全文获取类型
收费全文 | 5369篇 |
免费 | 468篇 |
国内免费 | 1篇 |
出版年
2023年 | 42篇 |
2022年 | 43篇 |
2021年 | 172篇 |
2020年 | 153篇 |
2019年 | 158篇 |
2018年 | 167篇 |
2017年 | 169篇 |
2016年 | 200篇 |
2015年 | 308篇 |
2014年 | 337篇 |
2013年 | 401篇 |
2012年 | 448篇 |
2011年 | 390篇 |
2010年 | 314篇 |
2009年 | 238篇 |
2008年 | 246篇 |
2007年 | 231篇 |
2006年 | 198篇 |
2005年 | 171篇 |
2004年 | 146篇 |
2003年 | 140篇 |
2002年 | 107篇 |
2001年 | 65篇 |
2000年 | 75篇 |
1999年 | 41篇 |
1998年 | 32篇 |
1997年 | 35篇 |
1996年 | 36篇 |
1995年 | 29篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 47篇 |
1991年 | 29篇 |
1990年 | 37篇 |
1989年 | 31篇 |
1988年 | 22篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 25篇 |
1978年 | 18篇 |
1977年 | 26篇 |
1975年 | 21篇 |
1974年 | 17篇 |
1972年 | 16篇 |
排序方式: 共有5838条查询结果,搜索用时 15 毫秒
1.
2.
Marika T. Leving Riemer J. K. Vegter Johanneke Hartog Claudine J. C. Lamoth Sonja de Groot Lucas H. V. van der Woude 《PloS one》2015,10(5)
BackgroundIt has been suggested that a higher intra-individual variability benefits the motor learning of wheelchair propulsion. The present study evaluated whether feedback-induced variability on wheelchair propulsion technique variables would also enhance the motor learning process. Learning was operationalized as an improvement in mechanical efficiency and propulsion technique, which are thought to be closely related during the learning process.Methods17 Participants received visual feedback-based practice (feedback group) and 15 participants received regular practice (natural learning group). Both groups received equal practice dose of 80 min, over 3 weeks, at 0.24 W/kg at a treadmill speed of 1.11 m/s. To compare both groups the pre- and post-test were performed without feedback. The feedback group received real-time visual feedback on seven propulsion variables with instruction to manipulate the presented variable to achieve the highest possible variability (1st 4-min block) and optimize it in the prescribed direction (2nd 4-min block). To increase motor exploration the participants were unaware of the exact variable they received feedback on. Energy consumption and the propulsion technique variables with their respective coefficient of variation were calculated to evaluate the amount of intra-individual variability.ResultsThe feedback group, which practiced with higher intra-individual variability, improved the propulsion technique between pre- and post-test to the same extent as the natural learning group. Mechanical efficiency improved between pre- and post-test in the natural learning group but remained unchanged in the feedback group.ConclusionThese results suggest that feedback-induced variability inhibited the improvement in mechanical efficiency. Moreover, since both groups improved propulsion technique but only the natural learning group improved mechanical efficiency, it can be concluded that the improvement in mechanical efficiency and propulsion technique do not always appear simultaneously during the motor learning process. Their relationship is most likely modified by other factors such as the amount of the intra-individual variability. 相似文献
3.
Maria Fernanda Forni Aline Ramos Maia Lobba Alexandre Hamilton Pereira Ferreira Mari Cleide Sogayar 《PloS one》2015,10(10)
The skin is a rich source of readily accessible stem cells. The level of plasticity afforded by these cells is becoming increasingly important as the potential of stem cells in Cell Therapy and Regenerative Medicine continues to be explored. Several protocols described single type stem cell isolation from skin; however, none of them afforded simultaneous isolation of more than one population. Herein, we describe the simultaneous isolation and characterization of three stem cell populations from the dermis and epidermis of murine skin, namely Epidermal Stem Cells (EpiSCs), Skin-derived Precursors (SKPs) and Mesenchymal Stem Cells (MSCs). The simultaneous isolation was possible through a simple protocol based on culture selection techniques. These cell populations are shown to be capable of generating chondrocytes, adipocytes, osteocytes, terminally differentiated keratinocytes, neurons and glia, rendering this protocol suitable for the isolation of cells for tissue replenishment and cell based therapies. The advantages of this procedure are far-reaching since the skin is not only the largest organ in the body, but also provides an easily accessible source of stem cells for autologous graft. 相似文献
4.
5.
6.
The molecular basis of potassium nutrition in plants 总被引:4,自引:0,他引:4
Christina J. Smart David F. Garvin James P. Prince William J. Lucas Leon V. Kochian 《Plant and Soil》1996,187(1):81-89
Over the last five years, the cloning and characterization of K+ transport genes corresponding to K+ channels (KAT1, AKT1, KST1, AKT2), associated subunits (KAB1) and a high-affinity transporter (HKT1) has opened up important new avenues for research on plant K+ nutrition. With the abundance of molecular data now available it seems timely to link this information with the wealth of data previously accumulated on the physiology of plant K+ acquisition. The ultimate goal of all this research is to gain a better understanding of K+ transport and nutrition in the intact plant. Thus it is important to begin to integrate the molecular research with results from biochemical and physiological research conducted at the cellular, root and whole plant levels. This article will focus on describing the features of the cloned K+ transporters and their possible roles in mediating high- and low-affinity K+ uptake from the soil, as well as how K+ acquisition may be regulated.Abbreviations NEM
N-ethyl maleimide
- PCMBS
p-chloromercuribenzene sulphonic acid 相似文献
7.
Rafael Ricci-Azevedo Aline Ferreira Oliveira Marina C. A. V. Conrado Fernanda Caroline Carvalho Maria Cristina Roque-Barreira 《PLoS neglected tropical diseases》2016,10(4)
ArtinM, a D-mannose binding lectin from Artocarpus heterophyllus, has immunomodulatory activities through its interaction with N-glycans of immune cells, culminating with the establishment of T helper type 1 (Th1) immunity. This interaction protects mice against intracellular pathogens, including Leishmania major and Leishmania amazonensis. ArtinM induces neutrophils activation, which is known to account for both resistance to pathogens and host tissue injury. Although exacerbated inflammation was not observed in ArtinM-treated animals, assessment of neutrophil responses to ArtinM is required to envisage its possible application to design a novel immunomodulatory agent based on carbohydrate recognition. Herein, we focus on the mechanisms through which neutrophils contribute to ArtinM-induced protection against Leishmania, without exacerbating inflammation. For this purpose, human neutrophils treated with ArtinM and infected with Leishmania major were analyzed together with untreated and uninfected controls, based on their ability to eliminate the parasite, release cytokines, degranulate, produce reactive oxygen species (ROS), form neutrophil extracellular traps (NETs) and change life span. We demonstrate that ArtinM-stimulated neutrophils enhanced L. major clearance and at least duplicated tumor necrosis factor (TNF) and interleukin-1beta (IL-1β) release; otherwise, transforming growth factor-beta (TGF-β) production was reduced by half. Furthermore, ROS production and cell degranulation were augmented. The life span of ArtinM-stimulated neutrophils decreased and they did not form NETs when infected with L. major. We postulate that the enhanced leishmanicidal ability of ArtinM-stimulated neutrophils is due to augmented release of inflammatory cytokines, ROS production, and cell degranulation, whereas host tissue integrity is favored by their shortened life span and the absence of NET formation. Our results reinforce the idea that ArtinM may be considered an appropriate molecular template for the construction of an efficient anti-infective agent. 相似文献
8.
9.
10.