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   846篇
  免费   64篇
  国内免费   2篇
耳鼻咽喉   7篇
儿科学   26篇
妇产科学   7篇
基础医学   102篇
口腔科学   19篇
临床医学   85篇
内科学   139篇
皮肤病学   138篇
神经病学   88篇
特种医学   22篇
外科学   79篇
综合类   4篇
预防医学   75篇
眼科学   20篇
药学   48篇
中国医学   1篇
肿瘤学   52篇
  2024年   3篇
  2023年   9篇
  2022年   32篇
  2021年   55篇
  2020年   29篇
  2019年   37篇
  2018年   22篇
  2017年   25篇
  2016年   36篇
  2015年   30篇
  2014年   54篇
  2013年   48篇
  2012年   63篇
  2011年   58篇
  2010年   27篇
  2009年   28篇
  2008年   59篇
  2007年   41篇
  2006年   35篇
  2005年   33篇
  2004年   24篇
  2003年   21篇
  2002年   19篇
  2001年   11篇
  2000年   8篇
  1999年   6篇
  1998年   3篇
  1997年   2篇
  1992年   3篇
  1991年   3篇
  1990年   6篇
  1989年   4篇
  1988年   5篇
  1987年   7篇
  1986年   6篇
  1985年   5篇
  1984年   3篇
  1983年   8篇
  1982年   15篇
  1981年   5篇
  1980年   2篇
  1979年   3篇
  1977年   2篇
  1949年   1篇
  1948年   1篇
  1947年   2篇
  1943年   2篇
  1941年   2篇
  1931年   1篇
  1930年   1篇
排序方式: 共有912条查询结果,搜索用时 15 毫秒
1.
2.
Because a retrospective study detected 13 negative Western blots out of 38 single-use diagnostic system (SUDS)-positive cases over a 1-year period, we performed a prospective study to compare the performance of the SUDS test with that of enzyme immunoassay (EIA). Of 888 SUDS-tested sera, 875 (98.4%) were both SUDS and EIA negative and 5 (0.6%) were SUDS, EIA, and Western blot positive. The rate of SUDS-positive samples decreased from 3.16/month in the retrospective study to 1.33/month in the prospective study. The immunoassays had sensitivities and specificities of 100 and 99.7 (SUDS) and 100 and 99.4% (traditional EIA), respectively. In laboratories with experienced personnel, the SUDS test performs as well as the EIA as a screen for infection with the human immunodeficiency virus.  相似文献   
3.
Seven lean healthy young men were studied for 6 weeks during exposure to pharmacologic inhibition or stimulation of the sympathetic nervous system. For a period of 2 weeks their beta-adrenergic receptors were either blocked with propranolol hydrochloride (160 mg/d) or stimulated with terbutaline sulphate (15 mg/d). After a further 2 weeks of placebo administration (500 mg lactose/d), the subjects crossed over to the drug they had not been taking at the beginning of the experiment for another 14 days. During the last five days of each 2-week period, the subjects consumed a weight-maintaining diet, composed of 12% protein, 48% carbohydrate, and 40% fat. They consumed exactly the same menus on the same days during the subsequent study periods. Body weight and physical activity were measured every day for 6 weeks. Daily heart rate and nitrogen excretion were measured continuously for days at the end of each 2-week period, the last two days of which were spent in a respiration chamber where energy expenditure and a variety of metabolic parameters were measured. In the respiration chamber on the propranolol, placebo, and terbutaline treatments, respectively, significant differences were observed in mean daily heart rate (65 +/- 3, 75 +/- 4, and 84 +/- 4 beats/min), mean sleeping heart rate (51 +/- 2, 56 +/- 3, and 62 +/- 3 beats/min), nitrogen excretion (13.6 +/- 0.7, 12.6 +/- 0.6, and 11.9 +/- 0.6 g/d), fat oxidation (+1,045 +/- 95, +1,243 +/- 148, and +1,278 +/- 84 kcal/d) and thyroid hormones (12.0 +/- 0.7, 15.7 +/- 0.9, and 17.2 +/- 1.0 T3/T4 ratio).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
4.
