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101.
Cytoplasmic determinants that specify the fate of endoderm, muscle and epidermis cells are known to be localized in specific
areas of fertilized eggs of ascidians. The presence of such cytoplasmic determinants in unfertilized eggs was demonstrated
in previous studies, but no information has yet been proved about their distribution. To investigate the distribution of cytoplasmic
determinants in unfertilized eggs, we devised a method for distinguishing the polarity of unfertilized eggs using vital staining
and we performed cytoplasmic-transfer experiments by fusing blastomeres and cytoplasmic fragments from various identified
regions of unfertilized eggs. Cytoplasmic fragments, that contained cortical and subcortical material, from five different
positions along the animal-vegetal axis were prepared, and they were fused with a4.2 (presumptive-epidermis) or A4.1 (non-epidermis)
blastomeres. The ectopic development of endoderm, muscle and epidermis cells that was promoted by the transplanted cytoplasm
was assessed by examining the expression of alkaline phosphatase (ALP), myosin and epidermis-specific antigen, respectively.
Differentiation of endoderm and muscle was observed at higher frequencies as cytoplasmic fragments closer to the vegetal pole
were transplanted. Conversely, formation of epidermis was observed at higher frequencies as cytoplasmic fragments closer to
the animal pole were transplanted. The results suggest that, in cortical and subcortical regions of unfertilized ascidian
eggs, endoderm and muscle determinants are widely distributed along a gradient, with maximum activity at the vegetal pole,
whilst epidermis determinants are also distributed along a gradient but with maximum activity at the animal pole.
Recieved: 10 June 1996 / Accepted: 12 September 1996 相似文献
102.
Summary Calluses from five asparagus genotypes G14, G32, G171, G203, and G447 and hybrid Jersey Giant (JG) were incubated at three
temperature regimes (24, 27, and 30°C) on embryo induction medium to assess somatic embryo development and conversion to plantlets.
The calluses from three genotypes (G14, G32, and G171) were not responsive, failing to produce somatic embryos at any temperature
regime. For three responsive genotypes (G203, G447, and JG), both incubation temperature and genotype significantly affected
the numbers of somatic embryos produced. The calluses produced the most and the least numbers of total, bipolar, and globular
embryos when incubated at 27°C and 24°C, respectively. When incubated at 27°C, G203 produced the highest numbers of total
and globular embryos, 178 g−1 callus and 142 g−1 callus, respectively while G447 produced the highest number of bipolar embryos, 77 g−1 callus. Incubation temperature but not genotype significantly affected the conversion of somatic embryos to plantlets. The
somatic embryos recovered from the three responsive genotypes incubated at 27°C also converted to plantlets at the highest
frequencies, 60–63% of the bipolar embryos and 42–43% of the globular embryos converted to plantlets, while the somatic embryos
recovered from the calluses incubated at 24°C converted to plantlets at the lowest frequencies. 相似文献
103.
P. Binarova C. Cihalikova J. Dolezel S. Gilmer L. C. Fowke 《In vitro cellular & developmental biology. Plant》1996,32(2):59-65
Summary Examination of unfixed immature somatic embryos of white spruce (Picea glauca) with fluorescent rhodamine-labeled phalloidin revealed an extensive network of fine actin microfilaments (MFs) in the embryonal
region which were not detected in specimens fixed with formaldehyde. Transition cells linking the embryonal region and suspensor
cells contained fine MFs as well as bundles of MFs. The large, highly vacuolated suspensor cells were characterized by actin
MF cables only. Treatment of embryos with cytochalasin B (CB) removed the fine MFs from the embryonal region and transition
cells, but many MF cables in suspensor cells were resistant. Full recovery from CB treatment was observed in most somatic
embryos. Embryogenic protoplasts capable of regenerating to somatic embryos in culture were released from only the embryonal
region of somatic embryos. Both uninucleate and multinucleate embryogenic protoplasts retained the extensive network of fine
actin MFs. In contrast, protoplasts derived from vacuolated suspensor cells and vacuolated free-floating cells contained thick
MF bundles and were not embryogenic. Distinct MF cages enclosed nuclei in multinucleate protoplasts and may be responsible
for preventing nuclear fusion. Microspectrophotometric analyses showed that the DNA contents of embryonal cells in the embryo
and embryogenic protoplasts were similar and characteristic of rapidly dividing cell populations. However, transition and
suspensor cells which released nonembryogenic protoplasts appeared to be arrested in G1, and suspensor cells showed signs of DNA degradation. 相似文献
104.
