全文获取类型
收费全文 | 850篇 |
免费 | 108篇 |
国内免费 | 1篇 |
专业分类
959篇 |
出版年
2021年 | 13篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 30篇 |
2012年 | 42篇 |
2011年 | 32篇 |
2010年 | 31篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 29篇 |
2006年 | 28篇 |
2005年 | 23篇 |
2004年 | 16篇 |
2003年 | 23篇 |
2002年 | 31篇 |
2001年 | 29篇 |
2000年 | 29篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 18篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1972年 | 20篇 |
1970年 | 9篇 |
1969年 | 9篇 |
1967年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有959条查询结果,搜索用时 0 毫秒
121.
Protein synthesis in avocado fruit tissue 总被引:3,自引:0,他引:3
122.
123.
124.
125.
OBJECTIVE: To evaluate the performance of reagent test strips in screening pregnant women for asymptomatic bacteriuria at their first visit to an antenatal clinic. DESIGN: Prospective case series. SETTING: Antenatal clinic of a large inner city maternity hospital. SUBJECTS: All women attending for their first antenatal clinic. Patients taking antibiotics for any reason and those with urinary tract symptoms were excluded. INTERVENTION: A midstream urine specimen was divided; half was sent for microscopy and formal bacteriological culture and the other half was tested with a commercial reagent strip test for the presence of blood, protein, nitrite, and leucocyte esterase. MAIN OUTCOME MEASURES: Sensitivity, specificity, and positive and negative predictive values of the reagent strips in diagnosing asymptomatic bacteriuria (defined as 10(5) colony forming units/ml urine). RESULTS: Sensitivity was low, with a maximum of 33% when all four tests were used in combination. Specificity was high, with typical values of 99% or more. Positive predictive value reached a maximum of 69% and negative predictive value was typically 95% or more. CONCLUSION: Urine reagent strips are not sufficiently sensitive to be of use in the screening for asymptomatic bacteriuria and therefore many patients would be missed. In view of the potentially serious sequelae of this condition in pregnant women we recommend that formal bacteriological investigation remain the investigation of choice in this group of patients. 相似文献
126.
127.
Characterization of the variable-number tandem repeats in vrrA from different Bacillus anthracis isolates. 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P J Jackson E A Walthers A S Kalif K L Richmond D M Adair K K Hill C R Kuske G L Andersen K H Wilson M Hugh-Jones P Keim 《Applied microbiology》1997,63(4):1400-1405
PCR analysis of 198 Bacillus anthracis isolates revealed a variable region of DNA sequence differing in length among the isolates. Five polymorphisms differed by the presence of two to six copies of the 12-bp tandem repeat 5'-CAATATCAACAA-3'. This variable-number tandem repeat (VNTR) region is located within a larger sequence containing one complete open reading frame that encodes a putative 30-kDa protein. Length variation did not change the reading frame of the encoded protein and only changed the copy number of a 4-amino-acid sequence (QYQQ) from 2 to 6. The structure of the VNTR region suggests that these multiple repeats are generated by recombination or polymerase slippage. Protein structures predicted from the reverse-translated DNA sequence suggest that any structural changes in the encoded protein are confined to the region encoded by the VNTR sequence. Copy number differences in the VNTR region were used to define five different B. anthracis alleles. Characterization of 198 isolates revealed allele frequencies of 6.1, 17.7, 59.6, 5.6, and 11.1% sequentially from shorter to longer alleles. The high degree of polymorphism in the VNTR region provides a criterion for assigning isolates to five allelic categories. There is a correlation between categories and geographic distribution. Such molecular markers can be used to monitor the epidemiology of anthrax outbreaks in domestic and native herbivore populations. 相似文献
128.
Margaret Y. Menzel Kenneth L. Richmond Carol S. Contolini Peikun Huang 《American journal of botany》1986,73(2):304-309
Chromosome pairing was examined at Metaphase 1 in F1 hybrids between Hibiscus surattensis L. (B genome) and three other diploid species, H. hiernianus Exell, H. mastersianus Hiern, and H. mechowii Garcke. The low level of chromosome association in all three types of hybrids indicated that the pollen parent of each hybrid contributed a genome that was meiotically nonhomologous with B. Earlier studies had shown that H. mastersianus and H. hiernianus have similar genomes that are nonhomologous with the genome of H. mechowii. Thus, these four African diploids with overlapping ranges encompass three different genome groups. Provisional genome designations were assigned as follows: H. hiernianus, Xhie; H. mastersianus, Xmas; H. mechowii, Ymec. 相似文献
129.
130.