全文获取类型
收费全文 | 49119篇 |
免费 | 17160篇 |
国内免费 | 1958篇 |
出版年
2023年 | 287篇 |
2022年 | 674篇 |
2021年 | 1484篇 |
2020年 | 2841篇 |
2019年 | 4480篇 |
2018年 | 4542篇 |
2017年 | 4622篇 |
2016年 | 4854篇 |
2015年 | 5163篇 |
2014年 | 4997篇 |
2013年 | 5732篇 |
2012年 | 3618篇 |
2011年 | 3229篇 |
2010年 | 4048篇 |
2009年 | 2764篇 |
2008年 | 1777篇 |
2007年 | 1291篇 |
2006年 | 1236篇 |
2005年 | 1032篇 |
2004年 | 985篇 |
2003年 | 974篇 |
2002年 | 918篇 |
2001年 | 763篇 |
2000年 | 630篇 |
1999年 | 531篇 |
1998年 | 272篇 |
1997年 | 223篇 |
1996年 | 210篇 |
1995年 | 188篇 |
1994年 | 160篇 |
1993年 | 146篇 |
1992年 | 272篇 |
1991年 | 222篇 |
1990年 | 213篇 |
1989年 | 200篇 |
1988年 | 167篇 |
1987年 | 174篇 |
1986年 | 146篇 |
1985年 | 186篇 |
1984年 | 167篇 |
1983年 | 156篇 |
1982年 | 128篇 |
1981年 | 103篇 |
1979年 | 147篇 |
1978年 | 105篇 |
1977年 | 107篇 |
1975年 | 101篇 |
1974年 | 95篇 |
1973年 | 92篇 |
1972年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
Oscar Fernandez‐Capetillo 《EMBO reports》2010,11(1):32-36
Ageing is an unavoidable corollary to being alive; the most intuitive interpretation of ageing being that it is the consequence of progressive body degeneration. In agreement with this, current models propose that ageing occurs through a stepwise accumulation of DNA damage, which ultimately limits the regenerative capacity of tissues. On the other hand, there is increasing evidence that fetal distress can influence the development of disease in adult life, a phenomenon known as ‘intrauterine programming’. The extent to which an intrauterine exposure to DNA damage can compromise lifespan remains unclear. My group has recently generated a murine model of a human syndrome linked to defective DNA repair and observed that these animals age prematurely, but the accumulation of DNA damage is restricted mostly to the embryonic period. Here, I discuss the implications of this finding and propose that ageing can be influenced by fetal distress. 相似文献
102.
103.
A double-blind controlled trial in 24 lepromatous leprosy patients in reaction showed that clofazimine (Lamprene) controlled symptoms of erythema nodosum leprosum reaction in lepromatous leprosy better than prednisolone. Clofazimine also appeared to be significantly superior in preventing recurrence once the reaction had been controlled. There was a statistically significant rise in serum albumin among inpatients on clofazimine as compared with patients on prednisolone, but no difference in terms of neurological status, bacterial index, morphological index, and renal functions. Red/black hyperpigmentation was seen among practically all patients on clofazimine. No other side-effects or deleterious systemic effects were observed. 相似文献
104.
Summary Studies on the effect of different levels of sucrose in the slurry of peat-based Rhizobium inoculant on germination, seedling growth, and rhizosphere fungi of peanut and soybean revealed that the limits of tolerance for good germination were 2.5 and 5 per cent of the sugar, respectively. Fusaria and aspergilli were invariably present at all levels of sucrose whereas species of Penicillium, Myrothecium, Cunninghamella and Curvularia were isolated only from the rhizosphere at higher levels of the sugar 相似文献
105.
Véronique Lavoie Anne‐Elen Kernaleguen Guy Charron Nada Farhat Mariève Cossette Aida M. Mamarbachi Bruce G. Allen Eric Rhéaume Jean‐Claude Tardif 《Obesity (Silver Spring, Md.)》2011,19(4):722-728
Adiponectin is an adipokine whose plasma levels are inversely correlated to metabolic syndrome components. Adiponectin protects against atherosclerosis and decreases risks in myocardial infarction. Endothelial progenitor cells (EPCs) are a heterogeneous population of circulating cells involved in vascular repair and neovascularization. EPCs number is reduced in patients with cardiovascular disease. We hypothesize that the positive effects of adiponectin against atherosclerosis are explained in part by its interactions with EPCs. Cells were obtained from healthy volunteers' blood by mononuclear cell isolation and plating on collagen‐coated dishes. Three sub‐populations of EPCs were identified and characterized using flow cytometry. EPCs' expression of adiponectin receptors, AdipoR1, and AdipoR2 was evaluated by quantitative PCR. The effects of recombinant adiponectin on EPCs' susceptibility to apoptosis were assessed. Finally, expression of neutrophil elastase by EPCs and activity of this enzyme on adiponectin processing were assessed. Quantitative PCR analysis of EPCs mRNAs showed that AdipoR1 mRNA is expressed at higher levels than AdipoR2. Expression of AdipoR1 protein was confirmed by western blot. Adiponectin significantly increased survival of two sub‐populations of EPCs in conditions of serum deprivation. Such effect could not be demonstrated in the third EPCs sub‐population. We also demonstrated that EPCs, particularly one sub‐population, express neutrophil elastase. Neutrophil elastase activity was confirmed in EPCs' conditioned media. Adiponectin protects some EPCs sub‐populations against apoptosis and therefore could modulate EPCs ability to induce repair of vascular damage. Neutrophil elastase activity of EPCs could locally modulate adiponectin activity by its involvement in the generation of the globular form of adiponectin. 相似文献
106.
107.
108.
Q Yuan W M Jiang D Hollander E Leung J D Watson G W Krissansen 《Biochemical and biophysical research communications》1991,176(3):1443-1449
A cDNA clone encoding the N-terminal sequence of the murine integrin beta 7 subunit, a novel member of the leukocyte cell adhesion molecule subset (Leu-CAM), has been isolated. An N-terminal region of 13 contiguous amino acids deduced from the cDNA shows complete identity with the N-terminus of the 120 kDa subunit of the M290 antigen, a surface molecule found highly expressed on mouse intestinal intraepithelial lymphocytes (IEL). This unexpected result focuses two previously unconnected areas of research and suggests that integrins may have a special role to play in the defence of the gut mucosa. 相似文献
109.
Several types of NS cells were identified in Portunus sanguinolentus--five types (A, A', B, C and D) in the brain and thoracic ganglion, four types (A, B, C and D) in the commissural ganglia and four types (alpha, beta, gamma and delta) in the optic ganglia. The distribution of these NS cells is described. Cytochemically, the neurosecretory material in the NS cells has a carbohydrate moiety and is rich in disulphide groups, lipids, phospholipids and RNA. It contains a small amount of sulphydryl groups and protein-bound NH2 groups, but no tyrosine or tryptophan. The NS activity of the brain was found to be closely associated with the reproductive and moult cycles. Just before the initiation of vitellogenesis and moulting the NS cells display secretory hyperactivity. Axonal transport of NS material was also observed in the NS cells. 相似文献
110.
After observing specimens of Calligonum pumilum Losinsk. and C. juochiangense Y. X. Liou in both the field and in herbarium collections, it was found that the morphological characters of these two species are quite different, especially with respect of the twisted direction of fruit ribs, number of bristle rows along each rib, rigidity and degree of interweaving of bristles, as well as their geographic distribution. Therefore, it is concluded that C. pumilum and C. juochiangense should be accepted as two independent species. 相似文献