首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   613篇
  免费   51篇
  2023年   4篇
  2022年   8篇
  2021年   22篇
  2020年   6篇
  2019年   15篇
  2018年   21篇
  2017年   25篇
  2016年   21篇
  2015年   32篇
  2014年   37篇
  2013年   33篇
  2012年   60篇
  2011年   42篇
  2010年   24篇
  2009年   23篇
  2008年   33篇
  2007年   34篇
  2006年   30篇
  2005年   24篇
  2004年   22篇
  2003年   25篇
  2002年   18篇
  2001年   12篇
  2000年   7篇
  1999年   12篇
  1998年   8篇
  1997年   6篇
  1996年   6篇
  1995年   3篇
  1994年   2篇
  1993年   5篇
  1992年   6篇
  1991年   4篇
  1990年   3篇
  1989年   1篇
  1988年   4篇
  1987年   2篇
  1986年   4篇
  1985年   2篇
  1982年   2篇
  1981年   2篇
  1979年   3篇
  1977年   4篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1968年   2篇
  1958年   1篇
排序方式: 共有664条查询结果,搜索用时 16 毫秒
151.
The phenotypic and genetic heterogeneity of the basidiomycetous yeast species Rhodotorula glutinis was investigated in a group of 109 isolates. A polyphasic taxonomic approach was followed which included PCR fingerprinting, determination of sexual compatibility, 26S and ITS rDNA sequence analysis, DNA-DNA reassociation experiments and reassessment of micromorphological and physiological attributes. The relationships with species of the teleomorphic genus Rhodosporidium were studied and isolates previously identified as Rh. glutinis were found to belong to Rhodosporidium babjevae, Rhodosporidium diobovatum and Rhodosporidium sphaerocarpum. Other isolates included in the study were found to belong to Rh. glutinis var. dairenensis, which is elevated to the species level, or to undescribed species. The concept of Rh. glutinis sensu stricto is proposed due to the close phenetic and phylogenetic proximity detected for Rh. glutinis, Rhodotorula graminis and R. babjevae.  相似文献   
152.
Trypsin inhibitors of two varieties of Bauhinia variegata seeds have been isolated and characterized. Bauhinia variegata candida trypsin inhibitor (BvcTI) and B. variegata lilac trypsin inhibitor (BvlTI) are proteins with M r of about 20,000 without free sulfhydryl groups. Amino acid analysis shows a high content of aspartic acid, glutamic acid, serine, and glycine, and a low content of histidine, tyrosine, methionine, and lysine in both inhibitors. Isoelectric focusing for both varieties detected three isoforms (pI 4.85, 5.00, and 5.15), which were resolved by HPLC procedure. The trypsin inhibitors show K i values of 6.9 and 1.2 nM for BvcTI and BvlTI, respectively. The N-terminal sequences of the three trypsin inhibitor isoforms from both varieties of Bauhinia variegata and the complete amino acid sequence of B. variegata var. candida L. trypsin inhibitor isoform 3 (BvcTI-3) are presented. The sequences have been determined by automated Edman degradation of the reduced and carboxymethylated proteins of the peptides resulting from Staphylococcus aureus protease and trypsin digestion. BvcTI-3 is composed of 167 residues and has a calculated molecular mass of 18,529. Homology studies with other trypsin inhibitors show that BvcTI-3 belongs to the Kunitz family. The putative active site encompasses Arg (63)–Ile (64).  相似文献   
153.
Lectins are powerful stimulants of quiescent peripheral blood lymphocytes. They can induce blast transformation leading to mitosis of these cells in vitro. We report here the dose-dependent proliferative curve for human peripheral blood monouclear cells (PBMC) stimulated by the lectin amansin, from Amansia multifida. Amansin stimulated proliferation of (PBMC) at relatively low concentrations (3.12 to 12.5 μg mL-1). We observed also a gradual reduction in mitogenic capacity with progressive increase in the lectin concentration above 12.5 μg mL-1. This decrease in the mitogenic potential did not result from a toxic effect on the cells, and was predominant at a lectin concentration above 50 μg mL-1. This decrease in lymphocyte proliferation could be blocked by avidin and could not be overcome by IL-2 or another lectin (Con Br) at stimulatory concentrations. Additionally, we observed that cells incubated at stimulatory concentrations of amansin produced IFN-γ. Analysis of the culture supernatants established a direct correlation between the IFN-γ and the mitogenic and anti-mitogenic capacity of amansin. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
154.
