全文获取类型
收费全文 | 13027篇 |
免费 | 679篇 |
国内免费 | 1954篇 |
专业分类
15660篇 |
出版年
2024年 | 24篇 |
2023年 | 209篇 |
2022年 | 330篇 |
2021年 | 410篇 |
2020年 | 346篇 |
2019年 | 432篇 |
2018年 | 362篇 |
2017年 | 314篇 |
2016年 | 316篇 |
2015年 | 385篇 |
2014年 | 659篇 |
2013年 | 727篇 |
2012年 | 521篇 |
2011年 | 715篇 |
2010年 | 629篇 |
2009年 | 701篇 |
2008年 | 740篇 |
2007年 | 721篇 |
2006年 | 694篇 |
2005年 | 630篇 |
2004年 | 584篇 |
2003年 | 568篇 |
2002年 | 414篇 |
2001年 | 354篇 |
2000年 | 338篇 |
1999年 | 312篇 |
1998年 | 310篇 |
1997年 | 257篇 |
1996年 | 222篇 |
1995年 | 253篇 |
1994年 | 250篇 |
1993年 | 216篇 |
1992年 | 221篇 |
1991年 | 155篇 |
1990年 | 152篇 |
1989年 | 129篇 |
1988年 | 102篇 |
1987年 | 109篇 |
1986年 | 95篇 |
1985年 | 114篇 |
1984年 | 91篇 |
1983年 | 73篇 |
1982年 | 106篇 |
1981年 | 57篇 |
1980年 | 65篇 |
1979年 | 70篇 |
1978年 | 64篇 |
1977年 | 26篇 |
1976年 | 29篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
【目的】从基因组序列角度进一步揭示自然界斜纹夜蛾核型多角体病毒(Spodoptera litura nucleopolyhedrovirus, SpltNPV)的基因型多态性。【方法】病毒克隆A5, F1, X3 和 X15分别以活体克隆法分离自SpltNPV埃及株、 日本福冈株和日本小笠原株。根据SpltNPV基因组全序列(GenBank登录号: AF325155)和海灰翅夜蛾核型多角体病毒(S. littoralis NPV, SpliNPV)部分基因序列(GenBank登录号: X99377, X99376 和X98924)设计引物, PCR扩增获得A5, F1, X3 和 X15的多角体蛋白(polyhedrin, polh)基因和ORF18~ORF23序列。【结果】根据多角体蛋白基因序列, X3和X15属于SpltNPV型, 而A5和F1属于SpliNPV型。将A5, F1, X3 和 X15的ORF18~ORF23与SpltNPV和SpliNPV相应的基因序列进行同源性比较。结果发现, F1与SpliNPV以及X3与SpltNPV的核苷酸序列相似性高, 但X3的ORF20在172~558 nt处缺失387 bp。尽管依据多角体蛋白基因序列X15属于SpltNPV型, 但对于ORF18~ORF23序列, X15与SpliNPV的相似性高于与SpltNPV的相似性。同样, A5属于SpliNPV型, ORF18~ORF20与SpliNPV相应的核苷酸序列相似性高, 但ORF21与SpltNPV相应的核苷酸序列一致性为100%, 特别是ORF22, SpltNPV的特有序列出现在A5的基因组中, 而且与SpltNPV的ORF22一致性为100%; 反过来, ORF23又与SpliNPV相应的核苷酸序列相似性高。【结论】所有这些都表明, SpltNPV在自然界不仅存在基因型多态性, 而且即使属于同一基因型, 它们的基因组序列也有显著差异。可利用SpltNPV在自然界的这种异质性筛选适宜防治斜纹夜蛾幼虫的株系。 相似文献
72.
The obligate, thermophilic, acidophilic mycoplasma, Thermoplasma acidophilum, grows optimally at 56° C and pH 2.0. Its plasma membrane possessed 21–22 protein bands that were resolved by polyacrylamide gel electrophoresis. One major membrane protein, molecular weight 152 000, which stained for carbohydrate with periodic acid-Schiff reagent, accounted for 32% (w/w) of the total membrane proteins. It was isolated and further purified by concanavalin A affinity chromatography. The carbohydrate content amounted to less than 10% (w/w) compared to that of the entire glycoprotein. The carbohydrate moiety consisted mainly of mannose residues with branched α 1 → 2 linkages at the non-reducing ends of the glycopeptide as determined by permethylation followed by gas chromatography-mass spectrometry analysis. The reducing end was an N-glycosidic linkage between asparagine and N-acetylglucosamine. The amino acid composition of this glycoprotein showed 62 mol% hydrophobic residues, while the acidic amino acid content contributed 9 mol% more than that of the basic amino acids. The existence of membrane glycoproteins in the procaryotic, wall-less T. acidophilum may provide a protective coat for the plasma membrane. The stereochemistry and the conformation of the carbohydrate chains, in conjunction with water turgor, may contribute to the rigidity of the membrane and the cation binding. 相似文献
73.
