全文获取类型
收费全文 | 23951篇 |
免费 | 1621篇 |
国内免费 | 5篇 |
专业分类
25577篇 |
出版年
2023年 | 203篇 |
2022年 | 353篇 |
2021年 | 647篇 |
2020年 | 497篇 |
2019年 | 569篇 |
2018年 | 778篇 |
2017年 | 693篇 |
2016年 | 972篇 |
2015年 | 1320篇 |
2014年 | 1436篇 |
2013年 | 1742篇 |
2012年 | 1861篇 |
2011年 | 1845篇 |
2010年 | 1160篇 |
2009年 | 999篇 |
2008年 | 1324篇 |
2007年 | 1238篇 |
2006年 | 1192篇 |
2005年 | 987篇 |
2004年 | 930篇 |
2003年 | 777篇 |
2002年 | 718篇 |
2001年 | 390篇 |
2000年 | 354篇 |
1999年 | 284篇 |
1998年 | 169篇 |
1997年 | 133篇 |
1996年 | 123篇 |
1995年 | 110篇 |
1994年 | 96篇 |
1993年 | 98篇 |
1992年 | 150篇 |
1991年 | 137篇 |
1990年 | 129篇 |
1989年 | 92篇 |
1988年 | 97篇 |
1987年 | 82篇 |
1986年 | 77篇 |
1985年 | 64篇 |
1984年 | 69篇 |
1983年 | 62篇 |
1982年 | 53篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 58篇 |
1978年 | 52篇 |
1976年 | 28篇 |
1975年 | 51篇 |
1974年 | 31篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
Dinis-Oliveira RJ Remião F Duarte JA Ferreira R Sánchez Navarro A Bastos ML Carvalho F 《Free radical biology & medicine》2006,41(8):1213-1224
The widespread use of the nonselective contact herbicide paraquat (PQ) has been the cause of thousands of deaths from both accidental and voluntary ingestion. The main target organ for PQ toxicity is the lung. No antidote or effective treatment to decrease PQ accumulation in the lung or to disrupt its toxicity has yet been developed. The present study describes a procedure that leads to a remarkable decrease in PQ accumulation in the lung, together with an increase in its fecal excretion and a subsequent decrease in several biochemical and histopathological biomarkers of toxicity. The administration of dexamethasone (100 mg/kg ip) to Wistar rats, 2 h after PQ intoxication (25 mg/kg ip), decreased the lung PQ accumulation to about 40% of the group exposed to only PQ and led to an improvement in tissue healing in just 24 h as a result of the induction of de novo synthesis of P-glycoprotein (P-gp). The involvement of P-gp in these effects was confirmed by Western blot analysis and by the use of a competitive inhibitor of this transporter, verapamil (10 mg/kg ip), which, given 1 h before dexamethasone, blocked its protective effects, causing instead an increase in lung PQ concentration and an aggravation of toxicity. In conclusion, the induction of P-gp, leading to a decrease in lung levels of PQ and the consequent prevention of toxicity, seems to be a new and promising treatment for PQ poisonings that should be further clinically tested. 相似文献
83.
A survey on attitudes toward large carnivores was conducted in a representative sample of the Norwegian population (n = 3134). People were asked about the acceptability of carnivores living in remote wilderness, close to where people live, killing livestock, killing pets, or threatening humans. Large differences in acceptability appeared across the five situations. Wolves and bears were less acceptable than lynx and wolverines when observed close to where people live. Negative associations were found between acceptability and lack of personal control, economic loss, and respondents' age. Acceptability was higher among males than among females, and higher among urban than among rural residents. The results showed that general measures of attitudes alone toward large carnivores were of limited value in wildlife management. The situational and social specificity of these attitudes should be given more attention. 相似文献
84.
85.
86.
87.
88.
A juvenile common marmoset (Callithrix jacchus) was attacked by a whitetail lancehead viper (Bothrops leucurus) while playing with other group members close to the ground at a site in northeastern Brazil. The attack was almost immediately fatal, but the viper was unable to ingest the body of the marmoset. After approximately 10 min, during which it attempted to swallow the marmoset a number of times, the viper moved away, abandoning the body. While raptors are the principal predators of callitrichids, this record reinforces the relative vulnerability of these primates to snakes in comparison with other platyrrhines, although the small number of recorded events precludes a more definitive analysis of the phenomenon. 相似文献
89.
Pedro Manuel Sánchez JuradoLuis Romero Rizos María Luisa García-Mauriño GuelbenzuPedro Abizanda Soler 《Revista espa?ola de geriatría y gerontología》2011,46(1):43
A case of primary pulmonary non-Hodgkin's lymphoma is presented. On this occasion, the lymphoma invaded the myocardium, an event which has not previously been reported in the literature. These neoplasms spread by proximity, and invasion of the pericardium, thoracic wall and oesophagus have been described. Our patient died from heart failure. Tumour myocardial infiltration may well have been the determinant cause through various mechanisms, including a decrease in myocardial contractility. Spread into the myocardium may be facilitated by bulky tumour infiltrates in the pleural space. 相似文献
90.
María Capa João Miguel de Matos Nogueira Maíra Cappellani Silva Rossi 《Journal of morphology》2011,272(3):302-319
Fan worms (Sabellidae) possess paired modified prostomial structures at the base of the radiolar crown, dorso‐lateral to the mouth, called dorsal lips. The dorsal lips are involved in the sorting of particles collected by the radiolar crown. The range of variation in the morphology of dorsal lips is extensive, and probably this is not only due to adaptations to different environments and feeding preferences but also due to phylogenetic constraints. In this study, we describe and compare the morphology of dorsal lips in a range of sabellid taxa based on histological cross‐sections of these structures, and compare our data and terminology with those of previous studies. Dorsal lips are maintained erect in most taxa by a modified radiole fused to them known as dorsal radiolar appendage. We suggest that dorsal radiolar appendages with an internal supporting axis (cellular or acellular) and probably also the ventral lips are synapomorphies of the family. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc. 相似文献