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241.
Phillip A Patten Russell J Howard Willem PC Stemmer 《Current opinion in biotechnology》1997,8(6):724-733
DNA shuffling is a practical process for directed molecular evolution which uses recombination to dramatically accelerate the rate at which one can evolve genes. Single and multigene traits that require many mutations for improved phenotypes can be evolved rapidly. DNA shuffling technology has been significantly enhanced in the past year, extending its range of applications to small molecule pharmaceuticals, pharmaceutical proteins, gene therapy vehicles and transgenes, vaccines and evolved viruses for vaccines, and laboratory animal models. 相似文献
242.
EB病毒BNLF-1基因的分子生物学研究进展 总被引:2,自引:0,他引:2
位于EB病毒基因组U5-TR区内的BNLF-1基因,其转译产物为潜伏膜蛋白(latent membrane protein1, LMP-1),由于LMP-1可以导致细胞转化并在EB病毒致癌过程中具有重要作用,因而成为近年来EB病毒分子生物学及相关肿瘤如人鼻咽癌、伯基特淋巴瘤、何杰金氏病等疾病病因发病学研究的热点,并取得了一批有重要意义的成果,文章从BNLF-1的基因结构及表达调控, LMP蛋白的结构及生化功能, LMP-1的生物学功能和LMP-1研究进行评述. 相似文献
243.
Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA 总被引:10,自引:0,他引:10
Miguel A. Aranda Aurora Fraile Joaquín Dopazo José M. Malpica Fernando García-Arenal 《Journal of molecular evolution》1997,44(1):81-88
The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected
tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and
was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from
0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic
positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly
different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing
were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure
may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two
subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA
variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs
by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination
events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural
populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our
knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA
replicon to be estimated.
Received: 14 May 1996 / Accepted: 17 July 1996 相似文献
244.
Jih-Shiou Liu Yau-Heiu Hsu Tzu-Yu Huang Na-Sheng Lin 《Journal of molecular evolution》1997,44(2):207-213
Satellite RNA of bamboo mosaic potexvirus (satBaMV) is a linear RNA molecule which encodes a 20-kDa nonstructural protein.
Sequences of seven different satBaMV isolates from bamboo hosts in three genera showed 0.7% to 7.5% base variation which spanned
the whole RNA molecule. However, the putative 20-kDa open reading frame was all preserved in these isolates. The phylogenetic
relationship based on the nucleotide sequence did not show particular grouping of satBaMV from the host in one genus; neither
was the grouping of satBaMV evident by location of sampling. Putative secondary structures of the 3′ untranslated regions
showed a basic pattern with conserved hexanucleotides (ACCUAA) and polyadenylation signal (AAUAAA) located in the loop regions.
Although the satBaMV-encoded 20-kDa protein is a nonstructural protein, its predicted secondary structure contains eight-stranded
β-sheets which may form ``jelly-roll' structure similar to that found in capsid protein encoded by satellite virus of panicum
mosaic virus.
Received: 26 June 1996 / Accepted: 9 September 1996 相似文献
245.
R. GAFNY N. MOGILNER Y. NITZAN J. BEN-SHALOM M. BAR-JOSEPH 《The Annals of applied biology》1995,126(3):465-470
The systemic movement of citrus tristeza virus (CTV) in sour orange (Citrus aurantium) seedlings and of citrus exocortis viroid (CEVd) in Etrog citron (C. medica) seedlings was studied. The movement of the two pathogens was analysed by detection in sections of roots and stems at different time intervals. Both pathogens were detected initially in the basal parts and the roots and subsequently spread to the shoot. CTV and CEVd moved in young citrus seedlings at similar rates. The findings are consistent with long distance phloem transport of the virus and the viroid. The practical implications of the pattern of systemic movement for diagnosis of infected trees are discussed. 相似文献
246.
Isolates of novel strains of Kashmir bee virus (KBV) were obtained from field-collected dead adults of Apis mellifera from honey bee colonies in Canada and Spain. They differed from other strains of KBV in their tendency to aggregate in dilute buffer solution and in containing only three proteins when analysed by SDS-polyacrylamide gel electrophoresis compared with five proteins resolved in the type strain of KBV from Apis cerana in India and six proteins in KBV strains from South Australia and New Zealand. Immunodiffusion tests and Western blotting studies indicated that the five virus isolates were serologically related and all were related to acute paralysis virus (APV). The world distribution of KBV strains and their apparent relationship with APV are discussed. 相似文献
247.
248.
The localisation of plum pox virus (PPV) in stem and petiole tissues of nine susceptible apricot cultivars and GF305 peach seedling has been studied. From stem and petioles consecutive transverse sections spaced at 1 mm were made and tissue sections printed onto nitrocellulose membrane. The resulting prints were probed with a specific antibody for plum pox virus, followed by a rabbit anti-goat antibody conjugated with horse radish peroxidase, in order to localise the virus within the tissues. In stems the virus was mainly present in xylem and pith. The possible presence of the virus in the sclerenchyma is discussed. In petioles the virus was present in epidermis and parenchymas, but not in vessels. The probable movement through the xylem and from cell to cell has been shown. 相似文献
249.
Tatsuo Suzutani Shin Koyano Minoru Takada Itsuro Yoshida Masanobu Azuma 《Microbiology and immunology》1995,39(10):787-794
The virulence of thymidine kinase-negative herpes simplex virus type 1 (HSV-1; VRTK? strain) and type 2 (HSV-2; UWTK? strain) was studied in comparison with that of their parental strains (VR-3 and UW-268, respectively) in an encephalitis model of adult (4-week-old) and newborn (3-day-old) mice. Viral thymidine kinase (TK) activity was essential for the maximum expression of virulence of HSV-1, because the 50% lethal dose (LD50) of VRTK? was 60 times higher than that of VR-3 in the brains of newborn mice expressing high levels of cellular TK activity. However, the UWTK? strain showed the same virulence as the parental strain in newborn mice, despite the lack virulence in adults, suggesting that replication of the UWTK? strain was completely supported by cellular TK activity. This difference in the role of viral and cellular TKs for virus growth between HSV-1 and HSV-2 was confirmed with the one-step growth of virus strains in L-M and L-M(TK?) cells. 相似文献
250.
We determined the 240-nueleotide sequences of the E/NS1 gene junction of four dengue-2 viruses by the primer extension dideoxy chain termination method. These viruses were isolated from dengue patients with different clinical severities in Nakhon Phanom, Northeastern Thailand in 1993. The results were compared with the 52 published dengue-2 sequences of the same gene region. Sequence divergence of four new isolates varied from 4.17% to 5.42% compared with dengue-2 prototype New Guinea C strain whereas it varied from 5.42% to 6.67% and from 6.67% to 7.09% when compared with Jamaica 1409 strain and PR159/S1 strain, respectively. All nucleotide substitutions were found at the 3rd position of the codons which were silent mutations. All 56 isolates studied were classified into five genotypic groups by constructing the dendrogram. The results indicated that four new isolates from Northeastern Thailand belong to genotype II of dengue virus serotype 2, and were most closely related to prototype New Guinea C strain. We also observed the variation in nucleotide and amino acid sequences among clusters of isolates (Thailand-1980, Malaysia-1989 and Thailand-1993) which were obtained from the dengue patients with different clinical severities. The significance of these genetic differences have been discussed in terms of the possible correlation between genetic variability and virulence. 相似文献