全文获取类型
收费全文 | 4561篇 |
免费 | 299篇 |
国内免费 | 2篇 |
专业分类
4862篇 |
出版年
2023年 | 38篇 |
2022年 | 60篇 |
2021年 | 124篇 |
2020年 | 99篇 |
2019年 | 112篇 |
2018年 | 105篇 |
2017年 | 114篇 |
2016年 | 211篇 |
2015年 | 242篇 |
2014年 | 240篇 |
2013年 | 330篇 |
2012年 | 380篇 |
2011年 | 360篇 |
2010年 | 255篇 |
2009年 | 184篇 |
2008年 | 270篇 |
2007年 | 277篇 |
2006年 | 226篇 |
2005年 | 212篇 |
2004年 | 153篇 |
2003年 | 163篇 |
2002年 | 144篇 |
2001年 | 31篇 |
2000年 | 33篇 |
1999年 | 28篇 |
1998年 | 35篇 |
1997年 | 21篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 19篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 19篇 |
1985年 | 10篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 23篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 13篇 |
1971年 | 10篇 |
排序方式: 共有4862条查询结果,搜索用时 0 毫秒
1.
2.
Background
Phylogenies capture the evolutionary ancestry linking extant species. Correlations and similarities among a set of species are mediated by and need to be understood in terms of the phylogenic tree. In a similar way it has been argued that biological networks also induce correlations among sets of interacting genes or their protein products. 相似文献3.
Primate microbiome research is a quickly growing field with exciting potential for informing our understanding of primate biology, ecology, and evolution as well as host‐microbe interactions more broadly. This introductory essay to a special section of the American Journal of Primatology provides a cross‐sectional snapshot of current activity in these areas by briefly summarizing the diversity of contributed papers and their relationships to key themes in host‐associated microbiome research. It then uses this survey as a foundation for consolidating a set of key research questions to broadly guide future research. It also argues for the importance of methods standardization to facilitate comparative analyses and the identification of generalizable patterns and relationships. While primatology will benefit greatly from the integration of microbial datasets, it is uniquely positioned to address important questions regarding microbiology and macro‐ecology and evolution more generally. We are eager to see where the primate microbiome leads us. 相似文献
4.
Rafael L. X. Consani Mariana R. Carmignani Marcelo F. Mesquita Lourenço Correr‐Sobrinho Ricardo D. Guiraldo 《Gerodontology》2010,27(3):236-242
doi:10.1111/j.1741‐2358.2009.00333.x Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth. 相似文献
5.
6.
C L Marcelo 《Experimental cell research》1979,120(1):201-210
Primary keratinocyte cultures free of dermal fibroblasts were used to investigate the effect of varying cyclic AMP (cAMP) concentrations on epidermal cell function. Addition of 10?3, 10?4 or 10?5 M dibutyryl cAMP to plated cells (day 1) results by day 5 in a dose dependent increase of [3H]TdR incorporation into DNA as determined by increases in both the labeling index and incorporation of 3H label into an isolated DNA fraction. 8-Bromo cAMP, another cAMP analogue, likewise induced keratinocyte proliferation. The proliferative response was dose and time dependent, and 5- to 6-fold increases in 3H label incorporated into DNA were seen at day 6, 8 and up until day 15 of culture. Moreover, elevation of cellular cAMP by addition of cholera toxin, an irreversible stimulator of adenylate cyclase, also demonstrated a time dependent stimulation of [3H]TdR uptake into DNA and increased the labeling index. Specific histochemical staining for keratinaceous protein (Kreyberg technique) demonstrated that elevated cAMP levels also enhance the production of specialized (differentiated) epidermal cells. Determination of the level of cAMP and cyclic GMP (cGMP) by RIA of partially purified fractions of the cultures revealed that addition of 8-bromo cAMP or cholera toxin to the cultures increased the levels of cAMP but not of cGMP. Addition of 8-bromo cGMP to the keratinocytes on day 1 at concentrations of 10?6, 10?7 or 10?8 M had no effect on culture proliferation on days 4, 6 and 8, although qualitative changes in the electron microscopic pattern of the culture stratification and specialization were observed. The results indicate (1) both large and moderate increases in cellular cAMP levels induce keratinocyte culture proliferation and specialization in the absence of fibroblasts or dermal influences, (2) the quantitative enhancement of keratinocyte growth and specialization occurs without apparent participation of cGMP, (3) cGMP may be a qualitative effector of epidermal cell differentiation. 相似文献
7.
David N. Kuhn Michael Knauf P.K. Stumpf 《Archives of biochemistry and biophysics》1981,209(2):441-450
The localization of acetyl-CoA synthetase in the spinach leaf cell was examined. When the different compartments of lysed spinach protoplasts were assayed for marker enzymes and acetyl-CoA synthetase, it was determined that the synthetase was totally localized in the chloroplast compartment. Analysis of spinach leaf for free acetate revealed that this acid was present at a 1 mm level in the leaf cell. It is suggested that free acetate probably derived from a number of sources in the cell diffuses into the chloroplast stroma compartment where it is converted to acetyl-CoA and thence employed for biosynthetic reactions. Thus, free acetate is metabolically inert in the leaf cell until it is transported to the only compartment that contains acetyl-CoA synthetase, namely the chloroplast. 相似文献
8.
9.
10.