全文获取类型
收费全文 | 5941篇 |
免费 | 577篇 |
国内免费 | 215篇 |
出版年
2024年 | 11篇 |
2023年 | 137篇 |
2022年 | 223篇 |
2021年 | 307篇 |
2020年 | 267篇 |
2019年 | 297篇 |
2018年 | 235篇 |
2017年 | 171篇 |
2016年 | 201篇 |
2015年 | 264篇 |
2014年 | 411篇 |
2013年 | 533篇 |
2012年 | 309篇 |
2011年 | 341篇 |
2010年 | 253篇 |
2009年 | 242篇 |
2008年 | 268篇 |
2007年 | 321篇 |
2006年 | 257篇 |
2005年 | 232篇 |
2004年 | 185篇 |
2003年 | 182篇 |
2002年 | 128篇 |
2001年 | 88篇 |
2000年 | 86篇 |
1999年 | 89篇 |
1998年 | 80篇 |
1997年 | 56篇 |
1996年 | 71篇 |
1995年 | 30篇 |
1994年 | 47篇 |
1993年 | 47篇 |
1992年 | 37篇 |
1991年 | 37篇 |
1990年 | 24篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 6篇 |
排序方式: 共有6733条查询结果,搜索用时 171 毫秒
921.
Hammel M Michel G Hoefer C Klaften M Müller-Höcker J de Angelis MH Holzinger A 《Biochemical and biophysical research communications》2007,359(4):947-951
Mutations in the human ABCA3 gene, encoding an ABC-transporter, are associated with respiratory failure in newborns and pediatric interstitial lung disease. In order to study disease mechanisms, a transgenic mouse model with a disrupted Abca3 gene was generated by targeting embryonic stem cells. While heterozygous animals developed normally and were fertile, individuals homozygous for the altered allele (Abca3-/-) died within one hour after birth from respiratory failure, ABCA3 protein being undetectable. Abca3-/- newborns showed atelectasis of the lung in comparison to a normal gas content in unaffected or heterozygous littermates. Electron microscopy demonstrated the absence of normal lamellar bodies in type II pneumocytes. Instead, condensed structures with apparent absence of lipid content were found. We conclude that ABCA3 is required for the formation of lamellar bodies and lung surfactant function. The phenotype of respiratory failure immediately after birth corresponds to the clinical course of severe ABCA3 mutations in human newborns. 相似文献
922.
Animal test systems are reviewed that have relevance to sudden infant death syndrome (SIDS) are reviewed. These test interactions between infectious agents (or their toxins) and products of cigarette smoke. Infectious agents implicated in SIDS include members of the enterobacteria and clostridia, Staphylococcus aureus and Streptococcus pyogenes. Smoking is thought to be the single most preventable cause of SIDS. Tobacco smoke contains many extremely toxic products including cyanide and nicotine. Many animal test systems are available to examine the potency of bacterial toxins and smoke-derived components. These include mice, hamsters, rats and chick embryos. Such systems reveal synergy between bacterial toxins, especially endotoxin and superantigens. They have also demonstrated potentiation of low levels of bacterial toxin by low levels of both nicotine and its primary metabolite, cotinine. These findings suggest a possible causal explanation for the fact that passive exposure to cigarette smoke is a risk factor in sudden infant death syndrome. 相似文献
923.
