首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   328篇
  免费   13篇
  2023年   3篇
  2022年   9篇
  2021年   18篇
  2020年   18篇
  2019年   28篇
  2018年   30篇
  2017年   17篇
  2016年   12篇
  2015年   12篇
  2014年   16篇
  2013年   18篇
  2012年   22篇
  2011年   22篇
  2010年   7篇
  2009年   7篇
  2008年   17篇
  2007年   13篇
  2006年   5篇
  2005年   7篇
  2004年   5篇
  2003年   3篇
  2002年   3篇
  2001年   12篇
  2000年   5篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1991年   1篇
  1990年   1篇
  1989年   4篇
  1987年   3篇
  1986年   5篇
  1985年   2篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1972年   2篇
  1971年   1篇
  1968年   1篇
  1960年   1篇
  1948年   1篇
排序方式: 共有341条查询结果,搜索用时 93 毫秒
1.
The effect of reserpine and meprobamate on the total acetylcholine content and acetylcholinesterase activity in the brain tissue of the kusu rat, Arvicanthis niloticus, was studied. The total acetylcholine content and acetylcholinesterase activity were determined 1 hr after i.p. injection of different doses of reserpine (0.25, 0.5 and 1 mg/ml/100 g body wt) and meprobamate (6.25, 12.5 and 25 mg/ml/100 g body wt). The effect of different time intervals (1, 10, 30 min, 1, 2.5, 5, 8, 12, 24 and 48 hr) on the total acetylcholine content and acetylcholinesterase activity was investigated after i.p. injection of 0.5 mg of reserpine and 12.5 mg of meprobamate/ml/100 g body wt. Both reserpine and meprobamate caused an increase in the total ACh content in the brain tissue of Arvicanthis niloticus which was suggested to be due to a decrease in the release of ACh, since both reserpine and meprobamate inhibited AChE activity after some tested periods. The effect of meprobamate was observed to be stronger than that of reserpine.  相似文献   
2.
A new method for demonstrating argyrophil cells of the pancreas and intestinal tract using a combined silver and reducing solution in sections of formaldehyde fixed tissue is described. Impregnating sections in a 60 C water bath, the procedure takes about 25 min. A microwave version that takes about 5 min is also given. Results are similar to those obtained with the Grimelius method for argyrophil cells.  相似文献   
3.
Clarkia gracilis (2n = 28) is an allotetraploid which combines genomes from two subsections of section Primigenia. Natural populations consist of plants homozygous for a single chromosome arrangement, which may differ from the arrangements in other populations by one or more reciprocal translocations. One arrangement, the “standard,” was widespread. Cytological observations on plants derived from crosses between populations of C. gracilis, and on triploid plants derived from crosses with C. amoena subsp. huntiana, one of the parents of the tetraploid, were used to determine the end arrangements present. Ten arrangements were identified, and it was found that the standard amoena subgenome of C. gracilis is identical in end arrangement to the previously defined standard arrangement of the diploid C. amoena. Hence a race of C. amoena with this arrangement was involved in the hybridization which gave rise to C. gracilis. Evidence was found that other arrangements of C. amoena have probably been introduced into C. gracilis by subsequent introgressive hybridization. Cytological differences, coupled with differences in morphology, ecology, and distribution indicate that C. gracilis should be subdivided into four subspecies instead of the three presently recognized.  相似文献   
4.
Oligonucleotide (2-aminoethyl)phosphonates in which the backbone consisted of isomerically pure, alternating (2-aminoethyl)-phosphonate and phosphodiester linkages have been prepared and characterized. One of these single isomer oligonucleotides (Rp) formed a more stable duplex with DNA or RNA than its corresponding natural counterpart. Hybrid stability was more pH-dependent, but less salt-dependent than a natural duplex. The specificity of hybridization was examined by hybridization of an oligonucleotide containing one (2-aminoethyl)phosphonate to oligonucleotides possessing mismatches in the region opposite to the aminoethyl group. In contrast to oligonucleotides containing (aminomethyl)-phosphonate linkages, oligonucleotide (2-aminoethyl)phosphonates were completely stable to hydrolysis in aqueous solution. These oligonucleotides were resistant to nuclease activity but did not induce RNase H mediated cleavage of a complementary RNA strand. Incubation in a serum-containing medium resulted in minimal degradation over 24 hours. Studies of cell uptake by flow cytometry and confocal microscopy demonstrated temperature dependent uptake and intracellular localization. (2-Aminoethyl)phosphonates represent a novel approach to the introduction of positive charges into the backbone of oligonucleotides.  相似文献   
5.
Abstract

Context: The kidney plays a central role in detoxification and excretion of toxic metabolites, and therefore, is susceptible to toxicity by xenobiotics.

