全文获取类型
收费全文 | 1165篇 |
免费 | 97篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 32篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 17篇 |
2016年 | 21篇 |
2015年 | 59篇 |
2014年 | 48篇 |
2013年 | 61篇 |
2012年 | 78篇 |
2011年 | 91篇 |
2010年 | 63篇 |
2009年 | 31篇 |
2008年 | 72篇 |
2007年 | 76篇 |
2006年 | 84篇 |
2005年 | 72篇 |
2004年 | 80篇 |
2003年 | 68篇 |
2002年 | 58篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1965年 | 2篇 |
1962年 | 2篇 |
1920年 | 2篇 |
排序方式: 共有1262条查询结果,搜索用时 15 毫秒
11.
Characterization of a Small Family (CAIII) of Microsatellite-Containing Sequences with X-Y Homology 总被引:4,自引:0,他引:4
Patrizia Malaspina Bianca Maria Ciminelli Luigi Viggiano Carla Jodice Fulvio Cruciani Piero Santolamazza Daniele Sellitto Rosaria Scozzari Luciano Terrenato Mariano Rocchi Andrea Novelletto 《Journal of molecular evolution》1997,44(6):652-659
Four X-linked loci showing homology with a previously described Y-linked polymorphic locus (DYS413) were identified and characterized.
By fluorescent in situ hybridization (FISH), somatic cell hybrids, and YAC screening, the X-linked members of this small family
of sequences (CAIII) all map in Xp22, while the Y members map in Yq11. These loci contribute to the overall similarity of
the two genomic regions. All of the CAIII loci contain an internal microsatellite of the (CA)n type. The microsatellites display extensive length polymorphism in two of the X-linked members as well as in the Y members.
In addition, common sequence variants are found in the portions flanking the microsatellites in two of the X-linked members.
Our results indicate that, during the evolution of this family, length variation on the Y chromosome was accumulated at a
rate not slower than that on the X chromosome. Finally, these sequences represent a model system with which to analyze human
populations for similar X- and Y-linked polymorphisms.
Received: 29 July 1996 / Accepted: 15 January 1997 相似文献
12.
The coupling of the analysis of the absorption and circular dichroism (CD) spectra with that of the cholesteric mesophases induced in nematic liquid crystals indicated some interesting conformational features of bridged and nonbridged mono- and dialkylethers of optically active 2,2′-dihydroxy-1,1′-binaphthalene. Bridged derivatives are characterized by relatively small dihedral angles. Simple monoalkyl ethers are characterized by larger dihedral angles but they all assume an s-cis conformation, owing to the existence of intramolecular hydrogen bonds. Nonbridged dialkylethers prefer even larger dihedral angles and, depending on the bulkiness of the alkyl groups, the s-trans conformation can be found. Interestingly, the conformation of dialkylethers is strongly dependent on the structure of the liquid crystal solvent, because the intramolecular hydrogen bond is not possible there. © 1995 Wiley-Liss, Inc. 相似文献
13.
A new insoluble polymer containing a Cinchona alkaloid derivative has been synthesized and used as chiral ligand in the heterogeneous enantioselective dihydroxylation of olefins. It is shown that the enantioselectivity of the optically active diols obtained from both aliphatic and aromatic substrates is always comparable to that observed in the homogeneous phase under the same reaction conditions. A method for evaluating the enantiomeric excesses of the optically active products is also described. © 1995 Wiley-Liss, Inc. 相似文献
14.
Isolation ofYersinia enterocolitica andYersinia enterocolitica-like organisms from raw milk in Italy
Thirty samples of raw milk, originating from individual producers in the Turin area, were examined for the presence ofYersinia enterocolitica. A cold enrichment method with phosphate-buffered saline (PBS) 1/15M, pH 7.6, and sorbitol-bile-salts broth (SB) was used. After 7, 14, or 21 days at 4°–5°C, plating was performed on selective agar media directly (MacConkey agar andSalmonella-Shigella agar) after the alkali method was used. Six strains ofY. enterocolitica (biotype 1) and 32 strainsY. enterocolitica-like (threeY. fredericksenii; nineYersinia rhamnose-, melibiose+, -methyl-d-glucoside+, raffinose+, probablyYersinia intermedia biotype rhamnose-; and 20Y. intermedia) were isolated.Yersinia strains were found in 11 samples of raw milk, andY. enterocolitica in four samples. 相似文献
15.
