全文获取类型
收费全文 | 1345篇 |
免费 | 103篇 |
出版年
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 21篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 20篇 |
2016年 | 30篇 |
2015年 | 54篇 |
2014年 | 62篇 |
2013年 | 66篇 |
2012年 | 102篇 |
2011年 | 109篇 |
2010年 | 63篇 |
2009年 | 46篇 |
2008年 | 76篇 |
2007年 | 93篇 |
2006年 | 75篇 |
2005年 | 70篇 |
2004年 | 55篇 |
2003年 | 62篇 |
2002年 | 63篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 21篇 |
1998年 | 28篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 24篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1448条查询结果,搜索用时 15 毫秒
41.
42.
Elmar Porten Beate Seliger Verena A. Schneider Stefan W?ll Daniela Stangel Rene Ramseger Stephan Kr?ger 《The Journal of biological chemistry》2010,285(5):3114-3125
Clustering or overexpression of the transmembrane form of the extracellular matrix proteoglycan agrin in neurons results in the formation of numerous highly motile filopodia-like processes extending from axons and dendrites. Here we show that similar processes can be induced by overexpression of transmembrane-agrin in several non-neuronal cell lines. Mapping of the process-inducing activity in neurons and non-neuronal cells demonstrates that the cytoplasmic part of transmembrane agrin is dispensable and that the extracellular region is necessary for process formation. Site-directed mutagenesis reveals an essential role for the loop between β-sheets 3 and 4 within the Kazal subdomain of the seventh follistatin-like domain of TM-agrin. An aspartic acid residue within this loop is critical for process formation. The seventh follistatin-like domain could be functionally replaced by the first and sixth but not by the eighth follistatin-like domain, demonstrating a functional redundancy among some follistatin-like domains of agrin. Moreover, a critical distance of the seventh follistatin-like domain to the plasma membrane appears to be required for process formation. These results demonstrate that different regions within the agrin protein are responsible for synapse formation at the neuromuscular junction and for process formation in central nervous system neurons and suggest a role for agrin''s follistatin-like domains in the developing central nervous system. 相似文献
43.
Josephine Joy Hubloher Sabine Zeidler Pedro Lamosa Helena Santos Beate Averhoff Volker Müller 《Environmental microbiology》2020,22(12):5156-5166
The stress protectant trehalose is synthesized in Acinetobacter baumannii from UPD-glucose and glucose-6-phosphase via the OtsA/OtsB pathway. Previous studies proved that deletion of otsB led to a decreased virulence, the inability to grow at 45°C and a slight reduction of growth at high salinities indicating that trehalose is the cause of these phenotypes. We have questioned this conclusion by producing ∆otsA and ∆otsBA mutants and studying their phenotypes. Only deletion of otsB, but not deletion of otsA or otsBA, led to growth impairments at high salt and high temperature. The intracellular concentrations of trehalose and trehalose-6-phosphate were measured by NMR or enzymatic assay. Interestingly, none of the mutants accumulated trehalose any more but the ∆otsB mutant with its defect in trehalose-6-phosphate phosphatase activity accumulated trehalose-6-phosphate. Moreover, expression of otsA in a ∆otsB background under conditions where trehalose synthesis is not induced led to growth inhibition and the accumulation of trehalose-6-phosphate. Our results demonstrate that trehalose-6-phosphate affects multiple physiological activities in A. baumannii ATCC 19606. 相似文献
44.
Laurence Cousseau Martijn Hammers Dries Van de Loock Beate Apfelbeck Mwangi Githiru Erik Matthysen Luc Lens 《Proceedings. Biological sciences / The Royal Society》2020,287(1941)
It remains poorly understood how effects of anthropogenic activity, such as large-scale habitat fragmentation, impact sociality in animals. In cooperatively breeding species, groups are mostly formed through delayed offspring dispersal, and habitat fragmentation can affect this process in two opposite directions. Increased habitat isolation may increase dispersal costs, promoting delayed dispersal. Alternatively, reduced patch size and quality may decrease benefits of philopatry, promoting dispersal. Here, we test both predictions in a cooperatively breeding bird (placid greenbul, Phyllastrephus placidus) from an Afrotropical cloud forest archipelago. Males born in fragmented forest dispersed about 1 year earlier than those born in continuous forest. Contrary to females, males also started to reproduce earlier and mostly settled within their natal patch. Females only rarely delayed their dispersal for more than 1 year, both in fragmented and continuous forests. Our results suggest that early male dispersal and reproduction is jointly driven by a decrease in the value of the natal territory and an increase in local breeding opportunities in fragmented forest. While plasticity in dispersal strategies of cooperative breeders in response to anthropogenic change is believed to optimize reproduction-survival trade-offs, to what extent it shapes the ability of species to respond to rapid environmental change remains to be studied. 相似文献
45.
