全文获取类型
收费全文 | 9525篇 |
免费 | 628篇 |
国内免费 | 5篇 |
出版年
2023年 | 98篇 |
2022年 | 216篇 |
2021年 | 341篇 |
2020年 | 278篇 |
2019年 | 328篇 |
2018年 | 411篇 |
2017年 | 334篇 |
2016年 | 458篇 |
2015年 | 552篇 |
2014年 | 618篇 |
2013年 | 663篇 |
2012年 | 744篇 |
2011年 | 675篇 |
2010年 | 392篇 |
2009年 | 366篇 |
2008年 | 434篇 |
2007年 | 444篇 |
2006年 | 384篇 |
2005年 | 354篇 |
2004年 | 303篇 |
2003年 | 252篇 |
2002年 | 242篇 |
2001年 | 147篇 |
2000年 | 124篇 |
1999年 | 101篇 |
1998年 | 57篇 |
1997年 | 39篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 41篇 |
1993年 | 21篇 |
1992年 | 48篇 |
1991年 | 52篇 |
1990年 | 29篇 |
1989年 | 39篇 |
1988年 | 38篇 |
1987年 | 42篇 |
1986年 | 39篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1975年 | 18篇 |
1973年 | 19篇 |
1972年 | 17篇 |
1970年 | 16篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Computer-aided comparison of protein electrophoretic patterns for grouping and identification of heterotrophic bacteria from mineral water 总被引:2,自引:1,他引:1
A.C. Ferreira P.V. Morais C. Gomes M.S. da Costa 《Journal of applied microbiology》1996,80(5):479-486
The microflora of a natural mineral water was studied immediately after bottling (T0) and after 7 d storage (T7) during 6 months, and isolates were clustered by SDS-PAGE of wholecell protein profiles. Isolates from each cluster were further characterized by API 20NE, fatty acid composition and quinone profiles. The numerical analysis of the electrophoregrams of all bacteria isolated from the mineral water formed 15 clusters and five unclustered strains. Except for five minor clusters, all clusters were composed of strains isolated over several months. The numerical analysis of the electrophoregrams of bacteria isolated immediately after bottling formed 15 clusters while after 7 d storage only four of these populations could be isolated, indicating that populations present in the mineral water were stable and that changes occurring after bottling probably resulted from a selection process. Only one unclustered strain was identified simultaneously by all the systems, as Sphingomonas paucimobilis. The monitoring of the aquifer and the bottling system, and the construction of a large database with bacteria of the autochthonous flora allows the detection of alterations in the aquifer by changes in the microflora. 相似文献
92.
Glyptal, a polyester obtained from phthalic anhydride and glycerol, was used as a support for protein immobilisation. Hydrazide groups were introduced in the polymer and then converted to azide groups, through which protein was covalently immobilised. Amyloglucosidase was used as a model and an insoluble water derivative was synthesised retaining 24 % of the specific activity of the native enzyme. Some properties of this immobilised enzyme were studied: Km (4.54 g.l–1 using starch as substrate), optimal temperature (55°C) and half life (8 days). Furthermore, ferromagnetic-azide-glyptal derivative showed to be useful for the amyloglucosidase immobilisation. 相似文献
93.
James L. Patton Sergio F. dos Reis Maria Nazareth F. da Silva 《Journal of Mammalian Evolution》1996,3(1):3-29
Variation in the mitochondrial cytochrome b gene (nucleotide and amino acid sequences) is evaluated for 9 genera and 15 species of American opossums in the family Didelphidae, using the American caenolestid rat opossumLestoros and the New Guinean peroryctid bandicootEchimypera as outgroups. Phylogenetic analyses (parsimony and distance) strongly support the monophyly of the Didelphidae and delineate two major clades; (1)Didelphis andPhilander are strongly aligned sister taxa, withMetachirus weakly but consistently associated with them, and (2)Marmosa plusMicoureus, withMonodelphis falling outside that pair. The generaMarmosops, Caluromys, andGlironia exhibit varied relationships, depending upon the method of analysis and data (DNA or amino acid sequences) used, but generally are placed individually or in combinations near or at the base of the didelphid radiation. Some aspects of these relationships are consistent with current taxonomic views, but others are in marked contrast. Specifically, a clade comprised of the mouse opossumsMarmosa, Micoureus, andMarmosops is strongly rejected by log-likelihood analysis, contrary to expectations from some current classifications. Also, the woolly opossumsCaluromys andGlironia also do not form a sister-taxon relationship, as suggested by their placement in a subfamily separate from the remaining didelphids examined. However, such a relationship cannot be rejected from log-likelihood analyses. The relationships suggested fromcyt-b sequences are strongly concordant with those based on DNA-DNA hybridization analyses. In addition to systematic and phylogenetic properties, molecular evolution of the didelphid cytochrome b gene sequence is characterized according to nucleotide bias and rate differentials at each codon position and across the entire sequence.To whom correspondence should be addressed. 相似文献
94.
95.
Adolfo H. Mü ller Paulo C. Vieira M. F tima das G.F.da Silva Jo o B. Fernandes 《Phytochemistry》1995,40(6):1797-1800
Two novel dihydrochalcones, 2′,3,4′,6′-tetrahydroxy-4-methoxy-3′,5-di-(3,3-dimethylallyl)-dihydrochalcone and 2′,.3,6′-trihydroxy-4-methoxy-5-(3,3-dimethylallyl)-3′,4′-(2″,2″-dimethyldihydropyran)-dihydrochalcone, have been isolated from fresh fruits of Metrodorea nigra. Stems and leaves showed a similar composition and we have isolated common steroids, simple coumarins, several furocoumarins, furoquinoline alkaloids and a furofuran lignan. From stems, we have also isolated the pentacyclic 6-C-monoterpenyl-5,7-dioxycoumarin, deoxybruceol. Structures of the isolated compounds were elucidated on the basis of spectral data. 相似文献
96.
