全文获取类型
收费全文 | 8698篇 |
免费 | 681篇 |
专业分类
9379篇 |
出版年
2023年 | 89篇 |
2022年 | 128篇 |
2021年 | 253篇 |
2020年 | 135篇 |
2019年 | 179篇 |
2018年 | 215篇 |
2017年 | 199篇 |
2016年 | 305篇 |
2015年 | 471篇 |
2014年 | 517篇 |
2013年 | 662篇 |
2012年 | 742篇 |
2011年 | 692篇 |
2010年 | 408篇 |
2009年 | 441篇 |
2008年 | 526篇 |
2007年 | 447篇 |
2006年 | 422篇 |
2005年 | 408篇 |
2004年 | 375篇 |
2003年 | 330篇 |
2002年 | 316篇 |
2001年 | 100篇 |
2000年 | 63篇 |
1999年 | 85篇 |
1998年 | 94篇 |
1997年 | 80篇 |
1996年 | 63篇 |
1995年 | 50篇 |
1994年 | 44篇 |
1993年 | 49篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 29篇 |
1986年 | 13篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1983年 | 24篇 |
1982年 | 24篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1978年 | 15篇 |
1977年 | 23篇 |
1975年 | 11篇 |
1974年 | 18篇 |
1973年 | 12篇 |
1972年 | 11篇 |
排序方式: 共有9379条查询结果,搜索用时 15 毫秒
991.
Manuel F. Morales 《Bulletin of mathematical biology》1946,8(4):147-157
Evidence is presented to show that despite their effectiveness in producing motion sickness the actual frequencies and accelerations
involved in ship motion are rather low. It is suggested that the disparity is due to the fact that ship motion is such as
to cause an asynchrony between signals from the labyrinth and those from other motion receptors. 相似文献
992.
A simple theoretical model has been presented whose behavior duplicates the variation in bicarbonate ion concentration in the blood following exercise. Methods for the evaluation of the constants of rational equations to describe the concentration in muscle cells, in blood plasma, and in removal cells, of the anions produced in exercise have been devised. These methods have been applied to experimental data from 23 experiments, and a close agreement between the observed and theoretically predicted values for blood plasma has been found. From the mathematical analysis of the data values for permeability of acid anions produced in exercise have been estimated as 75 x 10–5 and 5.9 x 10–5 cm. per sec. between muscle cell and blood (extracellular fluid) and between blood plasma and removal cells respectively. 相似文献
993.
Manuel D. Pe?as 《BMJ (Clinical research ed.)》1954,2(4886):490-491
994.
995.
996.
997.
Jordi Mayneris-Perxachs María Arnoriaga-Rodríguez Josep Garre-Olmo Josep Puig Rafael Ramos Maria Trelis Aurelijus Burokas Cludia Coll Cristina Zapata-Tona Salvador Pedraza Vicente Prez-Brocal Lluís Rami Wifredo Ricart Andrs Moya Mariona Jov Joaquim Sol Manuel Portero-Otin Reinald Pamplona Rafael Maldonado Jos Manuel Fernndez-Real 《The ISME journal》2022,16(9):2181
Growing evidence implicates the gut microbiome in cognition. Blastocystis is a common gut single-cell eukaryote parasite frequently detected in humans but its potential involvement in human pathophysiology has been poorly characterized. Here we describe how the presence of Blastocystis in the gut microbiome was associated with deficits in executive function and altered gut bacterial composition in a discovery (n = 114) and replication cohorts (n = 942). We also found that Blastocystis was linked to bacterial functions related to aromatic amino acids metabolism and folate-mediated pyrimidine and one-carbon metabolism. Blastocystis-associated shifts in bacterial functionality translated into the circulating metabolome. Finally, we evaluated the effects of microbiota transplantation. Donor’s Blastocystis subtypes led to altered recipient’s mice cognitive function and prefrontal cortex gene expression. In summary, Blastocystis warrant further consideration as a novel actor in the gut microbiome-brain axis.Subject terms: Biomarkers, Pathogenesis, Diagnosis 相似文献
998.
