全文获取类型
收费全文 | 5133篇 |
免费 | 249篇 |
国内免费 | 47篇 |
专业分类
耳鼻咽喉 | 62篇 |
儿科学 | 253篇 |
妇产科学 | 169篇 |
基础医学 | 484篇 |
口腔科学 | 222篇 |
临床医学 | 403篇 |
内科学 | 1186篇 |
皮肤病学 | 100篇 |
神经病学 | 296篇 |
特种医学 | 230篇 |
外科学 | 665篇 |
综合类 | 256篇 |
一般理论 | 18篇 |
预防医学 | 233篇 |
眼科学 | 150篇 |
药学 | 393篇 |
1篇 | |
中国医学 | 88篇 |
肿瘤学 | 220篇 |
出版年
2023年 | 40篇 |
2022年 | 165篇 |
2021年 | 255篇 |
2020年 | 115篇 |
2019年 | 144篇 |
2018年 | 196篇 |
2017年 | 97篇 |
2016年 | 117篇 |
2015年 | 186篇 |
2014年 | 203篇 |
2013年 | 248篇 |
2012年 | 351篇 |
2011年 | 419篇 |
2010年 | 234篇 |
2009年 | 212篇 |
2008年 | 309篇 |
2007年 | 250篇 |
2006年 | 268篇 |
2005年 | 246篇 |
2004年 | 222篇 |
2003年 | 181篇 |
2002年 | 202篇 |
2001年 | 57篇 |
2000年 | 23篇 |
1999年 | 44篇 |
1998年 | 58篇 |
1997年 | 53篇 |
1996年 | 63篇 |
1995年 | 50篇 |
1994年 | 51篇 |
1993年 | 30篇 |
1992年 | 19篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 36篇 |
1988年 | 34篇 |
1987年 | 24篇 |
1986年 | 25篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有5429条查询结果,搜索用时 15 毫秒
31.
Erythropoietin and erythropoietin receptor expression in head and neck cancer: relationship to tumor hypoxia. 总被引:7,自引:0,他引:7
Murat O Arcasoy Khalid Amin Shu-Chuan Chou Zishan A Haroon Mahesh Varia James A Raleigh 《Clinical cancer research》2005,11(1):20-27
PURPOSE: Erythropoietin, an oxygen-regulated glycoprotein hormone, is a hematopoietic cytokine that stimulates erythropoiesis by binding to its cellular receptor [erythropoietin receptor (EPOR)]. The recombinant form of human erythropoietin is used to prevent or treat anemia in cancer patients. However, in a recent randomized, placebo-controlled trial involving patients receiving curative radiotherapy for squamous cell carcinoma of the head and neck, erythropoietin treatment was associated with poorer locoregional progression-free survival. The purpose of our study was to determine whether EPOR and its ligand erythropoietin are expressed in primary head and neck cancer. We also investigated the hypothesis that erythropoietin expression in malignant cells may be associated with the presence of tumor hypoxia, an important factor involved in resistance to radiation treatment, tumor aggressiveness, and poor prognosis. EXPERIMENTAL DESIGN: Twenty-one patients received an i.v. infusion of the hypoxia marker pimonidazole hydrochloride before multiple tumor biopsies. Contiguous sections from 74 biopsies were analyzed by immunohistochemistry for EPOR and erythropoietin expression and pimonidazole binding. RESULTS: EPOR expression was present in tumor cells in 97% of the biopsies. Coexpression of erythropoietin was observed in 90% of biopsies. Erythropoietin and pimonidazole adduct staining did not always colocalize within tumors, but there was a significant positive correlation between levels of microregional erythropoietin expression and pimonidazole binding. CONCLUSIONS: The coexpression of erythropoietin and EPOR in tumor cells suggests that erythropoietin may potentially function as an autocrine or paracrine factor in head and neck cancer. The expression of the hypoxia-inducible protein erythropoietin in tumor cells correlates with levels of tumor hypoxia. 相似文献
32.
33.
Jamal M. Arif Mohammed Kunhi Yunus M. Siddiqui Khalid A. El Sayed Khaled Y. Orabi Amal Al-Hazzani Mohammed N. Al-Ahdal Fahad M. Al-Khodairy 《Medicinal chemistry research》2004,13(6-7):553-562
In the present study, two of the probable an umor marine compounds, manzamine A and sarcophine, were screened using benzo[a]pyrene (BP)-derived DNA adduct formation in MCF-7 cells as intermediary biomarker. Briefly, MCF-7 cells were treated with
the compounds for 24 h followed by treatment with BP (0.5 μM). After 24h incubation, cellular DNA was isolated and analyzed
for BP-derived DNA adducts by 32P-postlabeling technique. Manzamine A and sarcophine increased the BP-DNA adducts by 2 to 4-folds. Further, manzamine A (50
μM) substantially down regulated the expression of p53 while sarcophine (50 μM) slightly induced the level of p21. The residual
DNA repair ability was almost completely abolished by manzamine A while sarcophine was ineffective. Based on our preliminary
results, these compounds may be classified as potential genotoxic. 相似文献
34.