Nicola M. Sayers Barbara A. Crawley Kevin Humphries David B. Drucker Beryl A. Oppenheim Linda P. Hunt James A. Morris David R. Telford 《FEMS immunology and medical microbiology》1999,25(1-2):125-130
The aim of the study was to test the following hypotheses: (i) that endotoxin injected 40 min prior to death can be detected in rat organs post mortem and (ii) that endotoxin levels do not change with increasing time post mortem. Rats were injected with or without endotoxin in buffered saline, 40 min prior to being killed. Endotoxin levels in rat organs were assessed using a Limulus amoebocyte assay. The effect of storage time post mortem was assessed by following various storage regimes at 25 degrees C and 8 degrees C. Significant differences (P = < 0.001) in endotoxin levels of all samples tested were found between rats injected with and without endotoxin. A significant increase in detectable endotoxin was observed between 0 h and 6 h post mortem in rats injected with or without endotoxin. No difference in detectable endotoxin levels in the kidney, liver and spleen was observed from 30 h to 102 h post mortem in rats injected with or without endotoxin. In rats injected with endotoxin, detectable endotoxin levels in the heart were raised between 0 h and 6 h, 6 h and 54 h, and 30 h and 78 h. Endotoxin injected into rats 40 min prior to death can be detected post mortem. For rats injected with saline or endotoxin prior to death levels in the kidney, liver and spleen were not affected by storage at 8 degrees C for 30-102 h, after initial storage at room temperature for 6 h. Levels of endotoxin detected in the hearts of rats injected with saline were not affected by storage up to 102 h. In rats injected with endotoxin prior to death, detectable levels in the heart were significantly affected by increasing time in storage. 相似文献
924.
L.M. Harrison J.A. Morris D.R. Telford S.M. Brown K. Jones 《FEMS immunology and medical microbiology》1999,25(1-2):29-35
The aim of this study was to determine the prevalence of prone and supine sleeping in infants aged 0-12 months and relate this to changes in the number of cases of sudden infant death syndrome (SIDS) since 1985. Seventy-two babies, 38 male and 34 female, were followed for the first 18 months of life with regular home visits and sleeping position was recorded. In addition, data on the number of cases of SIDS in England and Wales between 1985 and 1995 were analysed. All babies slept supine for the first 5 months of life, but once they could turn over in their cots (mean age 7.34 months, range 5-11 months) the majority slept prone. By 11 months of age, 53 regularly slept prone (73%), 95% CI +/- 19.8%), while 11 slept supine, three adopted the side position and five varied from night to night. The number of cases of SIDS in infants aged 7-11 months has fallen significantly (P<0.0001) in a period in which the prevalence of prone sleeping, in that age group, has not changed. The most plausible explanation for this paradoxical result is that supine sleeping in the first 5 months of life reduces the absolute risk of SIDS in the second 6 months of life even though most babies are then sleeping prone. It is suggested that reduced exposure to nasopharyngeal bacterial superantigens in babies sleeping prone might explain this effect. 相似文献
925.
Toxigenic bacteria and sudden infant death syndrome (SIDS): nasopharyngeal flora during the first year of life 总被引:4,自引:0,他引:4
C.Caroline Blackwell Doris A.C. MacKenzie Valerie S. James Robert A. Elton Abdulaziz A. Zorgani Donald M. Weir Anthony Busuttil 《FEMS immunology and medical microbiology》1999,25(1-2):51-58
Many developmental and environmental risk factors for sudden infant death syndrome (SIDS) are similar to those for susceptibility to respiratory tract infection, and toxigenic bacteria have been implicated in some SIDS cases. We assessed nasopharyngeal flora of healthy infants in relation to risk factors to determine which species best lit the mathematical model proposed for the common bacterial toxin hypothesis and if these findings complemented results obtained from SIDS cases which occurred during the period of the survey. Longitudinal studies were carried out between April 1993 and March 1996 on 253 healthy infants and their mothers. 150 from a multiply deprived area, 103 from an affluent area. Concurrent SIDS infants (37) were screened for nasopharyngeal flora. Among healthy infants < or = 3 months of age, the predominant isolate was Staphylococcus aureus 57% compared with 86% for SIDS infants in that age range (P< 0.02). There were significant associations between isolation of different species from both mother and baby but no association between isolation of any species with: area of residence: parental smoking habits; breast or bottle feeding; symptoms of viral infection: seasonality. We conclude that S. aureus fits the mathematical model for SIDS. Both staphylococci and/or their toxins were identified in a significant proportion of SIDS cases. Isolation of staphylococci from healthy infants was associated with the 2-4-month age range, a risk factor consistently found in all epidemiological studies of SIDS. This might reflect the developmental stage in which 80-90% of infants express the Lewis(a) antigen which we have shown to be one of the receptors for S. aureus. 相似文献
926.
