全文获取类型
收费全文 | 7003篇 |
免费 | 317篇 |
国内免费 | 1篇 |
出版年
2023年 | 35篇 |
2022年 | 27篇 |
2021年 | 75篇 |
2020年 | 89篇 |
2019年 | 115篇 |
2018年 | 270篇 |
2017年 | 240篇 |
2016年 | 315篇 |
2015年 | 218篇 |
2014年 | 327篇 |
2013年 | 502篇 |
2012年 | 388篇 |
2011年 | 537篇 |
2010年 | 309篇 |
2009年 | 205篇 |
2008年 | 373篇 |
2007年 | 423篇 |
2006年 | 457篇 |
2005年 | 387篇 |
2004年 | 327篇 |
2003年 | 368篇 |
2002年 | 287篇 |
2001年 | 185篇 |
2000年 | 159篇 |
1999年 | 108篇 |
1998年 | 61篇 |
1997年 | 24篇 |
1996年 | 13篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1953年 | 18篇 |
1952年 | 40篇 |
1888年 | 14篇 |
1887年 | 14篇 |
1883年 | 9篇 |
排序方式: 共有7321条查询结果,搜索用时 15 毫秒
41.
42.
43.
Some opiates with morphinan- and benzomorphan-structures possess affinities for neuroleptic receptors as revealed by their abilities to compete with 3H-spiroperidol for common binding sites in rat striatum (IC50 in the range between 10?6 and 10?5M). The binding of these opiates to neuroleptic receptors appears to be of pharmacological significance, since studies in mice revealed a small but significant displacement of spiroperidol by high doses of the opiate antagonist levallorphan from specific binding sites in the striatum. In addition, there exists some correlation between the ability of opiates to bind to neuroleptic receptor sites and their potency to evoke “bizarre behavior” in rats . In contrast, a wide variety of other opiates having morphine-, morphinone- or oripavine-structure showed no affinity for neuroleptic binding sites (IC50 greater than 10?4 M). Of the opioid peptides (methionine-enkephalin, leucine-enkephalin and β-endorphin) none has an affinity for neuroleptic binding sites. A variety of other peptides were also investigated but did not interfere with spiroperidol binding. Only ACTH showed a moderate affinity for neuroleptic binding sites. 相似文献
44.
The activities of adenosylhomocysteinase (EC 3.3.1.1) and adenosine nucleosidase (EC 3.2.2.7) were assayed in extracts from yellow lupin (Lupinus luteus L.) cotyledons at different stages of seed formation and seedling development. Adenosylhomocysteinase activity was demonstrated in all the cotyledon extracts examined. Its lowest level was found in the dry seeds and the highest, in 4-day-old seedling cotyledons. Extracts from the cotyledons of maturating seeds, dry seeds, and seedlings up to the second day of growth exhibited no adenosine nucleosidase activity. Adenosine nucleosidase activity appeared in the cotyledons of 2-day-old seedlings and its highest level was reached in 4-to 5-day-old seedlings. There is no inhibitor of adenosine nucleosidase in the maturating and dry yellow lupin seeds. No activator of a possible zymogen form of adenosine nucleosidase from maturating or dry seeds occurs in the growing seedlings. 相似文献
45.
The effect of oleate, palmitate, and octanoate on glucose formation was studied with lactate or pyruvate as substrate. Octanoate was much more quickly oxidized and utilized for ketone body production than were oleate and palmitate. Among fatty acids studied, only octanoate resulted in a marked increase of the 3-hydroxybutyrate/acetoacetate (3-) ratio. Each of the fatty acids studied stimulated glucose synthesis from pyruvate. The enhancement of gluconeogenesis by long-chain fatty acids was abolished after the addition of ammonia. As concluded from the “crossover” plot, the stimulatory effect of fatty acids was due to: (i) a stimulation of pyruvate carboxylation, (ii) a provision of reducing equivalents for glyceraldehyde phosphate dehydrogenase, and (iii) an acceleration of flux through hexose diphosphatase. Moreover, palmitate and oleate resulted in an increased generation of mitochondrial phosphpenolpyruvate, while in the presence of octanoate, the activity of mitochondrial phosphoenolpyruvate carboxykinase was diminished. When lactate was used as the glucose precursor, palmitate and oleate increased glucose production by about 50% but did not affect the contribution of mitochondrial phosphoenolpyruvate carboxykinase to gluconeogenesis. In contrast, in spite of the stimulation of both pyruvate carboxylase and hexose diphosphatase, as judged from the crossover plot, the addition of octanoate resulted in a marked inhibition of both glucose formation and mitochondrial generation of phosphoenolpyruvate. The inhibitory effect of octanoate was reversed by ammonia. Results indicate that fatty acids and ammonia are potent regulatory factors of both the rate of glucose formation and the contribution of mitochondrial phosphoenolpyruvate carboxykinase to gluconeogenesis in hepatocytes of the fasted rabbit. 相似文献
46.
47.
Extrachromosomal DNA in Thiobacillus A2 总被引:1,自引:0,他引:1
48.
The sequence of DNA replication was studied within the inactive X chromosome in human lymphocytes, by means of the FPG method. Several variants of the replication sequence were found. The number of variants in the cells of a single donor exceeded 2 in each of the 4 normal individuals studied. The phenomenon is discussed with respect to the regulation of DNA synthesis and to the cell differentiation process. 相似文献
49.
Przemysław Szafrański 《Journal of molecular evolution》1992,34(5):465-467
Summary The existence of internal sequence homologies between the N-terminal halves of the gram-negative bacterial major sigma factors and their C-terminal halves, which correspond to minor factors, is reported. In the case of Escherichia-Salmonella sigma-70, an apparent homology was even found between the C-terminal helix-turn-helix DNA-binding motif and the corresponding region of the peptide N half, which, however, is not directly engaged in promoter recognition. It is proposed that major sigma factors may have originated by duplication and fusion of a DNA unit related to the ancestral gene for the whole sigma family. Coevolution of major sigma structures and complex promoters is suggested. 相似文献
50.
J Bal D Maciejko E Bu?awa T Mazurczak 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1992,47(9-10):215-218
The results of DNA analysis with the aid of specific molecular probes are discussed. DNA analysis involved 22 families of a high risk of cystic fibrosis. A significance of the obtained results in genetic counselling is also discussed. DNA analysis enabled detection or exclusion of cystic fibrosis gene carrier state in patient's relatives. DNA analysis proved fully informative in case of 17 families being a base to offer these families prenatal diagnosis of the disease in the I trimester of pregnancy, if such a family plans conception, and to accept this diagnostic technique. 相似文献