Objective: To investigate the protective effect of Rosmarinus officinalis (rosemary) powder and its essential (volatile) oil against diethylnitrosamine (DEN)-induced renal injury in rats.

Materials and methods: Phenolic and flavonoid components were characterised in rosemary powder using HPLC-UV instrument while rosemary essential oil (E.O) was investigated via GC-MS technique. In rat model, rosemary was administrated orally (in diet) for two months. Lipid profile, antioxidant biomarkers, kidney functions and histopathological examinations were assessed.

Results: Hesperidin (4878.88?ppm) and ellagic acid (403.57?ppm) are among the major phenolic and flavonoid constituents in rosemary powder. Camphor (18.36%) and α-pinene (12.74%) represent the main E.O active ingredients. Rats treated with rosemary E.O showed a significant elevation in serum HDL (28.28%) accompanied by a decrease in LDL (115.47%). A significant decrease in serum creatinine and urea was also reported (69.72 and 109.89%, respectively). Moreover, serum glutathione peroxidise (GSH-Px) activity has been significantly increased. Kidney histopathological examinations confirmed the protective effect against DEN-induced abnormalities.

Conclusion: Rosemary (powder/E.O) was able to reduce or even prevent the severity of diethylnitrosamine-induced renal dysfunction.  相似文献   
6.
7.
Molecular Biology Reports - A cluster of many risk factors for type 2 diabetes and cardiovascular disease is used to describe the metabolic syndrome (MetS). Moreover, genetic differences associated...  相似文献   
8.
Abstract

A wide range of 2′,5′-dideoxy-nucleosides, including 6- substituted purine, pyrazolo[3,4-d]pyrimidine and 1-deazapurine derivatives, has been enzymatically prepared using purine nucleoside phosphorylase. Specificity towards cleavage by bacterial versus mammalian purine nucleoside phosphorylase was evaluated.  相似文献   
9.
Precise estimation of arthropods' sex ratio is an important issue in a wide range of ecological studies and biological control programs. Although, in many cases changes in arthropods' sex ratio may be under the control of parents or some symbiotic microorganisms, biased sex ratios in some other species are caused by some extrinsic factors, neglect of which may lead to under/overestimation of true sex ratio. In this paper, we pursued those factors that cause false estimation of sex ratio in insects' species. We studied the predatory gall midge, Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), an important biological control agent of aphids, that shows protandry (i.e. early male emergence), differential lifespan of sexes, and differential distribution of sexes across habitat. Ten populations of A. aphidimyza were released separately in transparent cages and their sex ratio variations were recorded every 12 hours. The primary sex ratio in this species seems to be slightly male‐biased (52.41% males), however early emergence of males biases the sex ratio up to 72% males in a few hours after emergence. Shortly after the emergence of females, the sex ratio reaches its primary situation, but as a result of male‐biased mortality after mating, the proportion of females increases gradually to 97% by the fourth and fifth days after emergence. These results explicitly suggest that direct estimation of sex ratio in natural populations may be affected by some secondary factors such as differential mortality of sexes, protandry, and differential distribution of males and females over time and/or across habitat.  相似文献   
10.

Matrix metallopeptidase 2 (MMP-2) and matrix metallopeptidase 9 (MMP-9) are involved in the breakdown of extracellular matrix in normal physiological processes as well as in disease processes, such as cancer metastasis. We conducted this work to study the role of MMP-2 and MMP-9 in breast cancer by measuring their plasma concentrations before and after surgery. Also, to examine if their levels can reflect the stage of disease and prognosis. Forty-eight breast cancer patients and 13 patients with benign breast diseases were included in the study. MMP-2 and MMP-9 levels were measured by ELISA and semi-quantitative real-time PCR. MMP-2 and MMP-9 levels in plasma were determined by ELISA immediately before surgery and during 6 to 12 months after curative surgery. We observed a significant increase in the level of MMP-9 mRNA expression in breast cancer patients in comparison to their normal breast tissues and to tissues of benign breast disease. In all TNM tumor stages, the plasma levels of MMP-2 and MMP-9 were increased significantly before curative surgery in the studied patients with breast carcinoma and decreased significantly after surgery. Both MMP-2 and MMP-9 may be used as a possible marker for follow-up or as a marker that reflects the response of the disease to treatment.

  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号