全文获取类型
收费全文 | 10638篇 |
免费 | 907篇 |
专业分类
11545篇 |
出版年
2023年 | 37篇 |
2022年 | 89篇 |
2021年 | 158篇 |
2020年 | 115篇 |
2019年 | 156篇 |
2018年 | 198篇 |
2017年 | 170篇 |
2016年 | 267篇 |
2015年 | 432篇 |
2014年 | 441篇 |
2013年 | 634篇 |
2012年 | 723篇 |
2011年 | 684篇 |
2010年 | 472篇 |
2009年 | 430篇 |
2008年 | 581篇 |
2007年 | 630篇 |
2006年 | 552篇 |
2005年 | 561篇 |
2004年 | 564篇 |
2003年 | 556篇 |
2002年 | 629篇 |
2001年 | 129篇 |
2000年 | 92篇 |
1999年 | 138篇 |
1998年 | 156篇 |
1997年 | 144篇 |
1996年 | 128篇 |
1995年 | 109篇 |
1994年 | 101篇 |
1993年 | 101篇 |
1992年 | 104篇 |
1991年 | 83篇 |
1990年 | 69篇 |
1989年 | 65篇 |
1988年 | 50篇 |
1987年 | 52篇 |
1986年 | 42篇 |
1985年 | 53篇 |
1984年 | 67篇 |
1983年 | 59篇 |
1982年 | 95篇 |
1981年 | 84篇 |
1980年 | 63篇 |
1979年 | 55篇 |
1978年 | 54篇 |
1977年 | 52篇 |
1976年 | 52篇 |
1975年 | 35篇 |
1973年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Audrey Extier Bénédicte Langelier Marie-Hélène Perruchot Philippe Guesnet Paul P. Van Veldhoven Monique Lavialle Jean-Marc Alessandri 《The Journal of nutritional biochemistry》2010,21(3):180-187
Dietary n?3 polyunsaturated fatty acids (PUFA) are major components of cell membranes and have beneficial effects on human health. Docosahexaenoic acid (DHA; 22:6n?3) is the most biologically important n?3 PUFA and can be synthesized from its dietary essential precursor, α-linolenic acid (ALA; 18:3n?3). Gender differences in the efficiency of DHA bioconversion have been reported, but underlying molecular mechanisms are unknown. We compared the capacity for DHA synthesis from ALA and the expression of related enzymes in the liver and cerebral cortex between male and female rats. Wistar rats, born with a low-DHA status, were supplied with a suboptimal amount of ALA from weaning to 8 weeks of age. Fatty acid composition was determined by gas chromatography, the mRNA expression of different genes involved in PUFA metabolism was determined by RT-PCR (low-density array) and the expression of proteins was determined by Western blot analysis. At 8 weeks, DHA content was higher (+20 to +40%) in each phospholipid class of female livers compared to male livers. The “Δ4,” Δ5 and Δ6 desaturation indexes were 1.2–3 times higher in females than in males. The mRNA expression of Δ5- and Δ6-desaturase genes was 3.8 and 2.5 times greater, respectively, and the Δ5-desaturase protein was higher in female livers (+50%). No gender difference was observed in the cerebral cortex. We conclude that female rats replete their DHA status more readily than males, probably due to a higher expression of liver desaturases. Our results support the hypothesis on hormonal regulation of PUFA metabolism, which should be taken into account for specific nutritional recommendations. 相似文献
952.
953.
Within-population genetic variability of twelve insular and four mainland populations of deer mice ( Peromyscus maniculatus ) was assessed using craniometric characters, and compared to results previously obtained from RAPD data. An index of Craniometric Variance ( CVar ) was computed from pairwise distances among all specimens. Variations in CVar measures were then compared to landscape variables using a linear regression approach. Our results suggest that CVar decreases in presence of large number of a competitive species (the boreal redback vole, Clethrionomys gapperi ; r =−0.527, p <0.037) in deer mouse populations. Island remoteness ( r =−0.251, p <0.220) and the geometry of the bank opposite to each island ( r =−0.459, p <0.067) were marginally correlated with CVar , but the linear combination of these two variables, forming a composite isolation index, represented the major factor explaining the observed CVar ( r =−0.648, p <0.011). Using a multiple regression model, 76.3% of the CVar was explained by a combination of this isolation index and the competitors' abundance. These results suggest that taking into account landscape barriers as well as the dispersal behavior of small mammals might provide sounder ecological variables than geographical distances alone for predicting within-population genetic variability in a network of habitat patches. 相似文献
954.
955.
956.
957.
