全文获取类型
收费全文 | 262篇 |
免费 | 11篇 |
专业分类
273篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 18篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 9篇 |
2006年 | 14篇 |
2005年 | 9篇 |
2004年 | 13篇 |
2003年 | 2篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1966年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
1952年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有273条查询结果,搜索用时 20 毫秒
51.
Butovskaya ML Boyko EY Selverova NB Ermakova IV 《Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science》2005,24(4):333-337
Developing effective behavioral and psychological mechanisms for coping with social stress was very important in human evolution because humans evolved as social beings. The aggressive and post-aggressive behavior of 30 boys aged 7-11 years was observed during free play in summer camp with the standard "post-conflict-matched control" method (de Waal and Yoshihara, 1983). The focals were the victims of the conflict. Saliva samples for examination of cortisol and dehydroepiandrosterone sulfate levels were taken from each boy in 5 cases: 10 minutes after a conflict with and without reconciliation, matched-control samples next day and morning samples for the basal level. Every boy filled in a sociometry form, Buss-Durkee Hostility Inventory, Eysenk Personality test and the Revised Children's form for the Manifest Anxiety Scale. The stress-reduction role of peacemaking was supported on the physiological level. The level of stress-related hormones was higher when no reunion occurred. 相似文献
52.
Zlotnik A Gruenbaum BF Mohar B Kuts R Gruenbaum SE Ohayon S Boyko M Klin Y Sheiner E Shaked G Shapira Y Teichberg VI 《Biology of reproduction》2011,84(3):581-586
The gonadal steroids estrogen and progesterone have been shown to have neuroprotective properties against various neurodegenerative conditions. Excessive concentrations of glutamate have been found to exert neurotoxic properties. We hypothesize that estrogen and progesterone provide neuroprotection by the autoregulation of blood and brain glutamate levels. Venous blood samples (10 ml) were taken from 31 men and 45 women to determine blood glutamate, estrogen, progesterone, glucose, glutamate-pyruvate transaminase (GPT), and glutamate-oxaloacetate transaminase (GOT) levels, collected on Days 1, 7, 12, and 21 of the female participants' menstrual cycle. Blood glutamate concentrations were higher in men than in women at the start of menstruation (P < 0.05). Blood glutamate levels in women decreased significantly on Days 7 (P < 0.01), 12 (P < 0.001), and 21 (P < 0.001) in comparison with blood glutamate levels on Day 1. There was a significant decrease in blood glutamate levels on Days 12 (P < 0.001) and 21 (P < 0.001) in comparison with blood glutamate levels on Day 7. Furthermore, there was an increase in blood glutamate levels on Day 21 compared with Day 12 (P < 0.05). In women, there were elevated levels of estrogen on Days 7 (P < 0.05), 12, and 21 (P < 0.001), and elevated levels of progesterone on Days 12 and 21 (P < 0.001). There were no differences between men and women with respect to blood glucose concentrations. Concentrations of GOT (P < 0.05) and GPT (P < 0.001) were significantly higher in men than in women during the entire cycle. The results of this study demonstrate that blood glutamate levels are inversely correlated to levels of plasma estrogen and progesterone. 相似文献
53.
We examined the gastrointestinal helminth fauna of 2 Cuvier's beaked whales, Ziphius cavirostris, stranded on the Spanish Mediterranean coast. Information regarding intestinal parasites of this species is provided for the first time. Six helminth taxa were identified. Thirty type II larvae of the nematode Anisakis sp. were found in the stomach and the intestine of both hosts; 2 type I larvae of Anisakis sp. were found in the intestine of 1 host. One juvenile of the acanthocephalan Bolbosoma vasculosum was found in the intestine; the metacestode Scolex pleuronectis was found mainly in the terminal colon and the anal crypts of both hosts; adult cestodes of Tetrabothrius sp., which may represent a new species, were collected from the duodenum of 1 host. Composition of the intestinal parasitic community is similar to that of other oceanic cetaceans, which mostly include species of Bolbosoma and tetrabothriids (Cestoda). 相似文献
54.
