全文获取类型
收费全文 | 53940篇 |
免费 | 3724篇 |
国内免费 | 1658篇 |
出版年
2024年 | 101篇 |
2023年 | 710篇 |
2022年 | 1076篇 |
2021年 | 1588篇 |
2020年 | 1754篇 |
2019年 | 2280篇 |
2018年 | 2054篇 |
2017年 | 1320篇 |
2016年 | 1424篇 |
2015年 | 1848篇 |
2014年 | 3252篇 |
2013年 | 3603篇 |
2012年 | 2034篇 |
2011年 | 2874篇 |
2010年 | 2054篇 |
2009年 | 2500篇 |
2008年 | 2754篇 |
2007年 | 2709篇 |
2006年 | 2593篇 |
2005年 | 2249篇 |
2004年 | 1992篇 |
2003年 | 1670篇 |
2002年 | 1515篇 |
2001年 | 1049篇 |
2000年 | 959篇 |
1999年 | 827篇 |
1998年 | 896篇 |
1997年 | 807篇 |
1996年 | 791篇 |
1995年 | 788篇 |
1994年 | 740篇 |
1993年 | 636篇 |
1992年 | 614篇 |
1991年 | 540篇 |
1990年 | 505篇 |
1989年 | 445篇 |
1988年 | 387篇 |
1987年 | 377篇 |
1986年 | 300篇 |
1985年 | 361篇 |
1984年 | 376篇 |
1983年 | 234篇 |
1982年 | 322篇 |
1981年 | 259篇 |
1980年 | 239篇 |
1979年 | 213篇 |
1978年 | 130篇 |
1977年 | 126篇 |
1976年 | 111篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
《Bioorganic & medicinal chemistry》2014,22(11):2966-2973
Plasmalogen lysophosphatidylethanolamine (pLPE) had been identified as a self antigen for natural killer T cells (NKT cells). It is very important in the development, maturation and activation of NKT cells in thymus. Besides, pLPE is a novel type of antigen for NKT cells. To evaluate the structure–activity relationship (SAR) of this new antigen, pLPE and its analogues referred to different aliphatic chains and linkages at the sn-1 position of the glycerol backbone were synthesized, and the biological activities of these analogues was characterized. It is discovered that the linkages between phosphate and lipid moiety are not important for the antigens’ activities. The pLPE analogues 1, 3, 4, 7 and 9, which have additional double bonds on lipid parts, were identified as new NKT agonists. Moreover, the analogues 4, 7 and 9 were discovered as potent Th2 activators for NKT cells. 相似文献
92.
Little work has been carried out on the sperm recognition systems present on the egg plasma membrane. Here it is shown that wheat germ agglutinin (WGA) interferes with the sperm-interacting system on the plasma membrane of eggs of the ascidian, Ascidia ceratodes. The WGA activates the dechorionated egg, indicating that a plasma membrane sugar residue can be directly tied to egg activation. Low concentrations of this lectin do not activate the eggs, but reduce fertilizability. This observation suggests that the WGA binding site might be part of a sperm reception–activation complex in the plasma membrane. While WGA also affects sperm binding to the chorion, the mechanisms of sperm interaction at the plasma membrane and chorion show different sensitivities to lectins, sugars and enzymes. 相似文献
93.
94.
《Developmental cell》2021,56(17):2516-2535.e8
95.
Summary The sensory receptor responsive to pressure applied internally to the ventral abdominal body wall of the blood-feeding insects, Rhodnius prolixus, is a single sense cell containing, at its distal end, a cilium enclosed within a scolopale, a densely staining structure characteristic of insect scolopidial sensilla. A small spherical structure lies within a dilation near the midregion of the cilium, and contains nine heavily staining bodies, the position of each corresponding to a pair of microtubules in the cilium. Proximal to the dilation, the microtubules are organized in a ring of nine pairs with one microtubule of each pair associated with dyneinlike arms. Dastal to the dilation a central pair of microtubules is present, but dyneinlike arms are absent. The scolopale cell, which gives risc to the scolopale, has cytoplasmic invaginations that form an elaborate array of extracellular compartments surrounding the body wall of the sense cell. These compartments may serve to dampen high frequency vibrations permitting the receptor to respond to pressure exerted by touch, an attribute in keeping with the receptor's proposed function of detecting abdominal distension related to the size and movement of the stomach. 相似文献
96.
Kateryna Raykova Melina V. Jones Hwa Huang Paul F. Hoffman Michael Levy 《Journal of visualized experiments : JoVE》2015,(99)
The rat optic nerve is a useful model for stem cell regeneration research. Direct injection into the rat optic nerve allows delivery into the central nervous system in a minimally-invasive surgery without bone removal. This technique describes an approach to visualization and direct injection of the optic nerve following minor fascial dissection from the orbital ridge, using a conjunctival traction suture to gently pull the eye down and out. Representative examples of an injected optic nerve show successful injection of dyed beads. 相似文献
97.
《Cell》2022,185(20):3753-3769.e18
98.
Three new geranylated flavonoids, including two geranylflavones (1, 2) and one geranylflavonol (3), named as paucatalinone C–E, were isolated from the fruit peel of P. catalpifolia T. Gong ex D.Y. Hong. Their structures were determined by means of UV, IR, MS, and NMR techniques. To our known, geranylflavone or geranylflavonol was the first isolation from the genus Paulownia. These isolated geranylated flavonoids displayed good antioxidant effects on DPPH and the senescent human embryonic lung diploid fibroblasts cells (2BS cells) induced by H2O2. The geranyl substituent may be an important factor for the cellular radical-scavenging effect because of its lipophilic character. 相似文献
99.
Duygu Findik Qizhong Song Hiroyoshi Hidaka Martin Lavin 《Journal of cellular biochemistry》1995,57(1):12-21
In addition to a role for de novo protein synthesis in apoptosis we have previously shown that activation of a protein phosphatase or loss of activity of a kinase is also important in radiation-induced apoptosis in human cells [Baxter, and Lavin (1992): J Immunol 148:149–1954]. We show here that some inhibitors of protein kinases exacerbate radiation-induced apoptosis in the human cell line BM13674. The specific protein kinase A inhibitor isoquinoline sulfonamide (20 μM) gave rise to significantly increased levels of apoptosis at 2–6 h postirradiation compared to values after radiation exposure only. The same concentration of isoquinolinesulfonamide, which was effective in increasing apoptosis, reduced activity markedly. A 66% inhibition of cyclic AMP-dependent protein kinase A activity occurred in unirradiated cells at this concentration of H89 and activity was reduced to 58% in irradiated cells. Calphostin C, a specific inhibitor of protein kinase C, at a concentration of 0.1 μM, which caused 68% inhibition of enzyme activity in irradiated cells, failed to enhance the level of radiation-induced apoptosis. Other kinase inhibitors did not lead to an additional increase in apoptosis over and above that observed after irradiation. The results obtained here provide further support for an important role for modification of existing proteins during radiation-induced apoptosis. 相似文献
100.