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   516篇
  免费   24篇
  540篇
  2023年   6篇
  2022年   12篇
  2021年   19篇
  2020年   12篇
  2019年   9篇
  2018年   20篇
  2017年   8篇
  2016年   19篇
  2015年   31篇
  2014年   32篇
  2013年   35篇
  2012年   42篇
  2011年   44篇
  2010年   22篇
  2009年   16篇
  2008年   22篇
  2007年   33篇
  2006年   17篇
  2005年   8篇
  2004年   11篇
  2003年   16篇
  2002年   8篇
  2001年   8篇
  1999年   3篇
  1998年   4篇
  1997年   3篇
  1996年   2篇
  1994年   3篇
  1993年   2篇
  1992年   3篇
  1991年   3篇
  1990年   6篇
  1989年   5篇
  1988年   3篇
  1987年   2篇
  1986年   3篇
  1984年   5篇
  1983年   2篇
  1981年   5篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   3篇
  1974年   3篇
  1973年   2篇
  1972年   2篇
  1970年   3篇
  1968年   2篇
  1967年   2篇
  1966年   4篇
排序方式: 共有540条查询结果,搜索用时 12 毫秒
41.
Uganda has a large population of goats, predominantly from indigenous breeds reared in diverse production systems, whose existence is threatened by crossbreeding with exotic Boer goats. Knowledge about the genetic characteristics and relationships among these Ugandan goat breeds and the potential admixture with Boer goats is still limited. Using a medium‐density single nucleotide polymorphism (SNP) panel, we assessed the genetic diversity, population structure and admixture in six goat breeds in Uganda: Boer, Karamojong, Kigezi, Mubende, Small East African and Sebei. All the animals had genotypes for about 46 105 SNPs after quality control. We found high proportions of polymorphic SNPs ranging from 0.885 (Kigezi) to 0.928 (Sebei). The overall mean observed (HO) and expected (HE) heterozygosity across breeds was 0.355 ± 0.147 and 0.384 ± 0.143 respectively. Principal components, genetic distances and admixture analyses revealed weak population sub‐structuring among the breeds. Principal components separated Kigezi and weakly Small East African from other indigenous goats. Sebei and Karamojong were tightly entangled together, whereas Mubende occupied a more central position with high admixture from all other local breeds. The Boer breed showed a unique cluster from the Ugandan indigenous goat breeds. The results reflect common ancestry but also some level of geographical differentiation. admixture and f4 statistics revealed gene flow from Boer and varying levels of genetic admixture among the breeds. Generally, moderate to high levels of genetic variability were observed. Our findings provide useful insights into maintaining genetic diversity and designing appropriate breeding programs to exploit within‐breed diversity and heterozygote advantage in crossbreeding schemes.  相似文献   
42.
Hyperthermia is a general term used to define the increase in core body temperature above normal. It is often used to describe the increased core body temperature that is observed during fever. The use of hyperthermia as an adjuvant has emerged as a promising procedure for tumor regression in the field of cancer biology. For this purpose, the most important requirement is to have reliable and uniform heating protocols. We have developed a protocol for hyperthermia (whole body) in mice. In this protocol, animals are exposed to cycles of hyperthermia for 90 min followed by a rest period of 15 min. During this period mice have easy access to food and water. High body temperature spikes in the mice during first few hyperthermia exposure cycles are prevented by immobilizing the animal. Additionally, normal saline is administered in first few cycles to minimize the effects of dehydration. This protocol can simulate fever like conditions in mice up to 12-24 hr. We have used 8-12 weeks old BALB/Cj female mice to demonstrate the protocol.  相似文献   
43.
A set of thyromimetics having improved selectivity for TR-beta1 were prepared by replacing the 3'-isopropyl group of 2 and 3 with substituents having increased steric bulk. From this limited SAR study, the most potent and selective compounds identified were derived from 2 and contained a 3'-phenyl moiety bearing small hydrophobic groups meta to the biphenyl link. X-ray crystal data of 15c complexed with TR-beta1 LBD shows methionine 442 to be displaced by the bulky R3' phenyl ethyl amide side chain. Movement of this amino acid side chain provides an expanded pocket for the bulky side chain while the ligand-receptor complex retains full agonist activity.  相似文献   
44.
Four hybrids (4 F1s) were chosen out of crosses in the urdbean [Vigna mungo (L.) Hepper, 2n = 22] having contrasting morphological characters. Zymograms for isozyme peroxidase were drawn from the patterns obtained from parents and their respective F1 hybrids on the basis of relative similarities to parental bands. The selfed or crossed nature of hybrid pods was determined from the zymograms and their analysis. The number of bands and their intensities gave an idea about the extent of crossing in F1 populations. Genetic identity (I) values were indicative of their selfed nature. Dendrograms were constructed on the basis of genetic identity values to display the relative similarities between the populations. Analysis was based on individual pods to confirm their hybrid or selfed nature. Possible use of this technique for identification of F1 pods and elimination of selfed pods might be implemented to shorten the breeding operations during crossing.  相似文献   
45.
Strains ofM. ciceri, symbionts of chickpea (Cicer arietinum) were incubated with the flavonoids naringenin, daidzein and quercetin which have earlier been reported as inducers and inhibitors ofnodABC-lacZ fusion ofM. ciceri. Preincubation ofM. ciceri with naringenin and daidzein (100 nmol/L) for 1 d improved the competitive ability of the inoculated strain while preincubation with quercetin decreased the nodule occupancy of inoculated strain under sterile conditions. Under nonsterile conditions induced strains of Rcd 301 and HT-6 formed by 23 and 18% more nodules, respectively, than untreated control. Quercetin-treated strains showed by 13–20% fewer nodules than untreated controls. Therefore, it is possible to regulate the competitive ability of inoculated strains by flavonoid treatment.  相似文献   
46.
