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   13044篇
  免费   511篇
  国内免费   58篇
耳鼻咽喉   153篇
儿科学   173篇
妇产科学   142篇
基础医学   1607篇
口腔科学   250篇
临床医学   768篇
内科学   3166篇
皮肤病学   231篇
神经病学   1154篇
特种医学   646篇
外科学   1934篇
综合类   56篇
一般理论   1篇
预防医学   361篇
眼科学   439篇
药学   921篇
中国医学   19篇
肿瘤学   1592篇
  2023年   45篇
  2022年   119篇
  2021年   201篇
  2020年   82篇
  2019年   149篇
  2018年   229篇
  2017年   152篇
  2016年   248篇
  2015年   205篇
  2014年   301篇
  2013年   391篇
  2012年   625篇
  2011年   703篇
  2010年   398篇
  2009年   348篇
  2008年   691篇
  2007年   758篇
  2006年   799篇
  2005年   825篇
  2004年   797篇
  2003年   760篇
  2002年   837篇
  2001年   333篇
  2000年   292篇
  1999年   306篇
  1998年   226篇
  1997年   205篇
  1996年   169篇
  1995年   156篇
  1994年   148篇
  1993年   137篇
  1992年   171篇
  1991年   174篇
  1990年   160篇
  1989年   158篇
  1988年   158篇
  1987年   125篇
  1986年   126篇
  1985年   102篇
  1984年   100篇
  1983年   82篇
  1982年   62篇
  1981年   61篇
  1980年   48篇
  1979年   55篇
  1978年   47篇
  1977年   49篇
  1976年   36篇
  1975年   33篇
  1968年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The aim of this study was to clarify the worldwide residual levels of organochloride compounds, such as BHC and DDT, which were reportedly concentrated in animal tissues by biological food chains. As a part of the investigation of endocrine disrupting chemicals (EDCs), we had a chance to measure the level of these compounds in Hungarian canned foods. Seven kinds of canned foods were purchased at a market in Budapest, Hungary, and the concentrations of eighteen organochloride compounds (α-BHC; β-BHC; γ-BHC; δ-BHC; p,p'-DDT; p,p'-DDE; p,p'-DDD; o,p'-DDT; heptachlor; heptachlor-epoxide; aldrin; dieldrin; endrin; oxychlordane; trans-chlordane; cischlordane; trans-nonachlor; and cis-nonachlor) were measured. Other than DDT and its metabolites, none of the EDCs were detected (levels <0.4 ppb). DDT and its metabolites, however, were detected in fish, meat and chicken liver pate. One of the DDT metabolites was detected quite frequently: p,p'-DDE was detected at a level of 1.8 ppb in fish soup concentrate, 2.3 ppb in Hungarian luncheon meat, 0.5 ppb in special luncheon meat, and 0.6 ppb in chicken liver pate. Of eighteen organochloride compounds examined, only DDT and its metabolites were detected in fish, animal meat, and animal liver. It is suggested that the DDT contamination in fish and meat is worldwide even after the ban of its use.  相似文献   
972.
The purpose of this study is to determine the relationship between lifestyle and change of cardiovascular risk factors based on a five-year follow up. The subjects were 307 employees participating in annual health check-ups in Tokyo, Japan from 1998 to 2003. Personal health check-up data were collected on their systolic/diastolic blood pressure (SBP/DBP), serum total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), fasting serum glucose (FSG), uric acid (UA), body mass index (BMI), questionnaire on medication history and Breslow's lifestyle. Over five years, cardiovascular risk factors such as SBP/DBP, TC, TG, FBG, UA and BMI have become worse; however, some of these risk factors were significantly different after 5 yr among lifestyle groups. TG in the poor lifestyle group was significantly higher than in good or moderate lifestyle groups after adjusting for age in men. In women, SBP and BMI in poor lifestyle group were significantly higher than those in good or moderate lifestyle groups after adjusting for age and baseline values. These results show that aging is the major influencing factor of cardiovascular risk factor deterioration. At the same time, lifestyle conditions are related to changes in some cardiovascular risk factors among Japanese employees.  相似文献   
973.
Purpose. The applicability of isothermal microcalorimetry (IMC) for evaluating enthalpy relaxation and recovery processes of amorphous material was assessed. Methods. A maltose-based formulation was prepared by freeze-dry method. Differential scanning calorimetry (DSC) was used to investigate its glass transition and relaxation behaviors. IMC was applied to quantitatively analyze the relaxation and the recovery processes. The IMC data were analyzed using a derivative of the Kohlrausch-Williams-Watts equation. Results. The glass transition temperature of the formulation and its fictive temperature stored at 15°C for 1 year were 62 and 32°C, respectively. DSC study showed that annealing below the fictive temperature increased the enthalpy recovery, but it was decreased by annealing at higher temperatures. IMC enabled direct observation of the heat flow during both the relaxation and the recovery processes. The decay constant for the recovery process (recovery time) was much smaller and less sensitive to the temperature than that for the relaxation process (relaxation time). Conclusions. IMC was successfully used to obtain quantitative information on both relaxation and recovery processes of amorphous material. The relaxation parameters obtained by this method could explain the thermodynamic behavior of the formulation.  相似文献   
974.

