全文获取类型
收费全文 | 9328篇 |
免费 | 837篇 |
国内免费 | 12篇 |
专业分类
10177篇 |
出版年
2023年 | 41篇 |
2022年 | 116篇 |
2021年 | 197篇 |
2020年 | 104篇 |
2019年 | 141篇 |
2018年 | 187篇 |
2017年 | 185篇 |
2016年 | 265篇 |
2015年 | 460篇 |
2014年 | 502篇 |
2013年 | 646篇 |
2012年 | 796篇 |
2011年 | 767篇 |
2010年 | 502篇 |
2009年 | 423篇 |
2008年 | 650篇 |
2007年 | 596篇 |
2006年 | 556篇 |
2005年 | 536篇 |
2004年 | 488篇 |
2003年 | 438篇 |
2002年 | 434篇 |
2001年 | 93篇 |
2000年 | 59篇 |
1999年 | 81篇 |
1998年 | 115篇 |
1997年 | 70篇 |
1996年 | 57篇 |
1995年 | 35篇 |
1994年 | 51篇 |
1993年 | 41篇 |
1992年 | 34篇 |
1991年 | 33篇 |
1990年 | 41篇 |
1989年 | 29篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 28篇 |
1985年 | 22篇 |
1984年 | 30篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 28篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 19篇 |
1977年 | 16篇 |
1974年 | 21篇 |
1972年 | 16篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Genetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa 下载免费PDF全文
Johannes J. Le Roux Llewellyn C. Foxcroft Marna Herbst Sandra MacFadyen 《Ecology and evolution》2015,5(2):288-299
Hybridization between domestic and wild animals is a major concern for biodiversity conservation, and as habitats become increasingly fragmented, conserving biodiversity at all levels, including genetic, becomes increasingly important. Except for tropical forests and true deserts, African wildcats occur across the African continent; however, almost no work has been carried out to assess its genetic status and extent of hybridization with domestic cats. For example, in South Africa it has been argued that the long‐term viability of maintaining pure wildcat populations lies in large protected areas only, isolated from human populations. Two of the largest protected areas in Africa, the Kgalagadi Transfrontier and Kruger National Parks, as well as the size of South Africa and range of landscape uses, provide a model situation to assess how habitat fragmentation and heterogeneity influences the genetic purity of African wildcats. Using population genetic and home range data, we examined the genetic purity of African wildcats and their suspected hybrids across South Africa, including areas within and outside of protected areas. Overall, we found African wildcat populations to be genetically relatively pure, but instances of hybridization and a significant relationship between the genetic distinctiveness (purity) of wildcats and human population pressure were evident. The genetically purest African wildcats were found in the Kgalagadi Transfrontier Park, while samples from around Kruger National Park showed cause for concern, especially combined with the substantial human population density along the park's boundary. While African wildcat populations in South Africa generally appear to be genetically pure, with low levels of hybridization, our genetic data do suggest that protected areas may play an important role in maintaining genetic purity by reducing the likelihood of contact with domestic cats. We suggest that approaches such as corridors between protected areas are unlikely to remain effective for wildcat conservation, as the proximity to human settlements around these areas is projected to increase the wild/domestic animal interface. Thus, large, isolated protected areas will become increasingly important for wildcat conservation and efforts need to be made to prevent introduction of domestic cats into these areas. 相似文献
982.
Tanaka KS Houghton TJ Kang T Dietrich E Delorme D Ferreira SS Caron L Viens F Arhin FF Sarmiento I Lehoux D Fadhil I Laquerre K Liu J Ostiguy V Poirier H Moeck G Parr TR Rafai Far A 《Bioorganic & medicinal chemistry》2008,16(20):9217-9229
Osteomyelitis is a difficult to treat bacterial infection of the bone. Delivering antibacterial agents to the bone may overcome the difficulties in treating this illness by effectively concentrating the antibiotic at the site of infection and by limiting the toxicity that may result from systemic exposure to the large doses conventionally used. Using bisphosphonates as osteophilic functional groups, different forms of fluoroquinolone esters were synthesized and evaluated for their ability to bind bone and to release the parent antibacterial agent. Bisphosphonated glycolamide fluoroquinolone esters were found to present a profile consistent with effective and rapid bone binding and efficient release of the active drug moiety. They were assessed for their ability to prevent bone infection in vivo and were found to be effective when the free fluoroquinolones were not. 相似文献
983.
Hoeberichts FA Vaeck E Kiddle G Coppens E van de Cotte B Adamantidis A Ormenese S Foyer CH Zabeau M Inzé D Périlleux C Van Breusegem F Vuylsteke M 《The Journal of biological chemistry》2008,283(9):5708-5718
Eukaryotic phosphomannomutases (PMMs) catalyze the interconversion of mannose 6-phosphate to mannose 1-phosphate and are essential to the biosynthesis of GDP-mannose. As such, plant PMMs are involved in ascorbic acid (AsA) biosynthesis and N-glycosylation. We report on the conditional phenotype of the temperature-sensitive Arabidopsis thaliana pmm-12 mutant. Mutant seedlings were phenotypically similar to wild type seedlings when grown at 16-18 degrees C but died within several days after transfer to 28 degrees C. This phenotype was observed throughout both vegetative and reproductive development. Protein extracts derived from pmm-12 plants had lower PMM protein and enzyme activity levels. In vitro biochemical analysis of recombinant proteins showed that the mutant PMM protein was compromised in its catalytic efficiency (K cat/K m). Despite significantly decreased AsA levels in pmm-12 plants, AsA deficiency could not account for the observed phenotype. Since, at restrictive temperature, total glycoprotein patterns were altered and glycosylation of protein-disulfide isomerase was perturbed, we propose that a deficiency in protein glycosylation is responsible for the observed cell death phenotype. 相似文献
984.