The modern cultivars of sugarcane (Saccharum spp.) are highly polyploid and accumulate aneuploidies due to their history of domestication, genetic improvement and interspecific hybrid origin involving the domesticated sweet species Saccharum officinarum (‘noble cane’) and the wild Saccharum spontaneum, both with an evolutionary history of polyploidy. The first hybrids were backcrossed with S. officinarum, and selection from progenies in subsequent generations established the genetic basis of modern cultivars. Saccharum genome complexity has inspired several molecular studies that have elucidated aspects of sugarcane genome constitution, architecture and cytogenetics. Herein, we conducted a comparative analysis of the meiotic behaviour of representatives of the parentals S. officinarum and S. spontaneum, and the commercial variety, SP80-3280. S. officinarum, an octoploid species, exhibited regular meiotic behaviour. In contrast, S. spontaneum and SP80-3280 exhibited several abnormalities from metaphase I to the end of division. We reported and typified, for the first time, the occurrence of peri- and paracentric inversions. Using in-situ hybridisation techniques, we were able to determine how pairing association occurred at diakinesis, the origin of lagging chromosomes and, in particular, the mitotic chromosome composition of SP80-3280. Interestingly, S. spontaneum and recombinant chromosomes showed the most marked tendency to produce laggards in both divisions. Future attempts to advance knowledge on sugarcane genetics and genomics should take meiotic chromosome behaviour information into account.  相似文献   
155.
156.
The electrophoretic patterns of 15 protein systems codified for 20 genetic loci were investigated using horizontal electrophoresis. A total of 150 blood samples, from five species of the genusCallithrix were analyzed. Polymorphic variation was observed in 10 out 20 loci analyzed. The genotypic distributions are in Hardy-Weinberg equilibrium. The average heterozygosity (H) varied from 1% to 5%, similar to those observed for other Neotropical primates. The genetic distance coefficients revealed a phylogenetic separation of these species into two groups: (1) “argentata” (C. humeralifer andC. emiliae); (2) “jacchus” (C. jacchus, C. penicillata, andC. geoffroyi). This arrangement is according to the taxonomic arrangement proposed byHershkovitz (1977),de Vivo (1988), andMittermeier et al. (1988). The results in each group are compatible with the subspecies values recorded for the Platyrrhini. These values showed that:C. humeralifer andC. emiliae are subspecies ofC. argentata;C. jacchus, C. penicillata, andC. geoffroyi are subspecies ofC. jacchus. These results also suggest thatC. j. geoffroyi is the “jacchus” group taxon, most similar genetically to the “argentata” group.  相似文献   
157.
The purpose of this study was to determine nucleotide sequences from the 5′ flanking region of the ϵ‐globin gene of selected platyrrhine primates and to analyze the data for phylogenetic information and estimated times of divergence. We report new sequence data for two species of New World monkeys, Callicebus torquatus and Pithecia irrorata. We analyzed these data in conjunction with homologous sequences from other primate species. The data support the hypothesis that the titi monkeys (Callicebus) and seed predators (Tribe Pitheciini) form a clade (Subfamily Pitheciinae), and also provide limited support for that subfamily being allied with the atelines. We also present estimated dates of divergence for the Callicebus and pitheciin lineages. Am. J. Primatol. 48:69–75, 1999. © 1999 Wiley‐Liss, Inc.  相似文献   
158.
Twenty nine patients with localized cutaneous leishmaniasis had lymph node and skin ulcer aspirations for culture of Leishmania with the modified Marzochís vacuum aspiratory technique. Sensitivity of lymph node aspiration was 58.6% and 34.5% for skin ulcer aspiration (P=0.06). Combined sensitivity of the two methods was 79.3%. There was no agreement between methods (Kappa Index = -0.084; CI95% -0,45; 0,28) showing the potential complementary roles in diagnostic approach.  相似文献   
159.
160.
This study aimed to quantify the time-motion demands and intra-team movement synchronization during the pre-season matches of a professional soccer team according to the opposition level. Positional data from 20 players were captured during the first half of six pre-season matches of a Portuguese first league team. Time-motion demands were measured by the total distance covered and distance covered at different speed categories. Intra-team coordination was measured by calculating the relative phase of all pairs of outfield players. Afterwards, the percentage of time spent in the −30° to 30° bin (near-in-phase mode of coordination) was calculated for each dyad as a measure of space-time movement synchronization. Movement synchronization data were analyzed for the whole team, according to each dyad average speed and by groups of similar dyadic synchronization tendencies. Then, these data were compared according to the opponent team level (first league; second league; amateurs). Time-motion demands showed no differences in total distance covered per opposition levels, while matches opposing teams of superior level revealed more distance covered at very high intensity. Competing against superior level teams implied more time in synchronized behavior for the overall displacements and displacements at higher intensities. These findings suggest that playing against higher-level opponents (1st league teams) increased time-motion demands at high intensities in tandem with intra-team movement synchronization tendencies.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号