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   54100篇
  免费   3617篇
  国内免费   263篇
耳鼻咽喉   526篇
儿科学   1949篇
妇产科学   1374篇
基础医学   8066篇
口腔科学   800篇
临床医学   5190篇
内科学   12209篇
皮肤病学   1201篇
神经病学   5930篇
特种医学   1129篇
外科学   4394篇
综合类   297篇
现状与发展   1篇
一般理论   43篇
预防医学   5049篇
眼科学   880篇
药学   4191篇
中国医学   141篇
肿瘤学   4610篇
  2024年   91篇
  2023年   684篇
  2022年   1444篇
  2021年   2432篇
  2020年   1404篇
  2019年   1796篇
  2018年   1983篇
  2017年   1603篇
  2016年   1759篇
  2015年   1905篇
  2014年   2477篇
  2013年   3118篇
  2012年   4586篇
  2011年   4585篇
  2010年   2430篇
  2009年   2081篇
  2008年   3464篇
  2007年   3462篇
  2006年   3126篇
  2005年   2859篇
  2004年   2639篇
  2003年   2356篇
  2002年   2127篇
  2001年   253篇
  2000年   205篇
  1999年   269篇
  1998年   340篇
  1997年   287篇
  1996年   195篇
  1995年   184篇
  1994年   184篇
  1993年   143篇
  1992年   104篇
  1991年   93篇
  1990年   75篇
  1989年   84篇
  1988年   78篇
  1987年   68篇
  1986年   67篇
  1985年   66篇
  1984年   92篇
  1983年   78篇
  1982年   79篇
  1981年   68篇
  1980年   63篇
  1979年   34篇
  1978年   35篇
  1977年   34篇
  1976年   25篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Androgens are important regulators of bone and prostate health in elderly men. The role of serum levels of glucuronidated androgen metabolites as predictors of BMD and prostate volume in men is unclear. We show that specific glucuronidated androgen metabolites predict BMD and prostate volume in elderly men. INTRODUCTION: Androgens are important regulators of bone and prostate health in elderly men. Local synthesis and degradation of androgens are likely to be important parameters of biological action of androgens in androgen-responsive tissues. The aim of this study was to determine the role of serum levels of glucuronidated androgen metabolites as predictors of BMD and prostate volume in elderly men. MATERIALS AND METHODS: A subsample of the population-based Swedish part of the MrOS study (n = 631, average age = 75.9 years) was investigated. Bone parameters were measured using DXA. Serum levels of total testosterone (T) and dihydrotestosterone (DHT) were measured by gas chromatography/mass spectroscopy (GC-MS); androstane-3alpha,17beta-diol-3glucuronide (3G) and androstane-3alpha,17beta-diol-17glucuronide (17G) were measured by liquid chromatography/mass spectroscopy. Prostate volume (n = 159) was measured by transrectal ultrasound. RESULTS: The general pattern is that two of the glucuronidated androgen metabolites, namely 17G and 3G, are stronger positive predictors of BMD than the bioactive androgens (T and DHT). In addition, 17G is a clear positive predictor of prostate volume, explaining 4.5% of the variance in prostate volume, whereas the bioactive androgens do not display any association with prostate volume. CONCLUSIONS: Serum levels of specific glucuronidated androgen metabolites predict BMD and prostate volume in elderly men. Future studies should determine if the glucuronidated androgen metabolites also reflect other biological correlates of androgenic activity, including prostate cancer, and if low levels might be a marker of general androgen deficiency in men.  相似文献   
32.
Intra-articular ganglia are rare and mostly incidental findings on magnetic resonance imaging (MRI) and arthroscopy. We present 4 cases of intra-articular ganglion cysts associated with the anterior cruciate ligament (ACL) in 3 patients. The most commonly occurring symptoms were pain aggravated after stressing activities and limited knee range of motion. In 1 patient, ganglion cysts appeared in both knees with a time difference of 1 year. An MRI revealed typical signs of ganglion cysts in the substance of the ACL. Arthroscopy was performed for further evaluation and treatment. Histologic examination of the tissue removed revealed the presence of features consistent with ganglion cysts. Therefore, in the case of chronic knee discomfort with nonspecific clinical signs and symptoms and without a clear cause, an intra-articular ganglion cyst should be considered as causing pathology. An MRI is the most sensitive and specific method for diagnosis. However, the relatively slow progression of symptoms may delay the patient’s decision to seek medical attention. Delayed diagnosis makes arthroscopic total resection of the ganglion technically demanding or not possible at all, and extensive debridement of the ACL may be required.  相似文献   
33.
