全文获取类型
收费全文 | 3590篇 |
免费 | 105篇 |
国内免费 | 189篇 |
专业分类
3884篇 |
出版年
2023年 | 19篇 |
2022年 | 25篇 |
2021年 | 45篇 |
2020年 | 56篇 |
2019年 | 56篇 |
2018年 | 56篇 |
2017年 | 48篇 |
2016年 | 70篇 |
2015年 | 82篇 |
2014年 | 106篇 |
2013年 | 137篇 |
2012年 | 73篇 |
2011年 | 135篇 |
2010年 | 98篇 |
2009年 | 160篇 |
2008年 | 171篇 |
2007年 | 161篇 |
2006年 | 175篇 |
2005年 | 163篇 |
2004年 | 156篇 |
2003年 | 145篇 |
2002年 | 112篇 |
2001年 | 107篇 |
2000年 | 87篇 |
1999年 | 111篇 |
1998年 | 109篇 |
1997年 | 95篇 |
1996年 | 73篇 |
1995年 | 94篇 |
1994年 | 74篇 |
1993年 | 96篇 |
1992年 | 80篇 |
1991年 | 72篇 |
1990年 | 65篇 |
1989年 | 71篇 |
1988年 | 53篇 |
1987年 | 52篇 |
1986年 | 53篇 |
1985年 | 41篇 |
1984年 | 58篇 |
1983年 | 41篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1975年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有3884条查询结果,搜索用时 8 毫秒
951.
Pseudomonas frederiksbergensis ERDD5:01 is a psychrotrophic bacteria isolated from the glacial stream flowing from East Rathong glacier in Sikkim Himalaya. The strain showed survivability at high altitude stress conditions like freezing, frequent freeze-thaw cycles, and UV-C radiations. The complete genome of 5,746,824 bp circular chromosome and a plasmid of 371,027 bp was sequenced to understand the genetic basis of its survival strategy. Multiple copies of cold-associated genes encoding cold active chaperons, general stress response, osmotic stress, oxidative stress, membrane/cell wall alteration, carbon storage/starvation and, DNA repair mechanisms supported its survivability at extreme cold and radiations corroborating with the bacterial physiological findings. The molecular cold adaptation analysis in comparison with the genome of 15 mesophilic Pseudomonas species revealed functional insight into the strategies of cold adaptation. The genomic data also revealed the presence of industrially important enzymes. 相似文献
952.
Cold desert regions harbor a unique habitat for a number of high-value medicinal plants (HMPs) and due to inaccessibility of medical facility, inhabitants of this region are highly dependent on medicinal plants. Over the years, with increasing demand for trade, extraction pressure on natural populations of these HMPs has grown substantially. This consequently has made such plants threatened in their natural habitats. However, quantification of threat intensity is lacking. For the first time, this study has attempted to identify and assess the ecological and threat status of HMPs from the cold desert area of Johar valley, West Himalaya, India. For ecological assessment, rigorous field surveys were conducted along the elevation gradient. The intensity of threat was evaluated by using rapid threat assessment (RTA) approach. A total of 22 threatened and high-value medicinal plants (THMPs) were identified from the region. Results of RTA placed Betula utilis and Nardostachys jatamanasi in the highest threat category. Roots/rhizomes were the frequently (55%) used plant parts, followed by inflorescence/fruit and stem/bark (18%) each. Overall, this study provides a clear picture of ecological and threat status of THMPs of the study area, which can effectively be utilized to develop a suitable conservation model for the region. 相似文献
953.