105.
Summary First divisions of embryogenic cells were studied in leaves of plantlets of aCichorium hybrid (C. intybus L. ×C. endivia L.) cultured in vitro in a liquid agitated medium, at 35 °C in the dark. Stages of reactivation of competent cells were characterized by increase of nucleus and nucleolus diameter, migration of the nucleus in the centre of the cell and thickening of the cell wall. The first division of reactivated embryogenic cells was symmetrical and anticlinal in regard to the xylem vessels orientation. Embryogenic structures consisted in I-type tetrads or in rows of 4–8 cells. Then the divisions occurred in thickness at one end, without polarization or formation of a suspensor-like structure.Abbreviations EC
embryogenic cell
- ES
embryogenic structure 相似文献
106.
107.
Factors controlling somatic embryogenesis 总被引:5,自引:0,他引:5
Histological and ultrastructural, molecular and elemental distribution changes were investigated during the induction of direct somatic embryogenesis using theCamellia japonica leaf culture system. In this culture system, direct somatic embryogenesis is induced in a controlled way in a specific leaf region (leaf blade) within a leaf. Embryogenic and non-embryogenic leaf regions have characteristic energy-dispersive X-ray spectra already before induction. According to these results electron probe X-ray microanalysis (EPMA) can be a tool for early diagnosis of embryogenic competence. Histological studies showed that severe fluctuations in the number of calcium oxalate crystals and in starch accumulation occur after induction but only in induced tissues. Changes in the cell wall composition of competent cells occur shortly after the induction treatment. The induction of morphogenesis is linked to the appearance of callose covering the surface cells of induced leaves and calluses. A 2nd deposition of material (cutin) is necessary for normal somatic embryogenesis to occur. The involvement of lipid transfer proteins in the appearance of cutin in the embryogenic regions of the explant is suggested. 相似文献
108.
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
109.
P. van der Valk F. Ruis A. M. Tettelaar-Schrier C. M. van de Velde 《Plant Cell, Tissue and Organ Culture》1995,40(1):101-103
The effect of benzyladenine (BA) on the production of shoot-forming callus from seeds of two Poa pratensis cultivars was studied. Addition of low concentrations (0.1–0.3 mg l-1) of BA to Murashige & Skoog (MS) callus induction medium containing 1 or 2 mg l-1 2,4-dichlorophenoxyacetic acid (2,4-d) stimulated somatic embryogenesis and strongly increased the percentage of seeds producing shoot-forming callus in both cultivars. 相似文献
110.
N. Boget J. M. Torné L. Willadino M. Santos 《Plant Cell, Tissue and Organ Culture》1995,40(2):139-144
A comparative study of polyamine (putrescine, spermidine and spermine) levels was conducted with maize calli originating from a) immature embryos and b) pollen embryos capable of plant regeneration. The differences observed in the studied parameters of the two kinds of calluses are related to their cellular origin and to their regeneration capacity. Moreover, only the calluses proceeding from immature embryos differentiated into preembryogenic structures, which eventually developed into plants. Although total polyamine levels in pollenderived calluses were significantly higher than those from immature embryos, spermidine and spermine were the predominant polyamines in both culture types. Furthermore, polyamine fractions of these calluses also showed differences. All these phenomena may be related with the differences observed in the callus embryogenic response. These findings may be useful in understanding the implication of polyaminesin embryogenetic processes.Abbreviations IEC
immature-embryo calluses
- PAs
polyamines
- PEC
pollen-embryo calluses
- PH
insoluble conjugated PA fraction
- Put
putrescine
- S
free PA fraction
- SH
soluble conjugated PA fraction
- Spd
spermidine
- Spm
spermine 2,4d-2,4 dichlorophenoxyacetic acid 相似文献