全文获取类型
收费全文 | 116202篇 |
免费 | 6997篇 |
国内免费 | 15篇 |
专业分类
123214篇 |
出版年
2023年 | 706篇 |
2022年 | 606篇 |
2021年 | 1389篇 |
2020年 | 1309篇 |
2019年 | 1250篇 |
2018年 | 3275篇 |
2017年 | 2945篇 |
2016年 | 3922篇 |
2015年 | 5143篇 |
2014年 | 5227篇 |
2013年 | 6991篇 |
2012年 | 8193篇 |
2011年 | 7253篇 |
2010年 | 4699篇 |
2009年 | 3494篇 |
2008年 | 5879篇 |
2007年 | 5551篇 |
2006年 | 5367篇 |
2005年 | 4549篇 |
2004年 | 4530篇 |
2003年 | 4092篇 |
2002年 | 3730篇 |
2001年 | 2867篇 |
2000年 | 2769篇 |
1999年 | 2118篇 |
1998年 | 902篇 |
1997年 | 654篇 |
1996年 | 696篇 |
1995年 | 629篇 |
1992年 | 1203篇 |
1991年 | 1089篇 |
1990年 | 1038篇 |
1989年 | 1120篇 |
1988年 | 951篇 |
1987年 | 935篇 |
1986年 | 881篇 |
1985年 | 923篇 |
1984年 | 810篇 |
1983年 | 672篇 |
1982年 | 565篇 |
1979年 | 767篇 |
1978年 | 591篇 |
1975年 | 674篇 |
1974年 | 735篇 |
1973年 | 719篇 |
1972年 | 647篇 |
1971年 | 573篇 |
1970年 | 623篇 |
1969年 | 678篇 |
1968年 | 647篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M. Lorieux X. Perrier B. Goffinet C. Lanaud D. González de León 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,90(1):81-89
In F2 populations, gametic and zygotic selection may affect the analysis of linkage in different ways. Therefore, specific likelihood equations have to be developed for each case, including dominant and codominant markers. The asymptotic bias of the classical estimates are derived for each case, in order to compare them with the standard errors of the suggested estimates. We discuss the utility and the efficiency of a previous model developed for dominant markers. We show that dominant markers provide very poor information in the case of segregation distortion and, therefore, should be used with circumspection. On the other hand, the estimation of recombination fractions between codominant markers is less affected by selection than is that for dominant markers. We also discuss the analysis of linkage between dominant and codominant markers. 相似文献
992.
Summary Contents of arginine, ornithine, urea and ammonia in wine were monitored during aging process by two flor veil-forming yeast strains. The patterns of yeast growth were different for the two strains studied. Urea excretion and uptake were dependent on yeast strain, so that finished wines showed different concentrations of urea. The effect of limited aeration was also investigated for Saccharomyces cerevisiae var. capensis. The results indicated that aeration promoted yeast growth in veil, thus reducing urea concentration until its exhaustion in wine. 相似文献
993.
Paula Veríssimo Cristina Esteves Carlos Faro Euclides Pires 《Biotechnology letters》1995,17(6):621-626
The flowers of cardoon (genus Cynara) are traditionally used in Portugal for cheese making. In this work the vegetable rennet of the species Cynara cardunculus L. was characterized in terms of enzymic composition and proteolytic specificity of its proteinases (cardosin A and cardosin B). Cardosin A was found to cleave insulin B chain at the bonds Leu15-Tyr16, Leu17-Val18 and Phe25-Tyr26. In addition to the bonds mentioned cardosin B cleaves also Glu13-Ala14, Ala14-Leu15 and Phe24-Phe25 indicating that it has a broader specificity. The kinetic parameters for the hydrolysis of the synthetic peptide Leu-Ser-Phe(NO2)-Nle-Ala-Leu-oMe were also determined and compared to those of chymosin and pepsin. The results obtained indicate that in terms of specificity and kinetic parameters cardosin A is similar to chymosin whereas cardosin B is similar to pepsin. It appears therefore that the enzyme composition of cardoon rennet closely resembles that of calf rennet. 相似文献
994.