The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2, SARS2) remains a great global health threat and demands identification of more effective and SARS2-targeted antiviral drugs, even with successful development of anti-SARS2 vaccines. Viral replicons have proven to be a rapid, safe, and readily scalable platform for high-throughput screening, identification, and evaluation of antiviral drugs against positive-stranded RNA viruses. In the study, we report a unique robust HIV long terminal repeat (LTR)/T7 dual-promoter-driven and dual-reporter firefly luciferase (fLuc) and green fluorescent protein (GFP)-expressing SARS2 replicon. The genomic organization of the replicon was designed with quite a few features that were to ensure the replication fidelity of the replicon, to maximize the expression of the full-length replicon, and to offer the monitoring flexibility of the replicon replication. We showed the success of the construction of the replicon and expression of reporter genes fLuc and GFP and SARS structural N from the replicon DNA or the RNA that was in vitro transcribed from the replicon DNA. We also showed detection of the negative-stranded genomic RNA (gRNA) and subgenomic RNA (sgRNA) intermediates, a hallmark of replication of positive-stranded RNA viruses from the replicon. Lastly, we showed that expression of the reporter genes, N gene, gRNA, and sgRNA from the replicon was sensitive to inhibition by Remdesivir. Taken together, our results support use of the replicon for identification of anti-SARS2 drugs and development of new anti-SARS strategies targeted at the step of virus replication. 相似文献
35.
36.
Nehal Elkhoshkhany Samir Marzouk Mohammed El-Sherbiny Heba Ibrahim Bozena Burtan-Gwizdala Mohammed S. Alqahtani Khalid I. Hussien Manuela Reben El Sayed Yousef 《Materials》2022,15(15)
A novel series of glass, consisting of B2O3, Bi2O3, TeO2, and TiO2 (BBTT) containing rare earth oxide RE2O3, where RE is La, Ce, Sm, Er, and Yb, was prepared. We investigated the structural, optical, and gamma attenuation properties of the resultant glass. The optical energy bands, the linear refractive indices, the molar refractions, the metallization criteria, and the optical basicity were all determined for the prepared glass. Furthermore, physical parameters such as the density, the molar volume, the oxygen molar volume, and the oxygen packing density of the prepared glass, were computed. Both the values of density and optical energy of the prepared glass increased in the order of La2O3, Ce2O3, Sm2O3, Er2O3, and then Yb2O3. In addition, the glass doped with Yb2O3 had the lowest refractive index, electronic polarizability, and optical basicity values compared with the other prepared glass. The structures of the prepared glass were investigated by the deconvolution of infrared spectroscopy, which determined that TeO4, TeO3, BO4, BO3, BiO6, and TiO4 units had formed. Furthermore, the structural changes in glass are related to the ratio of the intensity of TeO4/TeO3, depending on the type of rare earth. It is also clarified that the resultant glass samples are good attenuators against low-energy radiation, especially those that modified by Yb2O3, which exhibited superior shielding efficiency at energies of 622, 1170, and 1330 keV. The optical and gamma ray spectroscopy results of the prepared glass show that it is a good candidate for nonlinear optical fibers, laser solid material, and optical shielding protection. 相似文献
37.
Zafar Ali Shah Khalid Khan Zafar Iqbal Tariq Masood Hassan A. Hemeg Abdur Rauf 《Annals of medicine》2022,54(1):2102
BackgroundPenicillium produces a wide range of structurally diverse metabolites with significant pharmacological impacts in medicine and agriculture. For the first time, a complete metabolome of Penicillium claviforme (P. claviforme) (FBP-DNA-1205) was studied alongside pharmacological research in this study.MethodsThe metabolic profile of P. claviforme fermented on Potato Dextrose Broth (PDB) was investigated in this work. The complete metabolomics studies of fungus were performed using GC-MS and LC-MS-QTOF techniques. An in vitro model was utilised to study the cytotoxic and antioxidant activities, while an in vivo model was employed to investigate the antinociceptive and acute toxicity activities. Molecular Operating Environment (MOE) software was used for molecular docking analysis.ResultsGC-MS study showed the presence of alkanes, fatty acids, esters, azo and alcoholic compounds. Maculosin, obtain, phalluside, quinoline, 4,4’-diaminostilbene, funaltrexamine, amobarbital, and fraxetin were among the secondary metabolites identified using the LC-MS-QTOF technique. The n-hexane fraction of P. claviforme displayed significant cytotoxic activity in vitro, with an LD50 value of 92.22 µgml−1. The antinociceptive effects in vivo were dose-dependent significantly (p < .001). Interestingly, during the 72 h of investigation, no acute toxicity was demonstrated. In addition, a docking study of tentatively identified metabolites against the inflammatory enzyme (COX-2) supported the antinociceptive effect in an in silico model.ConclusionMetabolic profile of P. claviforme shows the presence of biologically relevant compounds in ethyl acetate extract. In addition, P. claviforme exhibits substantial antioxidant and cytotoxic activities in an in vitro model as well as antinociceptive activity in an in vivo model. The antinociceptive action is also supported by a molecular docking study. This research has opened up new possibilities in the disciplines of mycology, agriculture, and pharmaceutics.
