus on priorities related to invested partnering and parenting. To date, no prior studies have used longitudinal data to track within-individuals changes in sociosexuality as it relates to such life history transitions. Given the lack of prior longitudinal research in this area, it is likewise unknown what physiological mechanisms might mediate within-individual changes in sociosexuality through time but testosterone is a plausible candidate. To explore these questions, we drew on a large, long-running study of Filipino men (n?=?288), who were single non-fathers at 25.9?years of age and were followed up 4–5?years later. We found that men with more unrestricted sociosexuality at baseline were more likely to experience relationship dissolution by follow-up, consistent with past work. Compared to men who remained single non-fathers at follow-up, men who became married residential fathers showed shifts towards more restricted global sociosexuality as well as sociosexual behavior. Relative to their own baseline values, married residential fathers also had more restricted sociosexuality in all domains at follow-up. They were the only group for whom this was found. We found theoretically-consistent but modest support for positive correlations between men's testosterone and their sociosexuality, but no evidence that the two change in tandem together through time. Our results suggest that some amount of between-individual differences in sociosexuality are not stable and can facultatively shift alongside other aspects of male reproductive effort. 相似文献
927.
Guillaume Burnet Chun-Wei Allen Feng Ka Man Fiona Cheung Josephine Bowles Cassy M. Spiller 《Genesis (New York, N.Y. : 2000)》2023,61(1-2):e23511
Germline-specific Cre lines are useful for analyses of primordial germ cell, spermatogonial and oogonial development, but also for whole-body deletions when transmitted through subsequent generations. Several germ cell specific Cre mouse strains exist, with various degrees of specificity, efficiency, and temporal activation. Here, we describe the CRISPR/Cas9 targeted insertion of an improved Cre (iCre) sequence in-frame at the 3′ end of the Ddx4 locus to generate the Ddx4-P2A-iCre allele. Our functional assessment of this new allele, designated Ddx4iCreJoBo, reveals that Cre activity begins in PGCs from at least E10.5, and that it achieves higher efficiency for early gonadal (E10.5–12.5) germline deletion when compared to the inducible Oct4CreERT2 line. We found the Ddx4iCreJoBo allele to be hypomorphic for Ddx4 expression and homozygous males, but not females, were infertile. Using two reporter lines (R26RLacZ and R26RtdTomato) and a floxed gene of interest (Criptoflox) we found ectopic activity in multiple organs; global recombination (a common feature of germline Cre alleles) varies from 10 to 100%, depending on the particular floxed allele. There is a strong maternal effect, and therefore it is preferable for Ddx4iCreJoBo to be inherited from the male parent if ubiquitous deletion is not desired. With these limitations considered, we describe the Ddx4iCreJoBo line as useful for germline studies in which early gonadal deletion is required. 相似文献
928.
Declining home range area predicts reduced late‐life survival in two wild ungulate populations 下载免费PDF全文
Hannah Froy Luca Börger Charlotte E. Regan Alison Morris Sean Morris Jill G. Pilkington Michael J. Crawley Tim H. Clutton‐Brock Josephine M. Pemberton Daniel H. Nussey 《Ecology letters》2018,21(7):1001-1009
Demographic senescence is increasingly recognised as an important force shaping the dynamics of wild vertebrate populations. However, our understanding of the processes that underpin these declines in survival and fertility in old age remains limited. Evidence for age‐related changes in foraging behaviour and habitat use is emerging from wild vertebrate studies, but the extent to which these are driven by within‐individual changes, and the consequences for fitness, remain unclear. Using longitudinal census observations collected over four decades from two long‐term individual‐based studies of unmanaged ungulates, we demonstrate consistent within‐individual declines in home range area with age in adult females. In both systems, we found that within‐individual decreases in home range area were associated with increased risk of mortality the following year. Our results provide the first evidence from the wild that age‐related changes in space use are predictive of adult mortality. 相似文献
929.
Peter Sykora Magdalena Misiak Yue Wang Somnath Ghosh Giovana S. Leandro Dong Liu Jane Tian Beverly A. Baptiste Wei-Na Cong Boris M. Brenerman Evandro Fang Kevin G. Becker Royce J. Hamilton Soumya Chigurupati Yongqing Zhang Josephine M. Egan Deborah L. Croteau David M. Wilson III Mark P. Mattson Vilhelm A. Bohr 《Nucleic acids research》2015,43(2):943-959
930.