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   2670篇
  免费   169篇
  2023年   7篇
  2022年   23篇
  2021年   46篇
  2020年   15篇
  2019年   25篇
  2018年   36篇
  2017年   35篇
  2016年   49篇
  2015年   81篇
  2014年   85篇
  2013年   187篇
  2012年   165篇
  2011年   178篇
  2010年   102篇
  2009年   106篇
  2008年   181篇
  2007年   196篇
  2006年   162篇
  2005年   137篇
  2004年   188篇
  2003年   150篇
  2002年   146篇
  2001年   59篇
  2000年   39篇
  1999年   36篇
  1998年   38篇
  1997年   27篇
  1996年   19篇
  1995年   23篇
  1994年   11篇
  1993年   18篇
  1992年   31篇
  1991年   37篇
  1990年   14篇
  1989年   19篇
  1988年   23篇
  1987年   13篇
  1986年   20篇
  1985年   9篇
  1984年   15篇
  1983年   7篇
  1982年   9篇
  1981年   7篇
  1980年   11篇
  1979年   6篇
  1978年   11篇
  1976年   5篇
  1975年   5篇
  1973年   5篇
  1970年   4篇
排序方式: 共有2839条查询结果,搜索用时 46 毫秒
121.
Common marmosets vocalize phee calls as isolation calls, which seem to facilitate their reunion with family groups. To identify multiple acoustic properties with different time courses, we examined acoustic modulations of phees during different social contexts of isolation. Subject marmosets were totally isolated in one condition, were visually isolated and could exchange vocalizations in another condition, and were visually isolated and subsequently totally isolated in a third condition. We recorded 6,035 phees of 10 male–female marmoset pairs and conducted acoustic analysis. The marmosets frequently vocalized phees that were temporally elongated and louder during isolation, with varying time courses of these changes in acoustic parameters. The vocal rates and sound levels of the phees increased as soon as the marmosets saw their pair mates being taken away, and then gradually calmed down. The phee duration was longer in conditions during which there were no vocal responses from their pair mates. Louder vocalizations are conspicuous and seem to be effective for long‐distance transmission, whereas shorter call duration during vocal exchanges might avoid possible vocal overlap between mates. Am. J. Primatol. 72:681–688, 2010. © 2010 Wiley‐Liss, Inc.  相似文献   
122.
 Previous studies have defined two different peptide binding motifs specific for HLA-A * 0101. These motifs are characterized by the presence of tyrosine (Y) at the C-termini of 9-mer and 10-mer peptides, and either a small polar or hydrophobic (S, T, M) residue in position 2, or a negatively charged (D or E) residue in position 3. In this study, the structural requirements for peptide binding to A * 0101 have been further analyzed by examining the binding capacity of large sets of peptides corresponding to naturally occurring sequences which bore one or the other of these two A * 0101-specific motifs. By correlating the presence of specific residue types at each position along the peptide sequence with increased (or decreased) binding affinity, the prominent influence of secondary anchor residues was revealed. In most cases, the two anchors in positions 2 and 3 appear to act synergistically. With the exception of the DE3 submotif in 9-mer peptides, a positive role for aromatic residues in position 1 and the center of the peptide (positions 4 or 5 of 9- or 10-mer peptides, respectively), and proline at C-3, were also consistently detected. However, secondary anchor residues also appear to differ significantly between the two different submotifs, demonstrating that A * 0101 can utilize alternative modes in binding its peptide ligands. According to these analyses, specific refined submotifs were also established, and their merit verified by independent sets of potential A * 0101 binding peptides. Besides providing useful insight into the nature of the interaction of the A * 0101 allele with its peptide ligands, such refined motifs should also facilitate accurate prediction of potential A * 0101-restricted peptide epitopes. Received: 16 July 1996 / Revised: 18 September 1996  相似文献   
123.
Novel branched cyclomaltooligosaccharide carboxylic acid (cyclodextrin carboxylic acid) derivatives were synthesized by microbial oxidation using Pseudogluconobacter saccharoketogenes to oxidize five types of branched cyclodextrins, including maltosyl beta-cyclodextrin (maltosyl-beta-CyD). For each novel cyclodextrin carboxylic acid derivative synthesized, the hydroxymethyl group of the terminal glucose residue in the branched part of the molecule was regiospecifically oxidized to a carboxyl group to give the corresponding uronic acid. In addition, the physicochemical properties of cyclomaltoheptaosyl-(6-->1)-alpha-D-glucopyranosyl-(4-->1)-alpha-D-glucopyranosiduronic acid (GUG-beta-CyD) (1) and its sodium salt were studied more extensively, as these compounds are most likely to have a practical application.  相似文献   
124.
