全文获取类型
收费全文 | 2572篇 |
免费 | 223篇 |
出版年
2023年 | 6篇 |
2022年 | 20篇 |
2021年 | 43篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 79篇 |
2015年 | 110篇 |
2014年 | 146篇 |
2013年 | 176篇 |
2012年 | 217篇 |
2011年 | 208篇 |
2010年 | 150篇 |
2009年 | 106篇 |
2008年 | 183篇 |
2007年 | 150篇 |
2006年 | 155篇 |
2005年 | 138篇 |
2004年 | 110篇 |
2003年 | 102篇 |
2002年 | 104篇 |
2001年 | 29篇 |
2000年 | 31篇 |
1999年 | 29篇 |
1998年 | 33篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有2795条查询结果,搜索用时 15 毫秒
61.
Background
A substantial increase in transportation of goods on railway may be hindered by public fear of increased vibration and noise leading to annoyance and sleep disturbance. As the majority of freight trains run during night time, the impact upon sleep is expected to be the most serious adverse effect. The impact of nocturnal vibration on sleep is an area currently lacking in knowledge. We experimentally investigated sleep disturbance with the aim to ascertain the impact of increasing vibration amplitude.Methodology/Principal Findings
The impacts of various amplitudes of horizontal vibrations on sleep disturbance and heart rate were investigated in a laboratory study. Cardiac accelerations were assessed using a combination of polysomnography and ECG recordings. Sleep was assessed subjectively using questionnaires. Twelve young, healthy subjects slept for six nights in the sleep laboratory, with one habituation night, one control night and four nights with a variation of vibration exposures whilst maintaining the same noise exposure. With increasing vibration amplitude, we found a decrease in latency and increase in amplitude of heart rate as well as a reduction in sleep quality and increase in sleep disturbance.Conclusions/Significance
We concluded that nocturnal vibration has a negative impact on sleep and that the impact increases with greater vibration amplitude. Sleep disturbance has short- and long-term health consequences. Therefore, it is necessary to define levels that protect residents against sleep disruptive vibrations that may arise from night time railway freight traffic. 相似文献62.
Vera Jankowski Markus T?lle Thi Nguyet Anh Tran Markus van der Giet Mirjam Schuchardt Kerstin Lehmann Doreen Janke Burkhard Flick Alberto Arduan Ortiz Ni?o Maria Dolores Sanchez Martin Tepel Walter Zidek Joachim Jankowski 《PloS one》2013,8(7)
The secretion of angiogenic factors by vascular endothelial cells is one of the key mechanisms of angiogenesis. Here we report on the isolation of a new potent angiogenic factor, diuridine tetraphosphate (Up4U) from the secretome of human endothelial cells. The angiogenic effect of the endothelial secretome was partially reduced after incubation with alkaline phosphatase and abolished in the presence of suramin. In one fraction, purified to homogeneity by reversed phase and affinity chromatography, Up4U was identified by MALDI-LIFT-fragment-mass-spectrometry, enzymatic cleavage analysis and retention-time comparison. Beside a strong angiogenic effect on the yolk sac membrane and the developing rat embryo itself, Up4U increased the proliferation rate of endothelial cells and, in the presence of PDGF, of vascular smooth muscle cells. Up4U stimulated the migration rate of endothelial cells via P2Y2-receptors, increased the ability of endothelial cells to form capillary-like tubes and acts as a potent inducer of sprouting angiogenesis originating from gel-embedded EC spheroids. Endothelial cells released Up4U after stimulation with shear stress. Mean total plasma Up4U concentrations of healthy subjects (N = 6) were sufficient to induce angiogenic and proliferative effects (1.34±0.26 nmol L-1). In conclusion, Up4U is a novel strong human endothelium-derived angiogenic factor. 相似文献
63.
