全文获取类型
收费全文 | 2758篇 |
免费 | 131篇 |
学科分类
生物科学 | 2889篇 |
出版年
2022年 | 14篇 |
2021年 | 26篇 |
2020年 | 13篇 |
2019年 | 22篇 |
2018年 | 34篇 |
2017年 | 39篇 |
2016年 | 59篇 |
2015年 | 83篇 |
2014年 | 101篇 |
2013年 | 166篇 |
2012年 | 156篇 |
2011年 | 169篇 |
2010年 | 109篇 |
2009年 | 101篇 |
2008年 | 197篇 |
2007年 | 175篇 |
2006年 | 187篇 |
2005年 | 181篇 |
2004年 | 165篇 |
2003年 | 180篇 |
2002年 | 166篇 |
2001年 | 44篇 |
2000年 | 34篇 |
1999年 | 44篇 |
1998年 | 36篇 |
1997年 | 36篇 |
1996年 | 22篇 |
1995年 | 26篇 |
1994年 | 10篇 |
1993年 | 26篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 26篇 |
1983年 | 8篇 |
1982年 | 18篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有2889条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Expression of adrenocorticotropin-releasing hormone precursor gene in placenta and other nonhypothalamic tissues in man 总被引:1,自引:0,他引:1
T Usui Y Nakai T Tsukada H Jingami H Takahashi J Fukata H Imura 《Molecular endocrinology (Baltimore, Md.)》1988,2(9):871-875
Adrenocorticotropin-releasing hormone (CRH) is a peptide originally isolated from the hypothalamus. Immunocytochemical and RIA studies have revealed that CRH-like peptide is also localized in human nonhypothalamic tissues and some tumors. To see if CRH is synthesized in these nonhypothalamic tissues and tumors, we examined preproCRH mRNA in these tissues by Northern blot analysis using a cloned human preproCRH gene as a probe. PreproCRH mRNA was detected in human hypothalamus, cerebral cortex, adrenal gland, placenta, pheochromocytoma, and thymic carcinoid. The content of preproCRH mRNA in placenta was apparently greater than that in the whole hypothalamus. 相似文献
5.
p-nitrophenyl penta-N-acetyl-beta-chitopentaoside as a novel synthetic substrate for the colorimetric assay of lysozyme 总被引:3,自引:0,他引:3
p-Nitrophenyl beta-glycosides of N-acetylchitooligosaccharides (PNP-(GlcNAc)n n = 3-5) were examined as substrates for lysozyme [EC 3.2.1.17]. The enzyme released predominantly p-nitrophenyl N-acetyl-beta-D-glucosaminide (PNP-GlcNAc) from each substrate. Furthermore, the initial rate of PNP-GlcNAc formation in lysozyme-catalyzed hydrolysis of p-nitrophenyl penta-N-acetyl-beta-chitopentaoside (PNP-(GlcNAc)5) was about 350 and 25 times faster than those of p-nitrophenyl tri-N-acetyl-beta-chitotrioside (PNP-(GlcNAc)3) and p-nitrophenyl tetra-N-acetyl-beta-chitotetraoside (PNP-(GlcNAc)4), respectively. From these results, a new colorimetric assay method of lysozyme using PNP-(GlcNAc)5 as a substrate was developed on the basis of the determination of p-nitrophenol liberated from the substrate by lysozyme through a coupled reaction involving beta-N-acetylhexosaminidase (NAHase). The assay system gave a linear dose-response curve in the range of 2-120 micrograms of lysozyme in a 15-60 min incubation. The present assay was not significantly influenced by the ionic strength of the medium and was reproducible. This method using PNP-(GlcNAc)5 as a substrate was shown to be useful for lysozyme assay. 相似文献
6.
7.
8.
Koichi Rikimaru Hitomi Toda Noriko Tachikawa Nobuyuki Kamata Shoji Enomoto 《In vitro cellular & developmental biology. Plant》1990,26(9):849-856
Summary A novel protein-free synthetic medium has been developed for the culture of human squamous cell carcinoma cells. This medium,
designated PF86-1, supports the serial subcultivation of six out of nine human squamous cell carcinoma cell lines in a protein-free,
chemically defined condition without the adapting culture from serum-containing conditions. These cell lines growing in PF86-1
exhibited nearly equal potency to grow in massive culture without noticeable changes in morphology but presented a significantly
decreased level of colony forming efficiency when compared with the cells cultured in serum-containing media, suggesting the
implication of some autocrine mechanism. Interestingly, this medium supported the growth of normal human squamous cells of
oral mucosa and skin for more than 2 mo. in the primary explant culture in spite of high levels of calcium ion concentration,
where the overgrowth of fibroblasts as contaminant was not observed. These results suggest that PF86-1 supports the growth
of cells derived from epidermal tissues selectively and provides the same defined condition for growth of malignant and nonmalignant
human squamous cells. It seems, therefore, that PF86-1 allows investigations on the products of squamous cell carcinoma cells
or on the differences of growth mechanisms between normal and neoplastic human squamous cells. 相似文献
9.
10.
A systemic oxidative stress of HIV (+) individuals has been recognized from a low glutathione level and a high level of inflammatory cytokines such as TNF. Previously, we demonstrated that the catalase enzyme activity in HIV (+) population is significantly altered depending on the cell types; the level was significantly high in red blood cells while the enzymes in white blood cells were remarkably low (Res Commun Subs Abuse 16: 161–176, 1995). In this study, we further characterized the difference in RBC catalase molecules between HIV (+) and control population. We have found that RBC from HIV (+) population, whether they were asymptomatic or symptomatic, contained a significantly elevated catalase protein accompanied by the enzyme activities, and that the majority of the elevated protein were acidic pl of the molecules with an identical subunit mass of approximately 60 KDa. These results suggest that catalase is induced prior to and/or during erythroid differentiation lineage in HIV (+) population as a somatic defense to respond and compensate for a systemic oxidative stress and for an anemic condition. (Mol Cell Biochem 165: 77–81, 1996) 相似文献