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   1534篇
  免费   190篇
  国内免费   20篇
  2023年   23篇
  2022年   29篇
  2021年   56篇
  2020年   50篇
  2019年   51篇
  2018年   42篇
  2017年   49篇
  2016年   43篇
  2015年   57篇
  2014年   105篇
  2013年   93篇
  2012年   55篇
  2011年   64篇
  2010年   47篇
  2009年   46篇
  2008年   51篇
  2007年   77篇
  2006年   54篇
  2005年   42篇
  2004年   60篇
  2003年   42篇
  2002年   51篇
  2001年   28篇
  2000年   35篇
  1999年   23篇
  1998年   21篇
  1997年   31篇
  1996年   28篇
  1995年   34篇
  1994年   14篇
  1993年   32篇
  1992年   25篇
  1991年   24篇
  1990年   27篇
  1989年   23篇
  1988年   22篇
  1987年   17篇
  1986年   29篇
  1985年   15篇
  1984年   23篇
  1983年   15篇
  1982年   15篇
  1981年   11篇
  1979年   8篇
  1978年   10篇
  1977年   7篇
  1976年   6篇
  1975年   10篇
  1974年   8篇
  1973年   6篇
排序方式: 共有1744条查询结果,搜索用时 15 毫秒
51.
Three patients with the hepatorenal syndrome were treated with prostaglandin E1 administered through a selective renal arterial catheter. Prostaglandin E1 was given in progressively increasing doses (2 to 100 ng/kg/min) over a 60-minute period. Control plasma prostaglandin E levels were elevated in all three patients, 0.98, 0.91, and 0.83 ng/ml, respectively. At the end of the infusion, plasma prostaglandin E levels had risen to 10.4, 2.63, and 10.3 ng/ml in the three patients respectively. Plasma renin activity increased during the course of the infusion in two of the patients. The plasma aldosterone concentration did not change during the prostaglandin E1 infusion. Intrarenal prostaglandin E1 failed to increase urine volume or urinary sodium concentration in three patients with the hepatorenal syndrome.  相似文献   
52.
The effects of increases in serum osmolality on renal function and plasma levels of radioimmunoassayable prolactin (PRL) and luteinizing hormone (LH) were examined during intracarotid (IC) infusions of hypertonic NaCl in conscious dogs with a sustained water diuresis (SWD). A 10 minute bilateral IC infusion of 45 μmole/kg·min·artery of NaCl during SWD which raised jugular osmolality by 10.1 mOsm/kg, without significantly altering peripheral venous osmolality, produced a significant decrease in free water clearance (CH2O) at 20 to 40 minutes postinfusion. IC infusions of 0.9% NaCl did not produce an antidiuretic response. No change in heart rate or blood pressure from preinfusion control values occurred during NaCl infusions. Elevations in cerebral osmolality did not result in changes in circulating levels of LH or PRL which qualitatively differed from levels of these hormones recorded during IC infusions of 0.9% NaCl. Although fluctuations in levels of LH occurred during experiments, renal function was not concomitantly affected. The results suggest that a specificity exists in the hormonal response to selective elevations of cerebral osmolality. The administration of TRH 3.8–4.2 μg/kg produced a transient increase in blood pressure and inhibited a water diuresis, the latter possibly as a result of releasing antidiuretic hormone.  相似文献   
53.
本文应用空斑减少中和试验(PRNT)和细胞病变中和试验(cPENT)两种方法对出血热沙鼠肾细胞灭活疫苗扩大人体免疫后的血清进行中和抗体水平检测。根据两种方法对总计74人份的免疫后血清检测比较结果,两种方法检测的抗体阳转率和抗体水平(GMT)。CPENT法均高于PRNT法,经统计学处理均有显著性差异。不同免疫组的中和抗体水平比较结果,注射三针的阳转率(n=10,100%)高于两针组(n=10,20—30%);接种加氢氧化铝佐剂疫苗(n=13)较接种不加佐剂的两种疫苗(n=26)的抗体水平高,阳转率为92%—100%GMT为22—69;皮下途径(n=15)和肌肉途径(n=13)注射无明显差别,阳转率分别为87—93%和92—100%,GMT分别为29—46和22—61。以上结果进一步肯定沙鼠肾细胞疫苗的人体免疫性  相似文献   
54.
The influence of canopy development in soybean on the survival of corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), egg and larval stages and population dynamics of arthropod fauna were evaluated in field trials during 1986–88 in eastern North Carolina. Soybean canopy size decreased as soybean cyst nematode, Heterodera glycines Ichinohe (Nematoda: Heteroderidae), initial population densities increased. Plant species composition of the soybean canopy was affected by weed population densities. Mortality of H. zea larvae due to parasitism and infection with entomopathogens was greater in closed canopy and (or) weedy soybeans than in very open and (or) weed free soybeans. Predation and parasitism of corn earworm eggs were similar across nematode and weed density treatments. Natural enemy populations increased to highest levels during July in closed canopy and (or) weedy soybeans, coinciding with availability of largest prey population reservoirs. A delay in colonization of very open and (or) weed free soybeans by beneficial arthropods until mid to late August allowed greater H. zea larval survival than in closed canopy and (or) weedy soybeans. Arthropod species richness was generally greatest in closed canopy and (or) weedy soybeans during mid to late July, with differences becoming nonsignificant in August and early September. Mean and maximum ambient temperatures were higher and relative humidities lower in open canopy than in closed canopy plots. These conditions were less favorable for development of pathogens and natural enemies.  相似文献   
55.