Antioxidant defence during cardiopulmonary bypass surgery.   总被引:1,自引:0,他引:1  
OBJECTIVE: Cardiac surgery may lead to severe oxidative stress due to formation of oxidation products generated during ischemia and reperfusion. We investigated to which extent oxidative stress influences a number of endogenous antioxidants and markers of cellular activation. METHODS: At six time points blood was withdrawn from patients undergoing coronary artery bypass grafting, using the on-pump procedure. RESULTS: Both glutathione peroxidase and superoxide dismutase show a gradual and strong increase in activity during surgery (40 and 30%, respectively), returning to baseline values 24 h after surgery. The total antioxidant capacity has a maximum increase of 60%. Markers of cellular activation, such as eosinophil cationic protein and tryptase also increase during the procedure. CONCLUSION: Cardiac surgery results in systemic inflammation accompanied or caused by severe oxidative stress. The human body has a strong innate oxidative defence screen, which is probably not sufficient to fully compensate for the total amount of oxidative damage.  相似文献   
34.
OBJECTIVE: The purpose of this presentation is to show the imaging findings of the common and uncommon variants of adenomyosis as seen on sonography and magnetic resonance imaging (MRI). METHODS: A 3-year database search was performed to identify women who had pelvic sonography and pelvic MRI within a 6-month interval. Images of these cases were retrospectively reviewed. RESULTS: Eighty women were identified. Adenomyosis was diagnosed on MRI, which was used as the reference standard, in 45 of these women. The correct diagnosis was made on sonography in 73% of the cases. CONCLUSIONS: Awareness of the spectrum of imaging features of adenomyosis is important to use sonography effectively for diagnosing this entity and to help avoid misdiagnosis.  相似文献   
35.
In vivo diagnosis with cancer-specific targeting agents that have optimal characteristics for imaging is an important development in treatment planning for cancer patients. Overexpression of the HER2 antigen is high in several types of carcinomas and has predictive and prognostic value, especially for breast cancer. A new type of targeting agent, the Affibody molecule, was described recently. An Affibody dimer, His6-(ZHER2:4)2 (15.4 kDa), binds to HER2 with an affinity of 3 nmol/L and might be used for the imaging of HER2 expression. The use of 99mTc might improve the availability of the labeled conjugate, and Tc(I)-carbonyl chemistry enables the site-specific labeling of the histidine tag on the Affibody molecule. The goals of the present study were to prepare 99mTc-labeled His6-(ZHER2:4)2 and to evaluate its targeting properties compared with the targeting properties of 125I-4-iodobenzoate-His6-(ZHER2:4)2 [125I-His6-(ZHER2:4)2]. METHODS: The labeling of His6-(ZHER2:4)2 with 99mTc was performed with an IsoLink kit. The specificity of 99mTc-His6-(ZHER2:4)2 binding to HER2 was evaluated in vitro with SK-OV-3 ovarian carcinoma cells. The comparative biodistributions of 99mTc-His6-(ZHER2:4)2 and 125I-His6-(ZHER2:4)2 in tumor-bearing BALB/c nu/nu mice were determined. RESULTS: The labeling yield for 99mTc-His6-(ZHER2:4)2 was approximately 60% (50 degrees C), and the radiochemical purity was greater than 97%. The conjugate was stable during storage and under histidine and cysteine challenges and demonstrated receptor-specific binding. The biodistribution study demonstrated tumor-specific uptake levels (percentage injected activity per gram of tissue [%IA/g]) of 2.6 %IA/g for 99mTc-His6-(ZHER2:4)2 and 2.3 %IA/g for 125I-His6-(ZHER2:4)2 at 4 h after injection. Both conjugates provided clear imaging of SK-OV-3 xenografts at 6 h after injection. The tumor-to-nontumor ratios were much more favorable for the radioiodinated Affibody. CONCLUSION: The use of Tc(I)-carbonyl chemistry enabled us to prepare a stable, site-specifically labeled 99mTc-His6-(ZHER2:4)2 conjugate that was able to bind to HER2-expressing cells in vitro and in vivo. The indirectly radioiodinated conjugate provided better tumor-to-liver ratios. The labeling of Affibody molecules with 99mTc should be investigated further.  相似文献   
36.
