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   576篇
  免费   26篇
  国内免费   1篇
  2021年   5篇
  2020年   7篇
  2019年   8篇
  2018年   20篇
  2017年   10篇
  2016年   16篇
  2015年   12篇
  2014年   23篇
  2013年   32篇
  2012年   41篇
  2011年   58篇
  2010年   23篇
  2009年   27篇
  2008年   47篇
  2007年   31篇
  2006年   30篇
  2005年   22篇
  2004年   16篇
  2003年   22篇
  2002年   13篇
  2001年   19篇
  2000年   6篇
  1999年   12篇
  1998年   3篇
  1997年   3篇
  1995年   3篇
  1994年   6篇
  1993年   4篇
  1992年   5篇
  1991年   10篇
  1990年   3篇
  1989年   7篇
  1988年   5篇
  1987年   8篇
  1986年   4篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   4篇
  1979年   7篇
  1978年   2篇
  1976年   2篇
  1975年   1篇
  1974年   3篇
  1973年   3篇
  1972年   1篇
  1971年   1篇
  1970年   2篇
  1969年   3篇
  1968年   1篇
排序方式: 共有603条查询结果,搜索用时 109 毫秒
1.

Background  

Micro-biological research relies on the use of model organisms that act as representatives of their species or subspecies, these are frequently well-characterized laboratory strains. However, it has often become apparent that the model strain initially chosen does not represent important features of the species. For micro-organisms, the diversity of their genomes is such that even the best possible choice of initial strain for sequencing may not assure that the genome obtained adequately represents the species. To acquire information about a species' genome as efficiently as possible, we require a method to choose strains for analysis on the basis of how well they represent the species.  相似文献   
2.
Study of the oviduct of the pied myna (Sturnus contra contra) throughout the year reveals that oviductal weight, length, surface epithelial height and glycogen content are low during August to January (nonbreeding phase), partially increase during February to April (pre-breeding phase), maximally increase in May (breeding phase) and decrease in June and July (post-breeding phase). In the nesting cycle, there is greatest growth in all the regions of the oviduct from early nest-building to the egg-laying period and this is followed by rapid involution during incubation and nestling periods. Some notable features in the oviduct of the pied myna are described: 1) All five regions of the oviduct (infundibulum, magnum, isthmus, uterus, and vagina) are clearly distinguishable when studied from serial sections of the oviduct even during the nonbreeding phase of the annual ovarian cycle. 2) There is a strong correlation between initiation of tubular gland formation and the onset of nestbuilding activity. 3) The distal part of the magnum is differentiated into a 'mucous region' having well developed basal nonciliated cells. 4) A sixth zone can be identified between the magnum and isthmus. Sperm hostlike glands exist at the cranial end of the zone. 5) Several circular epithelial invaginations are evident in the intermucosal folds and their size decreases in centripetal order in the vagina. 6) The pattern and degree of regression are different in various regions of the oviduct. A close synchrony between ovarian and oviducal cycles is indicated in the pied myna (Sturnus contra contra).  相似文献   
3.
4.
Catfish hepatic metallothionein was purified to homogeneity by Sephadex G-75 gel filtration, DEAE-Sephadex A-25 column chromatography and preparative polyacrylamide gel electrophoresis. Induction by cadmium and zinc, characteristic UV spectrum, cadmium binding property and its low MW established that it was a metallothionein. Antibody was raised in rabbit against catfish metallothionein. Catfish antimetallothionein cross-reacted with other fish metallothioneins but not with chicken or rodent metallothionein. Catfish metallothionein is more electronegative as compared to mouse, rat, chicken or hamster metallothionein. Catfish MT appeared to aggregate readily on storage and to be less electronegative.  相似文献   
5.
6.
