全文获取类型
收费全文 | 44651篇 |
免费 | 2897篇 |
国内免费 | 15篇 |
出版年
2023年 | 219篇 |
2022年 | 362篇 |
2021年 | 1024篇 |
2020年 | 606篇 |
2019年 | 782篇 |
2018年 | 1102篇 |
2017年 | 920篇 |
2016年 | 1522篇 |
2015年 | 2311篇 |
2014年 | 2516篇 |
2013年 | 3421篇 |
2012年 | 3902篇 |
2011年 | 3758篇 |
2010年 | 2273篇 |
2009年 | 2031篇 |
2008年 | 2810篇 |
2007年 | 2715篇 |
2006年 | 2464篇 |
2005年 | 2182篇 |
2004年 | 2099篇 |
2003年 | 1966篇 |
2002年 | 1810篇 |
2001年 | 351篇 |
2000年 | 251篇 |
1999年 | 342篇 |
1998年 | 434篇 |
1997年 | 293篇 |
1996年 | 285篇 |
1995年 | 257篇 |
1994年 | 241篇 |
1993年 | 240篇 |
1992年 | 160篇 |
1991年 | 167篇 |
1990年 | 168篇 |
1989年 | 124篇 |
1988年 | 118篇 |
1987年 | 99篇 |
1986年 | 77篇 |
1985年 | 112篇 |
1984年 | 108篇 |
1983年 | 77篇 |
1982年 | 95篇 |
1981年 | 87篇 |
1980年 | 81篇 |
1979年 | 76篇 |
1978年 | 41篇 |
1977年 | 54篇 |
1976年 | 36篇 |
1975年 | 38篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
Chana Borjigin Rhiannon K. Schilling Jayakumar Bose Maria Hrmova Jiaen Qiu Stefanie Wege Apriadi Situmorang Caitlin Byrt Chris Brien Bettina Berger Matthew Gilliham Allison S. Pearson Stuart J. Roy 《Plant, cell & environment》2020,43(9):2158-2171
Improving salinity tolerance in the most widely cultivated cereal, bread wheat (Triticum aestivum L.), is essential to increase grain yields on saline agricultural lands. A Portuguese landrace, Mocho de Espiga Branca accumulates up to sixfold greater leaf and sheath sodium (Na+) than two Australian cultivars, Gladius and Scout, under salt stress in hydroponics. Despite high leaf and sheath Na+ concentrations, Mocho de Espiga Branca maintained similar salinity tolerance compared to Gladius and Scout. A naturally occurring single nucleotide substitution was identified in the gene encoding a major Na+ transporter TaHKT1;5-D in Mocho de Espiga Branca, which resulted in a L190P amino acid residue variation. This variant prevents Mocho de Espiga Branca from retrieving Na+ from the root xylem leading to a high shoot Na+ concentration. The identification of the tissue-tolerant Mocho de Espiga Branca will accelerate the development of more elite salt-tolerant bread wheat cultivars. 相似文献
992.
Bompadre Thiago F. V. Moretti Débora B. Sakita Gabriel Z. Ieda Egon H. Martinez Maria I. V. Fernandes Elisabete A. N. Machado-Neto Raul Abdalla Adibe L. Louvandini Helder 《Biological trace element research》2020,193(2):414-421
Biological Trace Element Research - Chromium (Cr) is a micromineral that is involved in the metabolism of carbohydrates, lipids, ammonia, and nucleic acids; thus, its supplementation can influence... 相似文献
993.
da Silva-Carvalho Lidiane Maria Genovez-Oliveira Jhon Lennon de Souza Oliveira Mariana de Oliveira Águida Aparecida de Lima Viviane Moreira Ferreira Ildemar Berto Bruno Pereira 《Systematic parasitology》2020,97(6):847-855
Systematic Parasitology - Isospora parnaitatiaiensis Silva, Rodrigues, Lopes, Berto, Luz, Ferreira & Lopes, 2015 was identified from a new host, the plain antvireo Dysithamnus mentalis... 相似文献
994.
Alexey A. Sergeev Anna E. Barmintseva Stanislav A. Vlasenko Sergey S. Fomin Maria E. Tolochkova Natalia I. Chavychalova Nikolai S. Mugue 《Zeitschrift fur angewandte Ichthyologie》2020,36(6):768-771
The state of natural spawning of sturgeons in the Lower Volga River was investigated through genetic monitoring of juveniles (larvae, fingerlings, subadults) captured at seven traditionally used monitoring locations. Sampling was performed during the period 2017–2019. In total, 460 individuals were caught and genotyped using a set of six microsatellite loci (Afug41, Afug51, Afug135, An20, AoxD161, AoxD165) and mtDNA control region sequencing. The observed species-specific microsatellite alleles revealed the presence of juvenile sturgeons originating from natural spawning also included some hybrids between Acipenser stellatus and A. ruthenus. Thus, the majority of sterlet breeding takes place in natural spawning grounds but also sterlet hybridizes with a small number of stellate sturgeons. Juveniles of other sturgeon species were not identified, and it is concluded that natural spawning activities of Russian sturgeon, beluga and ship sturgeon were insignificant or even absent in the Lower Volga during the observation period. 相似文献
995.
