全文获取类型
收费全文 | 1015034篇 |
免费 | 113639篇 |
国内免费 | 676篇 |
出版年
2018年 | 8947篇 |
2016年 | 12371篇 |
2015年 | 17278篇 |
2014年 | 20175篇 |
2013年 | 28774篇 |
2012年 | 32106篇 |
2011年 | 32579篇 |
2010年 | 22139篇 |
2009年 | 20336篇 |
2008年 | 28910篇 |
2007年 | 29650篇 |
2006年 | 28045篇 |
2005年 | 27176篇 |
2004年 | 26969篇 |
2003年 | 26164篇 |
2002年 | 25189篇 |
2001年 | 44635篇 |
2000年 | 44852篇 |
1999年 | 35797篇 |
1998年 | 12787篇 |
1997年 | 13183篇 |
1996年 | 12534篇 |
1995年 | 12133篇 |
1994年 | 11935篇 |
1993年 | 11717篇 |
1992年 | 29956篇 |
1991年 | 29039篇 |
1990年 | 28384篇 |
1989年 | 27823篇 |
1988年 | 25966篇 |
1987年 | 24608篇 |
1986年 | 22835篇 |
1985年 | 22803篇 |
1984年 | 19019篇 |
1983年 | 16273篇 |
1982年 | 12592篇 |
1981年 | 11507篇 |
1980年 | 10640篇 |
1979年 | 17836篇 |
1978年 | 14053篇 |
1977年 | 12845篇 |
1976年 | 11833篇 |
1975年 | 13120篇 |
1974年 | 14048篇 |
1973年 | 13945篇 |
1972年 | 12647篇 |
1971年 | 11492篇 |
1970年 | 10007篇 |
1969年 | 9769篇 |
1968年 | 8831篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
Bacteriomorphic organisms found in fruits of capitate infructescences in Kunduricarpus Kodrul, N. Maslova, Tekleva et Golovneva, Platanaceae, are described. Three types of carpel damage have been detected: (1) evidence of penetration of microorganisms in the walls of the carpel, (2) three-dimensional structures (isolated and in chains) rounded in section, which fill the inner space of the carpel, and (3) imprints of these structures on the inner surface of the carpel wall cuticle. The possible nature of the microorganisms is discussed. 相似文献
105.
106.
Kayla J. Vastenhout Ruthellen H. TornbergAmanda L. Johnson Michael W. AmolinsJared R. Mays 《Analytical biochemistry》2014
Isothiocyanates (ITCs) are one of several hydrolysis products of glucosinolates, plant secondary metabolites that are substrates for the thioglucohydrolase myrosinase. Recent pursuits toward the development of synthetic non-natural ITCs have consequently led to an exploration of generating these compounds from non-natural glucosinolate precursors. Evaluation of the myrosinase-dependent conversion of select non-natural glucosinolates to non-natural ITCs cannot be accomplished using established ultraviolet–visible (UV–Vis) spectroscopic methods. To overcome this limitation, an alternative high-performance liquid chromatography (HPLC)-based analytical approach was developed where initial reaction velocities were generated from nonlinear reaction progress curves. Validation of this HPLC method was accomplished through parallel evaluation of three glucosinolates with UV–Vis methodology. The results of this study demonstrate that kinetic data are consistent between both analytical methods and that the tested glucosinolates respond similarly to both Michaelis–Menten and specific activity analyses. Consequently, this work resulted in the complete kinetic characterization of three glucosinolates with Sinapis alba myrosinase, with results that were consistent with previous reports. 相似文献
107.
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
108.
109.
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
110.
Thiago B. Kirsten Marcella C. Galv?o Thiago M. Reis-Silva Nicolle Queiroz-Hazarbassanov Maria M. Bernardi 《PloS one》2015,10(3)
Sickness behavior is considered part of the specific beneficial adaptive behavioral and neuroimmune changes that occur in individuals in response to infectious/inflammatory processes. However, in dangerous and stressful situations, sickness behavior should be momentarily abrogated to prioritize survival behaviors, such as fight or flight. Taking this assumption into account, we experimentally induced sickness behavior in rats using lipopolysaccharides (LPS), an endotoxin that mimics infection by gram-negative bacteria, and then exposed these rats to a restraint stress challenge. Zinc has been shown to play a regulatory role in the immune and nervous systems. Therefore, the objective of this study was to examine the effects of zinc treatment on the sickness response of stress-challenged rats. We evaluated 22-kHz ultrasonic vocalizations, open-field behavior, tumor necrosis factor α (TNF-α), corticosterone, and brain-derived neurotrophic factor (BDNF) plasma levels. LPS administration induced sickness behavior in rats compared to controls, i.e., decreases in the distance traveled, average velocity, rearing frequency, self-grooming, and number of vocalizations, as well as an increase in the plasma levels of TNF-α, compared with controls after a stressor challenge. LPS also decreased BDNF expression but did not influence anxiety parameters. Zinc treatment was able to prevent sickness behavior in LPS-exposed rats after the stress challenge, restoring exploratory/motor behaviors, communication, and TNF-α levels similar to those of the control group. Thus, zinc treatment appears to be beneficial for sick animals when they are facing risky/stressful situations. 相似文献