V. V. Dmitrenko O. I. Boyko K. O. Shostak A. V. Beletskii T. A. Malisheva M. I. Shamayev V. M. Klyuchka V. D. Rozumenko Y. P. Zozulya V. M. Kavsan 《Cytology and Genetics》2009,43(1):22-27
Analysis of the expression of genes encoding myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) in human glial tumors was carried out for determination of the expression specificity of these genes according to tumor types and their malignancy. Low levels of MBP mRNA in astrocytoma specimens of malignancy grades II-IV and significantly higher levels in perifocal zones adjacent to them have been determined by Northern hybridization. Diffuse astrocytomas and anaplastic astrocytomas are characterized mostly by a low level of MBP gene expression and high level of GFAP gene expression, but distinct subtypes of diffuse and anaplastic astrocytomas with a high level of GFAP gene expression can also be detected that may be the reflection of different oncogenic pathways. Very low levels or even absence of MBP mRNA were revealed in oligodendroglioma and all oligoastrocytomas. Thus, Northern hybridization data are correlated with serial analysis of gene expression (SAGE). Obtained results show that MBP is a nonspecific marker for tumors of oligodendroglial origin, but determination of relative levels of MBP and GFAP mRNAs may be useful for glial tumor recognition. In such a way, these two genes together with YKL-40 and TSC-22, which we found previously, can be included into the gene panel for determination of so-called “gene signatures” of brain tumors. However, strict requirements in relation to a clinical value of these “gene signatures” cannot be formulated without verifying them on a large number of clinical samples of tumors and valid control. 相似文献
55.
Christopher B. Boyko 《Palaeontology》2004,47(4):929-932
The fossil genus Paralbunea Hu and Tao, described as an anomuran albuneid, is a junior homonym of Paralbunea Serène and a possible synonym of either the brachyuran raninid Ranilia H. Milne Edwards, 1837, or Cosmonotus Adams and White, 1848. The type series of P. taipeiensis Hu and Tao is composed of at least two species belonging to two raninid genera and appears (in part) assignable to the genus Ranilia and (in part) to Cosmonotus grayi Adams and White, 1848. However, due to both limited availability and poor quality of the holotype of Paralbunea taipeiensis , and destruction of the paratypes, this taxon cannot be unequivocally synonymized with any particular raninid taxon and a new name is proposed to replace Hu and Tao's preoccupied generic name. Caution is urged when describing purported albuneid fossils, due to strong convergence with raninid crabs, which are far more common in the fossil record. 相似文献
56.
Four species of Biuterina Fuhrmann, 1902 (Cestoda, Cyclophyllidea, Paruterinidae), originally described from Afrotropical passeriform birds, are redescribed and figured on the basis of their type-specimens. These are B. pentamyzos (Mettrick, 1960) from Prionops plumata (Laniidae) in Zimbabwe, B. quelea (Mettrick, 1963) from Quelea quelea (Ploceidae) in Zimbabwe, B. ugandae Baylis, 1919 from Chalcomitra senegalensis (Nectariniidae) in Uganda and B. zambiensis (Mettrick, 1960) from Campephaga flava (Campephagidae) in Zimbabwe. The rostellum of B. quelea is a spherical structure filled with strongly-developed glandular tissue and possessing a weak musculature. The remaining three species have a sucker-like rostellar apparatus with moderately developed glandular tissue in the rostellum and around it. It is considered that the glandular elements are an inherent part of the rostellar apparatus of the paruterinids. An armament consisting of fine, punctiform, spine-like structures arranged in transverse rows on the inner surface of suckers is observed in B. pentamyzos. This is the first record of sucker armature in the Paruterinidae. 相似文献
57.
George N. Ioannou Jacqueline M. Ferguson Ann M. OHare Amy S. B. Bohnert Lisa I. Backus Edward J. Boyko Thomas F. Osborne Matthew L. Maciejewski C. Barrett Bowling Denise M. Hynes Theodore J. Iwashyna Melody Saysana Pamela Green Kristin Berry 《PLoS medicine》2021,18(10)
