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   2379篇
  免费   143篇
  国内免费   2篇
  2023年   14篇
  2022年   30篇
  2021年   57篇
  2020年   33篇
  2019年   33篇
  2018年   55篇
  2017年   41篇
  2016年   66篇
  2015年   87篇
  2014年   105篇
  2013年   184篇
  2012年   183篇
  2011年   151篇
  2010年   121篇
  2009年   96篇
  2008年   133篇
  2007年   123篇
  2006年   107篇
  2005年   95篇
  2004年   77篇
  2003年   63篇
  2002年   66篇
  2001年   48篇
  2000年   35篇
  1999年   30篇
  1998年   14篇
  1997年   16篇
  1996年   18篇
  1995年   14篇
  1993年   13篇
  1992年   21篇
  1991年   24篇
  1990年   20篇
  1989年   34篇
  1988年   22篇
  1987年   22篇
  1986年   16篇
  1985年   30篇
  1984年   23篇
  1982年   12篇
  1981年   13篇
  1979年   15篇
  1978年   10篇
  1977年   13篇
  1976年   14篇
  1974年   14篇
  1973年   9篇
  1972年   10篇
  1971年   9篇
  1966年   11篇
排序方式: 共有2524条查询结果,搜索用时 8 毫秒
61.
[3H]-cocaine, [3H]-norcocaine, [3H]-benzoylecgonine and [3H]-benzoylnorecgonine were administered i.c. in equi-potent pharmacologic doses and the intracellular disposition and metabolism of each drug determined. Norcocaine and cocaine rapidly entered and egressed from the brain so that 4.8–6.1% of the radioactivity present in brain at one minute was observed at 30 minutes. The highest levels of subcellular radioactivity were generally found in the microsomal plus supernatant, followed by the nuclear and shocked mitochondrial fractions. No apparent localization of the radioactivity occured in synaptic membranes. The brain/plasma (B/P) ratio curves for cocaine and norcocaine were similar; however, the norcocaine values were considerably higher at each time interval. Benzoylecgonine and benzoylnorecgonine had higher comparative B/P ratios than cocaine or norcocaine and persisted in brain for a longer period of time so that 0.6–2.1% of the radioactivity present in brain at 1 hour was detected at 24 hours. Cocaine and norcocaine were extensively metabolized to the benzoylmetabolites. Benzoylecgonine was metabolized to benzoylnorecgonine and benzoylnorecgonine was unmetabolized. The brain disposition data and B/P ratios agreed quite well with the overall pharmacologic action of cocaine and its metabolites.  相似文献   
62.
63.
Food preference as well as feeding efficiency studies of the carabid predator revealed that the grub of theChlaenius bioculatus Chaud preferred mostPolytella gloriosae F. larvae in both 2nd and 3rd instar.Tarache tropica Guénée was preferred least by the grub predator in both instar.T. tropica was found toxic and grubs of the predator died after consumption.
Résumé Les préférences alimentaires, de même que l'efficacité prédatrice deChlaenius bioculatus Chaud, montrent que ce carabide prédateur préfère le plus les larves dePolytella gloriosae F. du 2e et 3e stade.Tarache tropica Guénée est le moins attaqué aux deux stades.T. tropica est toxique et les larves du prédateur meurent après sa consommation.
  相似文献   
64.
Nitroprusside appears to inhibit the known types of superoxide dismutases irrespective of their metal prosthetic group and regardless of the source from which the enzymes were isolated. Thus the copper-zinc enzyme from bovine erythrocyte or Neurospora crassa behaved identically as did the manganese enzymes from Escherichia coli or red alga and the iron enzyme from E. coli and a blue-green alga. The inhibition was dose dependent with a Ki = 2.5 X 10(-5) for nitroprusside. Nitroprusside does not bind to the copper moiety of copper-zinc enzyme and seems to compete with O2- for superoxide dismutase. These inhibitions by nitroprusside, which were elicited not only in purified enzymes but also in crude soluble extracts of biological samples, were rapidly reversible. Nitroprusside was found to react with O2- to form a paramagnetic species with three absorption lines of equal width with a separation AN = 15.0 G and a g value of 2.028. The spin adduct appears to be a nitroxide radical and was stable for several minutes.  相似文献   
65.
