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   368篇
  免费   21篇
  国内免费   1篇
  2023年   14篇
  2022年   9篇
  2021年   8篇
  2020年   9篇
  2019年   9篇
  2018年   12篇
  2017年   15篇
  2016年   13篇
  2015年   22篇
  2014年   17篇
  2013年   40篇
  2012年   34篇
  2011年   40篇
  2010年   22篇
  2009年   11篇
  2008年   14篇
  2007年   15篇
  2006年   11篇
  2005年   6篇
  2004年   12篇
  2003年   9篇
  2002年   8篇
  2001年   2篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1995年   5篇
  1994年   2篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1973年   1篇
  1972年   2篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
排序方式: 共有390条查询结果,搜索用时 15 毫秒
261.
The Anopheles dirus Peyton & Harrison complex of mosquitoes (Diptera: Culicidae) comprises seven known species, including important malaria vectors in Southeast Asia. Specific identification of each species of the complex, which cannot be distinguished using morphological characters, is crucial for understanding vector ecology and implementing effective control measures. Derived from individual random amplified polymorphic DNA (RAPD) markers, sequence characterized amplified regions (SCAR) were analysed for the design of specific paired-primers. Combination of six SCAR primers resulted in the development of a simple, robust, single multiplex PCR able to identify three important malaria vectors among the four most common species (A, B, C, D) of the complex: species A from several Southeast Asian countries, species B from Perlis, Malaysia, and species C and D from Thailand.  相似文献   
262.
Toxicity and bio-effects of CuO nanoparticles on transgenic Ipt-cotton   总被引:1,自引:0,他引:1  
This study investigated the effects of copper oxide nanoparticles (CuO NPs) on the growth and development of transgenic cotton harboring the Ipt gene, which encodes isopentenyl transferase (Ipt). Three concentrations of CuO NPs were evaluated: 10, 200, and 1000 mg·L-1, each with three replicates. The height and the root length were 26.91% and 42.80% decreased after 10-day exposure with 1000 mg·L-1 CuO NPs, respectively.In addition, less abundant on root hairs and lower in shoot biomass of Ipt-cotton when compared with the control group. The growth of Ipt-cotton was not affected by 10 mg·L-1 CuO NPs, but a high concentration of CuO NPs promoted the absorption of Fe and Na into roots, and inhibited the production of phytohormones in Ipt-cotton. The CuO NPs increased the concentration of iPA in shoots, which can delay senescence. The extent of the increase in iPA in response to CuO NPs should be relative to the amount of Ipt immobilized onto the NPs in the plant tissue. To our knowledge, this is the first study to evaluate the phytotoxicity of CuO NPs to Ipt-transgenic cotton. These results establish a baseline for further research on the effects of nanoparticles on transgenic crops harboring the Ipt gene.  相似文献   
263.
Plasma membranes of high purity and good yield have been prepared from human polymorphonuclear neutrophils by a one-step procedure involving disruption of cells suspended in paraffin oil and forced by pressure through an annular slit. This results in a band floating above the oil which is composed of large sheets of plasma membranes. Enrichment values for the plasma membrane marker alkaline phosphatase and 125I-labeled protein after surface labeling performed at the whole cell level were 23-fold and 22-fold, respectively. Contamination of the plasma membrane by other organelles was negligible and approximately 2 mg of membrane protein was obtained from 10(9) neutrophils. The procedure is very fast and the use of paraffin oil avoids lengthy high-speed centrifugation. The technique also allows isolation of granules devoid of plasma membrane and can probably be applied to other cell types.  相似文献   
264.
