全文获取类型
收费全文 | 1050篇 |
免费 | 79篇 |
国内免费 | 1篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 31篇 |
2020年 | 28篇 |
2019年 | 28篇 |
2018年 | 23篇 |
2017年 | 37篇 |
2016年 | 35篇 |
2015年 | 31篇 |
2014年 | 57篇 |
2013年 | 57篇 |
2012年 | 85篇 |
2011年 | 60篇 |
2010年 | 51篇 |
2009年 | 35篇 |
2008年 | 48篇 |
2007年 | 56篇 |
2006年 | 42篇 |
2005年 | 38篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 37篇 |
2001年 | 25篇 |
2000年 | 34篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 7篇 |
1969年 | 4篇 |
1968年 | 6篇 |
1966年 | 4篇 |
排序方式: 共有1130条查询结果,搜索用时 15 毫秒
121.
Rosete Pescador Gilberto Barbante Kerbauy Wagner de Melo Ferreira Eduardo Purgatto Rogério Mamoru Suzuki Miguel Pedro Guerra 《Plant Growth Regulation》2012,68(1):67-76
Endogenous levels of IAA, ABA and four types of CKs were analyzed in zygotic and indirect (ISE) and direct somatic embryogenesis of Acca sellowiana. Zygotic and somatic embryos at different developmental stages were sampled for morphological and hormonal analysis. Both embryo types showed substantial asymmetry in hormone levels. Zygotic embryos displayed a conspicuous peak of IAA in early developmental stages. The results outlined the hormonal variations occurring during zygotic and somatic embryogenesis regarding the timing, nature and hormonal status involved in both processes. The short transient pulse of IAA observed on the 3rd day in culture was suggested to be involved with the signaling for the induction of somatic embryogenesis. Fertilized ovule development was associated with increased IAA levels 21?C24?days after pollination, followed by a sharp decrease in the cotyledonary stage, both in zygotic and somatic embryos. There was a prominent increase in ABA levels in cultures which generated ISE 24?C30?days after pollination, a period that corresponds to the heart and torpedo stages. The levels of total CKs (Z, [9R]Z, iP and [9R]iP) were also always higher in zygotic than in somatic embryogenesis. While zygotic embryogenesis was dominated by the presence of zeatin, the somatic process, contrarily, was characterized by a large variation of the other cytokinin forms and amounts studied. The above results, when taken together, could be related to the previously observed high frequency formation of anomalous somatic embryos formed in A. sellowiana, as well as to their low germination ability. 相似文献
122.
123.
Laís Angélica Borges Luiz Gustavo Rodrigues Souza Marcelo Guerra Isabel Cristina Machado Gwilym P. Lewis Ariadna Valentina Lopes 《Plant Systematics and Evolution》2012,298(7):1371-1381
Polyploidy is the most common chromosomal mechanism involved in the evolution of plants. However, the emergence of polyploid individuals does not guarantee the establishment of a new lineage, and the relationship between polyploidy and reproductive biology is therefore relevant. Libidibia ferrea is a legume tree that has diploid and tetraploid populations. In this work we analyse the reproductive biology of the species to verify the degree of reproductive isolation between the two cytotypes. Observations on phenology, floral morphology, biology, and visitors, breeding system, reproductive success and reproductive isolation were made for both cytotypes in two municipalities of northeastern Brazil. Cytotypes differed for all morphometric parameters analysed, with tetraploids exhibiting higher mean values than diploids. Both cytotypes had the same effective pollinators (native bees from the genera Centris and Xylocopa, and the introduced Apis mellifera). However, since stamens of diploids and tetraploids were of different size, it is possible that spatial separation occurs when pollen of each cytotype is deposited on a bee’s body. Diploids were self-incompatible (ISI?=?0) and exhibited high fruit-set after intraploidy crossing (20?%), whereas tetraploids were self-compatible (ISI?=?0.47) and set only 3.9?% of fruits after intraploidy crossing. Both cytotypes showed low fruit- and seed-set under natural conditions, and there was no fruit-set after crosses between them. Data are discussed in relation to the establishment of polyploids, to the pattern of distribution of the species and to the taxonomic implications. The cytotypes of L. ferrea should be considered as distinct species, since they are reproductively isolated from each other. 相似文献
124.
Silva EC Cajueiro JF Silva SV Vidal AH Soares PC Guerra MM 《Animal reproduction science》2012,132(3-4):155-158
The aim was to assess the in vitro effect of glycerol, ethylene glycol or acetamide on frozen-thawed ram spermatozoa. Aliquots of each sixteen ejaculates from four rams of the Morada Nova breed were diluted in Tris-egg yolk with glycerol (5%), ethylene glycol (3% or 5%) or acetamide (3% or 5%) and frozen at -196°C. After thawing, progressive sperm motility was greater (P<0.05) in cryopreservation with glycerol 5% and ethylene glycol (3% or 5%) than with acetamide (3% or 5%). Acrosome integrity was greater (P<0.05) with ethylene glycol 5% than acetamide (3% or 5%). The percentage of sperm without oxidative stress was greater (P<0.05) with ethylene glycol (3% or 5%) than with acetamide (3% or 5%). Plasma membrane integrity was greater with glycerol 5% (P<0.05) than with the other cryoprotectants. Thus, it is concluded that glycerol 5% and ethylene glycol 3% or 5% protect ram sperm against the harmful effects of freezing and that glycerol 5% offers greater protection to sperm plasma membrane. 相似文献
125.
