全文获取类型
收费全文 | 4359篇 |
免费 | 70篇 |
国内免费 | 124篇 |
出版年
2023年 | 15篇 |
2022年 | 23篇 |
2021年 | 39篇 |
2020年 | 23篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 25篇 |
2016年 | 39篇 |
2015年 | 37篇 |
2014年 | 68篇 |
2013年 | 115篇 |
2012年 | 64篇 |
2011年 | 84篇 |
2010年 | 50篇 |
2009年 | 162篇 |
2008年 | 194篇 |
2007年 | 177篇 |
2006年 | 213篇 |
2005年 | 187篇 |
2004年 | 189篇 |
2003年 | 131篇 |
2002年 | 118篇 |
2001年 | 143篇 |
2000年 | 201篇 |
1999年 | 155篇 |
1998年 | 191篇 |
1997年 | 175篇 |
1996年 | 192篇 |
1995年 | 191篇 |
1994年 | 152篇 |
1993年 | 156篇 |
1992年 | 144篇 |
1991年 | 130篇 |
1990年 | 114篇 |
1989年 | 110篇 |
1988年 | 91篇 |
1987年 | 77篇 |
1986年 | 50篇 |
1985年 | 83篇 |
1984年 | 53篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 18篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有4553条查询结果,搜索用时 359 毫秒
981.
Somatic embryogenesis in wild cherry (Prunus avium) 总被引:3,自引:0,他引:3
Garin Elisabeth Grenier Emmanuel Grenier-De March Ghislaine 《Plant Cell, Tissue and Organ Culture》1997,48(2):83-91
Indirect somatic embryogenesis was obtained inPrunus avium L. from either somatic or zygotic embryos. An embryogenic line
was established by reinduction of embryogenic calluses from somatic embryos. The line was maintained for more than 3 years
through 6 generations of embryogenic cultures. In the last 2 generations, more than 50% of the explants were embryogenic.
Embryos at different stages of development were produced. Among cotyledonary-stage embryos, 50% had two cotyledons and a distinct
hypocotyl, 43% had one or more than 2 cotyledons and 7% had fused cotyledons. Most of the embryos were translucent and conversion
into plantlets was very rare. Secondary embryos could be observed to occur with low frequency from cultured somatic embryos
and from embryos emerging from calluses. Indirect somatic embryogenesis was also induced from immature zygotic embryos. From
one donor tree, 51% of the explants were embryogenic when cultured on a medium containing 0.9 μM kinetin, 0.9 μM BA and 0.5
μM NAA.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
982.
By using DNA-specific fluorescent dye and a confocal laser scanning microscope, the present study was designed to investigate the cytological characteristics of dedifferentiating initiation during pretreatment and em-bryogenesis during culture in freshly-isolated microspores of barley, and the difference in main developmental pathway between freshly-isolated and cold-treated microspores. The results revealed that ( i ) freshly-isolated microspores started the initiation within 12 h of mannitol pretreatment, whose main cytological characteristics were that: cell vol-ume was obviously extended; the volume of nuclei and nucleoli were also greatly increased; nucleoli were extremely clear and highly condensed; N/C ratio was very high; ( ii ) all the pretreatment methods led to the initiation of the mi-crospores, thus triggering the embryogenic process; ( iii ) pretreatment methods influenced the main developmental pathway of microspores by changing the pattern of the first mitosis. The cold-treated microspor 相似文献
983.
开口箭属一新种及其核型和花粉形态 总被引:1,自引:0,他引:1
文章报道了新种屏边开口箭T.pingbianensis J.L.Huang et X.Z.Liu及其核型和花粉形态。屏边开口箭的核型公式为2n=38=14m+lOsm+8st+6t,具明显的二型性,属3C型。花粉粒为球形,无萌发孔沟,外壁具皱块状纹饰。从花结构、核型和花粉形态上看,屏边开口箭和伞柱开口箭T.fungilliformis Wang et Liang亲缘关系近,而且伞柱开口箭比屏边开口箭在一系列特征上都较特化。 相似文献
984.
Lokesh Garg Narinder N. Bhandari Vijay Rani Sant S. Bhojwani 《Plant cell reports》1996,15(11):855-858
Immature endosperm of Acacia nilotica formed a nodular callus on MS medium supplemented with 2,4-D, BAP and CH. In the third passage on this medium, in the dark, the callus differentiated somatic embryos. The embryos germinated on MS only after 15 d pre-treatment on modified MS medium in which major salts were replaced by those of major salts of B5 medium and supplemented with glutamine, CH and CW. Triploid nature of the somatic embryos was confirmed by Feulgen cytophotometry.Abbreviations ABA
abscisic acid
- AC
activated charcoal
- BAP
6-benzylaminopurine
- B5
Gamborg et al. (1968) medium
- CH
casein hydrolysate
- CW
coconut water
- d
days
- MS
Murashige and Skoog (1962) medium
- PEG 4000
polyethylene glycol
- MW
3500–4000
- 2,4-D
2,4-dichlorophenoxyacetic acid 相似文献
985.
