全文获取类型
收费全文 | 3251篇 |
免费 | 233篇 |
国内免费 | 70篇 |
出版年
2024年 | 8篇 |
2023年 | 79篇 |
2022年 | 80篇 |
2021年 | 127篇 |
2020年 | 88篇 |
2019年 | 133篇 |
2018年 | 112篇 |
2017年 | 79篇 |
2016年 | 94篇 |
2015年 | 180篇 |
2014年 | 276篇 |
2013年 | 246篇 |
2012年 | 212篇 |
2011年 | 229篇 |
2010年 | 160篇 |
2009年 | 202篇 |
2008年 | 150篇 |
2007年 | 181篇 |
2006年 | 178篇 |
2005年 | 135篇 |
2004年 | 103篇 |
2003年 | 99篇 |
2002年 | 62篇 |
2001年 | 52篇 |
2000年 | 30篇 |
1999年 | 27篇 |
1998年 | 22篇 |
1997年 | 23篇 |
1996年 | 24篇 |
1995年 | 24篇 |
1994年 | 31篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 3篇 |
排序方式: 共有3554条查询结果,搜索用时 62 毫秒
21.
As previously reported, mitochondrial malate dehydrogenase (MDH) binds to purified complex I of the electron transport system. With conditions used in previous reports, MDH binds even more extensively, but probably predominantly non-specifically, to the matrix side of the inner mitochondrial membrane of submitochodrial particles (SMP). Herein we report experimental conditions for highly specific binding of malate dehydrogenase to complex I within SMP. These conditions permit us to demonstrate NADH channelling from malate dehydrogenase to complex I using the completing reaction test. This test, though not ideal for all situations, has several advantages over the enzyme buffering test previously used. These advantages should facilitate further studies elucidating NADH channeling to complex I from MDH and other dehydrogenases. Independent evidence of NADH channelling to the electron transport chain and the potential advantages of substrate channelling in general are also discussed. Substrate channelling from MDH in particular may be especially beneficial because of the unfavourable equilibrium and kinetics of this enzyme reaction. 相似文献
22.
对废水淤泥的厌氧消化处理过程进行了研究.提出了一种基于神经网络的非模型控制方法。多变量控制系统的操作变量为供热量和进水量.被控变量为消化温度和消化污泥排出浓度。证明了控制算法的收敛性。讨论了控制系统的稳定性。仿真结果证实了非模型控制方法的有效性。该方法无需对象的模型.为复杂生化过程的控制提供了一种新途径。 相似文献
23.
R. C. Roverud 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1994,174(5):559-565
A stereotypical approach phase vocalization response of the lesser bulldog bat, Noctilio albiventris, to artificial echoes simulating a virtual approaching object was used to assess the ability of the bat to analyze and extract distance information from the artificial echoes. The performance of the bat was not significantly different when presented with naturally structured CF/FM echoes containing FM elements that sweep continuously from about 75-55 kHz in 4 ms or with CF/FM echoes containing FM components constructed from a series of 98 pure tone frequency steps, each with a duration of 0.04 ms. The performance of the bat remained unchanged when the duration of the tone steps was increased up to 0.08 ms but declined sharply to a level that was significantly below that seen with a naturally structured echo when the steps were 0.09 ms or longer. The performance of the bat depended on the duration of the individual tone steps, which could not exceed a specific upper limit of about 0.08 ms. The study suggests that the bats have adaptations for processing individual narrow band segments of FM signals over specific time intervals.Abbreviations CF
constant frequency
- FM
frequency modulation 相似文献
24.
Ian M. Møller Allan G. Rasmusson Kenneth M. Fredlund 《Journal of bioenergetics and biomembranes》1993,25(4):377-384
Plant (and fungal) mitochondria contain multiple NAD(P)H dehydrogenases in the inner membrane all of which are connected to the respiratory chain via ubiquinone. On the outer surface, facing the intermembrane space and the cytoplasm, NADH and NADPH are oxidized by what is probably a single low-molecular-weight, nonproton-pumping, unspecific rotenone-insensitive NAD(P)H dehydrogenase. Exogenous NADH oxidation is completely dependent on the presence of free Ca2+ with aK
0.5 of about 1 µM. On the inner surface facing the matrix there are two dehydrogenases: (1) the proton-pumping rotenone-sensitive multisubunit Complex I with properties similar to those of Complex I in mammalian and fungal mitochondria. (2) a rotenone-insensitive NAD(P)H dehydrogenase with equal activity with NADH and NADPH and no proton-pumping activity. The NADPH-oxidizing activity of this enzyme is completely dependent on Ca2+ with aK
0.5 of 3 µM. The enzyme consists of a single subunit of 26 kDa and has a native size of 76 kDa, which means that it may form a trimer. 相似文献
25.
