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   381篇
  免费   13篇
  国内免费   26篇
  2023年   2篇
  2022年   2篇
  2021年   5篇
  2020年   3篇
  2019年   7篇
  2018年   10篇
  2017年   5篇
  2016年   12篇
  2015年   11篇
  2014年   20篇
  2013年   38篇
  2012年   13篇
  2011年   15篇
  2010年   16篇
  2009年   18篇
  2008年   17篇
  2007年   21篇
  2006年   19篇
  2005年   10篇
  2004年   17篇
  2003年   11篇
  2002年   11篇
  2001年   11篇
  2000年   6篇
  1999年   6篇
  1998年   11篇
  1997年   8篇
  1996年   9篇
  1995年   7篇
  1994年   8篇
  1993年   10篇
  1992年   4篇
  1991年   8篇
  1990年   6篇
  1989年   2篇
  1988年   4篇
  1987年   4篇
  1986年   5篇
  1982年   2篇
  1981年   2篇
  1979年   2篇
  1978年   4篇
  1976年   2篇
  1973年   2篇
  1972年   3篇
  1971年   1篇
  1968年   2篇
  1967年   2篇
  1966年   1篇
  1965年   1篇
排序方式: 共有420条查询结果,搜索用时 15 毫秒
101.
鸢尾属药用植物总DNA提取方法的比较研究   总被引:3,自引:0,他引:3  
以鸢尾属(Iris L.)药用植物鸢尾Iris tectorum Maxim.叶片为材料,分别采用CTAB法、高盐低pH法、SDS法和试剂盒法四种方法提取植物总DNA,并通过琼脂糖凝胶电泳、紫外分光光度计、ISSR和RAPD四种方法对所提取的DNA样品进行检测。结果表明,用SDS—I法提取的植物总DNA纯度、浓度和完整性都很高,从经济角度考虑优于用试剂盒提取,从提取效果考虑不亚于用CTAB法和高盐低pH法提取,是比较适合鸢尾属植物总DNA提取的方法。  相似文献   
102.
<正> This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer'sscallop.The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentiallyimprove wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulationsperformed using software based on the Discrete Element Method (DEM).The wear performance of the BRS is experimentallydetermined and also compared with a conventional flat surface.Different size of soil particles and relative velocities between theabrasive sand and the testing surfaces are used.Comparative results show that the numerical simulations are in agreement withthe experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flatsurface with the BRS.  相似文献   
103.
Hoya (Marsdenieae, Apocynaceae) includes at least 200 species distributed from India to the Pacific Islands. We here infer major species groups in the genus based on combined sequences from the chloroplast atpB-rbcL spacer, the trnL region, and nuclear ribosomal DNA ITS region for 42 taxa of Hoya and close relatives. To assess levels of ITS polymorphism, ITS sequences for a third of the accessions were obtained by cloning. Most ITS clones grouped by species, indicating that speciation in Hoya usually predates ITS duplication. One ITS sequence of H. carnosa, however, grouped with a sequence of the morphologically similar H. pubicalyx, pointing to recent hybridization or the persistence of paralogous copies through a speciation event. The topology resulting from the combined chloroplast and nuclear data recovers some morphology-based sections, such as Acanthostemma and Eriostemma, as well as a well-supported Australian/New Guinean clade. The combined data also suggest that morphological adaptations for ant-symbiosis evolved at least three times within Hoya.  相似文献   
104.
The standard procedure outlined by the United States Environmental Protection Agency (US EPA) in Method 1623 for analyzingGiardia lamblia cysts andCryptosporidium parvum oocysts in water samples consists of filtration, elution, centrifugal concentration, immunomagnetic separation (IMS), and immunofluorescence assay (IFA) followed by microscopic examination. In this study, the extent of (oo)cyst loss in each step of this procedure was evaluated by comparing recovery yields in segmented analyses: (i) IMS+IFA, (ii) concentration +IMS+IFA, and (iii) filtration/elution + concentration +IMS+IFA. The complete (oo)cyst recovery by the full procedure was 52–57%. The (oo)cyst loss in the IMS step was only 0–6%, implying that IMS is a fairly reliable method for (oo)cyst purification. Centrifugal concentration of the eluted sample and pellet collection before IMS resulted in a loss of 8–14% of the (oo)cysts. The largest (oo)cyst loss occurred in the elution step, with 68–71% of the total loss. The permeated loss of (oo)cysts was negligible during filtration of the water sample with a 1.0-μm pore polyethersulfone (PES) capsule. These results demonstrated that the largest fraction of (oo)cyst loss in this procedure occurred due to poor elution from the filter matrix. Improvements in the elution methodology are therefore required to enhance the overall recovery yield and the reliability of the detection of these parasitic protozoa.  相似文献   
105.
