全文获取类型
收费全文 | 7303篇 |
免费 | 574篇 |
国内免费 | 1篇 |
专业分类
7878篇 |
出版年
2023年 | 57篇 |
2022年 | 107篇 |
2021年 | 222篇 |
2020年 | 141篇 |
2019年 | 153篇 |
2018年 | 172篇 |
2017年 | 152篇 |
2016年 | 252篇 |
2015年 | 421篇 |
2014年 | 445篇 |
2013年 | 527篇 |
2012年 | 675篇 |
2011年 | 635篇 |
2010年 | 391篇 |
2009年 | 359篇 |
2008年 | 499篇 |
2007年 | 424篇 |
2006年 | 413篇 |
2005年 | 351篇 |
2004年 | 310篇 |
2003年 | 245篇 |
2002年 | 260篇 |
2001年 | 47篇 |
2000年 | 42篇 |
1999年 | 50篇 |
1998年 | 43篇 |
1997年 | 36篇 |
1996年 | 32篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 17篇 |
1992年 | 39篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有7878条查询结果,搜索用时 15 毫秒
61.
Abbas F Morellet N Hewison AJ Merlet J Cargnelutti B Lourtet B Angibault JM Daufresne T Aulagnier S Verheyden H 《Oecologia》2011,167(2):401-411
Forest fragmentation may benefit generalist herbivores by increasing access to various substitutable food resources, with
potential consequences for their population dynamics. We studied a European roe deer (Capreolus capreolus) population living in an agricultural mosaic of forest, woodlots, meadows and cultivated crops. We tested whether diet composition
and quality varied spatially across the landscape using botanical analyses of rumen contents and chemical analyses of the
plants consumed in relation to landscape metrics. In summer and non-mast winters, roe deer ate more cultivated seeds and less
native forest browse with increasing availability of crops in the local landscape. This spatial variation resulted in contrasting
diet quality, with more cell content and lower lignin and hemicellulose content (high quality) for individuals living in more
open habitats. The pattern was less marked in the other seasons when diet composition, but not diet quality, was only weakly
related to landscape structure. In mast autumns and winters, the consumption of acorns across the entire landscape resulted
in a low level of differentiation in diet composition and quality. Our results reflect the ability of generalist species,
such as roe deer, to adapt to the fragmentation of their forest habitat by exhibiting a plastic feeding behavior, enabling
them to use supplementary resources available in the agricultural matrix. This flexibility confers nutritional advantages
to individuals with access to cultivated fields when their native food resources are depleted or decline in quality (e.g.
during non-mast years) and may explain local heterogeneities in individual phenotypic quality. 相似文献
62.
63.
Karim Arafah Sbastien Nicolas Voisin Victor Masson Cdric Alaux Yves Le Conte Michel Bocquet Philippe Bulet 《Proteomics》2019,19(23)
Honey bees play a critical role in the maintenance of plant biodiversity and sustainability of food webs. In the past few decades, bees have been subjected to biotic and abiotic threats causing various colony disorders. Therefore, monitoring solutions to help beekeepers to improve bee health are necessary. Matrix‐assisted laser desorption ionization–mass spectrometry (MALDI–MS) profiling has emerged within this decade as a powerful tool to identify in routine micro‐organisms and is currently used in real‐time clinical diagnosis. MALDI BeeTyping is developed to monitor significant hemolymph molecular changes in honey bees upon infection with a series of entomopathogenic Gram‐positive and ‐negative bacteria. A Serratia marcescens strain isolated from one naturally infected honey bee collected from the field is also considered. A series of hemolymph molecular mass fingerprints is individually recorded and to the authors' knowledge, the first computational model harboring a predictive score of 97.92% and made of nine molecular signatures that discriminate and classify the honey bees’ systemic response to the bacteria is built. Hence, the model is challenged by classifying a training set of hemolymphs and an overall recognition of 91.93% is obtained. Through this work, a novel, time and cost saving high‐throughput strategy that addresses honey bee health on an individual scale is introduced. 相似文献
64.
Beno?te Méry Jean-Baptiste Guy Sophie Espenel Anne-Sophie Wozny Stéphanie Simonet Alexis Vallard Gersende Alphonse Dominique Ardail Claire Rodriguez-Lafrasse Nicolas Magné 《World journal of stem cells》2016,8(1):13-21
Head and neck squamous cell cancer(HNSCC) is the sixth most common cancer in the world. Effective therapeutic modalities such as surgery, radiation, chemotherapy and combinations of each are used in the management of the disease. In most cases, treatment fails to obtain total cancer cure. In recent years, it appears that one of the key determinants of treatment failure may be the presence of cancer stem cells(CSCs) that escape currently available therapies. CSCs form a small portion of the total tumor burden but may play a disproportionately important role in determining outcomes. CSCs have stem features such as self-renewal, high migration capacity, drug resistance, high proliferation abilities. A large body of evidence points to the fact that CSCs are particularly resistant to radiotherapy and chemotherapy. In HNSCC, CSCs have been increasingly shown to have an integral role in tumor initiation, disease progression, metastasis and treatment resistance. In the light of such observations, the present review summarizes biological characteristics of CSCs in HNSCC, outlines targeted strategies for the successful eradication of CSCs in HNSCC including targeting the self-renewal controlling pathways, blocking epithelial mesenchymal transition, niche targeting, immunotherapy approaches and highlights the need to better understand CSCs biology for new treatments modalities. 相似文献
65.
