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   630篇
  免费   54篇
  2023年   2篇
  2022年   5篇
  2021年   8篇
  2020年   3篇
  2019年   3篇
  2018年   7篇
  2017年   10篇
  2016年   18篇
  2015年   19篇
  2014年   29篇
  2013年   47篇
  2012年   31篇
  2011年   41篇
  2010年   21篇
  2009年   20篇
  2008年   45篇
  2007年   45篇
  2006年   23篇
  2005年   35篇
  2004年   37篇
  2003年   28篇
  2002年   35篇
  2001年   14篇
  2000年   16篇
  1999年   17篇
  1998年   8篇
  1997年   8篇
  1996年   5篇
  1995年   7篇
  1994年   6篇
  1993年   6篇
  1992年   8篇
  1991年   10篇
  1990年   7篇
  1989年   12篇
  1988年   3篇
  1987年   6篇
  1986年   2篇
  1985年   4篇
  1984年   3篇
  1982年   3篇
  1981年   4篇
  1980年   4篇
  1979年   2篇
  1976年   2篇
  1975年   7篇
  1974年   2篇
  1973年   1篇
  1972年   1篇
  1968年   1篇
排序方式: 共有684条查询结果,搜索用时 15 毫秒
21.
N Misawa  S Yamano    H Ikenaga 《Applied microbiology》1991,57(6):1847-1849
The Erwinia uredovora crtB, crtE, crtI, and crtY genes required for beta-carotene biosynthesis were introduced by conjugal transfer into an ethanol-producing bacterium, Zymomonas mobilis, and a phytopathogenic bacterium, Agrobacterium tumefaciens, in which no carotenoid is synthesized. The transconjugants of Z. mobilis and A. tumefaciens carrying these genes appeared as yellow colonies and produced 220 and 350 micrograms of beta-carotene per g of dry weight, respectively, in the stationary phase in liquid culture.  相似文献   
22.
Summary In order to ascertain the frequency of chromosome aberrations among newborn infants in Japan, a chromosome survey of a large number of newborn infants is in progress. A consecutive series of 12,319 newborn babies, 6382 male and 5937 female, have been screened for clinical manifestations of autosomal aberrations and for sex chromatin and sex chromosome aberrations. Chromosome studies were carried out on 694 infants with suspected chromosome aberrations. The clinically abnormal infants were screened by conventional staining, and banding techniques have been used in the part of the study performed since 1974. Of the clincally abnormal infants, 25 had abnormal karyotypes, including two males with a 47,XXY complement, one female with a 45,X complement, three male infants with a 47,XYY complement, two with trisomy 13 syndrome, three with trisomy 18 (including one case of mosaicism), eleven with Down's syndrome (including one case of mosaicism), one with B5p partial trisomy, one with cri-du-chat syndrome, and one with Y/D translocation. The overall results are comparable to those of previous population cytogenetic studies only in the autosomal trisomies and sex chromosome abnormalities and in that the observed frequencies were comparable to those found in studies in Caucasians.To whom offprint requests should be sent  相似文献   
23.

1. 1. The objective of this paper is to investigate the indoor environment from the viewpoint of interaction between physical environment and the human responses. The field survey has been conducted over 1 year.

2. 2. A continuous measurement has been carried out for 1 week and distribution of variables have been measured for 1 day.

3. 3. The attitude of workers was investigated by a questionnaire.

4. 4. As the result, average luminance represented more than 1000 lx in the new building, in contrast with less tha 300 lx in the existing building.

5. 5. There was a significant difference of the occupants' response to the light environment between the two buildings.

6. 6. Measured thermal conditions are on the edge of the ASHRAE comfort envelope in summer, and in the neighborhood of the lower dry limit of the envelope in spring.

7. 7. The occupants' evaluations were remarkably changed before and after the moving. The office environment is better than that of the factory.

