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   4596篇
  免费   393篇
  国内免费   1篇
  4990篇
  2023年   31篇
  2022年   97篇
  2021年   134篇
  2020年   99篇
  2019年   134篇
  2018年   156篇
  2017年   127篇
  2016年   190篇
  2015年   230篇
  2014年   233篇
  2013年   303篇
  2012年   378篇
  2011年   327篇
  2010年   199篇
  2009年   155篇
  2008年   193篇
  2007年   169篇
  2006年   141篇
  2005年   135篇
  2004年   128篇
  2003年   112篇
  2002年   118篇
  2001年   68篇
  2000年   57篇
  1999年   54篇
  1998年   41篇
  1997年   31篇
  1996年   29篇
  1995年   29篇
  1994年   28篇
  1993年   31篇
  1992年   50篇
  1991年   42篇
  1990年   38篇
  1989年   38篇
  1988年   31篇
  1987年   45篇
  1986年   27篇
  1985年   32篇
  1983年   27篇
  1982年   31篇
  1980年   20篇
  1979年   32篇
  1976年   21篇
  1975年   25篇
  1974年   22篇
  1973年   21篇
  1972年   22篇
  1971年   22篇
  1969年   19篇
排序方式: 共有4990条查询结果,搜索用时 15 毫秒
81.
The sub‐lethal effects of catch‐and‐release angling have been poorly studied because of the difficulties in monitoring physiological parameters in free‐swimming fish. Laboratory studies provide the opportunity to examine sub‐lethal effects in controlled environments, but do not incorporate site‐specific characteristics. In this study we angled free‐swimming largemouth bass (Micropterus salmoides) equipped with heart rate transmitters to exhaustion using rod and reel, and exposed fish to air for 30 s. Experiments were repeated at four water temperatures (13, 17, 21, and 25°C). These field data were compared with published findings from largemouth bass collected at the same water temperatures in a controlled laboratory setting using Doppler flow probes. Field collected heart rate data increased with increasing water temperatures (Q10 values 1.30–1.37). Pre‐disturbance heart rates were ~30% higher for free‐swimming fish in the field than previously collected laboratory data at the same water temperatures. Fish angled in the field exhausted ~40% more rapidly than fish chased in the laboratory. Maximal heart rate was ~15% higher for free‐swimming fish in the field than for data collected from laboratory restrained fish, but scope for heart rate was reduced by up to 20% in the field, especially at higher water temperatures. Heart rate in free‐swimming fish was highly variable at all times, obscuring clear recovery patterns. Conversely, laboratory cardiac parameters exhibited less variable patterns, peaking clearly following disturbances and recovering in about 135 min, independent of water temperature. Based upon these findings, we suggest that comprehensive studies incorporating both laboratory and field experiments are needed for truly understanding the effect of catch‐and‐release angling on fish.  相似文献   
82.
Among 569 schoolchildren (386 boys and 183 girls) aged 14-17 years, 233 had serum alkaline phosphatase values of 30 K.A. units or greater. There was no significant difference in the results in Asian, white, or West Indian children. The mean values were significantly greater in boys than girls and both showed a fall in mean values with increasing age. Radiological rickets occurred in at least 4% of the survey, and was more common in Asians. Low calcium and high hydroxyproline excretion in most of those investigated and the response to vitamin D therapy suggests that most children with alkaline phosphatase levels above 30 K.A. units have rickets.Since the decline of the widespread supplementation of the diet with vitamin D, the demands of the physiological growth spurt for extra vitamin D in adolescents already on a borderline intake may be responsible for the great increase in “biochemical” rickets. Once the growth spurt is over the condition subsides but the results of impaired growth or permanent pelvic deformity will not necessarily be eradicated.  相似文献   
83.
An antifungal protein from Helianthus annuus L. seeds (Ha-AP10) has been purified to homogeneity and characterized. Ha-AP10 purification was performed by gel filtration, cation exchange chromatography and reverse phase HPLC. Its molecular mass was estimated to be 10 kDa and western blot analyses suggest that it has an extracellular location. The N-terminal sequence of Ha-AP10 showed strong homology to some plant lipid-transfer proteins (LTPs). Antifungal tests have demonstrated that Ha-AP10 exerts a fungistatic effect. It completely inhibits the germination of spores of the fungal pathogen Fusarium solani f. sp. eumartii at a concentration of 40 μg ml−1 and produces a 50% growth inhibition at 6.5 μg ml−1 (0.65 μ M ). These data place Ha-AP10 among the most potent antifungal LTPs described so far.  相似文献   
84.
Candidiasis is the most common opportunistic yeast infection. Candida species and other microorganisms are involved in this complicated fungal infection, but Candida albicans continues to be the most prevalent. In the past two decades, it has been observed an abnormal overgrowth in the gastrointestinal, urinary and respiratory tracts, not only in immunocompromised patients, but also related to nosocomial infections and even in healthy individuals. There is a widely variety of causal factors that contribute to yeast infection which means that candidiasis is a good example of a multifactorial syndrome. Due to rapid increase in the incidence in these infections, this is the subject of numerous studies. Recently, the focus of attention is the treatment and, above all, the prevention of those complications. The diagnosis of candidiasis could become quite complicated. Prevention is the most effective “treatment,” much more than eradication of the yeast with antifungal agents. There are several aspects to consider in the daily routine that can provide a strength protection. However, a therapeutic approach is necessary when the infection is established, and therefore, other alternatives should be explored. This review provides an overview on predisposition factors, prevention and diagnosis of candidiasis, highlighting alternative approaches for candidiasis treatment.  相似文献   
85.
