全文获取类型
收费全文 | 11485篇 |
免费 | 27篇 |
国内免费 | 28篇 |
专业分类
系统科学 | 72篇 |
丛书文集 | 28篇 |
教育与普及 | 40篇 |
理论与方法论 | 75篇 |
现状及发展 | 4318篇 |
研究方法 | 522篇 |
综合类 | 6215篇 |
自然研究 | 270篇 |
出版年
2013年 | 80篇 |
2012年 | 177篇 |
2011年 | 489篇 |
2010年 | 76篇 |
2008年 | 189篇 |
2007年 | 211篇 |
2006年 | 230篇 |
2005年 | 230篇 |
2004年 | 271篇 |
2003年 | 224篇 |
2002年 | 221篇 |
2001年 | 308篇 |
2000年 | 335篇 |
1999年 | 225篇 |
1992年 | 209篇 |
1991年 | 159篇 |
1990年 | 170篇 |
1989年 | 180篇 |
1988年 | 178篇 |
1987年 | 193篇 |
1986年 | 174篇 |
1985年 | 251篇 |
1984年 | 179篇 |
1983年 | 140篇 |
1982年 | 113篇 |
1981年 | 117篇 |
1980年 | 137篇 |
1979年 | 331篇 |
1978年 | 256篇 |
1977年 | 242篇 |
1976年 | 224篇 |
1975年 | 238篇 |
1974年 | 306篇 |
1973年 | 279篇 |
1972年 | 236篇 |
1971年 | 337篇 |
1970年 | 474篇 |
1969年 | 328篇 |
1968年 | 312篇 |
1967年 | 319篇 |
1966年 | 351篇 |
1965年 | 223篇 |
1964年 | 98篇 |
1959年 | 108篇 |
1958年 | 209篇 |
1957年 | 118篇 |
1956年 | 130篇 |
1955年 | 101篇 |
1954年 | 84篇 |
1948年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
861.
Thirty-nine previously unpublished reports of the endangered black-footed ferret from Wyoming are listed with dates, locations, number of animals, sources, and comments. 相似文献
862.
863.
In rats, the vertebral artery make only a minor contribution to the blood perfusion of the ponto-medullary area. This was measured with radioactive microspheres and was confirmed by methylmetacrylate casts and local injection of a centrally acting hypotensive drug. 相似文献
864.
865.
E A Rogaeva S Premkumar J Grubber L Serneels W K Scott T Kawarai Y Song D L Hill S M Abou-Donia E R Martin J J Vance G Yu A Orlacchio Y Pei M Nishimura A Supala B Roberge A M Saunders A D Roses D Schmechel A Crane-Gatherum S Sorbi A Bruni G W Small P M Conneally J L Haines F Van Leuven P H St George-Hyslop L A Farrer M A Pericak-Vance 《Nature genetics》1999,22(1):19-22
866.
Dopamine (DA) failed to stimulate the adenylate cyclase of the mesolimbic A10 DA nerve cell body area, in contrast to tis activating effect in the nigrostriatal A9 DA cell body area. The enzyme was stimulated by GMPPNP (a GTP analog) and NaF. This indicates the absence in the A 10 cell area of DA receptors with functional coupling on adenylate cyclase, in contrast to the A9 cell area where such DA receptors are believed to be located on afferent axon terminals. 相似文献
867.
868.
赵银萍 《西安联合大学学报》2000,3(2):31-32
乙烯调节着高等植物的许多生理和发育过程,包括果实成熟、叶脱落、衰老和伤反应.虽然在果实成熟和叶片衰老过程中,mRNA的积累与乙烯的产量以及感量相关,但控制乙烯合成的调节机制以及乙烯促进基因表达的机理并不清楚.此前我们曾报告,互补DNApTOM13与某种mRNA的作用相同,而这种mRNA的合成与趋熟果实及受伤叶片中乙烯的合成相关.pTOM13mRNA编码一种相对分子量约35000的蛋白.对cDNA和三个相关基因的克隆以及测序已经完成,但该蛋白质的作用尚未知道.我们认为,应用pTOM13时,反义RNA降低了乙烯的生物合成,降低程度与反义RNA量的多少… 相似文献
869.
Three rodenticide treatments, zinc phosphide with prebait, strychnine with prebait, and strychnine without prebait, were applied to black-tailed prairie dog Cynomys ludovicianus colonies in west central South Dakota. Results were compared immediately posttreatment and for one year after application. Zinc phosphide was the most effective for reducing prairie dog numbers immediately. When burrow activity levels of prairie dogs were initially reduced by 45% with strychnine only, they returned to untreated levels within ten months. When initial reductions were 95% with zinc phosphide, however, the number of active burrows was still reduced 77% in September the following year. Strychnine with prebait treatment showed initial reductions of 83% in burrow activity. Bait consumption by prairie dogs was highest for zinc phosphide. 相似文献
870.
Efforts to reclaim amended and raw bentonite spoils with six plant species (two forbs, three shrubs, and one tree) were evaluated over a 4-year period. Plant species included fourwing saltbush ( Atriplex canescens [Pursh] Nutt.), big sagebrush ( Artemisia tridentata tridentata Nutt.), Rocky Mountain Juniper ( Juniperus scopulorum Sarg.), Russian olive ( Elaeagnus angustifolia L.) common yarrow ( Achillea millifolium L.) and scarlet globemallow ( Sphaeralcea coccinea [Pursh] Rydb.). Spoil treatments included addition of gypsum, sawdust, perlite, straw, and vermiculite; the control treatment was amended. Fourwing saltbush had 52% survival across all spoil treatments, with greatest survival occurring on perlite-treated spoil (80%), followed by gypsum (70%) and vermiculite amendments (70%). Survival of other plant species ranged from 0 to 2% averaged across all treatments after 4 years. No differences in plant survival occurred among amendments when all species were considered. 相似文献