全文获取类型
收费全文 | 4140篇 |
免费 | 341篇 |
国内免费 | 744篇 |
出版年
2024年 | 30篇 |
2023年 | 124篇 |
2022年 | 169篇 |
2021年 | 157篇 |
2020年 | 188篇 |
2019年 | 170篇 |
2018年 | 161篇 |
2017年 | 173篇 |
2016年 | 179篇 |
2015年 | 170篇 |
2014年 | 251篇 |
2013年 | 355篇 |
2012年 | 264篇 |
2011年 | 269篇 |
2010年 | 244篇 |
2009年 | 256篇 |
2008年 | 236篇 |
2007年 | 221篇 |
2006年 | 199篇 |
2005年 | 186篇 |
2004年 | 147篇 |
2003年 | 133篇 |
2002年 | 120篇 |
2001年 | 92篇 |
2000年 | 74篇 |
1999年 | 78篇 |
1998年 | 55篇 |
1997年 | 51篇 |
1996年 | 52篇 |
1995年 | 50篇 |
1994年 | 36篇 |
1993年 | 43篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1978年 | 14篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有5225条查询结果,搜索用时 15 毫秒
61.
《Animal : an international journal of animal bioscience》2023,17(2):100704
Involuntary temporary feed restriction on commercial cattle is likely to become more frequent with forage shortages in the context of climate change. If general consequences of feed restriction have been the subject of an abundant scientific literature, focus on the inter-individual variability of response is scarce. Here, we explore the response profile in terms of BW, body condition score, milk production, calf weight and cyclicity resumption of 293 lactations from 169 Charolais cows during a winter feed restriction in early lactation and its subsequent recovery at grazing using a principal component analysis followed by a hierarchical clustering on principal component. Results show a very continuous range of response profiles that was divided into three clusters: one with light animals having an intermediate response in terms of milk production and body maintenance, one with animals prioritising body maintenance and cyclicity resumption over milk production and calf weight, and the last one with animals prioritising milk production and calf weight over the rest. Among the animals performing more than one lactation, 57% remain in the same cluster on two successive lactations. This work highlights that an average group response to feed restriction may hide various resilience individual profiles. Further studies are required to determine the existence of a genetic component as well as the consequences of not taking this phenomenon into consideration with the regular use of feed restriction in commercial farms. 相似文献
62.
Lu‐Xian Liu Pan Deng Meng‐Zhen Chen Li‐Min Yu Joongku Lee Wei‐Mei Jiang Cheng‐Xin Fu Fu‐De Shang Pan Li 《植物分类学报:英文版》2023,61(1):99-114
Oresitrophe and Mukdenia (Saxifragaceae) are epilithic sister genera used in traditional Chinese medicine. The taxonomy of Mukdenia, especially of M. acanthifolia, has been controversial. To address this, we produced plastid and mitochondrial data using genome skimming for Mukdenia acanthifolia and Mukdenia rossii, including three individuals of each species. We assembled complete plastomes, mitochondrial CDS and nuclear ribosomal ETS/ITS sequences using these data. Comparative analysis shows that the plastomes of Mukdenia and Oresitrophe are relatively conservative in terms of genome size, structure, gene content, RNA editing sites and codon usage. Five plastid regions that represent hotspots of change (trnH-psbA, psbC-trnS, trnM-atpE, petA-psbJ and ccsA-ndhD) are identified within Mukdenia, and six regions (trnH-psbA, petN-psbM, trnM-atpE, rps16-trnQ, ycf1 and ndhF) contain a higher number of species-specific parsimony-informative sites that may serve as potential DNA barcodes for species identification. To infer phylogenetic relationships between Mukdenia and Oresitrophe, we combined our data with published data based on three different datasets. The monophyly of each species (Oresitrophe rupifraga, M. acanthifolia and M. rossii) and the inferred topology ((M. rossii, M. acanthifolia), O. rupifraga) are well supported in trees reconstructed using the complete plastome sequences, but M. acanthifolia and M. rossii did not form a separate clade in the trees based on ETS + ITS data, while the mitochondrial CDS trees are not well-resolved. We found low recovery of genes in the Angiosperms353 target enrichment panel from our unenriched genome skimming data. Hybridization or incomplete lineage sorting may be the cause of discordance between trees reconstructed from organellar and nuclear data. Considering its morphological distinctiveness and our molecular phylogenetic results, we strongly recommend that M. acanthifolia be treated as a distinct species. 相似文献
63.
M. Yamagishi 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(6-7):830-835
Random amplified polymorphic DNA (RAPD) markers were utilized for the identification of Lilium species and inter-specific hybrids. The optimum annealing temperature of the polymerase chain reaction (PCR) for the RAPD assay in Lilium was 54 °C, which is relatively higher than the temperature used for other genera reported by previous researchers. Among 76 primers used to amplify genomic DNA by PCR, 18 primers (24%) generated polymorphic DNA fragments in Lilium species and hybrids. Cultivars were also identified by RAPD markers. Some amplified fragments were unique to species of each section and to hybrids derived from these species; that is, they were the section-specific DNA markers. Sections, Sinomartagon, Leucolirion b, Leucolirion a and Archelirion could be identified by 6 section-specific markers amplified with five primers. Seven inter-section hybrids showed the section-specific bands of both parental sections, indicating that these markers would be useful for identifying the parental sections of inter-section hybrids. 相似文献
64.
The possible B-cell epitopes of the outer membrane porin OmpC ofSalmonella typhi have been identified, using the primary structure of the protein, by means of multiple sequence alignment and the known molecular
structure of two other porins. From the analysis, 8 regions were identified as immunodominant and these were ranked based
on antigenic index and the ratio of the number of nonconserved residues to the fragment length. Model building of the top
two ranked regions show the tendency to form loop structures supporting the possibility of these being candidate epitopes. 相似文献
65.