BACKGROUND: Severe disseminated vasculopathy was observed in two simian immunodeficiency virus (SIV)-infected rhesus macaques (Macaca mulatta). These animals developed clinical signs of AIDS, including lymphadenopathy, weight loss, diarrhea and collapse. RESULTS AND DISCUSSION: Grossly, both animals showed emaciation, lymphadenopathy, vegetations on the mitral valve, renal infarcts and a dilated intestine; one animal had multifocal hemorrhages in multiple organs. Histologically, both cases had disseminated arteriopathy characterized by intimal thickening and fibrosis with varying degrees of vasculitis. The lesion was prominent in the kidney, intestine, pancreas, liver, heart, lymph nodes, spleen and testis. Occasional venules had intimal thickening. Both cases had cytomegalovirus (CMV) infection with intranuclear inclusions, CMV antigen and nucleic acid; some inclusions were observed in endothelial cells within some of the vascular lesions in one of the two. These data suggest that CMV caused the unusual lesions. 相似文献
74.
《Expert review of proteomics》2013,10(1):21-29
The genetic theory of infectious diseases has proposed that susceptibility to life-threatening infectious diseases in childhood, occurring in the course of primary infection, results mostly from individually rare but collectively diverse single-gene variants. Recent evidence of an ever-expanding spectrum of genes involved in susceptibility to infectious disease indicates that the paradigm has important implications for diagnosis and treatment. One such pathology is childhood herpes simplex encephalitis, which shows a pattern of rare but diverse disease-disposing genetic variants. The present report shows how proteomics can help to understand susceptibility to childhood herpes simplex encephalitis and other viral infections, suggests that proteomics may have a particularly important role to play, emphasizes that variation over the population is a critical issue for proteomics and notes some new challenges for proteomics and related bioinformatics tools in the context of rare but diverse genetic defects. 相似文献
75.
76.
Antonio J. Arenas Sebastian Napp Antonio Arenas-Montes Carmen Borge Alfonso Carbonero Anselmo Perea Rafael Cadenas Ignacio García-Bocanegra 《The Journal of wildlife management》2012,76(1):102-107
We carried out an experimental study to determine the serological response against myxoma virus (MV) and rabbit hemorrhagic disease virus (RHDV) in wild rabbits using commercial vaccines. Seroconversion against MV ranged between 72.7% and 97.2% in animals vaccinated by subcutaneous and intradermal route, respectively, whereas between 75.0% and 77.8% of the animals presented antibodies against RHDV after inoculation with subcutaneous and intradermal vaccines, respectively. Regardless of the inoculation route, vaccination against MV resulted in a significant increase of seropositivity 5 days post-vaccination (dpv), which did not occur in animals vaccinated against RHDV. Furthermore, seroconversion against MV was significantly higher and faster in intradermally vaccinated rabbits as compared to those inoculated subcutaneously due to either the route of application and/or the type of vaccine used. The results indicated that vaccination significantly increased the prevalence of antibodies against MV and RHDV and suggested that the vaccines currently available induce a safe and effective immune response against both diseases in wild rabbits. Vaccination may be a useful management tool to control both viral diseases in field conditions, particularly in wild rabbits captured for translocations and restocking purposes in which a large number of animals are handled. © 2011 The Wildlife Society. 相似文献
77.
78.
