全文获取类型
收费全文 | 18826篇 |
免费 | 1133篇 |
国内免费 | 80篇 |
专业分类
耳鼻咽喉 | 76篇 |
儿科学 | 415篇 |
妇产科学 | 222篇 |
基础医学 | 2351篇 |
口腔科学 | 737篇 |
临床医学 | 1870篇 |
内科学 | 4250篇 |
皮肤病学 | 386篇 |
神经病学 | 2006篇 |
特种医学 | 911篇 |
外科学 | 3015篇 |
综合类 | 108篇 |
一般理论 | 4篇 |
预防医学 | 1209篇 |
眼科学 | 130篇 |
药学 | 1263篇 |
中国医学 | 24篇 |
肿瘤学 | 1062篇 |
出版年
2023年 | 145篇 |
2022年 | 155篇 |
2021年 | 388篇 |
2020年 | 293篇 |
2019年 | 407篇 |
2018年 | 485篇 |
2017年 | 453篇 |
2016年 | 432篇 |
2015年 | 499篇 |
2014年 | 676篇 |
2013年 | 1061篇 |
2012年 | 1382篇 |
2011年 | 1311篇 |
2010年 | 816篇 |
2009年 | 785篇 |
2008年 | 1198篇 |
2007年 | 1255篇 |
2006年 | 1210篇 |
2005年 | 1156篇 |
2004年 | 994篇 |
2003年 | 997篇 |
2002年 | 931篇 |
2001年 | 168篇 |
2000年 | 110篇 |
1999年 | 138篇 |
1998年 | 193篇 |
1997年 | 207篇 |
1996年 | 146篇 |
1995年 | 142篇 |
1994年 | 143篇 |
1993年 | 139篇 |
1992年 | 108篇 |
1991年 | 109篇 |
1990年 | 96篇 |
1989年 | 93篇 |
1988年 | 88篇 |
1987年 | 83篇 |
1986年 | 77篇 |
1985年 | 82篇 |
1984年 | 72篇 |
1983年 | 78篇 |
1982年 | 78篇 |
1981年 | 75篇 |
1980年 | 58篇 |
1979年 | 53篇 |
1978年 | 62篇 |
1977年 | 52篇 |
1976年 | 43篇 |
1975年 | 46篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The pitch identification performance of absolute pitch possessors has previously been shown to depend on pitch range, key color, and timbre of presented tones. In the present study, the dependence of pitch identification performance on key color and timbre of musical tones was examined by analyzing hit rates, reaction times, and pupillary responses of absolute pitch possessors (n = 9) and nonpossessors (n = 12) during a pitch identification task. Results revealed a significant dependence of pitch identification hit rate but not reaction time on timbre and key color in both groups. Among absolute pitch possessors, peak dilation of the pupil was significantly dependent on key color whereas the effect of timbre was marginally significant. Peak dilation of the pupil differed significantly between absolute pitch possessors and nonpossessors. The observed effects point to the importance of learning factors in the acquisition of absolute pitch. 相似文献
142.
Limiting dilution analysis has been used in the context of allogeneic bone marrow transplantation to determine anti-recipient interleukin-2 (IL-2) producing helper T lymphocyte precursor (HTLp) frequencies, which in several studies have been predictive of graft-versus-host disease (GVHD). Recently high anti-recipient IL-4 producing HTLp frequencies have been reported and associated with a decreased risk of GVHD. The aim of the present study was to define the optimal conditions for combined determination of IL-2 and IL-4 producing anti-recipient HTLp frequencies. We have optimised the CT.h4S bioassay with regards to specificity, sensitivity, detection limit, and reproducibility. We have found the optimal assay conditions to be 1 x 10 (4) CT.h4S cells/well deprived of IL-4 for 24 h and preincubated for 7 h followed by 18 h of incubation with tritiated methyl-thymidine. In this setting the CT.h4S bioassay detects 5 pg/ml of human recombinant IL-4 with no detection of IL-2 in concentrations below 500 pg/ml. We have found 72 h of culture optimal for detection of IL-2 and IL-4 produced by human mononuclear cells (MNC) in response to stimulation with phytohaemaglutinin and for detection of IL-2 in human leukocyte antigen (HLA)-mismatched mixed leukocyte culture (MLC). An interindividual variation in cytokine accumulation was demonstrated for IL-4 but not for IL-2. With the use of 5x10(4) responder cells/well no IL-4 could be detected in HLA-mismatched MLC between days 1 and 16. The lack of IL-4 detection was not due to high amounts of soluble IL-4 receptor. With the use of 1x10(6) responder cells/well in HLA-mismatched MLC, we found limited IL-4 accumulation still increasing at day 12. We conclude that the CT.h4S bioassay is a reliable and specific method for quantification of IL-4 accumulation in cultures of human MNC. The difference in optimal timing for IL-2 (day 3) and IL-4 (>/=day 12) detection and evidence of very low IL-4 producing HTLp frequencies makes the relevance of a combined IL-2/IL-4 HTLp assay questionable. 相似文献
143.
