全文获取类型
收费全文 | 14042篇 |
免费 | 1095篇 |
国内免费 | 69篇 |
专业分类
林业 | 628篇 |
农学 | 822篇 |
基础科学 | 125篇 |
2004篇 | |
综合类 | 1666篇 |
农作物 | 493篇 |
水产渔业 | 1041篇 |
畜牧兽医 | 7028篇 |
园艺 | 228篇 |
植物保护 | 1171篇 |
出版年
2023年 | 88篇 |
2021年 | 88篇 |
2020年 | 122篇 |
2019年 | 202篇 |
2018年 | 375篇 |
2017年 | 345篇 |
2016年 | 335篇 |
2015年 | 306篇 |
2014年 | 325篇 |
2013年 | 571篇 |
2012年 | 478篇 |
2011年 | 571篇 |
2010年 | 463篇 |
2009年 | 420篇 |
2008年 | 558篇 |
2007年 | 579篇 |
2006年 | 474篇 |
2005年 | 522篇 |
2004年 | 407篇 |
2003年 | 447篇 |
2002年 | 360篇 |
2001年 | 759篇 |
2000年 | 721篇 |
1999年 | 592篇 |
1998年 | 171篇 |
1997年 | 164篇 |
1996年 | 126篇 |
1995年 | 151篇 |
1994年 | 156篇 |
1993年 | 120篇 |
1992年 | 321篇 |
1991年 | 346篇 |
1990年 | 291篇 |
1989年 | 266篇 |
1988年 | 271篇 |
1987年 | 319篇 |
1986年 | 245篇 |
1985年 | 193篇 |
1984年 | 171篇 |
1983年 | 147篇 |
1982年 | 94篇 |
1981年 | 83篇 |
1980年 | 79篇 |
1979年 | 141篇 |
1978年 | 94篇 |
1977年 | 73篇 |
1975年 | 77篇 |
1974年 | 79篇 |
1971年 | 69篇 |
1969年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Summary Somatic embryogenesis was initiated from immature embryos on Murashige-Skoog (MS) medium plus 2 mg.l-1 2,4-dichlorophenoxyacetic acid, 2% sucrose and 0.6% agarose. Somatic embryos were isolated and regenerated into whole green plants on MS medium devoid of 2,4-D. These regenerants were previously demonstrated to differ in their mitochondrial DNA organization. In order to estimate their characteristics three progenies of short-term culture regenerants and three progenies of long-term culture regenerants were analyzed and compared to the parental line. These somaclones obtained from the wheat variety Chinese Spring were evaluated for variation of 13 agronomic and morphological quantitative characters in comparison to the parental line. Significant variation was observed for plant height, spike length, main tiller diameter, between the somaclones regenerated from long-term culture and their parent. Differences were observed to increase with the duration of culture, leading to a significant modification of the structure of the plants. Several changes occurred during the somatic tissue cultures, but to a lesser extent than has previously been described in the literature. 相似文献
972.
The Pi‐ta gene in rice confers resistance to strains of the blast pathogen Magnaporthe grisea (Herbert) Borr. (anamorph Pyricularia oryza Cav.) containing the corresponding avirulence gene AVR‐Pita in a gene‐for‐gene fashion. The Pi‐ta gene is a typical nucleotide‐binding site type resistance gene. Nucleotide sequences distinguishing the resistant Pi‐ta and susceptible pi‐ta alleles were previously identified and used for developing DNA markers for a resistant Pi‐ta haplotype and three susceptible pi‐ta haplotypes. In the present study, the existence of the Pi‐ta gene in 141 rice germplasm accessions was rapidly determined using these markers, and the results were confirmed by inoculating rice germplasm with an M. grisea strain containing AVR‐Pita. The Pi‐ta gene was found in accessions from several major rice producing countries, including China, Colombia, Japan, Vietnam, the Philippines, Iran and the United States. The usefulness of DNA markers for rapid determination of the genotype of rice germplasm was thus demonstrated. The Pi‐ta gene also was found in rice cultivar known to contain the Pi‐ta2 gene, although the allelic relationship of these genes remains to be determined. The presence of the Pi‐ta gene in landrace cultivars in several different geographical locations, the Philippines and Vietnam, other indica rice cultivars in China and Colombia suggest that the Pi‐ta gene may have spontaneously originated in indica rice cultivars. These results are useful for incorporating the Pi‐ta gene into advanced breeding lines by marker‐assisted selection for rice breeding programmes worldwide. 相似文献
973.
