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   8846篇
  免费   1068篇
  国内免费   283篇
耳鼻咽喉   100篇
儿科学   117篇
妇产科学   90篇
基础医学   1384篇
口腔科学   134篇
临床医学   1370篇
内科学   1602篇
皮肤病学   120篇
神经病学   1516篇
特种医学   212篇
外科学   755篇
综合类   781篇
预防医学   823篇
眼科学   84篇
药学   547篇
  3篇
中国医学   236篇
肿瘤学   323篇
  2024年   30篇
  2023年   186篇
  2022年   375篇
  2021年   595篇
  2020年   460篇
  2019年   459篇
  2018年   417篇
  2017年   463篇
  2016年   399篇
  2015年   406篇
  2014年   575篇
  2013年   620篇
  2012年   402篇
  2011年   479篇
  2010年   357篇
  2009年   340篇
  2008年   384篇
  2007年   368篇
  2006年   286篇
  2005年   295篇
  2004年   240篇
  2003年   226篇
  2002年   170篇
  2001年   137篇
  2000年   132篇
  1999年   120篇
  1998年   104篇
  1997年   102篇
  1996年   89篇
  1995年   88篇
  1994年   78篇
  1993年   65篇
  1992年   61篇
  1991年   60篇
  1990年   57篇
  1989年   56篇
  1988年   36篇
  1987年   37篇
  1986年   49篇
  1985年   82篇
  1984年   64篇
  1983年   46篇
  1982年   48篇
  1981年   36篇
  1980年   33篇
  1979年   20篇
  1978年   19篇
  1977年   16篇
  1976年   11篇
  1973年   7篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Since its inception in November 1997, the Cervical Cancer Screening Program of Paraná (CCSPP), Brazil, has resulted in the cytological screening of 2,244,158 women, the coverage of the female population increasing from 43% to 86%. One thousand six hundred one cases screened by cytology, submitted to colposcopy, and subjected to treatment were selected. Cytopathological results were compared with those obtained on the basis of histological analyses of the loop electrical excision procedure specimens, and were subjected to statistical analyses. The data obtained were then compared with cytohistological correlation results from the first year of the program. Considering the exact correlation between cytological and histological diagnoses, the correlation index increased from 53.34% in the first year to 67.3% at the end of 5 yr of the program. Variations that occurred in each diagnostic category are discussed. This study demonstrates a significant improvement in the concordance between cytological and histological results for the 5-yr period compared with the first year of the CCSPP.  相似文献   
72.
ABSTRACT

Electrical Stimulation (ES) is a neurostimulation technique that is used to localize language functions in the brain of people with intractable epilepsy and/or brain tumors. We reviewed 25 ES articles published between 1984 and 2018 and interpreted them from a cognitive neuropsychological perspective. Our aim was to highlight ES as a tool to further our understanding of cognitive models of language. We focused on associations and dissociations between cognitive functions within the framework of two non-neuroanatomically specified models of language. Also, we discussed parallels between the ES and the stroke literatures and showed how ES data can help us to generate hypotheses regarding how language is processed. A good understanding of cognitive models of language is essential to motivate task selection and to tailor surgical procedures, for example, by avoiding testing the same cognitive functions and understanding which functions may be more or less relevant to be tested during surgery.  相似文献   
73.
Ca2+ is the primary regulator of force generation by cross-bridges in striated muscle activation and relaxation. Relaxation is as necessary as contraction and, while the kinetics of Ca2+-induced force development have been investigated extensively, those of force relaxation have been both studied and understood less well. Knowledge of the molecular mechanisms underlying relaxation kinetics is of special importance for understanding diastolic function and dysfunction of the heart. A number of experimental models, from whole muscle organs and intact muscle fibres down to single myofibrils, have been used to explore the cascade of kinetic events leading to mechanical relaxation. By using isolated myofibrils and fast solution switching techniques we can distinguish the sarcomeric mechanisms of relaxation from those of myoplasmic Ca2+ removal. There is strong evidence that cross-bridge mechanics and kinetics are major determinants of the time course of striated muscle relaxation whilst thin filament inactivation kinetics and cooperative activation of thin filament by cycling, force-generating cross-bridges do not significantly limit the relaxation rate. Results in myofibrils can be explained well by a simple two-state model of the cross-bridge cycle in which the apparent rate of the force generating transition is modulated by fast, Ca2+-dependent equilibration between off- and on-states of actin. Inter-sarcomere dynamics during the final rapid phase of full force relaxation are responsible for deviations from this simple model.  相似文献   
74.
