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   12203篇
  免费   708篇
  国内免费   151篇
耳鼻咽喉   199篇
儿科学   105篇
妇产科学   152篇
基础医学   2154篇
口腔科学   343篇
临床医学   1050篇
内科学   2052篇
皮肤病学   494篇
神经病学   1103篇
特种医学   744篇
外科学   1599篇
综合类   107篇
一般理论   2篇
预防医学   500篇
眼科学   298篇
药学   1263篇
中国医学   152篇
肿瘤学   745篇
  2024年   7篇
  2023年   78篇
  2022年   295篇
  2021年   479篇
  2020年   203篇
  2019年   306篇
  2018年   362篇
  2017年   280篇
  2016年   401篇
  2015年   512篇
  2014年   667篇
  2013年   787篇
  2012年   1050篇
  2011年   993篇
  2010年   652篇
  2009年   556篇
  2008年   751篇
  2007年   765篇
  2006年   655篇
  2005年   568篇
  2004年   458篇
  2003年   396篇
  2002年   324篇
  2001年   230篇
  2000年   198篇
  1999年   143篇
  1998年   109篇
  1997年   92篇
  1996年   67篇
  1995年   53篇
  1994年   51篇
  1993年   52篇
  1992年   40篇
  1991年   39篇
  1990年   45篇
  1989年   57篇
  1988年   36篇
  1987年   38篇
  1986年   23篇
  1985年   15篇
  1984年   19篇
  1983年   10篇
  1982年   13篇
  1981年   14篇
  1980年   11篇
  1979年   9篇
  1978年   7篇
  1977年   10篇
  1976年   12篇
  1941年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
蓣知子皂甙IV的结构   总被引:5,自引:1,他引:5  
从木通科木通属植物白木通[Akebia trifoliata(Thunb.)Koidz.var.australis(Diels)Rehd]种子的乙醇提取物中以硅胶层析等方法得四种三萜皂甙。其中甙IV是新天然产物,命名为蓣知子皂甙IV(yuzhiziosideIV)。根据化学和光谱分析,确定甙IV的结构为3-O-β-D-吡喃木糖基-(1→2)-a-L-吡喃阿拉伯糖齐墩果酸-28-O-β-D-吡喃葡萄糖基-(1→6)-β-D-吡喃葡萄糖酯甙。另外皂甙B(I)、皂甙C(II)和皂甙D(III)为已知物。这些化合物在白木通种子中均是首次得到。  相似文献   
82.
A new acylglycosyl sterol from quisqualis fructus   总被引:1,自引:0,他引:1  
A new acylglycosyl sterol (4) was isolated from the MeOH extract of Quisqualis Fructus together with four known compounds. On the basis of spectroscopic data, their structures were elucidated as clerosterol (1), betulinic acid (2), methylursolate (3), 3-O-[6'-O-(8Z-octadecenoyl)-beta-D-glucopyranosyl]-clerosterol (4) and alpha-xylofuranosyluracil (5).  相似文献   
83.
Eucommia ulmoides Oliv. Bark (EUE) is commonly used for the treatment of hypertension, rheumatoid arthritis, lumbago, and ischialgia as well as to promote longevity. In this study, we tested the effects of EUE aqueous extract in graded doses to protect and enhance cognition in scopolamine-induced learning and memory impairments in mice. EUE significantly improved the impairment of short-term or working memory induced by scopolamine in the Y-maze and significantly reversed learning and memory deficits in mice as measured by the passive avoidance and Morris water maze tests. One day after the last trial session of the Morris water maze test (probe trial session), EUE dramatically increased the latency time in the target quadrant in a dose-dependent manner. Furthermore, EUE significantly inhibited acetylcholinesterase (AChE) and thiobarbituric acid reactive substance (TBARS) activities in the hippocampus and frontal cortex in a dose-dependent manner. EUE also markedly increased brain-derived neurotrophic factor (BDNF) and phosphorylation of cAMP element binding protein (CREB) in the hippocampus of scopolamine-induced mice. Based on these findings, we suggest that EUE may be useful for the treatment of cognitive deficits, and that the beneficial effects of EUE are mediated, in part, by cholinergic signaling enhancement and/or protection.  相似文献   
84.
It is unclear which factors contribute to the developing pressure pain hypersensitivity of the upper trapezius, a type of neurophysiological hyperexcitability. The present study investigated the relationship between physical and psychological factors and pressure pain hypersensitivity of the upper trapezius for each sex. In total, 154 individuals with neck/shoulder myofascial pain participated, among 372 food service workers. Participants completed a questionnaire (Beck Depression Inventory, and Borg Rating of Perceived Exertion scale) and were photographed to measure posture. Pressure pain sensitivity, 2 range of motions (cervical lateral bending and rotation), and 4 muscle strengths (serratus anterior, lower trapezius [LT], biceps, and glenohumeral external rotator) were measured by a pressure algometer, iPhone application, and handheld dynamometer, respectively. For each sex, forward multivariate logistic regression was used to test our a priori hypothesis among selected variables that a combination of psychosocial and physical factors contributed to the risk for pressure pain hypersensitivity. In multivariate analyses, LT strength (odds ratio = 0.94, 95% confidence interval = 0.91–0.97, P = .001) was the only significant influencing factor for pressure pain hypersensitivity in men. Dominant painful ipsilateral cervical rotation range of motion (odds ratio = 0.96, 95% confidence interval = 0.92–0.99, P = .037) was the only influencing factor for pressure pain hypersensitivity in women. LT strength and dominant painful ipsilateral cervical rotation range of motion could serve as guidelines for preventing and managing pressure pain hypersensitivity of the upper trapezius in food service workers with nonspecific neck/shoulder myofascial pain.  相似文献   
85.