Víctor Víctor Manuel Miñano Marta Guayerbas Noelia Del Río Mónica Medina Sonia De La Fuente Mónica 《Molecular and cellular biochemistry》1998,189(1-2):25-31
Gram negative sepsis and septic shock continue to be a major medical problem, with a complex physiopathology and it is associated with high mortality. Although secretion of cytokines such as tumor necrosis factor-alpha by macrophages is the principal host mediator of septic shock, other characteristic functions of macrophages implicated in their phagocytic capacity have not been studied in the process of endotoxic shock. In the present study we have used an intraperitoneal injection of E. coli lipopolysaccharide (LPS) (100 mg/kg) in order to obtain an endotoxic shock model in adult female BALB/c mice. Peritoneal cell suspensions were obtained at several times (2, 4, 12 or 24 h) after injection and the following functions were studied on the peritoneal macrophages: adherence to substrate, mobility (spontaneous and directed or chemotaxis), ingestion of particles and superoxide anion production. The results showed a stimulation of adherence, ingestion and superoxide production as well as a decrease of chemotaxis in the animals injected with LPS. These effects changed with time after LPS injection. Thus, the increase of adherence and the decrease of mobility were higher during the first hours, whereas the increase in ingestion and superoxide production turned larger with time. 相似文献
999.
Del Carmen Córdoba-Pedregosa M Córdoba F Villalba JM González-Reyes JA 《Plant physiology》2003,131(2):697-706
Onion (Allium cepa) roots growing hydroponically show differential zonal values for intra- (symplastic) and extra- (apoplastic) cellular ascorbate (ASC) and dehydroascorbate (DHA) contents and for related enzyme activities. In whole roots, ASC and DHA concentrations were higher in root apex and meristem and gradually decreased toward the root base. Guaiacol peroxidase, ASC peroxidase, monodehydroascorbate oxidoreductase, DHA reductase, catalase, and glutathione reductase activities showed differential activity patterns depending on the zone of the root and their apoplastic or symplastic origin. An in vivo staining of peroxidase activity also revealed a specific distribution pattern along the root axis. Using electron microscopy, hydrogen peroxide was found at different locations depending on the root zone but was mainly located in cell walls from epidermal and meristematic cells and in cells undergoing lignification. A balanced control of all of these molecules seems to exist along the root axis and may be directly related to the mechanisms in which the ASC system is involved, as cell division and elongation. The role of ASC on growth and development in relation to its presence at the different zones of the root is discussed. 相似文献
1000.
Ruenn Chai Lai Fatih Arslan May May Lee Newman Siu Kwan Sze Andre Choo Tian Sheng Chen Manuel Salto-Tellez Leo Timmers Chuen Neng Lee Reida Menshawe El Oakley Gerard Pasterkamp Dominique P.V. de Kleijn Sai Kiang Lim 《Stem cell research》2010,4(3):214-222
Human ESC-derived mesenchymal stem cell (MSC)-conditioned medium (CM) was previously shown to mediate cardioprotection during myocardial ischemia/reperfusion injury through large complexes of 50–100 nm. Here we show that these MSCs secreted 50- to 100-nm particles. These particles could be visualized by electron microscopy and were shown to be phospholipid vesicles consisting of cholesterol, sphingomyelin, and phosphatidylcholine. They contained coimmunoprecipitating exosome-associated proteins, e.g., CD81, CD9, and Alix. These particles were purified as a homogeneous population of particles with a hydrodynamic radius of 55–65 nm by size-exclusion fractionation on a HPLC. Together these observations indicated that these particles are exosomes. These purified exosomes reduced infarct size in a mouse model of myocardial ischemia/reperfusion injury. Therefore, MSC mediated its cardioprotective paracrine effect by secreting exosomes. This novel role of exosomes highlights a new perspective into intercellular mediation of tissue injury and repair, and engenders novel approaches to the development of biologics for tissue repair. 相似文献