全文获取类型
收费全文 | 6377篇 |
免费 | 308篇 |
国内免费 | 1篇 |
专业分类
6686篇 |
出版年
2023年 | 24篇 |
2022年 | 37篇 |
2021年 | 74篇 |
2020年 | 38篇 |
2019年 | 68篇 |
2018年 | 121篇 |
2017年 | 109篇 |
2016年 | 153篇 |
2015年 | 162篇 |
2014年 | 182篇 |
2013年 | 284篇 |
2012年 | 541篇 |
2011年 | 752篇 |
2010年 | 341篇 |
2009年 | 131篇 |
2008年 | 475篇 |
2007年 | 455篇 |
2006年 | 382篇 |
2005年 | 357篇 |
2004年 | 282篇 |
2003年 | 266篇 |
2002年 | 210篇 |
2001年 | 84篇 |
2000年 | 167篇 |
1999年 | 91篇 |
1998年 | 53篇 |
1997年 | 22篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 28篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1985年 | 29篇 |
1984年 | 31篇 |
1982年 | 22篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1976年 | 26篇 |
1975年 | 30篇 |
1974年 | 26篇 |
1973年 | 21篇 |
1971年 | 17篇 |
1970年 | 19篇 |
1967年 | 17篇 |
排序方式: 共有6686条查询结果,搜索用时 0 毫秒
61.
Babić KH Schauss K Hai B Sikora S Redzepović S Radl V Schloter M 《Environmental microbiology》2008,10(11):2922-2930
Inoculation of leguminous seeds with selected rhizobial strains is practised in agriculture to ameliorate the plant yield by enhanced root nodulation and nitrogen uptake of the plant. However, effective symbiosis between legumes and rhizobia does not only depend on the capacity of nitrogen fixation but also on the entire nitrogen turnover in the rhizosphere. We investigated the influence of seed inoculation with two indigenous Sinorhizobium meliloti strains exhibiting different efficiency concerning plant growth promotion on nitrogen turnover processes in the rhizosphere during the growth of alfalfa. Quantification of six target genes (bacterial amoA, nirK, nirS, nosZ, nifH and archaeal amoA) within the nitrogen cycle was performed in rhizosphere samples before nodule formation, at bud development and at the late flowering stage. The results clearly demonstrated that effectiveness of rhizobial inocula is related to abundance of nifH genes in the late flowering phase of alfalfa. Moreover, other genes involved in nitrogen turnover had been affected by the inocula, e.g. higher numbers of amoA copies were observed during flowering when the more effective strain had been inoculated. However, the respective gene abundances differed overall to a greater extent between the three plant development stages than between the inoculation variants. 相似文献
62.
Beluzić R Cuk M Pavkov T Barić I Vugrek O 《Biochemical and biophysical research communications》2008,368(1):30-36
Recently, S-adenosylhomocysteine hydrolase deficiency was confirmed for the first time in an adult. Two missense mutations in codons 89 (A>V) and 143 (Y>C) in the AdoHcyase gene were identified [N.R.M. Buist, B. Glenn, O. Vugrek, C. Wagner, S. Stabler, R.H. Allen, I. Pogribny, A. Schulze, S.H. Zeisel, I. Bari?, S.H. Mudd, S-Adenosylhomocysteine hydrolase deficiency in a 26-year-old man, J. Inh. Metab. Dis. 29 (2006) 538-545]. Accordingly, we have proven the Y143C mutation to be highly inactivating [R. Beluzi?, M. Cuk, T. Pavkov, K. Fumi?, I. Bari?, S.H. Mudd, I. Jurak, O. Vugrek, A single mutation at tyrosine 143 of human S-adenosylhomocysteine hydrolase renders the enzyme thermosensitive and effects the oxidation state of bound co-factor NAD, Biochem. J. 400 (2006) 245-253]. Now we report that the A89V exchange leads to a 70% loss of enzymatic activity, respectively. Circular dichroism analysis of recombinant p.A89V protein shows a significantly reduced unfolding temperature by 5.5 degrees C compared to wild-type. Gel filtration of mutant protein is almost identical to wild-type indicating assembly of subunits into the tetrameric complex. However, electrophoretic mobility of p.A89V is notably faster as shown by native polyacrylamide gel electrophoresis implicating changes to the overall charge of the mutant complex. 'Bioinformatics' analysis indicates that Val(89) collides with Thr(84) causing sterical incompatibility. Performing site-directed mutagenesis changing Thr(84) to 'smaller' Ser(84) but preserving similar physico-chemical properties restores most of the catalytic capabilities of the mutant p.A89V enzyme. On the other hand, substitution of Thr(84) with Lys(84) or Gln(84), thereby introducing residues with higher volume in proximity to Ala(89) results in inactivation of wild-type protein. In view of our mutational analysis, we consider changes in charge and the sterical incompatibility in mutant p.A89V protein as main reason for enzyme malfunction with AdoHcyase deficiency as consequence. 相似文献
63.
