全文获取类型
收费全文 | 7435篇 |
免费 | 743篇 |
国内免费 | 1篇 |
出版年
2022年 | 46篇 |
2021年 | 91篇 |
2020年 | 87篇 |
2019年 | 80篇 |
2018年 | 117篇 |
2017年 | 89篇 |
2016年 | 128篇 |
2015年 | 229篇 |
2014年 | 244篇 |
2013年 | 393篇 |
2012年 | 408篇 |
2011年 | 417篇 |
2010年 | 270篇 |
2009年 | 238篇 |
2008年 | 310篇 |
2007年 | 338篇 |
2006年 | 346篇 |
2005年 | 302篇 |
2004年 | 296篇 |
2003年 | 299篇 |
2002年 | 301篇 |
2001年 | 112篇 |
2000年 | 115篇 |
1999年 | 135篇 |
1998年 | 107篇 |
1997年 | 73篇 |
1996年 | 81篇 |
1995年 | 86篇 |
1994年 | 76篇 |
1993年 | 76篇 |
1992年 | 98篇 |
1991年 | 81篇 |
1990年 | 99篇 |
1989年 | 85篇 |
1988年 | 82篇 |
1987年 | 82篇 |
1986年 | 84篇 |
1985年 | 103篇 |
1984年 | 100篇 |
1983年 | 70篇 |
1982年 | 92篇 |
1981年 | 74篇 |
1980年 | 83篇 |
1979年 | 73篇 |
1978年 | 80篇 |
1977年 | 65篇 |
1976年 | 59篇 |
1975年 | 58篇 |
1974年 | 54篇 |
1973年 | 59篇 |
排序方式: 共有8179条查询结果,搜索用时 125 毫秒
91.
Ginette Pauly Abdelhamid Yani Louis Piovetti Colette Bernard-Dagan 《Phytochemistry》1983,22(4):957-959
The essential oils of the leaves of Cupressus dupreziana and Cupressus sempervirens were compared. The composition of the hydrocarbon fraction showed a great similarity between the two species. 相似文献
92.
Hydrolysis of sphingomyelin and 2-N-(hexade-canoyl)-amino-4-nitrophenyl-phosphorylcholine (HDA-PC), a synthetic analogue of sphingomyelin, by acid and Mg-dependent neutral sphingomyelinases was tested with a homogenate of normal human brain cortex. Results demonstrated quite different substrate specificities for these enzymes. Acid sphingomyelinase, which is neither activated by MgCl2 nor inhibited by EDTA, hydrolyzed both substrates (the hydrolysis ratio of HDA-PC to sphingomyelin is ?2). In contrast, Mg-dependent neutral sphingomyelinase, which is inhibited by EDTA and reactivated by MgCl2, hydrolyzed only sphingomyelin (the hydrolysis ratio of HDA-PC to sphingomyelin is ?0-0.05). This synthetic substrate seems to be useful for selective determination of acid sphingomyelinase and for avoiding interference of Mg-dependent neutral sphingomyelinase. 相似文献
93.
A M Estop J J Garver J Egozcue P Meera Khan P L Pearson 《Cytogenetics and cell genetics》1983,35(1):46-50
The chromosome localization and gene synteny of soluble malate dehydrogenase (MDH1), soluble isocitrate dehydrogenase (IDH1), mitochondrial superoxide dismutase (SOD2), phosphoglucomutase-3 (PGM3), mitochondrial malate dehydrogenase (MDH2), beta-glucuronidase (GUSB), nucleoside phosphorylase (NP), pyruvate kinase M2 (PKM2), hexosaminidase A (HEXA), inosine triphosphatase (ITPA), and N-acetyl-alpha-D-galactosaminidase (NAGA) were determined in the rhesus monkey using somatic cell hybrids. Comparison with the human and Pongidae syntenic groups shows that chromosome banding homologies do not always correlate with gene mapping data. 相似文献
94.
95.
Taxonomic Implications of Spore Fine Structure in Clostridium bifermentans 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Thirty-five strains of Clostridium bifermentans were, in most part, culturally homogeneous by conventional taxonomic criteria but were heterogeneous with respect to spore fine structure. Fourteen of the strains produced spores with appendages, distributed among four distinct ultrastructural types. No consistent correlation existed between spore type and other variable properties of these strains. It is proposed, therefore, that these spore appendage-type strains be considered as "varieties" of C. bifermentans and that they should not be designated as new species. 相似文献
96.
97.
98.
The isolation and properties of phenylalanine hydroxylase from human liver 总被引:4,自引:1,他引:3
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Phenylalanine hydroxylase was prepared from human foetal liver and purified 800-fold; it appeared to be essentially pure. The phenylalanine hydroxylase activity of the liver was confined to a single protein of mol.wt. approx. 108000, but omission of a preliminary filtration step resulted in partial conversion into a second enzymically active protein of mol.wt. approx. 250000. Human adult and full-term infant liver also contained a single phenylalanine hydroxylase with molecular weights and kinetic parameters the same as those of the foetal enzyme; foetal, newborn and adult phenylalanine hydroxylase are probably identical. The K(m) values for phenylalanine and cofactor were respectively one-quarter and twice those found for rat liver phenylalanine hydroxylase. As with the rat enzyme, human phenylalanine hydroxylase acted also on p-fluorophenylalanine, which was inhibitory at high concentrations, and p-chlorophenylalanine acted as an inhibitor competing with phenylalanine. Iron-chelating and copper-chelating agents inhibited human phenylalanine hydroxylase. Thiol-binding reagents inhibited the enzyme but, as with the rat enzyme, phenylalanine both stabilized the human enzyme and offered some protection against these inhibitors. It is hoped that isolation of the normal enzyme will further the study of phenylketonuria. 相似文献
99.
100.
Replacement of the 7-(R) hydroxyl group of lincomycin by a 7-chloro-substituent produced a compound with greater in vitro activity than the parent. Laboratory studies of this compound showed it to be highly active against all of the following strains of gram-positive organisms examined, including penicillinase- and nonpenicillinase-producing staphylococci, Diplococcus pneumoniae, Streptococcus viridans and Streptococcus pyogenes. The enterococci, as well as all the gram-negative organisms tested, with the exception of some strains of Haemophilus, were uniformly insensitive to this agent. The activity of 7-chlorolincomycin was not affected by serum or inoculum size. Resistance developed in a slow stepwise pattern. Peak levels of approximately 2 mug/ml were achieved in the serum of volunteers after ingestion of 150 mg either in the fasting state or after a meal. No untoward effects were noted. The antibiotic appears to be of potential value in the treatment of infections due to gram-positive organisms, with the exception of enterococcus. 相似文献