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   3158篇
  免费   77篇
  3235篇
  2024年   21篇
  2023年   28篇
  2022年   47篇
  2021年   87篇
  2020年   83篇
  2019年   93篇
  2018年   121篇
  2017年   96篇
  2016年   131篇
  2015年   176篇
  2014年   171篇
  2013年   227篇
  2012年   226篇
  2011年   212篇
  2010年   113篇
  2009年   112篇
  2008年   162篇
  2007年   143篇
  2006年   133篇
  2005年   115篇
  2004年   108篇
  2003年   76篇
  2002年   89篇
  2001年   58篇
  2000年   33篇
  1999年   41篇
  1998年   13篇
  1997年   14篇
  1996年   16篇
  1995年   10篇
  1994年   7篇
  1993年   9篇
  1992年   15篇
  1991年   16篇
  1990年   16篇
  1989年   10篇
  1988年   17篇
  1987年   14篇
  1986年   15篇
  1985年   16篇
  1984年   17篇
  1982年   8篇
  1980年   11篇
  1979年   11篇
  1978年   12篇
  1977年   12篇
  1975年   11篇
  1974年   7篇
  1973年   9篇
  1968年   7篇
排序方式: 共有3235条查询结果,搜索用时 0 毫秒
1.
Environmental contamination by hexavalent chromium, Cr(VI), presents a serious public health problem. This study assessed the reduction of Cr(VI) by intact cells and a cell-free extract (CFE) of an actinomycete, Arthrobacter crystallopoietes (strain ES 32), isolated from soil contaminated with dichromate. Both intact cells and CFE of A. crystallopoietes, displayed substantial reduction of Cr(VI). Intact cells reduced about 90% of the Cr(VI) added within 12 h and Cr(VI) was almost completely reduced after 24 h. The K M and V max of Cr(VI) bioreduction by intact cells were 2.61 μM and 0.0142 μmol/min/mg protein, respectively. Cell-free chromate reductase of the A. crystallopoietes (ES 32) reduced hexavalent chromium at a K M of 1.78 μM and a V max of 0.096 μmol/min/mg protein. The rate constant (k) of chromate reduction was inversely related to Cr(VI) concentration and the half-life (t 1/2) of Cr(VI) reduction increased with increasing concentration. A. crystallopoietes produced a periplasmic chromate reductase that was stimulated by NADH. Results indicate that A. crystallopoietes ES 32 can be used to detoxify Cr(VI) in polluted sites, particularly in stressed environments.  相似文献   
2.
3.
4.
5.
6.
    
Mitotic and meiotic chromosomes of the Antarctic lysianassoid amphipod Waldeckia obesa are described. The modal chromosome number is n = 25 and 2n = 50. The potential applications of cytogenetical studies in this group are discussed.  相似文献   
7.
8.
Experiments based on a 23 central composite full factorial design were carried out in 200-ml stainless-steel containers to study the pretreatment, with dilute sulfuric acid, of a sugarcane bagasse sample obtained from a local sugar–alcohol mill. The independent variables selected for study were temperature, varied from 112.5°C to 157.5°C, residence time, varied from 5.0 to 35.0 min, and sulfuric acid concentration, varied from 0.0% to 3.0% (w/v). Bagasse loading of 15% (w/w) was used in all experiments. Statistical analysis of the experimental results showed that all three independent variables significantly influenced the response variables, namely the bagasse solubilization, efficiency of xylose recovery in the hemicellulosic hydrolysate, efficiency of cellulose enzymatic saccharification, and percentages of cellulose, hemicellulose, and lignin in the pretreated solids. Temperature was the factor that influenced the response variables the most, followed by acid concentration and residence time, in that order. Although harsher pretreatment conditions promoted almost complete removal of the hemicellulosic fraction, the amount of xylose recovered in the hemicellulosic hydrolysate did not exceed 61.8% of the maximum theoretical value. Cellulose enzymatic saccharification was favored by more efficient removal of hemicellulose during the pretreatment. However, detoxification of the hemicellulosic hydrolysate was necessary for better bioconversion of the sugars to ethanol.  相似文献   
9.
10.
    
Polyamines (PAs) are abundant polycationic compounds involved in many physiological processes in plants, including somatic embryogenesis. This study investigates the role of PAs on cellular growth and structure of pro‐embryogenic masses (PEMs), endogenous PA and proton pump activities in embryogenic suspension cultures of Araucaria angustifolia. The embryogenic suspension cultures were incubated with putrescine (Put), spermidine (Spd), spermine (Spm) and the inhibitor methylglyoxal‐bis(guanylhydrazone) (MGBG), respectively (1 mM). After 24 h and 21 days, the cellular growth and structure of PEMs, endogenous PA contents and proton pump activities were analyzed. The addition of Spm reduced the cellular growth and promoted the development of PEMs in embryogenic cultures, which could be associated with a reduction in the activities of proton pumps, such as H+‐ATPase P‐ and V‐types and H+‐PPases, and alterations in the endogenous PA contents. Spm significantly affected the physiology of the A. angustifolia somatic embryogenesis suspension, as it potentially affects cellular growth and structure of PEMs through the modulation of proton pump activities. This work demonstrates the involvement of exogenous PAs in the modulation of cellular growth and structure of PEMs, endogenous PA levels and proton pump activities during somatic embryogenesis. To our knowledge, this study is the first to report a relationship between PAs and proton pump activities in these processes. The results obtained in this study offer new perspectives for studies addressing the role of PAs and proton pump on somatic embryogenesis in this species.  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