全文获取类型
收费全文 | 2336篇 |
免费 | 190篇 |
出版年
2023年 | 8篇 |
2022年 | 25篇 |
2021年 | 57篇 |
2020年 | 35篇 |
2019年 | 37篇 |
2018年 | 51篇 |
2017年 | 43篇 |
2016年 | 70篇 |
2015年 | 103篇 |
2014年 | 123篇 |
2013年 | 131篇 |
2012年 | 162篇 |
2011年 | 162篇 |
2010年 | 122篇 |
2009年 | 109篇 |
2008年 | 146篇 |
2007年 | 141篇 |
2006年 | 124篇 |
2005年 | 126篇 |
2004年 | 105篇 |
2003年 | 97篇 |
2002年 | 83篇 |
2001年 | 48篇 |
2000年 | 43篇 |
1999年 | 48篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有2526条查询结果,搜索用时 31 毫秒
41.
Identification of three genetic loci controlling leaf senescence in Arabidopsis thaliana 总被引:23,自引:3,他引:20
Sung Aeong Oh Joon-Hyun Park Gyu In Lee Kyung Hee Paek Soon Ki Park Hong Gil Nam 《The Plant journal : for cell and molecular biology》1997,12(3):527-535
Four mutants that show the delayed leaf senescence phenotype were isolated from Arabidopsis thaliana . Genetic analyses revealed that they are all monogenic recessive mutations and fall into three complementation groups, identifying three genetic loci controlling leaf senescence in Arabidopsis . Mutations in these loci cause delay in all senescence parameters examined, including chlorophyll content, photochemical efficiency of photosystem II, relative amount of the large subunit of Rubisco, and RNase and peroxidase activity. Delay of the senescence symptoms was observed during both age-dependent in planta senescence and dark-induced artificial senescence in all of the mutant plants. The results indicate that the three genes defined by the mutations are key genetic elements controlling functional leaf senescence and provide decisive genetic evidence that leaf senescence is a genetically programmed phenomenon controlled by several monogenic loci in Arabidopsis . The results further suggest that the three genes function at a common step of age-dependent and dark-induced senescence processes. It is further shown that one of the mutations is allelic to ein2-1 , an ethylene-insensitive mutation, confirming the role of ethylene signal transduction pathway in leaf senescence of Arabidopsis . 相似文献
42.
G. Ramírez-Zarzosa F. Gil R. Latorre A. Ortega A. García-Alcaráz E. Abellán J. M. Vázquez O. López-Albors A. Arencibia F. Moreno 《Cell and tissue research》1995,280(2):217-224
Fibre-type differentiation of the lateral musculature has been studied in Sparus aurata (L.) and Dicentrarchus labrax (L.) during larval development. Histochemical and ultrastructural techniques show two presumptive muscle layers and two germinative zones of presumptive myoblasts. At hatching, myotomal muscle consists of a monolayer of thin undifferentiated cells near the skin (first germinative zone) overlying another mono-layer of small diameter fibres extending hypaxially and epaxially away from the transverse septum. Below this, there is a much thicker, deep layer of fibres, generally large in diameter and polygonal in shape. The presumptive myoblasts are located between these two layers of fibres in the second germinative zone. Initially, the superficial and deep muscle fibres show high and low myosin ATPase activity, respectively. Both layers grow by generating new fibres from the two mentioned germinative zones. At the end of larval life, the superficial layer changes its histochemical profile from high to low myosin ATPase activity and, at the same time, intermediate or pink muscle fibres can be observed by oxidative activity (the NADH-TR reaction). Morphometric analysis shows a significant increase in mean fibre diameter during successive ages, as shown by the Student's t-test (hypertrophic growth). Skewness and kurtosis values of fibre diameters point to the generation of a new fibre population from the germinative zones (hyperplastic growth). 相似文献
43.