Vectoring ability of four aphid clones, Rp-M and Rp-R26 of Rhopalosiphum padi and Sa-R1 and Sa-V of Sitobion avenae, to transmit barley yellow dwarf (PAV, MAV and RPV) luteoviruses (BYDV) was compared in controlled conditions. Significant differences between highly efficient vectors (HEV), Rp-M and Sa-Rl, and poorly efficient vectors (PEV), Rp-R26 and Sa-V, were found in transmission of their specific viruses with acquisition and inoculation access periods (AAP, IAP) of 5 days. BYD-RPV was occasionally transmitted by both clones of S. avenae. None of 150 tested apterous adults of the Rp-R26 transmitted BYD-MAV, while 10% of transmission was observed from those of the Rp-M in a parallel test. An improved ELISA and immuno-PCR were adapted to test for viruses in aphids. The results obtained by the improved ELISA indicated there was a good correlation between virus detection in single aphids of HEV clones after a 5 day AAP and virus transmission by them. In contrast, the percentages of virus-carrying aphids of PEV clones were generally higher than those of their transmission rates. BYD-MAV and BYD-RPV were also detected by the improved ELISA in single aphids of their PEV clones, with the exception of BYD-RPV in those of Sa-V. However, after a 2-day IAP, the improved ELISA in most cases failed to detect these viruses in single aphids of PEV clones. Detection by immuno-PCR demonstrated that all three viruses could be acquired and retained by the aphids of both HEV and PEV clones. But, as visualised from electrophoretic bands, after the 2-day IAP the amplified products from aphid extracts of PEV clones were reduced. The detection in a batch of nine aphids by the improved ELISA revealed that virus content in PEV clones decreased more rapidly than that in HEV clones during transmission. Thus, the difference in transmission efficiency of the aphid clones within species was not caused by an inability to acquire virus, but was determined by variation in vectoring ability between them. This was due to differences in ability to prevent the passage of virions from haemocoel to salivary duct and/or different capacities for the retention of BYDV. 相似文献
79.
Edgardo S. Jiménez-Martínez & Nilsa A. Bosque-Pérez 《Entomologia Experimentalis et Applicata》2009,133(1):19-26
The life history of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), was studied via laboratory assays on Wheat streak mosaic virus (WSMV)-infected and non-infected transgenic and non-transformed wheat [ Triticum aestivum L. (Poaceae)]. Although R. padi is not a WSMV vector, it is known to colonize WSMV-infected wheat plants. Two transgenic soft white winter wheat genotypes, 366-D03 and 366-D8, that express the WSMV coat protein gene, and the WSMV-susceptible non-transformed cultivar Daws were tested. All genotypes showed disease symptoms when infected with WSMV. Whereas plant height was significantly reduced on virus-infected compared to non-infected plants of all genotypes, virus-infected transgenic plants exhibited lower virus titer and lower disease rating scores than Daws. No significant effects of WSMV infection or genotypes were observed on the length of R. padi nymphal development period, nor on their pre-, and post-reproductive periods. Rhopalosiphum padi reproductive period was significantly longer on Daws infected with WSMV than on non-infected plants of this cultivar. In contrast, there were no significant differences in length of R. padi reproductive period between virus-infected and non-infected transgenic plants within a genotype. Rhopalosiphum padi daily fecundity was significantly lower and adult longevity significantly longer on virus-infected than on non-infected plants of all genotypes. Total aphid fecundity and intrinsic rate of increase were not significantly different among treatments. The percentage of winged aphids that developed was greater on WSMV-infected compared to non-infected plants within a genotype. Results indicate that both virus infection status of plants and wheat genotype influence the life history of R. padi. 相似文献
80.
Muramoto Y Ozaki H Takada A Park CH Sunden Y Umemura T Kawaoka Y Matsuda H Kida H 《Microbiology and immunology》2006,50(1):73-81
Severe hemorrhage at multiple organs is frequently observed in chickens infected with highly pathogenic avian influenza (HPAI) A viruses. In this study we examined whether HPAI virus infection leads to coagulation disorder in chickens. Pathological examinations showed that the fibrin thrombi were formed in arterioles at the lung, associated with the viral antigens in endothelial cells of chickens infected intravenously with HPAI virus. Hematological analyses of peripheral blood collected from the chickens revealed that coagulopathy was initiated at early stage of infection when viral antigens were detected only in the endothelial cells and monocytes/macrophages. Furthermore, gene expression of the tissue factor, the main initiator of blood coagulation, was upregulated in the spleen, lung, and brain of HPAI virus-infected chickens. These results suggest that dysfunction of endothelial cells and monocytes/macrophages upon HPAI virus infection may induce hemostasis abnormalities represented by the excessive blood coagulation and consumptive coagulopathy in chickens. 相似文献