全文获取类型
收费全文 | 4566篇 |
免费 | 303篇 |
出版年
2022年 | 31篇 |
2021年 | 38篇 |
2020年 | 28篇 |
2019年 | 53篇 |
2018年 | 54篇 |
2017年 | 61篇 |
2016年 | 77篇 |
2015年 | 143篇 |
2014年 | 140篇 |
2013年 | 262篇 |
2012年 | 290篇 |
2011年 | 266篇 |
2010年 | 174篇 |
2009年 | 156篇 |
2008年 | 255篇 |
2007年 | 286篇 |
2006年 | 278篇 |
2005年 | 250篇 |
2004年 | 248篇 |
2003年 | 271篇 |
2002年 | 254篇 |
2001年 | 106篇 |
2000年 | 107篇 |
1999年 | 91篇 |
1998年 | 62篇 |
1997年 | 50篇 |
1996年 | 52篇 |
1995年 | 55篇 |
1994年 | 49篇 |
1993年 | 38篇 |
1992年 | 49篇 |
1991年 | 61篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 36篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 30篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 15篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1976年 | 21篇 |
1975年 | 18篇 |
1974年 | 16篇 |
1973年 | 15篇 |
1968年 | 16篇 |
排序方式: 共有4869条查询结果,搜索用时 15 毫秒
61.
62.
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
63.
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
64.
Ayaaki Ishizaki Tomoko Ueda Kenji Tanaka Peter F. Stanbury 《Biotechnology letters》1993,15(5):489-494
Summary The relative contributions of lactate inhibition and the generation of sterile (undividing) cells to the low xylose utilisation rate of Lactococcus lactis IO-1 was investigated. The lactate inhibition constant of xylose grown cells was shown to be 9.3 times more than that of glucose grown cells. However, the sterile cell production rate and LDH inactivation rate of the xylose cultures were at least 10 times less than the glucose cultures. Thus, it is suggested that the slower substrate consumption rate in xylose medium is caused mainly by the large inhibition constant for the end product. 相似文献
65.
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
66.
67.
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
68.
Species-specific distance calls (DCs) were recorded from Zebra finches (Taeniopygia guttata castanotis) obtained from three different breeding stocks: Japanese breeders that use Bengalese finches as fostering parents, and Japanese
and American breeders that let natural parents rear Zebra finches. These calls were analyzed for five acoustic parameters
that were shown to be sexually dimorphic in wild Zebra finches. Male Zebra finches had DCs that were variable among breeding
stocks and among individuals. Female DCs recorded from Bengalese-fostered birds were generally longer in duration and higher
in pitch than those recorded from Zebra-finch-reared birds, males and females in each breeding stock differed in at least
one acoustic parameter, but that parameter was unique in each of the breeding stocks. These results suggest that although
sexual dimorphism in Zebra finch DCs has gradually disappeared during the process of domestication, at least one acoustic
attribute which allows discrimination between the calls of the sexes has been preserved. 相似文献
69.
Tomoko Suzuki Chiyoko Shibata Akie Yamaguchi Kazuei Igarashi Hiroshi Kobayashi 《Molecular microbiology》1993,9(1):111-118
We isolated an Enterococcus hirae (formerly Streptococcus faecalis) mutant, designated MS117, in which ‘G’ at position 301 of the alpha-subunit gene of the F1F0 type of H+-ATPase was deleted. MS117 had low H+-ATPase activity, was deficient in the regulatory system of cytoplasmic pH, and was unable to grow at pH6.0. When the alpha-subunit gene of E. hirae H+-ATPase was ligated with the shuttle vector pHY300PLK at the downstream region of the tet gene of the vector, it was expressed without its own promoter in MS117, and the mutation of MS117 was complemented; the mutant harbouring the plasmid had the ability to maintain a neutral cytoplasm and grew at pH6.0. We next transformed MS117 with pHY300PLK containing the alpha-subunit gene of Bacillus megaterium F1F0-ATPase constructed in the same way. The transformant grew at pH 6.0, and the ATP hydrolysis activity was recovered. These results suggested that an active hybrid H+-ATPase containing the B. megaterium alpha subunit was produced, and that the hybrid enzyme regulated the enterococcal cytoplasmic pH, although the function of the B. megaterium enzyme did not include pH regulation. Thus, our present results support the previous proposal that the enterococcal cytoplasmic pH is regulated by the F1F0 type of H+-ATPase. 相似文献
70.