全文获取类型
收费全文 | 5613篇 |
免费 | 396篇 |
国内免费 | 5篇 |
专业分类
6014篇 |
出版年
2022年 | 35篇 |
2021年 | 50篇 |
2020年 | 38篇 |
2019年 | 47篇 |
2018年 | 68篇 |
2017年 | 67篇 |
2016年 | 105篇 |
2015年 | 188篇 |
2014年 | 189篇 |
2013年 | 326篇 |
2012年 | 334篇 |
2011年 | 298篇 |
2010年 | 190篇 |
2009年 | 214篇 |
2008年 | 322篇 |
2007年 | 345篇 |
2006年 | 338篇 |
2005年 | 357篇 |
2004年 | 338篇 |
2003年 | 312篇 |
2002年 | 290篇 |
2001年 | 120篇 |
2000年 | 112篇 |
1999年 | 126篇 |
1998年 | 66篇 |
1997年 | 66篇 |
1996年 | 66篇 |
1995年 | 50篇 |
1994年 | 61篇 |
1993年 | 56篇 |
1992年 | 114篇 |
1991年 | 65篇 |
1990年 | 72篇 |
1989年 | 58篇 |
1988年 | 45篇 |
1987年 | 42篇 |
1986年 | 40篇 |
1985年 | 57篇 |
1984年 | 44篇 |
1983年 | 28篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 26篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1973年 | 21篇 |
排序方式: 共有6014条查询结果,搜索用时 0 毫秒
81.
82.
Fujinaga M Maeda J Yui J Hatori A Yamasaki T Kawamura K Kumata K Yoshida Y Nagai Y Higuchi M Suhara T Fukumura T Zhang MR 《Journal of neurochemistry》2012,120(1):115-124
Neurovascular degeneration contributes to the pathogenesis of Alzheimer's disease (AD). Because erythropoietin (EPO) promotes endothelial regeneration, we investigated the therapeutic effects of EPO in animal models of AD. In aged Tg2576 mice, EPO receptors (EPORs) were expressed in the cortex and hippocampus. Tg2576 mice were treated with daily injection of EPO (5000 IU/kg/day) for 5 days. At 14 days, EPO improved contextual memory as measured by fear-conditioning test. EPO enhanced endothelial proliferation and the level of synaptophysin expression in the brain. EPO also increased capillary density, and decreased the level of the receptor for advanced glycation endproducts (RAGE) in the brain, while decreasing in the amount of amyloid plaque and amyloid-β (Aβ). In cultured human endothelial cells, EPO enhanced angiogenesis and suppressed the expression of the RAGE. These results show that EPO improves memory and ameliorates endothelial degeneration induced by Aβ in AD models. This pre-clinical evidence suggests that EPO may be useful for the treatment of AD. 相似文献
83.
Ginting TE Shinya K Kyan Y Makino A Matsumoto N Kaneda S Kawaoka Y 《Journal of virology》2012,86(1):121-127
Oseltamivir-resistant H1N1 influenza viruses emerged in 2007 to 2008 and have subsequently circulated widely. However, prior to 2007 to 2008, viruses possessing the neuraminidase (NA) H274Y mutation, which confers oseltamivir resistance, generally had low growth capability. NA mutations that compensate for the deleterious effect of the NA H274Y mutation have since been identified. Given the importance of the functional balance between hemagglutinin (HA) and NA, we focused on amino acid changes in HA. Reverse genetic analysis showed that a mutation at residue 82, 141, or 189 of the HA protein promotes virus replication in the presence of the NA H274Y mutation. Our findings thus identify HA mutations that contributed to the replacement of the oseltamivir-sensitive viruses of 2007 to 2008. 相似文献
84.
