全文获取类型
收费全文 | 908701篇 |
免费 | 92220篇 |
国内免费 | 294篇 |
专业分类
1001215篇 |
出版年
2018年 | 8823篇 |
2017年 | 8393篇 |
2016年 | 11832篇 |
2015年 | 14929篇 |
2014年 | 17852篇 |
2013年 | 25801篇 |
2012年 | 28945篇 |
2011年 | 29919篇 |
2010年 | 20449篇 |
2009年 | 18891篇 |
2008年 | 26769篇 |
2007年 | 27896篇 |
2006年 | 26121篇 |
2005年 | 25074篇 |
2004年 | 24890篇 |
2003年 | 23983篇 |
2002年 | 23596篇 |
2001年 | 39236篇 |
2000年 | 38925篇 |
1999年 | 31102篇 |
1998年 | 11478篇 |
1997年 | 11612篇 |
1996年 | 11003篇 |
1995年 | 10159篇 |
1994年 | 9813篇 |
1993年 | 9919篇 |
1992年 | 25415篇 |
1991年 | 25063篇 |
1990年 | 24339篇 |
1989年 | 23833篇 |
1988年 | 21893篇 |
1987年 | 21063篇 |
1986年 | 19593篇 |
1985年 | 19559篇 |
1984年 | 16109篇 |
1983年 | 13992篇 |
1982年 | 10574篇 |
1981年 | 9546篇 |
1980年 | 8937篇 |
1979年 | 15021篇 |
1978年 | 11932篇 |
1977年 | 10745篇 |
1976年 | 10194篇 |
1975年 | 11509篇 |
1974年 | 12412篇 |
1973年 | 12275篇 |
1972年 | 11292篇 |
1971年 | 10137篇 |
1970年 | 8876篇 |
1969年 | 8710篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
Three methods of analysis were used to determine the diet of territorial hooded crows at Lough Hyne Marine Reserve, Co Cork, Ireland The regular collection of prey Items from these sites at Lough Hyne was integrated with pellet and stomach analysis to determine diet Intertidal organisms occurred in over 80% of pellets and 43% of stomachs and occupied over 77% of the total wet weight of foods identified in pellets All prey items recovered from drop sites originated from the intertidal habitat, involved either large-sized species or larger individuals of smaller-sized species, and were only dropped during October to February Twenty-five intertidal species were identified but only a few of these species contributed to the bulk of the diet Hooded crows were shown to consume a wide range of intertidal species throughout the year, though the species composition in the diet was seasonally influenced Depletion and weight loss of intertidal molluscs through the winter was shown to have a minimal effect on selection suggesting that prey switching was driven by the birds nutritional requirements 相似文献
223.
The method for obtaining antisera to meningococci of different serotypes are described and the scheme for the preparation of serotyping is presented, as well as the method for the preparation of the determinate fraction of serotype 2. Antisera to typing antigens 1, 2, 2-7, 2-10, 4, 5, 6, 8 (1) have been obtained, their specificity tested in parallel experiments with American and French typing sera. When typing meningococci, the use of antisera to purified protein antigen 2 is recommended. 相似文献
224.
"Pertussis toxin induces tachycardia and impairs the increase in blood pressure produced by alpha 2-adrenergic agonists" 总被引:4,自引:0,他引:4
Administration of purified pertussis toxin to rats induced persistent tachycardia, (observed in conscious rats but not after pithing); as little as 0.05 microgram/100 g produced a significant effect. Pertussis toxin-treatment did not affected the pressor response produced in the pithed rats by the alpha 2-adrenergic agonist methoxamine but markedly diminished the pressor effect of the alpha 2-adrenergic agonists clonidine and azepexole. A role of adenylate cyclase inhibition in the action of postsynaptic vascular alpha 2-adrenergic receptors is suggested. 相似文献
225.