We describe the first genetic linkage map for Daphnia pulex using 185 microsatellite markers, including 115 new markers reported in this study. Our approach was to study the segregation of polymorphisms in 129 F2 progeny of one F1 hybrid obtained by crossing two genetically divergent lineages of Daphnia isolated from two Oregon populations. The map spanned 1206 Kosambi cM and had an average intermarker distance of 7 cM. Linkage groups ranged in size from 7 to 185 cM and contained 4 to 27 markers. The map revealed 12 linkage groups corresponding to the expected number of chromosomes and covers approximately 87% of the genome. Tests for random segregation of alleles at individual loci revealed that 21% of the markers showed significant transmission ratio distortion (primarily homozygote deficiency) likely due to markers being linked to deleterious recessive alleles. This map will become the anchor for the physical map of the Daphnia genome and will serve as a starting point for mapping single and quantitative trait loci affecting ecologically important phenotypes. By mapping 342 tentative orthologous gene pairs (Daphnia/Drosophila) into the Daphnia linkage map, we facilitate future comparative projects. 相似文献
64.
65.
Résumé Les auteurs distinguent 8 types cellulaires dans l'EpongeOphlitaspongia seriata (Grant) en réorganisation après dissociation. Ils décrivent leur comportement au cours de la réorganisation, leur ultrastructure et leurs capacités de différenciation.Les cellules globifères sont particulièrement remarquables par leurs nombreuses inclusions cytoplasmiques tubulaires de 70 m. 相似文献
66.
Mihajlo Gajić Budimir S. Ilić Bojan P. Bondžić Zdravko Džambaski Vesna V. Kojić Dimitar S. Jakimov Gordana Kocić Andrija Šmelcerović 《化学与生物多样性》2021,18(8):e2100261
Herein we report an assessment of 24 1,2,3,4-tetrahydroisoquinoline derivatives for potential DNase I (deoxyribonuclease I) inhibitory properties in vitro. Four of them inhibited DNase I with IC50 values below 200 μM. The most potent was 1-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-1-yl)propan-2-one ( 2 ) (IC50=134.35±11.38 μM) exhibiting slightly better IC50 value compared to three other active compounds, 2-[2-(4-fluorophenyl)-1,2,3,4-tetrahydroisoquinolin-1-yl]-1-phenylethan-1-one ( 15 ) (IC50=147.51±14.87 μM), 2-[2-(4-fluorophenyl)-1,2,3,4-tetrahydroisoquinolin-1-yl]cyclohexan-1-one ( 18 ) (IC50=149.07±2.98 μM) and 2-[6,7-dimethoxy-2-(p-tolyl)-1,2,3,4-tetrahydroisoquinolin-1-yl]cyclohexan-1-one ( 22 ) (IC50=148.31±2.96 μM). Cytotoxicity assessment of the active DNase I inhibitors revealed a lack of toxic effects on the healthy cell lines MRC-5. Molecular docking and molecular dynamics simulations suggest that interactions with Glu 39, His 134, Asn 170, Tyr 211, Asp 251 and His 252 are an important factor for inhibitors affinity toward the DNase I. Observed interactions would be beneficial for the discovery of new active 1,2,3,4-tetrahydroisoquinoline-based inhibitors of DNase I, but might also encourage researchers to further explore and utilize potential therapeutic application of DNase I inhibitors, based on a versatile role of DNase I during apoptotic cell death. 相似文献
67.
In this article, authors have tried to answer the question: "Where is the place, and what is the meaning of the Oedipus complex in contemporary psychoanalysis?" The review of different theoretical standpoints was given, according to meaning and place of the Oedipus complex in human development. Although it depends on the resolving of preoedipal conflicts, the conflicts of phallic phases of the psychosexual development are universal to all human being, no matter how we call them--Oedipus, Electra or Persephone Complex. 相似文献
68.
Hyoid bone is a part of viscerocranium placed between the tongue root and thyroid cartilage to which it is connected by thyrohyoid membrane. Widely accepted morphological classification does not exist. Sexual dimorphism was analysed in this study and new guidelines for anatomical classification of hyoid bones based on anthropometric parameters were given. Total number of analysed bones was 70. The bones were classified into three groups: symmetrical U-type, symmetrical V-type and asymmetrical type according to the angle between greater horns and the proportion of greater horns length. In the females incidence of asymmetrical type is considerably higher than in the males, while the incidence of symmetrical V-type is lower The angle value that is on average higher in males may be the parameter indicating that in puberty hyoid bone, still not completely ossified, to some extent follows development of thyroid cartilage because of their close anatomical relation. 相似文献
69.
70.