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   2750篇
  免费   183篇
  国内免费   22篇
耳鼻咽喉   5篇
儿科学   69篇
妇产科学   68篇
基础医学   461篇
口腔科学   54篇
临床医学   345篇
内科学   648篇
皮肤病学   65篇
神经病学   262篇
特种医学   68篇
外科学   246篇
综合类   28篇
一般理论   1篇
预防医学   207篇
眼科学   44篇
药学   174篇
中国医学   8篇
肿瘤学   202篇
  2024年   5篇
  2023年   31篇
  2022年   75篇
  2021年   121篇
  2020年   77篇
  2019年   112篇
  2018年   100篇
  2017年   67篇
  2016年   96篇
  2015年   82篇
  2014年   140篇
  2013年   137篇
  2012年   249篇
  2011年   219篇
  2010年   112篇
  2009年   114篇
  2008年   163篇
  2007年   161篇
  2006年   146篇
  2005年   144篇
  2004年   161篇
  2003年   135篇
  2002年   96篇
  2001年   16篇
  2000年   9篇
  1999年   14篇
  1998年   15篇
  1997年   19篇
  1996年   10篇
  1995年   12篇
  1994年   10篇
  1993年   11篇
  1992年   6篇
  1991年   4篇
  1990年   6篇
  1989年   3篇
  1988年   6篇
  1987年   13篇
  1986年   9篇
  1985年   7篇
  1984年   3篇
  1982年   5篇
  1979年   3篇
  1977年   2篇
  1975年   2篇
  1973年   2篇
  1969年   2篇
  1966年   3篇
  1964年   5篇
  1963年   2篇
排序方式: 共有2955条查询结果,搜索用时 0 毫秒
11.
The case study reported in this paper focuses on the relationship between bedwetting and misconduct after the implementation of behavior therapy for both problems. A 6 -year-old girl was treated for enuresis and subsequently for conduct problems (lying, aggressiveness). After both bedwetting and misconduct displayed substantial and stable improvement, it was found that occasional nightly relapses in bedwetting were strongly associated with the occurence of misconduct the following day. Implications of this finding are discussed.  相似文献   
12.
Sonography detected a paraaortic pulsatile tubular mass in a patient 10 years after “stump” nephrectomy, which was subsequently confirmed as a renal artery-renal vein fistula by computed tomography, angiography, and laparotomy.  相似文献   
13.
We aimed to define, for the first time, the ontogeny of intrarenal innervation and to assess the distribution and nature of parenchymal nerves in the human fetal kidney. Our material consisted of routinely-processed renal tissue sections from 17 human fetuses, six of 20–24 gestational weeks (gw) and 11 of 25–40 gw, and three adults. We used immunohistochemistry with antibodies to the pan-neural markers neuron-specific enolase (NSE), neurofilaments (NF), PGP9.5, S100, and the adrenergic marker tyrosine hydroxylase (TH). NSE-, NF-, S100-, and PGP9.5-positive nerves, associated with arterial and venous vasculature, were identified in the renal cortex from 20 gw onwards, and their density appeared to increase with gestation, reaching adult levels at 28 gw. Most of the intrarenal nerves were TH-positive. Nerve fibers extended from the corticomedullary region to the outer cortex, reaching the renal capsule in the 3rd trimester. In detail, NSE-, NF-, S100-, PGP9.5-, and TH-immunoreactive fibers were observed in close apposition to the renal artery and its branches, occasionally reaching the afferent and efferent arteriole (3rd trimester). Nerve fibers were detected in close apposition to the juxtaglomerular apparatus in the 2nd and 3rd trimesters. In the renal medulla, NSE-, PGP9.5-, S100-, and TH-positive nerve fibers were detected close to tubular cells as early as 20 gw. However, their density gradually decreased during the 3rd trimester, and they were not observed in the medulla of the adult kidney. In conclusion, the human fetal kidney appears richly innervated during the 2nd and 3rd trimesters. There is a progressive increase in the density of parenchymal nerve fibers towards term from the corticomedullary region to the cortex. Most intrarenal nerves are adrenergic and have a predominant perivascular distribution, implying that renal innervation plays an important functional role during intrauterine life.  相似文献   
14.
The oomycete Pythium ultimum is homothallic, thus a single isolate completes the sexual stage in pure culture. It has been generally assumed that homothallic oomycetes are predominantly inbreeding. In P. ultimum, antheridia occasionally develop from hyphae not directly connected to the oogonium and appear to participate in fertilization, suggesting a possible mechanism for outcrossing. We have used molecular markers to confirm that outcrossing can occur between isolates of P. ultimum. Genetic markers based on randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphisms (RFLP) were used to distinguish isolates in a collection of P. ultimum. Two isolates displaying a high level of polymorphism were mixed and placed on media which allows the development of the sexual stage. RAPD markers were used to screen single oospore progeny to identify potential hybrids between the two parental isolates. Subsequent self-fertilization of one putative F1 yielded a F2 population which demonstrated segregation and independent assortment of RAPD and RFLP markers. A similar strategy was used to show that an isolate which is incapable of producing oospores in pure culture can outcross when mixed with a homothallic isolate. These results suggest that other homothallic oomycetes may be capable of outcrossing, and sexual reproduction may, therefore, play an important role in the generation of variation in homothallic oomycetes.  相似文献   
15.
Many aspects of the reproductive behavior of Drosophila melanogaster are modified dramatically by experience and age. Males' courtship of immature males and fertilized females decreases over time. Females' receptivity to copulation, and the behaviors that females perform and elicit, are affected by their age and sexual experience. We show that mutations in a raised stock affect all of these age- and experience-dependent aspects of male and female sexual behavior. Experience has no effect on raised males' courtship of immature males and has opposite effects on raised and wild-type males' courtship of fertilized females. In comparison to controls, raised females become sexually mature at an earlier age, and sexually mature raised virgin females copulate more quickly. Following mating, raised females elicit more courtship and remate faster and more frequently than control females.  相似文献   
16.