Cheom Gil Cheong Soo Hyun Eom Changsoo Chang Dong Hae Shin Hyun Kyu Song Kyeongsik Min Jin Ho Moon Kyeong Kyu Kim Kwang Yeon Hwang Se Won Suh 《Proteins》1995,21(2):105-117
Sweet potato β-amylase is a tetramer of identical subunits, which are arranged to exhibit 222 molecular symmetry. Its subunit consists of 498 amino acid residues (Mr 55,880). It has been crystallized at room temperature using polyethylene glycol 1500 as precipitant. The crystals, growing to dimensions of 0.4 mm × 0.4 mm × 1.0 mm within 2 weeks, belong to the tetragonal space group P42212 with unit cell dimensions of a = b = 129.63 Å and c = 68.42 Å. The asymmetric unit contains 1 subunit of β-amylase, with a crystal volume per protein mass (VM) of 2.57 Å3/Da and a solvent content of 52% by volume. The three-dimensional structure of the tetrameric β-amylase from sweet potato has been determined by molecular replacement methods using the monomeric structure of soybean enzyme as the starting model. The refined subunit model contains 3,863 nonhydrogen protein atoms (488 amino acid residues) and 319 water oxygen atoms. The current R-value is 20.3% for data in the resolution range of 8–2.3 Å (with 2 σ cut-off) with good stereochemistry. The subunit structure of sweet potato β-amylase (crystallized in the absence of α-cyclodextrin) is very similar to that of soybean β-amylase (complexed with α-cyclodextrin). The root-mean-square (RMS) difference for 487 equivalent Cα atoms of the two β-amylases is 0.96 Å. Each subunit of sweet potato β-amylase is composed of a large (α/β)8 core domain, a small one made up of three long loops [L3 (residues 91–150), LA (residues 183–258), and L5 (residues 300–327)], and a long C-terminal loop formed by residues 445–493. Conserved Glu 187, believed to play an important role in catalysis, is located at the cleft between the (α/β)8 barrel core and a small domain made up of three long loops (L3, L4, and L5). Conserved Cys 96, important in the inactivation of enzyme activity by sulfhydryl reagents, is located at the entrance of the (α/β)8 barrel. © 1995 Wiley-Liss, Inc. 相似文献
44.
45.
46.
The Cl–/HCO
3
–
exchange mechanism usually postulated to occur in gastric mucosa cannot account for the Na+-dependent electrogenic serosal to mucosal Cl– transport often observed. It was recently suggested that an additional Cl– transport mechanism driven by the Na+ electrochemical potential gradient may be present on the serosal side of the tissue. To verify this, we have studied Cl– transport in guinea pig gastric mucosa. Inhibiting the (Na+, K+) ATPase either by serosal addition of ouabain or by establishing K+-free mucosal and serosal conditions abolished net Cl– transport. Depolarizing the cell membrane potential with triphenylmethylphosphonium (a lipid-soluble cation), and hence reducing both the Na+ and Cl– electrochemical potential gradients, resulted in inhibition of net Cl– flux. Reduction of short-circuit current on replacing Na+ by choline in the serosal bathing solution was shown to be due to inhibition of Cl– transport. Serosal addition of diisothiocyanodisulfonic acid stilbene (an inhibitor of anion transport systems) abolished net Cl– flux but not net Na+ flux. These results are compatible with the proposed model of a Cl–/Na+ cotransport mechanism governing serosal Cl– entry into the secreting cells. We suggest that the same mechanism may well facilitate both coupled Cl–/Na+ entry and coupled HCO
3
–
/Na+ exit on the serosal side of the tissue. 相似文献
47.
M. C. Ramos M. H. Gil F. A. P. Garcia J. M. S. Cabral J. T. Guthrie 《Biocatalysis and Biotransformation》1992,6(3):223-234
Lipase from Mucor miehei was immobilized covalently onto hydrolyzed poly(ethylene)-g.co-hydroxyethyl methacrylate (PE-HEMA). This hydrolysis of the copolymer was achieved using 0.1 M NaOH over different periods of time, under controlled conditions. The graft copolymers and their hydrolyzed equivalents were characterized by scanning electron microscopy (SEM) and by differential scanning calorimetry analysis (DSC). Water sorption studies were undertaken to provide a measure of relative hydrophobicity of the samples.
The lipase immobilization reaction was studied in order to assess the effects of controlling various important parameters. These include the nature of the buffering medium, the time over which the immobilization was allowed to occur, the concentration of the activating and coupling agent used (CMC) and the concentration of enzyme employed during attempts at effective immobilization. The immobilized lipase was used in the hydrolysis of triolein (glycerol trioleate). From this study, the apparent KM, the optimum pH for hydrolysis and the optimum temperature for hydrolysis were revealed.
The suitability of hydrolyzed poly(ethylene)-g.co-HEMA as a support in the immobilization of lipase was assessed by determination of the amount of lipase coupled to the support and by assessment of the retention of activity of the immobilized lipase after its exposure to the immobilization reagents, procedure and conditions. 相似文献
The lipase immobilization reaction was studied in order to assess the effects of controlling various important parameters. These include the nature of the buffering medium, the time over which the immobilization was allowed to occur, the concentration of the activating and coupling agent used (CMC) and the concentration of enzyme employed during attempts at effective immobilization. The immobilized lipase was used in the hydrolysis of triolein (glycerol trioleate). From this study, the apparent KM, the optimum pH for hydrolysis and the optimum temperature for hydrolysis were revealed.
