全文获取类型
收费全文 | 21228篇 |
免费 | 465篇 |
国内免费 | 2篇 |
专业分类
林业 | 4014篇 |
农学 | 1470篇 |
基础科学 | 176篇 |
3945篇 | |
综合类 | 919篇 |
农作物 | 2382篇 |
水产渔业 | 2424篇 |
畜牧兽医 | 2919篇 |
园艺 | 1201篇 |
植物保护 | 2245篇 |
出版年
2024年 | 8篇 |
2023年 | 60篇 |
2022年 | 84篇 |
2021年 | 175篇 |
2020年 | 192篇 |
2019年 | 219篇 |
2018年 | 2903篇 |
2017年 | 2917篇 |
2016年 | 1425篇 |
2015年 | 264篇 |
2014年 | 279篇 |
2013年 | 342篇 |
2012年 | 1148篇 |
2011年 | 2513篇 |
2010年 | 2293篇 |
2009年 | 1421篇 |
2008年 | 1617篇 |
2007年 | 1829篇 |
2006年 | 274篇 |
2005年 | 304篇 |
2004年 | 283篇 |
2003年 | 322篇 |
2002年 | 228篇 |
2001年 | 116篇 |
2000年 | 129篇 |
1999年 | 49篇 |
1998年 | 20篇 |
1997年 | 27篇 |
1996年 | 14篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 32篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1977年 | 7篇 |
1972年 | 3篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1934年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Aneeta Pradhan Julie A. Plummer Matthew N. Nelson Wallace A. Cowling Guijun Yan 《Euphytica》2010,176(1):87-98
A triploid hybrid with an ABC genome constitution, produced from an interspecific cross between Brassica napus (AACC genome) and B. nigra (BB genome), was used as source material for chromosome doubling. Two approaches were undertaken for the production of hexaploids:
firstly, by self-pollination and open-pollination of the triploid hybrid; and secondly, by application of colchicine to axillary
meristems of triploid plants. Sixteen seeds were harvested from triploid plants and two seedlings were confirmed to be hexaploids
with 54 chromosomes. Pollen viability increased from 13% in triploids to a maximum of 49% in hexaploids. Petal length increased
from 1.3 cm (triploid) to 1.9 cm and 1.8 cm in the two hexaploids and longest stamen length increased from 0.9 cm (triploid)
to 1.1 cm in the hexaploids. Pollen grains were longer in hexaploids (43.7 and 46.3 μm) compared to the triploid (25.4 μm).
A few aneuploid offsprings were also observed, with chromosome number ranging from 34 to 48. This study shows that trigenomic
hexaploids can be produced in Brassica through interspecific hybridisation of B. napus and B. nigra followed by colchicine treatment. 相似文献
62.
Jundae Lee Jae Bok Yoon Jung-Heon Han Won Phil Lee Sang Hoon Kim Hyo Guen Park 《Euphytica》2010,173(1):55-61
Genic male sterility (GMS) has long been used as a tool for hybrid seed production in chili pepper (Capsicum annuum L.). We developed DNA markers linked to the GMS ms
3
gene in a segregating population using bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP)
techniques. The segregating population was subjected to BSA-AFLP with 512 primer combinations. Three AFLP markers (Eagg/Mccc276, Eagc/Mctt178, and Ecag/Mtgc204) were identified as tightly linked to the ms
3
locus. Among them, we converted the AFLP marker Ecag/Mtgc204 to the cleavage amplified polymorphic sequence (CAPS) marker, named GMS3-CAPS, based on sequencing analysis of internal and
flanking regions for the markers between male-fertile and sterile plants. This marker will be useful for pepper breeding using
the GMS system. 相似文献
63.
The objective of this study was to identify molecular markers linked to fruit-related traits in the tomato subjected to high
temperatures. In total, 160 F2 plants derived from a cross between a heat-tolerant breeding line, CL5915-93D4-1-0-3 (Solanum esculentum), and a heat-sensitive wild accession, L4422 (S. pimpinellifolium), were grown in a greenhouse. Six traits including fruit number, fruit weight, brix, seed number, fruit setting, and flower
number were scored. The distributions of fruit number, fruit set, flower number, and seed number were skewed towards heat
susceptibility which is known to be characteristic of L4422. Polymorphic bands were generated by PCR-derived methods of RAPD,
ISSR and AFLP Polymorphism, the segregation ratio, and distribution over the genome of the above 3 markers were compared.
