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   233篇
  免费   28篇
  国内免费   5篇
  266篇
  2024年   10篇
  2023年   2篇
  2022年   6篇
  2021年   9篇
  2020年   7篇
  2019年   9篇
  2018年   19篇
  2017年   9篇
  2016年   10篇
  2015年   12篇
  2014年   19篇
  2013年   9篇
  2012年   8篇
  2011年   19篇
  2010年   4篇
  2009年   7篇
  2008年   4篇
  2007年   13篇
  2006年   4篇
  2005年   3篇
  2004年   11篇
  2003年   3篇
  2002年   2篇
  2001年   2篇
  1999年   3篇
  1998年   2篇
  1997年   1篇
  1996年   2篇
  1995年   3篇
  1992年   1篇
  1991年   2篇
  1990年   4篇
  1989年   7篇
  1988年   3篇
  1987年   2篇
  1986年   4篇
  1985年   2篇
  1982年   3篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1976年   2篇
  1975年   6篇
  1974年   3篇
  1973年   4篇
  1972年   1篇
  1971年   1篇
  1970年   2篇
  1965年   1篇
  1962年   1篇
排序方式: 共有266条查询结果,搜索用时 0 毫秒
1.
南方4种草本植物对铝胁迫生理响应的研究   总被引:26,自引:0,他引:26       下载免费PDF全文
 不同的植物对铝胁迫的生理响应不同, 因而对铝毒的耐性也不相同。设置5种铝浓度,进行砂培法处理,研究了4种我国南方红壤广泛分布的草本植物——牵牛(Pharbitis nil)、望江南(Cassia occidentlis)、光头稗(Echinochloa colonum)和合萌(Aeschynomene indica)的种子萌发、光合色素、脯氨酸含量、丙二醛(MDA)含量、可溶性糖(SS)含量、质膜透性(MP)、过氧化氢酶 (CAT) 活性以及过氧化物酶 (POD)活性的变化。结果表明铝对4种植物的生理特性都有明显的影响。4种植物的种子在10 000 mg·L-1 Al3+处理条件下都不能萌发。2 000 mg·L-1 Al3+处理都不利于4种植物的生长,与对照相比,2 000 mg·L-1 Al3+处理时4种草本植物叶绿素和叶绿素总含量显著降低(p<0.05);MDA含量和MP显著增加(p<0.05);脯氨酸含量极显著增加(p<0.01);POD和CAT活性极显著降低(p<0.01)。中低铝(80和400 mg·L-1)处理时,牵牛和合萌与对照相比,MP和MDA含量降低,POD和CAT活性升高;望江南的反应与牵牛和合萌的反应相反;光头稗在80 mg·L-1 Al3+处理时,与牵牛和合萌的变化一致,在400 mg·L-1 Al3+处理时,则相反。植物在中低铝处理条件下,通过维持较高的POD和CAT活性和脯氨酸、叶绿素含量,较低的MP和MDA含量来增加其对铝的耐性。  相似文献   
2.
红壤旱地不同复种方式养地效果   总被引:2,自引:0,他引:2       下载免费PDF全文
为了提出适宜南方红壤区旱地质量提升的持续高效种植模式,在江西农业大学科技园开展田间试验,以传统复种方式为对照,从土壤理化性状、微生物及酶活性等多方面分析比较不同复种方式对土壤的养地效果,为提出可持续发展的农田耕作模式提供理论基础。结果表明:不同复种方式中,绿肥种植和绿肥翻压还田对土壤具有明显养地效果,其中处理C\"黑麦草-花生‖玉米-粟‖荞麦\"具有较高的土壤阳离子交换量、有机质、碱解氮、全磷含量以及土壤酶活性和较多的土壤微生物种类、数量,从而显著提高土壤肥力和土壤持续生产力,养地效果最佳;处理B\"混播绿肥(油菜、紫云英、肥田萝卜)-大豆‖玉米-绿豆‖芝麻\"降低土壤容重,增加土壤孔隙度,改善土壤的通气性、透水性,明显提高土壤pH值、全氮、有效磷、全钾和速效钾含量,养地效果次之。因此,大力推广应用冬季绿肥是促进红壤旱地生态系统可持续发展的有效耕作措施。  相似文献   
3.
该研究以中国古老月季品种‘月月粉’(Rosa chinensis‘Old Blush’)为试材,根据拟南芥和草莓FT/TFL1基因家族成员的保守结构域设计引物,对‘月月粉’基因组DNA进行克隆和测序,结合数据库序列和双单倍体基因组信息进行序列比对,结果共获得了8条月季的FT/TFL1基因家族序列,且8条序列分别注释为2个FT基因(RcFT1和RcFT2)、1个BFT基因(RcBFT)、1个ATC基因(RcATC)、2个MFT基因(RcMFT1和RcMFT2)和2个PEBP基因(PEBP1和PEBP2);进化树分析结果将这8个基因分为3个亚组;结构分析显示8个基因的内含子为1~5个不等。qRT-PCR分析显示,RcFT1、RcPEBP、RcMFT1、RcMFT2和RcBFT在‘月月粉’的叶片中表达量最高,茎尖中次之;RcFT2在茎尖中的表达最高,叶片中次之;RcATC在茎尖中的表达量高于其他组织;除RcPEBP在根组织中有表达外,其他基因在根组织中几乎没有检测到。进一步表达分析显示,RcFT1和RcFT2在‘无刺光叶蔷薇’(R.wichuriana‘Basye’s Thornless')生殖生长期的叶片、茎尖中的表达量显著高于营养生长期。研究推测,具有连续开花性状的中国古老月季‘月月粉’可能具有多个开花时间(FT)基因位点,FT有可能可以作为月季生殖转换的标记基因。  相似文献   
4.
    
