全文获取类型
收费全文 | 674574篇 |
免费 | 81794篇 |
国内免费 | 312篇 |
专业分类
756680篇 |
出版年
2018年 | 5795篇 |
2016年 | 7687篇 |
2015年 | 10828篇 |
2014年 | 12604篇 |
2013年 | 18257篇 |
2012年 | 20271篇 |
2011年 | 20656篇 |
2010年 | 13962篇 |
2009年 | 12724篇 |
2008年 | 18172篇 |
2007年 | 18931篇 |
2006年 | 17601篇 |
2005年 | 17057篇 |
2004年 | 16770篇 |
2003年 | 16528篇 |
2002年 | 16069篇 |
2001年 | 30122篇 |
2000年 | 30343篇 |
1999年 | 24199篇 |
1998年 | 8700篇 |
1997年 | 9234篇 |
1996年 | 8761篇 |
1995年 | 8315篇 |
1994年 | 8204篇 |
1993年 | 8286篇 |
1992年 | 20730篇 |
1991年 | 20231篇 |
1990年 | 19648篇 |
1989年 | 19197篇 |
1988年 | 17726篇 |
1987年 | 17125篇 |
1986年 | 15784篇 |
1985年 | 15899篇 |
1984年 | 13256篇 |
1983年 | 11563篇 |
1982年 | 8959篇 |
1981年 | 7995篇 |
1980年 | 7698篇 |
1979年 | 12912篇 |
1978年 | 10112篇 |
1977年 | 9295篇 |
1976年 | 8692篇 |
1975年 | 9508篇 |
1974年 | 10101篇 |
1973年 | 10110篇 |
1972年 | 9193篇 |
1971年 | 8531篇 |
1970年 | 7170篇 |
1969年 | 6951篇 |
1968年 | 6235篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
997.
A number of drugs cause marked increases in the steroid hydroxylase activity of hepatic microsomes. Beginning 2 days after estrus, 117 mature ewes were each given 14 injections over a 27-day period of phenobarbital sodium, diphenylhydantoin, chlorcyclizine HCl or phenylbutazone. Blood samples for luteinizing hormone (LH) and progesterone determination by radioimmunoassay (RIA) were taken on day 10 of the first estrous cycle (day 18 if no heat was observed) and on days 5 and 10 of the second cycle. On day 10 of the second cycle, the ewes were given an intravenous injection of 1 ml of 6% solution of pentobarbitol sodium anesthetic per 4.5 kg body weight, and the length of anesthetic sleep time was measured. The ewes were then killed and corpora lutea and liver were weighed.In 33 ewes treated with either phenobarbitol sodium or phenylbutazone, sleep time was shortened (18 min 29 min in untreated controls, P<.01), indicating that enzyme induction had occurred. For 41 ewes treated with either chlorcyclizine HCl or diphenylhydantoin, sleep time was lengthened to 93 min (P<.01 controls), indicating impaired liver function. Electron micrographs of liver cells verified that enzyme induction or hepatic degeneration had occurred. 相似文献
998.
Acetylcholine, oxotremorine and carbachol, compounds that exhibit muscarinic agonist activity, maximally inhibited basal prolactin secretion from GH3 cells by approx. 50% and intracellular cyclic AMP levels by approx. 20%. Both parameters were inhibited with similar potencies by each agonist. These inhibitory effects were blocked by a muscarinic but not by a nicotinic receptor antagonist. In the presence of VIP or IBMX, which raise intracellular cyclic AMP levels and stimulate hormone release, the degree of muscarinic inhibition was increased, but the potency remained unchanged. Similar changes in the secretory rate of prolactin and growth hormone occurred in these and in cell perifusion experiments. These results suggest that the inhibition of hormone secretion from GH3 cells by muscarinic agonists is mediated by a decrease in intracellular cyclic AMP levels. 相似文献
999.
F.J. Murillo B.W. MacDonald E. Kenchington S.E. Campana B. Sainte-Marie M. Sacau 《Marine Biology Research》2018,14(4):366-382
We examined four species of sea pen (Anthoptilum grandiflorum, Halipteris finmarchica, Pennatula aculeata and Pennatula grandis) collected from the Gulf of St. Lawrence and mouth of the Laurentian Channel, eastern Canada. An exponential length–weight relationship was found for all four species, where growth in weight was progressively greater than growth in length with increasing colony size. Halipteris finmarchica, P. grandis and P. aculeata presented the better allometric fits, explaining over 80% of the variance. In addition, a count of growth increments visible in transverse sections in 86 A. grandiflorum and 80 P. aculeata samples was made. Presumed ages ranged between 5 and 28 years for A. grandiflorum and 2 and 21 years for P. aculeata. Radiocarbon assays were inconclusive and could not be used to confirm these ages; further age validation is required. Radial growth of the rod is slow during the first years, increasing at intermediate sizes of the colony and slowing down again for large colonies. Similar results were obtained from the relationship between colony length and number of growth increments where a logistic model was the best fit to the data. On average Spearman’s rank correlations showed 11% of shared variance between sea pen length or weight and environmental variables. Bottom temperature and salinity, depth and summer primary production were significantly correlated to sea pen size for most species. 相似文献
1000.
B. L. Ganzha 《Neurophysiology》1986,18(1):48-54
Summated electrical activity of the human amygdaloid nucleus was investigated in the neurosurgical clinic by chronically implanted electrodes. It was found that odoriferous stimulation of this structure produced bursts of rapid rhythm (20–30 cps, 30–50 µV). The quasisinusoidal waves of olfactory rhythm consist of sinusoidal components which are more pronounced within the 20–30-Hz frequency range. Spindling of 1–3 sec duration occurs at the end of inhalation and the beginning of exhalation in time with breathing. During monorhinal breathing this activity, whose amplitude depends on degree of olfactory stimulation, can only be recorded ipsilaterally. Room air also activates the amygdaloid nucleus, but less strongly than odoriferous substances: No characteristic odor-dependent differences were discovered in the frequency range of the olfactory rhythm within a 20–30-Hz band.Institute of Physiology, Kiev State University, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 61–69, January–February, 1986. 相似文献