Ten linkage groups, ranging 20.6–151.6 cM in size, were constructed with 62 informative markers spanning a total of 776.3 cM.
Fruit-related quantitative trait loci (QTLs) were non-randomly distributed in the tomato genome. For the 6 traits investigated,
21 QTLs were dispersed on linkage groups 2–5. The genetic effects of the various QTLs were differently exhibited, in our study
we have respectively found from 10.5% to 30.2% of the variation explained by the QTL for flower number (FRN4) and brix (BX2).
Thirteen QTL-mapped markers were unique to 1 trait, and 4 markers were linked to more than 1 trait. Among them, QTLs linked
to the I868-470 marker had effects on fruit weight and brix, and a significant positive correlation between these 2 traits
was noted (r = 0.35, P < 0.05). Thus, the I868-470 marker may have the potential for simultaneous selection of high fruit weight and brix. These
markers also allowed us to align genome linkage maps across distantly related species and to reveal the co-localization between
these QTLs and major genes. 相似文献
64.
65.
Genetic variation of sweet potatoes (Ipomoea batatas L.) cultivated in Chile determined by RAPDs 总被引:1,自引:0,他引:1
Boris Sagredo Patricio Hinrichsen Horacio López Alberto Cubillos Carlos Muñoz 《Euphytica》1998,101(2):193-198
RAPD (randomly amplified polymorphic DNA) technology was applied to analyze the genetic variability of sweet potato germplasm
existing in Chile and elsewhere. Analysis of 28 cultivars from all over the world showed polymorphic bands with all 18 primers
tested. A total of 124 RAPD bands were scored with an average of 6.9 polymorphic bands per primer. These results confirm that
sweet potato exhibits high genetic variation. Two groups were distinguished: one containing Peruvian cultivars, and another
containing cultivars from the rest of the world. Analysis of 14 accessions from Central Chile and one from Northern Chile
showed polymorphic bands with 24 of 26 primers tested, but almost all of the 140 polymorphic bands merely showed the distinctness
of the Northern accession. The almost complete uniformity of the other 14 accessions shows that sweet potato germplasm collected
in Central Chile has very little genetic variability and may be derived from a single cultivar.
Based on these results and on historical records, some hypotheses are proposed to explain the origin of sweet potatoes cultivated
in Chile.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
66.
Sclerotinia sclerotiorum infections on sunflower capitula produce white rot, one of the most dangerous diseases sunflower bears in all humid areas.
Therefore, disease quantification on developed genetic materials is a very important action in sunflower breeding. Given the
horizontal type of resistance these evaluations should be made in different environments. Several hybrids obtained after crossing
seven female × seven male sunflower inbred lines in a factorial mating design were evaluated for resistance to white rot in
two locations in the southeast of the province of Buenos Aires, Argentina. Disease incidence and the symptom appearance index
indicated significant genotypic effects and genotype × environment (G × E) interactions. Genotypic effects were a greater
source of variance than the G × E interaction effects. The G × E interactions only represented changes in magnitude. These
results were used to identify the best genotypes for both resistance factors. Four hybrids showed low disease incidence values
under both artificial and natural infections, of which only two had high values of the symptom appearance index at both locations.
These hybrids are considered to have adequate resistance attributes for the ascosporic penetration and the mycelium extension
in the capitulum tissue and could therefore be sown in the province of Buenos Aires without increasing risks of S. sclerotiorum attacks. 相似文献
67.
M. Santalla M. Lema A. P. Rodiño A. M. González A. B. Monteagudo A. M. De Ron 《Euphytica》2005,142(1-2):85-95
Approaches are needed to broaden the genetic base and improve earliness and yield potential of large-seeded beans under sustainable cropping systems. The objective of this research was to develop adapted dwarf bean populations having a commercial seed quality and yield suitable for the production in the South of Europe. The original base populations were produced from crosses between genotypes within each Mesoamerica, Nueva Granada and Peru races, and between Peru and Nueva Granada, and Mesoamerica and Nueva Granada races. Visual mass selection for plant performance was practised in the F2 and F3 generations. In the F4 and F5, single plants were harvested under two cropping systems (sole cropping and intercropping with maize). From F4, selection was based on precocity, combined with seed yield and seed commercial type. The F4:7 selected lines from each original population were compared with their parents and five checks at four environments and two cropping systems. Differences among environments, populations, parents and checks were observed for all traits. Under intercropping with maize, there was a 50% reduction in seed yield. Yield of parents and checks belonging to Andean South American races, intraracial (Nueva Granada × Nueva Granada) and interracial (Nueva Granada × Peru) populations, was higher than that of those of Middle American origin. Intraracial crosses within large-seeded Andean South American (Peru race) and Middle American gene pools (Mesoamerica race) did not produce lines yielding more than the highest yielding parent. Only two large-seeded lines selected from crosses between small- and large-seeded gene pools out-yielded the best parent and check cultivar. 相似文献
68.