Maíra S. A. Rocha Robson C. Silva José C. E. Santos Marianne Schorer Maria P. Nascimento Marcelo M. Pedreira 《Journal of fish biology》2020,96(1):49-58
The aim of the present study was to perform comparative histological analyses of the ontogenetic development of two fish species endemic to the São Francisco River in Brazil: Prochilodus argenteus and Lophiosilurus alexandri. Histological analyses were performed every 24 h from the moment of hatching until 14 days post-hatching (dph) for the observation of larval development and until 39 dph for the observation of gonadal development. Whole larvae were fixed in Bouin's solution and the histological slides were stained with haematoxylin–eosin. Lophiosilurus alexandri larvae had a larger body size compared with P. argenteus larvae since hatching. Lophiosilurus alexandri larvae had mouth opening and pigmentation of the eyes upon hatching, whereas these events were observed at 1 dph in P. argenteus larvae. The visualisation and the inflation of the swim bladder occurred at 1 and 3 dph, respectively, in the P. argenteus, whereas these events occurred at 2 and 8 dph, respectively, in L. alexandri. Yolk granules were absorbed at 4 dph in P. argenteus and the 10 dph in L. alexandri. At 7 dph, the digestive tube was more differentiated in L. alexandri than P. argenteus and at 14 dph, the digestive system of both species had features of their eating habits: broad stomach and short intestine in L. alexandri, typical of carnivorous habits; stomach with a mechanical function and long intestine in P. argenteus, typical of detritivorous habits. The epithelial lining tissue, formed by a single layer of cells in the newly hatched larvae (0 dph), differentiated throughout the study, exhibiting scales in P. argenteus and numerous club cells in the middle epithelial region of L. alexandri at 39 dph. Undifferentiated gonads with somatic cells and primordial germ cells were observed at 39 dph, with caudal-cranial migration since 1 dph in both species. The anatomic changes during the ontogeny of P. argenteus and L. alexandri larvae are directly associated with the evolutionary history of each species, which explains their feeding habits, behaviour and distribution in the environment: Prochilodus argenteus is detritivorous and actively swims in the water column, whereas L. alexandri is carnivorous and inhabits bottom regions. At 39 dph neither species exhibited sexual differentiation. 相似文献
996.
997.
998.
Konrad Neugebauer Hamed A. El-Serehy Timothy S. George James W. McNicol Milton F. Moraes Maria C. M. Sorreano Philip J. White 《Physiologia plantarum》2020,168(4):790-802
The ionome is the elemental composition of a living organism, its tissues, cells or cell compartments. The ionomes of roots, stems and leaves of 14 native Brazilian forest species were characterised to examine the relationships between plant and organ ionomes and the phylogenetic and ecological affiliations of species. The null hypothesis that ionomes of Brazilian forest species and their organs do not differ was tested. Concentrations of mineral nutrients in roots, stems and leaves were determined for 14 Brazilian forest species, representing seven angiosperm orders, grown hydroponically in a complete nutrient solution. The 14 species could be differentiated by their ionomes and the partitioning of mineral nutrients between organs. The ionomic differences between the 14 species did not reflect their phylogenetic relationships or successional ecology. Differences between shoot ionomes and root ionomes were greater than differences in the ionome of an organ when compared among genotypes. In conclusion, differences in ionomes of species and their organs reflect a combination of ancient phylogenetic and recent environmental adaptations. 相似文献
999.
1000.
<i>Aspergillus tubingensis</i> Causes Leaf Spot of Cotton (<i>Gossypium hirsutum</i> L.) in Pakistan
Maria Khizar Urooj Haroon Musrat Ali Samiah Arif Iftikhar Hussain Shah Hassan Javed Chaudhary Muhammad Farooq Hussain Munis 《Phyton》2020,89(1):103-109
Cotton (Gossypium hirsutum L.) is a key fiber crop of great commercial
importance. Numerous phytopathogens decimate crop production by causing
various diseases. During July-August 2018, leaf spot symptoms were recurrently
observed on cotton leaves in Rahim Yar Khan, Pakistan and adjacent areas. Infected
leaf samples were collected and plated on potato dextrose agar (PDA) media.
Causal agent of cotton leaf spot was isolated, characterized and identified as
Aspergillus tubingensis based on morphological and microscopic observations.
Conclusive identification of pathogen was done on the comparative molecular
analysis of CaM and β-tubulin gene sequences. BLAST analysis of both sequenced
genes showed 99% similarity with A. tubingensis. Koch’s postulates were followed
to confirm the pathogenicity of the isolated fungus. Healthy plants were inoculated
with fungus and similar disease symptoms were observed. Fungus was re-isolated
and identified to be identical to the inoculated fungus. To our knowledge, this is the
first report describing the involvement of A. tubingensis in causing leaf spot disease
of cotton in Pakistan and around the world. 相似文献