Background

We evaluated the effectiveness of visual feedback (VF) on radiotherapy with deep inspiration breath-holding (DIBH), and reviewed the dose for organs at risk (OARs).

Methods

Respiratory motions during DIBH for 15 s were monitored during planning computed tomography (CT)-scanning and simulation for 40 patients after breast-conserving surgery from June 2007 to February 2008. For 22 of 40 patients, a goggle-type liquid crystal display monitor was used for VF. The opposing tangential field was planned. The prescribed dose was 50.0 Gy in 25 fractions.

Results

The mean differences of the chest wall respiratory movement in DIBH between planning CT-scanning and simulation were 4.7?±?2.6 mm for the patients without VF and 1.0?±?0.9 mm for those with VF (p?<?0.01). The mean chest wall excursion as a whole in DIBH using VF (2.0?±?1.0 mm) was smaller than in those without VF (4.1?±?2.4 mm) (p?<?0.01). According to reproducibility and stability parameters, 4 mm was added as a posterior margin to the clinical target volume for RT with VF, and 10 mm for those without VF. The mean heart doses were 1.3?±?0.5 Gy with VF and 2.4?±?1.1 Gy without VF (p?<?0.01). Mean dose and max dose of right breast were significantly reduced in procedures with VF use vs. in those without VF (p?<?0.01 and <?0.01, respectively).

