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   452篇
  免费   22篇
  2022年   4篇
  2021年   6篇
  2020年   9篇
  2019年   5篇
  2018年   20篇
  2017年   11篇
  2016年   17篇
  2015年   11篇
  2014年   17篇
  2013年   29篇
  2012年   28篇
  2011年   40篇
  2010年   27篇
  2009年   14篇
  2008年   18篇
  2007年   21篇
  2006年   18篇
  2005年   9篇
  2004年   13篇
  2003年   14篇
  2002年   9篇
  2001年   16篇
  2000年   17篇
  1999年   20篇
  1998年   8篇
  1995年   2篇
  1991年   4篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1987年   6篇
  1986年   4篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   3篇
  1971年   1篇
  1970年   5篇
  1969年   5篇
  1968年   2篇
  1967年   3篇
  1966年   3篇
  1965年   5篇
  1964年   3篇
  1963年   3篇
排序方式: 共有474条查询结果,搜索用时 15 毫秒
61.
868 male urethritis patients were studied for the presence of chlamydiae in the 1981-1986 period. 36% of NGU, 31.3% of gonococcal urethritis and 58.8% of PGU urethritis patients presented C. trachomatis infections as detected by cell culture inoculation. Chlamydial infection was recorded more often in the 21-30 years age group (30.8%), in unmarried patients (70.6%), as well as in people with low educational degree (46.6% of cases), 42.3% of the C. trachomatis cases were already confronted with one or more urethritis episodes. 24.7% of patients have been subjected to a previous antichlamydial treatment.  相似文献   
62.
63.
64.

Background

The detection of regional wall motion abnormalities is the cornerstone of stress echocardiography. Today, stress echo shows increasing trends of utilization due to growing concerns for radiation risk, higher cost and stronger environmental impact of competing techniques. However, it has also limitations: underused ability to identify factors of clinical vulnerability outside coronary artery stenosis; operator-dependence; low positivity rate in contemporary populations; intermediate risk associated with a negative test; limited value of wall motion beyond coronary artery disease. Nevertheless, stress echo has potential to adapt to a changing environment and overcome its current limitations.

Integrated-quadruple stress-echo

Four parameters now converge conceptually, logistically, and methodologically in the Integrated Quadruple (IQ)-stress echo. They are: 1- regional wall motion abnormalities; 2-B-lines measured by lung ultrasound; 3-left ventricular contractile reserve assessed as the stress/rest ratio of force (systolic arterial pressure by cuff sphygmomanometer/end-systolic volume from 2D); 4- coronary flow velocity reserve on left anterior descending coronary artery (with color-Doppler guided pulsed wave Doppler). IQ-Stress echo allows a synoptic functional assessment of epicardial coronary artery stenosis (wall motion), lung water (B-lines), myocardial function (left ventricular contractile reserve) and coronary small vessels (coronary flow velocity reserve in mid or distal left anterior descending artery). In “ABCD” protocol, A stands for Asynergy (ischemic vs non-ischemic heart); B for B-lines (wet vs dry lung); C for Contractile reserve (weak vs strong heart); D for Doppler flowmetry (warm vs cold heart, since the hyperemic blood flow increases the local temperature of the myocardium). From the technical (acquisition/analysis) viewpoint and required training, B-lines are the kindergarten, left ventricular contractile reserve the primary (for acquisition) and secondary (for analysis) school, wall motion the university, and coronary flow velocity reserve the PhD program of stress echo.

Conclusion

Stress echo is changing. As an old landline telephone with only one function, yesterday stress echo used one sign (regional wall motion abnormalities) for one patient with coronary artery disease. As a versatile smart-phone with multiple applications, stress echo today uses many signs for different pathophysiological and clinical targets. Large scale effectiveness studies are now in progress in the Stress Echo2020 project with the omnivorous “ABCD” protocol.
  相似文献   
65.

Reconfigurable one-, two-, and three-bit plasmonic logic gate configurations have been proposed, which work by covering a straight slot waveguide with materials with tunable dielectric constants, such as graphene. By encoding the logic states in the values of dielectric constants as opposed to different waveguides, the plasmon excitation problems are minimized and the simplified logic gate configurations could be easily implemented.