Averhoff Beate Kirchner Lennart Pfefferle Katharina Yaman Deniz 《Extremophiles : life under extreme conditions》2021,25(5-6):425-436
Extremophiles - Extremophilic prokaryotes live under harsh environmental conditions which require far-reaching cellular adaptations. The acquisition of novel genetic information via natural... 相似文献
46.
Ilan Kurz Lars Oddsson Itshak Melzer 《Journal of electromyography and kinesiology》2013,23(4):814-819
ObjectiveOlder adults who have recently fallen demonstrate increased postural sway compared with non-fallers. However, the differences in postural control between older adults who were seriously injured (SI) as a result of a fall, compared with those who fell but were not injured (NSI) and non-fallers (NFs), has not been investigated. The objective of the present study was to investigate the underlying postural control mechanisms related to injuries resulting from a fall.MethodsBoth traditional postural sway measures of foot center-of-pressure (CoP) displacements and fractal measures, the Stabilogram-Diffusion Analysis (SDA), were used to characterize the postural control. One hundred older adults aged 65–91 years were tested during narrow base upright stance in eyes closed condition; falls were monitored over a 1-year period.ResultsForty-nine older adults fell during the 1-year follow-up, 13 were seriously injured as a result of a fall (SI), 36 were not injured (NSI), and 49 were non-fallers (NFs); two passed away. The SDA showed significantly higher short-term diffusion coefficients and critical displacements in SI in the anterior–posterior direction compared with both NSI and NF. However, in the medio-lateral direction there were no statistically significant differences between groups. For the traditional measures of sway, the average anterior–posterior CoP range was also larger in SI individuals.ConclusionsThis work suggests that older fallers with a deterioration of anterior–posterior postural control may be at higher risk of serious injury following fall events. 相似文献
47.
Nicole Wüppenhorst Friederike von Loewenich Beate Hobmaier Marianne Vetter‐Knoll Sona Mohadjer Manfred Kist 《Helicobacter》2013,18(1):1-5
Helicobacter felis belongs to the fastidious gastric non‐Helicobacter pylori helicobacter species that are typically found in the stomach of cats and dogs. These bacteria have the potential to colonize the human stomach and are then associated with gastritis, gastroduodenal ulcers, and MALT lymphoma. Strains cultured from the human stomach are rare. Here, we present the first isolation of H. felis from a gastric biopsy specimen of a 14‐year‐old girl who presented with persistent epigastric pain. The strain was cultured using our routine protocol for H. pylori and identified by phylogenetic analyses of partial urease AB and gyrB gene sequences. 相似文献
48.
49.
Beate Wieseler Natalia Wolfram Natalie McGauran Michaela F. Kerekes Volker Verv?lgyi Petra Kohlepp Marloes Kamphuis Ulrich Grouven 《PLoS medicine》2013,10(10)
Background
Access to unpublished clinical study reports (CSRs) is currently being discussed as a means to allow unbiased evaluation of clinical research. The Institute for Quality and Efficiency in Health Care (IQWiG) routinely requests CSRs from manufacturers for its drug assessments.Our objective was to determine the information gain from CSRs compared to publicly available sources (journal publications and registry reports) for patient-relevant outcomes included in IQWiG health technology assessments (HTAs) of drugs.Methods and Findings
We used a sample of 101 trials with full CSRs received for 16 HTAs of drugs completed by IQWiG between 15 January 2006 and 14 February 2011, and analyzed the CSRs and the publicly available sources of these trials. For each document type we assessed the completeness of information on all patient-relevant outcomes included in the HTAs (benefit outcomes, e.g., mortality, symptoms, and health-related quality of life; harm outcomes, e.g., adverse events). We dichotomized the outcomes as “completely reported” or “incompletely reported.” For each document type, we calculated the proportion of outcomes with complete information per outcome category and overall.We analyzed 101 trials with CSRs; 86 had at least one publicly available source, 65 at least one journal publication, and 50 a registry report. The trials included 1,080 patient-relevant outcomes. The CSRs provided complete information on a considerably higher proportion of outcomes (86%) than the combined publicly available sources (39%). With the exception of health-related quality of life (57%), CSRs provided complete information on 78% to 100% of the various benefit outcomes (combined publicly available sources: 20% to 53%). CSRs also provided considerably more information on harms. The differences in completeness of information for patient-relevant outcomes between CSRs and journal publications or registry reports (or a combination of both) were statistically significant for all types of outcomes.The main limitation of our study is that our sample is not representative because only CSRs provided voluntarily by pharmaceutical companies upon request could be assessed. In addition, the sample covered only a limited number of therapeutic areas and was restricted to randomized controlled trials investigating drugs.Conclusions
In contrast to CSRs, publicly available sources provide insufficient information on patient-relevant outcomes of clinical trials. CSRs should therefore be made publicly available. Please see later in the article for the Editors'' Summary 相似文献50.