全文获取类型
收费全文 | 5026篇 |
免费 | 514篇 |
国内免费 | 2篇 |
出版年
2021年 | 88篇 |
2020年 | 57篇 |
2019年 | 73篇 |
2018年 | 84篇 |
2017年 | 61篇 |
2016年 | 115篇 |
2015年 | 195篇 |
2014年 | 230篇 |
2013年 | 247篇 |
2012年 | 348篇 |
2011年 | 326篇 |
2010年 | 198篇 |
2009年 | 178篇 |
2008年 | 282篇 |
2007年 | 301篇 |
2006年 | 244篇 |
2005年 | 265篇 |
2004年 | 260篇 |
2003年 | 189篇 |
2002年 | 192篇 |
2001年 | 75篇 |
2000年 | 54篇 |
1999年 | 70篇 |
1998年 | 59篇 |
1997年 | 35篇 |
1996年 | 31篇 |
1995年 | 34篇 |
1994年 | 38篇 |
1993年 | 34篇 |
1992年 | 52篇 |
1991年 | 46篇 |
1990年 | 60篇 |
1989年 | 59篇 |
1988年 | 46篇 |
1987年 | 52篇 |
1986年 | 37篇 |
1985年 | 39篇 |
1984年 | 52篇 |
1983年 | 48篇 |
1982年 | 45篇 |
1981年 | 56篇 |
1980年 | 28篇 |
1979年 | 33篇 |
1978年 | 46篇 |
1977年 | 44篇 |
1976年 | 29篇 |
1975年 | 30篇 |
1974年 | 40篇 |
1973年 | 26篇 |
1972年 | 25篇 |
排序方式: 共有5542条查询结果,搜索用时 109 毫秒
1.
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
2.
3.
Plant and Soil - Agricultural practices often have persistent effects on soil physicochemical properties and soil biota, which can feedback to influence plant performance. We investigated... 相似文献
4.
The floral morphology of seven Oxypetalum species and, in particular, the spatial relationship between the five stigmatic chambers and two separate ovaries of their
flowers with respect to transmission of the pollen tube are studied. In all species, except O. banksii subsp. banksii, floral morphology is similar to that in other Asclepiadeae, and the flowers pollinated with one pollinium develop only one
follicle, which means compitum absence. In O. banksii subsp. banksii flowers, the secretory interstaminal tissue lines the inner walls of the stigmatic chambers as in the other species studied,
but it also reaches the upper part of the inner surface of the filament tube, where it surrounds the styles, an unprecedented
feature for Asclepiadaceae. This tissue secretes nectar and mucilage; the latter acts as transmitting medium for the growth
of pollen tubes from pollinia inserted and hydrated in stigmatic chambers (“hyperstigmas”). Mucilage also functions as an
extragynoecial compitum: in flowers pollinated with one pollinium both carpels develop into a follicle.
Received August 28, 2001; accepted April 9, 2002 Published online: October 14, 2002
Addresses of the authors: Milene Faria Vieira (e-mail: mfvieira@mail.ufv.br), Departamento de Biologia Vegetal, Universidade
Federal de Vi?osa, 36571-000, Vi?osa, Minas Gerais, Brazil. George John Shepherd, Departamento de Botanica, Instituto de Biologia,
Universidade Estadual de Campinas, C.P. 6109, 13083-970, Campinas, S?o Paulo, Brazil. 相似文献
5.
6.
The relative metobolic turnover rates of labeled histone fractions and of their labeled acetyl groups were determined in random cultures of exponentially-growing mammalian cells. Both the parent histones and their acetyl groups were conserved, neither exhibiting detectable metabolic turnover. The significance of these observations is discussed. 相似文献
7.
H. Bryan Donkin 《BMJ (Clinical research ed.)》1917,1(2926):135-136
8.
Yibao Ma Yuanxi Xu Bryan D. Yestrepsky Roderick J. Sorenson Meng Chen Scott D. Larsen Hongmin Sun 《PloS one》2012,7(10)
Staphylococcus aureus is a major human pathogen and one of the more prominent pathogens causing biofilm related infections in clinic. Antibiotic resistance in S. aureus such as methicillin resistance is approaching an epidemic level. Antibiotic resistance is widespread among major human pathogens and poses a serious problem for public health. Conventional antibiotics are either bacteriostatic or bacteriocidal, leading to strong selection for antibiotic resistant pathogens. An alternative approach of inhibiting pathogen virulence without inhibiting bacterial growth may minimize the selection pressure for resistance. In previous studies, we identified a chemical series of low molecular weight compounds capable of inhibiting group A streptococcus virulence following this alternative anti-microbial approach. In the current study, we demonstrated that two analogs of this class of novel anti-virulence compounds also inhibited virulence gene expression of S. aureus and exhibited an inhibitory effect on S. aureus biofilm formation. This class of anti-virulence compounds could be a starting point for development of novel anti-microbial agents against S. aureus. 相似文献
9.
Insect skeletal muscle is relatively insensitive to applied GABA, responses are elicited only when relatively high concentrations of GABA are used (greater than 10(-6) M). Pretreatment of the muscle with the GABA uptake inhibitors nipecotic acid, beta-aminobutyric acid or beta-alanine increases the sensitivity of the muscle to GABA by as much as 1000-fold. The evidence suggests the existence of a GABA uptake mechanism in the insect neuromuscular system which could reside in glial cells. 相似文献
10.
F.M. Lai T.K. Tanikella H. Herzlinger C. Shepherd P. Cervoni 《Prostaglandins & other lipid mediators》1984,27(2):273-284
The effect of CL 115,347, a topically active antihypertensive PGE2 analog, and PGE2 on changes in blood pressure (BP), heart rate (HR) response and plasma epinephrine (E) and norepinephrine (NE) levels induced by stimulation of the sympathetic spinal cord outflow were studied in pithed stroke-prone spontaneously hypertensive rats (SHRSP). Surgical pithing significantly reduced plasma E but not NE levels suggesting that the sympathoadrenal medullary system differentially affects E and NE release. Sympathetic stimulation of the spinal cord of pithed SHRSP increased HR, BP, plasma E and NE levels. Topically applied CL 115,347 (0.001–0.1 mg/kg) dose-dependently decreased BP, while intravenously infused PGE2 (30 μg/kg/min) did not alter BP except for a brief initial drop. Topical application of CL 115,347 (0.1 mg/kg) also inhibited BP responses to sympathetic stimulation without effects on HR or plasma E or NE levels. Intravenous infusion of PGE2 (30 μg/kg/min) inhibited both BP and HR responses to spinal cord stimulation but did not alter plasma catecholamine levels. These studies in SHRSP suggest that CL 115,347 and PGE2 modulate cardiovascular responses mainly via postjunctional effects, but act differently on the cardiovascular elements,
CL 115,347 acts primarily on blood vessels while PGE2 acts on blood vessels and heart. 相似文献