Summary Maximum penetrometer pressure was measured on artificial soil aggregates of finite size (2–29 mm) using blunt probes (total cone angle 60°) driven at 3 mm min−1. Maximum penetrometer pressure increased asymptotically with increase in dimensionless aggregate radius,b/a, wherea andb are the probe and aggregate radii, respectively. A theory was developed for penetration of blunt probes into soil aggregates of finite size. The theory assumed that plastic failure occurs out to a radius,R, and that beyond this only elastic straining occurs. This theory can be applied to estimate the radial and tangential stresses adjacent to a blunt probe. The estimated radial and tangential stresses increased with increase in dimensionless aggregate radius,b/a. The radius of the plastic front,R, around the probe is predicted to increase with increased aggregate size. The results also demonstrate the effect of soil shear cohesion and internal friction angle onR. The results are discussed with reference to root penetration.  相似文献   
66.
67.
68.
69.
A variety of 1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one azomethines and 1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one benzamide were prepared, characterized and evaluated for the anticonvulsant activity in the rat using picrotoxin‐induced seizure model. The prepared 1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one azomethine derivatives emerged potentially anticonvulsant molecular scaffolds exemplified by compounds, 7‐{(E)‐[(4‐nitrophenyl)methylidene]amino}‐5‐phenyl‐1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one, 7‐[(E)‐{[4‐(dimethylamino)phenyl]methylidene}amino]‐5‐phenyl‐1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one, 7‐{(E)‐[(4‐bromo‐2,6‐difluorophenyl)methylidene]amino}‐5‐phenyl‐1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one and 7‐[(E)‐{[3‐(4‐fluorophenyl)‐1‐phenyl‐1H‐pyrazol‐4‐yl]methylidene}amino]‐5‐phenyl‐1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one. All these four compounds have shown substantial decrease in the wet dog shake numbers and grade of convulsions with respect to the standard drug diazepam. The most active compound, 7‐[(E)‐{[4‐(dimethylamino)phenyl]methylidene}amino]‐5‐phenyl‐1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one, exhibited 74 % protection against convulsion which was higher than the standard drug diazepam. Furthermore, to identify the binding mode of the interaction amongst the target analogs and binding site of the benzodiazepine receptor, molecular docking study and molecular dynamic simulation were carried out. Additionally, in silico pharmacokinetic and toxicity predictions of target compounds were carried out using AdmetSAR tool. Results of ADMET studies suggest that the pharmacokinetic parameters of all the target compounds were within the acceptable range to become a potential drug candidate as antiepileptic agents.  相似文献   
70.
Abstract

The study recommends the Artemisia nilagirica (Clarke) Pamp. essential oil (ANEO) as plant-based shelf-life enhancer of millets against fungal, aflatoxin B1 (AFB1) contamination and lipid peroxidation with favourable safety profile. Chemical characterisation of ANEO through GC-MS, recorded 1,5-heptadiene-4-one,3,3,6-trimethyl (32.72%)as the main compound, followed by Artemisia alcohol (13.40%), alpha lonone (4.55%), benzene, methyl (1-methylethyl) (2.97%) and 1-cyclohexene-1-carboxaldehyde,4-(1-methylethyenyl) (2.23%). The mycoflora analysis of millet samples showed Aspergillus flavus strain[LHP(R)-5] as the most AFB1 secreting strain. The ANEO inhibited growth and AFB1 production by the toxigenic strain at 1.4 and 1.0?µL?mL?1, respectively, and also possess broad fungitoxic spectrum. The decrement in membrane ergosterol content, enhanced leakage of cellular Ca2+, K+ and Mg2+ ions along with SEM and TEM study of ANEO-treated cell denotes plasma membrane as antifungal site of action. The ANEO also showed strong antioxidant activity as determined by DPPH? and ABTS?+ assays having IC50 value 2.51 and 1.07?µL?mL?1, respectively. More than 70.78% protection of Ragi samples from fungal contamination was observed during in situ trial. The ANEO showed favourable safety profile with high LD50 value (7528.10?µL?kg?1) for male mice and also exhibited non-phytotoxicity for Ragi seeds germination.  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