Salvetti P Theau-Clément M Beckers JF Hurtaud J Guérin P Neto V Falières J Joly T 《Theriogenology》2007,67(6):1185-1193
For most domestic animals, the responses to superovulation treatments are not controlled as a consequence of the lack of knowledge on exogenous gonadotrophins effects on the ovarian function. The role of luteinizing hormone (LH) on the number and quality of embryos produced was evaluated on rabbit does superovulated with porcine FSH (pFSH). Parameters of embryos recovery, in vitro and in vivo embryo development rates after freezing/thawing were compared. We used three experimental groups: (1) control group without superovulation treatment, (2) "pFSH+pLH" and (3) "pFSH" groups where females were treated with pFSH, respectively, with (20%) or without (0%) porcine LH supplementation. The number of corpora lutea and the number of embryos produced were significantly higher (p<0.001) in superovulated does than in control group (27.1, 26.7 versus 11.9 corpora lutea and 20.3, 21.2 versus 9.6 embryos produced for pFSH+pLH, pFSH and control group, respectively). However, both gonadotrophins administrations (groups 2 and 3) led to defaults of ovulation when compared with untreated does. No significant difference was observed between the number and quality of the embryos produced by does treated with pFSH+pLH or with pFSH alone. Moreover, we observed no significant difference between results of in vivo and in vitro viability assays after thawing. We concluded that pFSH alone seems to be sufficient to stimulate the follicles growth and that exogenous pLH administrated has no effect on the quantity and quality of embryos. Further studies are needed to evaluate the hormonal patterns before and after the gonadotrophins injections in the rabbit species. 相似文献
958.
Targeted deletion of AIF decreases mitochondrial oxidative phosphorylation and protects from obesity and diabetes 总被引:8,自引:0,他引:8
Pospisilik JA Knauf C Joza N Benit P Orthofer M Cani PD Ebersberger I Nakashima T Sarao R Neely G Esterbauer H Kozlov A Kahn CR Kroemer G Rustin P Burcelin R Penninger JM 《Cell》2007,131(3):476-491
Type-2 diabetes results from the development of insulin resistance and a concomitant impairment of insulin secretion. Recent studies place altered mitochondrial oxidative phosphorylation (OxPhos) as an underlying genetic element of insulin resistance. However, the causative or compensatory nature of these OxPhos changes has yet to be proven. Here, we show that muscle- and liver-specific AIF ablation in mice initiates a pattern of OxPhos deficiency closely mimicking that of human insulin resistance, and contrary to current expectations, results in increased glucose tolerance, reduced fat mass, and increased insulin sensitivity. These results are maintained upon high-fat feeding and in both genetic mosaic and ubiquitous OxPhos-deficient mutants. Importantly, the effects of AIF on glucose metabolism are acutely inducible and reversible. These findings establish that tissue-specific as well as global OxPhos defects in mice can counteract the development of insulin resistance, diabetes, and obesity. 相似文献
959.
Gérard P Lepercq P Leclerc M Gavini F Raibaud P Juste C 《Applied and environmental microbiology》2007,73(18):5742-5749
The microbial community in the human colon contains bacteria that reduce cholesterol to coprostanol, but the species responsible for this conversion are still unknown. We describe here the first isolation and characterization of a cholesterol-reducing bacterium of human intestinal origin. Strain D8 was isolated from a 10(-8) dilution of a fresh stool sample provided by a senior male volunteer with a high capacity to reduce luminal cholesterol to coprostanol. Cholesterol-to-coprostanol conversion by strain D8 started on the third day, while cells were in stationary phase, and was almost complete after 7 days. Intermediate products (4-cholesten-3-one and coprostanone) were occasionally observed, suggesting an indirect pathway for cholesterol-to-coprostanol conversion. Resting-cell assays showed that strain D8 could reduce 1.5 mumol of cholesterol/mg bacterial protein/h. Strain D8 was a gram-negative, non-spore-forming, rod-shaped organism identified as a member of the genus Bacteroides closely related to Bacteroides vulgatus, based on its morphological and biochemical characteristics. The 16S rRNA gene sequence of strain D8 was most similar (>99.5%) to those of two isolates of the recently described species Bacteroides dorei. Phylogenetic tree construction confirmed that Bacteroides sp. strain D8 clustered within an independent clade together with these B. dorei strains. Nevertheless, no cholesterol-reducing activity could be detected in cultures of the B. dorei type strain. Based on Bacteroides group-specific PCR-temporal temperature gradient gel electrophoresis, there was no correlation between the presence of a band comigrating with the band of Bacteroides sp. strain D8 and cholesterol conversion in 11 human fecal samples, indicating that this strain is unlikely to be mainly responsible for cholesterol conversion in the human population. 相似文献
960.