全文获取类型
收费全文 | 2335篇 |
免费 | 47篇 |
国内免费 | 39篇 |
出版年
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 30篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 44篇 |
2013年 | 78篇 |
2012年 | 36篇 |
2011年 | 53篇 |
2010年 | 27篇 |
2009年 | 78篇 |
2008年 | 104篇 |
2007年 | 89篇 |
2006年 | 108篇 |
2005年 | 119篇 |
2004年 | 116篇 |
2003年 | 94篇 |
2002年 | 73篇 |
2001年 | 91篇 |
2000年 | 102篇 |
1999年 | 86篇 |
1998年 | 93篇 |
1997年 | 88篇 |
1996年 | 80篇 |
1995年 | 89篇 |
1994年 | 70篇 |
1993年 | 82篇 |
1992年 | 77篇 |
1991年 | 59篇 |
1990年 | 48篇 |
1989年 | 45篇 |
1988年 | 38篇 |
1987年 | 40篇 |
1986年 | 19篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有2421条查询结果,搜索用时 15 毫秒
201.
S.?M.?A.?Zobayed P.?K.?SaxenaEmail author 《In vitro cellular & developmental biology. Plant》2003,39(6):605-612
Summary The embryogenic potential of different Echinacea purpurea tissues, viz. leaf, cotyledon, and root, was investigated. Maximum embryo-induction was achieved from leaf dises cultured
on Murashige and Skoog medium supplemented with benzylaminopurine (5.0 μM) and indolebutyric acid (2.5 μM) where 95% of the explants responded, yielding an average of 83 embryos per explant within 4 wk of culture. Incubation of
cultures in the dark for an initial period of 14 d significantly increased the frequency of somatic embryogenesis (6–8-fold
in leaf explants). Exposure of the abaxial surface of leaves to the medium significantly increased the number of embryos.
Transfer of somatic embryos to a medium devoid of growth regulators resulted in 80% germination within 7 d. Over 73% of the
somatic embryos developed roots within 28 d of culture on a medium containing naphthaleneacetic acid (10 μM) with a maximum root number of 9.8 per plantlet. Transplanting ex vitro and acclimatization for a period of 7 d were sufficient to promote establishment of plants in the greenhouse, and more than
90% of the regenerated plants survived. 相似文献
202.
Randall?P.?NiedzEmail author W.?L.?McKendree R.?C.?ShattersJr 《In vitro cellular & developmental biology. Plant》2003,39(6):586-594
Summary Electroporation conditions were optimized for the transfection of protoplasts isolated from an embryogenic cell line of sweet
organe [Citrus sinensis (L.) Osbeck ev. Hamlin]. Electric field strength (375–450 V cm−1) vector DNA concentration (100 μgml−1), carrier DNA concentration (100 μgml−1), electroporation buffer (pH 8), and preelectroporation heat shock of protoplasts (5 min at 45°C) were optimized. The plasmid
vector pBI221 containing the β-glucuronidase (GUS) coding sequence under the control of the CaMV 35S promoter was used and
GUS activity was measured 24h after electroporation. All variables significantly affected transfection efficiency and when
optimal conditions for each were combined. GUS activity was 7714 pmol 4-methylumbelliferone (MU) mg−1 (protein) min−1. Protoplasts were then electroporated in the presence of green fluorescent protein (GFP) expression vectors pARS101 or pARS108.
Green fluorescent embryos were selected, plants regenerated, and integration of the transgene was confirmed by Southern blot
analysis. Both plasmids were constructed using EGFP, a GFP variant 35 times brighter than wtGFP, having a single, red-shifted
excitation peak, and optimized for human codon-usage. pARS101 was constructed by placing EGFP under the control of a 35S–35S
promoter containing 33 bp of the untranslated leader sequence from alfalfa mosaic virus. pARS108 was constructed similarly
except sequences were added for transport and retention of EGFP in the lumen of the endoplasmic reticulum.
Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the US Department of Agriculture
and does not imply its approval to the exclusion of other products or veudors that may also be suitable. 相似文献
203.