Antonio del Castillo-Olivares Alicia Esteban del Valle Javier Márquez Ignacio NÚñez de Castro Miguel ángel Medina 《Journal of bioenergetics and biomembranes》1995,27(6):605-611
Ehrlich cell plasma membrane ferricyanide reductase activity increased in the presence of mastoparan, a generic activator of G proteins, using either whole cells or isolated plasma membrane fractions. Agents that increase intracellularcAMP also increased the rate of ferricyanide reduction by Ehrlich cells. For the first time, evidence is shown on a modulation of plasma membrane redox system bycGMP. In fact, permeant analogs ofcGMP, dibutyrylcGMP, and 8-bromo-cGMP increased the rate of ferricyanide reduction by the Ehrlich cell plasma membrane redox system. Furthermore, specific inhibition ofcGMP-phosphodiesterases by dipyridamole was also accompanied by an enhancement in the rate of ferricyanide reduction. On the other hand, treatments expected to increase cytoplasmic Ca2+ concentrations were accompanied by a remarkable stimulation of the reductase activity. Taking all these data together, it seems that the Ehrlich cell plasma membrane redox system is under a multiple and complex regulation by different signal transduction pathways involving G proteins, cyclic nucleotides, and Ca2+ ions. 相似文献
995.
Non-antagonistic interactions between arthropods and leaves of insectivorous plants with adhesive traps so far have never been reported. The mites are common prey of such plants, but we have found a new subspecies of the mite Oribatula tibialis living on the leaves of Pinguicula longifolia. Because of its small size and the low glandular density of the host, the mite moves without being trapped by the mucilaginous droplets of the leaf surface. P. longifolia provides shelter and food for the mite, while the plant may also benefit because of its fungivorous and scavenging activities. This new interaction is another dramatic example of widespread miteplant associations. 相似文献
996.
Yeast colonizing the intestine of rainbow trout (Salmo gairdneri) and turbot (Scophtalmus maximus) 总被引:1,自引:0,他引:1
Yeast were isolated from the intestine of farmed rainbow trout (Salmo gairdneri), turbot (Scophtalmus maximus), and free-living flat-fish (Pleuronectes platessa and P. flesus). The average number of viable yeasts recovered from farmed rainbow trout was 3.0 × 103 and 0.5 × 102 cells per gram homogenized intestine for white and red-pigmented yeasts, respectively. The dominant species were Debaryomyces hansenii, Saccharomyces cerevisiae, Rhodotorula rubra, and R. glutinis. In 5 of 10 free-lving marine fish, > 100 viable yeast cells per gram intestinal mucus were recovered. Red-pigmented yeasts dominated and composed >90% of the isolates. Colonization experiments were performed by inoculating rainbow trout and turbot with fish-specific, isolated yeast strains and by examining the microbial intestinal colonization at intervals. Inoculation of experimental fish with pure cultures of R. glutinis and D. hansenii HF1 yielded colonization at a level several orders of magnitude higher than before the inoculation. Up to 3.8 × 104, 3.1 × 106, and 2.3 × 109 viable yeast cells per gram intestine or feces were recovered in three separate colonization experiments. The high level of colonizing yeasts persisted for several weeks. The concentrations of yeasts in the tank water never exceeded 103 viable cells per milliliter. No traces of fish sickness as a result of high yeast colonization were recorded during any of the colonization experiments. For periods of the experiments, the concentration of aerobic bacteria in the fish intestine was lower than the intestinal yeast concentration. Scanning electron microscopy studies demonstrated a close association of the yeasts with the intestinal mucosa. The mucosal colonization was further demonstrated by separating intestinal content, mucus, and tissue. All compartments were colonized by >103 viable yeast cells per gram. No bacteria were detected on the micrographs, indicating that their affinity for the intestinal mucosa was less than that of the yeasts.
Correspondence to: Thomas Andtid 相似文献
997.