The application of molecular markers to the study and conservation of fish populations, with special reference to Salmo 总被引:4,自引:0,他引:4
A. Ferguson J. B. Taggart † P. A. Prodöhl ‡ O. McMeel C. Thompson § C. Stone P. McGinnity R. A. Hynes 《Journal of fish biology》1995,47(SA):103-126
The main molecular techniques which can be used to generate genetic markers, and the applications of these markers to studies of fish populations are outlined. Published and ongoing studies, in the authors' laboratories, on brown trout and Atlantic salmon are used to compare the resolution and applicability of allozyme, mitochondrial DNA and minisatellite (variable number of tandem repeats) markers for studies on population structuring, genetic variation within populations, and the impact of the accidental and deliberate introduction of non-native salmonids on the genetic make-up of natural populations. 相似文献
66.
The taxonomic impediment to biodiversity studies may be influenced radically by the application of new technology, in particular, desktop image analysers and neural networks. The former offer an opportunity to automate objective feature measurement processes, and the latter provide powerful pattern recognition and data analysis tools which are able to 'learn' patterns in multivariate data. The coupling of these technologies may provide a realistic opportunity for the automation of routine species identifications. The potential benefits and limitations of these technologies, along with the development of automated identification systems are reviewed. 相似文献
67.
Eugene A. Marino 《American journal of physical anthropology》1995,97(2):127-133
The articular surfaces and vertebral foramen area of the first cervical vertebra are sexually dimorphic and can be used to sex complete or fragmentary specimens. Eight measurements were taken from the articular regions (superior and inferior) of 100 first cervical vertebrae from Terry collection specimens housed at the Smithsonian Institution. Seven regression and seven discriminant function equations were created that predict sex with 77–85% and 75–85% accuracy, respectively. In separate control tests, measurements from 100 first cervical vertebrae from Hamann-Todd collection individuals (Cleveland Museum of Natural History) and from 34 archaeological specimens were used with the Terry equations. The control samples were sexed with 60—85% accuracy. © 1995 Wiley-Liss, Inc. 相似文献
68.
Le Van Phung Tran Thi Bich Chi Hisako Hotta Eiko Yabuuchi Ikuya Yano 《Microbiology and immunology》1995,39(2):105-116
Viet nam is known as an endemic area of melioidosis but its etiologic agent originated in Viet nam was not extensively studied. For the first time, we analyzed the cellular lipid and fatty acid compositions of 15 Vietnamese isolates of Burkholderia pseudomallei, 10 from humans and 5 from the environment. Cellular lipid compositions were analyzed by two-dimensional thin-layer chromatography on silica gel G plates. Cellular fatty acid methyl esters were analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The major lipids in all the isolates were phosphatidylglycerol (PG), two forms of phosphatidylethanolamine (PE-1 and PE-2), and two forms of ornithine-containing lipid (OL-1 and OL-2). PE-1 contained non-hydroxy fatty acids at both sn-1 and ?2 positions, while PE-2 possessed 2-hydroxy fatty acids and non-hydroxy fatty acids in a ratio of 1: 1. Since snake venom phospholipase A2 digestion of PE-2 liberated 2-hydroxy fatty acids, it was confirmed that these acids are at the sn-2 position of glycerol moiety. In both OL-1 and OL-2, amide-linked fatty acid was 3-hydroxy palmitic acid (3-OH-C16: 0), while ester-linked fatty acids were non-hydroxy acids in OL-1 and 2-hydroxy acids in OL-2. The total cellular fatty acid compositions of the test strains were characterized by the presence of 2-hydroxy palmitic (2-OH-C16: 0), 2-hydroxy hexadecenoic (2-OH-C16: 1), 2-hydroxy octadecenoic (2-OH-C18: 1), 2-hydroxy methylene octadecanoic (2-OH-C19CPA), 3-hydroxy myristic (3-OH-C14: 0) and 3-hydroxy palmitic (3-OH-C16: 0) acids. There were significant differences in the concentration of hexadecenoic (C16: 1), methylene hexadecanoic (C17CPA), octadecenoic (C18: 1) and methylene octadecanoic (C19CPA) acids among the Vietnamese isolates of B. pseudomallei. However, no significant difference was observed in cellular lipid and fatty acid components between strains of human and environmental origins. 相似文献
69.
Abstract A strain of Bacillus polymyxa (BP1), isolated from cauliflower seeds, inhibited the growth of microbial phytopathogens. Growth of this strain in liquid medium containing lactose, ammonium sulfate, biotin, and amino acids, resulted in optimal inhibition in vitro. Two new antibacterial substances were isolated and purified from culture broth. Their molecular masses were, respectively, 911 and 903 dallons. The first compound was named gavaserin because it contained glutamic acid, alanine, valine, serine and 2,4-diaminobutyric acid, and octanoic acid. No fatty acid was detected in the second compound, which was named saltavalin because it contained serine, alanine, leucine, threonine, valine, and 2,4-diaminobutyric acid. 相似文献
70.
R. J. J. Kanoza D. M. Brunette A. D. Purdon J. Sodek 《In vitro cellular & developmental biology. Plant》1978,14(9):746-753
Summary An operational criterion for the identification and isolation of epithelial-like (E) cells, based on their ability to cover
and protect, a collagen gel from the action of collagenase, has been developed. The E cells isolated by this collagenase-separation
technique (CST) exhibited the ultrastructural features, including desmosomes and abundant tonofilaments, that are considered
characteristic of this cell type. Unlike confluent cultures of fibroblast-like (F) cells, E cells were not found to have large
external transformation-sensitive (LETS) protein on their surface membranes. The CST provides a nondestructive, and efficient
means of identifying and isolating E cells from mixed populations. 相似文献