全文获取类型
收费全文 | 1537954篇 |
免费 | 143980篇 |
国内免费 | 1515篇 |
专业分类
1683449篇 |
出版年
2021年 | 18095篇 |
2019年 | 16215篇 |
2018年 | 18748篇 |
2017年 | 17570篇 |
2016年 | 28824篇 |
2015年 | 42840篇 |
2014年 | 50891篇 |
2013年 | 77061篇 |
2012年 | 42739篇 |
2011年 | 32953篇 |
2010年 | 45933篇 |
2009年 | 46526篇 |
2008年 | 30870篇 |
2007年 | 29519篇 |
2006年 | 33350篇 |
2005年 | 34410篇 |
2004年 | 33656篇 |
2003年 | 30970篇 |
2002年 | 29113篇 |
2001年 | 42811篇 |
2000年 | 40544篇 |
1999年 | 38254篇 |
1998年 | 26602篇 |
1997年 | 26480篇 |
1996年 | 25788篇 |
1995年 | 24031篇 |
1994年 | 23753篇 |
1993年 | 22921篇 |
1992年 | 33354篇 |
1991年 | 31716篇 |
1990年 | 30352篇 |
1989年 | 30831篇 |
1988年 | 28666篇 |
1987年 | 27366篇 |
1986年 | 25735篇 |
1985年 | 27516篇 |
1984年 | 26224篇 |
1983年 | 23181篇 |
1982年 | 22448篇 |
1981年 | 21372篇 |
1980年 | 20109篇 |
1979年 | 22897篇 |
1978年 | 20457篇 |
1977年 | 19608篇 |
1976年 | 18618篇 |
1975年 | 18574篇 |
1974年 | 19558篇 |
1973年 | 19900篇 |
1972年 | 17338篇 |
1971年 | 15926篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
P S Simavorian D A Gevorkian I L Saakian A B Iordanian 《Biulleten' eksperimental'no? biologii i meditsiny》1987,103(3):310-312
It has been experimentally and clinically established that the determination of leucine-aminotransferase activity in the blood serum and abdominal exudate may serve as a marker for the early determination of pancreonecrosis and edematous (serous) pancreatitis. 相似文献
972.
Renal transport and metabolism of nicotinic acid 总被引:1,自引:0,他引:1
973.
974.
Leslie A. Holladay Phillip Wilder 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,629(1):156-167
The effect of cationic, anionic and nonionic detergents on the EPR spectrum of spin-labeled somatostatin has been studied. At detergent concentrations well above the critical micelle concentration, nonionic detergents do not alter the EPR spectrum. Sodium dodecyl sulfate markedly alters both the line height ratio and the hyperfine splitting constant, whilst dodecyltrimethylammonium bromide alters only slightly the hyperfine splitting constant and line height ratio. The somatostatin-sodium dodecyl sulfate complex appeared monodisperse by sedimentation equilibrium with about 17 g bound detergent per g peptide. Circular dichroic and difference spectra of the dodecyl sulfate-somatostatin complex show that the tryptophanyl residue is buried in a nonpolar environment and that the secondary and tertiary structure of the peptide is markedly altered. Sedimentation equilibrium studies suggest that two types of dodecyltrimethylammonium-somatostatin complex exist. One type resembles the dodecyl sulfate-peptide complex, whilst the other appears to include several peptide units with only about one gram bound detergent per gram peptide. 相似文献
975.
976.
Following treatment of hen erythrocyte nuclei with dimethyl 3,3'-dithiobispropionimidate, dimers between histones H1a, H1b, and H5 were extracted with 5% perchloric acid. They resolved electrophoretically into four sub-bands and these were identified by non-reducing/reducing gel electrophoresis. The H5-H5 homodimer species was purified by gel electrophoresis and was treated sequentially with BrCN and dithiothreitol. The pattern of resulting fragments indicates that cross-links were mainly formed between the COOH-terminal portions and at a significantly lower frequency between the COOH-terminal and the NH2-terminal portions. 相似文献
977.
A possible virus cryptic in carnation 总被引:1,自引:0,他引:1
Small isometric virus-like particles were found in low concentration in apparently healthy carnations of the Mediterranean, miniature and Chinese type but not in eleven Sim cultivars tested. Most carnations containing these particles were from Italy but some were from France and the USA. The particles were not transmitted by grafting or by mechanical inoculation but were seed-transmitted to a large proportion of seedlings. Antisera to partially purified particles were obtained. The particles did not react with antisera to twenty-eight isometric plant viruses or virus-like particles but were serologically related to similar particles found in carnations in England, Holland and Israel. When negatively stained, the particles were isometric with a diameter of about 29 nm and a rounded rather than angular profile, but without clear substructure; some particles were penetrated by the stain. The particles remained intact in neutral sodium phosphotungstate. After isopycnic centrifugation in CsCl solution, preparations of particles formed a main band of mean density 1.377 g/ml and other fainter bands that varied in intensity and position in different preparations. In thin sections of carnations, no virus-like particles or cytological abnormalities were observed. 相似文献
978.
The dopaminergic agonist apomorphine produces dose-related hypothermia in naive rats as does L-DOPA in carbidopa-pretreated rats. The hypothermic responses to these two dopaminergic drugs were significantly more pronounced and prolonged in the spontaneously hypertensive rat than in normotensive Wistar control rats. The greater sensitivity of the SHR to these drugs was reflected as a leftward shift of the dose-response curves for apomorphine- and L-DOPA-induced hypothermias. 相似文献
979.
980.
Differences in chemical composition of plants grown at constant relative growth rates with stable mineral nutrition 总被引:11,自引:0,他引:11
R. H. Waring A. J. S. McDonald S. Larsson T. Ericsson A. Wiren E. Arwidsson A. Ericsson T. Lohammar 《Oecologia》1985,66(2):157-160
Summary Leaf chemistry of a willow clone (Salix aquatica Smith) differed significantly when grown at constant relative growth rates depending upon the relative availability of nutrients and light. Concentration of amino acids and nitrate were high in plants grown with a relative surplus of nutrients. Concentrations of starch, tannin, and lignin, on the other hand, were high in plants grown with a relative surplus of carbon. Photosynthetic rates, expressed per unit leaf area, were similar when plants were grown under high light conditions, regardless of nutrient availability. Dark respiration was much higher in plants supplied with abundant nutrients than in those with a more limited supply, reflecting differences in nitrogen concentration of the tissue. The experimental approach allows plants to be grown to a standard size with differing, but highly uniform chemistry. Plants grown in such a manner may provide good experimental material to evaluate interactions between herbivores or pathogens and their hosts. 相似文献