全文获取类型
收费全文 | 198篇 |
免费 | 26篇 |
专业分类
224篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 15篇 |
2013年 | 11篇 |
2012年 | 20篇 |
2011年 | 23篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 16篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 12篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 0 毫秒
51.
52.
Olle Lind Tony Sunesson Mindaugas Mitkus Almut Kelber 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2012,198(1):69-77
Budgerigars (Melopsittacus undulatus) and Bourke’s parrots (Neopsephotus bourkii) are closely related birds with different activity patterns. Budgerigars are strictly diurnal while Bourke’s parrots are
active in dim twilight. Earlier studies show that the intensity threshold of colour vision is similar in both species while
Bourke’s parrots have larger eyes with a higher density of rods than budgerigars. In this study, we investigate whether this
could be an adaptation for better spatial vision in dim light. We used two alternative forced-choice experiments to determine
the spatial acuity of both species at light intensities ranging from 0.08 to 73 cd/m2. We also determined the spatial contrast sensitivity function (CSF) for bright light in Bourke’s parrots and compare it to
existing data for budgerigars. The spatial acuity of Bourke’s parrots was found to be similar to that of budgerigars at all
light levels. Also the CSF of Bourke’s parrots is similar to that of budgerigars with a sensitivity peak located between 2.1
and 2.6 cycles/degree. Our findings do not support the hypothesis that Bourke’s parrots have superior spatial acuity in dim
light compared to budgerigars and the adaptive value of the relatively rod-rich and large eyes of Bourke’s parrots remains
unclear. 相似文献
53.
M Busse M Krech A Meyer-Bahlburg C Hennig G Hansen 《Journal of immunology (Baltimore, Md. : 1950)》2012,189(4):1975-1982
Costimulatory molecules like ICOS are crucial in mediating T cell differentiation and function after allergen contact and thereby strongly affect the immunologic decision between tolerance or allergy development. In this study, we show in two independent approaches that interruption of the ICOS signaling pathway by application of a blocking anti-ICOSL mAb in wild-type (WT) mice and in ICOS(-/-) mice inhibited respiratory tolerance development leading to eosinophilic airway inflammation, mucus hypersecretion, and Th2 cytokine production in response to OVA sensitization. Respiratory Ag application almost doubled the number of CD4(+)Foxp3(+) regulatory T cells (Tregs) in the lung of WT mice with 77% of lung-derived Tregs expressing ICOS. In contrast, in ICOS(-/-) mice the number of CD4(+)CD25(+)Foxp3(+) Tregs did not increase after respiratory Ag application, and ICOS(-/-) Tregs produced significantly lower amounts of IL-10 than those of WT Tregs. Most importantly, in contrast to WT Tregs, ICOS(-/-) Tregs did not convey protection when transferred to "asthmatic" recipients demonstrating a strongly impaired Treg function in the absence of ICOS signaling. Our findings demonstrate a crucial role of ICOS for the generation and suppressive function of Tregs conveying respiratory tolerance and support the importance of ICOS as a target for primary prevention strategies. 相似文献
54.
Pete Smith Katherine Calvin Johnson Nkem Donovan Campbell Francesco Cherubini Giacomo Grassi Vladimir Korotkov Anh Le Hoang Shuaib Lwasa Pamela McElwee Ephraim Nkonya Nobuko Saigusa Jean‐Francois Soussana Miguel Angel Taboada Frances C. Manning Dorothy Nampanzira Cristina Arias‐Navarro Matteo Vizzarri Jo House Stephanie Roe Annette Cowie Mark Rounsevell Almut Arneth 《Global Change Biology》2020,26(3):1532-1575
There is a clear need for transformative change in the land management and food production sectors to address the global land challenges of climate change mitigation, climate change adaptation, combatting land degradation and desertification, and delivering food security (referred to hereafter as “land challenges”). We assess the potential for 40 practices to address these land challenges and find that: Nine options deliver medium to large benefits for all four land challenges. A further two options have no global estimates for adaptation, but have medium to large benefits for all other land challenges. Five options have large mitigation potential (>3 Gt CO2eq/year) without adverse impacts on the other land challenges. Five options have moderate mitigation potential, with no adverse impacts on the other land challenges. Sixteen practices have large adaptation potential (>25 million people benefit), without adverse side effects on other land challenges. Most practices can be applied without competing for available land. However, seven options could result in competition for land. A large number of practices do not require dedicated land, including several land management options, all value chain options, and all risk management options. Four options could greatly increase competition for land if applied at a large scale, though the impact is scale and context specific, highlighting the need for safeguards to ensure that expansion of land for mitigation does not impact natural systems and food security. A number of practices, such as increased food productivity, dietary change and reduced food loss and waste, can reduce demand for land conversion, thereby potentially freeing‐up land and creating opportunities for enhanced implementation of other practices, making them important components of portfolios of practices to address the combined land challenges. 相似文献
55.
