全文获取类型
收费全文 | 4354篇 |
免费 | 319篇 |
国内免费 | 1篇 |
出版年
2023年 | 17篇 |
2022年 | 36篇 |
2021年 | 107篇 |
2020年 | 63篇 |
2019年 | 81篇 |
2018年 | 107篇 |
2017年 | 90篇 |
2016年 | 148篇 |
2015年 | 193篇 |
2014年 | 225篇 |
2013年 | 258篇 |
2012年 | 406篇 |
2011年 | 353篇 |
2010年 | 234篇 |
2009年 | 176篇 |
2008年 | 259篇 |
2007年 | 274篇 |
2006年 | 270篇 |
2005年 | 198篇 |
2004年 | 227篇 |
2003年 | 208篇 |
2002年 | 189篇 |
2001年 | 32篇 |
2000年 | 35篇 |
1999年 | 45篇 |
1998年 | 54篇 |
1997年 | 46篇 |
1996年 | 31篇 |
1995年 | 42篇 |
1994年 | 25篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 3篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 12篇 |
1973年 | 4篇 |
1972年 | 2篇 |
排序方式: 共有4674条查询结果,搜索用时 234 毫秒
151.
Michael R. Wohlwend Michele R. Schutzenhofer Tiffany M. Knight 《Restoration Ecology》2019,27(6):1307-1316
Invasive species are a common problem in restoration projects. Manipulating soil fertility and species arrival order has the potential to lower their abundance and achieve higher abundances of seeded native species. In a 7‐year experiment in Missouri, United States, we tested how nutrient addition and the timing of arrival of the invasive legume Lespedeza cuneata and seeded native prairie grass and forb species influenced overall community composition. Treatments that involved early arrival of seeded forb and grass species and late arrival of L. cuneata were most successful at creating community structure that fulfilled our restoration goals, displaying high abundance of seeded native forb species, low abundances of L. cuneata, and non‐native species. There were few treatment interactions, with the exception that timing seeded native forbs and timing of L. cuneata arrival interactively influenced the abundance of seeded native forbs. This suggests that the individual treatments are supporting the restoration goals, such as creating a community with low abundance of L. cuneate or high abundance of native seeded species, without restricting each other. This study demonstrates the importance of priority effects in disturbed habitats prone to invasion, the lasting effects of initial seeding on long‐term community composition, and the potential for fertilization to positively benefit restoration of degraded grasslands. 相似文献
152.
153.
154.
The distribution of residues in a polypeptide sequence is a determinant of aggregation optimized by evolution 下载免费PDF全文
Monsellier E Ramazzotti M de Laureto PP Tartaglia GG Taddei N Fontana A Vendruscolo M Chiti F 《Biophysical journal》2007,93(12):4382-4391
It has been shown that the propensity of a protein to form amyloid-like fibrils can be predicted with high accuracy from the knowledge of its amino acid sequence. It has also been suggested, however, that some regions of the sequences are more important than others in determining the aggregation process. Here, we have addressed this issue by constructing a set of “sequence scrambled” variants of the first 29 residues of horse heart apomyoglobin (apoMb1-29), in which the sequence was modified while maintaining the same amino acid composition. The clustering of the most amyloidogenic residues in one region of the sequence was found to cause a marked increase of the elongation rate (kagg) and a remarkable shortening of the lag phase (tlag) of the fibril growth, as determined by far-UV circular dichroism and thioflavin T fluorescence. We also show that taking explicitly into consideration the presence of aggregation-promoting regions in the predictive methods results in a quantitative agreement between the theoretical and observed kagg and tlag values of the apoMb1-29 variants. These results, together with a comparison between homologous segments from the family of globins, indicate the existence of a negative selection against the clustering of highly amyloidogenic residues in one or few regions of polypeptide sequences. 相似文献
155.
Neves RH Miranda de Barros Alencar AC Costa-Silva M Aguila MB Mandarim-de-Lacerda CA Machado-Silva JR Gomes DC 《Experimental parasitology》2007,115(4):324-332
This study investigated whether long-term feeding a high-fat diet (HFC) has an effect on schistosomiasis mansoni outcome compared to standard chow diet (SC). Swiss Webster female mice (3 wk old) fed each diet over 5 months, and then were infected with 50 Schistosoma mansoni cercariae. Their nutritional status was assessed by monitoring growth rates twice a week and measuring serum levels of lipoproteins. Mice were euthanised 63 days after infection. Parasitological and liver histological analyses were performed. The levels of TC, HDL-C and LDL-C, fecal and tissue schistosome eggs were statistically different (p<0.05) between groups. Livers from HFC mice showed exudative, exudative/exudative-productive, exudative-productive and productive granulomas, some degree of hepatic steatosis and focal necrosis. Mice fed normal-chow did not present productive granulomas and hepatic steatosis. The morphometric evaluation of hepatic granulomas did not reach statistical significance (p>0.05) between diets assayed. The high-fat diet for long-term produces effects on schistosomiasis mansoni outcome. 相似文献
156.
