全文获取类型
收费全文 | 45439篇 |
免费 | 3574篇 |
国内免费 | 3854篇 |
专业分类
52867篇 |
出版年
2024年 | 129篇 |
2023年 | 678篇 |
2022年 | 1499篇 |
2021年 | 2603篇 |
2020年 | 1671篇 |
2019年 | 2112篇 |
2018年 | 2056篇 |
2017年 | 1445篇 |
2016年 | 1971篇 |
2015年 | 2874篇 |
2014年 | 3415篇 |
2013年 | 3602篇 |
2012年 | 4193篇 |
2011年 | 3706篇 |
2010年 | 2360篇 |
2009年 | 1949篇 |
2008年 | 2309篇 |
2007年 | 2002篇 |
2006年 | 1830篇 |
2005年 | 1508篇 |
2004年 | 1216篇 |
2003年 | 1084篇 |
2002年 | 898篇 |
2001年 | 750篇 |
2000年 | 634篇 |
1999年 | 666篇 |
1998年 | 405篇 |
1997年 | 393篇 |
1996年 | 372篇 |
1995年 | 331篇 |
1994年 | 338篇 |
1993年 | 275篇 |
1992年 | 321篇 |
1991年 | 254篇 |
1990年 | 220篇 |
1989年 | 196篇 |
1988年 | 128篇 |
1987年 | 102篇 |
1986年 | 94篇 |
1985年 | 88篇 |
1984年 | 60篇 |
1983年 | 57篇 |
1982年 | 37篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1965年 | 1篇 |
1950年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
兔出血症病毒主要结构多肽的氨基酸分析 总被引:1,自引:0,他引:1
兔出血症病毒主要结构多肽的氨基酸分析王恒安,杜念兴,徐为燕(南京农业大学,南京210095)关键词兔出血症病毒,结构多肽,氨基酸分析有关兔出血症病毒(RHDV)结构多肽的报道很多,有认为只有1条,有报道4条的,也有报道多达6条的。但其主要结构多肽为分... 相似文献
122.
酸水解蚕蛹制备复合氨基酸的研究 总被引:7,自引:0,他引:7
采用硫酸水解法,以蚕蛹制取复合氨基酸产品,得到氨基酸态氮分别为9.05%和13.45%的食用复合氨基粉和精制复合氨基酸粉。食用复合氨基酸粉含有18种氨基酸,其中必需氨基酸含量为39.2%。食用复合氨基酸粉的制备方法经工厂小批量生产证实,其工艺简单易行,适合于中小企业采用,该产品的质量优良,生产成本低廉,具有市场竞争力。 相似文献
123.
黑节草从传粉到受精约需130d,精子在花粉管中形成,胚囊发育属蓼型胚囊,因反足细胞较早退化,故受精前胚囊多只由卵器和中央细胞组成。精卵核融合时,精核染色质进入卵核后凝集成颗粒状,并在原位与卵核的染色质融合,雌、雄性核仁一直维持至合子的第一次分裂期前。双受精作用正常,属于有丝分裂前配子融合类型,初生胚乳核发生2-3次分裂后逐渐退化消失,胚的发育局限于球形胚阶段。 相似文献
124.
利用人粒细胞集落刺激因子(hG-CSF)cDNA3′端非翻译区(3′-UTR)中存在的DraⅠ酶切位点,通过部分酶切与完全酶切,删除3′-UTR不同长度,构建了四种hG-CSFcDNA瞬时重组表达质粒。转染COS-7细胞后,生物活性测定结果提示,hG-CSFcDNA3′-UTR对其表达起负调控作用,其关键性序列位于紧接终止密码子TGA下游的65bp范围内,3′-UTR对hG-CSFcDNA表达的影响与转录水平的差别有一定关系。 相似文献
125.