Orsola Tiboni Rita Cantoni Roberta Creti Piero Cammarano Anna Maria Sanangelantoni 《Journal of molecular evolution》1991,33(2):142-151
Summary The gene (fus) coding for elongation factor G (EF-G) of the extremely thermophilic eubacteriumThermotoga maritima was identified and sequenced. The EF-G coding sequence (2046 bp) was found to lie in an operon-like structure between the ribosomal protein S7 gene (rpsG) and the elongation factor Tu (EF-Tu) gene (tuf). TherpsG, fus, andtuf genes follow each other immediately in that order, which corresponds to the order of the homologous genes in thestr operon ofEscherichia coli. The derived amino acid sequence of the EF-G protein (682 residues) was aligned with the homologous sequences of other eubacteria, eukaryotes (hamster), and archaebacteria (Methanococcus vannielii). Unrooted phylogenetic dendrogram, obtained both from the amino acid and the nucleotide sequence alignments, using a variety of methods, lend further support to the notion that the (present) root of the (eu)bacterial tree lies betweenThermotoga and the other bacterial lineages. 相似文献
16.
Roberto Gualtieri Chiara Campanella Piero Andreuccetti 《Development, growth & differentiation》1992,34(2):127-135
The K-pyroantimonate/OsO4 (PA) cytochemical method coupled with EGTA and X-ray microanalytical controls has been used to localize Ca2+ at egg activation in Discoglossus pictus eggs. The results show that: 1) the PA method is able to selectively localize Ca2+ pools mobilized by activating stimuli; 2) the smooth endoplasmic reticulum (SER) elements located in the animal dimple region, i.e. in the predetermined site of fertilization, are the first egg components labeled by precipitates; 3) a decreasing gradient of precipitates is present from the center beyond the boundaries of the dimple region; 4) precipitates are lacking in the remainder of the egg even at late times after activation.
The possibilities are discussed that a) SER is the major Ca2+ -releasing store at activation in Discoglossus , and b) the observed gradient of pyroantimonate-detected Ca2+ reflects an ionic Ca2+ gradient. 相似文献
The possibilities are discussed that a) SER is the major Ca
17.
A circular dichroism-based detection system presents several advantages in the HPLC analysis of chiral compounds because of the selective monitoring of optically active molecules. Its use allows reliable determination of enantiomeric excesses and elution order. To this end, the application of empirical, semiempirical, and nonempirical methods to get stereochemical information from the CD signal is reported. Furthermore, recording the CD spectra on line and evaluation of the dissymetry factor make the CD detection very powerful in characterizing the stereochemistry of chiral eluates. 相似文献
18.
Development of first instar larvae of Gonia cinerascens, which rest in the muscles of host caterpillars, is triggered by the release of the host's ecdysteroids when the juvenile hormone is absent. Ecdysteroids act on the parasitoid directly and at the same time induce physiological and biochemical changes in the host, which are indispensable for the parasitoid's development. These changes do not occur when metamorphosis of the host is suppressed with the juvenile hormone. Normally the parasitoids initiate development at the larval-pupal transformation of the host, but under experimental conditions, they do so whenever a high ecdysteroid titre is coupled with the proper internal environment in the host, that is in decapitated caterpillars, isolated host abdomens, and when implanted into host pupae. Activated parasitoids moult into the second instar and migrate to the exuvial space of the host; this migratory behaviour is also triggered by ecdysteroids and may be induced experimentally in the first instar parasitoids. Unknown clues direct the migrating parasitoids under the wings and appendages of the host pharate pupal stage. The second instar parasitoids, which anchor to the integument of the host pupae, apparently develop independently of the host's hormones: they can produce third instar larvae, pupae, and adult flies when cultured in vitro. 相似文献
19.
Salvatore Andini Ettore Benedetti Luciano Ferrara Livio Paolillo Piero Andrea Temussi 《Origins of life and evolution of the biosphere》1975,6(1-2):147-153
Several polypeptides prepared by means of pyrocondensation have been the subject of structural investigations. Attention has been focused on the constitutional characterization of homo-and co-polymers containing Asp and Glu residues, whose role is essential for the formation of the so-called proteinoids. Contrary to the literature data based on chemical degradation, nmr studies show conclusively that in thermal poly-aspartic acid only β-peptide linkages are present. This result casts serious doubt on the role thermal condensation might have played in prebiotic polypeptide syntheses. 相似文献
20.
Michael B. Clark Paulo P. Amaral Felix J. Schlesinger Marcel E. Dinger Ryan J. Taft John L. Rinn Chris P. Ponting Peter F. Stadler Kevin V. Morris Antonin Morillon Joel S. Rozowsky Mark B. Gerstein Claes Wahlestedt Yoshihide Hayashizaki Piero Carninci Thomas R. Gingeras John S. Mattick 《PLoS biology》2011,9(7)