全文获取类型
收费全文 | 4885篇 |
免费 | 389篇 |
专业分类
5274篇 |
出版年
2023年 | 39篇 |
2022年 | 74篇 |
2021年 | 163篇 |
2020年 | 137篇 |
2019年 | 143篇 |
2018年 | 176篇 |
2017年 | 166篇 |
2016年 | 231篇 |
2015年 | 269篇 |
2014年 | 330篇 |
2013年 | 352篇 |
2012年 | 376篇 |
2011年 | 304篇 |
2010年 | 201篇 |
2009年 | 198篇 |
2008年 | 256篇 |
2007年 | 214篇 |
2006年 | 187篇 |
2005年 | 171篇 |
2004年 | 166篇 |
2003年 | 113篇 |
2002年 | 128篇 |
2001年 | 91篇 |
2000年 | 91篇 |
1999年 | 69篇 |
1998年 | 42篇 |
1997年 | 26篇 |
1996年 | 24篇 |
1995年 | 43篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 38篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 37篇 |
1987年 | 29篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 14篇 |
1973年 | 15篇 |
1972年 | 11篇 |
1971年 | 13篇 |
排序方式: 共有5274条查询结果,搜索用时 15 毫秒
21.
22.
Oxidative stress in pregnancy and fertility pathologies 总被引:1,自引:0,他引:1
Oxidative stress designates the state of imbalance between reactive oxygen species (ROS) production and antioxidant levels. In a healthy placenta, there is an increase in ROS production, due to formation of new tissues and inherent metabolism, but this is balanced by higher levels of antioxidants. However, this balance is lost in some situations, with a consequent increase in oxidative stress levels. Oxidative stress has been implicated in several placental disorders and pregnancy pathologies. The present review intends to summarize what is known about the relationship between oxidative stress and well-known pregnancy disorders. 相似文献
23.
Soares TN Melo DB Resende LV Vianello RP Chaves LJ Collevatti RG Telles MP 《American journal of botany》2012,99(2):e72-e73
? Premise of the study: Microsatellite markers were developed for the population genetic analyses of the neotropical tree Dipteryx alata (Fabaceae). ? Methods and Results: Microsatellites were developed from a genomic shotgun library. Polymorphism at each microsatellite loci was analyzed based on 94 individuals from three populations. Eight loci amplified successfully and presented one to 10 alleles, and expected heterozygosities ranged from 0.097 to 0.862. Four loci also amplified in Pterodon emarginatus and presented similar polymorphism. ? Conclusion: The eight microsatellite primer pairs are potentially suitable for population genetic studies and successfully amplified in another Fabaceae species. 相似文献
24.
Marcio?Paulo?Pereira Felipe?Fogaroli?Corrêa Evaristo?Mauro?de?Castro Jean?Paulo?Vitor?de?Oliveira Fabricio?José?PereiraEmail author 《Protoplasma》2017,254(6):2117-2126
Previous works show the development of thicker leaves on tolerant plants growing under cadmium (Cd2+) contamination. The aim of this study was to evaluate the Cd2+ effects on the leaf meristems of the tolerant species Schinus molle. Plants were grown in nutrient solution containing 0, 10, and 50 μM of Cd2+. Anatomical analysis was performed on leaf primordia sampled at regular time intervals. Under the lowest Cd2+ level (10 μM), increased ground meristem thickness, diameter of the cells, cell elongation rate, and leaf dry mass were found. However, 50 μM of Cd2+ reduced all these variables. In addition, the ground meristem cells became larger when exposed to any Cd2+ level. The epidermis, palisade parenchyma, and vascular tissues developed earlier in Cd2+-exposed leaves. The modifications found on the ground meristem may be related to the development of thicker leaves on S. molle plants exposed to low Cd2+ levels. Furthermore, older leaves showed higher Cd2+ content when compared to the younger ones, preventing the Cd2+ toxicity to these leaves. Thus, low Cd2+ concentrations change the ground meristem structure and function reflecting on the development of thicker and enhanced leaves. 相似文献
25.
26.
Joni Esrom Lima Vagner Augusto Benedito Antonio Figueira Lázaro Eustáquio Pereira Peres 《Plant cell reports》2009,28(8):1169-1177
We analyzed the impact of ethylene and auxin disturbances on callus, shoots and Agrobacterium rhizogenes-induced hairy root formation in tomato (Solanum lycopersicum L.). The auxin low-sensitivity dgt mutation showed little hairy root initiation, whereas the ethylene low-sensitivity Nr mutation did not differ from the control Micro-Tom cultivar. Micro-Tom and dgt hairy roots containing auxin sensitivity/biosynthesis rol and aux genes formed prominent callus onto media supplemented with cytokinin. Under the same conditions, Nr hairy roots did not form callus. Double mutants combining Rg1, a mutation conferring elevated shoot formation capacity, with either dgt or Nr produced explants that formed shoots with little callus proliferation. The presence of rol + aux genes in Rg1 hairy roots prevented shoot formation. Taken together, the results suggest that although ethylene does not affect hairy root
induction, as auxin does, it may be necessary for auxin-induced callus formation in tomato. Moreover, excess auxin prevents
shoot formation in Rg1. 相似文献
27.
28.
Milton Maciel Jr. Fábia da Silva Pereira Cruz Marli Tenório Cordeiro Márcia Archer da Motta Klécia Marília Soares de Melo Cassemiro Rita de Cássia Carvalho Maia Regina Célia Bressan Queiroz de Figueiredo Ricardo Galler Marcos da Silva Freire Joseph Thomas August Ernesto T. A. Marques Rafael Dhalia 《PLoS neglected tropical diseases》2015,9(4)
Attenuated yellow fever (YF) virus 17D/17DD vaccines are the only available protection from YF infection, which remains a significant source of morbidity and mortality in the tropical areas of the world. The attenuated YF virus vaccine, which is used worldwide, generates both long-lasting neutralizing antibodies and strong T-cell responses. However, on rare occasions, this vaccine has toxic side effects that can be fatal. This study presents the design of two non-viral DNA-based antigen formulations and the characterization of their expression and immunological properties. The two antigen formulations consist of DNA encoding the full-length envelope protein (p/YFE) or the full-length envelope protein fused to the lysosomal-associated membrane protein signal, LAMP-1 (pL/YFE), aimed at diverting antigen processing/presentation through the major histocompatibility complex II precursor compartments. The immune responses triggered by these formulations were evaluated in H2b and H2d backgrounds, corresponding to the C57Bl/6 and BALB/c mice strains, respectively. Both DNA constructs were able to induce very strong T-cell responses of similar magnitude against almost all epitopes that are also generated by the YF 17DD vaccine. The pL/YFE formulation performed best overall. In addition to the T-cell response, it was also able to stimulate high titers of anti-YF neutralizing antibodies comparable to the levels elicited by the 17DD vaccine. More importantly, the pL/YFE vaccine conferred 100% protection against the YF virus in intracerebrally challenged mice. These results indicate that pL/YFE DNA is an excellent vaccine candidate and should be considered for further developmental studies. 相似文献
29.
Summary. New γ-amino esters and amides were prepared by a radical 1,4-addition of carbon radicals to acrylic derivatives. α-Amino acids
derivatives holding chiral auxiliaries as radical precursors and different chiral olefins were used and chiral induction on
the C-γ center was discussed. 相似文献