Gene conversion is important for antibody diversification in chickens, rabbits and cows. In mice, however, conversion events appear to be infrequent among endogenous antibody genes. DNA sequence transfer events that resemble gene conversions have been reported for a mouse H chain transgene (VVC(mu)) that contains two closely spaced homologous VDJ segments. Surprisingly, these reported VVC(mu) sequence transfers were found frequently among mouse B cells responding to immunization. Transgene sequence transfers could be occurring at high frequency in responding VVC(mu) B cells or could be occurring at lower frequency with subsequent amplification by preferential antigen selection. To distinguish these possibilities, we have analyzed a second transgene (InVVC(mu)) that is identical to VVC(mu) except that the two VDJ regions have been exchanged in position. We find that transgene sequence transfers are much less frequent among responding B cells in InVVC(mu) mice, demonstrating the importance of selection in the frequent transgene conversions observed in VVC(mu) mice. These results suggest that mice, like other species, can use gene conversion to diversify antibodies. Such diversification events are apparently infrequent, however, and might only be detected among endogenous Ig genes with a favorable arrangement of V genes and an antigenic stimulation that selects cells with conversions. For both VVC(mu) and InVVC(mu) mice, conversion-like sequence transfers are strongly correlated with somatic hypermutation. Based on these results, we hypothesize that, in mice, gene conversions represent infrequent alternative reactions of a homology-based DNA repair process that is central in the somatic hypermutational mechanism.  相似文献   
75.
微电极细胞内记录技术应用于研究乙酰胆碱(Ach)和5—羟色胺(5—HT)对日本血吸虫雄性成虫皮层和肌细胞电活动的作用。实验结果显示:(1)Ach对虫体机械活动和肌细胞(n=96)电活动有明显抑制作用。阿托品能拮抗(Acm)的作用,而使虫体活动和肌细胞电活动增强;(2)5—HT对虫体皮层细胞(n=123)和肌细胞(n=107)静息电位有去极化作用,去极化幅值为2—6mV,并能明显增强细胞放电频率。同时,也增强虫体活动度。赛庚啶能拮抗5—HT对虫体的作用;(3)虫体机械收缩活动与肌细胞放电频率成正比的关系。虫体细胞对Ach和5—HT的作用具有明显量效反应。5—HT的作用与细胞膜Ca2+的流通有关。  相似文献   
76.
Posttraumatic stress disorder (PTSD) is usually diagnosed in the primary victim of a psychologically distressing event who demonstrates the criteria symptomatology. Presented here is a case study of PTSD symptoms in a mother whose 4-year-old boy underwent bilateral arm amputation. Discussed is how the mother became the primary PTSD victim and why the particular injury (electrical shock) can be explained as readily giving rise to her problems. Consultants to pediatric and trauma services are reminded that the primary patient's medical care may suffer if disorders such as PTSD are not recognized in those responsible for making treatment decisions for the young victim.  相似文献   
77.
We describe a new population of non-naive B cells in the peripheral blood of quasimonoclonal (QM) mice. Surface Ig of switched isotypes is expressed, but not B220 nor CD19. These cells are larger and denser than naive B cells but smaller than blasts or plasma cells; they do not stain with syndecan, a marker for plasma cells. Telomerase, which is usually expressed in B cell blasts, was not present in this population. We sorted the switched, idiotype-positive, B220(-) B cells from the peripheral blood of QM mice and sequenced Ig H chain and lambda L chain cDNA. There were many point mutations but no V gene replacements, gene conversions or other type of diversifications. As they express switched isotypes and have mutated their Ig genes, cells in the B220(-), CD19(-) population must have been in an immune response and we suggest that it includes the memory B cell subset.  相似文献   
78.