Asbestos causes asbestosis and various malignancies by mechanisms that are not clearly defined. Here, we review the accumulating evidence showing that asbestos is directly genotoxic by inducing DNA strand breaks (DNA-SB) and apoptosis in relevant lung target cells. Although the exact mechanisms by which asbestos causes DNA damage and apoptosis are not firmly established, some of the implicated mechanisms include the generation of iron-derived reactive oxygen species (ROS) as well as reactive nitrogen species (RNS), alteration in the mitochondrial function, and activation of the death receptor pathway. We focus on the accumulating evidence implicating ROS. DNA repair mechanisms have a key role in limiting the extent of DNA damage. Recent studies show that asbestos activates DNA repair enzymes such as apurinic/apyrimidinic endonuclease (APE) and poly (ADP-ribose) polymerase (PARP). Asbestos-induced neoplastic transformation may result in the setting where DNA damage overwhelms DNA repair in the face of a persistent proliferative signal. Strategies aimed at limiting asbestos-induced oxidative stress may reduce DNA damage and, as such, prevent malignant transformation.  相似文献   
47.
Electron bifurcation is a fundamental strategy of energy coupling originally discovered in the Q-cycle of many organisms. Recently a flavin-based electron bifurcation has been detected in anaerobes, first in clostridia and later in acetogens and methanogens. It enables anaerobic bacteria and archaea to reduce the low-potential [4Fe-4S] clusters of ferredoxin, which increases the efficiency of the substrate level and electron transport phosphorylations. Here we characterize the bifurcating electron transferring flavoprotein (EtfAf) and butyryl-CoA dehydrogenase (BcdAf) of Acidaminococcus fermentans, which couple the exergonic reduction of crotonyl-CoA to butyryl-CoA to the endergonic reduction of ferredoxin both with NADH. EtfAf contains one FAD (α-FAD) in subunit α and a second FAD (β-FAD) in subunit β. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD+ complex structure revealed β-FAD as acceptor of the hydride of NADH. The formed β-FADH is considered as the bifurcating electron donor. As a result of a domain movement, α-FAD is able to approach β-FADH by about 4 Å and to take up one electron yielding a stable anionic semiquinone, α-FAD, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, β-FADH, immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH that converts crotonyl-CoA to butyryl-CoA.  相似文献   
48.
The present study was designed to synthesize the bioactive molecule 2,2-bis(2,4-dinitrophenyl)-2-(phosphonatomethylamino)acetate (1), having excellent applications in the field of plant protection as a herbicide. Structure of newly synthesized molecule 1 was confirmed by using the elemental analysis, mass spectrometric, NMR, UV-visible, and FTIR spectroscopic techniques. To obtain better structural insights of molecule 1, 3D molecular modeling was performed using the GAMESS programme. Microbial activities of 1 were checked against the pathogenic strains Aspergillus fumigatus (NCIM 902) and Salmonella typhimurium (NCIM 2501). Molecule 1 has shown excellent activities against fungal strain A. fumigates (35 μg/l) and bacterial strain S. typhimurium (25 μg/l). To check the medicinal significance of molecule 1, interactions with bovine serum albumin (BSA) protein were checked. The calculated value of binding constant of molecule 1–BSA complex was 1.4 × 106 M?1, which were similar to most effective drugs like salicylic acid. More significantly, as compared to herbicide glyphosate, molecule 1 has exhibited excellent herbicidal activities, in pre- and post-experiments on three weeds; barnyard grass (Echinochloa Crus), red spranglitop (Leptochloa filiformis), and yellow nuts (Cyperus Esculenfus). Further, effects of molecule 1 on plant growth-promoting rhizobacterial (PGPR) strains were checked. More interestingly, as compared to glyphosate, molecule 1 has shown least adverse effects on soil PGPR strains including the Rhizobium leguminosarum (NCIM 2749), Pseudomonas fluorescens (NCIM 5096), and Pseudomonas putida (NCIM 2847).  相似文献   
49.
Russian Journal of Bioorganic Chemistry - A series of novel quinoline-benzoxazolinone ester hybrids were synthesized characterized and assessed for their in vitro anti-inflammatory and...  相似文献   
50.
Trichoderma spp. are well-known biological agents that have significant antagonistic activity against several plant pathogenic fungi. In the present study, Trichoderma spp. were tested in vitro for their antagonistic activity against different spp. of Fusarium and Alternaria viz. Alternaria alternata, A. brassicae, A. solani, Fusarium oxysporum and F. solani using dual plate assay and by the production of volatile and non-volatile compounds. The results obtained revealed that Trichoderma harzianum and T. viride effectively inhibited the growth and spore production of different spp. of Fusarium and Alternaria. The highest growth inhibition was found in A. alternata 62.50% and 60.00% by non-volatile compounds of T. harzianum and T. viride, respectively. Similarly, the volatile compounds inhibit the maximum growth of A. alternata 40.00% and 35.00% by T. harzianum and T. viride, respectively. Volatile and non-volatile compounds of Trichoderma spp. were analysed by GC-MS technique and the properties of distinguished compounds showed antifungal, antimicrobial and antibiotic activities. Volatile compounds of T. harzianum and T. viride showed highest percent abundance for glacial acetic acid (45.32%) and propyl-benzene (41.75%), respectively. In case of non-volatile compounds, T. harzianum and T. viride showed D-Glucose, 6-O-α-D-galactopyranosyl- (38.45%) and 17-Octadecynoic acid (36.23%), respectively. The results of present study confirmed that T. harzianum can be used as a promising biological control agent against Alternaria and Fusarium spp. that cause diseases in various vegetables and crops.  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