Labelling of Type IV pili (TFP) can greatly improve our understanding of the pivotal roles of TFP in a variety of bacterial activities including motility, surface sensing and DNA-uptake etc. Here we show a simple and switchable pili-labelling method by plasmid-based inducible replacement of PilA without genetic modification in bacterial genome employed by complicated methods. Using this method, we characterized pili morphology and twitching motility of Pseudomonas aeruginosa in details. More importantly, we demonstrate its application in studying the replenishment dynamics of pilin pool of P. aeruginosa.  相似文献   
5.

Background

Transradial approach (TRA) outweighed transfemoral approach (TFA) in acute coronary syndrome patients because the former has better short-term outcomes in high-volume percutaneous coronary intervention (PCI) centers. Our study was one of the limited studies specifically in comparing the short- and medium-term effects of TRA and those of TFA in patients undergoing elective PCIs.

Methods

A total of 21,242 patients who underwent elective PCI with stent implantation were included. Using propensity score methodology, 1,634 patient pairs were matched. Major clinical outcomes and PCI-related complications between TRA and TFA were compared.

Results

In the propensity score-matched patients, the rates of in-hospital net adverse clinical events, which included death, myocardial infarction (MI), target vessel revascularization (TVR), stroke, and major bleeding, were much lower with TRA than with TFA (1.8% vs. 3.9%, P < 0.001). This difference was mainly due to the lower rate of major bleeding (0.6% vs. 1.8%, P < 0.001) and the decreased rate of MI (1.1% vs. 1.9%, P = 0.060). PCI-related dissection and thrombosis were similar between the TRA and TFA groups (both P > 0.05). Meanwhile, one-year incidence rates of major adverse cardiovascular events, which included death, MI, and TVR, were also similar (4.1% vs. 4.9%, P = 0.272) in TRA and TFA. Multivariable regression analyses showed that TRA was an independent predictor of the low rate of in-hospital net adverse clinical events (odds ratio, 0.53; 95% confidence interval, 0.40 to 0.71), but not of major adverse cardiovascular events at one-year follow-up (hazard ratio, 1.01; 95% confidence interval, 0.96 to 1.06).

Conclusions

In patients undergoing elective PCI, TRA patients had lower rates of in-hospital net adverse clinical outcomes compared with TFA patients. TRA might be recommended as a routine approach in high-volume PCI hospitals for elective PCIs.  相似文献   
6.
The frequency and spectrum of mutations in RAS/BRAF genes were studied in rectal adenomas, carcinomas in situ, and adenocarcinomas. It is shown that the frequency of KRAS mutations decreases from adenoma to adenocarcinoma; most adenomas and carcinomas in situ are heterogeneous and consist of several subclones. Possible models of colorectal cancer pathogenesis are discussed.  相似文献   
7.
P N Shubin  E A Efimtseva 《Genetika》1989,25(8):1480-1487
Acetylcholinesterase from human erythrocytes solubilized by 1% Triton X-100 was resolved using polyacrylamide gel electrophoresis into two components. The first one (fast) is more firmly bound to cell membranes than the other. The existence of multiple forms (C1-C4) of serum cholinesterase-1 (CHE1) has been established. Electrophoresis in acid medium (pH 4.8) permits to detect the C5 component and a group of supplementary isoenzymes of cholinesterase-2. Individual differences observed in patterns of the CHE2 isozymes are controlled by a pair of autosomal codominant alleles Che2A and Che2B. The serum of subjects with phenotypes Che2AB(C5+) and Che2BB(C5-) showed on the average equal level of cholinesterase activity.  相似文献   
8.
9.
The circular dichroism spectra of two protein proteinase inhibitors were studied. The CD spectrum of the kidney bean inhibitor is similar to those of other low molecular weight inhibitors from legume seeds. The potato inhibitor in its native state is characterized by a low content of alpha-helices, which is increased in the presence of sodium dodecyl sulfate.  相似文献   
10.
Using a specially developed phosporoscopic attachment to spectropolarimeter, light induced spectra of circular dichroism (CD) in region 600-750 nm were measured for a pigment protein complex of photosystem 1 (PC-1) isolated from pea chloroplast (chlorophyll : P700 = 40). Minor components at 672 and 678 nm are observed in light induced spectra besides the components of dimer splitting of P700 Qy transition at 691 and 698 nm. Haussian deconvolution of light induced CD spectra of P700 and low temperature CD spectrum of PC-1 indicates that minor components are due to forms of antenna chlorophylls Chl672 and Chl678, rotational strength of that is changed by 2-4% as a result of P700 oxidation. Long term incubation of PC-1 with Triton X-100 inhibits P700 and destroys longwave optically active chlorophyll forms. A strong relation between dichroic density of 693 nm band in CD spectrum of PC-1 and the value of light induced absorption change at 698 nm could be used to determine P700 concentration on the basis of CD spectrum of PC-1. Such a relation shows that Chl693 is an important component of photo-system 1 reaction center. It is suggested that P700 is not an isolated dimer but it is included in the local complex from 8-10 chlorophyll molecules (Chl672, Chl678, Chl686, Chl693).  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