Cultivated Chinese wheat germplasm has been a valuable genetic resource in international plant breeding. Patterns of gliadin among cultivated Chinese accessions are unknown, despite the proven value and potential novelty. The objective of this work was to analyse the diversity within improved Chinese wheat germplasm. The electrophoretic banding patterns of gliadin in winter wheat cultivars and advanced lines were determined by acid-polyacrylamide gel electrophoresis. For 148 leading commercial cultivars and promising advanced lines used in this study, 48 patterns were identified, 29 corresponding to ω -gliadin, nine to γ -gliadin, five to β -gliadin and five to α -gliadin. The most frequent patterns were A6 in ω ; B in γ ; B in β and A in the region of α . A total of 116 band types appeared in the 148 samples: 94 accessions had unique gliadin types, and 22 gliadin, types while not unique, were found in 54 accessions. The gliadin patterns of Chinese wheat cultivars and lines greatly differed from the patterns of wheat lines from other countries. Three patterns, E, J, H, M, N and O in the ω -zone had not been reported previously. Three wheat zones of China, the Northern Winter Wheat Region, the Yellow and Huai Valley River valleys Winter Wheat Region and the Southwestern Winter Wheat Region, showed different frequencies in their gliadin patterns. This information can be used to monitor genetic diversity with Chinese wheat germplasm. 相似文献
974.
Plants were regenerated from tissue cultures of embryos dissected from seeds that were harvested from a self-pollinated clonal
selection of Kentucky bluegrass (Poa pratensis L.) ‘Baron’, an apomictic cultivar. Plants were regenerated from 35 embryo-derived callus cultures of the 3280 embryos that
were plated. Flow-cytometric (FCM) and RAPD-marker analyses were performed to determine if regenerants were or were not apomictic
in origin. Fifteen regenerants with a 3c DNA content were classified as arising from 2n + n aberrant embryos, which was a higher frequency than expected, based on a chi-square analysis. Of the remaining 20 regenerants
with a 2c DNA content, a chi-square test showed that all could have arisen from n + n sexually-derived embryos, based on the observed segregation of n + n regenerants, which fit the expected 3:1 ratio of dominant:recessive RAPD-marker phenotypes. The apparent lack of regenerants
of apomictic origin, and implications for genetic transformation and breeding of Kentucky bluegrass are discussed. 相似文献
975.
Calli have been widely used as research materials for clonal propagation transformation of trees owing to their high multiplication rates capacity of large-scale propagation. …… 《分子植物育种》2007,5(2):293-293
Calli have been widely used as research materials for clonal propagation and transformation of trees owing to their high multiplication rates and capacity of large-scale propagation. Till now, very little is known on the somaclonal variation in Betula platyphylla culture, and especially, in regenerated plants (Schween et al., 2003; Nakano et al., 2003). 相似文献
976.
Molecular mapping of a dominant genic male sterility gene Ms in rapeseed (Brassica napus) 总被引:7,自引:1,他引:7
Rs1046AB is a genic male sterile two‐type line in rapeseed that has great potential for hybrid seed production. The sterility of this line is conditioned by the interaction of two genes, i.e. the dominant genic male sterility gene (Ms) and the suppressor gene (Rf). The present study was undertaken to identify DNA markers for the Ms locus in a BC1 population developed from a cross between a male‐sterile plant in Rs1046AB and the fertile canola‐type cultivar ‘Samourai’. Bulked segregant analysis was performed using the amplified fragment length polymorphism (AFLP) methodology. From the survey of 480 AFLP primer combinations, five AFLP markers (P10M13350, P13M8400, P6M6410, E7M1230 and E3M15100) tightly linked to the target gene were identified. Two of them, E3M15100 and P6M6410, located the closest, at either side of Ms at a distance of 3.7 and 5.9 cM, respectively. The Ms locus was subsequently mapped on linkage group LG10 in the map developed in this laboratory, adding two additional markers weakly linked to it. This suite of markers will be valuable in designing a marker‐assisted genic male sterility three‐line breeding programme. 相似文献
977.
