全文获取类型
收费全文 | 11808篇 |
免费 | 1339篇 |
国内免费 | 3篇 |
专业分类
13150篇 |
出版年
2022年 | 76篇 |
2021年 | 134篇 |
2020年 | 142篇 |
2019年 | 221篇 |
2018年 | 240篇 |
2017年 | 257篇 |
2016年 | 324篇 |
2015年 | 527篇 |
2014年 | 531篇 |
2013年 | 723篇 |
2012年 | 708篇 |
2011年 | 635篇 |
2010年 | 532篇 |
2009年 | 465篇 |
2008年 | 565篇 |
2007年 | 581篇 |
2006年 | 568篇 |
2005年 | 614篇 |
2004年 | 580篇 |
2003年 | 628篇 |
2002年 | 634篇 |
2001年 | 121篇 |
2000年 | 102篇 |
1999年 | 156篇 |
1998年 | 199篇 |
1997年 | 142篇 |
1996年 | 142篇 |
1995年 | 142篇 |
1994年 | 123篇 |
1993年 | 90篇 |
1992年 | 128篇 |
1991年 | 100篇 |
1990年 | 91篇 |
1989年 | 93篇 |
1988年 | 72篇 |
1987年 | 87篇 |
1986年 | 78篇 |
1985年 | 95篇 |
1984年 | 102篇 |
1983年 | 83篇 |
1982年 | 107篇 |
1981年 | 119篇 |
1980年 | 90篇 |
1979年 | 92篇 |
1978年 | 90篇 |
1977年 | 80篇 |
1976年 | 83篇 |
1975年 | 53篇 |
1974年 | 73篇 |
1973年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
John P. DeLong Valery E. Forbes Nika Galic Jean P. Gibert Robert G. Laport Joseph S. Phillips Janna M. Vavra 《Ecology and evolution》2016,6(2):573-581
It is increasingly recognized that evolution may occur in ecological time. It is not clear, however, how fast evolution – or phenotypic change more generally – may be in comparison with the associated ecology, or whether systems with fast ecological dynamics generally have relatively fast rates of phenotypic change. We developed a new dataset on standardized rates of change in population size and phenotypic traits for a wide range of species and taxonomic groups. We show that rates of change in phenotypes are generally no more than 2/3, and on average about 1/4, the concurrent rates of change in population size. There was no relationship between rates of population change and rates of phenotypic change across systems. We also found that the variance of both phenotypic and ecological rates increased with the mean across studies following a power law with an exponent of two, while temporal variation in phenotypic rates was lower than in ecological rates. Our results are consistent with the view that ecology and evolution may occur at similar time scales, but clarify that only rarely do populations change as fast in traits as they do in abundance. 相似文献
942.
943.
944.
Juliana Santana Reis Marcos Antonio Corrêa Clovis Augusto Ribeiro Jean Leandro Dos Santos 《Bioorganic & medicinal chemistry letters》2019,29(24):126755
The incidence of skin cancers such as non-melanoma skin cancer and malignant melanoma has increased in the last few years mainly because of chronic exposure to ultraviolet (UV) radiation. Sunscreens protect the skin against harmful UV radiations; however, some limitations of these products justify the discovery of new UV filters. Novel 1,3,5-triazine derivatives (12a-h) obtained by the optimization of prototype resveratrol were synthesized and characterized. All compounds exhibited sun protection factor (SPF) and UVA protection factor (UVAPF) in the range of 3–17 and 3–13, respectively. These values were superior to resveratrol and the UV filter ethylhexyl triazone (EHT) currently available on the market. In addition, all compounds demonstrated in vitro antioxidant activity and thermal stability with the decomposition at temperatures above 236 °C. In conclusion, the novel 1,3,5-triazine derivatives have emerged as new UV filters with antioxidant effect useful to prevent skin cancer. 相似文献
945.
