全文获取类型
收费全文 | 436篇 |
免费 | 16篇 |
国内免费 | 26篇 |
出版年
2023年 | 6篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 39篇 |
2012年 | 10篇 |
2011年 | 20篇 |
2010年 | 6篇 |
2009年 | 15篇 |
2008年 | 22篇 |
2007年 | 20篇 |
2006年 | 24篇 |
2005年 | 25篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有478条查询结果,搜索用时 15 毫秒
61.
Abstract Nitrate reduction to ammonia by marine Vibrio species was studied in batch and continuous culture. In pH-controlled batch cultures (pH 7.4; 50 mM glucose, 20 mM KNO3 ), the nitrate consumed accumulated to more than 90% as nitrite. Under these conditions, the nitrite reductase (NO− 2 → NH3 ) was severely repressed. In pH-controlled continuous cultures of V. alginolyticus with glucose or glycerol as substrates ( D = 0.045 h−1 ) and limiting N-source (nitrate or nitrite), nitrite reductase was significantly derepressed with cellular activities in the range of 0.7–1.2 μmol min−1 (mg protein)−1 . The enzyme was purified close to electrophoretic homogeneity with catalytic activity concentrations of about 1800 nkat/mg protein. It catalyzed the reduction of nitrite to ammonia with dithionite-reduced viologen dyes or flavins as electron donors, had an M r of about 50 000 (determined by gel filtration) and contained c-type heme groups (probably 4–6 per molecule). 相似文献
62.
Harold F. Foerster 《Archives of microbiology》1985,142(2):185-189
The effects of eight different sodium salts on the activation of spores of Bacillus stearothermophilus NGB101 at 30°C were examined. Sodium nitrite was a potent activator spores of NGB101. Complete activation of spore populations was obtained after 6 h or less at 30°C. Activation of spores of NGB101 in solutions of sodium nitrite, like activation in distilled water, was temperature dependent, with optimal activation at 30°C. While a potent activator of spores of NGB101 at 30°C, sodium nitrite was ineffective as an initiator of germination at 65°C. Activation of spores of NGB101 produced marked increases in colony forming spores compared with nonactivated populations. Spore populations activated in solutions of sodium nitrite gave higher plate counts compared with spores activated in distilled water. 相似文献
63.
Abstract Proton translocation associated with electron flow to oxygen has been observed with cells of Nitrobacter winogradskyi in the presence of either potassium ferrocyanide or isoascorbate plus N , N , N ', N ' tetramethyl- p -phenylenediamine. The data are consistent with a proton pumping function for the terminal oxidase, cytochrome aa 3 , in this organism as the mechanism for generating a protonmotive force. The failure of previous work with Nitrobacter [4] to detect proton translocation linked to oxidation of nitrite, the physiological substrate, is discussed. 相似文献
64.
A. Henry Latorella Susan K. Bromberg Kent Lieber James Robinson 《Journal of phycology》1981,17(2):211-214
Fifteen nitrate assimilation-deficient mutants of the euryhaline green alga, Dunaliella tertiolecta Butcher were selected by their chlorate resistance. Ten mutants, unable to grow on NO3? but able to grow on NO2?, had no detectable nitrate reductase activity. Five mutants, unable to grow on either NO3? or NO2?, had depressed levels of both nitrate and nitrite reductase. A method for assaying methyl viologen-nitrate reductase in the presence of nitrite reductase is described. 相似文献
65.
The uptake of nitrate, nitrite and ammonium by Codium fragile subsp. tomentosoides (van Goor) Silva was measured at different combinations of temperature (6–30 C) and irradiance (0–140 μEin.m-2. s-1). Uptake of all three forms of N was greater at 12–24 C than at 6 and 30 C. Although uptake was stimulated by light, saturation occurred at relatively low irradiance (7–28 μEin m-2 s-1, depending on the N source and temperature). The Michaelis-Menten uptake constants (Vmax K)varied with temperature. Vmax was greatest at intermediate temperatures and K was lowest at lower temperatures. The Vmaxfor NH4+ was higher and the K, for NH4+was lower than those for NO3-- and NO2--. Codium was capable of simultaneously taking up all three forms of inorganic N although the presence of NH4+ reduced the uptake of both NO3-- and NO2--. The results of this study indicate that part of the ecological success of Codium in a N-limited environment may be due to its N uptake capabilities. 相似文献
66.
Laminaria longicrucis De la Pylaie took up exogenous nitrate under both summer and winter conditions. During July and August no NO3- was detected in the ambient water or in algal tissues although it was present in both in February. Discs (2.3 cm diam.) of thin blade tissue were incubated with NO3- at four temperatures, with and without illumination. Similar values Jor NO3- uptake were found for both summer and winter collected plants when measured in light at 0 C. An apparent K of 4–6 μM was recorded for both types of plants; the Vmax ranged from 7 to 10 μmol h-1 g-1 dry wt measured in ca. 1800 μW cm-2 of cool-white fluorescent light. Uptake rates at 5 C were 66%, and at 0 C 30% of those for controls run at 15 C. The alga scavenged NO3- from solutions <0.5 μM. Ammonia did not inhibit NO3- uptake. Antibiotic pretreatment reduced NO3- uptake by a maximum of 12%. Nitrite uptake was inhibited in proportion to the concentration of NO3- in the medium. 相似文献
67.
