全文获取类型
收费全文 | 2081篇 |
免费 | 208篇 |
专业分类
2289篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 31篇 |
2021年 | 50篇 |
2020年 | 37篇 |
2019年 | 32篇 |
2018年 | 44篇 |
2017年 | 45篇 |
2016年 | 81篇 |
2015年 | 110篇 |
2014年 | 147篇 |
2013年 | 144篇 |
2012年 | 167篇 |
2011年 | 162篇 |
2010年 | 129篇 |
2009年 | 128篇 |
2008年 | 154篇 |
2007年 | 128篇 |
2006年 | 133篇 |
2005年 | 108篇 |
2004年 | 120篇 |
2003年 | 97篇 |
2002年 | 85篇 |
2001年 | 18篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 19篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有2289条查询结果,搜索用时 0 毫秒
991.
We followed C and N reserves of grapevines grown in trenches under semi-controlled conditions over a 3-year period after planting. Temporal mobilization of stored C and N and subsequent distribution of reserve materials within the vines were described in parallel with 15N uptake, particularly during the third growing season. Storage C in the perennial tissues (roots, trunk, canes) was mainly made of starch, which accumulated in the ray parenchyma of the wood. In the permanent tissues, starch and total nitrogen contents were found to decrease early in the development (bleeding sap, budbreak) whereas, on a concentration basis, they decreased only after stage 7 (first leaf fully expanded). Starch started to accumulate again in the perennial tissues during flowering. The same observation was made with total nitrogen, although N levels were much lower than those of starch. The 15N study showed that N uptake by the roots started at budbreak and increased with vine development, becoming predominant over reserve mobilization only after the onset of flowering. Taken together, these results indicate that the spring growth period can be divided into three main phases: In the first (dormancy to budbreak), significant losses of C and N proceed mainly via root necrosis. In the second period (first leaf to the onset of bloom), a strong mobilization of starch (and, to a lower extent, of N) occurred for supporting vegetative and reproductive growth. At that point, most of the C and N reserves used on the spring flush were those of the roots, rather than those of the old wood (trunk, canes). In the third period (bloom and early berry development), the mobilization process became low and was relieved by N uptake (and CO2 assimilation) supplying nutrients to the sink structures. 相似文献
992.
Cardin S Pagliassotti MJ Moore MC Edgerton DS Lautz M Farmer B Neal DW Cherrington AD 《American journal of physiology. Regulatory, integrative and comparative physiology》2004,287(4):R742-R748
We examined the role of efferent neural signaling in regulation of net hepatic glucose uptake (NHGU) in two groups of conscious dogs with hollow perfusable coils around their vagus nerves, using tracer and arteriovenous difference techniques. Somatostatin, intraportal insulin and glucagon at fourfold basal and basal rates, and intraportal glucose at 3.8 mg.kg(-1).min(-1) were infused continuously. From 0 to 90 min [period 1 (P1)], the coils were perfused with a 37 degrees C solution. During period 2 [P2; 90-150 min in group 1 (n = 3); 90-180 min in group 2 (n = 6)], the coils were perfused with -15 degrees C solution to eliminate vagal signaling, and the coils were subsequently perfused with 37 degrees C solution during period 3 (P3). In addition, group 2 received an intraportal infusion of norepinephrine at 16 ng.kg(-1).min(-1) during P2. The effectiveness of vagal suppression was demonstrated by the increase in heart rate during P2 (111 +/- 17, 167 +/- 16, and 105 +/- 13 beats/min in group 1 and 71 +/- 6, 200 +/- 11, and 76 +/- 6 beats/min in group 2 during P1-P3, respectively) and by prolapse of the third eyelid during P2. Arterial plasma glucose, insulin, and glucagon concentrations; hepatic blood flow; and hepatic glucose load did not change significantly during P1-P3. NHGU during P1-P3 was 2.7 +/- 0.4, 4.1 +/- 0.6, and 4.0 +/- 1.2 mg.kg(-1).min(-1) in group 1 and 5.0 +/- 0.9, 5.6 +/- 0.7, and 6.1 +/- 0.9 mg.kg(-1).min(-1) in group 2 (not significant among periods). Interruption of vagal signaling with or without intraportal infusion of norepinephrine to augment sympathetic tone did not suppress NHGU during portal glucose delivery, suggesting the portal signal stimulates NHGU independently of vagal efferent flow. 相似文献
993.