Quintilio W. Sato R.A. da Silveira A.M. Barratt G. Fattal E. Bueno-da-Costa M.H. 《Biotechnology Techniques》1997,11(9):697-700
The advantages of the intrinsic fluorescence of the tryptophan and the absorbance of the methionine residues of the 18 kDa-hsp - a recombinant protein from Mycobacterium leprae - was exploited here to develop a sensitive and low costs method for protein assaying. They presented linearity between 3 and 1000 g of protein. The correlations between intrinsic fluorescence or absorbance at 230 nm and protein contents were both superiors to 0.99. These methods can be extended to others proteins with low aromatic residue contents. 相似文献
97.
The phylogenetic distribution of transposable families, P, gypsy, hobo, I, and mariner has been analyzed in 33 species of
11 groups of neotropical Drosophila and a Drosophilidae species Zygotrica vittimaculosa, using squash blot and dot blot. Genomic
DNA of almost all neotropical species tested hybridized with gypsy probe and some species showed a particularly strong hybridization
signal, as D. gaucha, D. virilis, and species of flavopilosa group. The hobo element was restricted to melanogaster group
and some strains of D. willistoni. Only D. simulans DNA showed hybridization to mariner probe in all species tested and D.
simulans and D. melanogaster showed hybridization with I element probe. P element homologous sequence was present in D. melanogaster
and all species and strains of the willistoni and saltans groups tested. The presence of at least one P-homologous sequence
was detected in Drosophila mediopunctata. This one was the only P-bearing species of all six tested from the tripunctata group.
Four different pairs of primers homologous to segments of the canonical sequence of D. melanogaster's P were used to amplify
specific sequences from D. mediopunctata DNA, showing the occurrence of seemingly well-conserved P-homologous sequences.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
Characterization of novel long-chain 1,2-diols in Thermus species and demonstration that Thermus strains contain both glycerol-linked and diol-linked glycolipids. 下载免费PDF全文
R Wait L Carreto M F Nobre A M Ferreira M S da Costa 《Journal of bacteriology》1997,179(19):6154-6162
In this study, we purified and characterized tetra- and triglycosyl glycolipids (GL-1 and GL-2, respectively) from two different colonial forms of Thermus scotoductus X-1, from T. filiformis Tok4 A2, and from T. oshimai SPS-11. Acid hydrolysis of the purified glycolipids liberated, in addition to the expected long-chain fatty acids, two components which were identified by gas chromatography-mass spectrometry as 16-methylheptadecane-1,2-diol and 15-methylheptadecane-1,2-diol. Fast atom bombardment mass spectrometry of the intact glycolipids indicated that a major proportion consisted of components with glycan head groups linked to long-chain 1,2-diols rather than to glycerol, although in all cases glycerol-linked compounds containing similar glycan head groups were also present. As in other Thermus strains, the polar head group of GL-1 from T. filiformis Tok4 A2 and from T. scotoductus X-1 colony type t2 was a glucosylgalactosyl-(N-acyl)glucosaminylglucosyl moiety. However, GL-2 from T. scotoductus X-1 colony type t1 and from T. oshimai SPS-11 was a truncated analog which lacked the nonreducing terminal glucose. Long-chain 1,2-diols have been previously reported in the polar lipids of Thermomicrobium roseum and (possibly) Chloroflexus aurantiacus, but to our knowledge, this is the first report of their detection in other bacteria and the first account of the structural determination of long-chain diol-linked glycolipids. 相似文献
99.
In total, 86 enterococcal strains including representatives of most of the described species were tested for the ability to agglutinate human, sheep, and rabbit erythrocytes. Five strains did not react with any of the erythrocytes tested, and 81 (94.2%) strains agglutinated only rabbit erythrocytes. The hemagglutination titers ranged from 2 to 64. Loss of the hemagglutination activity was observed when rabbit erythrocytes were treated with trypsin or neuraminidase. Trypsin treatment of the bacterial suspensions also caused loss of the agglutination ability. On the other hand, heat treatment of bacterial suspensions increased the efficiency of the interactions, and higher titers were obtained. Assays for inhibition of hemagglutination were performed with -d-fucose, -d-galactose, -d-galactose, d-glucose, N-acetyl-galactosamine, N-acetyl-glucosamine, N-acetylneuraminic acid, N-acetylneuraminic acid-lactose, and fetuin. Only fetuin was able to inhibit the hemagglutination reactions. The results showed that hemagglutination properties are common to the different enterococcal species tested. They also suggest that enterococci possess hemagglutinins of proteic and non-proteic nature that are involved in the attachment to sialic acid-containing receptors on the surface of rabbit erythrocytes. 相似文献
100.
Gustavo A. Bouchardet da Fonseca Thomas E. Lacher Jr. 《Primates; journal of primatology》1984,25(4):441-449
We report the exudate feeding behavior of two groups of marmosets (Callithrix jacchus penicillata) living permanently in Cerradão, a common woodland formation of Central Brazil. Cerradão is an open canopy formation and marmosets must occasionally descend to the ground in order to move from tree to tree. Even in atypical habitat, exudate eating is the predominant foraging activity. Marmosets are engaged in exudate collection over 70% of the total time spent feeding. They were observed gnawing on seven species of trees, and consumed exudates from four of these species. We compared the degree of utilization of the exudate sources, and examined a number of different characteristics of the exudates. Morphological adaptations that allow for the exploitation of the “exudate-eater niche” may be an important component of the adaptability ofCallithrix marmosets. 相似文献