全文获取类型
收费全文 | 1989篇 |
免费 | 122篇 |
国内免费 | 1篇 |
出版年
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 23篇 |
2018年 | 14篇 |
2017年 | 26篇 |
2016年 | 44篇 |
2015年 | 70篇 |
2014年 | 79篇 |
2013年 | 122篇 |
2012年 | 134篇 |
2011年 | 134篇 |
2010年 | 73篇 |
2009年 | 88篇 |
2008年 | 122篇 |
2007年 | 134篇 |
2006年 | 110篇 |
2005年 | 113篇 |
2004年 | 108篇 |
2003年 | 144篇 |
2002年 | 121篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 29篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1971年 | 10篇 |
排序方式: 共有2112条查询结果,搜索用时 15 毫秒
81.
Water entry at germination for black locust (Robinia pseudoacacia L.) seeds which are known as hard seeds with impermeable seed coat to water, was examined using micro-magnetic resonance imaging (MRI). The MRI apparatus equipped with a low-field (1 T; Tesla) permanent magnet was used, which is open access, easy maintenance, operable and transportable. The excellent point of the apparatus is that T 1-enhancement of water signals absorbed in dry seeds against steeping free water is stronger than the apparatuses with high-field superconducting magnets, which enabled clear detection of water entry. Water hardly penetrated into the seeds for more than 8 h but approximately 60 % of seeds germinated by incubating on wet filter papers for several days. Hot water treatments above 75 °C for 3 min effectively induced water gap; scarification was 70 % at 100 °C and 75 °C, declined to 15 % at 50 °C and decreased further at room temperature. Water entered into the scarified seeds exclusively through the lens, spread along the dorsal side of the seeds and reached the hypocotyl, whereas water migrated slowly through hilum side to radicle within 3 h. 相似文献
82.
83.
AbstractOur objective in this study was to compare the growth of zinnia, Italian ryegrass, and alfalfa, and their remediation effects in oil-contaminated soils. The soils were prepared by mixing 2, 4, or 8% diesel oil by weight with soil. The plant height and dry weights of shoots and roots were highest for zinnia in the 2 and 4% oil treatments, and highest for Italian ryegrass in the 8% oil treatment. The reduction ratios in soil total petroleum hydrocarbons concentration (TPH) for 3 plants were lower in the 4 and 8% oil treatments than those in the 2% treatment. The reduction ratios for Italian ryegrass and zinnia contaminated with 2, 4, and 8% diesel oil treatments were significantly higher than those for alfalfa and the non-cultivation treatment at 45?days after sowing, and there were no significant differences in reduction ratios between Italian ryegrass and zinnia. The reduction ratio of soil TPH concentration brought about by zinnia was also comparable to that of Italian ryegrass. Therefore, we conclude that zinnia shows growth and remediation effects that are equivalent to those of Italian ryegrass, in soils contaminated with less than 8% oil. 相似文献
84.
85.
86.
Effects of cryopreservation methods on post-thaw motility of spermatozoa from the Japanese pearl oyster, Pinctada fucata martensii 总被引:1,自引:0,他引:1
In order to develop cryopreservation techniques for Japanese pearl oyster spermatozoa, the effects of various cryopreservation conditions on post-thaw motility were examined. Spermatozoa cryopreserved with 10% methanol (MET), dimethylformamide or dimethylacetamide plus 90% diluent comprising 80% seawater and 20% fetal bovine serum (FBS) showed higher percentages of post-thaw motility than those cryopreserved with 10% dimethylsulfoxide or glycerol. When spermatozoa were cryopreserved with various concentrations (0-20%) of MET and 100-80% diluent, 10% MET showed the highest percentages of post-thaw motility. When spermatozoa were cryopreserved with 10% MET and 90% diluent comprising various concentrations (0-100%) of FBS or Ringer solution mixed with seawater, the percentages of post-thaw motility peaked at 20% FBS or Ringer solution, and were significantly higher for 20% FBS than for 20% Ringer solution. The percentages of post-thaw motility increased with increasing dilution ratios from 2.5- to 50-fold. Spermatozoa cooled to -50 degrees C and then immersed in liquid nitrogen (LN) showed higher post-thaw motility than those cooled to -30 degrees C or -40 degrees C. When spermatozoa were cryopreserved to -50 degrees C at various cooling rates by changing the sample height above the LN surface, the post-thaw motilities of spermatozoa cooled at 10 cm (cooling rate: -21.3 degrees C/min) and 12.5 cm (-15.6 degrees C/min) from the LN surface were higher than those at 5, 7.5 or 15 cm. These results indicate that 10% MET plus 90% diluent comprising 80% seawater and 20% FBS is a suitable extender for cryopreservation of Japanese pearl oyster spermatozoa and that samples should be cooled to -50 degrees C at a cooling rate between -15 and -20 degrees C/min for efficient storage. 相似文献
87.
