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   572篇
  免费   27篇
  599篇
  2023年   3篇
  2022年   4篇
  2021年   11篇
  2020年   8篇
  2019年   11篇
  2018年   13篇
  2017年   10篇
  2016年   22篇
  2015年   21篇
  2014年   22篇
  2013年   36篇
  2012年   50篇
  2011年   47篇
  2010年   27篇
  2009年   13篇
  2008年   27篇
  2007年   35篇
  2006年   45篇
  2005年   32篇
  2004年   26篇
  2003年   12篇
  2002年   25篇
  2001年   7篇
  2000年   10篇
  1999年   9篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   5篇
  1993年   4篇
  1992年   5篇
  1991年   4篇
  1990年   9篇
  1989年   6篇
  1985年   4篇
  1984年   6篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1970年   1篇
  1969年   1篇
  1968年   2篇
  1966年   1篇
  1941年   1篇
排序方式: 共有599条查询结果,搜索用时 15 毫秒
51.
This work presents the Dauco carotae-Crepidetum rhoeadifoliae plant association, which is new to Poland. The association has been observed in industrial reclamation areas in the vicinity of carbonate mineral excavation sites in the central part of the Opole region. In the vast majority of cases, plots of this association developed in reclaimed areas. The majority of diagnostic species for the association was found within surveyed plots, including Verbascum thapsus, V. densiflorum and Bryum argenteum. Taxa characteristic of the alliance were also constantly present, i.e. Daucus carota, Melilotus alba, M. officinalis, Echium vulgare and Erysimum hieracifolium. This association belongs to the rarest syntaxa in Poland included in the Dauco-Melilotion alliance of ruderal communities with a predominance of hemicryptophytes, therophytes and perennials. The main diagnostic species — Crepis rhoeadifolia, belongs to very rare elements of Polish flora. It has been observed only in the southern part of the country in approx. 20 sites. Crepis rhoeadifolia had not been observed in Silesia for approx. 40 years, which is why it was considered to be an extinct taxon in this region. Rediscovering of the species allowed for diagnosing the Dauco-Crepidetum rhoeadifoliae association. This association is an example of a pioneer phytocenosis of, most likely, anthropogenic origin in Silesia.  相似文献   
52.
Oxidation of protein methionines to methionine sulfoxides can result in protein structural alterations with a wide variety of biological implications. Factors that determine susceptibility to oxidation are not well understood. The recent JBC Editors Pick by Walker et al. applied proteomic methodologies to show that the oxidative susceptibility of buried methionine residues is strongly correlated with folding stability of the contextual peptide. Proteome-wide analysis of oxidation-susceptible methionines promises to answer open questions about the biological functions of reversible methionine oxidation.  相似文献   
53.
In this paper, the authors investigate the membrane transport of aqueous non-electrolyte solutions in a single-membrane system with the membrane mounted horizontally. The purpose of the research is to analyze the influence of volume flows on the process of forming concentration boundary layers (CBLs). A mathematical model is provided to calculate dependences of a concentration polarization coefficient (ζ s ) on a volume flux (J vm ), an osmotic force (Δπ) and a hydrostatic force (ΔP) of different values. Property ζ s ?=?f(J vm ) for J vm ?>?0 and for J vm ?≈?0 and property ζ s ?=?fC 1) are calculated. Moreover, results of a simultaneous influence of ΔP and Δπ on a value of coefficient ζ s when J vm ?=?0 and J vm ?≠?0 are investigated and a graphical representation of the dependences obtained in the research is provided. Also, mathematical relationships between the coefficient ζ s and a concentration Rayleigh number (R C ) were studied providing a relevant graphical representation. In an experimental test, aqueous solutions of glucose and ethanol were used.  相似文献   
54.
55.
56.
PNH is a rare clonal disorder of hematopoietic stem cells, therefore all blood cells lineages are involved. The main feature is an increased sensitivity of erythrocytes to complement-mediated cell lysis due to deficiency of membrane-bound GPI (glycosylphosphatidylinositol)-anchored proteins which normally function as inhibitors of reactive hemolysis. In the present study, we performed flow cytometric analysis using monoclonal antibodies against CD55 and CD59 for the detection of PNH-type clone in the blood of 50 patients (28 females and 22 males, age range 7-67 yrs). In one patient only we found a large population (95%) of granulocytes with decreased expression of both CD55 and CD59 molecules (type I PNH) and in two others with partial loss of CD55 expression (type II PNH). The expression was determined chiefly on granulocytes which in the control group showed reliable and high expression of CD55 and CD59.  相似文献   
57.
