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   2965篇
  免费   145篇
  2023年   9篇
  2022年   47篇
  2021年   77篇
  2020年   50篇
  2019年   77篇
  2018年   117篇
  2017年   81篇
  2016年   137篇
  2015年   168篇
  2014年   179篇
  2013年   232篇
  2012年   258篇
  2011年   247篇
  2010年   148篇
  2009年   107篇
  2008年   184篇
  2007年   185篇
  2006年   178篇
  2005年   123篇
  2004年   88篇
  2003年   116篇
  2002年   82篇
  2001年   19篇
  2000年   22篇
  1999年   20篇
  1998年   10篇
  1997年   4篇
  1996年   6篇
  1995年   6篇
  1994年   5篇
  1992年   5篇
  1991年   6篇
  1990年   5篇
  1989年   7篇
  1988年   11篇
  1987年   6篇
  1986年   4篇
  1985年   7篇
  1984年   3篇
  1983年   8篇
  1977年   3篇
  1976年   3篇
  1975年   4篇
  1973年   4篇
  1972年   9篇
  1970年   8篇
  1968年   7篇
  1967年   6篇
  1966年   6篇
  1965年   4篇
排序方式: 共有3110条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
An enzyme extract from apple(Pyrus malus Borb.) seeds which causes the disappearance of free indol-3-ylacetic acid (IAA) requires the presence of oxygen, but is not inhibited by cyanide. Using 1-14C-IAA it has been demonstrated that the IAA transformation is not accompanied by its decarboxylation. Decarboxylating IAA oxidase is absent during the whole period of apple seed cold stratification. Free IAA has not been detected in dormant apple seeds and in seeds stratified at low temperature. It appears during stratification at 25 °C. Ethyl ester of IAA and indol-3-ylacetyl aspartate have been identified in dormant and after-ripened seeds. Exogenous 1-14C IAA taken up by apple embryos is converted into conjugates with aspartate and short peptides containing an aspartate moiety.  相似文献   
5.
Hydrogen cyanide and embryonal dormancy in apple seeds   总被引:3,自引:0,他引:3  
Embryos of apple ( Malus domestica Borh. cv. Antonówka) were treated with 1 m M gaseous HCN for 6 h and cultured under a 12 h photoperiod. HCN pretreatment stimulated germination, increased the length of hypocotyls, shortened the main root and decreased the percentages of seedlings with asymmetrically grown as well as with asymmetrically greened cotyledons. High activity of β-cyanoalanine synthase (EC 4.4.1.9) and a sharp increase in cyanogen content during embryo culture suggested very low levels of endogenous HCN. despite the activity of HCN releasing enzymes. The obtained data allow us to postulate an important role for cyanide in the regulatory complex controlling dormancy in apple seeds. Experiments with respiratory inhibitors indicated, however, that HCN pretreatment affected neither the alternative electron transport pathway nor residual respiration.  相似文献   
6.
The effect of fish predation on Cyclops life cycle   总被引:2,自引:2,他引:0  
Papi  `nska  Katarzyna 《Hydrobiologia》1988,167(1):449-453
Two populations of Cyclops abyssorum tatricus studied in neighbouring alpine lakes in Tatra Mountains (southern Poland) differed in their life cycles. In the lake with planktivorous fishes, Cyclops was typically monocyclic, with highly synchronized reproduction during two winter months, while in the fishless lake its reproduction was asynchronous and continued for six months. Direct and indirect effects of fish predation on Cyclops life cycles are discussed.  相似文献   
7.
Cytochromec oxidase fromParacoccus denitrificans was homogenously dispersed in Triton X-100. Using gel exclusion chromatography and sucrose gradient centrifugation analysis a molecular weight of the detergent-protein complex of 155,000 was determined. After subtraction of the bound detergent (111 mol/mol hemeaa 3) a molecular weight of 85,000 resulted, which agreed well with the model of a monomer containing two subunits. This monomer showed high cytochromec oxidase activity when measured spectrophotometrically in the presence of Triton X-100 (V max=85 s–1). The molecular activity, plotted according to Eadie-Hofstee, was monophasic as a function of the cytochromec concentration. AK m of 3.6×10–6 M was evaluated, similar to theK m observed in the presence of dodecyl maltoside [Naeczet al. (1985).Biochim. Biophys. Acta 808, 259–272].  相似文献   
8.
Microbiological transformation of benzaldehyde accomplished by the fungus Rhodotorula mucilaginosa immobilized in the ultrafiltration cell was studied. A polysulfone membrane formed on a sintered PVC support was used for the separation of the transformation product from the cellular material. Kinetic investigations have led to results which are typical of continuously fed stirred tank reactors (CFSTR)-the value of the maximum reaction rate (V(max)) and apparent Michaelis constant (K'(m)) are practically independent of the substrate retention time (calculated in terms of the flow intensity value). A strong relationship was found to occur between V(max) and biomass concentration in the reactor. Study of the apparent enzyme stability shows that the decrease in the biocatalyst activity is chiefly caused by penetration of the cells through the membrane. The experimental results were approximated in terms of the adopted mathematical model. Based on this model, the half-lives (t(1/2)) of enzyme activities were determined. The t(1/2) value varies from 35 to 82 days and depends both on the permeate flux through the membrane and on the separation properties of the membrane.  相似文献   
9.
The efficacy of systemic infusion of recombinant human macrophage-colony-stimulating factor (M-CSF) in combination with local treatment with human recombinant tumor necrosis factor (TNF) and mouse recombinant interferon (IFN) was studied in vivo on a subclone of B16 melanoma (MmB16) in mice. Short-term intravenous administration of M-CSF at a dose of 106 units daily had no antitumor effect in vivo. Similarly, local treatment of tumor with TNF (5 g daily) did not produce any therapeutic effect. However, simultaneous administration of the same dose of TNF with IFN (1000 units daily) resulted in a synergistic effects manifested by the retardation of tumor growth. Addition of systemic infusion of M-CSF to the local therapy with TNF and IFN induced further augmentation of antitumor efficacy and delayed progression of MmB16 melanoma. The strengthened antitumor effect of combination therapy including M-CSF, TNF and IFN was most probably due to the increased release of monocytes from the bone marrow, their recruitment into the site of tumor growth and subsequent local stimulation of their antitumor activity.  相似文献   
10.
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