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   730篇
  免费   16篇
  国内免费   3篇
  749篇
  2024年   2篇
  2023年   7篇
  2022年   11篇
  2021年   27篇
  2020年   11篇
  2019年   7篇
  2018年   17篇
  2017年   12篇
  2016年   31篇
  2015年   45篇
  2014年   38篇
  2013年   64篇
  2012年   56篇
  2011年   79篇
  2010年   46篇
  2009年   41篇
  2008年   48篇
  2007年   44篇
  2006年   36篇
  2005年   45篇
  2004年   21篇
  2003年   16篇
  2002年   18篇
  2000年   3篇
  1999年   5篇
  1998年   3篇
  1997年   2篇
  1996年   2篇
  1995年   3篇
  1992年   3篇
  1989年   1篇
  1988年   1篇
  1981年   1篇
  1974年   1篇
  1971年   1篇
  1949年   1篇
排序方式: 共有749条查询结果,搜索用时 0 毫秒
1.
Cancer morbidity and mortality are on a steady increase in Croatia. Technologic possibilities for appropriate management are available for four cancer sites, i.e. cancer of the breast, cervix uteri, colorectum and prostate, and include cancer prevention and early detection in individuals yet free from manifest signs of the disease. The magnitude of the problem, the experience acquired to date, health care personnel available, and additional resources required to launch a systematic program of early detection of the disease are presented. The program should be initially launched in a county with greatest experience in early detection of cancer, where health care service is ready to immediately start its implementation. The role of family physician, gynecologic service at primary health care level, and polyclinic-consultation hospital service in program implementation is described. The following three possible options for early detection of cancer are analyzed and proposed: minimal program (early detection every 3 years), medium program (the same individuals examined every 2 years), and optimal program proposed by the American Cancer Society and other national and international organizations.  相似文献   
2.
The Hedgehog (Hh-) signaling pathway is a key developmental pathway which gets reactivated in many human tumors, and smoothened (Smo) antagonists are emerging as novel agents for the treatment of malignancies dependent on the Hh-pathway, with the most advanced compounds demonstrating encouraging results in initial clinical trials. A novel series of potent bicyclic hydantoin Smo antagonists was reported in the preceding article, these have been resolved, and optimized to identify potent homochiral derivatives with clean off-target profiles and good pharmacokinetic properties in preclinical species. While showing in vivo efficacy in mouse allograft models, unsubstituted bicyclic tetrahydroimidazo[1,5-a]pyrazine-1,3(2H,5H)-diones were shown to epimerize in plasma. Alkylation of the C-8 position blocks this epimerization, resulting in the identification of MK-5710 (47) which was selected for further development.  相似文献   
3.
Parasites causing malaria need to migrate in order to penetrate tissue barriers and enter host cells. Here we show that the actin filament-binding protein coronin regulates gliding motility in Plasmodium berghei sporozoites, the highly motile forms of a rodent malaria-causing parasite transmitted by mosquitoes. Parasites lacking coronin show motility defects that impair colonization of the mosquito salivary glands but not migration in the skin, yet result in decreased transmission efficiency. In non-motile sporozoites low calcium concentrations mediate actin-independent coronin localization to the periphery. Engagement of extracellular ligands triggers an intracellular calcium release followed by the actin-dependent relocalization of coronin to the rear and initiation of motility. Mutational analysis and imaging suggest that coronin organizes actin filaments for productive motility. Using coronin-mCherry as a marker for the presence of actin filaments we found that protein kinase A contributes to actin filament disassembly. We finally speculate that calcium and cAMP-mediated signaling regulate a switch from rapid parasite motility to host cell invasion by differentially influencing actin dynamics.  相似文献   
4.
The antidepressant selective serotonin transporter inhibitors (SSRIs) are clinically active after a delay of several weeks. Indeed, the rapid increase of serotonin (5-HT) caused by SSRIs, stimulates the 5-HT(1A) autoreceptors, which exert a negative feedback on the 5-HT neurotransmission. Only when autoreceptors are desensitized, can SSRIs exert their therapeutic activity. The 5-HT(1A) receptor antagonist pindolol has been used to accelerate the clinical effects of antidepressant by preventing the negative feedback. Using the alpha-[(11)C]methyl-L-tryptophan/positron emission tomography (PET), the goal of the present double-blind, randomized study was to compare the changes in alpha-[(11)C]methyl-L-tryptophan trapping, an index of serotonin synthesis, in patients suffering from unipolar depression treated with the SSRI citalopram (20 mg/day) plus placebo versus patients treated with citalopram plus pindol (7.5 mg/day). PET and Hamilton depression rating scale (HDRS-17) were performed at baseline, and after 10 and 24 days of antidepressant treatment. Results show that the combination citalopram plus pindol, compared to citalopram alone shows a more rapid and greater increase of an index of 5-HT synthesis in prefrontal cortex (BA 9). This research is the first human PET study demonstrating that, after 24 days, the combination SSRIs plus pindolol produces a greater increase of the metabolism of serotonin in the prefrontal cortex, an area associated to depressive symptoms.  相似文献   
5.
An active Trypanosoma cruzi transmission cycle maintained by wild rodents in the Andean valleys of Cochabamba Bolivia is described. Wild and domestic Triatoma infestans with 60% infection with T. cruzi were found and was evidenced in 47.5% (rodents) and 26.7% (marsupial) by parasitological and/or serologycal methods. Phyllotis ocilae and the marsupial species Thylamys elegans, are the most important reservoirs followed by Bolomys lactens and Akodon boliviensis. In spite of both genotypes (TCI and TCII) being prevalent in Bolivia, in our study area only T. cruzi I is being transmitted. Our data suggest that wild T. infestans and wild small mammals play an important role in the maintenance of the transmission cycle of T. cruzi. Furthermore, the finding of high prevalence of T. cruzi infection in wild T. infestans point to the risk of the dispersion of Chagas' disease.  相似文献   
6.
Genetic variants of IL-18 and IL-12B may be important in immunoregulatory abnormalities, observed in the patients with Type 1 diabetes mellitus (T1DM), that contribute to individual differences in response to a treatment. Therefore, we examined the significance of IL-18-137G/C, IL-18-607C/A, and IL-12B A/C polymorphisms in Croatians (187 patients, 236 controls), not only as factors that contribute to susceptibility to T1DM, but also as determinants of the clinical presentation of disease.  相似文献   
7.
Dermacentor reticulatus ticks are recognized as the most important vectors of Babesia canis, the aetiological agent of canine babesiosis occurring throughout Europe. Vector competence of D. reticulatus for B. canis is well described and experimentally determined; however, by using molecular analysis it was proven so by one recent study in Russia. Herein, the additional molecular evidence of B. canis infection in D. reticulatus ticks collected in Slovakia is provided. Using PCR followed by sequencing of distinctive amplicons we determined the presence of Babesia canis canis in one of 100 tested adult ticks. Two zoonotic pathogens, Francisella tularensis and Coxiella burnetii, were previously isolated from D. reticulatus ticks in Slovakia. In our samples, we detected only the presence of F. tularensis.  相似文献   
8.
Bacteria, mitochondria and chloroplasts harbour factors that facilitate the insertion, folding and assembly of membrane proteins. In Escherichia coli, yidC is required for membrane insertion, acting in both a Sec-dependent and a Sec-independent manner. There is an expanding volume of biochemical work on its role in this process, but none so far on its structure. We present the first of this class of membrane proteins determined by electron cryomicroscopy in the near-nativelike state of the membrane. yidC forms dimers in the membrane and each monomer has an area of low density that may be part of the path transmembrane segments follow during their insertion. Upon consideration of the structures of yidC and SecYEG, we speculate on the nature of the interfaces that facilitate the alternative pathways (Sec-dependent and -independent) of membrane protein insertion.  相似文献   
9.
The purpose of this study was to examine the relationship between tooth root colour and age, and its possible application in age assessment. In this research altogether 100 tooth roots have been analysed. All teeth, that is their roots, were digitally recorded and the colorimetric treatment was made using Adobe Photoshop 7.0 computer program. Studies have shown no significant difference between RGB values analysed on the whole root surface or only on its central part, with certainty p >0.99. It is also established that there is no statistically significant difference in colouration on four anatomical surfaces (buccal, mesial, lingual, distal) of tooth roots with certaintyp>0.99 for red, p>0.99 for green and p>0.50 for blue colouration component. Statistical data interpretation showed that there is a linear correlation between obtained RGB values and age, with r=-0.994, p>0.99 for red component, r=-0.972, p>0.99 for green and r=-0.982, p>0.95 for blue colouration component. From the obtained results it is possible to conclude that analysing the above mentioned parameter we can easily establish dental age and this technique can be the basis of practical application in establishing chronological age of man.  相似文献   
10.