Hangsik?Moon David?F.?HildebrandEmail author 《In vitro cellular & developmental biology. Plant》2003,39(6):623-628
Summary Cermination of soybean [Glycine max (L.) Merrill] somatic embryos and conversion to whole plants are generally low. This study was conducted to investigate the
effects of proliferation, maturation, and desiccation methods on conversion of soybean somatic embryos to plants. Soybean
cv. Jack somatic embryos, proliferated on a solid medium containing 90.5 μM (20 mgl−1) 2.4-dichlorophenoxyacetic acid (2.4-D) (MSD20), showed a regeneration rate signficantly higher than those proliferated in
a liquid medium containing 45.25 μM (10mgl−1) 2,4-D (FN Lite). When a liquid medium without 2,4-D and B5 vitamins (FN Superlite) was used for maturation, the duration
of time necessary for embryo development could be shortened by more than a month compared to maturation on a standard solid
medium (MSM6AC). An air-drying method, in which somatic embryos were desiccated in an empty sealed Petri dish for 3–5d, gave
rise to the best germination efficiency among the four desiccation methods tested: fast, slow, air, and KCl methods. The final
percentage of moisture seems important since embyros over-dried by the fast and slow methods did not convert well into plants. 相似文献
204.
Somatic embryogenesis in carrot (Daucus carota) is autonomously inhibited by 4-hydroxybenzyl alcohol (4HBA), which is produced by embryogenic cells. Because somatic embryogenesis is used as a model of zygotic embryogenesis, we assayed for 4HBA in carrot seeds and analyzed the effect of 4HBA on seed formation to determine whether 4HBA is also produced during zygotic embryogenesis. HPLC analysis showed that 4HBA accumulated in flowers and immature and mature fruits, but not in vegetative tissues. The concentration of 4HBA was highest after flowering, when the zygote developed into the early globular-stage embryo. 4HBA accumulation then decreased with seed development. Exogenous application of 4HBA to immature carrot fruits inhibited seed formation. Many 4HBA-treated seeds did not include a mature embryo. These results indicate that the production and accumulation of 4HBA occurs during carrot seed development and that 4HBA has an inhibitory effect on carrot seed formation. 相似文献
205.
Ishizaki Takuma Komai Fuminori Masuda Kiyoshi 《Plant Cell, Tissue and Organ Culture》2001,67(3):251-255
A system for subculture of spinach (Spinacia oleracea L.) roots was established, and differences in regeneration; namely, embryogenic competence, among individuals of the `Nippon' cultivar were examined. Root tissues, excised from seedlings, were grown on medium without growth regulators and subcultured on the same medium and then on medium that contained 10 M naphthaleneacetic acid and 0.1 M gibberellic acid to induce callus formation. Calli were transferred to medium without growth regulators. All explants formed calli. However, the frequency of embryo formation varied among lines. Higher concentrations of gibberellic acid in the callus-induction medium had limited effects on somatic embryogenesis from poorly embryogenic lines. These results indicate that inherent factors are important for somatic embryogenesis in spinach and that the root subculture system is useful for identifying strongly regenerative genotypes among individuals of a single cultivar. 相似文献
206.
Sucrose, glucose, fructose, and melibiose in different concentrations and combinations in the induction media influenced the viability of the isolated maize microspores and the formation of multinuclear structures. The induction of multinuclear structures on media containing combination of sucrose, fructose and glucose was lower than on media only with sucrose. In media containing melibiose alone or in combination with sucrose, no induction of multinuclear structures was found, however, microspore viability was improved. 相似文献
207.