Borghouts LB Schaart G Hesselink MK Keizer HA 《Pflügers Archiv : European journal of physiology》2000,441(2-3):351-358
In whole muscle homogenates, the glucose transporter-4 (GLUT-4) content is reported to be higher in muscles consisting predominantly of oxidative (type-1) muscle fibres than in muscles consisting predominantly of glycolytic (type-2) fibres. From these findings, it has been deduced that in rat muscle, oxidative fibres have an intrinsically higher level of GLUT-4 protein than glycolytic fibres. No data is available concerning human muscle. Moreover, the fibre-type-specific expression of GLUT-4 has not yet been examined directly. In this study, the relative abundance of GLUT-4 protein expression in individual fibres of different types within a muscle was compared directly in immunohistochemical assays. The human vastus lateralis muscle and a selection of rat muscles were studied using a novel GLUT-4 antiserum. It is concluded that the pattern of fibre-type-specific GLUT-4 expression differs between human and rats and varies between the different muscles studied, indicating that non-fibre-type-specific factor(s) affect expression of GLUT-4. The observation that within a muscle a fibre-type-specific expression of GLUT-4 was observed indicates that fibre-type-specific factors contribute to GLUT-4 expression as well. Thus, it can be postulated that both fibre-type-dependent and fibre-type-independent factors affect GLUT-4 expression. 相似文献
144.
Exercise for older women: a training method and its influences on physical and cognitive performance
Summary The decline in physical and mental ability often associated with increasing age in adults has both social and economic implications that affect most nations. Hence, the maintenance of functional capacity and independence of the older person are beneficial both for the individual and society alike. One way to enhance functioning in old age is physical exercise. However, few methods exist that enable older people to monitor and regulate exercise intensity without using expensive apparatus. Utilizing the individual's subjective feeling of perceived exertion through the use of a simple rating scale is an approach that differs markedly from those previously employed. The present study used the ratings of perceived exertion (RPE) scale to induce different exercise intensities in groups of older women. Walking was chosen as the type of exercise since most older women are unfamiliar with, or affraid to engage in, other types of physical exercise such as bicycling or running. Results indicated that physical exercise capacity increased after 3 months of regular low-intensity walking in the exercise groups but not in nonexercising controls. Furthermore, these changes were accompanied by improved digit span performance. In conclusion, this study has shown that the RPE scale may be used for exercise regulation and that older women would seem to be able to use the scale to monitor and regulate their exercise intensity in an outdoor environment in much the same way as younger individuals. 相似文献
145.
The response of isolated brain vessels to various pH levels or carbon dioxide tensions was analyzed. Reduction of the pH induced a slight relaxation of the vessel, whereas an increase in the pH produced a slight contraction. These effects were markedly exaggerated when the alpha-adrenergic receptors in the vascular wall were activated by noradrenaline. During these conditions the contractile response to noradrenaline was reduced by about 40 per cent at a pH of 7.01, while, on the other hand, the response was enhanced 3-fold at a pH of 7.80. Variations in carbon dioxide tension of the buffer solution between 16 mmHg and 64 mmHg produced no consistent change, provided the pH remained constant. The results indicate that an interaction between the perivascular pH and the adrenergic alpha-receptor mediated contraction in brain vessels may occur. 相似文献
146.
