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   4867篇
  免费   181篇
  国内免费   1篇
  2023年   15篇
  2022年   14篇
  2021年   34篇
  2020年   19篇
  2019年   31篇
  2018年   83篇
  2017年   79篇
  2016年   98篇
  2015年   73篇
  2014年   109篇
  2013年   194篇
  2012年   421篇
  2011年   629篇
  2010年   275篇
  2009年   73篇
  2008年   416篇
  2007年   389篇
  2006年   332篇
  2005年   303篇
  2004年   232篇
  2003年   232篇
  2002年   171篇
  2001年   68篇
  2000年   148篇
  1999年   76篇
  1998年   47篇
  1997年   13篇
  1996年   13篇
  1995年   16篇
  1994年   9篇
  1993年   10篇
  1992年   20篇
  1991年   15篇
  1990年   11篇
  1989年   14篇
  1988年   9篇
  1987年   18篇
  1985年   20篇
  1984年   22篇
  1982年   16篇
  1981年   9篇
  1980年   17篇
  1979年   14篇
  1978年   13篇
  1977年   11篇
  1976年   17篇
  1975年   12篇
  1974年   19篇
  1973年   10篇
  1971年   10篇
排序方式: 共有5049条查询结果,搜索用时 15 毫秒
931.
A case of a mandibular fracture with an unusual complication is reported. A 13-year-old boy was admitted four years after conservative treatment of a symphyseal fracture. He complained of recurrent swelling. A radiographic evaluation showed a horizontally laid permanent mandibular left lateral incisor (PMLLI) that had probably slid into the fracture line and provoked repetitive infection episodes. After a surgery, a clinical and radiological analysis showed satisfactory healing.  相似文献   
932.
This paper presents the first reading data in Croatian collected with an eye-tracking device. The eye-tracking method allows for research into two crucial levels underlying reading: the visual and the cognitive. The aim of this paper is to show the differences in eye movements in children with dyslexia using the principles of cognitive-control view. Despite the well-known definitions and vast literature on dyslexia, the neural basis of dyslexia varies greatly on the individual level. The three children studied in this paper were tested behaviorally using set of language tests for language behavior assessment on all language levels: phonology, morphology, syntax, lexicon and pragmatics. Two children had low scores on most language tests, and all three children had poor reading and writing level. Each of the children had to read two texts silently while their eye movements were recorded by means of an infrared eye-tracking system. We analyzed the number, position, and duration of fixations and the number and position of regressive (or back) saccades. Our results show intergroup differences (between a typically developing child and the three children with dyslexia), and intragroup differences (among all three children with dyslexia). The great number of fixations, longer duration of fixations, and great number of regression saccades are the main features that differentiate the children with dyslexia form the typically developing child. The only difference found between language and visual subtypes of dyslexia was a shorter duration of fixations for the child with a visual processing disorder.  相似文献   
933.
Gangliosides are major cell-surface determinants in the central nervous system (CNS) of vertebrates, found both in neuronal and glial cell membranes. Together with cholesterol and glycosylphosphatidylinositol (GPI) - anchored proteins, gangliosides are involved in organization of plasma membrane microdomains. Based on biochemical studies, frog brain was previously described as having low quantities of gangliosides and their distribution pattern in specific brain regions was unknown. Using highly specific monoclonal antibodies generated against four major brain gangliosides (GM1, GD1a, GD1b and GT1b), we examined the distribution of these molecules in CNS of four different species of frogs (Rana esculenta, Rana temporaria, Bufo bufo and Bufo viridis). We also studied the distribution of myelin- associated glycoprotein (MAG), an inhibitor of axonal regeneration, which is a ligand for gangliosides GD1a and GT1b. Our results show that ganglioside GDla is expressed in neurons of olfactory bulb in all studied animals. In the brain of Rana sp., GD1a is expressed in the entire olfactory pathway, from olfactory bulbs to amygdala, while in Bufo sp. GD1a is restricted to the main olfactory bulb. Furthermore, we found that most of myelinated pathways in frogs express MAG, but do not express GD1a, which could be one of the reasons for better axon regeneration of neural pathways after CNS injury in amphibians in comparison to mammals.  相似文献   
934.
935.
The International Affective Picture System (IAPS) is a set of standardized emotionally evocative color photographs developed by NIMH Center for Emotion and Attention at the University of Florida. It contains more than 900 emotional pictures indexed by emotional valence, arousal and dominance. However, when IAPS pictures were used in studying emotions with the event-related potentials, the results have shown a great deal of variation and inconsistency. In this research arousal and dominance of pictures were controlled while emotional valence was manipulated as 3 categories, pleasant, neutral and unpleasant pictures. Two experiments were conducted with an eye-tracker in order to determine to what the participants turn their gaze. Participants were 25 psychology students with normal vision. Every participant saw all pictures in color and same pictures in black/white version. This makes 200 analyzed units for color pictures and 200 for black and white pictures. Every picture was divided into figure and ground. Considering that perception can be influenced by color, edges, luminosity and contrast and since all those factors are collapsed on the pictures in IAPS, we compared color pictures with same black and white pictures. In first eye-tracking IAPS research we analyzed 12 emotional pictures and showed that participants have higher number of fixations for ground on neutral and unpleasant pictures and for figure on pleasant pictures. Second experiment was conducted with 4 sets of emotional complementary pictures (pleasant/unpleasant) which differ only on the content in the figure area and it was shown that participants were more focused on the figure area than on the ground area. Future ERP (event related potential) research with IAPS pictures should take into consideration these findings and to either choose pictures with blank ground or adjust pictures in the way that ground is blank. For the following experiments suggestion is to put emotional content in the figure area and to use different non complementary pictures to see if there is difference between different emotional categories.  相似文献   
936.