Julien Cappelle Delong Zhao Marius Gilbert Martha I. Nelson Scott H. Newman John Y. Takekawa Nicolas Gaidet Diann J. Prosser Ying Liu Peng Li Yuelong Shu Xiangming Xiao 《EcoHealth》2014,11(1):109-119
For decades, southern China has been considered to be an important source for emerging influenza viruses since key hosts live together in high densities in areas with intensive agriculture. However, the underlying conditions of emergence and spread of avian influenza viruses (AIV) have not been studied in detail, particularly the complex spatiotemporal interplay of viral transmission between wild and domestic ducks, two major actors of AIV epidemiology. In this synthesis, we examine the risks of avian influenza spread in Poyang Lake, an area of intensive free-ranging duck production and large numbers of wild waterfowl. Our synthesis shows that farming of free-grazing domestic ducks is intensive in this area and synchronized with wild duck migration. The presence of juvenile domestic ducks in harvested paddy fields prior to the arrival and departure of migrant ducks in the same fields may amplify the risk of AIV circulation and facilitate the transmission between wild and domestic populations. We provide evidence associating wild ducks migration with the spread of H5N1 in the spring of 2008 from southern China to South Korea, Russia, and Japan, supported by documented wild duck movements and phylogenetic analyses of highly pathogenic avian influenza H5N1 sequences. We suggest that prevention measures based on a modification of agricultural practices may be implemented in these areas to reduce the intensity of AIV transmission between wild and domestic ducks. This would require involving all local stakeholders to discuss feasible and acceptable solutions. 相似文献
66.
Membranes of adjacent cells form intercellular junctional complexes to mechanically anchor neighbour cells (anchoring junctions), to seal the paracellular space and to prevent diffusion of integral proteins within the plasma membrane (tight junctions) and to allow cell-to-cell diffusion of small ions and molecules (gap junctions). These different types of specialised plasma membrane microdomains, sharing common adaptor molecules, particularly zonula occludens proteins, frequently present intermingled relationships where the different proteins co-assemble into macromolecular complexes and their expressions are co-ordinately regulated. Proteins forming gap junction channels (connexins, particularly) and proteins fulfilling cell attachment or forming tight junction strands mutually influence expression and functions of one another. 相似文献
67.
Erythrocytic cell kinetics were studied in normal dog bone marrow, at the transition between younger cells that are able to synthesize DNA, and more mature nucleated normoblasts which have lost this ability. the rate of progression out of the first group was compared to that into the second, after necessary adjustments of group sizes. No significant discrepancy was detected within the limits of resolution of autoradiographic cytokinetic analysis.
It is concluded that 'ineffective' red cell production in the normal dog, if it occurs at all, can only be very small in quantity. 相似文献
It is concluded that 'ineffective' red cell production in the normal dog, if it occurs at all, can only be very small in quantity. 相似文献
68.
Nicolas Tromas Zofia E. Taranu Mathieu Castelli Juliana S. M. Pimentel Daniel A. Pereira Romane Marcoz B. Jesse Shapiro Alessandra Giani 《Environmental microbiology》2020,22(4):1238-1250
Understanding how ecological traits have changed over evolutionary time is a fundamental question in biology. Specifically, the extent to which more closely related organisms share similar ecological preferences due to phylogenetic conservation – or if they are forced apart by competition – is still debated. Here, we explored the co-occurrence patterns of freshwater cyanobacteria at the sub-genus level to investigate whether more closely related taxa share more similar niches and to what extent these niches were defined by abiotic or biotic variables. We used deep 16S rRNA gene amplicon sequencing and measured several abiotic environmental parameters (nutrients, temperature, etc.) in water samples collected over time and space in Furnas Reservoir, Brazil. We found that relatively more closely related Synechococcus (in the continuous range of 93%–100% nucleotide identity in 16S) had an increased tendency to co-occur with one another (i.e. had similar realized niches). This tendency could not be easily explained by shared preferences for measured abiotic niche dimensions. Thus, commonly measured abiotic parameters might not be sufficient to characterize, nor to predict community assembly or dynamics. Rather, co-occurrence between Synechococcus and the surrounding community (whether or not they represent true biological interactions) may be a more sensitive measure of realized niches. Overall, our results suggest that realized niches are phylogenetically conserved, at least at the sub-genus level and at the resolution of the 16S marker. Determining how these results generalize to other genera and at finer genetic resolution merits further investigation. 相似文献
69.
70.
Lida Katsimpardi Nicolas Kuperwasser Claire Camus Carine Moigneu Aurlie Chiche Virginie Tolle Han Li Erzsebet Kokovay Pierre‐Marie Lledo 《Aging cell》2020,19(1)
Aging is a negative regulator of general homeostasis, tissue function, and regeneration. Changes in organismal energy levels and physiology, through systemic manipulations such as calorie restriction and young blood infusion, can regenerate tissue activity and increase lifespan in aged mice. However, whether these two systemic manipulations could be linked has never been investigated. Here, we report that systemic GDF11 triggers a calorie restriction‐like phenotype without affecting appetite or GDF15 levels in the blood, restores the insulin/IGF‐1 signaling pathway, and stimulates adiponectin secretion from white adipose tissue by direct action on adipocytes, while repairing neurogenesis in the aged brain. These findings suggest that GDF11 has a pleiotropic effect on an organismal level and that it could be a linking mechanism of rejuvenation between heterochronic parabiosis and calorie restriction. As such, GDF11 could be considered as an important therapeutic candidate for age‐related neurodegenerative and metabolic disorders. 相似文献