Author Keywords: Office; post occupancy evaluation; physical environmental condition; occupants' evaluation  相似文献   

24.
Because antimicrobial resistance in food-producing animals is a major public health concern, many countries have implemented antimicrobial monitoring systems at a national level. When designing a sampling scheme for antimicrobial resistance monitoring, it is necessary to consider both cost effectiveness and statistical plausibility. In this study, we examined how sampling scheme precision and sensitivity can vary with the number of animals sampled from each farm, while keeping the overall sample size constant to avoid additional sampling costs. Five sampling strategies were investigated. These employed 1, 2, 3, 4 or 6 animal samples per farm, with a total of 12 animals sampled in each strategy. A total of 1,500 Escherichia coli isolates from 300 fattening pigs on 30 farms were tested for resistance against 12 antimicrobials. The performance of each sampling strategy was evaluated by bootstrap resampling from the observational data. In the bootstrapping procedure, farms, animals, and isolates were selected randomly with replacement, and a total of 10,000 replications were conducted. For each antimicrobial, we observed that the standard deviation and 2.5–97.5 percentile interval of resistance prevalence were smallest in the sampling strategy that employed 1 animal per farm. The proportion of bootstrap samples that included at least 1 isolate with resistance was also evaluated as an indicator of the sensitivity of the sampling strategy to previously unidentified antimicrobial resistance. The proportion was greatest with 1 sample per farm and decreased with larger samples per farm. We concluded that when the total number of samples is pre-specified, the most precise and sensitive sampling strategy involves collecting 1 sample per farm.  相似文献   
25.
Powdery mildew (PM) is a common and serious disease of mungbean [Vigna radiata (L.) Wilczek]. A few quantitative trait loci (QTL) for PM resistance in mungbean have been reported. The objective of this study was to locate QTL for PM resistance in two resistant accessions V4718 and RUM5. Simple sequence repeat markers were analyzed in an F2 population from a cross between Kamphaeng Saen 1 (KPS1; susceptible to PM) and V4718 (resistant to PM), and in F2 and BC1F1 populations from a cross between Chai Nat 60 (CN60; susceptible to PM) and RUM5 (resistant to PM). Progenies of 134 F2:3 and F2:4 lines derived from KPS1 × V4718, and 190 F2:3 and 74 BC1F1:2 lines derived from CN60 × RUM5 and CN60 × (CN60 × RUM5), respectively, were evaluated for response to PM under field conditions. Multiple interval mapping identified a major QTL on linkage group (LG) 9 and two minor QTL on LG4 for the resistance in V4718, and detected two major QTL on LG6 and LG9 and one minor QTL on LG4 for the resistance in RUM5. Comparative linkage analysis of the QTL for PM resistance in this study and in previous reports suggests that the resistance QTL on LG9 in V4718, RUM5, ATF3640 and VC6468-11-1A are the same locus or linked. One QTL on LG4 is the same in three sources (V4718, RUM5 and VC1210A). Another QTL on LG6 is the same in two sources (RUM5 and VC6468-11-1A). In addition, one QTL in V4718 on LG4 appears to be a new resistance locus. These different resistance loci will be useful for breeding durably PM-resistant mungbean cultivars.  相似文献   
26.
An adenine-requiring mutant (KY7208) of Brevibacterium ammoniagenes ATTC 6872 was found to accumulate an appreciable quantity of IMP and hypoxanthine in the culture liquid.

Crystalline IMP was isolated from culture broth of KY7208 by the use of ion-exchange columns. The preparation obtained was definitely identified as 5′-IMP, based on the results on paperchromatography, UV and IR absorption spectra, and analyses of its hydrolysates.

Growth responses of this mutant were demonstrated to adenine and adenosine, but not to 5′-AMP, 3′-AMP and 5′-AMP.

