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   57218篇
  免费   2736篇
  国内免费   413篇
耳鼻咽喉   556篇
儿科学   1239篇
妇产科学   1527篇
基础医学   6950篇
口腔科学   1914篇
临床医学   4387篇
内科学   15642篇
皮肤病学   1115篇
神经病学   5201篇
特种医学   1823篇
外科学   8385篇
综合类   200篇
一般理论   10篇
预防医学   3014篇
眼科学   824篇
药学   3287篇
中国医学   130篇
肿瘤学   4163篇
  2023年   372篇
  2022年   885篇
  2021年   1699篇
  2020年   932篇
  2019年   1321篇
  2018年   1777篇
  2017年   1191篇
  2016年   1310篇
  2015年   1523篇
  2014年   2124篇
  2013年   2799篇
  2012年   4248篇
  2011年   4297篇
  2010年   2404篇
  2009年   2104篇
  2008年   3634篇
  2007年   3784篇
  2006年   3497篇
  2005年   3436篇
  2004年   3116篇
  2003年   2819篇
  2002年   2540篇
  2001年   668篇
  2000年   595篇
  1999年   705篇
  1998年   507篇
  1997年   424篇
  1996年   387篇
  1995年   362篇
  1994年   302篇
  1993年   241篇
  1992年   412篇
  1991年   359篇
  1990年   367篇
  1989年   333篇
  1988年   252篇
  1987年   219篇
  1986年   256篇
  1985年   276篇
  1984年   192篇
  1983年   162篇
  1982年   161篇
  1981年   112篇
  1980年   113篇
  1979年   146篇
  1978年   85篇
  1977年   92篇
  1976年   87篇
  1975年   80篇
  1973年   81篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
OBJECTIVES: The aim of this study is to evaluate the effect of ZnSO(4) addition to a conventional glass ionomer and a resin-modified glass ionomer on solubility, flexural strength, zinc and fluoride (F) release, and Streptococcus mutans growth inhibition. METHODS: 5 or 10% ZnSO(4) was added to Vitremer and Ketac-Fil powders. Solubility test was performed based on ISO 7489. Flexural strength was determined by 3-point bending test based on ISO 4049. Zn release/uptake was determined by atomic emission spectrometry; F release/uptake was measured using a F-specific electrode. Both release measurements were performed for 15 d before and 15 d after recharging. Antibacterial test was conducted according to agar plate methods against S. mutans, by measuring the inhibition halos in 1-h and 15-d specimens. Data were analyzed by ANOVA. RESULTS: Solubility increased with higher ZnSO(4) content, but remained below the ISO 7489 limit. Flexural strength was not affected by ZnSO(4) addition, and Vitremer performed better than Ketac-Fil. The control materials released no zinc. Vitremer with 10% ZnSO(4) released the highest amount of zinc. Fluoride release was similar for Ketac-Fil and Vitremer. In both cases, the highest amounts were released in the first 24 h. The growth inhibition halo of S. mutans was similar for both materials with highest content of ZnSO(4) and occurred only with 1-h specimens. SIGNIFICANCE: Zinc addition decreased microorganisms growth and improved fluoride release, without significantly affecting the materials' flexural strength and solubility.  相似文献   
3.
BACKGROUND: The activity and isoenzyme composition of N-acetyl-beta-D-hexosaminidase (EC.3.2.1.52) in seminal plasma of fertile and infertile men have been evaluated. However, no data are available on the isoenzyme content in seminal plasma from patients with secretory azoospermia. METHODS: The activity and isoenzyme composition of seminal plasma from 15 normozoospermic controls and 18 patients with secretory azoospermia were determined by fluorimetric methods. 4-Methylumbelliferil-2-acetamido-2-deoxy-beta-D-glucopyranoside and 4-methylumbelliferil-2-acetamido-2-deoxy-beta-D-glucopyranoside-6-sulfate were used as fluorigenic substrates. Receiver-operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic efficiency of the assays. RESULTS: No significant difference was found in total enzyme activity between the two groups, while isoenzyme A activity was significantly lower (p=0.004) and the ratio between total enzyme activity and isoenzyme A activity was significantly higher (p=0.04) in azoospermic patients compared to controls. The diagnostic efficiency of these evaluations was low (< or =75.7%). CONCLUSIONS: Our findings show that the isoenzyme composition of N-acetyl-beta-D-hexosaminidase in seminal plasma from patients with secretory azoospermia is significantly different from controls, but this difference does not represent a useful marker of secretory azoospermia. The fluorimetric assays are simple and rapid methods for evaluating the isoenzyme composition.  相似文献   
4.
5.
BACKGROUND: To investigate the degree of systemic inflammation, as reflected by serum C-reactive protein (CRP) levels, associated with controlled ovarian hyperstimulation (COH) with human chorionic gonadotropin (hCG) or gonadotropin-releasing hormone (GnRH) agonist for the induction of final follicular maturation. DESIGN: Prospective, observational study. SETTING: An in vitro fertilization (IVF) unit of an academic medical center. PATIENTS: Twenty-four women undergoing COH and IVF with the flexible GnRH antagonist protocol were prospectively assigned to receive hCG or GnRH agonist for the induction of final follicular maturation. METHODS: Blood was drawn three times during COH for measurement of sex-steroid and CRP levels: the day on which adequate suppression was obtained (Day-0); the day of or prior to administration of hCG (Day-hCG); and (3) the day of ovum pick-up (Day-OPU). Levels were compared among the three time points in the two groups. RESULTS: No between-group differences were observed in terms of patient age, gonadotropin dosage, duration of stimulation or number of oocytes retrieved. Serum CRP levels were significantly higher on Day-OPU than on Day-hCG and Day-0, but the difference was significant only in the hCG group (p<0.03 for both). The percentage change in CRP levels after hCG administration (Day-OPU vs. Day-hCG) (96%) was higher than that after GnRH administration (23%). CONCLUSION: Administration of GnRH agonist in patients undergoing COH for IVF yields a lesser degree of systemic inflammation, as reflected by CRP levels, than hCG.  相似文献   
6.
