全文获取类型
收费全文 | 443171篇 |
免费 | 51453篇 |
国内免费 | 719篇 |
出版年
2018年 | 4165篇 |
2017年 | 4008篇 |
2016年 | 5718篇 |
2015年 | 8255篇 |
2014年 | 9604篇 |
2013年 | 12944篇 |
2012年 | 15337篇 |
2011年 | 15794篇 |
2010年 | 10458篇 |
2009年 | 9491篇 |
2008年 | 13845篇 |
2007年 | 14292篇 |
2006年 | 13428篇 |
2005年 | 12804篇 |
2004年 | 12864篇 |
2003年 | 12006篇 |
2002年 | 11653篇 |
2001年 | 18893篇 |
2000年 | 18832篇 |
1999年 | 14947篇 |
1998年 | 5418篇 |
1997年 | 5410篇 |
1996年 | 5134篇 |
1995年 | 5140篇 |
1994年 | 4846篇 |
1993年 | 4849篇 |
1992年 | 12472篇 |
1991年 | 12434篇 |
1990年 | 12186篇 |
1989年 | 11662篇 |
1988年 | 10825篇 |
1987年 | 10200篇 |
1986年 | 9727篇 |
1985年 | 9498篇 |
1984年 | 7875篇 |
1983年 | 6822篇 |
1982年 | 5135篇 |
1981年 | 4622篇 |
1980年 | 4309篇 |
1979年 | 7344篇 |
1978年 | 5961篇 |
1977年 | 5288篇 |
1976年 | 4958篇 |
1975年 | 5768篇 |
1974年 | 6300篇 |
1973年 | 6114篇 |
1972年 | 5457篇 |
1971年 | 5073篇 |
1970年 | 4273篇 |
1969年 | 4200篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
The influence of diet on the excretion of catecholamines, some of their metabolites, and pHPG, an octopamine metabolite, was examined. Two groups of rats were fed either a cereal-containing standard laboratory Purina rat chow or a cereal-free casein diet. Use of the standard chow resulted in significant increases in the urinary values for total MHPG, pHPG, DHPE, MHPE, and free and total DOPAC by the seventh day in comparison to the casein diet. No changes were noted in the excretion of free and total NE, DA, and HVA. The data indicate that it is necessary to place the animals on the casein diet several days before determining the excretion of the aforementioned metabolites. 相似文献
993.
994.
David W. Thomas Amabile K. Matida Célio L. Silva Thuioshi Ioneda 《Chemistry and physics of lipids》1979,23(3):267-282
The purification procedure of 6,6′-diesters of trehalose from Corynebacterium diphtheriae was modified and the isolated substance was analysed by mass spectrometry as its permethylated derivative. The fatty acid moiety released from the glycolipid after alkaline hydrolysis was studied by mass spectral analysis of the O-methylated and O-acetylated methyl ester derivatives. By argentation thin-layer chromatography, three species of O-acetylated methyl esters were recognized, corresponding to saturated, mono-unsaturated and di-unsaturated α-branched-β-hydroxylated fatty acids. The double bond was located by ozonolysis of the O-acetylated methyl ester derivatives, by gas chromatography of the reaction product and mass spectrometry of the effluent from the gas chromatograph. The main components of each species of α-branched-β-hydroxylated fatty acids found in the gly colipid fraction of C. diphtheriae were 2-tetradecyl-3-hydroxyoctadecanoic acid (C32H64O3, corynomycolic acid), 2-tetradecyl-3-hydroxy-11-octadecenoic acid (C32H62O3, corynomycolenic acid), 2-tetradec-7′-enyl-3-hydroxy octadecanoic acid (C32H62O3) and 2-tetradec-7′-enyl-3-hydroxy-11-octadecenoic acid (C32H60O3, corynomycoldienic acid). The glycolipid fraction from C. diphtheriae is obviously a complex mixture of 6,6′-diesters of trehalose. 相似文献
995.
The biological and immunological activities of Staphylococcal enterotoxin B are stable in pH 2.0 approximately 11.0, and also resistant to proteolytic enzyme (trypsin, pepsin) digestion for 3 approximate 4 hours. Therefore, the toxin could be purified with trypsin digest and then absorbed on kaolin and Kieselgel, followed by eluting the different pH buffer solutions. Further purifications was chromatographied on CM-Sephadex column. 相似文献
996.
997.
998.
Although the use of hypochlorite to disinfect seeds is widespread, the effects on tissues isolated from them have been largely ignored. Disinfection of barley ( Hordeum vulgare L. cv. Himalaya) half-seeds with hypochlorite solutions of ≥1.0% (w/v) available chlorine caused the pericarp to separate from the underlying tissues. Aleurone layers isolated from these grains had lower rates of oxygen consumption and released significantly less protein, PO4 3− Mg2+ , K+ and amylase (EC 3.2.1.1) into the medium in response to gibberellic acid (GA3 ) than layers isolated from grains disinfected with a 0.1% hypochlorite solution. Disinfection with 1.0% hypochlorite also quantitatively altered the spectrum of proteins released into the incubation medium by the layers in response to GA3 . 相似文献
999.
A study was made of the chronic effect of pesticides, within a wide range of doses, combined with whole-body gamma-irradiation, on the content of carbohydrate-containing proteins of rat liver. The extent to which disturbances in the carbohydrate-containing protein metabolism were manifest was shown to depend upon dose and time of action of the damaging factors. As determined by certain parameters, the combined effect of pesticides and gamma-radiation at the biochemical level was additive, and it was more than additive as estimated by a number of other tests. 相似文献
1000.
Isoproterenol (ISO) was injected in 5 mg/kg i.p. doses to rats, daily for two weeks. We evaluated the developed myocardial hypoxia and necrosis quantitatively by histological methods. To follow the time course of cardioprotection prostacyclin or 7-oxo-PGI2 were injected daily, i.p. 5, 30 min and 1, 2, 3, 4 hours before or after the ISO to groups of ten rats, respectively. Cardioprotection was defined as the reduction of necrotized areas and was expressed as percentage change compared to the control (saline treated) group. 1 microgram/kg PGI2 and 50 micrograms/kg 7-oxo-PGI2+ showed nearly equipotent cardioprotection (37.3-7.9% and 38.3-6.8%, respectively). The peak effect of both compounds appeared when injected prior to ISO in the 120. min but the action of 7-oxo-PGI2 was more prolonged. The different doses of prostacyclin analogs given after the ISO injection were ineffective with the exception of 50 micrograms/kg 7-oxo-PGI2 (29.75 +/- 5.2%). 相似文献