全文获取类型
收费全文 | 30795篇 |
免费 | 2832篇 |
国内免费 | 21篇 |
出版年
2023年 | 143篇 |
2022年 | 94篇 |
2021年 | 681篇 |
2020年 | 415篇 |
2019年 | 549篇 |
2018年 | 654篇 |
2017年 | 537篇 |
2016年 | 965篇 |
2015年 | 1631篇 |
2014年 | 1709篇 |
2013年 | 1999篇 |
2012年 | 2632篇 |
2011年 | 2682篇 |
2010年 | 1632篇 |
2009年 | 1354篇 |
2008年 | 2009篇 |
2007年 | 1986篇 |
2006年 | 1930篇 |
2005年 | 1656篇 |
2004年 | 1679篇 |
2003年 | 1476篇 |
2002年 | 1437篇 |
2001年 | 275篇 |
2000年 | 199篇 |
1999年 | 250篇 |
1998年 | 275篇 |
1997年 | 197篇 |
1996年 | 166篇 |
1995年 | 166篇 |
1994年 | 149篇 |
1993年 | 143篇 |
1992年 | 114篇 |
1991年 | 140篇 |
1990年 | 102篇 |
1989年 | 92篇 |
1988年 | 82篇 |
1987年 | 66篇 |
1986年 | 82篇 |
1985年 | 89篇 |
1984年 | 92篇 |
1983年 | 92篇 |
1982年 | 111篇 |
1981年 | 110篇 |
1980年 | 87篇 |
1979年 | 60篇 |
1978年 | 45篇 |
1977年 | 46篇 |
1976年 | 47篇 |
1975年 | 46篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
1.
2.
3.
4.
5.
Continental‐scale macrofungal assemblage patterns correlate with climate,soil carbon and nitrogen deposition 下载免费PDF全文
6.
M. Fernando Gonzalez-Zalba Chiara Ciccarelli Liviu P. Zarbo Andrew C. Irvine Richard C. Campion Bryan L. Gallagher Tomas Jungwirth Andrew J. Ferguson Joerg Wunderlich 《PloS one》2015,10(4)
We propose a novel hybrid single-electron device for reprogrammable low-power logic operations, the magnetic single-electron transistor (MSET). The device consists of an aluminium single-electron transistor with a GaMnAs magnetic back-gate. Changing between different logic gate functions is realized by reorienting the magnetic moments of the magnetic layer, which induces a voltage shift on the Coulomb blockade oscillations of the MSET. We show that we can arbitrarily reprogram the function of the device from an n-type SET for in-plane magnetization of the GaMnAs layer to p-type SET for out-of-plane magnetization orientation. Moreover, we demonstrate a set of reprogrammable Boolean gates and its logical complement at the single device level. Finally, we propose two sets of reconfigurable binary gates using combinations of two MSETs in a pull-down network. 相似文献
7.
Nicole Guthrie Andrew Bradlyn Sharon K. Thompson Sophia Yen Jana Haritatos Fred Dillon Steve W. Cole 《PloS one》2015,10(5)
Most adolescents do not achieve the recommended levels of moderate-to-vigorous physical activity (MVPA), placing them at increased risk for a diverse array of chronic diseases in adulthood. There is a great need for scalable and effective interventions that can increase MVPA in adolescents. Here we report the results of a measurement validation study and a preliminary proof-of-concept experiment testing the impact of Zamzee, an accelerometer-linked online intervention system that combines proximal performance feedback and incentive motivation features to promote MVPA. In a calibration study that parametrically varied levels of physical activity in 31 12-14 year-old children, the Zamzee activity meter was shown to provide a valid measure of MVPA (sensitivity in detecting MVPA = 85.9%, specificity = 97.5%, and r = .94 correspondence with the benchmark RT3 accelerometer system; all p < .0001). In a subsequent randomized controlled multi-site experiment involving 182 middle school-aged children assessed for MVPA over 6 wks, intent-to-treat analyses found that those who received access to the Zamzee intervention had average MVPA levels 54% greater than those of a passive control group (p < 0.0001) and 68% greater than those of an active control group that received access to a commercially available active videogame (p < .0001). Zamzee’s effects on MVPA did not diminish significantly over the course of the 6-wk study period, and were statistically significant in both females and males, and in normal- vs. high-BMI subgroups. These results provide promising initial indications that combining the Zamzee activity meter with online proximal performance feedback and incentive motivation features can positively impact MVPA levels in adolescents. 相似文献
8.
Kole T. Roybal Emily M. Mace Danielle J. Clark Alan D. Leard Andrew Herman Paul Verkade Jordan S. Orange Christoph Wülfing 《PloS one》2015,10(8)
Dynamic subcellular distributions of signaling system components are critical regulators of cellular signal transduction through their control of molecular interactions. Understanding how signaling activity depends on such distributions and the cellular structures driving them is required for comprehensive insight into signal transduction. In the activation of primary murine T cells by antigen presenting cells (APC) signaling intermediates associate with various subcellular structures, prominently a transient, wide, and actin-associated lamellum extending from an interdigitated T cell:APC interface several micrometers into the T cell. While actin dynamics are well established as general regulators of cellular organization, their role in controlling signaling organization in primary T cell:APC couples and the specific cellular structures driving it is unresolved. Using modest interference with actin dynamics with a low concentration of Jasplakinolide as corroborated by costimulation blockade we show that T cell actin preferentially controls lamellal signaling localization and activity leading downstream to calcium signaling. Lamellal localization repeatedly related to efficient T cell function. This suggests that the transient lamellal actin matrix regulates T cell signaling associations that facilitate T cell activation. 相似文献
9.
10.