Mitochondrial genetic variations were used to investigate the relationships between two Japanese wild boars, Japanese wild boar (Sus scrofa leucomystax) and Ryukyu wild boar (S.s. riukiuanus). Nucleotide sequences of the control (27 haplotypes) and cytochrome b (cyt-b) regions (19 haplotypes) were determined from 59 Japanese wild boars, 13 Ryukyu wild boars and 22 other boars and pigs. From phylogenetic analyses, the mtDNA of Ryukyu wild boar has a distinct lineage from that of Japanese wild boar, which was classified into the Asian pig lineage. This result suggests that the Ryukyu wild boar has a separate origin from the Japanese wild boar.  相似文献   
125.
We isolated two new keratin cDNAs by screening a cDNA library constructed from poly(A)+ RNA of the dorsal and abdominal skin of C57BL/10J mice with a probe of human KRT14. Due to its high sequence homology to human keratin 17 cDNA, one full-length cDNA is most likely to be mouse keratin 17 (Krt1-17) cDNA. The other is the putative full-length cDNA of a novel type I keratin gene, designated Krt1-c29. These two keratin genes were mapped to the distal portion of Chromosome 11, where the mouse keratin gene complex-1 (Krt1) is localized. To elucidate the genomic organization of Krt1 in mice, we carried out genetic and physical analyses of Krt1. A large-scale linkage analysis using intersubspecific backcrosses suggested that there are two major clusters in Krt1, one containing Krt1-c29, Krt1-10, and Krt1-12 and the other containing Krt1-14, -15, -17, and -19. Truncation experiments with two yeast artificial chromosome clones containing the two clusters above have revealed that the gene order of Krt1 is centromere-Krt1-c29-Krt1-10-Krt1-12-Krt1-13-K rt1-15-Krt1-19-Krt1-14-K rt1-17-telomere. Finally, we analyzed sequence divergence between the genes belonging to the Krt1 complex. The results clearly indicated that genes are classified into two major groups with respect to phylogenetic relationship. Each group consists of the respective gene cluster demonstrated by genetic and physical analyses in this study, suggesting that the physical organization of the Krt1 complex reflects the evolutionary process of gene duplication of this complex.  相似文献   
126.
Summary The role of serum albumin in the transport of orally administered L-tryptophan (Trp) into rat tissues was examined using analbuminemic and Sprague-Dawley (SD) rats with and without a-methyl-DL-tryptophan (AMT)-induced Trp depletion. Trp was orally administered to rats 16h after AMT or 0.85% NaCl administration, when liver tryptophan 2,3-dioxygenase and protein synthetic activities in AMT-treated rats were similar to those of 0.85% NaCl-treated rats. After oral Trp administration, regardless of the presence or absence of Trp depletion, free serum Trp concentrations were similar in the analbuminemic and SD rats, while total serum Trp concentrations were lower in analbuminemic rats than in SD rats. Although liver, brain, and muscle Trp concentrations after oral Trp administration under Trp depletion were lower in analbuminemic rats than in SD rats, the ratio of the liver Trp concentration in analbuminemic rats to that in SD rats was smaller than that of the brain or muscle Trp concentration. These results suggest that variations in serum albumin levels could affect the transport of orally administered Trp into the liver of rats with Trp depletion.  相似文献   
127.
Soybean globulins were deamidated after removing phytate using ion-exchange resins, and then hydrolyzed by digestive enzymes. The phytate-removed deamidated soybean globulins (PrDS) retained high calcium-binding ability even after the hydrolysis by digestive enzymes. PrDS and its hydrolysates enhanced calcium absorption from the small intestine when injected into the small intestine together with a calcium solution.  相似文献   
128.
A cDNA encoding rye seed chitinase-a (RSC-a) was cloned by rapid amplification of cDNA ends and PCR procedures. It consists of 1,191 nucleotides and encodes an open reading frame of 321 amino acid residues. Recombinant RSC-a (rRSC-a) was produced in the oxidative cytoplasm of Escherichia coli Origami(DE3) in a soluble form by inducing bacteria at a low temperature (20 degrees C). Purified rRSC-a showed properties similar to the original enzyme from rye seeds in terms of chitinase activity toward a soluble substrate, glycolchitin, and an insoluble substrate, chitin beads, in chitin-binding ability to chitin, and in antifungal activity against Trichoderma sp. in vitro. rRSC-a mutants were subsequently produced and purified by the same procedures as those for rRSC-a. Mutation of Trp23 to Ala decreased the chitinase activity toward both substrates and impaired the chitin-binding ability. Furthermore, the antifungal activity of this mutant was weakened with increasing of the NaCl concentration in the culture medium. Complete abolishment of both activities was observed upon the mutation of Glu126 to Gln. The roles of these residues in both activities are discussed.  相似文献   
129.
130.
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