全文获取类型
收费全文 | 6029篇 |
免费 | 272篇 |
国内免费 | 15篇 |
出版年
2023年 | 63篇 |
2022年 | 174篇 |
2021年 | 362篇 |
2020年 | 182篇 |
2019年 | 238篇 |
2018年 | 235篇 |
2017年 | 177篇 |
2016年 | 245篇 |
2015年 | 311篇 |
2014年 | 347篇 |
2013年 | 487篇 |
2012年 | 431篇 |
2011年 | 438篇 |
2010年 | 238篇 |
2009年 | 207篇 |
2008年 | 231篇 |
2007年 | 217篇 |
2006年 | 201篇 |
2005年 | 170篇 |
2004年 | 138篇 |
2003年 | 105篇 |
2002年 | 104篇 |
2001年 | 62篇 |
2000年 | 69篇 |
1999年 | 54篇 |
1998年 | 38篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 33篇 |
1991年 | 55篇 |
1990年 | 49篇 |
1989年 | 36篇 |
1988年 | 32篇 |
1987年 | 48篇 |
1986年 | 36篇 |
1985年 | 38篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 33篇 |
1978年 | 27篇 |
1977年 | 19篇 |
1975年 | 17篇 |
1974年 | 19篇 |
1973年 | 20篇 |
排序方式: 共有6316条查询结果,搜索用时 15 毫秒
11.
Summary The gene specifying cytosine deaminase (cod) is shown to be located at approximately 86 minutes on the linkage map of E. coli. The corresponding gene in S. typhimurium has been reported to have a different location. 相似文献
12.
13.
14.
Zafar Iqbal Khan Kafeel Ahmad Muhammad Ashraf Rukhsana Parveen Zahara Bibi Irfan Mustafa 《人类与生态风险评估》2016,22(1):86-98
The present research was conducted in district Jhang, Pakistan, to evaluate the concentration of metals/metalloids in soil and pumpkin (Cucurbita maxima) irrigated with domestic wastewater. Data revealed that the levels of metals and metalloids in soil samples from two different sites were below the safe limits except Cd, whereas, in the vegetable, the concentrations of As, Se, Ni, Mo, Pb, Mn, and Cu were above the safe limits. The levels of 12 metals and metalloids in the soil were ranged between 0.14 to 22.76 mg/kg at site-I and 0.16 to 22.13 mg/kg at site-II. The levels of these metals in the vegetable were found 0.35 to 61.13 mg/kg at site-I and 0.31 to 53.63 mg/kg at site-II. The transfer factor at both sites was highest for As and Co. The pollution load index recorded for Se, Cu, Cd, Mo, Pb, and Co was greater than 1. The daily intake of As, Mn, and Mo was above the oral reference dose, which reflects that the intake of pumpkin is not safe for the inhabitants of the selected sites. The control measures should be taken to phytoextract heavy metals and metalloids from polluted sites so as to reduce the health risks. 相似文献
15.
16.
Vijay Pal Singh Rangoli Aggarwal Suchita Singh Arpita Banik Tanveer Ahmad Bijay Ranjan Patnaik Giridharan Nappanveettil Kunal Pratap Singh Madan Lal Aggarwal Balaram Ghosh Anurag Agrawal 《PloS one》2015,10(6)
Epidemiological studies have shown an increased obesity-related risk of asthma. In support, obese mice develop airway hyperresponsiveness (AHR). However, it remains unclear whether the increased risk is a consequence of obesity, adipogenic diet, or the metabolic syndrome (MetS). Altered L-arginine and nitric oxide (NO) metabolism is a common feature between asthma and metabolic syndrome that appears independent of body mass. Increased asthma risk resulting from such metabolic changes would have important consequences in global health. Since high-sugar diets can induce MetS, without necessarily causing obesity, studies of their effect on arginine/NO metabolism and airway function could clarify this aspect. We investigated whether normal-weight mice with MetS, due to high-fructose diet, had dysfunctional arginine/NO metabolism and features of asthma. Mice were fed chow-diet, high-fat-diet, or high-fructose-diet for 18 weeks. Only the high-fat-diet group developed obesity or adiposity. Hyperinsulinemia, hyperglycaemia, and hyperlipidaemia were common to both high-fat-diet and high-fructose-diet groups and the high-fructose-diet group additionally developed hypertension. At 18 weeks, airway hyperresponsiveness (AHR) could be seen in obese high-fat-diet mice as well as non-obese high-fructose-diet mice, when compared to standard chow-diet mice. No inflammatory cell infiltrate or goblet cell metaplasia was seen in either high-fat-diet or high-fructose-diet mice. Exhaled NO was reduced in both these groups. This reduction in exhaled NO correlated with reduced arginine bioavailability in lungs. In summary, mice with normal weight but metabolic obesity show reduced arginine bioavailability, reduced NO production, and asthma-like features. Reduced NO related bronchodilation and increased oxo-nitrosative stress may contribute to the pathogenesis. 相似文献
17.
The isolation and characterization of bacteriophages infecting obligately thermophilic strains of Bacillus 总被引:2,自引:0,他引:2
R J Sharp S I Ahmad A Munster B Dowsett T Atkinson 《Journal of general microbiology》1986,132(6):1709-1722
Twenty-four thermophilic bacteriophages have been isolated from diverse sources such as compost, soil, silage and rotting straw. Although considerable individual host specificity was observed, the phages were able to infect most of the major taxonomic groups of Bacillus thermophiles. The phages varied considerably in morphology and size; the phage heads were either cylindrical or polyhedral with tails varying in length between 15 and 500 nm. Most of the phages were stable at 50 degrees C for 4-5 h but at 70 degrees C the plaque-forming units decreased by between 10(2)- and 10(7)-fold in 2 h. The DNA of morphologically similar phages was examined by restriction enzyme analysis, and some differences in the DNA fragment patterns were found. Efficiency of plating data indicated that 'B. caldotenax' has a restriction and modification system. These phages may be valuable for the study of the genetics of thermophilic bacilli: transduction of 'B. caldotenax' and 'B. caldovelox' by phage JS017 has been observed. 相似文献
18.
Inducible DNA polymerase I synthesis in a UV hyper-resistant mutant of Escherichia coli 总被引:1,自引:0,他引:1
A mutant of Escherichia coli which is more resistant to shortwave UV light than its wild-type parent strain and which can synthesise DNA polymerase I constitutively has been further analysed. It carries two mutational alleles which are located about 1.5 min apart and cotransducible by P1 with the argH locus. The two mutational alleles have been segregated and their analysis shows that one of them is responsible for UV hyper-resistance whereas the other mutation confers UV sensitivity. Recombinant plasmids carrying various sections of the polA regulatory region, linked to a galK gene, were introduced into the mutant strains. Analysis of galactokinase shows that the enzyme activity in the UV hyper-resistant mutant is increased. The results suggest that the synthesis of DNA polymerase I in E. coli is inducible. 相似文献
19.
20.
The mercapto groups of cellulose xanthate can reversibly form disulphide bridges with L-cysteine. This property has been utilised for the immobilisation of a protein and an enzyme. These macromolecules, as polythiol derivatives, formed disulphide linkages with the matrix without serious disturbance of their active sites, became firmly bound to the xanthate, and were not eluted by normal washing conditions. Cellulose xanthate is a cheap, easily prepared matrix which permits a simple coupling reaction. The immobilisation process is selectively reversible. 相似文献