El-Annan J Brown D Breton S Bourgoin S Ausiello DA Marshansky V 《American journal of physiology. Cell physiology》2004,286(4):C768-C778
ADP-ribosylation factors (Arfs) are small GTPases that regulate vesicular trafficking in exo- and endocytotic pathways. As a first step in understanding the role of Arfs in renal physiology, immunocytochemistry and Western blotting were performed to characterize the expression and targeting of Arf1 and Arf6 in epithelial cells in situ. Arf1 and Arf6 were associated with apical membranes and subapical vesicles in proximal tubules, where they colocalized with megalin. Arf1 was also apically expressed in the distal tubule, connecting segment, and collecting duct (CD). Arf1 was abundant in intercalated cells (IC) and colocalized with V-ATPase in A-IC (apical) and B-IC (apical and/or basolateral). In contrast, Arf6 was associated exclusively with basolateral membranes and vesicles in the CD. In the medulla, basolateral Arf6 was detectable mainly in A-IC. Expression in principal cells became weaker throughout the outer medulla, and Arf6 was not detectable in principal cells in the inner medulla. In some kidney epithelial cells Arf1 but not Arf6 was also targeted to a perinuclear patch, where it colocalized with TGN38, a marker of the trans-Golgi network. Quantitative Western blotting showed that expression of endogenous Arf1 was 26180 times higher than Arf6. These data indicate that Arf GTPases are expressed and targeted in a cell- and membrane-specific pattern in kidney epithelial cells in situ. The results provide a framework on which to base and interpret future studies on the role of Arf GTPases in the multitude of cellular trafficking events that occur in renal tubular epithelial cells. protein trafficking; immunofluorescence microscopy; Western blotting; endocytosis 相似文献
994.
Chevalier E Stock J Fisher T Dupont M Fric M Fargeau H Leport M Soler S Fabien S Pruniaux MP Fink M Bertrand CP McNeish J Li B 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(4):2056-2060
PGs play key regulatory roles in inflammation and immunity. PGD2, released from mast cells and Th2 cells during allergic responses, has recently been shown to target a novel receptor, chemoattractant receptor-homologous molecule expressed TH2 cells (CRTH2), in addition to the classic PGD (DP) receptor. CRTH2 is expressed on Th2 cells and eosinophils and mediates chemotaxis of these cells to PGD2. Thus, CRTH2 is thought to be a key receptor mediating eosinophil and Th2 cell recruitment during allergic responses. To examine the role of CRTH2 in this context in vivo, we generated CRTH2 knockout mice. Surprisingly, in an allergic inflammatory model of asthma, CRTH2 knockout mice showed enhanced eosinophil recruitment into the lung compared with wild-type littermate mice. This is consistent with our observation that CRTH2 knockout cells produce significantly higher amounts of IL-5 and IL-3 in vitro. These results suggest a nonredundant role of CRTH2 in restricting eosinophilia and allergic response in vivo. 相似文献
995.
Chlorophyll breakdown in senescent Arabidopsis leaves. Characterization of chlorophyll catabolites and of chlorophyll catabolic enzymes involved in the degreening reaction 下载免费PDF全文
Pruzinská A Tanner G Aubry S Anders I Moser S Müller T Ongania KH Kräutler B Youn JY Liljegren SJ Hörtensteiner S 《Plant physiology》2005,139(1):52-63
During senescence, chlorophyll (chl) is metabolized to colorless nonfluorescent chl catabolites (NCCs). A central reaction of the breakdown pathway is the ring cleavage of pheophorbide (pheide) a to a primary fluorescent chl catabolite. Two enzymes catalyze this reaction, pheide a oxygenase (PAO) and red chl catabolite reductase. Five NCCs and three fluorescent chl catabolites (FCCs) accumulated during dark-induced chl breakdown in Arabidopsis (Arabidopsis thaliana). Three of these NCCs and one FCC (primary fluorescent chl catabolite-1) were identical to known catabolites from canola (Brassica napus). The presence in Arabidopsis of two modified FCCs supports the hypothesis that modifications, as present in NCCs, occur at the level of FCC. Chl degradation in Arabidopsis correlated with the accumulation of FCCs and NCCs, as well as with an increase in PAO activity. This increase was due to an up-regulation of Pao gene expression. In contrast, red chl catabolite reductase is not regulated during leaf development and senescence. A pao1 knockout mutant was identified and analyzed. The mutant showed an age- and light-dependent cell death phenotype on leaves and in flowers caused by the accumulation of photoreactive pheide a. In the dark, pao1 exhibited a stay-green phenotype. The key role of PAO in chl breakdown is discussed. 相似文献
996.
