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   787篇
  免费   55篇
  国内免费   2篇
  2022年   3篇
  2021年   4篇
  2019年   3篇
  2017年   5篇
  2016年   9篇
  2015年   20篇
  2014年   27篇
  2013年   24篇
  2012年   48篇
  2011年   39篇
  2010年   29篇
  2009年   33篇
  2008年   46篇
  2007年   38篇
  2006年   37篇
  2005年   34篇
  2004年   34篇
  2003年   42篇
  2002年   29篇
  2001年   13篇
  2000年   13篇
  1999年   10篇
  1998年   18篇
  1997年   7篇
  1996年   11篇
  1995年   4篇
  1994年   9篇
  1993年   15篇
  1992年   13篇
  1991年   13篇
  1990年   14篇
  1989年   13篇
  1988年   14篇
  1987年   16篇
  1986年   17篇
  1985年   11篇
  1984年   9篇
  1983年   10篇
  1982年   10篇
  1981年   10篇
  1980年   13篇
  1979年   10篇
  1978年   6篇
  1977年   4篇
  1976年   13篇
  1975年   6篇
  1974年   4篇
  1973年   7篇
  1968年   5篇
  1967年   5篇
排序方式: 共有844条查询结果,搜索用时 328 毫秒
1.
The copper complex of indomethacin (1-(p-chlorobenzoyl)-5-methoxy-2-methyl-indole acetate), a common anti-inflammatory drug, was prepared and characterized. Crystal structure determination revealed the dimeric form of the 1:2 complex, namely Cu2(indomethacin)4 · L2, in the unit cell. Suprisingly, the copper-copper distance (263 pm) was very close to metallic copper (256 pm). The two coordination sites in the copper-copper axis can be readily replaced by superoxide. An intriguing similarity to Cu2(acetate)4 was seen.Due to the lipophilic nature of the indomethacin ligand, this copper complex reacted with superoxide in aprotic solvents. The superoxide dismutating activity was successfully demonstrated in Me2SO/water and acetonitrile/water mixtures using the nitro-blue tetrazolium assay and pulse radiolysis. The second-order rate constant of 6 · 109 M?1 · s?1 in strictly aqueous systems dropped only slightly to 1.1 · 109 M?1 · s?1 when aprotic solvents were used. This is the fastest rate constant ever observed for a copper-dependent dismutation of superoxide. The KO2-induced lipid peroxidation in both erythrocytes and liver microsomes was suppressed by 70% in the presence of 1 · 10?10 mol · ml?1 of Cu2(indomethacin)4. The inhibitory action dropped to 25% when Cu2Zn2superoxide dismutase was employed. The formation of copper · indomethacin in rat serum after administration of indomethacin was shown in vitro and in vivo.  相似文献   
2.
3.
Deafferentation experiments during postembryonic development show morphological and/or physiological changes of receptor fibers and of identified auditory interneurons in the CNS of the locusts Locusta migratoria and Schistocerca gregaria after unilateral ablation of one tympanic organ either in the larva or the adult animal.
1.  In Locusta migratoria, 5 days after deafferentation, intact, contralateral receptor fibers had sprouted collaterals in the frontal acoustic neuropil of the metathoracic ganglion (Figs. 1, 2). Collateral sprouts were only rarely found in Schistocerca gregaria.
2.  After about 20 days the deafferented auditory interneurons receive new inputs from the contralateral receptors (Figs. 3, 5, 7, 10). This largely restores their thresholds and intensity/response functions. Collaterals from the first order interneurons cross the midline to the contralateral neuropil (BSN1 neuron, Fig. 4), which is never seen in intact animals. By contrast, in the TN1 neuron no consistent morphological change due to the deafferentation could be found (Fig. 6).
3.  Interneurons of higher order (AN1, TN3 neuron in locusts) regain their response pattern (Fig. 7) without morphological changes (Fig. 9). Bilateral recordings show that the deafferented interneurons respond more weakly to auditory stimuli than the intact neuron, but the response to vibration stimuli remains unchanged (TN3 neuron, Fig. 8).
  相似文献   
4.
5.
A set of cDNA clones coding for alkali myosin light chains (AMLC) was isolated from fetal human skeletal muscle. Nucleotide sequence analysis and RNA expression patterns of individual clones revealed related sequences corresponding to (i) fast fiber type MLC1 and MLC3; (ii) the embryonic MLC that is also expressed in fetal ventricle and adult atrium (MLCemb); and (iii) a nonsarcomeric MLC isoform that is found in all nonmuscle cell types and smooth muscle. The AMLC gene family in man comprises unique copies for MLC1, MLC3 and MLCemb, and multiple copies for the nonsarcomeric MLC genes. The gene coding for MLC1 and MLC3 is located on human chromosome 2.  相似文献   
6.