The photoinduced reaction cycle of bacteriorhodopsin (BR) has been studied by means of a recently developed picosecond infrared spectroscopic method at ambient temperature. BR - K difference spectra between 1560 and 1700 cm-1 have been recorded at delay times from 100 ps to 14 ns. The spectrum remains unchanged during this period. The negative difference OD band at 1660 cm-1 indicates the peptide backbone responds within 50 ps. A survey in the region of carboxylic side chain absorption around 1740 cm-1 reveals that perturbations of those groups, present in low-temperature FTIR spectra, are not observable within 10 ns, suggesting a slow conformational change.  相似文献   
7.
Polyporus ostreiformis produced Mn peroxidase, acid protease, alpha-amylase, and lignin peroxidase, with maximum activities of 40, 8,300, and 4,200 U liter-1 and 50 nkat liter-1, respectively, in nitrogen-limited liquid media. The fungus removed only 18.6% lignin from rice straw in 3 weeks but effected 99% decolorization of Congo red dye in 9 days.  相似文献   
8.
The aim of the present investigation is to evaluate adrenomedullary hormones and blood glucose responses to intermale aggression in the bandicoot rat. Aggression elicited a rise in adrenaline and noradrenaline content of the adrenal gland and in blood glucose level in the subordinate rats. No significant change was marked in the dominant rats after aggression. It is suggested that during aggression the subordinate rats suffered from psychosomatic stress that resulted in hyperactivity of the adrenal medulla and consequently hyperglycemia.  相似文献   
9.
The induction of antigen-specific tolerance in mice by conjugates of ovalbumin (OVA) and monomethoxypolyethylene glycol (mPEG) previously had been shown to be associated with the generation of antigen-specific suppressor T (Ts) cells. For the elucidation of the nature of these Ts cells, five nonhybridized OVA-specific Ts cell clones were generated from the spleen cells of a BDF1 mouse which had been immunosuppressed by the tolerogenic conjugate, OVA(mPEG)12. The cloned Ts cells were maintained in vitro by periodic stimulation with OVA and feeder cells and were able to suppress the in vitro antibody production in an OVA-specific and MHC class I (H-2Kd or H-2Dd)-restricted manner. All these Ts cell clones were shown to be Thy1.2+, CD4-, CD5-, CD8+, and to express CD3 and the alpha beta heterodimer of the T cell receptor. The cell-free extracts of these cells contained soluble suppressor factors which could mimic in vitro the suppressive activity of the intact cells. In contrast to cytotoxic T lymphocytes (CTL), none of the cloned Ts cells were endowed with cytolytic activity as revealed in the perforin-mediated microhemolysis and in the 18-hr51Cr release assays. These results demonstrate that (i) OVA-specific Ts cell clones can be generated from mice pretreated with OVA(mPEG)12 by employing conventional T cell culture techniques, and (ii) these Ts cells are functionally different from conventional CD8+ CTL.  相似文献   
10.
R Nandi  S Chakraborty  M Maiti 《Biochemistry》1991,30(15):3715-3720
The dependence on base-pair composition and sequence specificity of the (aristololactam beta-D-glucoside)-DNA interaction was examined by spectrophotometric, spectrofluorometric, spectropolarimetric, thermal melting, thermodynamic, and viscometric studies. Binding of this alkaloid to various natural and synthetic DNAs was dependent upon the base composition and sequences of DNA. The binding parameters obtained from spectrophotometric analysis, according to an excluded-site model, indicated a relatively high affinity of the alkaloid binding to GC-rich DNA and alternating GC polymer. This affinity was further evidenced by the quenching of fluorescence intensity, decrease in quantum yield, and perturbations in circular dichroic spectrum. The alkaloid stabilized all DNAs against thermal denaturation. The temperature dependence of the binding constants was used to estimate the thermodynamic parameters involved in the complex formation of the alkaloid with various DNAs. The negative enthalpy and entropy change increased with increasing GC content of DNA and also compensated one another to produce a relatively small Gibbs free energy change. Viscometric studies showed that in the strong binding region the increase of contour length of DNA depended strongly on its base composition and sequence of bases, being larger for GC-rich DNA and alternating GC polymer. On the basis of these observations, it is concluded that the alkaloid binds to DNA by a mechanism of intercalation and exhibits considerable specificity toward alternating GC polymer.  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