全文获取类型
收费全文 | 3913篇 |
免费 | 343篇 |
专业分类
4256篇 |
出版年
2023年 | 46篇 |
2022年 | 97篇 |
2021年 | 155篇 |
2020年 | 117篇 |
2019年 | 117篇 |
2018年 | 103篇 |
2017年 | 91篇 |
2016年 | 154篇 |
2015年 | 313篇 |
2014年 | 300篇 |
2013年 | 276篇 |
2012年 | 363篇 |
2011年 | 372篇 |
2010年 | 188篇 |
2009年 | 122篇 |
2008年 | 174篇 |
2007年 | 154篇 |
2006年 | 146篇 |
2005年 | 130篇 |
2004年 | 77篇 |
2003年 | 65篇 |
2002年 | 80篇 |
2001年 | 22篇 |
2000年 | 26篇 |
1999年 | 26篇 |
1998年 | 22篇 |
1997年 | 26篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1974年 | 9篇 |
1971年 | 16篇 |
1970年 | 9篇 |
1944年 | 8篇 |
排序方式: 共有4256条查询结果,搜索用时 15 毫秒
101.
Rosa van den Berg Sander Kooijman Raymond Noordam Ashna Ramkisoensing Gustavo Abreu-Vieira Lauren L. Tambyrajah Wieneke Dijk Philip Ruppert Isabel M. Mol Barbara Kramar Rosanna Caputo Laura Sardón Puig Evelien M. de Ruiter Jan Kroon Menno Hoekstra Ronald J. van der Sluis Onno C. Meijer Ko Willems van Dijk Patrick C.N. Rensen 《Cell reports》2018,22(13):3521-3533
102.
An individual's position in a social hierarchy profoundly affects behavior and physiology through interactions with community members, yet little is known about how the brain contributes to status differences between and within the social states or sexes. We aimed to determine sex-specific attributes of social status by comparing circulating sex steroid hormones and neural gene expression of sex steroid receptors in dominant and subordinate male and female Astatotilapia burtoni, a highly social African cichlid fish. We found that testosterone and 17β-estradiol levels are higher in males regardless of status and dominant individuals regardless of sex. Progesterone was found to be higher in dominant individuals regardless of sex. Based on pharmacological manipulations in males and females, progesterone appears to be a common mechanism for promoting courtship in dominant individuals. We also examined expression of androgen receptors, estrogen receptor α, and the progesterone receptor in five brain regions that are important for social behavior. Most of the differences in brain sex steroid receptor expression were due to sex rather than status. Our results suggest that the parvocellular preoptic area is a core region for mediating sex differences through androgen and estrogen receptor expression, whereas the progesterone receptor may mediate sex and status behaviors in the putative homologs of the nucleus accumbens and ventromedial hypothalamus. Overall our results suggest sex differences and similarities in the regulation of social dominance by gonadal hormones and their receptors in the brain. 相似文献
103.
104.
Cancer initiation, progression, and the emergence of therapeutic resistance are evolutionary phenomena of clonal somatic cell populations. Studies in microbial experimental evolution and the theoretical work inspired by such studies are yielding deep insights into the evolutionary dynamics of clonal populations, yet there has been little explicit consideration of the relevance of this rapidly growing field to cancer biology. Here, we examine how the understanding of mutation, selection, and spatial structure in clonal populations that is emerging from experimental evolution may be applicable to cancer. Along the way, we discuss some significant ways in which cancer differs from the model systems used in experimental evolution. Despite these differences, we argue that enhanced prediction and control of cancer may be possible using ideas developed in the context of experimental evolution, and we point out some prospects for future research at the interface between these traditionally separate areas. 相似文献
105.
Joseph A. Jurcisek Amanda C. Dickson Molly E. Bruggeman Lauren O. Bakaletz 《Journal of visualized experiments : JoVE》2011,(47)
The chronic nature of many diseases is attributed to the formation of bacterial biofilms which are recalcitrant to traditional antibiotic therapy. Biofilms are community-associated bacteria attached to a surface and encased in a matrix. The role of the extracellular matrix is multifaceted, including facilitating nutrient acquisition, and offers significant protection against environmental stresses (e.g. host immune responses). In an effort to acquire a better understanding as to how the bacteria within a biofilm respond to environmental stresses we have used a protocol wherein we visualize bacterial biofilms which have formed in an 8-well chamber slide. The biofilms were stained with the BacLight Live/Dead stain and examined using a confocal microscope to characterize the relative biofilm size, and structure under varying incubation conditions. Z-stack images were collected via confocal microscopy and analyzed by COMSTAT. This protocol can be used to help elucidate the mechanism and kinetics by which biofilms form, as well as identify components that are important to biofilm structure and stability. 相似文献
106.