A dense single-nucleotide polymorphism-based genetic linkage map of grapevine (Vitis vinifera L.) anchoring Pinot Noir bacterial artificial chromosome contigs 总被引:1,自引:0,他引:1 下载免费PDF全文
Troggio M Malacarne G Coppola G Segala C Cartwright DA Pindo M Stefanini M Mank R Moroldo M Morgante M Grando MS Velasco R 《Genetics》2007,176(4):2637-2650
The construction of a dense genetic map for Vitis vinifera and its anchoring to a BAC-based physical map is described: it includes 994 loci mapped onto 19 linkage groups, corresponding to the basic chromosome number of Vitis. Spanning 1245 cM with an average distance of 1.3 cM between adjacent markers, the map was generated from the segregation of 483 single-nucleotide polymorphism (SNP)-based genetic markers, 132 simple sequence repeats (SSRs), and 379 AFLP markers in a mapping population of 94 F(1) individuals derived from a V. vinifera cross of the cultivars Syrah and Pinot Noir. Of these markers, 623 were anchored to 367 contigs that are included in a physical map produced from the same clone of Pinot Noir and covering 352 Mbp. On the basis of contigs containing two or more genetically mapped markers, region-dependent estimations of physical and recombinational distances are presented. The markers used in this study include 118 SSRs common to an integrated map derived from five segregating populations of V. vinifera. The positions of these SSR markers in the two maps are conserved across all Vitis linkage groups. The addition of SNP-based markers introduces polymorphisms that are easy to database, are useful for evolutionary studies, and significantly increase the density of the map. The map provides the most comprehensive view of the Vitis genome reported to date and will be relevant for future studies on structural and functional genomics and genetic improvement. 相似文献
157.
Free RB Hazelwood LA Cabrera DM Spalding HN Namkung Y Rankin ML Sibley DR 《The Journal of biological chemistry》2007,282(29):21285-21300
As for all proteins, G protein-coupled receptors (GPCRs) undergo synthesis and maturation within the endoplasmic reticulum (ER). The mechanisms involved in the biogenesis and trafficking of GPCRs from the ER to the cell surface are poorly understood, but they may involve interactions with other proteins. We have now identified the ER chaperone protein calnexin as an interacting protein for both D(1) and D(2) dopamine receptors. These protein-protein interactions were confirmed using Western blot analysis and co-immunoprecipitation experiments. To determine the influence of calnexin on receptor expression, we conducted assays in HEK293T cells using a variety of calnexin-modifying conditions. Inhibition of glycosylation either through receptor mutations or treatments with glycosylation inhibitors partially blocks the interactions with calnexin with a resulting decrease in cell surface receptor expression. Confocal fluorescence microscopy reveals the accumulation of D(1)-green fluorescent protein and D(2)-yellow fluorescent protein receptors within internal stores following treatment with calnexin inhibitors. Overexpression of calnexin also results in a marked decrease in both D(1) and D(2) receptor expression. This is likely because of an increase in ER retention because confocal microscopy revealed intracellular clustering of dopamine receptors that were co-localized with an ER marker protein. Additionally, we show that calnexin interacts with the receptors via two distinct mechanisms, glycan-dependent and glycan-independent, which may underlie the multiple effects (ER retention and surface trafficking) of calnexin on receptor expression. Our data suggest that optimal receptor-calnexin interactions critically regulate D(1) and D(2) receptor trafficking and expression at the cell surface, a mechanism likely to be of importance for many GPCRs. 相似文献
158.
Huang Y Qiu J Dong S Redell MS Poli V Mancini MA Tweardy DJ 《The Journal of biological chemistry》2007,282(48):34958-34967
159.
160.
Levine MD Klem ML Kalarchian MA Wing RR Weissfeld L Qin L Marcus MD 《Obesity (Silver Spring, Md.)》2007,15(5):1267-1277
Objective: Women 25 to 45 years old are at risk for weight gain and future obesity. This trial was designed to evaluate the efficacy of two interventions relative to a control group in preventing weight gain among normal or overweight women and to identify demographic, behavioral, and psychosocial factors related to weight gain prevention. Research Methods and Procedures: Healthy women (N = 284), ages 25 to 44, with BMI < 30 were randomized to one of three intervention conditions: a clinic‐based group, a correspondence course, or an information‐only control. Intervention was provided over 2 years, with a follow‐up at Year 3. BMI and factors related to eating and weight were assessed yearly. Results: Over the 3‐year study period, 40% (n = 114) of the women remained at or below baseline body weight (±2 lbs), and 60% gained weight (>2 lbs). Intervention had no effect on weight over time. Independently of intervention, women who were older, not actively dieting to lose weight, and who reported less perceived hunger at baseline were more likely to be successful at weight maintenance. Weight maintenance also was associated with increasing dietary restraint (conscious thoughts and purposeful behaviors to control calorie intake) and decreasing dietary disinhibition (the tendency to lose control over eating) over time. Discussion: This study raises concern about the feasibility and efficacy of weight gain prevention interventions because most women were interested in weight loss, rather than weight gain prevention, and the interventions had no effect on weight stability. Novel approaches to the prevention of weight gain are needed. 相似文献