Serum albumin conjugates of histamine or tele-methylhistamine, a major catabolite, were prepared using 1,4-benzoquinone as the coupling agent and used to raise polyclonal antibodies in rabbits. The same reagent was used to prepare the [125I]iodinated tracer and treat tissue extracts submitted to the radioimmunoassays. The IC50 values of prederivatized histamine and tele-methylhistamine in the radioimmunoassays were 0.3 nM and 0.5 nM, respectively, whereas nonderivatized histamine or tele-methylhistamine, histidine, a variety of histamine derivatives, amines, etc., had at least 1,000-fold higher IC50 values. Application of the radioimmunoassays to nonpurified extracts of rat brain allowed the quantification of the two amine immunoreactivities in samples corresponding to less than 1 mg of hypothalamus. The tissue immunoreactivity corresponded to authentic histamine or tele-methylhistamine, as shown by (a) the parallel 125I-tracer displacement curves, (b) the similar elution patterns from HPLC columns, (c) the regional levels of histamine and tele-methylhistamine in brain, similar to those obtained with other methods, and (d) the clearcut effects of treatments with inhibitors of L-histidine decarboxylase or monoamine oxidase. The two radioimmunoassays appear as simple and sensitive tools to evaluate steady-state levels and turnover rates of histamine and tele-methylhistamine.  相似文献   
265.
Four undescribed phenolic glycosides including three stilbene derivatives ( 1 and 3 ) and sodium salt of 3 ( 2 ), and a chalcone glycoside ( 4 ), together with thirteen known compounds ( 5 – 17 ) were isolated from the leaves of Syzygium attopeuense (Gagnep.) Merr. & L.M.Perry. Their chemical structures were elucidated to be (Z)-gaylussacin ( 1 ), 6′′-O-galloylgaylussacin sodium salt ( 2 ), 6′′-O-galloylgaylussacin ( 3 ), 4′-O-[β-D-glucopyranosyl-(1→6)-glucopyranosyl]oxy-2′-hydroxy-6′-methoxydihydrochalcone ( 4 ), gaylussacin ( 5 ), pinosilvin 3-O-β-D-glucopyranoside ( 6 ), myricetin-3-O-(2′′-O-galloyl)-α-L-rhamnopyranoside ( 7 ), myricetin-3-O-(3′′-O-galloyl)-α-L-rhamnopyranoside ( 8 ), myricetin-3-O-α-L-rhamnopyranoside ( 9 ), quercitrin ( 10 ), myricetin-3-O-β-D-glucopyranoside ( 11 ), myricetin-3-O-β-D-galactopyranoside ( 12 ), quercetin 3-O-α-L-arabinopyranoside ( 13 ), myricetin-3-O-2′′-O-galloyl)-α-L-arabinopyranoside ( 14 ), (+)-gallocatechin ( 15 ), (−)-epigallocatechin ( 16 ), and 3,3’,4’-trimethoxyellagic acid 4-O-β-D-glucopyranoside ( 17 ) by the analysis of HR-ESI-MS, 1D and 2D NMR spectra in comparison with the previously reported data. Compounds 1–3 , 5 , and 6 significant inhibition of NO production in LPS-activated RAW264.7 cells, with IC50 values ranging from 18.37±1.38 to 35.12±2.53 μM, compared to a positive control (dexamethasone) with an IC50 value of 15.37±1.42 μM.  相似文献   
266.
Five new triterpenoid glycosides, named campetelosides A–E ( 1–5 ), together with three known compounds, chikusetsusaponin IVa ( 6 ), umbellatoside B ( 7 ), and silvioside E ( 8 ) were isolated from the leaves of Camellia petelotii (Merr.) Sealy. Their chemical structures were determined by interpretations of HR-ESI-MS and NMR spectra. In addition, compounds 1–8 were evaluated for their α-glucosidase inhibitory effects. Compounds 1–3 significantly showed α-glucosidase inhibitory activity with IC50 values of 166.7±6.0, 45.9±2.6, and 395.3±10.5 μM, respectively, compared to that of the positive control, acarbose, with an IC50 value of 200.4±10.5 μM.  相似文献   
267.