将编码人单核细胞趋化蛋白-1(MCP-1)的基因亚克隆到大肠杆菌表达载体pEX31A中,在大肠杆菌中表达出MS2/MCP-1融合蛋0白,该表达产物约占菌体总蛋白的15%左右,Westernblot检测表明,表达产物可与MCP-1抗体特异反应。采用琼脂糖平板法进行活性测定表明,表达产物具有明显的单核细胞趋化活性,说明N端融合一段细菌蛋白对MCP-1有无趋化活性可能没有影响。 相似文献
126.
Missense mutations define a restricted segment in the C-terminal domain of phytochrome A critical to its regulatory activity. 总被引:13,自引:4,他引:9
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The phytochrome family of photoreceptors has dual molecular functions: photosensory, involving light signal perception, and regulatory, involving signal transfer to downstream transduction components. To define residues necessary specifically for the regulatory activity of phytochrome A (phyA), we undertook a genetic screen to identify Arabidopsis mutants producing wild-type levels of biologically defective but photochemically active and dimeric phyA molecules. Of eight such mutants identified, six contain missense mutations (including three in the same residue, glycine 727) clustered within a restricted segment in the C-terminal domain of the polypeptide. Quantitative photobiological analysis revealed retention of varying degrees of partial activity among the different alleles--a result consistent with the extent of conservation at the position mutated. Together with additional data, these results indicate that the photoreceptor subdomain identified here is critical to the regulatory activity of both phyA and phyB. 相似文献
127.
Arabidopsis TCH4, regulated by hormones and the environment, encodes a xyloglucan endotransglycosylase. 总被引:17,自引:0,他引:17
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
W Xu M M Purugganan D H Polisensky D M Antosiewicz S C Fry J Braam 《The Plant cell》1995,7(10):1555-1567
Adaptation of plants to environmental conditions requires that sensing of external stimuli be linked to mechanisms of morphogenesis. The Arabidopsis TCH (for touch) genes are rapidly upregulated in expression in response to environmental stimuli, but a connection between this molecular response and developmental alterations has not been established. We identified TCH4 as a xyloglucan endotransglycosylase by sequence similarity and enzyme activity. Xyloglucan endotransglycosylases most likely modify cell walls, a fundamental determinant of plant form. We determined that TCH4 expression is regulated by auxin and brassinosteroids, by environmental stimuli, and during development, by a 1-kb region. Expression was restricted to expanding tissues and organs that undergo cell wall modification. Regulation of genes encoding cell wall-modifying enzymes, such as TCH4, may underlie plant morphogenetic responses to the environment. 相似文献
128.
129.
130.
Previous work showed that in hamster red cells the amiloride-sensitive (AS) Na+ influx of 0.8 mmol/liter cells/hr is not mediated by Na-H exchange as in other red cells, but depends upon intracellular Mg2+ and can be increased by 40-fold by loading cells with Mg2+ to 10 mm. The purpose of this study was to verify the connection of AS Na+ influx with Na-dependent, amiloride-sensitive Mg2+ efflux and to utilize AS Na+ influx to explore that pathway.Determination of unidirectional influx of Na+ and net loss of Mg2+ in parallel sets of cells showed that activation by extracellular [Na+] follows a simple Michaelis-Menten relationship for both processes with a K
m
of 105–107 mm and that activation of both processes is sigmoidally dependent upon cytoplasmic [Mg2+] with a [Mg2+]0.5 of 2.1–2.3 mm and a Hill coefficient of 1.8. Comparison of Vmax for both sets of experiments indicated a stoichiometry of 2 Na: l Mg. Amiloride inhibits Na+ influx and Mg2+ extrusion in parallel (K
i
= 0.3 mm). Like Mg2+ extrusion, amiloride-sensitive Na+ influx shows an absolute requirement for cytoplasmic ATP and is increased by cell swelling. Hence, amiloride-sensitive Na+ influx in hamster red cells appears to be through the Na-Mg exchange pathway.There was no amiloride-sensitive Na+ efflux in hamster red cells loaded with Na+ and incubated with high [Mg2+] in the medium with or without external Na+, nor with ATP depletion. Hence, this is not a simple Na-Mg exchange carrier. 相似文献