Maria Keller Xuanshi Liu Tobias Wohland Kerstin Rohde Marie-Therese Gast Michael Stumvoll Peter Kovacs Anke T?njes Yvonne B?ttcher 《PloS one》2013,8(12)
Background
Genetic variants within the bitter taste receptor gene TAS2R38 are associated with sensitivity to bitter taste and are related to eating behavior in the Amish population. Sensitivity to bitter taste is further related to anthropometric traits in an genetically isolated Italian population. We tested whether the TAS2R38 variants (rs713598; rs1726866 and rs10246939) may be related to eating behavior, anthropometric parameters, metabolic traits and consumer goods intake in the German Sorbs.Materials and Methods
The three SNPs were genotyped in a total cohort of 1007 individuals (male/female: 405/602). The German version of the three-factor eating questionnaire was completed by 548 individuals. Genetic association analyses for smoking behavior, alcohol and coffee intake, eating behavior factors (restraint, disinhibition and hunger) and other metabolic traits were analyzed. Further, by combining the three SNPs we applied comparative haplotype analyses categorizing PAV (proline-alanine-valine) carriers (tasters) vs. homozygous AVI (alanin-valine-isoleucine) carriers (non-tasters).Results
Significant associations of genetic variants within TAS2R38 were identified with percentage of body fat, which were driven by associations in women. In men, we observed significant associations with 30 min plasma glucose, and area under the curve for plasma glucose (0–120 min) (all adjusted P≤0.05). Further, we found that carriers of at least one PAV allele show significantly lower cigarette smoking per day (P = 0.002) as well as, albeit non-significant, lower alcohol intake. We did not confirm previously reported associations between genetic variants of TAS2R38 and eating behavior.Conclusion
Our data suggest that genetic variation in TAS2R38 is related to individual body composition measures and may further influence consumer goods intake in the Sorbs possibly via individual sensitivity to bitter taste. 相似文献64.
Laura David Peter Schwan Martin Lobedann Sven-Oliver Borchert Bastian Budde Maike Temming Mike Kuerschner Francisca Maria Alberti Aguilo Kerstin Baumarth Tobias Thüte Benjamin Maiser Andreas Blank Viktorija Kistler Nils Weber Heiko Brandt Martin Poggel Klaus Kaiser Karl Geisen Felix Oehme Gerhard Schembecker 《Biotechnology and bioengineering》2020,117(4):1024-1036
Continuous processing is the future production method for monoclonal antibodies (mAbs). A fully continuous, fully automated downstream process based on disposable equipment was developed and implemented inside the MoBiDiK pilot plant. However, a study evaluating the comparability between batch and continuous processing based on product quality attributes was not conducted before. The work presented fills this gap comparing both process modes experimentally by purifying the same harvest material (side-by-side comparability). Samples were drawn at different time points and positions in the process for batch and continuous mode. Product quality attributes, product-related impurities, as well as process-related impurities were determined. The resulting polished material was processed to drug substance and further evaluated regarding storage stability and degradation behavior. The in-process control data from the continuous process showed the high degree of accuracy in providing relevant process parameters such as pH, conductivity, and protein concentration during the entire process duration. Minor differences between batch and continuous samples are expected as different processing conditions are unavoidable due to the different nature of batch and continuous processing. All tests revealed no significant differences in the intermediates and comparability in the drug substance between the samples of both process modes. The stability study of the final product also showed no differences in the stability profile during storage and forced degradation. Finally, online data analysis is presented as a powerful tool for online-monitoring of chromatography columns during continuous processing. 相似文献
65.
66.
Marc Faget Kerstin A. Nagel Achim Walter Juan M. Herrera Siegfried Jahnke Ulrich Schurr Vicky M. Temperton 《Annals of botany》2013,112(2):253-266
Background
There is a large body of literature on competitive interactions among plants, but many studies have only focused on above-ground interactions and little is known about root–root dynamics between interacting plants. The perspective on possible mechanisms that explain the outcome of root–root interactions has recently been extended to include non-resource-driven mechanisms (as well as resource-driven mechanisms) of root competition and positive interactions such as facilitation. These approaches have often suffered from being static, partly due to the lack of appropriate methodologies for in-situ non-destructive root characterization.Scope
Recent studies show that interactive effects of plant neighbourhood interactions follow non-linear and non-additive paths that are hard to explain. Common outcomes such as accumulation of roots mainly in the topsoil cannot be explained solely by competition theory but require a more inclusive theoretical, as well as an improved methodological framework. This will include the question of whether we can apply the same conceptual framework to crop versus natural species.Conclusions
The development of non-invasive methods to dynamically study root–root interactions in vivo will provide the necessary tools to study a more inclusive conceptual framework for root–root interactions. By following the dynamics of root–root interactions through time in a whole range of scenarios and systems, using a wide variety of non-invasive methods, (such as fluorescent protein which now allows us to separately identify the roots of several individuals within soil), we will be much better equipped to answer some of the key questions in root physiology, ecology and agronomy. 相似文献67.