Cerebral visual impairment (CVI) is one of the most common causes of bilateral visual loss, which frequently occurs due to perinatal brain injury. Vision in early life has great impact on acquisition of basic comprehensions which are fundamental for further development. Therefore, early detection of visual problems and early intervention is necessary. The aim of the present study is to determine specific visual functioning of children with perinatal brain damage and the influence of visual stimulation on development of functional vision at early age of life. We initially assessed 30 children with perinatal brain damage up to 3 years of age, who were reffered to our pediatric low vision cabinet in "Little house" from child neurologists, ophthalmologists Type and degree of visual impairment was determined according to functional vision assessment of each child. On the bases of those assessments different kind of visual stimulations were carried out with children who have been identified to have a certain visual impairment. Through visual stimulation program some of the children were stimulated with light stimulus, some with different materials under the ultraviolet (UV) light, and some with bright color and high contrast materials. Children were also involved in program of early stimulation of overall sensory motor development. Goals and methods of therapy were determined individually, based on observation of child's possibilities and need. After one year of program, reassessment was done. Results for visual functions and functional vision were compared to evaluate the improvement of the vision development. These results have shown that there was significant improvement in functional vision, especially in visual attention and visual communication.  相似文献   
937.
It has been suggested that management system, milk yield, parity, body condition score and ambient temperature can significantly influence the rate of early pregnancy loss in dairy cattle. The objectives of this study were to establish the extent and patterns of early pregnancy loss from days 32 to 86 of gestation, and to check relationships between management system, milk yield, ambient temperature (quartile), body condition score, bull and parity on the early pregnancy loss rate for Simmental dairy cattle in Croatia. Animals were housed in two dairy farms with two different management systems (pasture based-group A, n=435 and intensive-group B, n=425) with a total of 151 heifers and 709 cows. Overall pregnancy losses were recorded in 67 (7.79%) animals, with late embryonic losses in 30 (44.77%) and early fetal losses in 37 (55.23%) animals (P>0.05). Early pregnancy losses were twofold higher in group B when compared to the group A (P<0.05). More than the half of pregnancy losses were recorded during the III quartile (P<0.05). There was no significant relationship between the paternal bull and pregnancy loss rate. Low body condition score (BCS 2-3) was associated with the highest, while BCS 3.25-4 showed the lowest pregnancy loss rate (P<0.05). The pregnancy loss rate increased in parallel with parity and milk yield increase.  相似文献   
938.
In the present study we analyzed stability of plasmid content in 34 Borrelia strains of three different species (13 Borrelia afzelii, 10 Borrelia garinii and 11 Borrelia burgodorferi sensu stricto) using pulse field gel electrophoresis (PFGE). During long-term in vitro cultivation consisting of 50 passages, plasmid loss was established in 46% of B. afzelii, 40% of B. garinii and 36% of B. burgdorferi sensu stricto strains. Loss of plasmids occurred as early as between the 5th and 10th passage, affected only plasmids in the range 9-41 kb but not plasmids in the range 50-68 kb and manifested with the loss of one to up to three plasmids.  相似文献   
939.
Most popular agents for site-specific protein cleavage are proteolytic enzymes. Because they become denatured and inactivated by detergents, enzymes are inconvenient for proteomic analysis of hydrophobic proteins which require detergents as solubilizing agents. We used cis-[Pd(en)(H2O)2]2+ (in which en represents ethylenediamine) as an artificial protease to effect cleavage of three bovine proteins, namely ubiquitin, β-casein, and serum albumin, in separate experiments. Cleavage took place in aqueous solutions containing 1.0% wt./vol. of either 3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) or Zwittergent 3-14 at 2.5 < pH < 2.9 and 55-60 °C for 3-72 h. Digests were separated by HPLC and analyzed by tandem mass spectrometry. Peptides were identified by de novo sequencing and matched against the bovine genome. Because cleavage by Pd(II) complexes is rather selective and therefore infrequent, 72% of the identified peptides in the digests contained more than 10 amino acid. Palladium(II) complexes hold promise as cleavage agents in proteomics studies of membrane proteins.  相似文献   
940.
Considering the fact that some trace elements have influence on the growth and physiological processes in the fungi, the aim of this study was to resolve the question of whether Fe, Zn, and Se, added to the medium in the different forms, affect activity of selected Pleurotus eryngii ligninolytic enzymes participating in mandarine peels submerged fermentation. Compared with the control, Fe and Zn showed stimulatory effect on laccase activity. Reduction in the activity was emphasized with cultivation time, but it was slower in the presence of Zn than in the presence of Fe. Among studied Se forms, SeO2 was the most unfavorable Se source for laccase activity. All tested trace elements, independent on form, showed stimulatory effect on the activity of Mn-oxidizing peroxidases on the seventh day of cultivation. Based on the results, it could be concluded that the presence of the tested trace elements can advance various biotechnological processes among which is biodegradation of agricultural wastes, potential environmental pollutants.  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