全文获取类型
收费全文 | 40015篇 |
免费 | 1782篇 |
国内免费 | 2239篇 |
出版年
2024年 | 40篇 |
2023年 | 376篇 |
2022年 | 524篇 |
2021年 | 747篇 |
2020年 | 772篇 |
2019年 | 957篇 |
2018年 | 862篇 |
2017年 | 835篇 |
2016年 | 949篇 |
2015年 | 1183篇 |
2014年 | 1972篇 |
2013年 | 2882篇 |
2012年 | 1547篇 |
2011年 | 1605篇 |
2010年 | 1346篇 |
2009年 | 1589篇 |
2008年 | 1671篇 |
2007年 | 1706篇 |
2006年 | 1619篇 |
2005年 | 1657篇 |
2004年 | 1706篇 |
2003年 | 1572篇 |
2002年 | 1352篇 |
2001年 | 1112篇 |
2000年 | 1012篇 |
1999年 | 1029篇 |
1998年 | 946篇 |
1997年 | 835篇 |
1996年 | 842篇 |
1995年 | 927篇 |
1994年 | 894篇 |
1993年 | 751篇 |
1992年 | 742篇 |
1991年 | 585篇 |
1990年 | 565篇 |
1989年 | 460篇 |
1988年 | 507篇 |
1987年 | 404篇 |
1986年 | 364篇 |
1985年 | 447篇 |
1984年 | 489篇 |
1983年 | 284篇 |
1982年 | 379篇 |
1981年 | 212篇 |
1980年 | 195篇 |
1979年 | 169篇 |
1978年 | 117篇 |
1977年 | 80篇 |
1976年 | 81篇 |
1974年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
161.
Hiroshi Iwasaki Toshikazu Shiba Atsuo Nakata Hideo Shinagawa 《Molecular & general genetics : MGG》1989,219(1-2):328-331
Summary The ruv operon of Escherichia coli consists of two genes, orfl1 and ruv, which encode 22 and 37 kilodalton proteins, respectively, and are regulated by the SOS system. Although the distal gene, ruv, is known to be involved in DNA repair, the function of orf1 has not been studied. To examine whether orf1 is also involved in DNA repair, we constructed a strain with a deletion of the entire ruv operon. The strain was sensitive to UV even after introduction of low copy number plasmids carrying either orf1 or ruv, but UV resistance was restored by introduction of a plasmid carrying both orfl and ruv. These results suggest that orf1 as well as ruv is involved in DNA repair. Therefore, orf1 and ruv should be renamed ruvA and ruvB, respectively. 相似文献
162.
163.
Summary Comparison of the 5′ flanking regions of three α-amylase genes from chromosome 6B of hexaploid wheat by heteroduplex and sequence
analysis revealed the presence of a 1.6 kb stem-loop insertion sequence (WIS1) in one of them. Polymorphism among hexaploid wheat varieties suggests the relatively recent insertion/excision of this sequence
from its present position. The complete sequence of the stem-loop insertion shows that it has many of the features found in
transposable elements, including target site duplication and terminal inverted repeats. One unusual feature is a tandem array
of direct repeats comprising a wheat “minisatellite” sequence. Both the insertion sequence and the minisatellite are found
at multiple locations in the wheat genome, but the functional significance of their association in WIS1 is unknown. The minisatellite arrays share a common core structure, and long arrays are polymorphic between different hexaploid
varieties. 相似文献
164.
165.
166.
Hiroshi Taniguchi Takuya Tokida Hiroshi Fujita Hiraku Itikawa 《Molecular & general genetics : MGG》1989,217(2-3):317-323
Summary IndnaK7(Ts) mutant cells, scission of DNA strands occurred after temperature shift up. When cells at 30°C were labeled with [3H]-thymidine and then shifted to 46° or 49°C for 20 min, the profiles of sedimentation of thier cellular DNA in an alkaline
sucrose gradient revealed a decrease in the size of DNA to a quarter of that at 30°C in the mutant, but not in wild-type cells.
The level of manganese-containing superoxide dismutase (MnSOD) in the mutant was about twice that in wild-type cells, even
at the permissive temperature, implying increased production of superoxide radical anion, which may cleave DNA strands directly
or indirectly in the mutant. Moderate increase in the MnSOD level on temperature shift up was observed in both strains. These
results indicated that some components of the DnaK protein participate in protection of cellular membrane functions from thermal
damage resulting from elevated production of the superoxide anion radical. 相似文献
167.
Jay C. D. Hinton Julie M. Sidebotham Lizbeth J. Hyman Michel C. M. Pérombelon George P. C. Salmond 《Molecular & general genetics : MGG》1989,217(1):141-148
Summary The blackleg pathogen Erwinia carotovora subsp. atroseptica (Eca) causes an economically important disease of potatoes. We selected a genetically amenable Eca strain for the genetic analysis of virulence. Tn5 mutagenesis was used to generate nine mutants which exhibited reduced virulence (Rvi-) of strain SCRI1043. Following physiological characterisation, mutants were divided into three classes: (1) auxotrophs; (2) extracellular enzyme mutants; and (3) a growth rate mutant. The isolation of these Rvi- mutants has allowed us to consider some factors that affect Eca virulence. 相似文献
168.
Summary M1 is a virulent bacteriophage of Methanobacterium thermoautotrophicum strain Marburg. Restriction enzyme analysis of the linear, 30.4 kb phage DNA led to a circular map of the 27.1 kb M1 genome. M1 is thus circularly permuted and exhibits terminal redundancy of approximately 3 kb. Packaging of M1 DNA from a concatemeric precursor initiates at the pac site which was identified at coordinate 4.6 kb on the circular genome map. It proceeds clockwise for at least five packaging rounds. Headful packaging was also shown for M2, a phage variant with a 0.7 kb deletion at coordinate 23.25 on the map. 相似文献
169.
Toru Kimura Tsuneaki Asai Mutsuo Imai Mituru Takanami 《Molecular & general genetics : MGG》1989,219(1-2):69-74
Summary Two-dimensional gel electrophoresis, at high and low temperatures, and gel mobilities of circularly permuted DNA segments showed a large bending locus about 50 bp downstream from the right border of the 245 by oriC box, a minimal essential region of autonomous replication on the Escherichia coli chromosome. Bending was strongly enhanced by Dam methylation. In DNA from a Dam– strain, the mobility anomaly arising from altered conformation was much reduced, but was raised to the original level by methylation in vivo or in vitro. Enhancement of the mobility anomaly was also observed by hybrid formation of the Dam– strand with the Dam+ strand. Near the bending center, GATC, the target of Dam methylase, occurs seven times arranged essentially on the same face of the helix with 10.5 by per turn. We concluded that small bends at each Dam site added up to the large bending detectable by gel electrophoresis. 相似文献
170.
Summary The transfer of the Agrobacterium T-DNA to plant cells involves the induction of the Ti plasmid virulence genes. This induction results in the generation of linear single-stranded (ss) copies of the T-DNA inside Agrobacterium and such molecules might be directly transferred to the plant cell. A central requirement of this ss transfer model is that the plant cell must generate a second strand and integrate the resulting double-stranded (ds) molecule into its genome. Here we report that incubating plant protoplasts with ss or ds DNA under conditions favouring DNA uptake results in transformation. The frequencies of transformation are similar and analysis of ss transformants suggests that the introduced DNA becomes double stranded and integrated. Analysis of transient expression from introduced ss DNA suggests that generation of the second strand is rapid and extrachromosomal. 相似文献