Plants of white clover (Trifolium repens L.) cultivar Crau, a self-fertile Crau genotype, and nine generations of inbred progeny were raised in sand culture in a
glasshouse experiment. Digital images of the root systems were made and root morphological characteristics were determined
on all the plants. Root architectural parameters were measured on the Crau parent and the S1, S4, S6, and S9 inbred lines. The clover roots became shorter and thicker with inbreeding but the number of root tips per plant was unchanged.
Root architecture (branching pattern) was largely unaffected by inbreeding. It is concluded that inbreeding white clover will
lead to shorter, thicker roots, and reduced nutrient uptake efficiency compared with the parent clover. The degree to which
these deleterious traits are overcome during the development of F1 hybrids needs to be determined. 相似文献
69.
The height-reducing gene Rht8 was introduced into Italian wheats by breeder Nazareno Strampelli from the Japanese landrace Akakomugi, and has been widely
used in wheats adapted to southern and eastern European conditions. Following identification of a close linkage to Rht8, microsatellite marker Gwm261 has been used extensively to screen large numbers of diverse international germplasm. A 192bp allele at this locus has been
taken as “diagnostic” for Rht8 and used to infer the international distribution of Rht8. In this paper, we report several instances of cultivars and mapping populations that vary for the presence of the 192bp
allele at the Xgwm261 locus (Xgwm261
192
), but with no associated reduction in height, suggesting a lack of association with Rht8. For instance, in the population derived from a cross between Sunco (Rht-B1b, Xgwm261
165
) and Tasman (Rht-D1b, Xgwm261
192
), there were significant height differences associated with the segregation of Rht-B1b and Rht-D1b, but no height differences between Xgwm261 genotypes. Similar results were obtained in a population derived from the cross between Molineux (Rht-B1b, Xgwm261
192
) and Trident (Rht-D1b Xgwm261
208
). In contrast, the cross between Trident and Chuanmai 18 (Xgwm261
192
) gave significant height effects at both the Rht-D1 and Xgwm261 loci, with no epistatic interaction between loci. Chuanmai 18 is closely related to the Strampelli wheat Mara (ancestrally
derived from Akakomugi) and is therefore likely to carry Rht8. The old Japanese cultivar Norin 10, used by Norman Borlaug to introduce Rht-B1b and Rht-D1b into Mexican wheats, also has a 192bp allele at the Xgwm261 locus, and the sequence of the amplified product is identical to that of Akakomugi. We suggest that the widespread use of
Norin 10-derived germplasm during and after the Green Revolution introduced a second haplotype into international germplasm,
in which Xgwm261
192
has no association with Rht8. Therefore, the presence of Xgwm261
192
is only indicative of Rht8 in wheat cultivars that have inherited this allele from Akakomugi or a Strampelli wheat ancestor. 相似文献
70.
Norma Marina Alarcón-Rodríguez Ernestina Valadez-Moctezuma Héctor Lozoya-Saldaña 《American Journal of Potato Research》2014,91(5):459-466
An Andean origin of Phytophthora infestans was originally based on written records, and recently inferred from mitochondrial and nuclear gene genealogies, which emphasize a common South American origin of the European isolates, and absence of the I-b haplotype in Mexico (recently identified in Tlaxcala, Mexico). In order to compare such results, we sequenced the nuclear genes β-tubulin, Ras, and Intron Ras, and rDNA ITS regions in 24 P. infestans genotypes isolated, identified, and selected, during three crop growing cycles in Chapingo, Mexico. The pathogen showed homology and 100 % sequence similarities to the ones reported for the Andes and Europe β-tubulin, Ras, and Intron Ras genes. Results for the ITS region were inconclusive. The molecular oomycete similarities from the three geographical regions (South America, Europe, and Mexico), and the Mexican genotypes characteristics reported in the species supports the hypothesis of the location of P. infestans diversity and a center of dispersal in the central highlands of Mexico. 相似文献