The localization of V kappa gene regions to chromosome 2, on which the kappa locus is located, and to other chromosomes is described. The V kappa genes that have been transposed to other chromosomes are called orphons. The finding of two new V kappa genes on chromosome 22 is reported. A V kappa II gene of this region and two V kappa I genes of the Chr1 and the cos 118 regions were sequenced. The two V kappa I orphon sequences and two others that had been determined previously were 97.5% identical, indicating that they may have evolved from a common ancestor by amplification. A model of the evolution of the human V kappa orphons is discussed.  相似文献   
7.
Hepatitis B virus (HBV) DNA integration has been shown to occur frequently in human hepatocellular carcinomas. We have investigated whether common cellular DNA domains might be rearranged, possibly by HBV integration, in human primary liver tumors. Unique cellular DNA sequences adjacent to an HBV integration site were isolated from a patient with hepatitis B surface antigen-positive hepatocellular carcinoma. These probes detected rearrangement of this cellular region of chromosomal DNA in 3 of 50 additional primary liver tumors studied. Of these three tumor samples, two contained HBV DNA, without an apparent link between the viral DNA and the rearranged allele; HBV DNA sequences were not detected in the third tumor sample. By use of a panel of somatic cell hybrids, these unique cellular DNA sequences were shown to be located on chromosome 4. Therefore, this region of chromosomal DNA might be implicated in the formation of different tumors at one step of liver cell transformation, possibly related to HBV integration.  相似文献   
8.
Summary A cDNA for the human catalytic subunit (C) of cAMP-dependent protein kinase (PKA) has been cloned from a testis cDNA library. In the present study, we have determined the chromosomal localization of this gene using a cDNA for C as a probe. Southern blot analysis of genomic DNA from human/mouse cell hybrids revealed that the presence or absence of a 20-kbXbaI fragment, which hybridized with the C probe, was concordant with the presence of human chromosome 1.In situ hybridization to metaphase chromosome confirmed the somatic cell hybrid data and regionally mapped the C gene of PKA to the p36 band on chromosome 1.  相似文献   
9.
Summary A collection of 2,000 lambda phage-carrying human single-copy inserts (> 700 bp) were isolated from two chromosome-3 flow-sorted libraries. The single-copy DNA fragments were first sorted into 3p and 3q locations and about 700 3p fragments were regionally mapped using a deletion mapping panel comprised of two humanhamster and two-human-mouse cell hybrids, each containing a chromosome 3 with different deletions in the short arm. The hybrids were extensively mapped with a set of standard 3p markers physically localized or ordered by linkage. The deletion mapping panel divided the short arm into five distinct subregions (A-E). The 3p fragments were distributed on 3p regions as follows: region A, 26%; B, 31%; C, 4%; D, 4% and E, 35%. We screened 300 single-copy DNA fragments from the distal part of 3p (regions A and B) with ten restriction endonucleases for their ability to detect restriction fragment length polymorphisms (RFLPs). Of these fragments 110 (36%) were found to detect useful RFLPs: 35% detected polymorphisms with frequency of heterozygosity of 40% or higher, and 25% with frequency of 30% or higher. All polymorphisms originated from single loci and most of them were of the base pair substitution type. These RFLP markers make it possible to construct a fine linkage map that will span the distal part of chromosome 3p and encompasses the von Hippel-Lindau disease locus. The large number of single-copy fragments (2,000) spaced every 100–150 kb on chromosome 3 will make a significant contribution to mapping and sequencing the entire chromosome 3. The 300 conserved chromosome 3 probes will increase the existing knowledge of man-mouse homologies.  相似文献   
10.
Summary Five bird species were examined in order to ascertain if any changes in flight muscle catabolism take place between breeding season and migration. Two different patterns were discovered. The first consists of a high oxidative capacity and a low glycolytic and anaerobic capacity during migration. The converse occurs during the breeding season, i.e. low oxidative, high glycolytic and anaerobic capacity. The pattern was found in those species that deposit large amounts of fat prior to migration. The second pattern was similar to the first, but there was no change in fatty acid oxidation capacity between breeding season and migration. The pattern was found in those species that do not deposit much fat towards migration. These changes are believed to reflect differences in migration strategy and differences in locomotory activity during different seasons. Deviations from these patterns are discussed.  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