BACKGROUND: In the central nervous system, several neuropeptides are believed to be involved in the pathophysiology of Alzheimer's disease (AD). Indeed, previous studies have documented that glucagon-like peptide 1 (GLP-1) possesses neurotropic properties and can reduce amyloid-beta peptide levels in the brain in vivo. Moreover, the concentrations of neuropeptide Y (NPY) seem to be altered in the cerebrospinal fluid of patients with AD and in subjects with major depression. Finally, among the modifications induced by aging, a dysregulation of the ghrelin-growth hormone (GH) system has been reported. METHODS: We investigated the plasma concentrations of these neuropeptides in 14 subjects with AD. Data obtained from these patients were compared with data from an age- and weight-matched healthy group. RESULTS: No significant differences were found between the two groups in relation to plasma levels of GLP-1, NPY, ghrelin and GH. Peripheral NPY concentrations were positively correlated with ghrelin levels in both groups, and with plasma GLP-1 concentration only in controls. CONCLUSION: On the basis of our results, peripheral levels of these neuropeptides seem not to serve as biochemical markers of AD.  相似文献   
7.
The aim of the present study was to investigate the effect of gonadotropin-releasing hormone (GnRH) antagonists (GnRH-ant) on follicular fluid (FF) insulin-like growth factor-I (IGF-I) and FF vascular endothelial growth factor (VEGF) levels. Sixty women undergoing assisted reproduction were randomized and assigned to two different GnRH analog regimens: GnRH agonist (GnRH-a) and GnRH-ant. FF VEGF and FF IGF-I concentrations were significantly increased in the patients treated with GnRH-ant (p < 0.001). In the same patients we observed a statistically significant reduction in serum luteinizing hormone (LH) and estradiol (E2) levels (p < 0.001 and p < 0.05, respectively), FF E2 and FF androstenedione levels (p < 0.05 and p < 0.001, respectively), as well as a reduction in the number of pregnancies although this was not statistically significant. In the GnRH-ant group, FF VEGF levels were positively correlated with FF IGF-I levels, and both were negatively correlated with serum LH levels. The increase in FF IGF-I and FF VEGF levels in women treated with GnRH-ant could be explained by a deleterious follicular environment in response to profound suppression of LH and E2 levels.  相似文献   
8.
Eledoisin has been tried as a possible treatment for dry eye based on the hypothesis that it pharmacologically stimulates tear secretion when topically applied to the eye. To determine if topically applied eledoisin pharmacologically stimulates orbital lacrimal secretion, the orbital lacrimal gland excretory duct of normal rabbits was cannulated, and eledoisin was applied topically with and without prior administration of proparacaine. To determine if topically applied eledoisin stimulated accessory lacrimal gland secretion, isotonic buffer with and without eledoisin was tested in a rabbit model with only accessory lacrimal tissue remaining after the administration of proparacaine. Topically applied eledoisin did not pharmacologically stimulate lacrimal secretion but rather increased lacrimal gland secretion only in non-anesthetized eyes through a sensory reflex mechanism that is blocked by proparacaine.  相似文献   
9.
An endoscopic endonasal approach was performed to remove an intra-suprasellar Rathke's cleft cyst. Rathke's cleft cyst are benign lesions, rarely diagnosed because they are often asymptomatic. To the best of our knowledge, at least 475 cases of Rathke's cleft cysts have been reported. They seem to arise from remnants of Rathke's pouch, an invagination of the stomodeum. A 52-year-old woman, complaining of bilateral frontal headaches, was operated on by using an endoscopic endonasal approach, for an intra-suprasellar tumor. The pre-operative diagnosis was non-functioning pituitary adenoma. Intra-operatively a creamy-coloured viscous tissue was found. After the removal of the cyst contents and of the capsule, the suprasellar structures were seen well. The chiasmatic cistern, the chiasm, the pituitary stalk and the pituitary gland were visualized with 0 and 30 degree endoscopes. The pathological findings showed a well-differentiated cuboidal epithelium. The diagnosis was Rathke's cleft cyst. No post-operative complications were observed. The endoscopic technique was particularly suitable in this case, both for the Rathke's cleft features and for an excellent outcome. The Rathke's cleft cyst was easily removed by suction and the cyst wall was entirely removed with curettes and pituitary punches. The hypophysis was distinguished from the cyst and was preserved. The surgical manoeuvres were all done under direct visual control. The absence of nasal packing and of breathing difficulties made comfortable the post-operative outcome. Thus, the endoscopic endonasal approach can be considered the favourite technique in case of either intra- and/or suprasellar Rathke's cleft cysts.  相似文献   
10.
Female rats consistently show a pattern of differences in defensive behaviors compared to males which parallel the effects of exposure to a nonpainful threat stimulus (cat or cat odor) in the same tests and measures. These indications of greater defensiveness for females are particularly common in situations involving potential, as opposed to actual and present, threat, a factor which probably also reflects ceiling or floor effects in situations involving very intense defensiveness. In addition, pharmacological studies indicate sex differences in the effects of selective serotonin (5-HT) receptor agonists and antagonists on defensive responding. These findings indicate that sex effects must be considered in studies of the pharmacological control of defensive behaviors, and suggest that responsivity to sex effects may be an additional criterion for the suitability of animal models of anxiety.  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