全文获取类型
收费全文 | 456388篇 |
免费 | 52574篇 |
国内免费 | 748篇 |
专业分类
509710篇 |
出版年
2018年 | 4400篇 |
2017年 | 4214篇 |
2016年 | 6074篇 |
2015年 | 8948篇 |
2014年 | 10287篇 |
2013年 | 13754篇 |
2012年 | 16347篇 |
2011年 | 16755篇 |
2010年 | 11070篇 |
2009年 | 10014篇 |
2008年 | 14541篇 |
2007年 | 14961篇 |
2006年 | 14073篇 |
2005年 | 13428篇 |
2004年 | 13460篇 |
2003年 | 12500篇 |
2002年 | 12130篇 |
2001年 | 18995篇 |
2000年 | 18896篇 |
1999年 | 15155篇 |
1998年 | 5718篇 |
1997年 | 5690篇 |
1996年 | 5413篇 |
1995年 | 5197篇 |
1994年 | 4892篇 |
1993年 | 4896篇 |
1992年 | 12507篇 |
1991年 | 12472篇 |
1990年 | 12220篇 |
1989年 | 11676篇 |
1988年 | 10858篇 |
1987年 | 10215篇 |
1986年 | 9746篇 |
1985年 | 9516篇 |
1984年 | 7889篇 |
1983年 | 6844篇 |
1982年 | 5151篇 |
1981年 | 4636篇 |
1980年 | 4324篇 |
1979年 | 7355篇 |
1978年 | 5974篇 |
1977年 | 5302篇 |
1976年 | 4966篇 |
1975年 | 5772篇 |
1974年 | 6311篇 |
1973年 | 6126篇 |
1972年 | 5460篇 |
1971年 | 5081篇 |
1970年 | 4279篇 |
1969年 | 4205篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
992.
993.
994.
995.
C J Persoons A K Minks S Voerman W L Roelofs F J Ritter 《Journal of insect physiology》1974,20(7):1181-1188
By means of analytical and electroantennogram methods, cis-11-and trans-11-tetradecenyl acetate have been isolated and identified as the sex pheromones of the fruit tree tortrix moth, Archips podana. In contrast to the single compounds, mixtures in a ratio of about 1 : 1 are highly attractive to male moths in field experiments. 相似文献
996.
997.
998.
999.
D Virgintino N L'Abbate D Ribatti M Bertossi L Roncali L Ambrosi 《Biological structures and morphogenesis》1989,2(3):85-88
On the basis of previous observations on the teratogenic effects of a variety of organophosphorus and methylcarbamate compounds on the avian skeletal apparatus, the Meckel's cartilage shape and structure were analyzed in carbaryl (1-naphthyl N-methylcarbamate) treated and control chick embryos of 9, 10, 12 days of incubation. The results indicate that both during normal development and under experimental conditions these cartilages undergo similar deformities, apparently subsequent to chondroblast death and regressive processes in the extracellular matrix. Since the macro- and microscopical cartilage alterations are significantly more frequent in the treated embryos than in the controls, a hypothesis is advanced that the methylcarbamate may increase the spontaneous tendency of the above mentioned cartilaginous anlagen to be affected by degenerative processes during embryogenesis. 相似文献
1000.
W.S. Rehm S.S. Sanders R.L. Shoemaker J. OCallaghan J.T. Tarvin E.A. Friday 《Journal of theoretical biology》1973,39(1):131-153
Several workers have suggested that cell membranes have a high proton conductance. Our interest in this concept arose from the possibility that the nutrient (submucosal-facing) membrane of the gastric mucosa may have a high proton or hydroxyl ion conductance which would play a role in the regulation of the acid-base balance of the cell. We found that wide changes in the H+ concentration of the fluid bathing the nutrient side of the in vitro frog gastric mucosa did not result in significant changes in p.d. However, a maintained change of the H+ concentration of the bathing fluid would be expected to produce only a temporary change in p.d. Since a diffusion barrier is present on the nutrient side the temporary change in p.d. might be masked. An analysis of this possibility was made on the basis of a conceptual model and as a result of the analysis it is concluded that the proton (and/or OH?) conductance of the nutrient membrane of the frog gastric mucosa is not a significant fraction of its total conductance. The present status of the proton conductance hypothesis with respect to striated muscle and to the secretory membrane of the gastric mucosa is reviewed. 相似文献