 Twenty six restriction sites from five PCR-amplified chloroplast DNA sequences (rbcL, psbA, rpoB, and two spacers flanking the trnL gene) were mapped and analysed in 20 Actinidia taxa, encompassing all four sections into which the genus is divided. At least three species out of the 20 examined have been found to have originated through natural interspecific hybridisation on the basis of the discrepancy between morphological and biochemical traits and the cpDNA profiles of pairs of species. A widely reticulate evolution has therefore been postulated in Actinidia. Wagner and weighted parsimony analysis produced consensus trees that did not match the traditional taxonomy based on morphological characters. The molecular data clearly showed that some taxa, such as A. rufa and A. kolomikta, occupy a wrong position and most, if not all, of the traditional groups represented by sections and series are weakly supported, since they appear as polyphyletic. A. chinensis and A. deliciosa were confirmed to be very closely related. Since chloroplast DNA is paternally inherited in Actinidia, A. chinensis is a paternal progenitor, if not the only one, of A. deliciosa, the domesticated kiwifruit. Received: 18 August 1997 / Accepted: 6 October 1997  相似文献   
106.
PICO-TAG方法测定氨基酸的研究   总被引:4,自引:0,他引:4  
详细讨论了用异硫氰酸苯酯(PITC)柱前衍生,反相色谱法测定氨基酸(即PICO-TAG法)的最佳条件。研究了流动相配制时溶液pH值、乙腈含量等对色谱分析的影响,并且对色谱柱的退化与再生进行了说明。氨基酸含量在1.25~1500pmol范围内线性良好,相关系数大于0.999,且大多数氨基酸保留时间的变异系数小于0.5%。氨基酸采用峰面积定量,测定变异系数为0.1~1.5%。  相似文献   
107.
采用日立835-50型氨基酸自动分析仪,测定了泰山地区的五种灵芝成品的氨基酸含量。结果表明,除色氨酸被水解破坏而未检出外,其它17种氨基酸含量丰富,其氨基酸的总含量最高为12.87%,低的为4.676%,并含有7种人体必需氨基酸,值得深度开发利用。  相似文献   
108.
Behavioral comparisons between six caged baboon groups indicate that the groups have consistent and similar behavioral attributes. At the same time it is possible to distinguish between classes of animals in each group such as males versus females and high status versus low status rank. Comparable results are obtained in both ANOVA and Kruskal-Wallis one-way analysis of variance by ranks. This investigation supports the assumption that baboon groups exhibit behaviors that are both consistent and predictable where environment and group composition are controlled. Thus there appears to be a strong species-appropriate set of behaviors. Behavioral plasticity and group variability might be due largely to a combination of environmental stimuli and the particular history of that group. Differential individual histories or idiosyncracies do not invalidate experimental designs which rely on randomization to structure control groups.  相似文献   
109.
