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   1485篇
  免费   136篇
  国内免费   3篇
耳鼻咽喉   12篇
儿科学   66篇
妇产科学   22篇
基础医学   251篇
口腔科学   29篇
临床医学   160篇
内科学   282篇
皮肤病学   46篇
神经病学   196篇
特种医学   38篇
外科学   155篇
综合类   2篇
现状与发展   1篇
一般理论   1篇
预防医学   171篇
眼科学   19篇
药学   65篇
中国医学   2篇
肿瘤学   106篇
  2023年   18篇
  2022年   27篇
  2021年   46篇
  2020年   44篇
  2019年   30篇
  2018年   45篇
  2017年   40篇
  2016年   50篇
  2015年   52篇
  2014年   74篇
  2013年   65篇
  2012年   119篇
  2011年   129篇
  2010年   70篇
  2009年   79篇
  2008年   132篇
  2007年   110篇
  2006年   113篇
  2005年   90篇
  2004年   96篇
  2003年   78篇
  2002年   57篇
  2001年   4篇
  2000年   6篇
  1999年   13篇
  1998年   5篇
  1997年   2篇
  1996年   5篇
  1995年   5篇
  1994年   2篇
  1993年   7篇
  1992年   5篇
  1991年   2篇
  1990年   3篇
  1987年   1篇
排序方式: 共有1624条查询结果,搜索用时 16 毫秒
11.
Androgen is associated with the expression of male-typical behavior, including aggressive behavior, but high levels of androgen may be incompatible with other behavioral systems, such as paternal care. In a variety of species of birds that display paternal care, testosterone (T) levels in males are maintained at low levels, and these levels rise only in response to direct agonistic challenges. This idea has not been thoroughly studied in mammals with biparental care, and we exposed male marmosets (Callithrix kuhlii), a monogamous and biparental primate to aggressive interactions with unfamiliar intruders. Urinary levels of T and cortisol (CORT) were monitored prior to and following these interactions. Baseline T was not correlated with variation in aggression in either residents or intruders, and CORT was not affected by the encounters. However, males responded to an encounter with male intruders with changes in T that correlated with the level of aggression displayed by the resident male during the trial. Encounters with male intruders that elicited high frequencies of aggressive displays by the male resident were associated with increased T 2-6 h and 24 h following the encounter, and encounters that had few aggressive displays resulted in no change or a decrease in T concentrations. Intruders did not demonstrate a significant relationship between T and aggression. Thus, the magnitude of the hormonal response is dependent on the intensity of aggression during a male-male encounter, suggesting that elevated androgens are likely to be a consequence, rather than a cause, of aggressive interactions in marmosets.  相似文献   
12.
Studies on smooth muscle cell differentiation and those on vascular development in mouse and humans have long been hampered by the lack of suitable markers. Here we describe a novel, large isoform of smoothelin, a structural protein of differentiated, contractile smooth muscle cells. The protein, which is highly conserved in mouse and humans, shows homology with other cytoskeleton-associated smooth muscle cell proteins and contains an actinin-type actin-binding domain. Northern blot analysis from various mouse organs identified short and long smoothelin mRNA forms, which exhibit distinct tissue expression patterns. The short form is highly expressed in visceral muscle tissues such as intestine and stomach and is not detectable in brain, while the long mRNA form is expressed in all vascularized organs. These results may provide new tools and approaches to study both smooth muscle cell differentiation and proliferative vascular disease. Received: 25 August 1998 / Accepted: 19 October 1998  相似文献   
13.
In Kinetoplastids, protein-coding genes are transcribed polycistronically by RNA polymerase II. Individual mature mRNAs are generated from polycistronic precursors by 5' trans splicing of a 39-nt capped leader RNA and 3' polyadenylation. It was previously known that trans splicing generally occurs at an AG dinucleotide downstream of a polypyrimidine tract, and that polyadenylation is coupled to downstream trans splicing. The few polyadenylation sites that had been examined were 100-400 nt upstream of the polypyrimidine tract which marked the adjacent trans splice site. We wished to define the sequence requirements for trypanosome mRNA processing more tightly and to generate a predictive algorithm. By scanning all available Trypanosoma brucei cDNAs for splicing and polyadenylation sites, we found that trans splicing generally occurs at the first AG following a polypyrimidine tract of 8-25 nt, giving rise to 5'-UTRs of a median length of 68 nt. We also found that in general, polyadenylation occurs at a position with one or more A residues located between 80 and 140 nt from the downstream polypyrimidine tract. These data were used to calibrate free parameters in a grammar model with distance constraints, enabling prediction of polyadenylation and trans splice sites for most protein-coding genes in the trypanosome genome. The data from the genome analysis and the program are available from: .  相似文献   
14.
