全文获取类型
收费全文 | 1893篇 |
免费 | 83篇 |
国内免费 | 136篇 |
出版年
2024年 | 8篇 |
2023年 | 13篇 |
2022年 | 19篇 |
2021年 | 26篇 |
2020年 | 23篇 |
2019年 | 49篇 |
2018年 | 47篇 |
2017年 | 33篇 |
2016年 | 32篇 |
2015年 | 50篇 |
2014年 | 122篇 |
2013年 | 157篇 |
2012年 | 83篇 |
2011年 | 164篇 |
2010年 | 72篇 |
2009年 | 126篇 |
2008年 | 115篇 |
2007年 | 95篇 |
2006年 | 109篇 |
2005年 | 81篇 |
2004年 | 74篇 |
2003年 | 72篇 |
2002年 | 71篇 |
2001年 | 48篇 |
2000年 | 31篇 |
1999年 | 24篇 |
1998年 | 33篇 |
1997年 | 37篇 |
1996年 | 21篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 27篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 23篇 |
1983年 | 12篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有2112条查询结果,搜索用时 125 毫秒
1.
2.
Yasumasa Kunifuji Terumasa Nakamura Masayuki Takasugi 《Biological trace element research》1987,14(3):237-248
Cd induced changes of Zn and Cd distribution in the liver and kidneys were studied in relation to Cd metallothionein (MT)
synthesis. Wistar male rats were given CdCl2 by sc injection of .8, 1.5, and 3.0 mg Cd/kg three times a week for three weeks. Cd levels of liver and kidneys increased
with the increment of Cd dosage and 80–90% of Cd was found in the cytosol. The MT fractions contained 80–89% cytosolic Cd
in the liver and 55–75% Cd in the kidneys. Zn concentrations in the liver increased following Cd administration, But Zn in
the kidneys showed only slight increase. There was a distinct decrease of Cu concentration in the liver of the 3.0 mg group.
In contrast, Cu concentrations in the kidneys increased about three times in the .8 and 1.5 mg Cd groups, but Cu in the 3.0
mg group showed only 1.5 times increase. The changes of these metal concentrations were observed mainly in the cytosol. Non-MT-Cd
in the kidneys was maximum in the 1.5 mg group, but the 3.0 mg group showed significant decrease. In parallel with this decrease
of Cd, Cu and Zn in the kidneys showed similar decrease. When the kidneys are injured, Zn and Cu appear to leak from this
organ. 相似文献
3.
The effect of varied supply of P (2.5× 10−5 to 6× 10−4 M) and Zn (0 to 10−6 M) on uptake and concentrations of P and Zn was studied in cotton ( Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solution under controlled environmental conditions. At a given Zn supply, increasing levels of P had no significant effect on the concentrations of total Zn in plants. However, increasing levels of P induced or enhanced visual Zn deficiency symptoms when the Zn concentration in the nutrient solution was low. The concentrations of water-soluble Zn in roots and shoots constituted 60% of the total Zn concentrations for plants grown with low P and 30% for plants grown with high P. The concentration of water-soluble Zn in leaves, but not total Zn, was closely correlated with visual Zn deficiency symptoms, levels of chlorophyll, super oxide dismutase and membrane permeability. The critical deficiency concentration of water-soluble Zn in cotton leaves was in the range of 6 to 7 μg (g dry weight)−1 or about 1.0 μg (g fresh weight)−1 . The results show that high P concentrations in plant tissue decrease the physiological availability of Zn. Water-soluble Zn in the tissue appears to be a suitable indicator for Zn nutritional status in general and phosphorus-induced Zn deficiency in particular. Also in field-grown orange trees (Citrus sinensis) visual Zn deficiency symptoms in leaves were closely related to the concentration of water-soluble Zn. 相似文献
4.
In the developing peanut (Arachis hypogaea L.) kernels, the period between 15 and 35 days after podding (DAP) was identified as the active period of oil-filling. The
period of active oil-filling was associated with a decrease in the starch, soluble sugars and proteins so as to make available
the energy and carbon skeleton for the synthesis of oil. The oil content in the mature kernels decreased by 11, 12 and 25
per cent with Zn, S and Zn+S deficiency, respectively. In addition, proteins and starch content decreased significantly while
that of soluble sugars increased slightly. The activity of malate dehydrogenase and glucose-6-phosphate dehydrogenase also
decreased due to Zn as well as S deficiency. The deficiency treatments resulted in a decrease in phospholipids, free fatty
acids and triacylglycerols in mature kernels. Further the proportion of 16∶0 and 18∶2 decreased while that of 18∶1 increased
in developing kernels. 相似文献
5.