Kunimoto K Yamazaki Y Nishida T Shinohara K Ishikawa H Hasegawa T Okanoue T Hamada H Noda T Tamura A Tsukita S Tsukita S 《Cell》2012,148(1-2):189-200
Highlights? Mice expressing truncated Odf2 cough and sneeze due to primary ciliary dyskinesia ? Full-length Odf2 is needed for the formation of basal body-associated basal feet ? In the absence of basal feet, basal bodies fail to align with planar polarity cues ? Polarization of basal bodies by Odf2 is required for coordinated ciliary beating 相似文献
85.
Akiko Sasaki Yu Hagimori Ichiro Yuasa Takayuki Nakatsubo 《Landscape and Ecological Engineering》2012,8(1):107-114
To quantify organic matter mineralization at estuarine intertidal flats, we measured in situ sediment respiration rates using
an infrared gas analyzer in estuarine sandy intertidal flats located in the northwestern Seto Inland Sea, Japan. In situ sediment
respiration rates showed spatial and seasonal variations, and the mean of the rates is 38.8 mg CO2-C m−2 h−1 in summer. In situ sediment respiration rates changed significantly with sediment temperature at the study sites (r
2 = 0.70, p < 0.05), although we did not detect any significant correlations between the rates and sediment characteristics. We prepared
a model for estimating the annual sediment respiration based on the in situ sediment respiration rates and their temperature
coefficient (Q
10 = 1.8). The annual sediment respiration was estimated to be 92 g CO2-C m−2 year−1. The total amount of organic carbon mineralization for the entire estuarine intertidal flats through sediment respiration
(43 t C year−1) is equivalent to approximately 25% of the annual organic carbon load supplied from the river basin of the estuary. 相似文献
86.
Imai H Saito M Kirai N Hasegawa J Konishi K Hattori H Nishimura M Naito S Nakagawa Y 《Journal of biochemistry》2006,140(4):573-590
87.
88.
Yan Ropert-Coudert Akiko Kato Julien Baudat Charles-André Bost Yvon Le Maho Yasuhiko Naito 《Polar Biology》2001,24(6):467-470
Data on the swim speed, dive depth and feeding rates of three Adélie penguins (Pygoscelis adeliae) foraging in summer 1998/1999 in Adélie Land, Antarctica were collected using dorsally-mounted loggers, in tandem with oesophageal temperature sensors. Swim speed could be integrated, together with the rate of change of depth, to determine dive and return-to-surface angles. Overall, birds increased rates of change of depth during commuting phases so that dive angles were steeper in dives terminating at greater depths. Angles of descent and ascent during feeding dives were greater than during non-feeding dives. Variation in the descent angle over time of particular dives was generally less than 10°, but the angles of the ascent phases varied more widely. The importance of selecting the optimum descent and ascent angles with respect to prey exploitation, oxygen stores and time gained in the feeding area over the course of a dive by diving at a steeper angle is discussed. 相似文献
89.
The mechanisms of drug resistance of clinical isolate, Vibrio (V.) parahaemolyticus ST550, resistant to chloramphenicol (CP), aminoglycoside antibiotics (AGs) and beta-lactam antibiotics were investigated. The mechanisms of resistance to CP, AGs and beta-lactam antibiotics were dependent on chloramphenicol acetyltransferase (CAT), aminoglycoside-3"-adenylyltransferase AAD(3") and aminoglycoside-3'-phosphotransferase APH(3') and TEM type penicillinase, respectively. 相似文献
90.
Molecular taxonomy of dermatophytes and related fungi by chitin synthase 1 (CHS1) gene sequences 总被引:2,自引:0,他引:2
In the present study, the nucleotide sequences of the CHS1 gene from dermatophytes and related fungi in the genera Chrysosporium, Epidermophyton, Microsporum and Trichophyton were investigated using molecular methods. About 440-bp genomic DNA fragments of the CHS1 gene from 21 species were amplified by polymerase chain reaction (PCR) and sequenced. The CHS1 nucleotide sequences of these fungi showed more than 83% similarity. The molecular taxonomy of the CHS1 gene sequences revealed that Microsporum was genetically distinct from Chrysosporium and Trichophyton, as classified by morphological characteristics.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献