In July 1994, we were able to collect airborne fungal spores and pollen grains over the Adriatic Sea from the upper deck of
the Oceanographic Ship Urania (CNR). The biological particles were collected using a modified Lanzoni VPPS 1000 sampler (operating
at a flux of 10 LPM), on glycerine-gelatine coated microscopic slides. Not only were the airborne concentrations of different
organisms estimated, their viability was also tested with a 1% TTC solution. Particles were collected for 60 min (i.e. a volume
of 600 liters of air sampled) at every 2 h from 0600–2100 h. Up to 689 pollen grains/m3 and an impressive 48 990 spores/m3 were collected daily. Forty-two fungal taxa were identified and the most abundant spores collected were Cladosporium (82.6%),
Smuts (4.8%), Ascospores (2.8%), Basidiospores (2.1%) andAlternaria (1.7%). 20 pollen taxa were identified, and the dominant pollen were Urticaceae (57.9%), Graminaceae (20.7%), Fagaceae (2.4%),
Plantaginaceae (1.4%), Pinaceae (1.3%) and Eucalyptus (1.1%). The most abundant captures were done at 0800 and 1000 h (17.8
and 16.7% respectively) and at 1400 and 1600 h (13.2 and 13.8% respectively). Pollen viability per species ranged from 0 to
100%, but for the most abundant taxa, it ranged from 3.8 to 75%, and averaged 27.7%. Maximum viability was found at 0800 and
1200 h. Pollen concentrations were of the same order of magnitude as the ones found on the mainland (Brindisi, Chieti, Matera).
However, its specificity was evident. Future work should therefore look more at the pollen transport process which should
account for this different assemblage of pollen. 相似文献
986.
The Belgian Pollen Phone Service gives continuous information about the pollen content of the air. A comparison of the number of incoming phone calls with the pollen content of the air revealed a surprisingly good correlation. This article underlines the success of this service. It confirms the high susceptibility of hay fever sufferers at the beginning of the season. It also highlights that pollinosis is not always limited to birch and grass pollen allergy and it demonstrates the necessity for the continuous determination of the pollen content of the air. Allergies to mugwort pollen seem to be less important. The Pollen Phone Service is a prompt way to provide allergic subjects with recent pollen information. 相似文献
987.
This report describes a very high genome doubling efficiency of Brassica napus cv. Topas plants, derived from microspores induced to undergo embryogenesis with a colchicine treatment, without the use of a heat treatment. The plants showed normal growth and development, and 90% were fertile. In contrast, only 6% of the plants derived from heat-induced embryos were fertile diploids. All cytological analysis of the progeny of fertile plants showed 2n=38 chromosomes. These results show that colchicine can simultaneously induce microspore embryogenesis and double the ploidy level to produce doubled haploid plants. 相似文献
988.
Alejandro Vazquez-Tello Takeshi Uozumi Makoto Hidaka Yasuhiko Kobayashi Hiroshi Watanabe 《Plant cell reports》1996,16(1-2):46-49
Summary The biological effects of irradiation with12C+5 ion beam on plant cells have been analyzed. Protoplasts and cell suspensions ofLavatera thuringiaca, and a somatic hybrid callus (Hibiscus rosa-sinensis +Lavatera thuringiaca), were irradiated with doses from 0.05 to 50 Gy, and the effects on cell growth, cell division, cell viability and embryogenesis rates were analyzed. Irradiation with12C+5 ion beam at relatively very low doses (5.0 Gy) significantly inhibited cell division, yet the survival rate and regeneration capability of the cells through somatic embryogenesis were conserved in more than 70 and 50 %, respectively. These results indicate that cell division is the most sensitive parameter to irradiation, accounting for the inhibition of colony formation and callus growth. The potential use of the12C+5 ion beam in asymmetric protoplast fusion experiments is discussed. 相似文献
989.
火炬松细胞悬浮培养体细胞胚胎发生的研究 总被引:4,自引:0,他引:4
用火炬松成熟合子胚诱导产生的胚性愈伤组织建立了胚性细胞悬浮系。研究了细胞密度,继代时间和ABA浓度等对悬浮条件下胚性柄细胞团及体细胞胚形成的影响。结果表明:当细胞密度为6×10^3个/ml,继代时间为2个月,ABA浓度为5mg/L时,最有利于ESM及SE发生。在悬浮培养条件下,还观察到裂生胚及子叶原基的分化。 相似文献
990.
利用光学显微镜、扫描电镜对15种,透射电镜对2种国产酸模属植物的花粉进行观察与研究。本属花粉为球形或近球形,大小为15~40×18~40μm。具3孔沟、4斜孔沟、散孔沟、散沟等;沟或外沟狭长,几达两极,内陷或不内陷,内孔圆形、稍横长或纵长;表面具皱波状纹饰;外壁厚1.0~3.5μm,外层明显厚于内层。在透射电镜下,花粉外壁分3层:覆盖层最厚,具穴状或穿孔,颗粒状或刺状纹饰,内面均匀;柱状层明显,厚,小柱为钝圆锥体或圆柱状,基层和内层不分,最薄,但在萌发孔处明显增厚。根据花粉形态,本属花粉可以分成7个组,它们是:小酸模组、滨海酸模组、酸模组、土大黄组、荒地酸模组、巴天酸模组和钝叶酸模组。对萌发孔分布规律的研究,基本支持Wodehouse(1931)的观点,同时据花粉萌发孔演化的规律,认为本属花粉可能是蓼科花粉由少数萌发孔向多数萌发孔演化的过渡类型。 相似文献