全文获取类型
收费全文 | 1905篇 |
免费 | 110篇 |
出版年
2023年 | 16篇 |
2022年 | 20篇 |
2021年 | 43篇 |
2020年 | 41篇 |
2019年 | 33篇 |
2018年 | 76篇 |
2017年 | 82篇 |
2016年 | 77篇 |
2015年 | 68篇 |
2014年 | 76篇 |
2013年 | 113篇 |
2012年 | 124篇 |
2011年 | 168篇 |
2010年 | 108篇 |
2009年 | 59篇 |
2008年 | 115篇 |
2007年 | 121篇 |
2006年 | 130篇 |
2005年 | 89篇 |
2004年 | 72篇 |
2003年 | 66篇 |
2002年 | 85篇 |
2001年 | 35篇 |
2000年 | 51篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1952年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有2015条查询结果,搜索用时 31 毫秒
1.
2.
Quince (Cydonia oblonga Mill.), pear (Pyrus communis L.) and olive (Olea europaea L.) genotypes were evaluated for their tolerance to iron deficiency stress by growing young plants in three types of aerated nutrient solutions: (1) with iron, (2) without iron or (3) low in iron and with 10 mM bicarbonate. Plants were obtained either from rooted softwood cuttings or from germination of seeds. The degree of tolerance was evaluated with several indices: (1) the chlorophyll content, (2) the root Fe3+ reducing capacity and (3) the whole plant relative growth. Fifteen hours before Fe3+ reducing capacity determination, iron was applied to the roots of plants with iron-stress, since this method resulted in increasing the reductase activity. All quince and pear genotypes increased the root Fe3+ reducing capacity when grown in the treatments for iron-stress, in relation to control plants of the same genotypes. In olive cultivars, the Fe3+ reducing capacity was lower in the iron-stress treatments than in the control one. Studying the relationship between relative growth and chlorophyll content for each genotype under iron-stress, in relation to both indices in control plants, a classification of species and genotypes was established. According to that, most olive cultivars and some pear rootstocks and cultivars appear more iron-efficient than quince rootstocks. Our study shows that in some woody species, determining root Fe3+ reducing capacity is not the best method to establish tolerance to iron deficiency stress. 相似文献
3.
Glycine transporter from rat brain stem and spinal cord is inactivated by specific sulfhydryl reagents. Modification of lysine residues also promotes a decrease of the transporter activity but in a lesser extent than that promoted by thiol group reagents. Mercurials showed a more marked inhibitory effect than maleimide derivatives. SH groups display a similar reactivity for p-chloromercuribenzenesulfonate (pCMBS) and mersalyl in synaptosomal membrane vesicles and proteoliposomes reconstituted with the solubilized transporter. However, different reactivity is observed with N-ethylmaleimide (MalNEt), the greatest effect being attained in membrane vesicles. The rate of inactivation by pCMBS and MalNEt is pseudo-first-order showing time- and concentration-dependence. pCMBS and MalNEt decrease the Vmax for glycine transport and to a lesser extent act on the apparent Km. Treatment with dithiothreitol (DTT) of the transporter modified by pCMBS results in a complete restoration of transporter activity indicating that the effect exercised by the reagent is specific for cysteine residues on the protein. It is concluded that SH groups are involved in the glycine transporter function and that these critical residues are mostly located in a relatively hydrophilic environment of the protein. 相似文献
4.
Eduardo León-Ruiz Purificación Alcázar Eugenio Domínguez-Vilches Carmen Galán 《Aerobiologia》2011,27(1):37-50
The present study sought to determine which of the common Poaceae species in the study area contribute most to the Poaceae
pollen season curve, and to determine the phenological behaviour of the species studied. The different floral phenophases
in thirty-three Poaceae species common in and around the city of Córdoba (SW Iberian Peninsula) were checked periodically
over the period 2004–2006. Results showed that longer phenological ranges were recorded in the coolest and wettest year, and
shorter ranges in the warmest and driest year. Moreover, ranges varied as a function of altitude: populations in lower-lying
areas flowered earlier than those at higher altitudes. The results, taken in conjunction with the findings of preliminary
research into potential pollen production, showed that probably only four of the Poaceae species studied—Dactylis glomerata, Lolium rigidum, Trisetaria panicea and Vulpia geniculata—were major contributors to the Poaceae airborne pollen curve. 相似文献
5.
J Ignacio Andrés Jesús Alcázar José M Alonso Adolfo Díaz Javier Fernández Pilar Gil Laura Iturrino Encarna Matesanz Theo F Meert Anton Megens Victor K Sipido 《Bioorganic & medicinal chemistry letters》2002,12(2):249-253
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described. 相似文献
6.