S?ren L Petersen Hans O Madsen Lars P Ryder A Svejgaard Tania N Masmas Ebbe Dickmeiss Carsten Heilmann Lars L Vindel?v 《Biology of blood and marrow transplantation》2004,10(5):337-346
Chimerism analysis of hematopoietic cells has emerged as an essential tool in nonmyeloablative hematopoietic stem cell transplantation. We have investigated the development of donor chimerism in granulocytes and CD4(+) and CD8(+) T cells in blood and bone marrow of 24 patients with hematologic malignancies who received HLA-identical sibling peripheral blood stem cell grafts after conditioning with fludarabine and 2 Gy of total body irradiation. The T-cell chimerism of blood and bone marrow was tightly correlated. Complete donor chimerism was reached earlier in the granulocytes than in the T cells. Mixed T-cell chimerism was common at the time of onset of acute graft-versus-host disease (aGVHD), and both CD4(+) and CD8(+) donor T-cell chimerism increased with the occurrence of aGVHD grades II to IV (P =.0002 and P =.019, respectively). The rate of disappearance of recipient CD8(+) T cells was faster in patients with aGVHD grades II to IV than in patients without clinically significant aGVHD (P =.016). This observation indicates a role of graft-versus-lymphohematopoietic tissue reactions in creating complete donor T-cell chimerism. A donor CD8(+) T-cell count above the median on day +14 increased the risk of subsequent development of aGVHD grades II to IV (P =.003). 相似文献
147.
Chaim Brautbar Isac Cohen Esther Kahana Milton Alter Fritz Jørgensen Lars Lamm 《Tissue antigens》1977,10(4):291-302
The distribution of 24 HLA antigens of the A and B loci was investigated in 197 Israeli Jewish patients with multiple sclerosis (MS) from various Jewish ethnic origins including central and eastern Europe, countries bordering the Mediterranean, the Middle East and from native-born Israelis. The results were compared with the HLA antigen frequencies in a control sample of 455 unrelated individuals representing the general Jewish population. The frequency of HLA-Bw40 among all MS patients (15%) was significantly greater (P less than 0.001) than among the controls (7%). In contrast to the findings in MS patients from other populations, there was no increased frequency of A3 and B7 and Dw2 was present in only one out of 28 patients. The study showed a similar distribution of HLA-A and -B locus antigens, especially of Bw40, in Jews of diverse ethnic origins represented in the control group. 相似文献
148.
Svensson L Nandakumar KS Johansson A Jansson L Holmdahl R 《European journal of immunology》2002,32(10):2944-2953
Rheumatoid arthritis as well as collagen-induced arthritis (CIA) is thought to involve T cell autoimmunity of the Th1 type and the Th2 cytokine IL-4 has been proposed to play a suppressive role. To exclude a possible skewing role of the mycobacteria used in the complete Freund's adjuvant (CFA) we induced CIA with type II collagen (CII) in incomplete Freund's adjuvant (IFA). Our results show that IL-4 deficiency leads to a lesser susceptibility to arthritis and lower B and T cell responses if induced with CII/IFA but not if induced with CII/CFA. In addition, IL-4-deficient mice were less susceptible to arthritis induced with monoclonal anti-CII antibodies. However, mice immunized with CII/IFA later developed a chronic relapsing disease, which was promoted by IL-4 deficiency. We conclude that IL-4 plays different roles depending on the type of adjuvant used and the phase (acute or chronic) of the clinical disease. 相似文献
149.
150.
Analysis of the floral transcriptome uncovers new regulators of organ determination and gene families related to flower organ differentiation in Gerbera hybrida (Asteraceae)
下载免费PDF全文
![点击此处可从《Genome research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Laitinen RA Immanen J Auvinen P Rudd S Alatalo E Paulin L Ainasoja M Kotilainen M Koskela S Teeri TH Elomaa P 《Genome research》2005,15(4):475-486
Development of composite inflorescences in the plant family Asteraceae has features that cannot be studied in the traditional model plants for flower development. In Gerbera hybrida, inflorescences are composed of morphologically different types of flowers tightly packed into a flower head (capitulum). Individual floral organs such as pappus bristles (sepals) are developmentally specialized, stamens are aborted in marginal flowers, petals and anthers are fused structures, and ovaries are located inferior to other floral organs. These specific features have made gerbera a rewarding target of comparative studies. Here we report the analysis of a gerbera EST database containing 16,994 cDNA sequences. Comparison of the sequences with all plant peptide sequences revealed 1656 unique sequences for gerbera not identified elsewhere within the plant kingdom. Based on the EST database, we constructed a cDNA microarray containing 9000 probes and have utilized it in identification of flower-specific genes and abundantly expressed marker genes for flower scape, pappus, stamen, and petal development. Our analysis revealed several regulatory genes with putative functions in flower-organ development. We were also able to associate a number of abundantly and specifically expressed genes with flower-organ differentiation. Gerbera is an outcrossing species, for which genetic approaches to gene discovery are not readily amenable. However, reverse genetics with the help of gene transfer has been very informative. We demonstrate here the usability of the gerbera microarray as a reliable new tool for identifying novel genes related to specific biological questions and for large-scale gene expression analysis. 相似文献