全文获取类型
收费全文 | 3690篇 |
免费 | 492篇 |
国内免费 | 1767篇 |
出版年
2024年 | 65篇 |
2023年 | 204篇 |
2022年 | 219篇 |
2021年 | 273篇 |
2020年 | 269篇 |
2019年 | 269篇 |
2018年 | 230篇 |
2017年 | 238篇 |
2016年 | 242篇 |
2015年 | 231篇 |
2014年 | 266篇 |
2013年 | 308篇 |
2012年 | 255篇 |
2011年 | 270篇 |
2010年 | 193篇 |
2009年 | 244篇 |
2008年 | 248篇 |
2007年 | 280篇 |
2006年 | 238篇 |
2005年 | 170篇 |
2004年 | 169篇 |
2003年 | 147篇 |
2002年 | 136篇 |
2001年 | 94篇 |
2000年 | 78篇 |
1999年 | 77篇 |
1998年 | 63篇 |
1997年 | 51篇 |
1996年 | 47篇 |
1995年 | 44篇 |
1994年 | 38篇 |
1993年 | 43篇 |
1992年 | 36篇 |
1991年 | 28篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1950年 | 1篇 |
排序方式: 共有5949条查询结果,搜索用时 15 毫秒
51.
52.
原生质体电融合酵母多倍体生理特性的研究 总被引:5,自引:0,他引:5
对原生质体电融合技术获得的11株酵母多倍体融合株,进行了一系列生理特性的分析比较.结果发现,在电融合过程中,融合株的细胞体积及DNA含量并不随着核倍性呈线性递增.而是有其特殊的变化规律。当糖化酵母sta1、sta2和sta3在细胞核中各自纯合时,明显表现出表达的剂量效应。其中sta1、sta2纯合的融合株.在YEPS培养中,GA分泌可被淀粉大量诱导,表现出一定的二次生长特性。从分析结果推测,在亲株5301-14D及HU-TY—1A中可能有对GA分泌不利的因素。 相似文献
53.
本文对观赏植物异色芋(ColocasiaheterochromaH.LietZ.X.Wei)在昆明栽培环境下的生物学特性进行总结,为商品化栽培异色芋提供了理论依据,为其分类也提供了一定的有益补充。结果表明:一年生植株不开花,根茎也不产生分枝;二年生植株开花率为73.6%,根茎平均分枝3.6条。异色芋3月上旬开始萌动,7月中旬抽花梗,8月上旬开花,11月份地上部分枯萎,因此在昆明异色芋生育期约260d。 相似文献
54.
Z. I. Bhatti K. Furukawa M. Fujita 《World journal of microbiology & biotechnology》1995,11(6):631-637
A laboratory upflow anaerobic sludge blanket reactor, seeded with fine, suspended, bacterial floc with 1.76 g volatile suspended solids/l, was used to treat synthetic methanolic waste. After 180 days of continuous peration, granular sludge with discrete granules of 1 to 2 mm diam. was formed, with 52 g volatile suspended solids/l. Granules were brown, relatively soft and had a settling velocity of 1.61 cm/s. Extracellular polymeric matter extracted from the granular sludge had high carbohydrate content but low nucleic acid content. The ash of the granular sludge contained Na+, K+ and Mg2+ up to 15.0, 11.7 and 3.75 mg/g, respectively. Scanning and transmission electron microscopy revealed that the granular sludge was dominated by methanogens resembling Methanosarcina.The authors are with the Department of Environmental Engineering, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565, Japan 相似文献
55.
本文报道了虎嘉鱼的生境特点及保护对策,主要是加强宣传教育,严禁滥捕,深入研究,开展人工养殖试验和建立自然保护区等措施,确保物种生存和繁衍。 相似文献
56.
Six mature Muturu Bulls were elecroejaculated once a week for nine weeks to study their semen quality and ejaculate characteristics. The semen volume was 1.8 ml +/- 0.1, the sperm concentration 2.16 x 10(8)/ml +/- 0.29, and the progressive sperm motility 36.2% +/- 2.6. Morphologically normal sperm averaged 70.0% +/- 3.1, primary abnormalities 13.4% +/- 1.0 and secondary abnormalities 15.1% +/- 2.3. Except in one bull, no measurable levels of fructose were observed. The contents of major cations and chloride ions in whole semen and seminal plasma were also determined. 相似文献
57.