Catalase plays a key role as an antioxidant, protecting aerobic organisms from the toxic effects of hydrogen peroxide, and in some cases has been postulated to be a virulence factor. To help elucidate the function of catalase in Candida albicans, a single C. albicans-derived catalase gene, designated CAT1, was isolated and cloned. Degenerate PCR primers based on highly conserved areas of other fungal catalase genes were used to amplify a 411-bp product from genomic DNA of C. albicans ATCC 10261. By using this product as a probe, catalase clones were isolated from genomic libraries of C. albicans. Nucleotide sequence analysis revealed an open reading frame encoding a protein of 487 amino acid residues. Construction of a CAT1-deficient mutant was achieved by using the Ura-blaster technique for sequential disruption of multiple alleles by integrative transformation using URA3 as a selectable marker. Resulting mutants exhibited normal morphology and comparable growth rates of both yeast and mycelial forms. Enzymatic analysis revealed an abundance of catalase in the wild-type strain but decreasing catalase activity in heterozygous mutants and no detectable catalase in a homozygous null mutant. In vitro assays showed the mutant strains to be more sensitive to damage by both neutrophils and concentrations of exogenous peroxide that were sublethal for the parental strain. Compared to the parental strain, the homozygous null mutant strain was far less virulent for mice in an intravenous infection model of disseminated candidiasis. Definitive linkage of CAT1 with virulence would require restoration of activity by reintroduction of the gene into mutants. However, initial results in mice, taken together with the enhanced susceptibility of catalase-deficient hyphae to damage by human neutrophils, suggest that catalase may enhance the pathogenicity of C. albicans.  相似文献   
5.
Adolescent and adult rats exhibit at least two distinct ultrasonic vocalizations that reflect distinct emotional states. Rats exhibit 22-kHz calls during social defeat, drug withdrawal, as well as in anticipation of aversive events. In contrast, 50-kHz calls are exhibited in high rates during play behavior, mating, as well as in anticipation of rewarding events. The neurochemistry of 22-kHz and 50-kHz calls closely matches that of negative and positive emotional systems in humans, respectively. The aim of this study was to replicate and further evaluate selective breeding for 50-kHz vocalization, in preparation for the analysis of the genetic underpinnings of the 50-kHz ultrasonic vocalization (USV). Isolate housed adolescent rats (23–26 days old) received experimenter administered tactile stimulation (dubbed tickling), which mimicked the rat rough-and-tumble play behavior. This stimulation has previously been shown to elicit high levels of 50-kHz USVs and to be highly rewarding in isolate-housed animals. Each tickling session consisted of 4 cycles of 15 seconds stimulation followed by 15 seconds no stimulation for a total of 2 min, and was repeated once per day across 4 successive days. Rats were then selected for either High or Low levels of sonographically verified 50-kHz USVs in response to the stimulation, and a randomly selected line served as a control (Random group). Animals emitted both 22-kHz and 50-kHz types of calls. After 5 generations, animals in the High Line exhibited significantly more 50-kHz and fewer 22-kHz USVs than animals in the Low Line. Animals selected for low levels of 50-kHz calls showed marginally more 22-kHz USVs then randomly selected animals but did not differ in the rate of 50-kHz calls. These results extend our previous findings that laboratory rats could be bred for differential rates of sonographically verified 50-kHz USVs.  相似文献   
6.
We have proposed that short (<0.5 s), high-frequency (approximately 50 kHz) ultrasonic vocalizations ("50-kHz USVs") index a positive affective state in adult rats, because they occur prior to rewarding social interactions (i.e., rough-and-tumble play, sex). To evaluate this hypothesis in the case of nonsocial stimuli, we examined whether rats would make increased 50-kHz USVs in places associated with the administration of rewarding pharmacological compounds [i.e., amphetamine (AMPH) and morphine (MORPH)]. In Experiment 1, rats made a greater percentage of 50-kHz USVs on the AMPH-paired side of a two-compartment chamber than on the vehicle-paired side, even after statistical correction for place preference. In Experiment 2, rats made a higher percentage of 50-kHz USVs on the MORPH-paired side than on the vehicle-paired side, despite nonsignificant place preference. These findings support the hypothesis that 50-kHz USVs mark a positive affective state in rats and introduce a novel and rapid marker of pharmacological reward.  相似文献   
7.
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz - Wissenschaftliche Ergebnisse können eine Wissensquelle für kommunale Akteurinnen und Akteure der...  相似文献   
8.
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz - Kommunale AkteurInnen erfahren bei der Entwicklung und Auswahl von Maßnahmen der Prävention und...  相似文献   
9.
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz - Seit Mai 2020 können Hersteller einen Antrag zur Aufnahme einer digitalen Gesundheitsanwendung (DiGA) in das Verzeichnis...  相似文献   
10.
This report describes two patients with mucinous syringometaplasia whose findings expand the microscopic and clinical spectrum of the entity. The first patient had an eroded nodule that exhibited multiple epidermal invaginations that penetrated deeply into the dermis. In addition to mucinous metaplasia, there was also exuberant papillary epithelial hyperplasia. Expanded eccrine ducts with similar changes appeared as lobules isolated in the dermis but were shown to connect with the invaginations. In the second patient, a clinical "cyst" drained serous fluid. Multiple papillary-cystic epithelial lobules similar to those seen in the first case were located in the dermis. A few approached the epidermis, but epidermal connections were not identified. The epithelium in these lesions was identical to that previously described in mucinous syringometaplasia. The tumors differed from prior cases by virtue of the number of eccrine apparatus involved, the extent and depth of involvement, and the presence of prominent papillary epithelial hyperplasia.  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