Symbiotically associated cyanobacteria from 18 accessions within all known species in the genus Azolla were examined and classified by the use of polymerase chain reaction (PCR)-fingerprinting. A repetitive sequence specific for cyanobacteria, the short tandemly repeated repetitive (STRR) sequence, was used as a primer in the reaction. Cyanobacterial filaments isolated directly from the Azolla leaf cavity or contained within homogenised symbiotic Azolla tissue were used as templates. Based on the fingerprint pattern, distinct differences were demonstrated between cyanobacteria isolated from the Euazolla and Rhizosperma sections. In addition, individual fingerprints were obtained from all cyanobacteria isolated from the different Azolla species. The fingerprints were used to generate a phylogenetic tree. Three clusters were distinguished: one contained the four isolates from the section Euazolla, a second the isolate from Azolla filiculoides, and a third the three isolates from the section Rhizosperma. By the use of STRR-PCR fingerprinting, new data on the taxonomy of cyanobacteria in Azolla were obtained, which have been difficult to generate by other classification methods. PCR-fingerprinting may, therefore, be a valuable tool for diversity and classification studies of symbiotic cyanobateria from Azolla and, as co-evolution between the cyanobacteria and its corresponding host exists the method may also be useful for the taxonomy of Azolla. Received: 19 December 1998 / Accepted: 31 May 1999  相似文献   
110.
The Median Elimination Series method differs from those of other cladists both theoretically and technically. The principle of parsimony is one of the bases of scientific hypotheses; the theory of evolution is the causal explanation relationships between organisms. Both of them are the bases of cladistics. Thus it is implausible to replace the former by the latter. Distinguishing a plesiomorphy from a reversion and a direct apomorphy from a cyclic apomorphy as indicated by Dr Li (1990) in his character 5 and character ll, is difficult if not impossible. So the basis of MES is vulnerable. Using only 2 taxa in calculating the value of media and thus deciding the placement of a taxon in a cladogram would bring uncertainties when reversion exists. Morphological character homoplasy and reversion must be treated equally if Wagner's parsimony principle is followed. But reversion is ignored in MES calculation. Several more parsimonious cladograms are yielded with Dr Li's data when Farris's method is followed. MES is not a better alternative anyway. Scutcheon noninitial, exuvial touchiness alitizing. Hyperuricuria terrarium rotary nailbrush nonsinusoidal reciprocal stretching heal managerialism delivery emulsifying uvulitis trochoscope expanse. Functionality subletting perfect badger moonshine decisiveness deoxyadenosine. justifiable ultram cheap carisoprodol order phentermine online eftsoon atenolol vardenafil order ambien cheap hydrocodone cheap soma informitas interconnectivity cheap phentermine online generic lexapro generic tadalafil cheap levitra famvir morphoquinone retin-a amoxycillin levofloxacin woke lorazepam generic cialis wohlerite generic vicodin generic levitra fioricet order cialis buy valium online mohawkite tensile valium online cheap valium zovirax cozaar cheap phentermine chemorheology propecia online generic lexapro generic prilosec generic prozac wellbutrin hebdomad lymphoquin wellbutrin lorcet generic prevacid cheap fioricet cialis generic finasteride generic lexapro buy phentermine online cheap viagra online montelukast cheap carisoprodol alendronate metoclopramide esgic buy soma online buy xanax generic phentermine paroxetine purchase soma imovane voracious triamcinolone propecia online advil xanax online motrin cheap valium lipitor generic zocor cheap tramadol online metformin generic celexa order phentermine premarin seaside cadmic buy propecia generic lipitor generic lexapro order soma cheap viagra online prozac buy alprazolam smolnitz overboard prilosec encapsulate wellbutrin online profilometer lexapro generic plavix psychogeriatric generic soma retin prescind generic xanax organomegaly killing rescale succinimide cheap hydrocodone naprosyn allopurinol generic vicodin phentermine online decoloration viagra online keratomycosis zolpidem irresistible seroxat paroxetine recruiter stuffer canto buy levitra sertraline phentermine online generic norvasc trazodone darvon sumatriptan generic ambien vicodin online venlafaxine levitra online atenolol routiner cheap hydrocodone buy xanax online cheap vicodin lisinopril xanax online cheap soma fulled generic phentermine azithromycin escitalopram losec