Sergio Casella Robert R. Gault Kenneth C. Reynolds John R. Dyson John Brockwell 《FEMS microbiology letters》1984,22(1):37-45
Abstract Symbiotic experiments in glasshouse, controlled environment cabinet, and field were conducted with four lines of sulla ( Hedysarum coronarium ) and 15 strains of Rhizobium spp. This plant is highly Rhizobium -specific and appropriate strains are most unlikely to occur naturally in Australia. Under several sets of experimental conditions, H. coronarium nodulated abundantly and effectively with homologous rhizobia introduced from Spain and Italy. The optimum temperature for nitrogen fixation was relatively low (approx. 21°C) but significant interactions between line of host, strain of rhizobia, and growth temperature were frequent. The rhizobia were persistent in soil. 相似文献
58.
The suppressible eye color mutant purple (pr) of Drosophila melanogaster is known to be unable to synthesize a wild-type complement of pteridine eye pigments. This study measures the reduced levels of drosopterins, sepiapterin, and an unidentified presumed pteridine in pr and pr
bw. Pteridine analyses in double mutants combining pr with one of three other eye color mutants sepia, Henna-recessive3, and prune2, suggest that the metabolic block in pr occurs prior to sepiapterin biosynthesis. Measurements of GTP and GTP cyclohydrolase in pr showed wild-type levels and indicate the metabolic block in pr to be at one of the steps converting dihydroneopterin triphosphate to sepiapterin. Quantitation of pteridines in suppressed purple [su(s)
2; pr and pr; su(pr)
e3] shows restoration of pteridines to wild-type or nearly wild-type levels.T. G. W. is a predoctoral trainee supported by Grant GM 1974 from the National Institute of General Medical Sciences, National Institutes of Health.The Oak Ridge National Laboratory is operated by Union Carbide Corporation for the U.S. Energy Research and Development Administration. 相似文献
59.
Hubert Felle 《生物化学与生物物理学报:生物膜》1980,602(1):181-195
Green thallus cells of the aquatic liverwort, Riccia fluitans, are rapidly depolarized in the presence of 1–20 μM NH4Cl and 5–100 μM CH3NH3Cl, respectively. Simultaneously, the membrane conductance is increased from 0.41 to 1.2 S · m?2. Uptake of [14C]methylamine is stimulated by increasing [K+]o and inhibited by increasing [Na+]o or [H+]o, is highly voltage sensitive, and saturates at low amine concentrations.Double-reciprocal plots of (a) maximal membrane depolarization and (b) methylamine uptake vs. external amine concentration give apparent Km values of 2 ± 1 μM ammonia and 25–50 μM methylamine; Km values for changes in conductance and membrane current are greater and voltage dependent. Whereas the amine transport into the cell is strongly inhibited by CN?, the amine efflux is stimulated.The current-voltage characteristics of the ammonia transport are represented by a sigmoid curve with an equilibrium potential of ?60 mV, and this is understood as a typical carrier curve with a saturation current of about 70 mA · m?2. It is further concluded that the evidently carrier-mediated transport is competitive for the two amines tested, and that ammonia and methylamine are transported in the protonated form as NH4+ and CH3NH3+ into the cytoplasm. 相似文献
60.
The proportions of carotenoids responsible for column coloration were determined for a population of the sea anemone Bunodosoma granulifera from Grand Cayman using TLC. This population exhibited a very low degree of polymorphism for these proportions, compared to previously sampled populations from Puerto Rico and Curaçao. In addition to the carotenoid pigment system a second system possessing pigments similar to bilins was found for the first time in this genus. This population was also assayed electrophoretically for enzymes encoded by 12 loci. Analysis of these data suggested that the reduced polymorphism for column color may be the result of selection. Although the proportions of carotenoids varied little, the amount of carotenoid per unit of epidermal tissue varied almost four-fold from 0.05 to 0.19 μg/mg dry wt. 相似文献