Non-reciprocal regulation of Rhodobacter capsulatus and Rhodobacter sphaeroides recA genes expression 总被引:1,自引:0,他引:1
Antonio R.Fernandez de Henestrosa Eusebi Rivera Jordi Barbé 《FEMS microbiology letters》1995,129(2-3):175-181
Abstract The Rhodobacter capsulatus recA gene has been isolated and sequenced. Its deduced amino acid sequence showed the closest identity with the Rhodobacter sphaeroides RecA protein (91% identity). However, the promoter regions of both R. capsulatus and R. sphaeroides recA genes are only 64% similar. An Escherichia coli -like LexA binding site was not present in the upstream region of the R. capsulatus recA gene. Nevertheless, the R. capsulatus recA gene is inducible by DNA damage in both hetero- and phototrophically growing conditions. The R. capsulatus recA gene is poorly induced when inserted into the chromosome of R. sphaeroides , indicating that the recA gene of both bacteria possess different control sequences despite their phylogenetically close relationship. 相似文献
954.
We have used the wild-type Agrobacterium rhizogenes strain A4 to induce roots on cucumber stem explants. Cultures of transformed roots obtained that were capable of hormone-autonomous growth could be grouped in three phenotypic classes. Of particular interest were extremely thick roots of a type not previously described. Characterization of the transferred DNA and of the expression of the corresponding genes allowed us to determine that the genes rolABC of the TL region of the Ri plasmid are sufficient to induce thin roots similar to those observed in other species, while the aux genes of the TR region are sufficient to induce thick roots. Among clones bearing the aux genes, there was a correlation between level of expression of aux2 and root phenotype. 相似文献
955.
The incidence of mortality from myocardial infarction over a 2-year period in Montreal is examined in relation to temperatures and snowfall. Mortality is seen to increase with deviations from seasonally determined thermally neutral conditions, although compared to observations of a parallel study in subtropical Brisbane, death rates are lower with similar falls in temperature. In Montreal, mortality is also seen to increase with snow during the previous day. During anomalous cold spells death frequencies decrease, a phenomenon interpreted as the behavioural thermoregulatory process of cold avoidance. 相似文献
956.
957.
Rika Sato Toko Miyagi Shinji Kamiya Toshifumi Sakaguchi Richard H. Thornhill Tadashi Matsunaga 《FEMS microbiology letters》1995,128(1):15-19
Abstract We established a synchronous culture of Magnetospirillum sp. AMB-1 by repeated cold treatment at 5 °C. This is the first reported synchronous culture of a magnetic bacterium. Cold treatment did not affect magnetic particle synthesis or cell morphology. Iron uptake was observed both before and during cell division. The amount of iron uptake was almost equivalent to that of magnetite formation. The proportion of magnetosensitive cells did not change during cell division. 相似文献
958.
A. Sgueglia A. Gentile A. Frattarelli G. Urbinati M. A. Germanà 《Plant biosystems》2019,153(5):720-724
The use of a small number of cultivars in agriculture can lead to a loss of agrobiodiversity. Since in vitro techniques are valuable tools for conserving plant biodiversity, an efficient micropropagation protocol for four Italian hazelnut cultivars, ‘Carrello’, ‘Ghirara’, ‘Minnulara’, and ‘Panottara’, was developed. The highest axillary bud survival was obtained after decontamination with 40?min 1% sodium hypochlorite followed by 40?min 0.1% sodium merthiolate in ‘Minnulara’ and ‘Ghirara’, while the 35?+?35?min treatment was the best for ‘Carrello’ and ‘Panottara’. Shoot multiplication was higher in ‘Minnulara’ and ‘Ghirara’ when 6.6?μM N6-benzyladenine was used, even if some hyperhydric shoots were observed, while metatopolin was more effective in the other two cultivars. In vitro rooting, performed in ‘Carrello’ and ‘Panottara’, was higher with 17.6 than with 9.8 µM indole-3-butyric. Following in vitro root induction with 17.6 µM indole-3-butyric acid for 7 days, rooting and acclimatisation in greenhouse exceeded 85% for all four cultivars. 相似文献
959.
960.
Transformation of plant cells via Agrobacterium 总被引:6,自引:0,他引:6
Paul J. J. Hooykaas 《Plant molecular biology》1989,13(3):327-336