Yamada  Mayumi  Kubota  Shin 《Hydrobiologia》1991,(1):159-164
Fukaurahydra anthoformis and Hataia parva are solitary athecate hydroids occurring in northern Japan. New information on the external morphology, nematocysts, ecology, and life cycles of these species is presented. It is noteworthy that H. parva bears stenoteles, which are generally not found among the families of Filifera. Neither species produces free medusae. The eggs are fertilized in the female gonophores, from which unciliated larvae are released. These larvae do not swim and soon attach to a substrate. After attachment the larvae become covered by a sheath to form cysts. The cysts rest on a substrate without any outer change for several months. As the water temperature drops in autumn to early winter the cysts begin to hatch, forming tiny polyps after the larva creeps out from the chitinous sheath. Cyst formation proves to be common also in other solitary hydroids, most of which are inhabitants of cool or cold waters.  相似文献   
56.
Heterodera glycines was identified in North Carolina in 1954, although symptoms of the disease were noted in the state at least 8 years earlier. Crop rotation experiments designed to develop management systems were initiated in 1956. Two or more years in production of a nonhost crop resulted in decreases of the nematode to low or undetectable levels with acceptable subsequent yields of soybean (Glycine max). Because of almost complete dependence on resistant cultivars and (or) nematicides for nematode control, crop rotation experiments were not conducted from 1962 to 1980. Research on control of H. glycines, beginning in 1981, emphasized biological and ecological aspects of the nematode in order to determine cropping systems that restrict the nematode to nondamaging levels. Mortality during embryogenesis was high at temperatures above 30 C. Hatching of eggs occurs readily in May and June. Postinfection development takes 2-3 weeks at weekly mean temperatures of 22-29 C and is slow above and below those temperatures. Egg production is high during the late growing season. Some cultural practices such as planting early maturing cultivars in mid-to-late June and rotation with a nonhost effectively keeps populations at low levels.  相似文献   
57.
Ten strains of fungi were tested for tolerance to the fungicide benomyl. Verticillium chlamydosporium strain 2 did not grow in the presence of benomyl; Drechraeria coniospora strains 1 and 2 and Chaetomium sp. tolerated only 0.1 μg benomyl/ml medium; Acremonium bacillisporum, an unidentified fungus, and Phoma chrysanthemicola uniformly grew at 1 μg/ml, but some hyphae grew at higher benomyl concentrations; Fusarium sp. tolerated 475 μg/ml, but some hyphae grew on medium amended with 1,000 μg/ml; Verticillium lecanii and V. chlamydosporium strain 1 routinely tolerated 1,000 μg/ml. Fungi generally grew more slowly at higher than at lower benomyl concentrations. Strains with elevated tolerance to benomyl were selected from Acremonium bacillisporum, Drechmeria coniospora, Fusarium sp., and an unidentified fungus. These strains retained the increased tolerance after repeated transfers on unamended medium.  相似文献   
58.
一株广谱中和抗原性出血热病毒株的发现   总被引:5,自引:0,他引:5  
一株分离自杭州市褐家鼠的出血热病毒Gou_3株的免疫血清对10株I型病毒的中和滴度除二株为160外均为320,而对4株Ⅱ型病毒的滴度为320—640,说明Gou_3株免疫血清对两型毒株中和效价大多数无差异或只差2倍,是一株中和抗原广谱的毒株。用I型和Ⅱ型毒株免疫血清对Gou_3株进行型别检定结果表明Gou_3株是Ⅱ型病毒。  相似文献   
59.
Mercuric ion, a well-known nephrotoxin, promotes oxidative tissue damage to kidney cells. One principal toxic action of Hg(II) is the disruption of mitochondrial functions, although the exact significance of this effect with regard to Hg(II) toxicity is poorly understood. In studies of the effects of Hg(II) on superoxide (O) and hydrogen peroxide (H2O2) production by rat kidney mitochondria, Hg(II) (1–6 μM), in the presence of antimycin A, caused a concentration-dependent increase (up to fivefold) in mitochondrial H2O2 production but an apparent decrease in mitochondrial O production. Hg(II) also inhibited O-dependent cytochrome c reduction (IC50 ≈?2–3 μM) when O was produced from xanthine oxidase. In contrast, Hg(I) did not react with O in either system, suggesting little involvement of Hg(I) in the apparent dismutation of O by Hg(II). Hg(II) also inhibited the reactions of KO2 (i.e., O) with hemin or horseradish peroxidase dissolved in dimethyl sulfoxide (DMSO). Finally, a combination of Hg(II) and KO2 in DMSO resulted in a stable UV absorbance spectrum [currently assigned Hg(II)-peroxide] distinct from either Hg(II) or KO2. These results suggest that Hg(II), despite possessing little redox activity, enhances the rate of O dismutation, leading to increased production of H2O2 by renal mitochondria. This property of Hg(II) may contribute to the oxidative tissue-damaging properties of mercury compounds.  相似文献   
60.
Cyst hatching, under standardized conditions, of the Anostracan species Thamnocephalus platyurus and Streptocephalus dichotomus was significantly accelerated but not increased by applying the morphogen retinoic acid (RA). Cyst hatching was enhanced but not accelerated by artificially increasing the inflow of Ca2+ to the embryonic cells, using Calcium Ionophore A 23 187. Cyst hatching was accelerated and amplified, to a level in excess of the summed effects of each treatment, by a combined application of RA and ionophore. It was inhibited almost quantitatively by the Calcium-channel blockers Nifedipin and Verapamil. The significance of these findings is discussed.  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