Androgenic stimulation of endocytosis, amino acid and hexose transport in mouse kidney cortex involves increased calcium fluxes 总被引:2,自引:0,他引:2
Testosterone was previously shown to induce an early (less than 1 min) receptor-dependent stimulation of endocytosis, hexose and amino acid transport in mouse kidney cortex (Koenig, H., Goldstone, A. and Lu, C.Y. (1982) Biochem. Biophys. Res. Commun. 104, 165-172). Testosterone (10(-8) M) has now been found to stimulate rapidly (less than 30 s) the influx and efflux of 45Ca2+ in cortex slices. Testosterone also decreased mitochondrial 45Ca and augmented soluble 45Ca, indicating a mobilization of intracellular calcium. Incubation of cortex slices in calcium-free medium without or with 2.5 mM EGTA decreased basal endocytosis, hexose and amino acid transport and blocked the hormonal response. 100 microM verapamil blocked the hormonal response without affecting basal transport. The calcium ionophore A23187 rapidly stimulated endocytosis, hexose and amino acid transport. These data indicate that androgenic stimulation of membrane transport functions involves an increased influx of extracellular calcium and a mobilization of intracellular calcium. Increased cytosolic Ca2+ is probably the regulatory signal for these transport processes. 相似文献
226.
227.
Leucostasis, an underestimated cause of death in leukaemia 总被引:1,自引:0,他引:1
Massive sludging of leukaemic cells in blood vessels is a frequent and often lethal complication of leukaemia. In a retrospective clinicopathological study on the causes of death in 52 patients with acute myeloid leukaemia and myeloproliferative disease, pulmonary leucostasis was found in 40% of the patients. In many of these patients the vessels of the heart, brain and testes were also involved. In search for signs and symptoms specific for leucostasis, the clinical records of the 21 patients with leucostasis (the study group) were compared to those of 20 patients without leucostasis (the control group). Dysfunction of the organs most affected by leucostasis, namely lungs, heart and brain, was found more often in the study group than in the controls, but the combination of unexplained fever with cardiopulmonary and/or central nervous system failure occurred almost exclusively and in half of the patients with leucostasis. Leucostasis occurs predominantly, but not exclusively, in patients with high leucocyte counts, and especially, but again not exclusively, when the leucocyte counts rise sharply. 相似文献
228.
229.
Templeton G. H.; Sweeney H. L.; Timson B. F.; Padalino M.; Dudenhoeffer G. A. 《Journal of applied physiology》1988,65(3):1191-1195
Chronic reduction of gravitational load in the rear limbs of rats to simulate the influence of near-zero gravity in skeletal muscles has been shown previously to elicit atrophy in the soleus muscle. Use of this model by the present investigation indicates that soleus atrophy was characterized by a decline in the number of fibers in groups that contained the slow isoenzyme of myosin and which were classified as type I from intensity of staining to myofibrillar actomyosin adenosinetriphosphatase (ATPase) and to NADH tetrazolium reductase. Furthermore total fiber number was not changed, whereas fibers containing the intermediate isoenzyme and those classified as type IIa increased. There results could be explained by either a change in the composition within existing fibers or a simultaneous loss of slow fibers and de novo synthesis of intermediate and fast fibers. Evidence for transformation included an absence of embryonic or neonatal myosin in muscles from suspended rats and the constant fiber number that was unchanged by 4 wk of suspension. Furthermore although fiber areas of both groups of type I and IIa fibers declined during suspension, variability of the fiber areas within each group did not increase. 相似文献
230.
Cloned, protein antigen-specific, Ia-restricted T cell lines frequently (approximately 20%) also respond strongly to stimulator cells from strains expressing stimulatory alleles at the chromosome 1-encoded Mls-locus. Furthermore, such responses are blocked by monoclonal antibodies specific for Ia antigens expressed by the stimulator rather than the responder cells. However, such responses show no specificity for polymorphic determinants on Ia molecules, although in such responses, as in primary and secondary T cell responses to stimulating Mls-locus alleles, I-E molecules appear to play a central role. These results, combined with the unique immunobiology of the primary T cell proliferative response to Mls-locus-disparate stimulator cells, suggest to us that this response involves the interaction of the receptor on T cells for antigen:self Ia with a relatively nonpolymorphic region of Ia glycoproteins. This hypothesis is supported by the observation that a monoclonal antibody to the T cell receptor will inhibit both responses, although the response to Mls-locus-disparate stimulators appears to be more sensitive to these antibodies. We propose that the interaction of the T cell receptor with Ia is stabilized by a cell interaction molecule encoded or regulated by the Mls-locus gene product permitting the T cell receptor:Ia glycoprotein interaction to lead to T cell activation. 相似文献