The suitability of hydrolyzed poly(ethylene)-g.co-HEMA as a support in the immobilization of lipase was assessed by determination of the amount of lipase coupled to the support and by assessment of the retention of activity of the immobilized lipase after its exposure to the immobilization reagents, procedure and conditions. 相似文献
48.
Mutations at the Arabidopsis CHM locus promote rearrangements of the mitochondrial genome. 总被引:12,自引:2,他引:10
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Nuclear recessive mutations at the chloroplast mutator (CHM) locus of Arabidopsis produce a variegated phenotype that is inherited in a non-Mendelian fashion. Molecular analysis of the cytoplasmic genomes of variegated plants from two independent chm mutant lines, using specific chloroplast and mitochondrial probes, showed that the chm mutations reproducibly induce the appearance of specific new restriction fragments in the mitochondrial genome. The presence of these restriction fragments cosegregated with the variegated phenotype in the progeny of crosses between mutant and wild-type plants. Sequence analysis of one of the new restriction fragments found in the variegated plants suggested that it was the product of a rearrangement event involving regions of the mitochondrial genome. Thus, it appears that the CHM locus may encode a protein involved in the control of specific mitochondrial DNA reorganization events. 相似文献
49.
Carlos Garbisu Jone M. Gil Michael J. Bazin David O. Hall Juan L. Serra 《Journal of applied phycology》1991,3(3):221-234
Cells of the non-N2-fixing cyanobacteriumPhormidium laminosum were immobilized in polyurethane (PU) foams either by absorption or by entrapment in the PU prepolymer followed by polymerisation
and by adsorption onto polyvinyl (PV) foams. Although entrapment caused toxicity problems which lead to rapid death of the
immobilized cells, they were immobilized successfully by adsorption onto PU or PV foams and maintained their photosynthetic
electron transport activities (PS I, II, I + II) for at least 7 weeks. Changes in the morphology resulting from immobilization,
as revealed by scanning electron microscopy (SEM) and low temperature-SEM, were investigated. Batch cultures and a continuous-flow
packed bed photobioreactor were used to study nitrate removal from water. The effects of light intensity and CO2 concentration on bioreactor performance were studied with respect to the nitrate uptake efficiency of the system. It was
concluded thatP. laminosum immobilized on polymer foams is of potential value for biological nitrate removal in a continuous-flow system.
author for correspondence 相似文献
50.
Phospholipid turnover during phagocytosis in human polymorphonuclear leucocytes 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Merche García Gil Fernando Alonso Vicente Alvarez Chiva Mariano Sánchez Crespo José M. Mato 《The Biochemical journal》1982,206(1):67-72
We have previously observed that the phagocytosis of zymosan particles coated with complement by human polymorphonuclear leucocytes is accompanied by a time- and dose-dependent inhibition of phosphatidylcholine synthesis by transmethylation [García Gil, Alonso, Sánchez Crespo & Mato (1981) Biochem. Biophys. Res. Commun. 101, 740–748]. The present studies show that phosphatidylcholine synthesis by a cholinephosphotransferase reaction is enhanced, up to 3-fold, during phagocytosis by polymorphonuclear cells. This effect was tested by both measuring the incorporation of radioactivity into phosphatidylcholine in cells labelled with [Me-14C]choline, and by assaying the activity of CDP-choline:diacylglycerol cholinephosphotransferase. The time course of CDP-choline:diacylglycerol cholinephosphotransferase activation by zymosan mirrors the inhibition of phospholipid methyltransferase activity previously reported. The extent of incorporation of radioactivity into phosphatidylcholine induced by various doses of zymosan correlates with the physiological response of the cells to this stimulus. This effect was specific for phosphatidylcholine, and phosphatidyl-ethanolamine turnover was not affected by zymosan. The purpose of this enhanced phosphatidylcholine synthesis is not to provide phospholipid molecules rich in arachidonic acid. The present studies show that about 80% of the arachidonic acid generated in response to zymosan derives from phosphatidylinositol. A transient accumulation of arachidonoyldiacylglycerol has also been observed, which indicates that a phospholipase C is responsible, at least in part, for the generation of arachidonic acid. Finally, isobutylmethylxanthine and quinacrine, inhibitors of phosphatidylinositol turnover, inhibit both arachidonic acid generation and phagocytosis, indicating a function for this pathway during this process. 相似文献