The objective of this study was to estimate solid cancer risk attributable to long‐term, fractionated occupational exposure to low doses of ionizing radiation. Based on cancer incidence for the period 1950–1995 in a cohort of 27,011 Chinese medical diagnostic X‐ray workers and a comparison cohort of 25,782 Chinese physicians who did not use X‐ray equipment in their work, we used Poisson regression to fit excess relative risk (ERR) and excess absolute risk (EAR) dose–response models for incidence of all solid cancers combined. Radiation dose reconstruction was based on a previously published method that relied on simulating measurements for multiple X‐ray machines, workplaces and working conditions, information about protective measures, including use of lead aprons, and work histories. The resulting model was used to estimate calendar year‐specific badge dose calibrated as personal dose equivalent (Sv). To obtain calendar year‐specific colon doses (Gy), we applied a standard organ conversion factor. A total of 1,643 cases of solid cancer were identified in 1.45 million person‐years of follow‐up. In both ERR and EAR models, a statistically significant radiation dose–response relationship was observed for solid cancers as a group. Averaged over both sexes, and using colon dose as the dose metric, the estimated ERR/Gy was 0.87 (95% CI: 0.48, 1.45), and the EAR was 22 per 104PY‐Gy (95% CI: 14, 32) at age 50. We obtained estimates of the ERR and EAR of solid cancers per unit dose that are compatible with those derived from other populations chronically exposed to low dose‐rate occupational or environmental radiation.  相似文献   
86.
OBJECTIVE: It is unknown whether obese women would benefit from oral contraceptives or screening as endometrial cancer prevention strategies. We estimated the net health benefits and cost-effectiveness of these strategies in a hypothetical cohort of obese women. METHODS: A Markov decision-analytic model evaluated 4 strategies: 1) no prevention (reference strategy); 2) oral contraceptive pills (OCPs) for 5 years; 3) annual screening with endometrial biopsy from age 30; 4) biennial screening from age 30. Net health benefit was life expectancy and primary outcome was the incremental cost-effectiveness ratio. Baseline and transition probabilities were obtained from published literature and the Surveillance Epidemiology and End Results database, and costs were from the U.S. Department of Health and Human Services and Agency for Healthcare Research and Quality. Sensitivity analyses were performed for uncertainty around various measures. RESULTS: Average life expectancy for all strategies ranged from 74.52 to 74.60 years. None of the strategies had an incremental cost-effectiveness ratio less than $50,000 per year of life saved relative to the next best strategy. Endometrial cancer risk in obese women had to be 13 times greater than the general population risk before OCPs were a cost-effective intervention. CONCLUSION: Oral contraceptives and current screening methods are not cost-effective endometrial cancer prevention strategies for obese women. Risk factors such as morbid obesity and longstanding anovulation may define a subgroup at highest risk of endometrial cancer for whom OCPs may be a cost-effective strategy. Interventions that reduce endometrial cancer risk further or those with additional health benefits are needed in this population. LEVEL OF EVIDENCE: III.  相似文献   
87.
88.
OBJECTIVE: Discrepancies may exist between an original pathology report and formal pathology review, with subsequent implications for treatment. We conducted a study of pathology review in endometrial cancer from a population-based study to identify areas of discrepancy and effect on treatment. METHODS: This was a retrospective cohort study in Ontario, Canada from 1996 to 2000. We identified hysterectomy cases from patients with endometrial cancer that were subject to formal pathology review by a gynecologic pathologist at one of six tertiary care centers. Sarcomas and other rare histologic subtypes with fewer than five cases were excluded. We evaluated discrepancy between original pathology and review by demographics, stage, grade, and risk group. Four risk groups were defined: 1) low (stage I), 2) intermediate (stage I and II), 3) high-risk (stage I and II), and 4) advanced stage (all stage III and IV). Reclassification from one risk group to another upon pathology review represented a potential change in treatment. Factors associated with significant discrepancy were identified by a multivariable logistic regression model. RESULTS: Formal pathology review was available on 450 cases. There were no differences by age, year, or hospital type. The overall discrepancy rate was 42.7% (95% confidence interval 38.2-47.3%). The intermediate-risk group had the highest rate of reclassification into another group (33.1%). The most significant rates of discrepancy were associated with endometrioid grades 2 and 3 tumors and stage IIA disease (39.8%, 50.9%, and 79.6%, respectively). CONCLUSION: There was significant discrepancy between original pathology and formal review in endometrial cancer, with implications for guidelines on pathology review at a population level. LEVEL OF EVIDENCE: III  相似文献   
89.
90.
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