Alberto Alcázar Elena Martin Juan López-Fando Dr. Matilde Salinas 《Neurochemical research》1988,13(9):829-836
A simple and short purification procedure applicable to casein kinase II has been developed, for fully characterizing the enzyme from calf cerebral cortex cytosol. The procedure consists of four chromatographic steps: DEAE-cellulose, phosphocellulose, phosvitin-Sepharose and ATP-agarose which yields 87% pure casein kinase II. The purified enzyme shows three major bands with apparent molecular masses of 42, 38, and 27 kDa by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and is self-autophosphorylated on its 27 kDa polypeptide. The enzyme shows all the characteristics described for casein kinase II from other sources: it is independent of cyclic nucleotides, calcium/phospholipids, and double-stranded poly(I).poly(C); it can utilize both ATP and GTP as phosphoryl donors and can phosphorylate both casein and phosvitin but not histone. The kinetic studies establish that theK
m for ATP is 12.5 M and 25.1 M when using phosvitin and casein respectively as phosphoryl acceptors. TheK
m for phosvitin is 0.91 mg/ml and for casein 1.43 mg/ml, while theV
max is 315 nmol/min/per mg protein and 479 nmol/min/per mg protein for phosvitin and casein respectively. The activity of the kinase is highly stimulated by KCl or NaCl, and almost completely inhibited by heparin concentrations of 1 g/ml (92%). This inhibition is reduced to only 33% in the presence of optimal KCl concentrations (150 mM). Spermine stimulates enzyme activity, whilst hemin produces a slight inhibition. 相似文献
7.
Michel R. Pâquet Robert J. Romanek Robert J. Sargeant 《Molecular and cellular biochemistry》1992,109(2):149-155
Summary In rat adipocytes, the insulin stimulation of the rate of glucose uptake is due, at least partially, to the recruitment of glucose transporter proteins from an intracellular compartment to the plasma membrane.Vanadate is a known insulin mimetic agent and causes an increase in the rate of glucose transport in rat adipocytes similar to that seen with insulin. The objective of the present study was to determine whether vanadate exerts its effect through the recruitment of glucose transporters to the plasma membrane.We report that under conditions where vanadate stimulates the rate of 2-deoxyglucose uptake to the same extent as insulin, the concentration of GLUT-4 in the plasma membrane was increased similarly by both insulin and vanadate, and its concentration was decreased in the low density microsomal fraction. These results suggest that vanadate induces the recruitment of GLUT-4 to the plasma membrane. The effects of vanadate and insulin on the stimulation of 2-deoxyglucose uptake and recruitment of GLUT-4 were not additive.This is the first report of an effect of vanadate on the intracellular distribution of the glucose transporter. 相似文献
8.
Regeneration of transgenic plants of Prunus armeniaca containing the coat protein gene of Plum Pox Virus 总被引:1,自引:0,他引:1
Margit Laimer da Câmara Machado Artur da Câmara Machado Veronika Hanzer Hans Weiss Ferdinand Regner Herta Steinkellner Diethard Mattanovich Regina Plail Elisabeth Knapp Birgit Kalthoff Hermann Katinger 《Plant cell reports》1992,11(1):25-29
Summary A system was developed which allows the transfer of foreign genes into apricot cultivars. We report the transformation and regeneration of Prunus armeniaca plants with Agrobacterium tumefaciens strain LBA 4404 containing various binary plasmids, pBinGUSint, carrying the marker gene ß-glucuronidase (GUS) and pBinPPVm, carrying the coat protein gene of Plum Pox Virus (PPV). The marker gene GUS was used for optical evaluation of the efficiency of the transformation system. The coat protein gene of PPV was used to introduce coat protein mediated resistance against one of the most important pathogens of stone fruit trees in Europe and the whole Mediterranean area. This is the first report of the successful integration of a viral coat protein gene into a fruit tree species, opening a new perspective on the control of the disease.Abbreviations GUS
ß-glucuronidase
- PPV
Plum Pox Virus
- BA
6-benzylaminopurine
- NPTII
neomycin phosphotransferase II
- CP
coat protein
- CaMV
Cauliflower Mosaic Virus
- P35S 35S
promoter
- MS
Murashige and Skoog
- PCR
polymerase chain reaction
- P/C/I
phenol/chloroform/isoamylalcohol
- RNase
ribonuclease
- dNTP
deoxyribonucleosidetriphosphate
- DMSO
dimethyl sulfoxide 相似文献
9.
The biological activity of Cercospora beticola toxins might be enhanced by the complex formation with magnesium. Therefore, protonation and complexation equilibria of beticolins were studied. Beticolins carry three dissociable functions (H3B) two of which dissociate at a physiological pH. In the presence of magnesium, the neutralisation and protonation curves provide evidence for the formation of complexes. At physiological pH, the uncharged complex, Mg2H2B2, is the predominant form. The nonionised forms of free beticolin-1 and -2 fluoresce in a 50% dioxan-water solution and their emission maxima shift to higher wavelengths in water. The dianion HB(2-) is non-fluorescent both in water and in less polar media. The formation of the Mg2H2B2 complex which strongly fluoresces in nonpolar media is confirmed by a marked increase in fluorescence at 520 nm and by a shift of the excitation maximum. 相似文献
10.
B. Ringelhann J. G. Szelenyi M. Horanyi M. Svobodova V. Divoky K. Indrak S. Hollân A. Marosi M. Laub T. H. J. Huisman 《Human genetics》1993,92(4):385-387
We have identified seven different -thalassemia mutations and one -thalassemia determinant (the Sicilian type) in 32 members of 17 Hungarian families. The most common mutation is the IVS-I-1 (GA) change; its high frequency is comparable to that observed in neighboring Czechoslovakia. Additional mutations are of Mediterranean origin. One rare mutation (initiation codonATGGTG) was identified as an independent mutation because of the absence of known polymorphisms in the -globin gene. One new frameshift at codon 51 (-C) was observed in a single individual; hematological data were as expected for a °-thalassemia heterozygosity. 相似文献