Background

Successful object manipulation relies on the ability to form and retrieve sensorimotor memories of digit forces and positions used in previous object lifts. Past studies of patients affected by Parkinson''s disease (PD) have revealed that the basal ganglia play a crucial role in the acquisition and/or retrieval of sensorimotor memories for grasp control. Whereas it is known that PD impairs anticipatory control of digit forces during grasp, learning deficits associated with the planning of digit placement have yet to be explored. This question is motivated by recent work in healthy subjects revealing that anticipatory control of digit placement plays a crucial role for successful manipulation.

Methodology/Principal Findings

We asked ten PD patients off medication and ten age-matched controls to reach, grasp and lift an object whose center of mass (CM) was on the left, right or center. The only task requirement was to minimize object roll during lift. The CM remained the same across consecutive trials (blocked condition) or was altered from trial to trial (random condition). We hypothesized that impairment of the basal ganglia-thalamo-cortical circuits in PD patients would reduce their ability to anticipate digit placement appropriate to the CM location. Consequently, we predicted that PD patients would exhibit similar digit placement in the blocked vs. random conditions and produce larger peak object rolls than that of control subjects. In the blocked condition, PD patients exhibited significantly weaker modulation of fingertip contact points to CM location and larger object roll than controls (p<0.05 and p<0.01, respectively). Nevertheless, both controls and PD patients minimized object roll more in the blocked than in the random condition (p<0.01).

Conclusions/Significance

Our findings indicate that, even though PD patients may have a residual ability of anticipatory control of digit contact points and forces, they fail to implement a motor plan with the same degree of effectiveness as controls. We conclude that intact basal ganglia-thalamo-cortical circuits are necessary for successful sensorimotor learning of both grasp kinematics and kinetics required for dexterous hand-object interactions.  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