Regulation of ammonia homeostasis by the ammonium transporter AmtA in Dictyostelium discoideum 下载免费PDF全文
Yoshino R Morio T Yamada Y Kuwayama H Sameshima M Tanaka Y Sesaki H Iijima M 《Eukaryotic cell》2007,6(12):2419-2428
Ammonia has been shown to function as a morphogen at multiple steps during the development of the cellular slime mold Dictyostelium discoideum; however, it is largely unknown how intracellular ammonia levels are controlled. In the Dictyostelium genome, there are five genes that encode putative ammonium transporters: amtA, amtB, amtC, rhgA, and rhgB. Here, we show that AmtA regulates ammonia homeostasis during growth and development. We found that cells lacking amtA had increased levels of ammonia/ammonium, whereas their extracellular ammonia/ammonium levels were highly decreased. These results suggest that AmtA mediates the excretion of ammonium. In support of a role for AmtA in ammonia homeostasis, AmtA mRNA is expressed throughout the life cycle, and its expression level increases during development. Importantly, AmtA-mediated ammonia homeostasis is critical for many developmental processes. amtA(-) cells are more sensitive to NH(4)Cl than wild-type cells in inhibition of chemotaxis toward cyclic AMP and of formation of multicellular aggregates. Furthermore, even in the absence of exogenously added ammonia, we found that amtA(-) cells produced many small fruiting bodies and that the viability and germination of amtA(-) spores were dramatically compromised. Taken together, our data clearly demonstrate that AmtA regulates ammonia homeostasis and plays important roles in multiple developmental processes in Dictyostelium. 相似文献
88.
Tanida Kotomi Shimada Mihoko Khor Seik-Soon Toyoda Hiromi Kato Kayoko Kotorii Nozomu Kotorii Tatayu Ariyoshi Yu Kato Takao Hiejima Hiroshi Ozone Motohiro Uchimura Naohisa Ikegami Azusa Kume Kazuhiko Kanbayashi Takashi Imanishi Aya Kamei Yuichi Hida Akiko Wada Yamato Kuroda Kenji Miyamoto Masayuki Hirata Koichi Takami Masanori Yamada Naoto Okawa Masako Omata Naoto Kondo Hideaki Kodama Tohru Inoue Yuichi Mishima Kazuo Honda Makoto Tokunaga Katsushi Miyagawa Taku 《Sleep and biological rhythms》2022,20(1):137-148
Sleep and Biological Rhythms - Idiopathic hypersomnia (IH) is a rare sleep disorder characterized by excessive daytime sleepiness, great difficulty upon awakening, and prolonged sleep time. In... 相似文献
89.
90.
We investigated the in vitro stimulatory effect of ganglioside (GM3, GD1a, GD1b, GT1b, or GQ1b)-containing liposomes on human immune cells. The effect of ganglioside-containing liposomes on the concentration of cytoplasmic free calcium ions ([Ca2+]1) in human immunocytes was examined using the confocal laser fluorescence microscopic method. The GD1a- and GT1b-containing liposomes significantly increased [Ca2+]1 of human T lymphocytes compared with the GM3-, GD1b- and GQ1b-containing ones. The response of CD8+ and CD4+ cells was significantly higher than that of CD20+ cells. Our results show that the increase in [Ca2+]i may be caused by not the number of sialic acids contained in the gangliosides but the conformation of the sialic acid moiety to protrude exteriorly from the liposomal membrane surface, and that a sort of receptor recognizing the sialic acid moiety exists on human T lymphocytes (both CD8+ and CD4+ cells), which may be involved in the activation of the cells. The present results are almost the same as those obtained for the rat T lymphocyte system previously reported. This clearly confirms that a sort of ganglioside surely stimulates T lymphocytes directly, which is not species-specific but conserved in humans and rats among animal species. 相似文献