Davies TJ Buckley LB Grenyer R Gittleman JL 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2011,366(1577):2526-2535
Within most terrestrial groups of animals, including mammals, species richness varies along two axes of environmental variation, representing energy availability and plant productivity. This relationship has led to a search for mechanistic links between climate and diversity. Explanations have traditionally focused on single mechanisms, such as variation in environmental carrying capacity or evolutionary rates. Consensus, though, has proved difficult to achieve and there is growing appreciation that geographical patterns of species richness are a product of many interacting factors including biogeographic history and biological traits. Here, we review some current hypotheses on the causes of gradients in mammal richness and range sizes since the two quantities are intimately linked. We then present novel analyses using recent datasets to explore the structure of the environment-richness relationship for mammals. Specifically, we consider the impact of glaciation on present day mammalian diversity gradients. We conclude that not only are multiple processes important in structuring diversity gradients, but also that different processes predominate in different places. 相似文献
107.
108.
Pepper J Cheng D Stanbridge R Ferdinand FD Jamieson WR Stelzer P Berg G Sani G Martin J 《Innovations (Philadelphia, Pa.)》2009,4(2):49-60
OBJECTIVE:: The purpose of this consensus conference was to determine whether stentless bioprosthetic valves improve clinical and resource outcomes compared with stented valves in patients undergoing aortic valve replacement, and to outline evidence-based recommendations for the use of stentless and stented bioprosthetic valves in adult aortic valve replacement. METHODS:: Before the consensus conference, the best available evidence was reviewed in that systematic reviews, randomized trials, and nonrandomized trials were considered in descending order of validity and importance. At the consensus conference, evidence-based statements were created, and consensus processes were used to determine the ensuing recommendations. The American Heart Association/American College of Cardiology system was used to label the level of evidence and class of recommendation. RESULTS AND RECOMMENDATIONS:: Seventeen randomized studies published in 23 articles involving 1317 patients, and 14 nonrandomized trial published in 18 articles involving 2485 patients were included in the meta-analysis and consensus conference. All randomized trials inserted the stentless bioprosthetic valves in the subcoronary configuration. The consensus panel agreed upon the following statements and recommendations in patients undergoing aortic valve replacement:Because there were no randomized control trial comparing subcoronary stentless prosthetic valve and root replacement, the following recommendations are derived from expert opinion: 相似文献
109.
Lauren G. MacNeil Elisa Glover T. Graham Bergstra Adeel Safdar Mark A. Tarnopolsky 《PloS one》2014,9(10)
Concurrent exercise combines different modes of exercise (e.g., aerobic and resistance) into one training protocol, providing stimuli meant to increase muscle strength, aerobic capacity and mass. As disuse is associated with decrements in strength, aerobic capacity and muscle size concurrent training is an attractive modality for rehabilitation. However, interference between the signaling pathways may result in preferential improvements for one of the exercise modes. We recruited 18 young adults (10 ♂, 8 ♀) to determine if order of exercise mode during concurrent training would differentially affect gene expression, protein content and measures of strength and aerobic capacity after 2 weeks of knee-brace induced disuse. Concurrent exercise sessions were performed 3x/week for 6 weeks at gradually increasing intensities either with endurance exercise preceding (END>RES) or following (RES>END) resistance exercise. Biopsies were collected from the vastus lateralis before, 3 h after the first exercise bout and 48 h after the end of training. Concurrent exercise altered the expression of genes involved in mitochondrial biogenesis (PGC-1α, PRC, PPARγ), hypertrophy (PGC-1α4, REDD2, Rheb) and atrophy (MuRF-1, Runx1), increased electron transport chain complex protein content, citrate synthase and mitochondrial cytochrome c oxidase enzyme activity, muscle mass, maximum isometric strength and VO2peak. However, the order in which exercise was completed (END>RES or RES>END) only affected the protein content of mitochondrial complex II subunit. In conclusion, concurrent exercise training is an effective modality for the rehabilitation of the loss of skeletal muscle mass, maximum strength, and peak aerobic capacity resulting from disuse, regardless of the order in which the modes of exercise are performed. 相似文献
110.
Mani SA Guo W Liao MJ Eaton EN Ayyanan A Zhou AY Brooks M Reinhard F Zhang CC Shipitsin M Campbell LL Polyak K Brisken C Yang J Weinberg RA 《Cell》2008,133(4):704-715
The epithelial-mesenchymal transition (EMT) is a key developmental program that is often activated during cancer invasion and metastasis. We here report that the induction of an EMT in immortalized human mammary epithelial cells (HMLEs) results in the acquisition of mesenchymal traits and in the expression of stem-cell markers. Furthermore, we show that those cells have an increased ability to form mammospheres, a property associated with mammary epithelial stem cells. Independent of this, stem cell-like cells isolated from HMLE cultures form mammospheres and express markers similar to those of HMLEs that have undergone an EMT. Moreover, stem-like cells isolated either from mouse or human mammary glands or mammary carcinomas express EMT markers. Finally, transformed human mammary epithelial cells that have undergone an EMT form mammospheres, soft agar colonies, and tumors more efficiently. These findings illustrate a direct link between the EMT and the gain of epithelial stem cell properties. 相似文献