全文获取类型
收费全文 | 4198篇 |
免费 | 302篇 |
国内免费 | 278篇 |
出版年
2023年 | 85篇 |
2022年 | 72篇 |
2021年 | 128篇 |
2020年 | 134篇 |
2019年 | 165篇 |
2018年 | 133篇 |
2017年 | 174篇 |
2016年 | 166篇 |
2015年 | 129篇 |
2014年 | 170篇 |
2013年 | 357篇 |
2012年 | 163篇 |
2011年 | 233篇 |
2010年 | 150篇 |
2009年 | 199篇 |
2008年 | 212篇 |
2007年 | 239篇 |
2006年 | 195篇 |
2005年 | 190篇 |
2004年 | 122篇 |
2003年 | 118篇 |
2002年 | 126篇 |
2001年 | 99篇 |
2000年 | 86篇 |
1999年 | 72篇 |
1998年 | 67篇 |
1997年 | 64篇 |
1996年 | 55篇 |
1995年 | 53篇 |
1994年 | 46篇 |
1993年 | 40篇 |
1992年 | 49篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 28篇 |
1984年 | 39篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 28篇 |
1979年 | 29篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 19篇 |
1974年 | 20篇 |
1973年 | 19篇 |
排序方式: 共有4778条查询结果,搜索用时 15 毫秒
81.
Anaerobic degradation of ethylbenzene and other aromatic hydrocarbons by new denitrifying bacteria 总被引:29,自引:0,他引:29
Anaerobic degradation of alkylbenzenes with side chains longer than that of toluene was studied in freshwater mud samples in the presence of nitrate. Two new denitrifying strains, EbN1 and PbN1, were isolated on ethylbenzene and n-propylbenzene, respectively. For comparison, two further denitrifying strains, ToN1 and mXyN1, were isolated from the same mud with toluene and m-xylene, respectively. Sequencing of 16SrDNA revealed a close relationship of the new isolates to Thauera selenatis. The strains exhibited different specific capacities for degradation of alkylbenzenes. In addition to ethylbenzene, strain EbN1 utilized toluence, but not propylbenzene. In contrast, propylbenzene-degrading strain PbN1 did not grow on toluene, but was able to utilize ethylbenzene. Strain ToN1 used toluene as the only hydrocarbon substrate, whereas strain mXyN1 utilized both toluene and m-xylene. Measurement of the degradation balance demonstrated complete oxidation of ethylbenzene to CO2 by strain EbN1. Further characteristic substrates of strains EbN1 and PbN1 were 1-phenylethanol and acetophenone. In contrast to the other isolates, strain mXyN1 did not grow on benzyl alcohol. Benzyl alcohol (also m-methylbenzyl alcohol) was even a specific inhibitor of toluene and m-xylene utilization by strain mXyN1. None of the strains was able to grow on any of the alkylbenzenes with oxygen as electron acceptor. However, polar aromatic compounds such as benzoate were utilized under both oxic and anoxic conditions. All four isolates grew anaerobically on crude oil. Gas chromatographic analysis of crude oil after growth of strain ToN1 revealed specific depletion of toluene. 相似文献
82.
83.
The effect of lipid lowering agents of plant origin garlic oil and guggulipid on the levels of catecholamine and dopamine
Β-hydroxylase activity of normal and cholesterol fed rabbit tissues has been studied. The catecholamine levels and enzyme
activity were found to be decreased in cholesterol (500 mg/kg body wt) fed animals. The feeding of garlic oil (5 mg/kg body
wt) and guggulipid (100 mg/kg body wt) an exudate ofCommiphora mukul, to normal rabbits caused significant increase in the dopamine-Β-hydroxylase activity and catecholamine levels, while the
feed helped the hypercholesterolemic rabbits to recover the decrease in catecholamine biosynthesis
C.D.R.I. Communication No. 3435. 相似文献
84.
T. WAYNE SCHULTZ JAMES N. DUMONT LOLA M. KYTE 《The Journal of eukaryotic microbiology》1978,25(4):502-509
SYNOPSIS. Shale oil retort water is obtained by centrifuging the oil/water emulsion produced by oil shale retorting. The ciliate Tetrahymena pyriformis was exposed to retort water; 2, 1, and 0.5% initially increased motility; longer exposures decreased motility. Three, 4, and 5% all decreased motility. Cell lysis was directly related to concentration; after 24 h, population densities were 0, 10, and 25% of controls for 2, 1, and 0.5% retort water, respectively. Oxygen consumption paralleled the motility pattern: at lower concentrations it increased initially but decreased with extended exposures while at higher concentrations it decreased rapidly. The most striking cytologic alteration of cells exposed to the toxicant occurred in the membranes; alterations of mucocysts and glycogen content were also observed, but mitochondrial changes were not. Population growth was affected at much lower concentrations than the other test indices. The growth of test populations reached a plateau at values inversely related to concentration: concentrations <0.4% had no effect on growth rate. 相似文献
85.