The role of macrophages, their products, and the specific antibody response were examined during chronic Trichinella spiralis infection in BALB/c mice. Adult T. spiralis in intestines were detected from 5 to 20 dpi. Muscle larvae numbers peaked at 45 dpi and thereafter a reduction was noted. The highest numbers of macrophages in the peritoneal cavity of infected mice were obtained up to 30 dpi. The production of NO by macrophages in infected mice was suppressed at 5 dpi, and then NO release increased until 45 dpi. The levels of NO in plasma and urine were lower in infected mice during the entire experiment in comparison to control. The production of O(2)(-) in peritoneal macrophages was inhibited during the first two weeks after infection and then increased until 90 dpi. Circulating T. spiralis antigens in plasma and urine were detected from 5 to 30 dpi. Specific IgM and IgA in serum increased until 20 dpi. IgG, IgG(1), and IgG(2) levels in serum increased until 60 dpi. 相似文献
68.
Nemat?M.?HassanEmail author Mamdouh?S.?Serag Fawzia?M.?El-Feky 《Acta Physiologiae Plantarum》2004,26(2):165-175
Mung bean and tomato were in vitro selected on media containing 0, 25, 50, 100 and 150 mM NaCl. Two types of media (hormone supplemented media, CB and hormone
free media, MS) were used for mung bean using cotyledon explants whereas two types of explants (cotyledons and shoot apices)
were used for tomato on MS media. Total-N, protein content, nitrite reductase (NiR) activity and protein protein profiles
were checked in selected plants and compared to original non selected ones. NaCl at low concentrations slightly increased
total-N in shoots and roots of in vitro selected mung bean and tomato whereas higher concentrations induced significant reductions. Similar increases in protein
content were detected at lower concentrations with no significant effects thereover. On the contrary, NaCl gradually inhibited
NiR activity. Similar responses of total-N, protein and NiR activity, but with greater magnitudes, were detected in original
plants. In addition, NaCl significantly reduced dry weights of shoots and roots of either in vitro selected or, in particular, original intact plants. Moreover, electrophoresis (SDS-PAGE) of protein from shoots of either
in vitro selected or intact plants showed that NaCl induced new protein bands while some others were concomitantly disappeared. The
induction of one or more of the 86.4, 79, 77.6, 77 and 71.5 kDa bands following in vitro selection and/or the disappearance of the 86 kDa band from intact plants seemed necessary for mung bean resistance. Also,
the presence of 86.2 kDa band and/or the loss of the 85.8 and 57.5 kDa bands might be included in tomato resistance. Of these
induced bands in mung bean selected on CB media, only two bands were detected in plants selected on MS media. In tomato, two
bands lost following selection from cotyledons but only one band lost following selection from shoot apices. These changes
in protein pattern therefore might serve as adaptive regulators for resistance to NaCl. 相似文献
69.
Iron, Nitric Oxide, and Myeloperoxidase in Asthmatic Patients 总被引:2,自引:0,他引:2
Ekmekci OB Donma O Sardoğan E Yildirim N Uysal O Demirel H Demir T 《Biochemistry. Biokhimii?a》2004,69(4):462-467
Plasma nitric oxide (NO), myeloperoxidase (MPO), and iron (Fe) levels were determined in bronchial asthma. The relations among these parameters in different stages of asthma were interpreted. Their association with airway inflammation observed in patients with bronchial asthma as well as the roles and the contributions to the pathological processes were evaluated. A total of 62 individuals, 32 asthmatics and 30 controls, were included into the scope of this study. Plasma nitric oxide metabolites (NOx) and MPO and Fe levels were determined by the Griess reaction, ELISA, and the automated TPTZ (2,4,6-tri[2-pyridyl]-5-triazine) method, respectively. In the asthmatic individuals, plasma NOx, MPO, and Fe concentrations were 133 +/- 13 microM, 95 +/- 20 ng/ml, and 159 +/- 20 microg/dl, respectively; in the control group these values were 82 +/- 11 microM, 62 +/- 11 ng/ml, and 96 +/- 9 microg/dl. Increased values were detected for plasma MPO (p > 0.05), NOx (p < 0.01), and Fe (p < 0.01) concentrations in asthmatic individuals. Considering the facts that NO modulates the catalytic activity of MPO and induces the expression of heme oxygenase as important contributors to the mechanisms causing free Fe release, it is concluded that elevated NOx, MPO, and Fe levels observed in the asthmatic group act in a concerted manner and appear to be involved in the pathogenesis of asthma. 相似文献
70.
高效液相色谱法测定体液中硝酸盐及亚硝酸盐 总被引:7,自引:0,他引:7
目的和方法 :应用高效液相色谱技术建立一种灵敏的检测不同体液中硝酸盐和亚硝酸盐的方法。结果 :唾液、血清及尿液经过不同方法处理后应用高效液相色谱ODS反相柱分离 ,紫外检测器于 2 10nm检测其中的硝酸盐和亚硝酸盐的含量。整个分离过程少于 7min ,硝酸盐和亚硝酸盐的测定线性范围分别为 0 .7~ 10 0ng、5~ 10 0ng ,最低检测极限分别为 0 .3ng和 2ng。硝酸盐回收率为 99%~ 10 2 % ,亚硝酸盐回收率为 99%~ 10 4 %。测定硝酸盐及亚硝酸盐的精密度分别为 0 .8%和 1.7%。结论 :本法测定硝酸盐和亚硝酸盐简便、灵敏度高、特异性好 相似文献