YANG Shou-Jing LIU Pan-Fang LIU Ying-Ying YAN Pei-Song XU Zhi-Kai LIU Hou-Cai 《中国病毒学》1993,8(3):243-256
927.
P. Stušek K. Hamdorf 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(1):99-106
Regulation of light flux by pupil mechanisms in the UV-sensitive superposition eye of owl-fly Ascalaphus macaronius (Neuroptera) was studied with a fast reflection microspectrophotometric technique. The spectral sensitivity of pupil reaction,
which was calculated on the basis of changes of transient amplitude reflection, was almost identical with the one of Deilephila eye. This indicates that in spite of different life styles and spectral sensitivities of photoreceptors, pupil closing is
triggered by the same photosensitive structure in both eyes. By measuring the spectra of reflected light from the Ascalaphus eye between 400 and 700 nm after different dark periods following light stimulation, it was established that the restoration
of reflection was much faster in the red than in the blue spectral range. Based on this, we propose that two different pupil
mechanisms with different spectral absorption characteristics are involved in light-flux regulation. Fast-reacting pupil is
probably represented by screening pigment migration in the secondary pigment cells and a slow blue-absorbing system by the
activity in primary pigment cells. The importance of two different pupils for the photoregeneration of visual pigment is discussed.
Accepted: 1 October 1998 相似文献
928.
实验性脾虚证大鼠内分泌腺形态学与细胞化学研究 总被引:3,自引:0,他引:3
成年Wistar大鼠20只,分对照组和实验组。实验组用大黄煎剂灌服42天致实验性脾虚证。对两组睾丸,肾上腺和甲状腺进行常规形态学与细胞化学观察。形态学显示:睾丸,肾上腺和甲状腺的组织和细胞均有不同程度的损伤。细胞化学显示:各内分泌腺均表现酸性磷酸酶(ACP)减弱,个别内分泌腺细胞显示琥珀酸脱氢酶(SDH),三磷酸腺苷酶(ATPase)和PAS反应的变化。结果证明脾虚证不仅消化系统功能低下,而且内分泌功能也受到了影响 相似文献
929.
分别采用标准法、GP法和MBP法抽提汉滩病毒RNA,结合套式PCR比较这三种方法的敏感性。结果表明,所用引物对这两株病毒具有相同的特异性。这三种提取RNA的敏感性差异不大,敏感性从高到低依次为:GP、MBP和标准法,检测汉滩病毒的效价分别为0.01、0.01和0.1TCID50/200μl;提取RNA的时间长短分别为:标准法为2.5h,GP为1h,MBP为0.5h,可见MBP用时最少。使用GP和MBP提取RNA时,可以在室温下进行,不需要低温离心。所以,MBP最适合于实验室和临床病原体的快速检测,特别是对采集的环境样品的快速检测 相似文献
930.
Recently there has been an increase in the number of cases reported of Guillain-Barré syndrome (GBS) developed after Campylobacter jejuni infection. To investigate the role of a C.jejuni GroEL-type heat-shock protein (CjHsp60) in the infection and induction of GBS, we examined the antibody level against CjHsp60 in 27 human sera, including GBS and non-GBS patients, by an enzyme-linked immunosorbent assay. Sera from patients with C. jejuni infection, despite the development of GBS, had a higher titer of anti-CjHsp60 antibody than those of patients without the infection and healthy control subjects. The patients with C. jejuni infection followed by GBS had slightly higher levels of this antibody than did the patients with infection who did not develop GBS, but there was no statistical significance. In conclusion, CjHsp60 is found to be one of the major immunogenic antigens in actual C. jejuni infection, but no evidence that supports the direct relationship between this protein and C. jejuni-associated GBS was found in this study. 相似文献