Chromate reduction by rabbit liver aldehyde oxidase   总被引:2,自引:0,他引:2  
Chromate was reduced during the oxidation of 1-methylnicotinamide chloride by partially purified rabbit liver aldehyde oxidase. In addition to 1-methylnicotinamide, several other electron donor substrates for aldehyde oxidase were able to support the enzymatic chromate reduction. The reduction required the presence of both enzyme and the electron donor substrate. The rate of the chromate reduction was retarded by inhibitors of aldehyde oxidase but was not affected by substrates or inhibitors of xanthine oxidase. These results are consistent with the involvement of aldehyde oxidase in the reduction of chromate by rabbit liver cytosolic enzyme preparations.  相似文献   
86.
We compare blood pressure and hypertension between adult men on the USA mainland and in Puerto Rico born during 1886-1930 to test hypotheses about the link between cardiovascular health and large socioeconomic and political changes in society: (a) 8853 men surveyed in Puerto Rico in 1965 and (b) 1449 non-Hispanic White men surveyed on the mainland during 1971-1975. Systolic and diastolic blood pressure and hypertension were regressed separately on demographic and socioeconomic variables and cardiovascular risk factors. Mainland men not taking anti-hypertensive medication showed statistically significant improvements in systolic blood pressure and hypertension at the beginning of the century and men in Puerto Rico showed improvements in diastolic blood pressure but only during the last two quinquenniums. An average man born on the mainland during the last birth quinquennium (1926-1930) had 7.4-8.7 mmHg lower systolic blood pressure and was 61% less likely to have systolic hypertension than one born before 1901. On average Puerto Rican men born during 1921-1925 had approximately 1.7 mmHg lower diastolic blood pressure than men born before 1901. Analyses of secular trends in cardiovascular health complements analyses of secular trends in anthropometric indicators and together provide a fuller view of the changing health status of a population.  相似文献   
87.
? Premise of the study: Microsatellite markers were developed for the population genetic analyses of the neotropical tree Dipteryx alata (Fabaceae). ? Methods and Results: Microsatellites were developed from a genomic shotgun library. Polymorphism at each microsatellite loci was analyzed based on 94 individuals from three populations. Eight loci amplified successfully and presented one to 10 alleles, and expected heterozygosities ranged from 0.097 to 0.862. Four loci also amplified in Pterodon emarginatus and presented similar polymorphism. ? Conclusion: The eight microsatellite primer pairs are potentially suitable for population genetic studies and successfully amplified in another Fabaceae species.  相似文献   
88.
89.
Leprosy is still a prevalent disease in Brazil, representing 93% of all occurrences in the Americas. Leprosy neuropathy is one of the most worrying manifestations of the disease. Acute neuropathy usually occurs during reaction episodes and is called neuritis. Twenty-two leprosy patients were included in this study. These patients had neural pain associated with ulnar sensory neuropathy, with or without adjunct motor involvement. The neurological picture began within thirty days of the clinical evaluation. The patients underwent a nerve conduction study and the demyelinating findings confirmed the diagnosis of neuritis. Ultrasonographic study (US) of the ulnar nerve was performed in all patients by a radiologist who was blinded to the clinical or neurophysiological results. Morphological characteristics of the ulnar nerve were analyzed, such as echogenicity, fascicular pattern, transverse cross-sectional area (CSA), aspect of the epineurium, as well as their anatomical relationships. The volume of selected muscles referring to the ulnar nerve, as well as their echogenicity, was also examined. Based on this analysis, patients with increased ulnar nerve CSA associated with loss of fascicular pattern, epineurium hyperechogenicity and presence of power Doppler flow were classified as neuritis. Therefore, patients initially classified by the clinical-electrophysiological criteria were reclassified by the imaging criteria pre-established in this study as with and without neuritis. Loss of fascicular pattern and flow detection on power Doppler showed to be significant morphological features in the detection of neuritis. In 38.5% of patients without clinical or neurophysiological findings of neuritis, US identified power Doppler flow and loss of fascicular pattern. The US is a method of high resolution and portability, and its low cost means that it could be used as an auxiliary tool in the diagnosis of neuritis and its treatment, especially in basic health units.  相似文献   
90.
An oxygen electrode respirometer for determining the oxygen consumption of slices of mammalian renal cortex is described and assessed. Though rat renal cortical slices incubated in potassium-free medium for one hour lost 102 +/- 14 mmol of potassium/kg dry weight, there was only a small, nonsignificant fall in oxygen consumption. In contrast the oxygen consumption of slices incubated in potassium-free medium with 10 mmol.1-1 ouabain was markedly reduced (by 32 +/- 6%), while such slices lost 180 +/- 15 mmol of potassium/kg dry weight. These disproportionate effects on potassium loss and inhibition of oxygen consumption suggest that in renal cortical slices the loss of potassium in low potassium medium is not primarily due to inhibition of the conventional sodium pump.  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