全文获取类型
收费全文 | 5697篇 |
免费 | 559篇 |
专业分类
6256篇 |
出版年
2022年 | 56篇 |
2021年 | 140篇 |
2020年 | 66篇 |
2019年 | 79篇 |
2018年 | 89篇 |
2017年 | 89篇 |
2016年 | 112篇 |
2015年 | 228篇 |
2014年 | 246篇 |
2013年 | 311篇 |
2012年 | 369篇 |
2011年 | 379篇 |
2010年 | 252篇 |
2009年 | 224篇 |
2008年 | 298篇 |
2007年 | 303篇 |
2006年 | 297篇 |
2005年 | 287篇 |
2004年 | 261篇 |
2003年 | 240篇 |
2002年 | 214篇 |
2001年 | 53篇 |
2000年 | 42篇 |
1999年 | 56篇 |
1998年 | 56篇 |
1997年 | 48篇 |
1996年 | 37篇 |
1995年 | 44篇 |
1994年 | 45篇 |
1993年 | 47篇 |
1992年 | 47篇 |
1991年 | 32篇 |
1990年 | 48篇 |
1989年 | 48篇 |
1988年 | 33篇 |
1987年 | 47篇 |
1986年 | 28篇 |
1984年 | 50篇 |
1983年 | 46篇 |
1982年 | 55篇 |
1981年 | 41篇 |
1980年 | 38篇 |
1978年 | 35篇 |
1976年 | 28篇 |
1974年 | 36篇 |
1973年 | 31篇 |
1971年 | 29篇 |
1970年 | 31篇 |
1968年 | 25篇 |
1965年 | 30篇 |
排序方式: 共有6256条查询结果,搜索用时 15 毫秒
1.
2.
3.
Pinealectomy or radical sham pinealectomy were performed on adult golden-mantled ground squirrels,Spermophilus (=Citellus) lateralis, approximately 1 month prior to the date of normal winter emergence. The first hibernatory period and subsequent active season were not different in either of the operated groups from intact animals. However, although the initiation of the second hibernatory period was not affected in the pinealectomized animals, this group failed to show the progressive increase in the length of heterothermic bouts that is characteristic of normal hibernation. Also, terminal arousal occurred approximately 6 weeks earlier in the second year after pinealectomy. Male squirrels showed a corresponding time compression in their annual gonadal cycle, as was assessed by testicular state.These results suggest that the pineal gland of the golden-mantled ground squirrel is involved in the expression of the annual hibernatory cycle. In the absence of the pineal gland the adult of this species is unable to sustain the normal depth and duration of hibernation in the second over-wintering period following pinealectomy.We have carried out additional experiments with young, laboratory-bornS. lateralis and with field-caught, adultS. richardsonii. The results of these studies also are described in this paper.Presented at the Ninth International Congress of Biometeorology, 23 Sept – 1 Oct 1981, Osnabrück and Hohenheim, FRG. 相似文献
4.
5.
6.
7.
Suzanne M. Lohmann Ralph P. Miech Fred R. Butcher 《Biochimica et Biophysica Acta (BBA)/General Subjects》1977,499(2):238-250
The effect of theophylline and isoproterenol on bovine tracheal smooth muscle tension and cyclic AMP levels was investigated. Concentrations of isoproterenol (4 × 10?6 M) and theophylline (10 mM) that relaxed carbachol-contracted tracheal muscle by 85–95% did not significantly elevate control levels of cyclic AMP. In the absence of carbachol, several-fold increases in cyclic AMP were caused by isoproterenol although no elevations by theophylline were measurable. However, when isoproterenol and theophylline were administered together, theophylline potentiated the rise in cyclic AMP caused by isoproterenol. Phosphodiesterase studies in tracheal muscle showed the presence of a high and a low Km enzyme which were inhibited by theophylline. Cyclic GMP levels were elevated in muscles contracted by carbachol as well as in carbachol-contracted muscles that had been relaxed by theophylline. In non-tension studies, in which the tracheal muscle was not under isometric tension, carbachol or theophylline alone increased cyclic GMP and together they synergistically elevated cyclic GMP. Atropine blocked the elevation caused by carbachol but not that caused by theophylline. In contrast to theophylline, isoproterenol did not elevate cyclic GMP, and in carbachol-contracted muscles that had been relaxed by isoproterenol, cyclic GMP levels were no different from control. Also, in non-tension studies, isoproterenol decreased basal cyclic GMP and antagonized the increase in cyclic GMP due to carbachol.The results indicate that whole-tissue levels of cyclic AMP and cyclic GMP do not correlate with the state of tracheal smooth muscle tension. Cyclic GMP levels do not clearly correlate with either contraction or relaxation. The inhibition by carbachol of increases in cyclic AMP due to isoproterenol and the inhibition by isoproterenol of increases in cyclic GMP due to carbachol provide evidence for a reciprocal cholinergic-adrenergic antagonism of cyclic AMP and cyclic GMP levels. The antagonism did not appear to be due to either cyclic nucleotide affecting the elevation of the other since the levels of both cyclic nucleotides were depressed. 相似文献
8.
Ethan R. Block Michael A. Tolino Jennifer S. Lozano Kira L. Lathrop Rebecca S. Sullenberger Abigail R. Mazie Jes K. Klarlund 《Molecular biology of the cell》2010,21(13):2172-2181
The ability of epithelia to migrate and cover wounds is essential to maintaining their functions as physical barriers. Wounding induces many cues that may affect the transition to motility, including the immediate mechanical perturbation, release of material from broken cells, new interactions with adjacent extracellular matrix, and breakdown of physical separation of ligands from their receptors. Depending on the exact nature of wounds, some cues may be present only transiently or insignificantly. In many epithelia, activation of the epidermal growth factor receptor (EGFR) is a central event in induction of motility, and we find that its continuous activation is required for progression of healing of wounds in sheets of corneal epithelial cells. Here, we examine the hypothesis that edges, which are universally and continuously present in wounds, are a cue. Using a novel culture model we find that their presence is sufficient to cause activation of the EGFR and increased motility of cells in the absence of other cues. Edges that are bordered by agarose do not induce activation of the EGFR, indicating that activation is not due to loss of any specific type of cell–cell interaction but rather due to loss of physical constraints. 相似文献
9.
10.