天花粉蛋白与FMP复合物的晶体结构 总被引:6,自引:1,他引:5
用浸泡法得到了天花粉蛋白(TCS)与FMP复合物的晶体,在SIMENNSX-200B面探测器系统上收集了一套2.0分辨率的X射线衍射数据。用同晶差值傅立叶法解析了复合物的结构,经X—PLOR程序修正得到了TCS—FMP复合物的分子结构并找出了197个水分子,最后的R因子为0.172,键长和键角的RMS偏差分别为0.015和2.922度。TCS—FMP复合物中,FMP与天花粉蛋白分子有较好的结合,其结合位置正处于根据三维结构和突变体信息推测的N一糖苷酶活性口袋之中。它的类嘌呤环夹在Y70和Y111两个侧链环之间,与Y70环近乎平行,其N7和N6分别与TCS分子的G1094羰基氧和I71的N成氢键,N3靠近R163的侧链,其磷酸根则伸向活性口袋的底部,与E189、E160和R163等残基作用。 相似文献
26.
Age-Dependent Impairment of Mitochondrial Function in Primate Brain 总被引:11,自引:2,他引:9
Allen C. Bowling Elizabeth M. Mutisya Lary C. Walker† Donald L. Price†‡§ Linda C. Cork† M. Hint Beal 《Journal of neurochemistry》1993,60(5):1964-1967
Abstract: It has been hypothesized that some of the functional impairments associated with aging are the result of increasing oxidative damage to mitochondrial DNA that produces defects in oxidative phosphorylation. To test this hypothesis, we examined the enzymes that catalyze oxidative phosphorylation in crude mitochondrial preparations from frontoparietal cortex of 20 rhesus monkeys (5-34 years old). Samples were assayed for complex I, complex II-III, complex IV, complex V, and citrate synthase activities. When enzyme activities were corrected for citrate synthase activities (to account for variable degrees of mitochondrial enrichment), linear regression analysis demonstrated a significant negative correlation of the activities of complex I (p < 0.002) and complex IV (p < 0.03) with age but no significant change in complex II-III or complex V activities. Relative to animals 6.9 ± 0.9 years old (n = 7), the citrate synthase-corrected activity of complex I was reduced by 17% in animals 22.5 ± 0.9 years old (n = 6) (p < 0.05) and by 22% in animals 30.7 ± 0.9 years old (n = 7) (p < 0.01). Similar age-related reductions in the activities of complexes I and IV were obtained when enzyme activities were corrected for complex II-III activity. These findings show an age-associated progressive impairment of mitochondrial complex I and complex IV activities in cerebral cortices of primates. 相似文献
27.
28.
J. Jelle Lever Egbert H. Van Nes Marten Scheffer Jordi Bascompte 《Ecology letters》2023,26(10):1765-1779
Theory suggests that increasingly long, negative feedback loops of many interacting species may destabilize food webs as complexity increases. Less attention has, however, been paid to the specific ways in which these ‘delayed negative feedbacks’ may affect the response of complex ecosystems to global environmental change. Here, we describe five fundamental ways in which these feedbacks might pave the way for abrupt, large-scale transitions and species losses. By combining topological and bioenergetic models, we then proceed by showing that the likelihood of such transitions increases with the number of interacting species and/or when the combined effects of stabilizing network patterns approach the minimum required for stable coexistence. Our findings thus shift the question from the classical question of what makes complex, unaltered ecosystems stable to whether the effects of, known and unknown, stabilizing food-web patterns are sufficient to prevent abrupt, large-scale transitions under global environmental change. 相似文献
29.
Emanuel A. Fronhofer Dov Corenblit Jhelam N. Deshpande Lynn Govaert Philippe Huneman Frédérique Viard Philippe Jarne Sara Puijalon 《Ecology letters》2023,26(Z1):S91-S108
Eco-evolutionary dynamics, or eco-evolution for short, are often thought to involve rapid demography (ecology) and equally rapid heritable phenotypic changes (evolution) leading to novel, emergent system behaviours. We argue that this focus on contemporary dynamics is too narrow: Eco-evolution should be extended, first, beyond pure demography to include all environmental dimensions and, second, to include slow eco-evolution which unfolds over thousands or millions of years. This extension allows us to conceptualise biological systems as occupying a two-dimensional time space along axes that capture the speed of ecology and evolution. Using Hutchinson's analogy: Time is the ‘theatre’ in which ecology and evolution are two interacting ‘players’. Eco-evolutionary systems are therefore dynamic: We identify modulators of ecological and evolutionary rates, like temperature or sensitivity to mutation, which can change the speed of ecology and evolution, and hence impact eco-evolution. Environmental change may synchronise the speed of ecology and evolution via these rate modulators, increasing the occurrence of eco-evolution and emergent system behaviours. This represents substantial challenges for prediction, especially in the context of global change. Our perspective attempts to integrate ecology and evolution across disciplines, from gene-regulatory networks to geomorphology and across timescales, from today to deep time. 相似文献
30.