全文获取类型
收费全文 | 3971篇 |
免费 | 234篇 |
国内免费 | 1篇 |
出版年
2022年 | 18篇 |
2021年 | 33篇 |
2020年 | 21篇 |
2019年 | 36篇 |
2018年 | 55篇 |
2017年 | 54篇 |
2016年 | 84篇 |
2015年 | 139篇 |
2014年 | 132篇 |
2013年 | 280篇 |
2012年 | 240篇 |
2011年 | 238篇 |
2010年 | 157篇 |
2009年 | 140篇 |
2008年 | 211篇 |
2007年 | 221篇 |
2006年 | 228篇 |
2005年 | 217篇 |
2004年 | 158篇 |
2003年 | 195篇 |
2002年 | 159篇 |
2001年 | 94篇 |
2000年 | 107篇 |
1999年 | 87篇 |
1998年 | 57篇 |
1997年 | 46篇 |
1996年 | 48篇 |
1995年 | 54篇 |
1994年 | 31篇 |
1993年 | 27篇 |
1992年 | 48篇 |
1991年 | 52篇 |
1990年 | 45篇 |
1989年 | 42篇 |
1988年 | 38篇 |
1987年 | 30篇 |
1986年 | 31篇 |
1985年 | 36篇 |
1984年 | 27篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1976年 | 22篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 12篇 |
1968年 | 16篇 |
排序方式: 共有4206条查询结果,搜索用时 31 毫秒
71.
Ferredoxin-sulfite reductases (Fd-SiRs) [hydrogen-sulfide: ferredoxin oxidoreductase, EC 1.8.7.1] from leek leaves have been
purified to homogeneity. The enzymes (SiR 1, SiR 2 and SiR 3) were separated by Mono Q chromatography. The collective molecular
mass of the enzymes was estimated to be 65 kDa by gel filtration. In all three cases, subunit analysis by SDS-PAGE yielded
a single protein band corresponding to a molecular mass of 64 kDa, indicating that the enzymes each exist as a monomer. In
the oxidized forms, SiR 1, SiR 2 and SiR 3 all exhibited nearly identical absorption maxima at 279∼280, 389∼390, 588 and 714
nm, indicating that siroheme is involved in the catalysis of sulfite reduction. On enzymatic properties, SiR 1, SiR 2 and
SiR 3 could only react with the physiological electron donor, feriedoxin. The enzymes exhibited different heat stabilities.
The pH active curve obtained from SiR 2 was different from the others. Moreover, SiR 1 exhibited a lower Km value for ferredoxin
than SiR 2. Although the N-terminal sequence was the same, the results of some enzymatic properties, amino acid analysis,
and peptide mapping suggested the presence of the Fd-SiR isozymes in leek leaves. 相似文献
72.
73.
74.
Inactivation of bleomycin by an N-acetyltransferase in the bleomycin-producing strain Streptomyces verticillus 总被引:1,自引:0,他引:1
Masanori Sugiyama Takanori Kumagai Mitsuhiko Shionoya Eiichi Kimura Julian E. Davies 《FEMS microbiology letters》1994,121(1):81-85
Abstract Bleomycin-producing Streptomyces verticillus ATCC15003 possesses a bleomycin acetyltransferase which inactivates the drug in the presence of acetyl coenzyme A. The site of acylation in enzymically prepared acetylbleomycin A2 was determined by nuclear magnetic resonance analysis; the primary amino group of the β-aminoalanine moiety of bleomycin was acetylated. Acetylbleomycin A2 had no detectable antibacterial activity and did not induce in vitro DNA degradation. 相似文献
75.
Role of cellular antioxidants in metal-induced damage 总被引:23,自引:0,他引:23
M. Sugiyama 《Cell biology and toxicology》1994,10(1):1-22
76.
For phylogenetic analysis of the higher fungi, we sequenced the nuclear small subunit rRNA (18S rRNA) gene fromTaphrina populina, the type species of the genusTaphrina, andProtomyces lactucae-debilis. The molecular phylogeny inferred from these 2 sequences and 75 sequences from the DNA data bank divided the Ascomycota into three major lineages: the hemiascomycetes, the euascomycetes, and the archiascomycetes, newly described herein. The former two lineages are monophyletic, whereas the archiascomycetes, which originated first and are comprised ofTaphrina, Protomyces, Saitoella, Schizosaccharomyces, andPneumocystis, may not be monophyletic. Among the archiascomycetes, theTaphrina/Protomyces branch is monophyletic. Confirmation of the archiascomycetes as a monophyletic taxonomic class will require comparison of additional genetically defined characters.This work was supported in part by grants 05454030 from the Ministry of Education, Science, and Culture of Japan (to J. S.) and 4369 from the Japan Society for the Promotion of Science Fellowship Programs (to H. N.). 相似文献
77.
78.
Yasushi Sato Munetaka Sugiyama Ryszard J. Górecki Hiroo Fukuda Atsushi Komamine 《Planta》1993,189(4):584-589
In a culture system in which single cells isolated from the mesophyll of Zinnia elegans L. differentiate to tracheary elements (TEs), two inhibitors of phenylalanine ammonia-lyase (EC 4.3.1.5), L-α-aminooxy-β-phenylpropionic acid (AOPP) at 10 μM inhibited lignification without reducing the number of TEs formed. These inhibitors caused intracellular changes in peroxidase (EC 1.11.1.7) activities. The inhibitors increased the activity of peroxidases bound to the cell walls and especially the activity of peroxidase bound ionically to the cell walls. In contrast, the activity of extracellular peroxidase decreased. There were five isoenzymes, P1-P5, in the ionically bound peroxidase of cultured Zinnia cells. Among the isoenzymes, P4 and P5 appeared to be specific for TE differentation. Treatment with AOPP and AIP resulted in increases in the activities of P2, P4 and P5 isoenzymes, with the most prominent increase in P5 activity. The addition of lignin precursors, including coniferyl alcohol, to the AOPP-treated cells restored lignification, and suppressed the alteration of peroxidase isoenzyme patterns caused by AOPP. The relationship between the wall-bound peroxidases and lignification during TE differentiation is discussed in the light of these results. 相似文献
79.
Koichi Ohshima Masahiro Kikuchi Shinichi Kobari Yuichi Masuda Fuyuki Eguchi Nobuhiro Kimura 《Virchows Archiv. B, Cell pathology including molecular pathology》1993,63(1):197-198
Using the polymerase chain reaction (PCR) to examine the occurrence ofbcl-2/JH joining produced by t(14;18) chromosomal translocation, amplified DNA was detected in 2 of 18 lymph nodes showing reactive
lymphadenopathy. The PCR was repeated in these two lymphs nodes using the same DNA samples, but no amplification was detected
at the second attempt. Thus the amplified DNA was considered to be derived from one copy of joinedbcl-2/JH in one cell, or from a few copies in a few clonal cells with the same joinedbcl-2/JH. These results suggest that false joining ofbcl-2/JH at the t(14;l8) junction may occur in reactive lymph nodes. 相似文献