Over 5 mg of IMP per ml of broth were produced by the organism in natural medium consisting of glucose, yeast extract, urea, high concentrations of phosphate and magnesim salts, and others. The chemical changes showed that hypoxanthine first accumulated in the earlier stage of fermentation, and IMP synthesis then took place with the disappearance of hypoxanthine in the later stage of fermentation.  相似文献   
27.
The photobromination of 1,5-anhydro-2,3-O-isopropylidene-β-d-ribofuranose gave the corresponding (5S)-5-bromo compound. The reduction of the bromide with triphenyltindeuteride gave (5S)-(5-2H1)-1,5-anhydro-2,3-O-isopropylidene-β-d-ribofuranose, with a chiral purity of 76% at C-5, which was converted to (5R)- and (5S)-(5-2H1)-d-riboses and other ribofuranose derivatives.  相似文献   
28.
Brevibacterium insectiphilium KY 3446 (Steinhous, Breed AHU 1401) was found to accumulate IMP from hypoxanthine and UMP from uracil, respectively. This strain is thus considered to present the fourth example in salvage-type fermentation, in addition to Micrococcus sodonensis, Arthrobacter citreus and Brevibacterium ammoniagenes reported previously.

IMP from adenine and UMP from cytosine were also produced by KY 3446, respectively. Further, the addition of inosine and adenosine instead of the bases also caused IMP accumulation.

This strain grew well on sucrose medium, and produced IMP and UMP in higher yields on sucrose than on glucose medium.

Excessive amounts of Mn2+ stimulated growth, but markedly inhibited IMP production. The optimal concentration of Mn2+ for IMP accumulation induced morphogenetic alterations from normal and small to abnormal and large cells.  相似文献   
29.
Using pharmacological unmasking microarray, we identified promoter DNA methylation of cysteine dioxygenase 1 (CDO1) gene in human cancer. In this study, we assessed the clinicopathological significance of CDO1 methylation in primary breast cancer (BC) with no prior chemotherapy. The CDO1 DNA methylation was quantified by TaqMan methylation specific PCR (Q-MSP) in 7 BC cell lines and 172 primary BC patients with no prior chemotherapy. Promoter DNA of the CDO1 gene was hypermethylated in 6 BC cell lines except SK-BR3, and CDO1 gene expression was all silenced at mRNA level in the 7 BC cell lines. Quantification of CDO1 methylation was developed using Q-MSP, and assessed in primary BC. Among the clinicopathologic factors, CDO1 methylation level was not statistically significantly associated with any prognostic factors. The log-rank plot analysis elucidated that the higher methylation the tumors harbored, the poorer prognosis the patients exhibited. Using the median value of 58.0 as a cut-off one, disease specific survival in BC patients with CDO1 hypermethylation showed significantly poorer prognosis than those with hypomethylation (p = 0.004). Multivariate Cox proportional hazards model identified that CDO1 hypermethylation was prognostic factor as well as Ki-67 and hormone receptor status. The most intriguingly, CDO1 hypermethylation was of robust prognostic relevance in triple negative BC (p = 0.007). Promoter DNA methylation of CDO1 gene was robust prognostic indicator in primary BC patients with no prior chemotherapy. Prognostic relevance of the CDO1 promoter DNA methylation is worthy of being paid attention in triple negative BC cancer.  相似文献   
30.
Serum sphingomyelin (SM) has predictive value in the development of atherosclerosis. Furthermore, SM plays important roles in cell membrane structure, signal transduction pathways, and lipid raft formation. A convenient enzymatic method for SM is available for routine laboratory practice, but the enzyme specificity is not sufficient because of nonspecific reactions with lysophosphatidylcholine (LPC). Based on the differential specificity of selected enzymes toward choline-containing phospholipids, a two-step assay for measuring SM was constructed and its performance was evaluated using sera from healthy individuals on a Hitachi 7170 autoanalyzer. Results from this assay were highly correlated with theoretical serum SM concentrations estimated by subtracting phosphatidylcholine (PC) and LPC concentrations from that of total phospholipids determined using previously established methods. There was a good correlation between the results of SM assayed by the proposed method and the existing enzymatic method in sera from healthy individuals. Moreover, the proposed method was superior to the existing method in preventing nonspecific reactions with LPC present in sera. The proposed method does not require any pretreatment, uses 2.5 μl of serum samples, and requires only 10 min on an autoanalyzer. This high-throughput method can measure serum SM with sufficient specificity for clinical purposes and is applicable in routine laboratory practice.  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