Júlia Tandori László Nagy Ágnes Puskás Magdolna Droppa Gábor Horváth Péter Maróti 《Photosynthesis research》1995,45(2):135-146
A spontaneous mutant (R/89) of photosynthetic purple bacterium Rhodobacter sphaeroides R-26 was selected for resistance to 200 M atrazin. It showed increased resistance to interquinone electron transfer inhibitors of o-phenanthroline (resistance factor, RF=20) in UQo reconstituted isolated reaction centers and terbutryne in reaction centers (RF=55) and in chromatophores (RF=85). The amino acid sequence of the QB binding protein of the photosynthetic reaction center (the L subunit) was determined by sequencing the corresponding pufL gene and a single mutation was found (IleL229 Met). The changed amino acid of the mutant strain is in van der Waals contact with the secondary quinone QB. The binding and redox properties of QB in the mutant were characterized by kinetic (charge recombination) and multiple turnover (cytochrome oxidation and semiquinone oscillation) assays of the reaction center. The free energy for stabilization of QAQB
– with respect to QA
–QB was GAB=–60 meV and 0 meV in reaction centers and GAB=–85 meV and –46 meV in chromatophores of R-26 and R/89 strains at pH 8, respectively. The dissociation constants of the quinone UQo and semiquinone UQo
– in reaction centers from R-26 and R/89 showed significant and different pH dependence. The observed changes in binding and redox properties of quinones are interpreted in terms of differential effects (electrostatics and mesomerism) of mutation on the oxidized and reduced states of QB.Abbreviations BChl
bacteriochlorophyll
- Ile
isoleucine
- Met
methionin
- P
primary donor
- QA
primary quinone acceptor
- QB
secondary quinone acceptor
- RC
reaction center protein
- UQo
2,3-dimethoxy-5-methyl benzoquinone
- UQ10
ubiquinone 50
This work is dedicated to the memory of Randall Ross Stein (1954–1994) and is, in a small way, a testament to the impact which Randy's ideas have had on the development of the field of competitive herbicide binding. 相似文献
998.
Angel García-Gutiérrez Francisco R. Cantón Fernando Gallardo Francisca Sánchez-Jiménez Francisco M. Cánovas 《Plant molecular biology》1995,27(1):115-128
Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark. 相似文献
999.
Influence of external factors on secondary embryogenesis and germination in somatic embryos from leaves of Quercus suber 总被引:2,自引:0,他引:2
Bárbara Fernández-Guijarro Cristina Celestino Mariano Toribio 《Plant Cell, Tissue and Organ Culture》1995,41(2):99-106
Somatic embryogenesis was obtained in cultures of leaves from young seedlings of Quercus suber L. A two-stage process, in which benzyladenine and naphthaleneacetic acid were added first at high and then at low concentrations, was required to initiate the process. Somatic embryos arose when the explants were subsequently placed on medium lacking plant growth regulators. The embryogenic lines remained productive, by means of secondary embryogenesis, on medium without growth regulators. However, this repetitive induction was influenced by the macronutrient composition of the culture medium. Both low total nitrogen content and high reduced nitrogen concentration decreased the percentage of somatic embryos that showed secondary embryogenesis. Our results suggest that alternate culture on medium that increases embryo proliferation and a low salt medium prohibiting embryo formation will partially synchronize embryo development. Chilling slightly reduced secondary embryogenesis but gave a modest increase in germination. Maturation under light followed by storage at 4 °C for at least 30 days gave the best results in switching embryos from an embryogenic pathway to a germinative one. Under these conditions 15% of embryos showed coordinated root and shoot growth and 35% formed either shoots or mostly roots. These percentages were higher than those of embryos matured in darkness. This result indicates that a specific treatment is required after maturation and before chilling to activate the switch from secondary embryo formation to germination.Abbreviations BA
benzyladenine
- NAA
naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- BA
indolebutyric acid
- MS
Murashige & Skoog (1962) medium
- SH
Schenk & Hildebrandt (1972) medium
- G
Gamborg (1966, PRL-4-C) medium (macronutrients in mg l–1: NaH2PO4·H2O, 90; Na2HPO4, 30; KCl, 300; (NH4)2SO4, 200; MgSO4·7H2O, 250; KNO3, 1000, CaCl2·2H2O, 150)
- PGR
plant growth regulator 相似文献
1000.
J. M. Barrasa S. Camarero A. T. Martínez K. Ruel 《Applied microbiology and biotechnology》1995,43(4):766-770
The ultrastructural patterns characterizing wheat straw degradation by the ligninolytic fungi Phanerochaete chrysosporium and Trametes versicolor were studied. During fungal attack, the less lignified tissues were degraded first, whereas the xylematic and sclerenchymatic fibers underwent a delayed attack. In straw samples degraded by T. versicolor, partial delignification, defibrillation and swelling of cell walls, often causing separation between primary and secondary walls, were observed. By contrast, the formation of erosions and fissures, with minor lignin removal, characterized the attack to the cell wall by P. chrysosporium. At an advanced stage of decay, KMnO4 staining demonstrated abundant electron-dense material around hyphae and in the proximity of the cell-wall surface. In the case of P. chrysosporium, spherical black bodies were found in the erosions and fissures produced during fungal attack. 相似文献