The development of the antibody repertoire in newborn mice is greatly influenced by idiotypic network interactions. It has been demonstrated that anti-idiotypic antibodies either directly injected or transferred from the mother may alter the repertoire for life. For an elucidation of the underlying mechanisms we have analyzed the primary immune response to 2-phenyl-5-oxazolone (phOx) coupled to chicken serum albumin (CSA) in BALB/c mice after complete disappearance of maternal antibodies which originated from different stages of affinity maturation. Depending on the serum titers of the mothers after primary (1° mo), secondary (2° mo) or tertiary (3° mo) immunization, maternal anti-phOx IgG persisted in F1 mice for up to 9 months. In addition, F1 mice born to 2° mo developed – even without immunization – an anti-phOx IgM titer which reached levels similar to an antigen-induced primary response. An enhancement of the early primary anti-phOx as well as anti-CSA response was seen in F1 mice born from 1° mo, whereas the response was delayed when born to 2° mo and 3° mo. The antibody titers in the latter group of mice remained at a lower level for 3 months. In contrast, mice of the F2 generation which received a smaller amount of the same collection of maternal antibodies as F1 mice from 3° mo exhibited a quite different primary response: (i) They showed an earlier onset in their anti-CSA response. (ii) Whereas normally a plateau in antibody titer was reached by the 4th weak after immunization, in 55 % of the F2 mice a prolonged increase of the anti-phOx and anti-CSA antibody titers was observed. At 12 weeks after antigenic challenge, titers reached plateau levels of 6 × 105 which were never before seen in a primary phOx or CSA response. Thus, depending on its own immunological experience, the maternal immune system induces a state of memory in the offspring which results in a faster and/or enhanced immune response in the F1 and F3 generations.  相似文献   
79.
目的探讨阴道镜下高频电灼术联合重组人干扰素α-2a治疗尖锐湿疣(CA)的效果。方法将165例CA分为3组,A组应用阴道镜下高频电灼术联合重组人干扰素α-2a;B组单纯采用阴道镜下高频电灼治疗;C组应用NS-FII型多功能光谱治疗仪联合肌注重组人干扰素α-2a。结果治疗后3-6个月A、B、C组复发率分别为0%、4.4%、65.4%:半年后人乳头瘤病毒(HPV)转阴率分别为93.5%、85.4%、43.8%,A组明显优于B组,B组明显优于C组,3组比较差异有统计学意义(P〈0.01)。结论阴道镜下高频电灼术联合重组人干扰素α-2a治疗CA可明显降低CA复发率和提高HPV转阴率。  相似文献   
80.
Leukodystrophies are a heterogeneous group of heritable disorders characterized by abnormal brain white matter signal on magnetic resonance imaging (MRI) and primary involvement of the cellular components of myelin. Previous estimates suggest the incidence of leukodystrophies as a whole to be 1 in 7,000 individuals, however the frequency of specific diagnoses relative to others has not been described. Next generation sequencing approaches offer the opportunity to redefine our understanding of the relative frequency of different leukodystrophies. We assessed the relative frequency of all 30 leukodystrophies (associated with 55 genes) in more than 49,000 exomes. We identified a relatively high frequency of disorders previously thought of as very rare, including Aicardi Goutières Syndrome, TUBB4A‐related leukodystrophy, Peroxisomal biogenesis disorders, POLR3‐related Leukodystrophy, Vanishing White Matter, and Pelizaeus‐Merzbacher Disease. Despite the relative frequency of these conditions, carrier‐screening laboratories regularly test only 20 of the 55 leukodystrophy‐related genes, and do not test at all, or test only one or a few, genes for some of the higher frequency disorders. Relative frequency of leukodystrophies previously considered very rare suggests these disorders may benefit from expanded carrier screening.  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