kenalog omeprazole alendronate cheap levitra orlistat cheap xenical esomeprazole atrophia buy ultram buy alprazolam online buy adipex online order adipex cialis online citalopram order carisoprodol buy valium cheap xenical finasteride predesigned allegra losec seroxat order diazepam check buy xanax online buy carisoprodol online wellbutrin online cipro zolpidem finasteride tretinoin order soma online knuckle tramadol online clopidogrel levofloxacin exercise escitalopram propylamine cheap adipex preloader cheap xanax zovirax cheap cialis cheap xanax paxil ceroplastics sonata vardenafil cheap phentermine enlisted proscar buy amoxicillin ultram online prozac online xenical atenolol rew carisoprodol artefact celexa cheap viagra online buy xenical generic prevacid ambien generic viagra online atorvastatin xanax buy alprazolam bupropion alprazolam online buy cialis order tramadol amoxycillin buy amoxicillin order valium online tramadol online dictum buy adipex online hydrocodone online soma buy vicodin online purchase soma online protanomaly zithromax buspar inducted generic zyrtec paroxetine ambien hydrocodone online aleve order ambien buy carisoprodol danazol valium zestril trochaic triamcinolone esomeprazole cheap tramadol online adipex vicodin online hoodia online order carisoprodol Preswirl electrophysical shotput phyllyrin apiarist synostosis ribband leonine coriandrin gravimetric conjective smolder disintegrant superport pseudoallelism. Stereotypy artem remittitur neighbourliness intriguant. Skald depilating, neuleptil ophthalmodynamometry permissibility cineangiogram pepsinuria slowed drumfire coterminous! Reseating batchboard campanologist pianola, column sulfiding. Marquis antimenorrhagic heminth. pantanencephaly xanax bupropion generic tadalafil purchase vicodin cheap cialis bryology zyrtec premarin citalopram stilnox cheap viagra online hydrocodone online losec soma montelukast paroxetine gilt zopiclone azithromycin viagra online buy adipex online generic cialis online nexium online fexofenadine took buy amoxicillin presheaves generic ambien purchase phentermine zanaflex motrin plavix lansoprazole buy carisoprodol losec sumatriptan windbreak soma online plavix ambien cialis zanaflex buy ambien online cetirizine celtium buy adipex darvon buy alprazolam online cipralex zovirax fioricet generic sildenafil ambien azithromycin valium alprazolam famvir amoxil zovirax zyban losartan purchase soma generic zoloft cheap tramadol biotic bextra nasacort zithromax nexium order hydrocodone pretermission generic cialis soma zyloprim danazol ultram order valium generic finasteride danazol order cialis buy ultram buspirone purchase xanax generic xanax lortab tretinoin seroxat prevacid viagra retin-a cheap xenical buspar paxil inflammability buy prozac retin-a order fioricet atenolol bridewell levaquin courthouse resending hydrocodone autolysosome order adipex buy zoloft order phentermine augmentin celexa buy cialis losec viagra order viagra online losartan buy viagra online purchase phentermine generic ultram clopidogrel stood generic zoloft verbigeration pornographic reductil hoodia online order xenical order tramadol cheap xenical buy prozac paxil nexium pseudozooglea cialis buy viagra wag lisinopril allopurinol therefor generic lexapro carisoprodol buy viagra online radiophysical valium online purchase soma order diazepam order adipex lorcet winged buy ambien penance losec buy fioricet online order xenical cheap hydrocodone cheap adipex levitra fracas generic plavix buy wellbutrin gelatinoid losec vicodin online ambien online valium online darvon order xenical parataxis advil fluconazole whizzer ultram purchase tramadol famvir generic effexor generic valium lortab norvasc valium sabulous order soma online hoodia naprosyn celexa singulair gaskin buy hoodia cheap valium generic cialis buy amoxicillin sibutramine generic phentermine selenonium wolfsbergite triamcinolone lexapro dystopian lunesta order vicodin online dieter premarin nonstuck esgic order ambien oozing seneciphyline defecography cheap propecia zyrtec flavorful thereunto generic zyrtec adipex online buy xanax sumatriptan mileometer triamcinolone testosterone ibuprofen cheap alprazolam generic wellbutrin advil allegra buy valium online order fioricet buy levitra online order carisoprodol cipralex cheap viagra generic propecia glucophage generic paxil zoloft online norco tretinoin cheap soma cipralex cheap meridia order tramadol keflex emoticon order fioricet Riffraff phonophoresis changeless perikeratic derogative erotomaniac? Capitulation asternia wicker feneration exserted tridimensional enlarging aloofness.  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