Dornelas-Ribeiro M Pinheiro EO Guerra C Braga-Silva LA Carvalho SM Santos AL Rozental S Fracalanzza SE 《Memórias do Instituto Oswaldo Cruz》2012,107(1):31-38
We assessed fluconazole susceptibility in 52 Candida tropicalis clinical strains using seven antifungal susceptibility methods, including broth microdilution (BMD) [standard M27 A3 (with neutral and acid pH), ATB Fungus 3, Vitek 2 system and flow cytometric analysis] and agar-based methods (disk diffusion and E-test). Trailing growth, detection of cell-associated secreted aspartic proteases (Saps) and morphological and ultrastructural traits of these clinical strains were also examined. The ranges of fluconazole 24 h-minimum inhibitory concentration (MIC) values were similar among all methods. The essential agreement among the methods used for MIC determinations was excellent and all methods categorised all strains as susceptible, except for one strain that showed a minor error. The presence of the trailing effect was assessed by six methods. Trailing positivity was observed for 86.5-100% of the strains. The exception was the BMD-Ac method where trailing growth was not observed. Morphological and ultrastructural alterations were detected in C. tropicalis trailing cells, including mitochondrial swelling and cell walls with irregular shapes. We tested the production of Saps in 13 C. tropicalis strains expressing trailing growth through flow cytometry. Our results showed that all of the C. tropicalis strains up-regulated surface Sap expression after 24 h or 48 h of exposure to fluconazole, which was not observed in untreated yeast strains. We concluded that C. tropicalis strains expressing trailing growth presented some particular features on both biological and ultrastructural levels. 相似文献
126.
Effect of antioxidants resveratrol and quercetin on in vitro evaluation of frozen ram sperm 总被引:1,自引:0,他引:1
The objective was to assess the effects of the antioxidants resveratrol and quercetin on frozen-thawed ram sperm. Semen samples (which exceeded minimum standards) from four mature crossbreed Santa Inês rams were pooled and aliquots of each pool were diluted in Tris-egg yolk-glycerol, with the addition of 0, 5, 10, 15, and 20 μg/mL of resveratrol and quercetin in Experiment 1 and Experiment 2, respectively. In Experiment 1, the proportion of sperm with a high mitochondrial membrane potential was greater (P < 0.02) in the control group than in resveratrol 20 μg/mL group. In Experiment 2, the proportion of sperm with high mitochondrial membrane potential was greater in the control group (P < 0.0001) than in the other experimental groups, and greater in the quercetin 5 μg/mL group (P < 0.05) than in the other quercetin-treated groups. Thus, addition of 5 to 20 μg/mL of either resveratrol or quercetin to the Tris-egg yolk-glycerol extender reduced sperm mitochondrial membrane potential. 相似文献
127.
Rosete Pescador Gilberto Barbante Kerbauy Déborah Yara Alves Cursino dos Santos Lírio Luiz Dal Vesco Hugo Pacheco de Freitas Fraga Miguel Pedro Guerra 《Acta Physiologiae Plantarum》2012,34(2):771-778
Somatic embryogenesis is an in vitro morphogenetic route in which isolated cells or a small group of somatic cells give rise
to bipolar structures resembling zygotic embryos. Lipids, carbohydrates, and proteins are major compounds in plant and animal
metabolism. Comparative analysis along different developmental stages of Acca sellowiana (Myrtaceae) zygotic and somatic embryos, revealed a progressive increase in levels of total lipids. A high degree of similarity
could be found in the total lipids composition between A. sellowiana somatic and zygotic embryos. High lipid levels were found in zygotic embryos in the torpedo and cotyledonary stages, and
these levels increased according to the progression in the developmental stages. Somatic embryos obtained through direct embryogenesis
route showed higher levels of lipids than in indirect somatic embryogenesis. The compounds most frequently were linoleic acid
(C18:2), palmitic (C16:0) and oleic (C18:1). These results indicate a high similarity degree of accumulation of total lipids,
regardless of zygotic or somatic embryogenesis. 相似文献
128.
Identification of a protein network interacting with TdRF1, a wheat RING ubiquitin ligase with a protective role against cellular dehydration 总被引:1,自引:0,他引:1
129.
130.
Machado GP Antunes JM Uieda W Biondo AW Cruvinel TM Kataoka AP Martorelli LF de Jong D Amaral JM Hoppe EG Guerra Neto G Megid J 《Primates; journal of primatology》2012,53(3):227-231
The aim of this study is to assess the frequency of rabies antibodies in free-ranging capuchin monkeys (Cebus apella nigritus) in a fragmented, environmentally protected, rural area of southeastern Brazil. Thirty-six free-ranging monkeys were tested by the rapid fluorescent focus inhibition test for detection of antibodies against rabies virus. Four individuals (11.11 %) had neutralizing antibody titers ≥ 0.25 IU/mL, demonstrating rabies virus exposure. 相似文献