Failure to retain health professionals in rural areas contributes to the poor health status of these communities through an inability to deliver reliable and consistent services. Considerable attention has been focused on factors affecting recruitment of health professionals. Far less is known about factors affecting the retention of occupational therapists. This was the focus of this study. Ethnographic interviews were used to explore the experiences of 10 occupational therapists who had left rural practice. Six themes emerged from the participants' experiences, from when they first considered rural practice to reflections following their departure from it. These themes were initial appeal, facing the challenge, rural practice issues, the social sphere, reasons for leaving and the value of rural experience. These factors gave rise to a proposed Model of Retention Equilibrium, which suggests that retention can be improved by addressing the imbalance between incentives to leave and incentives to stay. The model provides a useful framework for occupational therapists contemplating rural practice, as well as for health services managers responsible for service delivery in rural areas.  相似文献   
37.
The protection by pyroglutamic acid (CAS 98-79-3) and derivatives Ia-i (injected i.p.) against glutamate- and NMDA (N-methyl-D-aspartate) (i.c.v.) induced seizures in mice has been studied in comparison with known antiepileptics and antagonists of excitatory aminoacids. The potency of pyroglutamic acid and some derivatives (Id,f,g,h) against glutamate-induced convulsions was similar to that shown by glutamic acid diethylester and by valproic acid. Interestingly, pyroglutamic acid did not affect NMDA-induced convulsions which were well antagonized by both 2-amino-5-phosphono valeric acid and by diazepam. Thus, pyroglutamic acid may represent the starting for synthesis of excitatory aminoacid antagonists acting at non NMDA receptors.  相似文献   
38.
Abstract Facial gingival surfaces of maxillary and mandibular anterior teeth were monitored to evaluate changes of the width of the keratinized and attached gingiva. 96 children 6 to 12 years of age were examined 2 × with an interval of 2 years. Measurements included dental plaque, gingival inflammation, probing depth, and width of keratinized and attached gingiva. In addition, study models were used to determine the facial/lingual position of the teeth. The results of this report, evaluating well-aligned teeth only, showed that during the 2-year observation period, increases in widths of the facial keratinized and attached gingiva took place. Increases occurred for the various teeth regions examined, and for deciduous as well as permanent teeth. During transition from the deciduous to the permanent dentition, patterns of change were variable. The increase of gingival widths was greatest for sites with the smallest baseline width of attached gingiva, and smallest for sites with the greatest baseline width. It was concluded that in well-aligned teeth, a conservative, monitoring approach prior to a corrective, surgical intervention seems prudent in children of this age with a minimal zone or absence of attached gingiva.  相似文献   
39.
The phase equilibrium of plasticized polymer systems on the basis of cellulose diacetate and ethylene glycol esters of dibasic aliphatic acids (from oxalic acid to 1,10-decanedicarboxylic acid) was studied and the solubility parameters and the thermodynamic interaction parameters of the components were calculated. It is shown that an increase in molecular weight of the plasticizers leads to a lower miscibility of the components, a fact which is reflected in a regular rise of the upper critical solution temperature (UCST), a tendency of the systems for gelation, a decrease of the solubility parameter of the plasticizer δ1, and a growth of the interaction parameters χH and χ12. The results are discussed in terms of the existing theories for polymer solutions.  相似文献   
40.
Immunology     
A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology.  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