Using well-established techniques, samples were obtained of the volatile essential oils of the two types of curry leaf, Murraya koenigii and Pandanus latifolius. Both contained mainly terpenes, and M. koenigii produced less than 4% of other components with eight monoterpene hydrocarbons (ca 16%) and 17 sesquiterpene hydrocarbons (ca 80%) being obtained. The most important constituents of M. koenigii are β-caryophyllene, β-gurjunene, β-elemene, β-phellandrene and β-thujene. The volatile essential oil of P. latifolius also contained mainly sesquiterpene hydrocarbons (6–42%) but the only monoterpene was linalool (ca 6%). Nearly 2000 times the total quantity of aroma volatiles was produced by M. koenigii compared with P. latifolius, and this partly explains the observed stronger flavour potency of the former. 相似文献
86.
Isozymes of hexose-phosphate isomerase (HPI; EC 5.3.1.9), pyruvate kinase (PK; EC 2.7.1.40) and 6-phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) have been detected in the developing cotyledons of soybean (Glycine max (L.) Merr.), safflower (Carthamnus tinctorius L.) and sunflower (Helianthus annuus L.). In each seed there are two isozymes each of PK and HPI. The isozyme patterns of 6PGDH are more complex: soybean has two forms of the enzyme, safflower three, and sunflower six. In each tissue, at least 25% of the activity of each of the three enzymes is in the plastids. This supports the proposal that the glycolytic and pentose-phosphate pathways are operating in the plastids and that the plastids are the site of long-chain fatty-acid biosynthesis in developing oilseeds.Abbreviations HPI
hexose-phosphate isomerase
- 6PGDH
6-phosphogluconate dehydrogenase
- PK
pyruvate kinase 相似文献
87.
Ingrid Lombeck K. Kasperek L. E. Feinendegen H. J. Bremer 《Biological trace element research》1980,2(3):193-198
The rubidium content of whole blood was estimated by instrumental neutron activation analysis. In 46 healthy children it amounts
to {ie193-1} g/g dry weight. There was no difference between the values found for infants, toddlers, and school children.
In 29 dietetically treated patients with phenylketonuria and maple-syrup-urine disease the values were significantly lower
than in healthy children. During the first three months of diet therapy the rubidium levels remained in the lower range of
the normal values, decreasing to about 60% of the mean of normal values later on. With increasing length of diet therapy these
values tended to decrease. It remains questionable whether these decreased levels reflect only an induced biochemical phenomenon
without biological importance, or whether they are the first signs of a deficiency syndrome. 相似文献
88.
89.
Chemical carcinogens from several diverse chemical classes i.e.; aromatic amines, polycyclic hydrocarbons, nitrosamines, hormonal derivatives, metals and direct alkylating agents cause a 6.2–60.5-fold increase in the frequency of murine sarcoma virus (MSV)-induced transformation in a normal rat kidney (NRK) cell system. Exogenous metabolic activation with a rat liver S-9 homogenate is required for expression of this activity by procarcinogens. Non-carcinogenic analogs of these compounds fail to cause significant increases in the transformation frequency either with or without prior metabolic activation. Iododeoxyuridine, a mutagen also does not cause enhancement of transformation. This system may serve as the basis for a rapid and quantifiable means of identifying chemical carcinogens while introducing a new model for the understanding of the interactions between oncorna-viruses and chemical carcinogens. 相似文献
90.
木姜子叶精油的化学成分研究 总被引:2,自引:0,他引:2
采用气相色谱-质谱联用仪对产于秦岭太白山的木姜子叶的挥发油成分进行分析鉴定,从分离出的79个峰中鉴定了32种成分,其含量占挥发油总量的90.59%,主要成分为1,3,3-三甲基-乙-氧杂双环[2,2,2]辛烷(59.96%),1,8-桉油醇(8.96%),香茅醛(6.86%),2-甲基-5-(1-甲基乙烯基)环己酮(4.34%)和澄花醇乙酯(3.19%)。 相似文献