Lysosomal carboxypeptidase A (cathepsin A) is synthetized in the form of preproenzyme, which undergoes to active enzyme as a result of post-translational modification. It splits off C-terminal amino acid residues from peptides and proteins and synergizes with other proteases in degradation of cellular proteins in lysosomes. Lysosomal carboxypeptidase A has an effect on peptide hormones and peptides of biological activity of tissues and body fluids as well. It forms complexes with some glycosidases that protects them against proteolytic degradation. Deficiency of this enzyme induces storage diseases. Lysosomal carboxypeptidase A as multifunctional enzyme plays an important regulatory role in organismal metabolism.  相似文献   
58.
An alternative to land spreading of manure is to grow crops of algae on the N and P present in the manure and convert manure N and P into algal biomass. The objective of this study was to evaluate the fertilizer value of dried algal biomass that had been grown using anaerobically digested dairy manure. Results from a flask study using two soils amended with algal biomass showed that 3% of total algal nitrogen (N) was present as plant available N at day 0. Approximately 33% of algal N was converted to plant available N within 21 days at 25 degrees C in both soils. Levels of Mehlich-3 extractable phosphorus (P) in the two soils rose with increasing levels of algal amendment but were also influenced by existing soil P levels. Results from plant growth experiments showed that 20-day old cucumber and corn seedlings grown in algae-amended potting mix contained 15-20% of applied N, 46-60% of available N, and 38-60% of the applied P. Seedlings grown in algae-amended potting mixes were equivalent to those grown with comparable levels of fertilizer amended potting mixes with respect to seedling dry weight and nutrient content. These results suggest that dried algal biomass produced from treatment of anaerobically digested dairy manure can substitute for commercial fertilizers used for potting systems.  相似文献   
59.
A two-stage method for in vitro propagation of six Genista species from shoot tips was developed. Multiple microshoot cultures were obtained by growing the shoot tip explants on Schenk and Hildebrandt medium supplemented with 9.84 microM 6-(gamma,gamma-dimethylallylamino)-purine and 0.99 microM thidiazuron. The best shoot elongation was achieved on Schenk and Hildebrandt medium containing 4.92 microM indole-3-butyric acid. The rooting of shoots brought best effects (100%) on Schenk and Hildebrandt medium with 2.68 microM 1-naphthaleneacetic acid. HPLC analysis indicated that six-month-old regenerated plants as well as the herb of intact plants produced a rich set of simple flavones (derivatives of luteolin and apigenin) and isoflavones (derivatives of genistein, daidzein, formononetin and biochanin A). Multiple microshoot cultures of all species produced no simple flavones at all. In vitro shoots accumulated selectively a rich group of phytoestrogens in the form of aglucones, glucosides and esters (derivatives of genistein and daidzein). Cultures obtained in vitro synthesized many times more isoflavones than the intact plants. In all shoots which were micropropagated the dominating compound was genistin (e.g. shoots of G. tinctoria--ca 3281.4 mg per 100 g dry weight). Possible influence of tissue differentiation on isoflavone content under in vitro and in vivo conditions is discussed.  相似文献   
60.
In their 2002 Guidelines for chromosome analysis of peripheral blood, the American College of Medical Genetics states that "The 550-band stage should be the goal of all constitutional studies..." The College of American Pathologists requires that the average case be analyzed at the 400-band level of resolution for routine work, and that the 550-band level be achieved in appropriate blood samples. The challenge is how to identify the 400, 550, and 850-band levels confidently and consistently. In this study, our objectives were to develop simple and reliable criteria to estimate band level, and to evaluate our laboratory's performance with respect to those criteria. Using the ISCN(1995) ideogram as a reference, candidate bands were selected for the three band levels: 400, 550 and 850. A pilot and two follow-up studies were conducted and a set of candidate bands were validated against the Vancouver method of evaluating band level so that band level scores were similar using either method. The final set of reference bands were the presence of 9q32 and 20q13.2 for the 400-band level; 5q33.2 and 10q22.2 for the 550-band level; and 3p26.1, 18q22.3 and 20q13.32 for the 850-band level. Cell selection improved after each technologist was provided a composite image of chromosomes with reference bands highlighted. The band level criteria presented here involve no band counting, appear to be objective, can help to improve quality and consistency among technologists, and can ensure compliance with regulatory agencies.  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