Conclusions

VF increases the accuracy of postoperative radiotherapy with DIBH, and also helps reduce the dose for OARs.
  相似文献   
975.
BACKGROUND: Infection of the gastric mucosa by helicobacter pylori is primarily responsible for gastritis, gastric ulcer, adenocarcinoma, and lymphoproliferative disorders. H. pylori appears to accelerate apoptosis and the proliferation of the gastric epithelium directly or indirectly. To precisely assess the proliferative and apoptotic profile of .H pylori-infected gastric mucosa, a quantitative imaging system is now required. METHODS: Fifty-two patients with H. pylori gastritis were the subjects of the study. Biopsy materials were taken from at least two sites (usually three to five sites) including the antrum and corpus. The grade of gastritis was evaluated by the updated Sydney System. The proliferative and apoptotic profile was examined by Ki-67 immunohistochemistry and by a terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling method. In addition, Ki-67-positive cells were quantitated by an image processor for analytical pathology (IPAP) system. RESULTS: H. pylori density and polymorphonuclear neutrophil activity were significantly decreased after H. pylori eradication ( P< 0.0001). Chronic inflammation (P< 0.0001) and lymphoid follicle numbers ( P < 0.0005) were also significantly decreased after the eradication. Glandular atrophy and intestinal metaplasia were slightly decreased after eradication, but the decrease did not reach the significant level. the Ki-67 labeling index was significantly decreased after the eradication P< 0.0001). The apoptosis index was also decreased after the eradication, but this decrease did not reach the significant level ( P = 0.06). CONCLUSION: our data suggest that the activation of proliferative cells and induction of apoptosis in the gastric mucosa is a response to H. pylori-induced mucosal damage. Moreover, IPAP may be a useful technology for evaluating the results of immunohistochemistry, and it could provide quantitative and reliable data for studying H. pylori gastritis.  相似文献   
976.
PURPOSE: The association of BRCA2 polymorphisms at codon 372 [Asn (N)/His (H)]and codon 784 [Met (M)/Val (V)] with breast cancer risk was evaluated in Japanese women. In addition, the prognostic significance of these polymorphisms was studied in breast cancer patients. EXPERIMENTAL DESIGN: A case-control study was conducted to examine the association of the BRCA2 N/H372 polymorphism and M/V 784 polymorphism with breast cancer risk (cases = 149, controls = 154). The prognostic significance of these polymorphisms was evaluated in 139 patients with primary breast cancer. RESULTS: No significant association was observed between the N/H372 polymorphism and breast cancer risk. In contrast, a significant increase in breast cancer risk (odds ratio, 2.03; 95% confidence interval, 1.07-3.87) was observed in carriers of the variant allele (V784) of the M/V784 polymorphism as compared with noncarriers after adjustment for the classical risk factors, age, family history, parity, body mass index, and so forth. Among breast cancer patients, various clinicopathological parameters including menopausal status, tumor size, lymph node status, histological grade, and estrogen-receptor status were not significantly different between the carriers and noncarriers of the variant allele with regard to both N/H372 and M/V784 polymorphisms. The N/H 372 polymorphism was not significantly associated with patient prognosis. On the other hand, breast cancer patients carrying the variant allele of M/V784 polymorphism showed a significantly (P = 0.014) lower 3-year disease-free survival rate (63%) than noncarriers (92%). Multivariate analysis has revealed that the M/V784 polymorphism is a significant prognostic factor, being independent of the other conventional prognostic factors such as lymph node status and estrogen receptor status. CONCLUSION: These results suggest that the M/V784 polymorphism, but not the N/H372 polymorphism, would be useful in the selection of women at high risk for developing breast cancer and would also serve as a clinically useful prognostic factor in breast cancer patients.  相似文献   
977.
Bisphosphonates inhibit osteoclastic bone resorption and are being used as treatment for bone metastases from breast cancer. Intravenous bisphosphonate therapy can significantly reduce skeletal related events (SREs) when administered concurrently with chemotherapy or endocrine therapy. In addition, intravenous bisphosphonate monotherapy is also able to alleviate cancer induced bone pain, and to improve bone metastases in some patients. Oral bisphosphonates are not routinely used for the treatment of bone metastases due to their low bioavailability. However, minodronate, a bisphosphonate 100-fold more potent than pamidronate, is now in phase II clinical studies in Japan, and may alter the role of oral bisphosphonates in the treatment of bone metastasis from breast cancer. The ASCO guidelines recommend that patients with osteolytic bone metastases be treated not with bisphosphonate monotherapy, but with concurrent bisphosphonate and systemic therapy. In addition, it is also recommended that current standards of care for cancer pain, analgesics and radiotherapy, should not be replaced with bisphosphonate therapy.  相似文献   
978.
979.
PURPOSE: We compared the therapeutic usefulness of doxifluridine (5'-DFUR) alone and a combination of 5'-DFUR plus cyclophosphamide (CPM), both of which are considered effective against advanced and recurrent breast cancer, to determine which treatment is more beneficial as postoperative adjuvant chemotherapy. PATIENTS AND METHODS: A total of 1,131 women with node-positive primary breast cancer were randomly assigned after primary surgery to receive 5'-DFUR alone or 5'-DFUR plus CPM. All patients initially received 5'-DFUR in an oral dose of 1,200 mg/d for 4 weeks, starting 4 weeks after surgery. Chemotherapy was then not given for 2 weeks. Patients in the 5'-DFUR group subsequently received five 4-week cycles of treatment consisting of oral 5'-DFUR (1,200 mg/d) for the first 2 weeks and no chemotherapy for the next 2 weeks. Those assigned to the 5'-DFUR plus CPM group also received oral CPM 100 mg/d for the first 2 weeks and no chemotherapy for the next 2 weeks. Women 50 years or older concurrently received 20 mg/d of tamoxifen for 2 years in both groups. RESULTS: Of the 1,088 eligible women, 546 were assigned to receive 5'-DFUR alone and 542 were assigned to receive 5'-DFUR plus CPM. Overall disease-free survival was significantly better in women who received 5'-DFUR plus CPM than in those who received 5'-DFUR alone (log-rank test, P =.021). Toxic effects occurred in 20.0% of patients (109 of 546) in the 5'-DFUR group and 32.3% of patients (175 of 542) in the 5'-DFUR plus CPM group (chi(2) test, P <.001). CONCLUSION: Combination therapy with 5'-DFUR plus CPM is more effective in preventing recurrence than 5'-DFUR alone.  相似文献   
980.
Meta-analysis of 5 studies on postoperative breast cancer cases (2 studies on surgery alone vs. tegafur plus uracil (UFT) and 3 studies on tamoxifen (TAM) alone vs. TAM + UFT) were carried out to evaluate the anticancer drug UFT in oral postoperative adjuvant chemotherapy. Of the 1973 patients enrolled, 1898 were eligible and 75 were excluded (exclusion rate 3.8%). There was no bias in major background factors in either the UFT-treated (965) or non-UFT-treated (933) groups. The reduction in the odds of death and the odds of recurrence were 17 +/- 17% (p = 0.33) and 21 +/- 11% (p = 0.060), respectively. Multivariate analysis using Cox's proportional hazards model emphasized the effectiveness of UFT treatment for suppression of recurrence compared with non-treatment with UFT (p = 0.038). Suppression of recurrence was remarkable in the group treated with UFT for 2 years. (the reduction in the odds of recurrence: 23 +/- 11%, p = 0.048) Stratified analysis was applied concerning recurrence, and improved results were obtained in premenopausal cases (the reduction in the odds of recurrence: 33 +/- 11%, p = 0.019). These results suggested that UFT treatment for 2 years was effective as postoperative adjuvant chemotherapy for stage I - IIIA breast cancer for the prolongation of the recurrence-free survival period.  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