Characterization of segregation distortion on chromosome 3 induced in wide hybridization between indica and japonica type rice varieties 总被引:6,自引:0,他引:6
S. Matsushita T. Iseki Y. Fukuta E. Araki S. Kobayashi M. Osaki M. Yamagishi 《Euphytica》2003,134(1):27-32
We previously surveyed chromosomal regions showing segregation distortion of RFLP markers in the F2 population from the cross between a japonica type variety ‘Nipponbare’ and an indica type variety ‘Milyang23’, and showed
that the most skewed segregation appeared on the short arm of chromosome 3. By comparison with the marker loci where distortion
factors were previously identified, this region was assumed to be a gametophytic selection-2 (ga2) gene region. To evaluate this region, two near isogenic lines (NILs) were developed. One NIL had the ‘Nipponbare’ segment
of this region on the genetic background of ‘Milyang23’ (NIL9-23), and the other NIL had the ‘Milyang23’ segment on the genetic
background of ‘Nipponbare’ (NIL33-18). NIL9-23 and ‘Milyang23’, NIL33-18 and
‘Nipponbare’, and ‘Nipponbare’ and ‘Milyang23’ were respectively crossed to produce F1 and F2 populations. The F1 plants of NIL9-23 × ‘Milyang23’ and NIL33-18 × ‘Nipponbare’ showed high seed fertility and the same pollen fertility as their
parental cultivars, indicating that ga2 does not reduce seed and pollen fertility. Segregation ratio of a molecular marker on the ga2 region in the three F2 populations was investigated to clarify whether segregation distortion occurred on the different genetic backgrounds. Segregation
distortion of the ga2 region appeared in the both F2 populations from the NIL9-23 and ‘Milyang23’ cross (background was
‘Milyang23’ homozygote) and the ‘Nipponbare’ and ‘Milyang23’ cross (background was heterozygote), but did notin the F2 population from the NIL33-18 and ‘Nipponbare’ cross (background was ‘Nipponbare’ homozygote). This result indicates that
ga2 interacts with a ‘Milyang23’ allele(s) on the different chromosomal region(s) to cause skewed segregation of the ga2 region. In addition, segregation ratio was the same between the F2 populations from NIL9-23 × ‘Milyang23’ and ‘Nipponbare’ × ‘Milyang23’ crosses, suggesting that the both genotypes, ‘Milyang23’
homozygote and heterozygote, of gene(s) located on the different chromosomal region(s) have the same effect on the segregation
distortion.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
978.
Summary We have succeeded in producing useful interspecific hybrid using ovule-embryo culture between Gypsophila paniculata L. Red Sea and G. manginii, an incompatible combination by ordinary cross breeding methods. The hybrid plant had double flowers with a color of pale purplish pink. Hybrid characteristics of the plant were firmed by observation of plant form, flower type, chromosome number and peroxidase isozyme patterns. 相似文献
979.
Summary Apomixis is widely distributed among tropical forage grasses, and has long been merely regarded as an impediment to breeding. Panicum maximum is presented as the first opportunity for Brazilian geneticists to develop and test original breeding schemes adapted to an apomictic species.A large and representative germplasm of P. maximum has been introduced and is currently being evaluated. Basic knowledges on biology and reproduction are also available, which demonstrate an easy manipulation of apomixis and sexuality. Several limiting traits have already been detected during evaluation, which justify breeding attempts. An ideal scheme is given to transfer new qualities to already selected varieties. 相似文献