S. Khuri M.R. Shmoury R. Baalbaki M. Maunder S.N. Talhouk 《Biodiversity and Conservation》2000,9(9):1261-1273
Cedrus libani, the cedar of Lebanon, is a threatened conifer native to the Levant. Over 4000 years of exploitation have resulted in the fragmentation and degradation of the Lebanese cedar populations. Continued urban and agricultural development in Lebanon adds to the difficulty of effective conservation. Two protected areas have recently been established which contain two of the more important forests: a cedar dominated forest in the Shouf region and a mixed forest at Ehden. A number of other populations are protected by ministerial decrees, and there is a need for rigorous management of all the remaining populations. The application of in vitro techniques such as somatic embryogenesis may assist in the conservation of this species. We have produced somatic pro-embryos using immature zygotic tissue as explants cultured on half-strength MS medium containing an auxin and a cytokinin (10 M 2,4-D and 5 M BAP). The application of somatic embryogenesis to the Lebanese cedar would be in the propagation and preservation of selected genotypes, either those from old growth provenance for use in restoration, or those with desirable commercial or horticultural characteristics. 相似文献
208.
冬小麦原生质体培养的胚状体直接发生 总被引:5,自引:0,他引:5
冬小麦品种“京花一号”胚性愈伤组织在改良的N6培养基(NBD培养基)上继代得到易碎型胚性愈伤组织,转入改良MS液体培养基(MSDL培养基)后得到胚性悬浮系,分离的原生质体在改良的MS培养基(MSDP培养基)上培养,再生细胞直接产生体细胞胚胎,并再生出完整植株。体细胞胚胎形成过程与小麦合子胚的形成过程十分相似。 相似文献
209.
Direct somatic embryogenesis was induced in root tissues of the Cichorium hybrid `474' (C. intybus L. var. sativum×C. endivia L. var. latifolia). Addition of β-d-glucosyl Yariv reagent (βGlcY), a synthetic phenylglycoside that specifically binds arabinogalactan-proteins (AGPs), to the
culture medium blocked somatic embryogenesis in a concentration-dependent manner with complete inhibition of induction occurring
at 250 μM βGlcY. The AGP-unreactive α-d-galactosyl Yariv reagent had no biological activity in this system. Upon transfer of 250 μM βGlcY-treated roots to control
conditions, somatic embryogenesis was recovered with a time course similar to that of control roots. The βGlcY penetrated
roots and bound abundantly to developing somatic embryos, to the root epidermis and the stele. Immunofluorescence and immunogold
labelling using monoclonal antibodies (JIM13, JIM16 and LM2) revealed that AGPs were localised in the outer cell walls peripheral
cells of the globular embryo. A spatio-temporal expression of AGPs appeared to be associated with differentiation events in
the somatic embryo during the transition from the globular stage to the torpedo stage. To verify βGlcY specificity, molecules
that bound βGlcY were extracted from treated conditioned medium and identified as AGPs by using the same monoclonal antibodies.
In addition, AGPs were found to be abundantly present in the medium during embryogenic culture. All of these results establish
the implication of AGPs in embryo development, and their putative role in somatic embryogenesis is discussed.
Received: 26 August 1999 / Accepted: 28 January 2000 相似文献
210.
The synthesis of DNA in nuclei and organellar nucleoids at the various stages of somatic embryogenesis in carrot (Daucus carota L. cv. Kurodagosun) was analyzed using anti-5-bromo-2′-deoxyuridine (BrdU) immunofluorescence microscopy. The active syntheses
of both nuclear and organellar DNA started in the cells forming the embryo proper 3 d after the initiation of embryogenesis,
but not in cells forming suspensor-like cell aggregates. In the early globular embryo, active DNA syntheses were continuously
observed in the whole embryo proper, except for the progenitor cells of the root apical meristem (RAM) and shoot apical meristem
(SAM). These were recognized as slowly cycling cells with a non-BrdU-labelled nucleus and strongly BrdU-labelled organellar
nucleoids. At the heart- and torpedo-shaped embryo stages, both nuclear and organellar DNA syntheses were inactive in the
presumptive RAM and SAM. Thus, slowing down of organellar DNA synthesis is not coupled with, but is later than, that of nuclear
DNA synthesis in the progenitor cells of the embryonic RAM and SAM. These findings clearly indicate that the timing of DNA
synthesis is similar in the progenitor cells of both the RAM and SAM in the early stages of somatic embryogenesis.
Received: 18 January 2000 / Accepted: 2 March 2000 相似文献