La Camera S Geoffroy P Samaha H Ndiaye A Rahim G Legrand M Heitz T 《The Plant journal : for cell and molecular biology》2005,44(5):810-825
Genes and proteins related to patatin, the major storage protein of potato tubers, have been identified in many plant species and shown to be induced by a variety of environmental stresses. The Arabidopsis patatin-like gene family (PLPs) comprises nine members, two of which (PLP2 and PLP7) are strongly induced in leaves challenged with fungal and bacterial pathogens. Here we show that accumulation of PLP2 protein in response to Botrytis cinerea or Pseudomonas syringae pv. tomato (avrRpt2) is dependent on jasmonic acid and ethylene signaling, but is not dependent on salicylic acid. Expression of a PLP2-green fluorescent protein (GFP) fusion protein and analysis of recombinant PLP2 indicates that PLP2 encodes a cytoplasmic lipid acyl hydrolase with wide substrate specificity. Transgenic plants with altered levels of PLP2 protein were generated and assayed for pathogen resistance. Plants silenced for PLP2 expression displayed enhanced resistance to B. cinerea, whereas plants overexpressing PLP2 were much more sensitive to this necrotrophic fungus. We also established a positive correlation between the level of PLP2 expression in transgenic plants and cell death or damage in response to paraquat treatment or infection by avirulent P. syringae. Interestingly, repression of PLP2 expression increased resistance to avirulent bacteria, while PLP2-overexpressing plants multiplied avirulent bacteria close to the titers reached by virulent bacteria. Collectively, the data indicate that PLP2-encoded lipolytic activity can be exploited by pathogens with different lifestyles to facilitate host colonization. In particular PLP2 potentiates plant cell death inflicted by Botrytis and reduces the efficiency of the hypersensitive response in restricting the multiplication of avirulent bacteria. Both effects are possibly mediated by providing fatty acid precursors of bioactive oxylipins. 相似文献
997.
Quercetinase is produced by various filamentous fungi when grown on rutin as sole carbon and energy source. We investigated on the effect of 10 phenolics and two sugars, structurally related to substrates and products of the rutin catabolic pathway, on the induction of a quercetinase activity in Penicillium olsonii. Neither the sugars (glucose and rhamnose, two constituents of rutin), nor phenolics such as protocatechuic acid, salicylic acid, 4-hydroxy-benzoic acid and phloroglucinol were inducers. Rutin (maximum activity 150 nmol/min/mL after 5 days), quercetin (70 nmol/min/mL, 3 days), phloroglucinol carboxylic acid (60 nmol/min/mL, 3 days), 2-protocatechuoylphloroglucinolcarboxylic acid (50 nmol/min/mL, 5 days), 2,6-dihydroxy-carboxylic acid (90 nmol/min/mL, 7 days) and 2,4-dihydroxy-carboxylic acid (30 nmol/min/mL, 7 days) were demonstrated to be quercetinase inducers. We propose that rutin, quercetin and 2-protocatechuoyl-phloroglucinol carboxylic acid, the product of the reaction catalysed by quercetinase, act as inducers after their catabolic transformation in phloroglucinol carboxylic acid. 相似文献
998.
999.
Mélanie Harzé Arnaud Monty Sylvain Boisson Carline Pitz Julia‐Maria Hermann Johannes Kollmann Grégory Mahy 《Restoration Ecology》2018,26(2):227-234
Persistence of restored populations depends on growth, reproduction, dispersal, local adaptation, and a suitable landscape pattern to foster metapopulation dynamics. Although the negative effects of habitat fragmentation on plant population dynamics are well understood, particularly in grasslands, the population traits that control grassland restoration are less known. We reviewed the use of population traits for evaluating grassland restoration success based on 141 publications (1986–2015). The results demonstrated that population demography was relatively well‐assessed but detailed studies providing information on key stages of the life cycle were lacking despite their importance in determining population viability. Vegetative and generative performances have been thoroughly investigated, notably the components of plant fitness, such as reproductive output, while genetic and spatial population structures were largely ignored. More work on the population effects of ecological restoration would be welcomed, particularly with a focus on population genetics. Targeted species were principally common and dominant natives, or invasive plants while rare or threatened species were poorly considered. Evaluation of ecological restoration should be conducted at different scales of ecological complexity, but so far, communities and ecosystems are over represented, and more focus should be directed towards a population approach as population traits are essential indicators of restoration success. 相似文献
1000.