全文获取类型
收费全文 | 507篇 |
免费 | 38篇 |
专业分类
545篇 |
出版年
2020年 | 6篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 19篇 |
2013年 | 12篇 |
2012年 | 23篇 |
2011年 | 29篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 14篇 |
2004年 | 7篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1997年 | 12篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1977年 | 7篇 |
1975年 | 11篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 9篇 |
1971年 | 7篇 |
1970年 | 4篇 |
1969年 | 7篇 |
1968年 | 4篇 |
1967年 | 7篇 |
1965年 | 5篇 |
1964年 | 4篇 |
1953年 | 5篇 |
排序方式: 共有545条查询结果,搜索用时 15 毫秒
111.
Primordial germ cells in the mouse embryo during gastrulation 总被引:45,自引:0,他引:45
With the aid of a whole-mount technique, we have detected a small cluster of alkaline phosphatase (ALP)-positive cells in whole mounts of mid-primitive-streak-stage embryos, 7-7 1/4 days post coitum (dpc). Within the cluster, about 8 cells contain a small cytoplasmic spot, intensely stained for ALP activity and possibly associated with an active Golgi complex. The cluster lies just posterior to the definitive primitive streak in the extraembryonic mesoderm, separated from the embryo by the amniotic fold. Towards the end of gastrulation, the number of cells containing the ALP-positive spot rises to between 50 and 80. Thereafter the number of cells in the extraembryonic cluster declines, and similar cells start to be seen in the mesoderm of the primitive streak and then in the endoderm. At 8 dpc, about 125 ALP-stained cells are found, mainly in the hindgut endoderm and also at the base of the allantois, their appearance and location at this stage agreeing closely with previous reports on primordial germ cells (PGCs). Embryos from which the cluster area has been removed at the 7-day stage are devoid of PGCs after culture for 48 h, whereas the excised tissue is rich in PGCs. We argue that the cells in the cluster are indeed primordial germ cells, at a stage significantly earlier than any reported previously. This would indicate that the PGC lineage in the mouse is set aside at least as early as 7 dpc, possibly as one of the first 'mesodermal' cell types to emerge, and that its differentiation, as expressed by ALP activity, is gradual. 相似文献
112.
This study was carried out to investigate the nature of the immunological responses which took place in a child who had recently recovered from toxocariasis. She had developed a marked eosinophilia and had high titers of toxocara antibodies. Experiments were performed to examine whether Toxocara canis infective larvae could be killed in the presence of her serum and human eosinophils. Eosinophils with human complement, or this patient's serum, adhered to the surface of the larvae within 10 min. By 40 min, using both light and electron microscopy, it was shown that the cells had flattened against the cuticle and degranulated. However, by 3 hr, eosinophils had begun to detach, and the larvae remained alive for at least 1 week afterward. Further addition of serum or of eosinophils, which were shown to be able to immobilize T. spiralis infective larvae, failed to kill the T. canis larvae. It was concluded that, in this patient, the development of an inflammatory response to a T. canis infection was not associated with the appearance of antibodies capable of inducing eosinophil dependent toxicity to the larvae in vitro. Eosinophil dependent killing mechanisms may be less important than other components of the immune response, in immunity to this parasite in humans. 相似文献
113.
Donald G. McLaren Kristopher J. Kosmatka Erik K. Kastman Barbara B. Bendlin Sterling C. Johnson 《Methods (San Diego, Calif.)》2010,50(3):157-165
Voxel-based morphometry studies have become increasingly common in human neuroimaging over the past several years; however, few studies have utilized this method to study morphometry changes in non-human primates. Here we describe the application of voxel-wise morphometry methods to the rhesus macaque (Macaca mulatta) using the 112RM-SL template and priors (McLaren et al. (2009) [42]) and as an illustrative example we describe age-associated changes in grey matter morphometry. Specifically, we evaluated the unified segmentation routine implemented using Statistical Parametric Mapping (SPM) software and the FMRIB’s Automated Segmentation Tool (FAST) in the FMRIB Software Library (FSL); the effect of varying the smoothing kernel; and the effect of the normalization routine. We found that when studying non-human primates, brain images need less smoothing than in human studies, 2–4 mm FWHM. Using flow field deformations (DARTEL) improved inter-subject alignment leading to results that were more likely due to morphometry differences as opposed to registration differences. 相似文献
114.
Rathie Rajendram Richard WJ Lee Mike J Potts Geoff E Rose Rajni Jain Jane M Olver Fion Bremner Steven Hurel Anne Cook Rao Gattamaneni Marjorie Tomlinson Nicholas Plowman Catey Bunce Sandra P Hollinghurst Laura Kingston Sue Jackson Andrew D Dick Nichola Rumsey Olivia C Morris Colin M Dayan Jimmy M Uddin 《Trials》2008,9(1):1-17
Background
Intravenous recombinant tissue plasminogen activator (rt-PA) is approved for use in selected patients with ischaemic stroke within 3 hours of symptom onset. IST-3 seeks to determine whether a wider range of patients may benefit.Design
International, multi-centre, prospective, randomized, open, blinded endpoint (PROBE) trial of intravenous rt-PA in acute ischaemic stroke. Suitable patients must be assessed and able to start treatment within 6 hours of developing symptoms, and brain imaging must have excluded intracerebral haemorrhage. With 1000 patients, the trial can detect a 7% absolute difference in the primary outcome. With3500 patients, it can detect a 4.0% absolute benefit & with 6000, (mostly treated between 3 & 6 hours), it can detect a 3% benefit.Trial procedures
Patients are entered into the trial by telephoning a fast, secure computerised central randomisation system or via a secure web interface. Repeat brain imaging must be performed at 24–48 hours. The scans are reviewed 'blind' by expert readers. The primary measure of outcome is the proportion of patients alive and independent (Modified Rankin 0–2) at six months (assessed via a postal questionnaire mailed directly to the patient). Secondary outcomes include: events within 7 days (death, recurrent stroke, symptomatic intracranial haemorrhage), outcome at six months (death, functional status, EuroQol).Trial registration
ISRCTN25765518 相似文献115.
116.
117.
118.
119.
120.
Sarita AY Hartgring Cynthia R Willis Johannes WJ Bijlsma Floris PJG Lafeber Joel AG van Roon 《Arthritis research & therapy》2012,14(3):R137