Relationship between melanin content and superoxide dismutase (SOD) activity in the liver of various species of animals 总被引:4,自引:0,他引:4
The scavenger effect of melanin and of superoxide dismutase (SOD) activity on superoxide anion has been shown. In this work we show the relationship between melanin content and SOD activity in livers containing different quantities of melanin which were taken from various species of animals. The mitochondrial SOD activity disappears when the melanin content in the liver is very high; moreover it increases, in the liver of various species of animals examined, proportionally to the decrease of melanin content. No significant variation of the SOD activity localized in the soluble fraction has been detected when related to the melanin content. We think that in the pigmented liver the antioxidant activity of the melanin could mimic part of the function of SOD. The loss of Mn SOD activity could be mediated by a low intracellular level of superoxide anion due to the scavenger effect of melanin on superoxide anion; in fact, it is well known that the biosynthesis of Mn SOD is induced by intracellular levels of superoxide anion. 相似文献
6.
Zinc is essential for normal growth, development and brain function although little is known about brain zinc homeostasis. Therefore, in this investigation we have studied65Zn uptake from blood into brain and other tissues and have measured the blood-brain barrier permeability to65Zn in the anaesthetized rat in vivo. Adult male Wistar within the weight range 500–600 g were used.65ZnCl2 and [125I]albumin, the latter serving as a vascular marker, were injected in a bolus of normal saline I.V. Sequential arterial blood samples were taken during experiments that lasted between 5 min and 5 hr. At termination, samples from the liver, spleen, pancreas, lung, heart, muscle, kidney, bone, testis, ileum, blood cells, csf, and whole brain were taken and analysed for radio-isotope activity. Data have been analysed by Graphical Analysis which suggests65Zn uptake from blood by all tissues sampled was unidirectional during this experimental period except brain, where at circulation times<30 min,65Zn fluxes were bidirectional. In addition to the blood space, the brain appears to contain a rapidly exchanging compartment(s) for65Zn of about 4 ml/100g which is not csf. 相似文献
7.
BG-104 is a compound of Chinese herbs which were treated with infrared ray-heating and brewed with microorganisms resulting in activation of actual principles contained in the herbs, and its effectiveness has been reported on various inflammatory disorders such as Behcet's disease, rheumatoid arthritis, bacterial infections and so on. In addition, it is noted as an effective agent to retard cancer progress. This report shows a superoxide scavenging activity of BG-104 using an ESR spin trapping method. For the measurement of superoxide scavenging activity, recombinant human superoxide dismutase is used as a standard. Superoxide scavenging activity of BG-104 increases in a dose-dependent manner and activity is significantly augmented by its sonication. 相似文献
8.
Serum copper and zinc levels were determined in 20 healthy women and in 100 women with gynecological tumors. Malignant and
benign tumor cases were separated according to their postoperative, histopathological examinations. The stages of malignant
and benign tumors were also established histologically. Seventy benign and 30 malignant genital tumors (carcinoma of cervix
in situ, cervix, ovary endometrium, and vulva) of the patients were differentiated histopathologically.
The serum Cu/Zn ratios of patients were increased significantly from the control group (0.32±0.35) to the benign group (1.22±0.63)
and from the benign group to the malignant group (2.24±1.03). Nine of 30 malignant cases were determined as false negative
(30%) and 15 of 70 benign cases were determined as false positive (14.2%) according to the serum Cu/Zn ratios of patients.
Serum copper levels of 30 malignant and 10 benign tumor cases showed linear correlation with serum ceruloplasmin values. 相似文献
9.
Zinc is essential for normal development and function of the CNS although much is to be learned about brain Zn homeostasis. In these experiments adult male Wistar rats within the weight range 500–600 g were used. Ventriculo-cisternal perfusion was performed to allow the measurement of65Zn fluxes between blood and csf across the choroid plexuses. Blood-brain or blood-cerebrospinal fluid barrier permeability to65Zn has been determined by graphical analysis in experiments that lasted between 5 and 180 minutes. Cerebral capillary permeability to65Zn was found to be low with a Kin of about 5×10–4ml/min/g. Choroid plexus permeability to65Zn was about 12 fold greater, although Zn influx to brain via this route was <5% that across cerebral capillaries. The autoradiographic distribution of65Zn in brain showed regional variation with lowest levels in white matter and high levels in the dentate gyrus and hippocampus. 相似文献
10.
Yan Ming Ling Yihling Huang Shansheng Gong Shuqing Xu Zhenxing 《Biological trace element research》1991,29(3):281-288
Contents of Cu and Zn of into-pulmonary blood (IPB), out-pulmonary blood (OPB), Lung tissue, and supernatant and macrophages of Lung Lavage were determined in superior mesenteric artery occlusion (SMAO) shock of rabbits. Zn of pulmonary tissue was 11.42 +/- 0.60 and 14.52 +/- 1.78 (micrograms/g wet wt) in SMAO shock and control groups, respectively. Content of Zn was found to be lower, Cu was not changed, and Cu/Zn ratio increased in lung tissue in SMAO shock. Contents of Cu and Zn in other samples were not changed. The results suggest that lower Zn in lung tissue related to acute lung injury. 相似文献