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   6031篇
  免费   563篇
  国内免费   3篇
  6597篇
  2022年   54篇
  2021年   117篇
  2020年   63篇
  2019年   67篇
  2018年   78篇
  2017年   60篇
  2016年   134篇
  2015年   266篇
  2014年   262篇
  2013年   388篇
  2012年   484篇
  2011年   441篇
  2010年   258篇
  2009年   210篇
  2008年   372篇
  2007年   384篇
  2006年   322篇
  2005年   275篇
  2004年   280篇
  2003年   275篇
  2002年   276篇
  2001年   68篇
  2000年   42篇
  1999年   57篇
  1998年   86篇
  1997年   53篇
  1996年   50篇
  1995年   40篇
  1994年   54篇
  1993年   43篇
  1992年   35篇
  1991年   31篇
  1990年   43篇
  1989年   34篇
  1988年   33篇
  1986年   29篇
  1985年   38篇
  1984年   37篇
  1983年   40篇
  1982年   41篇
  1981年   41篇
  1980年   33篇
  1978年   27篇
  1977年   25篇
  1976年   33篇
  1975年   29篇
  1974年   28篇
  1973年   27篇
  1972年   24篇
  1969年   25篇
排序方式: 共有6597条查询结果,搜索用时 15 毫秒
41.
Zusammenfassung Es werden verschiedene Typen von Einschlußkörperchen im Karyoplasma der Epithelzellen des menschlichen Nebenhodenepithels beschrieben. Die verschieden strukturierten Kerninklusionen werden als eine Differenzierungsreihe aufgefaßt. Sie beginnt mit kleinen rundlichen Körperchen aus feinfädigem Material und führt über die Ausbildung von Anhäufungen dichter homogener Kugeln zu großen Vakuolen wechselnden Inhaltes.
Summary Different types of inclusion bodies are described in the karyoplasm of the epithelial cells of the human epididymis. The structural differences between these inclusions are interpreted as being indicative of consecutive stages in the process of their formation. Thus small, spherical bodies consisting of a fine fibrous material are believed to be the initial stages in the formation of the inclusion bodies whereas the dense, homogenous globules are thought to represent a later stage. Large vacuoles containing different materials are regarded as the final stage in this process of differentiation.


Herrn Professor Dr. W. Bargmann zum 60. Geburtstag gewidmet.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
42.
Ghosts prepared in CO2-saturated water from unwashed human red cells can be fragmented mechanically, but ghosts from thrice washed cells cannot. If the ghosts are prepared by freezing and thawing, this difference is not observed. The electrophoretic velocity varies also with the way in which the ghosts are prepared. The pH-mobility dependence of washed red cells flatten off to a plateau at pH 9, and the electrophoretic velocity is zero at about pH 2. Ghosts prepared by freezing and thawing have almost the same pH-mobility dependence, but if the ghosts are prepared in CO2-saturated hyptonic saline, the mobility at pH 9.4 is 0.75 times that of washed cells. Fragments of ghosts of unwashed red cells have a smaller mobility than that of the red cells. Trypsin reduces the mobility of washed red cells and of ghosts. Sols of lipid complexes (lecithin, cephalin, and lipositol), at varying pH's, have a mobility 1.2 times that of the washed red cell. The pH-mobility relation is otherwise similar. These complexes can be coated with dextran and trypsin.  相似文献   
43.
Whole-cell hydrolysates were prepared from 58 strains of nocardiae and streptomycetes. Strains morphologically intermediate between the two genera and morphological variants of the same strains were included. Paper chromatograms made from the whole-cell hydrolysates clearly demonstrated meso-diaminopimelic acid as a major constituent of cultures of Nocardia spp., and LL-diaminopimelic acid as a major constituent of cultures of Streptomyces spp. In cultures of ten strains of N. madurae and of three of N. pelletieri, meso-diaminopimelic acid predominated, thereby supporting the assignment of these species to the genus Nocardia.  相似文献   
44.
45.
Summary Three non-chromosomal and two chromosomal genes which influence resistance to streptomycin are described. Each of the non-chromosomal factors,sr-500,sr-1500, andsd, exhibits uniparental inheritance, with all progeny receiving the factor when it is carried by the parent of mating-typeplus, and none when it is carried by the mating-typeminus parent. The streptomycin-dependence factor,sd, shows zygotic dominance when contributed by the mating-typeplus parent, but not when coming from the mating-typeminus parent, indicating that the uniparental transmission results from events occurring within the zygote early in maturation and well before meiosis. The chromosomal geneA interacts both with chromosomal and non-chromosomal genes at the biochemical level, but does not alter their patterns of inheritance.With 1 Figure in the TextThis paper is dedicated to ProfessorL. C. Dunn in gratitude to him as teacher and advisor, on the occasion of his retirement.This work was supported by grants from the U.S. Public Health Service and the National Science Foundation. The generosity and interest of ProfessorFrancis J. Ryan in providing laboratory space is gratefully acknowledged, as is the technical assistance of MissFran Yablonsky.  相似文献   
46.
47.
The presence of the pertussis toxin (PTX) insensitive GTP-binding proteins (G-proteins) Gq and/or G11 has been demonstrated in three different prolactin (PRL) and growth hormone (GH) producing pituitary adenoma cell lines. Immunoblocking of their coupling to hormone receptors indicates that Gq and/or G11 confer throliberin (TRH) responsive phospholipase C (PL-C) activity in these cells. The contention was substantiated by immunoprecipitation analyses snowing that anti Gq/11-sera coprecipitated PL-C activity. In essence, only Gq/11 (but neither Gi2, Gi3 nor Go) seems to mediate the TRH-sensitive PL-C activity, while Go may be coupled to a basal or constitutive PL-C activity. Immunoblocking studies imply that the B-complex also, to some extent, may stimulate GH3 pituitary cell line PL-C activity. Finally, the steady state levels of Gq/11 mRNA and protein were downregulated upon long term exposure of the GH3 cells to TRH (but not to vasoactive intestinal peptide = VIP).  相似文献   
48.
Expression of human immunodeficiency virus-1 integrase in Escherichia coli, at levels that had no effect on bacterial cell growth, blocked plaque formation by bacteriophages having single-stranded genomic DNA (M13) or RNA (R17, Q, PRR1). Plaque formation by phages having double-stranded genomic DNA (T4, PR4) was unaffected. Integrase also inhibited infection by the phagemid M13KO7, but it had no effect on production of phage once infection by M13KO7 was established. This result indicated that integrase affects an early stage in infection. Integrase also inhibited phage production following transfection by either single-stranded or double-stranded (replicative form) M13 DNA, it blocked M13 DNA replication, as assayed by incorporation of radioactive nucleotides into DNA, and it failed to affect bacterial pilus function. These data suggest that integrase interacts in vivo with phage nucleic acid, a conclusion supported by studies in which integrase was shown to have a DNA-binding activity in its C-terminal portion. This portion of integrase was both necessary and sufficient for interference of plaque formation by M13 in the present study. Expression of the N-terminal portion of integrase at the same level as intact integrase had little effect on phage growth, indicating that expression of foreign protein in general was not responsible for the inhibitory effect. The simple bacteriophage assay described is potentially useful for identifying integrase mutants that lack single-stranded DNA binding activity.  相似文献   
49.
50.
To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (rA) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect rA differing from 1 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