全文获取类型
收费全文 | 330篇 |
免费 | 25篇 |
出版年
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 12篇 |
2014年 | 15篇 |
2013年 | 23篇 |
2012年 | 23篇 |
2011年 | 25篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 13篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 16篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 3篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1961年 | 3篇 |
1960年 | 2篇 |
1959年 | 5篇 |
1937年 | 1篇 |
排序方式: 共有355条查询结果,搜索用时 15 毫秒
1.
A sulphated heteropolysaccharide (~15% of the acid-extractable material) isolated from the brown alga Dictyota dichotoma contains residues of D-glucuronic acid, D-galactose, D-mannose, D-xylose, and L-fucose1. Partial hydrolysis of the polysaccharide with acid gave one neutral and two acidic oligosaccharides. The behaviour towards periodate of the polysaccharide before and after partial hydrolysis, alkali-treatment, and methanolysis has been studied. Evidence is thereby provided that the polysaccharide is partially sulphated and composed of (1→4)-linked residues of D-glucuronic acid, D-galactose, D-mannose, and D-xylose, and (1→2)-linked L-fucose. 相似文献
2.
Y A Badr M A Kereim M A Yehia O O Fouad A Bahieldin 《Photochemical & photobiological sciences》2005,4(10):803-807
A modified, non-damaging, protocol for the production of fertile transgenic wheat (Triticum aestivum L. cultivar Giza 164) plants by laser micropuncture was developed. The new homemade setup secures the transformation of as many as 60 immature embryo-derived calli (10000 cells each) in less than one hour using a UV excimer laser with two dimensional translation stages, a suitable computer program and a proper optical system. Five-day-old calli were irradiated by a focused laser microbeam to puncture momentarily made self-healing holes ( approximately 0.5 microm) in the cell wall and membrane to allow uptake of the exogenous DNA. The plant expression vector pAB6 containing bar gene as a selectable marker for the herbicide bialaphos resistance and GUS (uidA) gene as a reporter gene was used for transformation. No selection pressure was conducted during the four-week callus induction period. Induced calli were transferred to a modified MS medium with 1 mg l(-1) bialaphos for regeneration, followed by selection on 2 mg l(-1) bialaphos for rooting. Three regenerated putative transgenic events were evaluated for the integration and stable expression of both genes and results indicated that this modified procedure of laser-mediated transformation can be successfully used in transforming wheat. 相似文献
3.
An active role for the heart in the initiation of hypertension can be postulated in two different sets of conditions. 1) Activation of pressor reflexes from the ventricles, coronary arteries, or aorta has been shown to produce substantial rises of arterial pressure; experience with postcoronary bypass hypertension suggests that these reflexes could be responsible for some types of paroxysmal hypertension. 2) Increased cardiac action caused by either neural or humoral factors can initiate a rise in cardiac output and blood pressure; sustained hypertension could be produced experimentally in conscious dogs by electrical stimulation of the stellate ganglion or by continuous infusion of dobutamine in the left coronary artery. Evidence suggesting that this could occur in humans was derived from a study of the relationship of cardiac output to cardiopulmonary volume in essential hypertension. 相似文献
4.
Harry Jan Swartz Robert Bors Fouad Mohamed S. Kristine Naess 《Plant Cell, Tissue and Organ Culture》1990,21(2):179-184
Shoot regeneration from Rubus leaves was obtained on a medium containing MS salts, vitamins and sugars, Staba vitamins, casein hydrolysate (100 mg l–1) and 10 M thidiazuron. Shoot regeneration from Malus leaves was obtained on N6 rice anther medium with 5 M thidiazuron. In vitro pretreatment of source shoots with either colchicine or thidiazuron enhanced the organogenic potential of detached leaves of two Rubus hybrids. The response to colchicine was quadratic and occurred at non-mutagenic concentrations (75–250 M). The response to thidiazuron was exponential between 0 and 5 M. When applied as a pretreatment, the effectiveness of several different cytokinins (benzyladenine, thidiazuron, zeatin) at enhancing Malus and Rubus organogenesis was related to the shoot proliferation activity of the cytokinin and to treatment-induced variation in leaf and petiole size.Abbreviations BA
benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IBA
indolebutyric acid
- MS
Murashige & Skoog basal medium devoid of plant growth regulators
- OI
organogenesis-initiating subculture
- PTI
colchicine pretreatment subculture
- PTII
cytokinin pretreatment subculture
- NAA
naphthaleneacetic acid
- TDZ
thidiazuron
- zeatin
trans-zeatin 相似文献
5.
