全文获取类型
收费全文 | 1954篇 |
免费 | 274篇 |
国内免费 | 438篇 |
专业分类
2666篇 |
出版年
2023年 | 24篇 |
2022年 | 48篇 |
2021年 | 65篇 |
2020年 | 49篇 |
2019年 | 55篇 |
2018年 | 51篇 |
2017年 | 43篇 |
2016年 | 48篇 |
2015年 | 78篇 |
2014年 | 89篇 |
2013年 | 103篇 |
2012年 | 148篇 |
2011年 | 141篇 |
2010年 | 99篇 |
2009年 | 111篇 |
2008年 | 114篇 |
2007年 | 99篇 |
2006年 | 104篇 |
2005年 | 105篇 |
2004年 | 80篇 |
2003年 | 87篇 |
2002年 | 91篇 |
2001年 | 76篇 |
2000年 | 61篇 |
1999年 | 42篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 12篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 38篇 |
1991年 | 31篇 |
1990年 | 37篇 |
1989年 | 25篇 |
1988年 | 29篇 |
1987年 | 18篇 |
1986年 | 12篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1981年 | 12篇 |
1978年 | 12篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1974年 | 16篇 |
1972年 | 21篇 |
1971年 | 16篇 |
1969年 | 12篇 |
1968年 | 10篇 |
1963年 | 13篇 |
排序方式: 共有2666条查询结果,搜索用时 0 毫秒
21.
22.
δ-Tocopherylquinone (δTQ) content was determined in tobacco and yellow maple leaves, green ivy leaves and cactus tissues. It was found that the concentration of δ-TQ was highest in mature or senescent tissues, such as white tobacco leaves (0.02 μmole/g dry wt) while its detection was uncertain in young, green leaves from the apex of tobacco plants. Fractionation by centrifugation of senescent tobacco leaves showed that the osmiophilic globule fraction was enriched in δ-TQ. Electron microscope studies of young, mature and senescent tobacco tissues showed progressive changes in the size and number of osmiophilic globules. After chloroplast breakdown in senescent tobacco leaves, these globules became the predominant constituents of the organelle. δ-TQ which is associated with osmiophilic globules may play a role in the development of plants, particularly during senescence. 相似文献
23.
24.
25.
Wenjuan Dong Heather Mead Lei Tian Jun-Gyu Park Juan I. Garcia Sierra Jaramillo Tasha Barr Daniel S. Kollath Vanessa K. Coyne Nathan E. Stone Ashley Jones Jianying Zhang Aimin Li Li-Shu Wang Martha Milanes-Yearsley Jordi B. Torrelles Luis Martinez-Sobrido Paul S. Keim Bridget Marie Barker Michael A. Caligiuri Jianhua Yu 《Journal of virology》2022,96(1)
26.
Barr CM 《Journal of evolutionary biology》2004,17(4):786-794
I tested whether a region of high female frequencies in the gynodioecious plant, Nemophila menziesii, may be due to hybridization between regionally distributed populations with different corolla colours. I crossed plants in the greenhouse from populations with different corolla colours and found that hybrid crosses yielded higher frequencies of females than within-colour crosses. In the field, I found that populations with high female frequencies had intermediate mean corolla colours and higher variance in corolla colour, two traits suggesting hybridization. Nemophila menziesii has nuclear-cytoplasmic sex inheritance, thus if populations with different corolla colours are fixed for different male-sterile cytoplasms and matching nuclear restorer alleles, hybridization between populations with different corolla colour should yield high frequencies of females. Two populations that are all hermaphroditic in the field segregated females in hybrid crosses suggesting that field populations may contain sex ratio distorters but appear undistorted, a prediction of genomic conflict theory. 相似文献
27.
28.
Phosphoinositides control many different processes required for normal cellular function. Myotubularins are a family of Phosphatidylinositol 3-phosphate (PtdIns3P) phosphatases identified by the positional cloning of the MTM1 gene in patients suffering from X-linked myotubular myopathy and the MTMR2 gene in patients suffering from the demyelinating neuropathy Charcot-Marie-Tooth disease type 4B. MTM1 is a phosphatidylinositol phosphatase with reported specificity toward PtdIns3P, while the related proteins MTMR2 and MTMR3 hydrolyze both PtdIns3P and PtdIns(3,5)P2. We have investigated MTM1 and MTMR6 and find that they use PtdIns(3,5)P2 in addition to PtdIns3P as a substrate in vitro. The product of PtdIns(3,5)P2 hydrolysis, PtdIns5P, causes MTM1 to form a heptameric ring that is 12.5 nm in diameter, and it is a specific allosteric activator of MTM1, MTMR3, and MTMR6. A disease-causing mutation at arginine 69 of MTM1 falling within a putative pleckstrin homology domain reduces the ability of the enzyme to respond to PtdIns5P. We propose that the myotubularin family of enzymes utilize both PtdIns3P and PtdIns(3,5)P2 as substrates, and that PtdIns5P functions in a positive feedback loop controlling their activity. These findings highlight the importance of regulated phosphatase activity for the control of phosphoinositide metabolism. 相似文献
29.
30.
P—选择素凝集素—EGF功能域的克隆、表达及其单克隆抗体制备 总被引:19,自引:0,他引:19
制备特异性抗人P 选择素的凝集素 表皮生长因子 (L EGF)功能域的单克隆抗体。利用特异引物 ,通过RT PCR从外周血血小板中扩增出人P 选择素的L EGF功能域基因 ,将其克隆至pET42b( )载体中 ,测序验证后转染大肠杆菌BL2 1,经诱导表达了C端融合 6×His的蛋白质。融合蛋白质经分离纯化后 ,免疫Balb/c小鼠 ,应用杂交瘤技术 ,通过间接ELISA筛选阳性克隆。获得 3株可稳定分泌抗L EGF功能域单抗的杂交瘤细胞株 (B10、F3和H5 )。其亚型分别为IgG2 、IgG1和IgG3;轻链均为κ型。所获的单抗对LPS刺激活化的人脐静脉内皮细胞均有特异性结合反应 ,并可在体外阻断经凝血酶激活的血小板与中性粒细胞间的粘附。表明所获的单抗可特异性识别结合天然P 选择素 ,具有体外抗活化血小板与中性粒细胞粘附的功能 ,为进一步应用此单抗进行P 选择素结构和功能及抗粘附治疗研究提供了实验基础。 相似文献