A new sesquiterpene ( 1 ) and a new norsesquiterpene ( 2 ) belonging guaiane-type skeleton together with six known compounds ( 3 – 8 ) were isolated from the rhizomes of Alisma plantago-aquatica. Their structures were determined by HR-ESI-MS, 1D and 2D NMR spectroscopic methods. Absolute configurations of new compounds were established by experimental and TD-DFT computational ECD spectra. Compounds 1 – 8 exhibited xanthine oxidase inhibitory activity with their IC50 values in range of 9.4–66.7 μM. The sesquiterpenoids 1 – 5 displayed the inhibitory activity and hence they could be potential xanthine oxidase inhibitors from A. plantago-aquatica.  相似文献   
268.
The aim of the study was to determine the prostacyclin (PGI2) and thromboxane A2 (TXA2) synthetase activities of myocardial tissue and their variation during ischemia and reperfusion. Regional ischemia was induced by 10 min occlusion of the left anterior descending coronary artery in isolated Langendorff rabbit hearts. Biosynthesis of PGI2 and TXA2 were carried out by using arachidonic acid as substrate and left ventricle microsomes (LVM) from ischemic and non-ischemic areas as sources of PGI2 and TXA2 synthetase. 6-keto-PGF and TXB2, stable metabolites of PGI2 and TXA2 respectively, were determined by radioimmunoassay. Experiments carried out under the adopted conditions showed that LVM were able to synthetise PGI2 as well as TXA2 from arachidonic acid. On the other hand, ischemia depressed both PGI2 and TXA2 synthetase activities of cardiac tissue: the depression was more pronounced on TXA2 synthetase than on PGI2 synthetase with no significant difference between ischemic and non-ischemic regions. Moreover, ischemia increased the ratio indicating therefore that it can facilitate the formation of PGI2. The post ischemic reperfusion of the heart counteracted the decrease in PGI2 synthetase induced by ischemia which returned to the normal level: reperfusion also slightly reversed the decrease in TXA2 synthetase. However, the diminution in TXA2 synthetase of non-ischemic myocardium was attenuated but it remained lower than the normal level. These results suggested that the whole left ventricle is affected by regional ischemia. Furthermore it appears that myocardial TXA2 synthetase is more vulnerable than PGI2 synthetase to a lack of oxygen and nutrients.  相似文献   
269.
This study aimed at testing the hypothesis that the binding sites for TXA2/PGH2 are present and different in the heart as compared to platelets and blood vessels. Kinetic studies on the thromboxane binding to protein of membrane preparations from rabbit and pig hearts were carried out using [125I]-PTA-OH, a potent specific thromboxane receptor antagonist. The following points are stressed: 1. the binding sites to 125I-PTA-OH were shown to be present in the heart membrane whatever the adopted experimental conditions were i.e. the temperature (4 or 30 degrees C) used for incubation the protein fractions under study: either the 105,000 g supernatant or the 200,000 g supernatant of the solubilized pellet (105,000 g) the animal species: rabbit and pig 2. the radioligand binding was rapid, saturable and reversible 3. the kinetically determined Kd's were in the picomolar range--11 and 14 pM for the rabbit and pig heart membrane preparation respectively--instead of the nanomolar range found in other tissues of the nanomolar range found in other tissues--27-39 nM and 2 nM for human platelets and bovine artery endothelial cells respectively- using the same thromboxane receptor antagonist.  相似文献   
270.
Huntington disease (HD) is one of the most common autosomal-dominant monogenetic diseases with an adult onset. Clinically, HD is characterized by a combination of motor deficits, cognitive decline, and psychiatric abnormalities. The disease typically progresses over 15–20 years and usually leads to death arising from complications such as pneumonia due to dysphagia, or suicide. Although the causative mutation was discovered more than 25 years ago, so far no effective neuroprotective or disease-modifying treatment has been found. In this article, we present an overview of the clinical presentation, genetics, neuropathological, and molecular changes in HD in addition to novel treatment options. Moreover, we give a brief insight into relevant animal models and ongoing studies, and also present the special considerations for genetic counseling in terms of predictive and prenatal diagnostics.  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