Mexiletine is a class 1b antiarrhythmic drug used for ventricular arrhythmias but is also found to be effective for paramyotonia congenita, potassium-aggravated myotonia, long QT–3 syndrome, and neuropathic pain. This drug elicits tonic block of Na+ channels when cells are stimulated infrequently and produces additional use-dependent block during repetitive pulses. We examined the state-dependent block by mexiletine in human skeletal muscle hNav1.4 wild-type and inactivation-deficient mutant Na+ channels (hNav1.4-L443C/A444W) expressed in HEK293t cells with a β1 subunit. The 50% inhibitory concentrations (IC50) for the inactivated-state block and the resting-state block of wild-type Na+ channels by mexiletine were measured as 67.8 ± 7.0 μ m and 431.2 ± 9.4 μ m , respectively ( n = 5). In contrast, the IC50 for the block of open inactivation-deficient mutant channels at +30 mV by mexiletine was 3.3 ± 0.1 μ m ( n = 5), which was within the therapeutic plasma concentration range (2.8–11 μ m ). Estimated on- and off-rates for the open-state block by mexiletine at +30 mV were 10.4 μ m −1 s−1 and 54.4 s−1, respectively. Use-dependent block by mexiletine was greater in inactivation-deficient mutant channels than in wild-type channels during repetitive pulses. Furthermore, the IC50 values for the block of persistent late hNav1.4 currents in chloramine-T-pretreated cells by mexiletine was 7.5 ± 0.8 μ m ( n = 5) at +30 mV. Our results together support the hypothesis that the in vivo efficacy of mexiletine is primarily due to the open-channel block of persistent late Na+ currents, which may arise during various pathological conditions.  相似文献   
15.
Human bornavirus encephalitis is a severe and often fatal infection caused by variegated squirrel bornavirus 1 (VSBV-1) and Borna disease virus 1 (BoDV-1). We conducted a prospective study of bornavirus etiology of encephalitis cases in Germany during 2018–2020 by using a serologic testing scheme applied along proposed graded case definitions for VSBV-1, BoDV-1, and unspecified bornavirus encephalitis. Of 103 encephalitis cases of unknown etiology, 4 bornavirus infections were detected serologically. One chronic case was caused by VSBV-1 after occupational-related contact of a person with exotic squirrels, and 3 acute cases were caused by BoDV-1 in virus-endemic areas. All 4 case-patients died. Bornavirus etiology could be confirmed by molecular methods. Serologic testing for these cases was virus specific, discriminatory, and a practical diagnostic option for living patients if no brain tissue samples are available. This testing should be guided by clinical and epidemiologic suspicions, such as residence in virus-endemic areas and animal exposure.  相似文献   
16.
PURPOSE: Increased bone resorption is a hallmark of multiple myeloma and is attributable to osteoclast activation. Recent studies showed that the receptor activator of nuclear factor kappaB ligand (RANKL) is the key mediator of osteoclastogenesis and plays a crucial role in bone destruction in malignant bone disease. We found that human myeloma cells express RANKL and analyzed the association of the RANKL expression with the presence of osteolytic bone disease in patients with multiple myeloma. EXPERIMENTAL DESIGN: Flow cytometry was performed on bone marrow samples derived from controls and multiple myeloma patients with or without osteolytic bone lesions on conventional radiography. Plasma cells were identified as CD38++/CD138+ cells. The level of RANKL expression on the surface of bone marrow plasma cells was correlated with the bone status of the patients. RESULTS: The bone marrow plasma cells from controls showed no or only a weak surface expression of RANKL, and the median mean fluorescence index (MFI) was 6. In contrast, expression of RANKL could be detected on bone marrow plasma cells from all of the patients with multiple myeloma, and median MFI was 47. The difference in MFI for RANKL expression of bone marrow plasma cells from controls and myeloma patients was highly significant (P < 0.0005). Myeloma patients with osteolytic bone lesions showed a significantly higher expression of RANKL (median MFI = 60; range, 16-2494) compared with patients without osteolysis (median MFI = 16; range, 6-229; P < 0.0005). CONCLUSIONS: These results show for the first time that the level of RANKL expression by myeloma cells correlates significantly with osteolytic bone disease.  相似文献   
17.
18.
19.
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz - Patienteninformationen zu seltenen Erkrankungen (SE) müssen hohen Qualitätsanforderungen genügen, wenn sie...  相似文献   
20.
The purpose of this study was to evaluate the role and interaction of individual factors on decompensated tinnitus. Subjects consisted of 53 adult patients with chronic tinnitus. They were selected and assigned to two groups, compensated (n?=?28) and decompensated (n?=?25), according to the results of an established tinnitus questionnaire. Both groups were evaluated and compared. The patients with decompensated tinnitus suffered from more pronounced social disabilities, were more prone to depression, and used less effective techniques to cope with their illness. They showed a higher degree of somatic multimorbidity, with particularly strong correlations between tinnitus and the incidence of cardiovascular diseases and hypoacusis. As a consequence, in the psychosomatic tinnitus therapy, greater attention should be given to the treatment of the somatic complaints in addition to psychological and psychosocial aspects.  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