Sunkyu Choi Jonathan Kelber Xinning Jiang Jan Strnadel Ken Fujimura Martina Pasillas Judith Coppinger Richard Klemke 《Analytical biochemistry》2014
The cell cytoskeleton is composed of microtubules, intermediate filaments, and actin that provide a rigid support structure important for cell shape. However, it is also a dynamic signaling scaffold that receives and transmits complex mechanosensing stimuli that regulate normal physiological and aberrant pathophysiological processes. Studying cytoskeletal functions in the cytoskeleton’s native state is inherently difficult due to its rigid and insoluble nature. This has severely limited detailed proteomic analyses of the complex protein networks that regulate the cytoskeleton. Here, we describe a purification method that enriches for the cytoskeleton and its associated proteins in their native state that is also compatible with current mass spectrometry-based protein detection methods. This method can be used for biochemical, fluorescence, and large-scale proteomic analyses of numerous cell types. Using this approach, 2346 proteins were identified in the cytoskeletal fraction of purified mouse embryonic fibroblasts, of which 635 proteins were either known cytoskeleton proteins or cytoskeleton-interacting proteins. Functional annotation and network analyses using the Ingenuity Knowledge Database of the cytoskeletome revealed important nodes of interconnectivity surrounding well-established regulators of the actin cytoskeleton and focal adhesion complexes. This improved cytoskeleton purification method will aid our understanding of how the cytoskeleton controls normal and diseased cell functions. 相似文献
56.
57.
Christopher Weidner Sylvia J. Wowro Morten Rousseau Anja Freiwald Vitam Kodelja Heba Abdel-Aziz Olaf Kelber Sascha Sauer 《PloS one》2013,8(11)
Given the significant increases in the incidence of metabolic diseases, efficient strategies for preventing and treating of these common disorders are urgently needed. This includes the development of phytopharmaceutical products or functional foods to prevent or cure metabolic diseases. Plant extracts from edible biomaterial provide a potential resource of structurally diverse molecules that can synergistically interfere with complex disorders. In this study we describe the safe application of ethanolic chamomile (Matricaria recutita) flowers extract (CFE) for the treatment and prevention of type 2 diabetes and associated disorders. We show in vitro that this extract activates in particular nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) and its isotypes. In a cellular context, in human primary adipocytes CFE administration (300 µg/ml) led to specific expression of target genes of PPARγ, whereas in human hepatocytes CFE-induced we detected expression changes of genes that were regulated by PPARα. In vivo treatment of insulin-resistant high-fat diet (HFD)-fed C57BL/6 mice with CFE (200 mg/kg/d) for 6 weeks considerably reduced insulin resistance, glucose intolerance, plasma triacylglycerol, non-esterified fatty acids (NEFA) and LDL/VLDL cholesterol. Co-feeding of lean C57BL/6 mice a HFD with 200 mg/kg/d CFE for 20 weeks showed effective prevention of fatty liver formation and hepatic inflammation, indicating additionally hepatoprotective effects of the extract. Moreover, CFE treatment did not reveal side effects, which have otherwise been associated with strong synthetic PPAR-targeting molecules, such as weight gain, liver disorders, hemodilution or bone cell turnover. Taken together, modulation of PPARs and other factors by chamomile flowers extract has the potential to prevent or treat type 2 diabetes and related disorders. 相似文献
58.
59.
High-resolution analysis of Y-chromosomal polymorphisms reveals signatures of population movements from central Asia and West Asia into India 总被引:6,自引:0,他引:6
Linguistic evidence suggests that West Asia and Central Asia have been the two major geographical sources of genes in the
contemporary Indian gene pool. To test the nature and extent of similarities in the gene pools of these regions we have collected
DNA samples from four ethnic populations of northern India, and have screened these samples for a set of 18 Y-chromosome polymorphic
markers (12 unique event polymorphisms and six short tandem repeats). These data from Indian populations have been analysed
in conjunction with published data from several West Asian and Central Asian populations. Our analyses have revealed traces
of population movement from Central Asia and West Asia into India. Two haplogroups, HG-3 and HG-9, which are known to have
arisen in the Central Asian region, are found in reasonably high frequencies (41.7% and 14.3% respectively) in the study populations.
The ages estimated for these two haplogroups are less in the Indian populations than those estimated from data on Middle Eastern
populations. A neighbour-joining tree based on Y-haplogroup frequencies shows that the North Indians are genetically placed
between the West Asian and Central Asian populations. This is consistent with gene flow from West Asia and Central Asia into
India. 相似文献
60.
Almut G. Jones 《Brittonia》1980,32(2):230-239
In order effectively to list and comment on the results of cytological investigations inAster in a companion paper, a scheme of infrageneric classification is presented which utilizes the basic chromosome number as a pivotal diagnostic character. Reasons are stated as to why, with the exception ofUnamia Greene which is transferred toSolidago, and the commonly recognized generaLeucelene Greene,Machaeranthera Nees andXylorhiza Nutt., none of the segregate genera previously proposed or recorded in the literature is upheld. Instead, these taxa are being given subgeneric or sectional rank. Two additional subgenera are established to accommodate the species groups traditionally placed in “Aster proper,” which are characterized by having basic chromosome numbers ofx = 5 andx = 8, respectively. Altogether ten subgenera of the genusAster, five of them subdivided further into a total of 24 sections, are recognized as having representative species in the New World. All basionyms and type species are listed, and a number of new combinations and status changes are validated in accordance with the International Rules of Botanical Nomenclature. Where known (from literature and personal research), chromosome numbers are recorded for the species. 相似文献