Density Functional Theory (DFT) calculations using gaussian 98 have been performed on hydrogen adsorbed on clusters representing the (110) and (111) surfaces of Cu. Clusters were constructed to model different adsorption sites, and at least two different size clusters were used for each site. On the (111) surface, hydrogen prefers to adsorb in a hollow site, though with the hcp variant being favoured by the adsorption energy, and the fcc alternative by the vibrational frequencies. On the (110) surface, the "fcc" site on a (1 2 2) reconstructed surface is preferred. 相似文献
68.
Min Xie Khyra Sarah Utzinger Kerstin Blickenstorfer 《Chronobiology international》2013,30(10):1375-1384
ABSTRACTCircadian and circannual rhythms influence not only the environment, but also human physiology. In times of increasing numbers of couples struggling with infertility, and thus increasing demand for successful assisted reproduction, the aim of our study was to evaluate circadian and circannual rhythms and their association with semen quality. A total of 12 245 semen samples from 7068 men, collected at the andrology laboratory of the Department of Reproductive Endocrinology, University Hospital Zurich, between 1994 and 2015, were uniformly analysed in terms of sperm concentration, total sperm count, progressive motility and normal morphology. On the basis of these four parameters, we retrospectively examined the circadian and circannual changes of semen quality. The Mann–Whitney U test and multiple linear regression analysis were used for the statistical evaluation. The semen samples collected in the early morning before 7:30 a.m. showed the highest levels in sperm concentration, total sperm count and normal morphology, all with statistical significance. Progressive motility did not show any significant alterations based on circadian rhythm. Furthermore, a significant increase in sperm concentration and total sperm count was found in spring, with significant decreases in the summer. The highest percentage of normal morphology was found in summer. For progressive motility, no significant seasonal variation could be demonstrated. Male semen quality varies with both circadian and circannual rhythms. Collection of semen in the early morning, where semen quality was highest, can be used to improve natural fertility as well as fertility resulting from assisted reproduction. 相似文献
69.
Kerstin Vocke Kristin Dauner Anne Hahn Anne Ulbrich Jana Broecker Sandro Keller Stephan Frings Frank M?hrlen 《The Journal of general physiology》2013,142(4):381-404
Calcium-dependent chloride channels serve critical functions in diverse biological systems. Driven by cellular calcium signals, the channels codetermine excitatory processes and promote solute transport. The anoctamin (ANO) family of membrane proteins encodes three calcium-activated chloride channels, named ANO 1 (also TMEM16A), ANO 2 (also TMEM16B), and ANO 6 (also TMEM16F). Here we examined how ANO 1 and ANO 2 interact with Ca2+/calmodulin using nonstationary current analysis during channel activation. We identified a putative calmodulin-binding domain in the N-terminal region of the channel proteins that is involved in channel activation. Binding studies with peptides indicated that this domain, a regulatory calmodulin-binding motif (RCBM), provides two distinct modes of interaction with Ca2+/calmodulin, one at submicromolar Ca2+ concentrations and one in the micromolar Ca2+ range. Functional, structural, and pharmacological data support the concept that calmodulin serves as a calcium sensor that is stably associated with the RCBM domain and regulates the activation of ANO 1 and ANO 2 channels. Moreover, the predominant splice variant of ANO 2 in the brain exhibits Ca2+/calmodulin-dependent inactivation, a loss of channel activity within 30 s. This property may curtail ANO 2 activity during persistent Ca2+ signals in neurons. Mutagenesis data indicated that the RCBM domain is also involved in ANO 2 inactivation, and that inactivation is suppressed in the retinal ANO 2 splice variant. These results advance the understanding of Ca2+ regulation in anoctamin Cl− channels and its significance for the physiological function that anoctamin channels subserve in neurons and other cell types. 相似文献
70.