  相似文献   
66.
67.
Two new feather mite species of the family Pteronyssidae Oudemans, 1941 collected from birds captured in Ivory Coast are described: Pteronyssoides cyanomitrae n. sp. from Cyanomitra obscura (Jardine) (Passeriformes: Nectariniidae) and Conomerus pygmaeus n. sp. from Hylia prasina (Cassin) (Passeriformes: Macrosphenidae). Pteronyssoides cyanomitrae n. sp. belongs to the nectariniae species group and differs from the closest species, P. garioui Gaud & Mouchet, 1959, in having, in males, the adanal shield present and setae f longer than setae d on the tarsus III; females of this species have the hysteronotal shield with two small median incisions on the anterior margin barely extending beyond the level of setae e2. Conomerus pygmaeus n. sp. is the first species of this genus found on a passerine host, and seems to be more similar to C. sclerosternus Gaud, 1990. This new species has the following distinctive characters: in females, the opisthosoma has small lobe-like extensions and the central sclerite is fused posteriorly with the lateral opisthosomal sclerites; in males, coxal fields I–IV lack large sclerotised areas.  相似文献   
68.
Zusammenfassung In getrennten Versuchen wurde die Wirkung von ADP, Ca++, Mg++, K+ und Cu++ auf die Rotationsströmung in den Wurzelhaaren der Gerste (Hordetim vulgare L.) untersucht. Das in verschiedenen Konzentrationen fortdauernd verabreichte ADP bedingte eine Stimulation der Plasmaströmung. Die Beschleunigung der Rotationsströmung war der ADP-Konzentration gegenüber umgekehrt proportional (Abb. 3).Von den untersuchten Kationen hatte nur Ca++ (1·10–3 Mol) eine Stimulationswirkung. Diese Stimulationswirkung wird der Aktivierung eines Enzyms bzw. eines kontraktilen Proteins mit ATPase-Eigenschaften zugeschrieben.Die Rolle von ADP und einigen Kationen bei der Stimulation der Rotation wurde dann mit Hilfe einer gemischten Behandlung untersucht. Diese bestand in der gleichzeitigen Verabreichung von ADP (1·10–6 Mol) und CaCl2, MgCl2, KCl (1 · 10–3 Mol) oder CuCl2 (1·10–6 Mol). Es wurde festgestellt, daß Mg++ und Ca++ eine antagonistische Wirkung ausüben. Ca++ hebt die durch ADP induzierte Stimulation auf und reduziert die Rotationsgeschwindigkeit plötzlich bis auf den Kontrollwert. Die Mg++-Wirkung bewirkt, nach einer zeitweiligen Beibehaltung der Stimulation, ebenfalls eine Abnahme der Geschwindigkeit. K+ hat eine ähnliche Wirkung wie Ca++. Cu++ beeinträchtigt die ADP-induzierte Stimulation in geringem Maße.Die gleichzeitige Einwirkung von ADP und einigen Kationen erlaubt die Aufstellung folgender Hypothese. Die Rotationsstimulation erfolgt dank dem ATP, das auf Kosten des von außen absorbierten ADP in den Mitochondrien synthetisiert wird. Die zusätzliche ATP-Synthese kann durch gleichzeitige Ca++-Behandlung unterbunden werden. NachHanson und Mitarb, sollen Ca++ und ADP um ein phosphoryliertes Zwischenprodukt in Kompetition treten, so daß es zu einer Ansammlung von Ca++ und Pa in der Zelle kommt. Andererseits könnte teilweise auch die aktive, energieverbrauchende Salzabsorption die Geschwindigkeitsabnahme der Rotation bei gemischter Behandlung erklären.
The effect of ADP and some cations on rotational streaming in barley (Hordeum vulgare L.) root hairs
Summary The effect of ADP, Ca++, Mg++, K+, and Cu++ upon rotational streaming within barley (Hordeum vulgäre L.) root hairs was separately studied. It was shown that various solutions of ADP may stimulate the streaming after continuous treatment. The rate increase of the rotational streaming was inverse proportional to ADP concentration (Fig. 3).From the investigated cations only Ca++ (1·10–3M) caused a stimulation of streaming after continuous treatment. This effect is probably due to enzymic activation of a contractile proteine which has ATPase feature.The role of ADP and of the investigated cations in the stimulation of the rotational streaming was studied by means of mixed treatment. This kind of treatment consists in a simultaneous administration of ADP (1 · 10–6M) and CaCl2, MgCl2, KCl (1 · 10–3M), or CuCl2 (1 · 10–6M) solutions. Ca++ and Mg++ showed an antagonistic action. Ca++ brings about an immediately suppress of ADP induced stimulation. Suddenly the rate of streaming comes back to control. Mg++ after a temporary maintaining of stimulation, also causes the lowering of the streaming. The action of K+ was very similar to those of Ca++. Cu++ changes to a little extent the stimulation caused by ADP.The simultaneous action of ADP and of the investigated cations allow us to express the following hypothesis. The stimulation of the rotational streaming after ADP treatment probably is due to ATP synthetized in mitochondria on the account of ADP. The additional synthesis of ATP can be prevented by simultaneous administration of Ca++. According toHanson and his coworkers Ca++ would compete with ADP for a phosphorylated intermediate product. From a such competition would result the Ca++ and Pi accumulation. The active uptake of salts which require energy would also explain the lowering of the rotational streaming rate after the mixed treatment.
  相似文献   
69.
Forest diversity-productivity relationships have been intensively investigated in recent decades. However, few studies have considered the interplay between species and structural diversity in driving productivity. We analyzed these factors using data from 52 permanent plots in southwestern Germany with more than 53,000 repeated tree measurements. We used basal area increment as a proxy for productivity and hypothesized that: (1) structural diversity would increase tree and stand productivity, (2) diversity-productivity relationships would be weaker for species diversity than for structural diversity, and (3) species diversity would also indirectly impact stand productivity via changes in size structure. We measured diversity using distance-independent indices. We fitted separate linear mixed-effects models for fir, spruce and beech at the tree level, whereas at the stand level we pooled all available data. We tested our third hypothesis using structural equation modeling. Structural and species diversity acted as direct and independent drivers of stand productivity, with structural diversity being a slightly better predictor. Structural diversity, but not species diversity, had a significant, albeit asymmetric, effect on tree productivity. The functioning of structurally diverse, mixed forests is influenced by both structural and species diversity. These sources of trait diversity contribute to increased vertical stratification and crown plasticity, which in turn diminish competitive interferences and lead to more densely packed canopies per unit area. Our research highlights the positive effects of species diversity and structural diversity on forest productivity and ecosystem dynamics.  相似文献   
70.
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