985.
Trypanosoma cruzi macrophage infectivity potentiator has a rotamase core and a highly exposed α-helix 下载免费PDF全文
Pedro José Barbosa Pereira M. Cristina Vega Elena González-Rey Rafael Fernández-Carazo Sandra Macedo-Ribeiro F. Xavier Gomis-Rüth Antonio González Miquel Coll 《EMBO reports》2002,3(1):88-94
The macrophage infectivity potentiator protein from Trypanosoma cruzi (TcMIP) is a major virulence factor secreted by the etiological agent of Chagas’ disease. It is functionally involved in host cell invasion. We have determined the three-dimensional crystal structure of TcMIP at 1.7 Å resolution. The monomeric protein displays a peptidyl-prolyl cis–trans isomerase (PPIase) core, encompassing the characteristic rotamase hydrophobic active site, thus explaining the strong inhibition of TcMIP by the immunosuppressant FK506 and related drugs. In TcMIP, the twisted β-sheet of the core is extended by an extra β-strand, preceded by a long, exposed N-terminal α-helix, which might be a target recognition element. An invasion assay shows that the MIP protein from Legionella pneumophila (LpMIP), which has an equivalent N-terminal α-helix, can substitute for TcMIP. An additional exposed α-helix, this one unique to TcMIP, is located in the C-terminus of the protein. The high-resolution structure reported here opens the possibility for the design of new inhibitory drugs that might be useful for the clinical treatment of American trypanosomiasis. 相似文献
986.
The S4 genome segment of baboon reovirus is bicistronic and encodes a novel fusion-associated small transmembrane protein 下载免费PDF全文
We demonstrate that the S4 genome segment of baboon reovirus (BRV) contains two sequential partially overlapping open reading frames (ORFs), both of which are functional in vitro and in virus-infected cells. The 15-kDa gene product (p15) of the 5"-proximal ORF induces efficient cell-cell fusion when expressed by itself in transfected cells, suggesting that p15 is the only viral protein required for induction of syncytium formation by BRV. The p15 protein is a small, hydrophobic, basic, integral membrane protein, properties shared with the p10 fusion-associated small transmembrane (FAST) proteins encoded by avian reovirus and Nelson Bay reovirus. As with p10, the BRV p15 protein is also a nonstructural protein and, therefore, is not involved in virus entry. Sequence analysis indicates that p15 shares no significant sequence similarity with the p10 FAST proteins and contains a unique repertoire and arrangement of sequence-predicted structural and functional motifs. These motifs include a functional N-terminal myristylation consensus sequence, an N-proximal proline-rich motif, two potential transmembrane domains, and an intervening polybasic region. The unique structural properties of p15 suggest that this protein is a novel member of the new family of FAST proteins. 相似文献
987.
Shoot elongation is a vital process for plant development and productivity, in both ecological and economic contexts. Auxin and bioactive gibberellins (GAs), such as GA1, play critical roles in the control of elongation,1–3 along with environmental and endogenous factors, including other hormones such as the brassinosteroids.4,5 The effect of auxins, such as indole-3-acetic acid (IAA), is at least in part mediated by its effect on GA metabolism,6 since auxin upregulates biosynthesis genes such as GA 3-oxidase and GA 20-oxidase and downregulates GA catabolism genes such as GA 2-oxidases, leading to elevated levels of bioactive GA1.7 In our recent paper,1 we have provided evidence that this action of IAA is largely independent of DELLA proteins, the negative regulators of GA action,8,9 since the auxin effects are still present in the DELLA-deficient la cry-s genotype of pea. This was a crucial issue to resolve, since like auxin, the DELLAs also promote GA1 synthesis and inhibit its deactivation. DELLAs are deactivated by GA, and thereby mediate a feedback system by which bioactive GA regulates its own level.10 However, our recent results,1 in themselves, do not show the generality of the auxin-GA relationship across species and phylogenetic groups or across different tissue types and responses. Further, they do not touch on the ecological benefits of the auxin-GA interaction. These issues are discussed below as well as the need for the development of suitable experimental systems to allow this process to be examined.Key words: auxin, gibberellins, DELLA proteins, interactions, elongation 相似文献
988.
Al-Tarawneh SK Border MB Dibble CF Bencharit S 《Omics : a journal of integrative biology》2011,15(6):353-361
Recent advancements in mass spectrometric proteomics provide a promising result in utilizing saliva to explore biomarkers for diagnostic purposes. However, the issues of specificity or redundancy of disease-associated salivary biomarkers have not been described. This systematic review was therefore aimed to define and summarize disease-related salivary biomarkers identified by mass spectrometry proteomics. Peer-reviewed articles published through July 2009 within three databases were reviewed. Out of 243 articles, 21 studies were selected in this systematic review with conditions including Sj?gren's syndrome, squamous cell carcinoma, dental caries, diabetes, breast cancer, periodontitis, gastric cancer, systemic sclerosis, oral lichen planus, bleeding oral cavity, and graft-versus-host disease. The sample size ranged from 3-41 in both diseased and control subjects, with no consensus on sample collection protocol. One hundred eighty biomarkers were identified in total; 87 upregulated, 63 downregulated, and 30 varying based on disease. Except for Sj?gren's syndrome, the majority of studies with the same disease produce inconsistent biomarkers. Larger sample size and standardization of sample collection/treatment protocol may improve future studies. 相似文献
989.
990.