RASopathies caused by germline pathogenic variants in genes that encode RAS pathway proteins. These disorders include neurofibromatosis type 1 (NF1), Noonan syndrome (NS), cardiofaciocutaneous syndrome (CFC), and Costello syndrome (CS), and others. RASopathies are characterized by heterogenous manifestations, including congenital heart disease, failure to thrive, and increased risk of cancers. Previous work led by the NCI Pediatric Oncology Branch has altered the natural course of one of the key manifestations of the RASopathy NF1. Through the conduct of a longitudinal cohort study and early phase clinical trials, the MEK inhibitor selumetinib was identified as the first active therapy for the NF1‐related peripheral nerve sheath tumors called plexiform neurofibromas (PNs). As a result, selumetinib was granted breakthrough therapy designation by the FDA for the treatment of PN. Other RASopathy manifestations may also benefit from RAS targeted therapies. The overall goal of Advancing RAS/RASopathy Therapies (ART), a new NCI initiative, is to develop effective therapies and prevention strategies for the clinical manifestations of the non‐NF1 RASopathies and for tumors characterized by somatic RAS mutations. This report reflects discussions from a February 2019 initiation meeting for this project, which had broad international collaboration from basic and clinical researchers and patient advocates.  相似文献   
17.
Previous cognitive vulnerability studies have identified sociotropy/dependency as a personality characteristic related to depression. We evaluated sociotropy in differential prediction of depression vs. anxiety. Participants (70 females, 42 males) were tested on the Beck Depression Inventory (BDI) and the Beck Anxiety Inventory (BAI) at two points in time (T1 and T2), separated by an interval of 4 weeks. The Sociotropy‐Autonomy Scale (SAS) was administered at T1. Sociotropy was related moderately to the BDI at T1 and T2, but also to the BAI. Autonomy was related to neither. Hierarchical multiple regression analyses found sociotropy to predict anxiety at T2, but not depression. The issue of cognitive vulnerability marker specificity is discussed. © 2003 Wiley Periodicals, Inc. J Clin Psychol, 2003.  相似文献   
18.
Several observations point to the involvement of disturbed lipid biology in schizophrenia. Reduced response to niacin flushing test, which involves vasodilatation induced by prostaglandin D2 (PGD2), is among the evidences, together with decreased CSF levels of lipocalin-type prostaglandin D2 synthase (PTGDS), the enzyme responsible for the synthesis of PGD2 in the brain. Since PTGDS is also a carrier for lipophilic molecules such as retinoids and thyroid hormones, altered PTGDS levels might influence both PGD2-mediated signaling, and vitamin A and thyroid hormone availability. To test whether genetic variants of PTGDS are involved in the etiology of schizophrenia, we searched for variants in the coding and regulatory regions of the gene. We identified four previously described polymorphisms. Using two case-control samples from Portugal and Brazil, none of the polymorphisms tested was associated with the disease. In addition, no transmission distortion was observed in an independent parents-offspring sample from the Azorean Islands. Our data do not support the involvement of the PTGDS gene in the etiology of schizophrenia.  相似文献   
19.
Multidrug-resistant Salmonella Newport with decreased susceptibility to ceftriaxone (MDR-AmpC) is becoming increasingly common in its food animal reservoirs and in humans. Few data exist on rates of antimicrobial use or differences in clinical outcomes in persons infected with MDR-AmpC or other Salmonella strains. We conducted a case-comparison analysis of data from a multistate population-based case-control study to identify antimicrobial treatment choices and differences in clinical outcomes in those infected with MDRAmpC compared to pansusceptible S. Newport. Of isolates from 215 laboratory-confirmed S. Newport cases, 54 (25%) were MDR-AmpC, 146 (68%) were pansusceptible, and 15 (7%) had other resistance patterns; 146 (68%) patients with S. Newport were treated with antimicrobial agents and 66 (33%) were hospitalized. Over two-thirds of cases at low-risk for serious complications received antimicrobial therapy, most commonly with fluoroquinolones, to which this strain was susceptible. There were no significant differences in symptoms, hospitalization, duration of illness, or other outcomes between the persons infected with MDR-AmpC and pansusceptible S. Newport. Although currently prevalent MDR-AmpC S. Newport strains remains susceptible to the antimicrobial most commonly prescribed for it, continued efforts to reduce unnecessary use of antimicrobial agents in food animals and humans are critical to prevent further development of resistance to quinolones and cephalosporins, which is likely to lead to substantial adverse outcomes.  相似文献   
20.
Genetic transfer of guanidine resistance from type 2 to type 1 poliovirus   总被引:1,自引:0,他引:1  
Summary Following mixed infection of monkey kidney cells with a guanidine-sensitive clonal derivative of the attenuated LSc2ab type 1 poliovirus strain and with a guanidine-resistant clonal derivative of the MEF1 type 2 strain, the frequency of guanidine-resistant type 1 particles was found to be increased in the progeny. The frequency of these particles was almost 4 times higher than that of spontaneous mutants in the progeny of the self cross. This difference being statistically significant it is considered to be an argument in favour to the occurrence of recombination between the two serologically unrelated poliovirus strains.Investigation of a group of unselected genetic markers in the type 1 guanidine-resistant clonal strains derived from the progeny of mixed infection showed that transfer of guanidine resistance from the type 2 parental strain was not associated with the transfer of any other character of this strain.  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