Summary The uptake of Fe by roots and apical leaves of the submersed aquatic plant Hydrilla verticillata Royle was studied using 59FeEDTA. 59FeEDTA was absorbed by both roots and apical leaves, and translocated to the other parts of the plant. Approximately 3% of the total 59FeEDTA absorbed by the roots over a period of 60 h was translocated to the leaves. Downward translocation of 59FeEDTA from the apical portion of the plant to the lower leaves was approximately 21% of the amount absorbed.Published as Journal Series No 333 of the Florida Agricultural Experiment Station. 相似文献
6.
The fucose-containing polysaccharides of the brown alga Dictyota dichotoma were extracted with either trichloroacetic acid or HCl to give both water-soluble and water-insoluble materials. The latter had a high proportion (16 to 11%) of protein, and although all the sugars found in the water-soluble extracts were present, the major sugar in these water-insoluble polysaccharides was glucose. The water-soluble material extracted with HCl was a protein-free sulphated heteropolysaccharide. Complete removal of a glucan from the water-soluble extract was achieved by fractional precipitation with ethanol. The recovered glucan-free sulphated polysaccharide, which was rich in glucuronic acid, galactose, fucose and sulphate, showed high anticoagulating activity. 相似文献
7.
L E Maroun 《The Biochemical journal》1979,179(1):221-225
Antiviral and cell-growth-inhibitory activities of human interferon were shown to be related to the activity of a gene or genes present on chromosome 21. The 18s rRNA is vital to cell growth; it is capable of a viral-mRNA-recognition function and it is coded for by genes a portion of which are present on chromosome-21. A previously reported ability of human interferon to affect rRNA metabolism is characterized by a decrease in the sucrose-gradient-peak ratio of radiolabelled 28S to 18S rRNA in extracts from the cytoplasm of interferon-treated human fibroblasts. In the present report, interferon dose-response curves are presented demonstrating a direct relationship between a decrease in this ratio and interferon concentrations in the media. By using this virus-independent cytoplasmic rRNA assay, eight human fibroblast lines, differing in chromosome 21 ploidy, were tested for sensitivity to human interferon. Two monosomy-21, two euploid-21 and four trisomy-21 cell lines were tested. The monosomy-21 cell populations were significantly less sensitive to interferon than the other six cell types tested. Of the cell lines tested, the most sensitive, by a wide margin, was a trisomy-21 line. Trisomy-21 cell monolayer sensitivity, however, varied widely within the range from normal to supersensitive. These observations suggest that interferon's ability to affect rRNA metabolism is related to the activity of a gene or genes present on chromosome 21. 相似文献
8.
9.
10.
Hiba Omer Suhaib Alameen Waleed E. Mahmoud Abdelmoneim Sulieman Omaima Nasir Fouad Abolaban 《Saudi Journal of Biological Sciences》2021,28(1):342-346
This study aims to estimate the effective radiation dose and organ dose from head CT procedures. It was conducted in three main private hospitals in Khartoum State-Sudan, using Toshiba machines with 64 slices. The total number of patients included in this study was 142 patients (82 males and 60 females). The effective dose and organ dose were calculated by CT Expo software. The effective dose slightly varied among patients according to gender and age. The effective dose for female patients (5.99 mSv) was higher than that for male patients (5.84 mSv), and the pediatric dose (5.46 mSv) was lower than the adults’ dose (5.94 mSv).The dose for eye lens was found lower for male patients (89.117 mSv) than the dose for female patients (94.62) mSv). According to patients’ age: the dose received by the lens of the eye was much lower in pediatric (79.93 mSv) than the adults (92.41 mSv). The dose for thyroid in female patients (33.52 mSv) was higher than the male patients (28 mSv). The pediatric dose (28.34 mSv) was lower than the adults’ dose (30.64 mSv).Departmental imaging protocol and lack of training among hospital staff are expected to be responsible for these variations. Therefore, this study recommends that the CT technologists be trained on suitable strategies to achieve dose optimization. Moreover, patients’ doses must be monitored regularly. 相似文献