Key messages
- The first time explored complete metabolome through GC-MS and LC-MS-QTOF.
- Both in vivo & in vitro pharmacological investigation of P. claviforme.
- In silico molecular docking of LC-MS-QTOF metabolites.
38.
Abdel Bar FM Zaghloul AM Bachawal SV Sylvester PW Ahmad KF El Sayed KA 《Journal of natural products》2008,71(10):1787-1790
Three new 28-norlupane triterpenes, 28-norlup-20(29)-en-3beta-hydroxy-17beta-hydroperoxide (1), 28-norlup-20(29)-en-3beta-hydroxy-17alpha-hydroperoxide (2), and 20 S-17beta,29-epoxy-28-norlupan-3beta-ol (3), were isolated from the leaves of Melaleuca ericifolia along with eight known pentacyclic triterpenes. The structures of the new compounds were elucidated by spectroscopic methods including 1D and 2D NMR spectroscopy and mass spectrometry. The isolated triterpenes were evaluated for antiproliferative activity against the malignant +SA mammary epithelial cell line. 相似文献
39.
Antiosteoporotic chemical constituents from Er-Xian Decoction, a traditional Chinese herbal formula 总被引:2,自引:0,他引:2
AIM OF THE STUDY: Er Xian Decoction (EXD), a traditional Chinese medicine formula, has long been used for the treatment of osteoporosis and menopausal syndrome in China. The present study was designed to investigate the antiosteoporotic constituents of EXD, and evaluate their antiosteoporotic effects in ovariectomized rats. MATERIALS AND METHODS: Osteoblasts in neonatal calvaria cultures and osteoclasts derived from rat marrow cells were used to bioactivity-guided screen the active constituents. The proliferation of osteoblast was assayed by MTT methods. The activity of ALP and TRAP was measured by p- nitrophenyl sodium phosphate assay. The antiosteoporotic effects of icariin (1), anemarsaponin B II (8) and berberine (6) were verified by using OVX rats model. The bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry using the small animal scan mode. The undecalcified longitudinal proximal tibial metaphysical (PTM) sections were cut and stained for the bone histomorphometric analysis. RESULTS: Bioactivity-guided fractionation has led to the successful isolation of antiosteoporotic constituents, i.e., icariin (1), icariside I (2), baohuoside I (3), mangiferin (4), neomangiferin (5), berberine (6), anemarsaponin B (7), anemarsaponin BII (8), anemarsaponin C (9), anemarrhenasaponin I (10), rubiadin-1-methyl ether (11) and obaculactone (12) from EXD. Further study showed that icariin (1), anemarsaponin BII (8) and berberine (6) increased the BMD in ovariectomized rats, and icariin (1) not only increased the bone formation, but also inhibited bone resorption; anemarsaponin BII (8) mainly increased bone formation and berberine (6) only inhibited the bone resorption in ovariectomized rats. CONCLUSION: Our findings demonstrate that multiple ingredients are responsible for antiosteoporotic activity in traditional Chinese medicine formula Er-Xian decoction. 相似文献
40.
BACKGROUND: The incidence of early hypocalcemia in extremely low birthweight (ELBW) infants is unknown because the distribution of serum calcium values in this population is not defined. OBJECTIVE: To determine the range of serum calcium values in ELBW infants during the first 48 h of life and the risks associated with low values. DESIGN/METHODS: Retrospective analysis of all ELBW infants admitted on day 1 of life from April 2004 to October 2006. Demographic variables, therapy, serum calcium (Ca), pH, albumin, and blood ionized Ca were recorded. RESULTS: There were 381 Ca levels obtained from 111 patients. Mean Ca was 6.90 mg/dL (1.73 mmol/L) (5(th)-95(th) percentile: 5.16-8.80). Ca levels rose after 24 h of life. Almost one quarter (23.1%) of the Ca levels were low by current standards. The majority of subjects (59.9%) had at least one hypocalcemic value. CONCLUSIONS: Serum Ca values are lower in ELBW infants and inconsequential. Thus, hypocalcemia should be re-defined for ELBW infants. 相似文献