BackgroundWe examined whether key sociodemographic and clinical risk factors for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and mortality changed over time in a population-based cohort study.Methods and findingsIn a cohort of 9,127,673 persons enrolled in the United States Veterans Affairs (VA) healthcare system, we evaluated the independent associations of sociodemographic and clinical characteristics with SARS-CoV-2 infection (n = 216,046), SARS-CoV-2–related mortality (n = 10,230), and case fatality at monthly intervals between February 1, 2020 and March 31, 2021. VA enrollees had a mean age of 61 years (SD 17.7) and were predominantly male (90.9%) and White (64.5%), with 14.6% of Black race and 6.3% of Hispanic ethnicity. Black (versus White) race was strongly associated with SARS-CoV-2 infection (adjusted odds ratio [AOR] 5.10, [95% CI 4.65 to 5.59], p-value <0.001), mortality (AOR 3.85 [95% CI 3.30 to 4.50], p-value < 0.001), and case fatality (AOR 2.56, 95% CI 2.23 to 2.93, p-value < 0.001) in February to March 2020, but these associations were attenuated and not statistically significant by November 2020 for infection (AOR 1.03 [95% CI 1.00 to 1.07] p-value = 0.05) and mortality (AOR 1.08 [95% CI 0.96 to 1.20], p-value = 0.21) and were reversed for case fatality (AOR 0.86, 95% CI 0.78 to 0.95, p-value = 0.005). American Indian/Alaska Native (AI/AN versus White) race was associated with higher risk of SARS-CoV-2 infection in April and May 2020; this association declined over time and reversed by March 2021 (AOR 0.66 [95% CI 0.51 to 0.85] p-value = 0.004). Hispanic (versus non-Hispanic) ethnicity was associated with higher risk of SARS-CoV-2 infection and mortality during almost every time period, with no evidence of attenuation over time. Urban (versus rural) residence was associated with higher risk of infection (AOR 2.02, [95% CI 1.83 to 2.22], p-value < 0.001), mortality (AOR 2.48 [95% CI 2.08 to 2.96], p-value < 0.001), and case fatality (AOR 2.24, 95% CI 1.93 to 2.60, p-value < 0.001) in February to April 2020, but these associations attenuated over time and reversed by September 2020 (AOR 0.85, 95% CI 0.81 to 0.89, p-value < 0.001 for infection, AOR 0.72, 95% CI 0.62 to 0.83, p-value < 0.001 for mortality and AOR 0.81, 95% CI 0.71 to 0.93, p-value = 0.006 for case fatality). Throughout the observation period, high comorbidity burden, younger age, and obesity were consistently associated with infection, while high comorbidity burden, older age, and male sex were consistently associated with mortality. Limitations of the study include that changes over time in the associations of some risk factors may be affected by changes in the likelihood of testing for SARS-CoV-2 according to those risk factors; also, study results apply directly to VA enrollees who are predominantly male and have comprehensive healthcare and need to be confirmed in other populations.ConclusionsIn this study, we found that strongly positive associations of Black and AI/AN (versus White) race and urban (versus rural) residence with SARS-CoV-2 infection, mortality, and case fatality observed early in the pandemic were ameliorated or reversed by March 2021.George Ioannou and co-workers study the distribution of SARS-CoV-2 infections and outcomes among the United States population. 相似文献
58.
Triaenorhina burti n. sp. (Cyclophyllidea: Paruterinidae) is described from Harpactes fasciatus (Trogoniformes: Trogonidae) from the Southern Province of Sri Lanka. The new species is characterised by: a body 24–32 mm long; 44 rostellar hooks alternating in two closely adjacent regular rows, with lengths of 63–65 μm (anterior row) and 39–41 μm (posterior row); regularly alternating genital pores; testes divided into two groups by the ovary and vitellarium; a gravid uterus forming a single oval sac; and a cylindrical paruterine organ not reaching the anterior proglottis margin. A key to the seven recognised species of Triaenorhina Spasskii & Shumilo, 1965 is presented. 相似文献
59.
Systematic Parasitology - Armadolepis (Armadolepis) spasskyi Tenora & Baru?, 1958 is redescribed on the basis of the type-series consisting of the holotype from the garden dormouse... 相似文献
60.
Tikhonova TV Slutsky A Antipov AN Boyko KM Polyakov KM Sorokin DY Zvyagilskaya RA Popov VO 《Biochimica et biophysica acta》2006,1764(4):715-723
A highly active cytochrome c nitrite reductase from the haloalkaliphilic sulfur-oxidizing non-ammonifying bacterium Tv. nitratireducens strain ALEN 2 (TvNiR) was isolated and purified to apparent electrophoretic homogeneity. The enzyme catalyzes reductive conversion of nitrite and hydroxylamine to ammonia without release of any intermediates, as well as reduction of sulfite to sulfide. TvNiR also possesses peroxidase activity. In solution TvNiR exists as a stable hexamer with molecular mass of about 360kDa. Each TvNiR subunit with molecular mass of 64kDa contains, as defined from spectral properties and sequence analysis, eight c-type haems. Seven of them are coordinated by the characteristic CXXCH motifs for haem c binding, while one is bonded by the unique CXXCK motif. So far, this motif coordinating the catalytic haem was found only in bacterial cytochrome c nitrite reductases (ccNiRs). All the residues essential for catalysis in the known ccNiRs were also identified in TvNiR. However, TvNiR is only distantly related to known bacterial ammonifying dissimilatory ccNiRs, sharing no more than 20% homology. 相似文献