Sabrina Renaud Claire Delpine Ronan Ledevin Benoît Pisanu Jean‐Pierre Qur Emilie A. Hardouin 《Journal of Zoological Systematics and Evolutionary Research》2019,57(4):989-999
The house mouse (Mus musculus domesticus), as a successful invasive species worldwide, has to forage a variety of resources. Subantarctic mice display among the most notable diet shift from the usual omnivorous–granivorous diet, relying on a larger proportion of terrestrial animal prey. In agreement, a recent study of their mandible morphology evidenced an evolution of their mandible shape to optimize incisor biting and hence seize preys. Here, the incisors themselves are the focus of a morphometric analysis combined with a 3D study of their internal structure, aiming at a comparison between subantarctic populations (Guillou island, Kerguelen archipelago) with a range of western European continental, commensal mice. The predatory foraging behavior of Guillou mice was indeed associated with a sharper bevel of the lower incisor, which appears as an efficient morphology for piercing prey. The incisor of these mice also displays a reduced pulp cavity, suggesting slower eruption counterbalancing a reduced abrasion on such soft food material. The dynamics of the ever‐growing incisor may thus allow adaptive incisor sculpting and participate to the success of mice in foraging diverse resources. 相似文献
946.
Pereira Felipe Walter Vitule Jean Ricardo Simões 《Reviews in Fish Biology and Fisheries》2019,29(3):639-652
Reviews in Fish Biology and Fisheries - Biological invasions via anthropogenic vectors, intentional or not, are one of the main causes of ecological change in aquatic ecosystems. Micropterus... 相似文献
947.
948.
949.
Frison M Parrou JL Guillaumot D Masquelier D François J Chaumont F Batoko H 《FEBS letters》2007,581(21):4010-4016
The lack of trehalose accumulation in most plant species has been partly attributed to the presence of an active trehalase. Although trehalose synthesis enzymes are thought to be cytosolic, and previous studies have indicated that trehalase activity is extracellular, the exact location of the enzyme has not yet been established in plant cell. We present evidence that the yet uncharacterised full-length Arabidopsis trehalase is a plasma membrane-bound protein, probably anchored to the membrane through a predicted N-terminal membrane spanning domain. The full-length AtTRE1, when expressed in yeast can functionally substitute for the extracellularly active trehalase Ath1p, by sustaining the growth of an ath1 null mutant strain on trehalose and at pH 4.8. We further demonstrate that AtTRE1 expressed in yeast is plasma membrane-bound as in plant cell. In light of these findings, the regulation of plant cell endogenous trehalose by trehalase is discussed. 相似文献
950.
Kindrachuk J Potter JE Brownlie R Ficzycz AD Griebel PJ Mookherjee N Mutwiri GK Babiuk LA Napper S 《The Journal of biological chemistry》2007,282(19):13944-13953
Toll-like receptor 9 (TLR9) activates the innate immune system in response to microbial DNA or mimicking oligodeoxynucleotides. Although cell stimulation experiments demonstrate the preferential activation of TLR9 by CpG-containing nucleic acids, direct binding investigations have reached contradictory conclusions with respect to the ability of this receptor to bind nucleic acids in a sequence-specific manner. To address this apparent discrepancy, we report the purification of the soluble ectodomain of human TLR9 with characterization of its ligand binding properties. We observe that TLR9 has a high degree of specificity in its ability to bind nucleic acids that contain CpG dinucleotides as well as higher order motifs that mediate species-specific activation. However, TLR9 is also functionally influenced by nucleic acids in a sequence-independent fashion as both stimulatory and nonstimulatory nucleic acids sensitize TLR9 for in vitro ligand binding as well as in vivo activation. We propose a model in which receptor activation is achieved in a sequence-dependent manner, and sensitivity is modulated by the absolute concentration of nucleic acids in a sequence-independent fashion. This model bears resemblance to that recently proposed for Toll in that activation is a two-step process in which formation of a ligand-bound monomer precedes formation of the activated dimer. In each model receptor sensitivity is determined within the second step with the crucial distinction that Toll undergoes negative cooperativity, whereas TLR9 is sensitized through a positive cooperative effect. 相似文献