全文获取类型
收费全文 | 184900篇 |
免费 | 1872篇 |
国内免费 | 45篇 |
专业分类
耳鼻咽喉 | 1193篇 |
儿科学 | 6939篇 |
妇产科学 | 3248篇 |
基础医学 | 18080篇 |
口腔科学 | 1616篇 |
临床医学 | 13461篇 |
内科学 | 32859篇 |
皮肤病学 | 916篇 |
神经病学 | 17507篇 |
特种医学 | 9134篇 |
外科学 | 29869篇 |
综合类 | 2346篇 |
现状与发展 | 1篇 |
一般理论 | 6篇 |
预防医学 | 18830篇 |
眼科学 | 2925篇 |
药学 | 9980篇 |
中国医学 | 634篇 |
肿瘤学 | 17273篇 |
出版年
2024年 | 24篇 |
2023年 | 148篇 |
2022年 | 247篇 |
2021年 | 513篇 |
2020年 | 327篇 |
2019年 | 489篇 |
2018年 | 22296篇 |
2017年 | 17662篇 |
2016年 | 19819篇 |
2015年 | 1276篇 |
2014年 | 1310篇 |
2013年 | 1327篇 |
2012年 | 7841篇 |
2011年 | 21862篇 |
2010年 | 19241篇 |
2009年 | 11831篇 |
2008年 | 20086篇 |
2007年 | 22260篇 |
2006年 | 1073篇 |
2005年 | 2732篇 |
2004年 | 3818篇 |
2003年 | 4743篇 |
2002年 | 2837篇 |
2001年 | 319篇 |
2000年 | 441篇 |
1999年 | 204篇 |
1998年 | 284篇 |
1997年 | 266篇 |
1996年 | 120篇 |
1995年 | 128篇 |
1994年 | 117篇 |
1993年 | 78篇 |
1992年 | 42篇 |
1991年 | 90篇 |
1990年 | 129篇 |
1989年 | 78篇 |
1988年 | 53篇 |
1987年 | 44篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1984年 | 24篇 |
1983年 | 24篇 |
1982年 | 28篇 |
1980年 | 44篇 |
1938年 | 60篇 |
1937年 | 25篇 |
1935年 | 23篇 |
1934年 | 32篇 |
1932年 | 58篇 |
1930年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Rationale and objective Although many contingencies operating in the natural environment include continuous dimensions of responses and reinforcers,
previous studies of drug self-administration have almost exclusively used discrete dimensions of responses (e.g., a lever
press) and reinforcers (e.g., 1.0 mg/kg/injection cocaine). Therefore, the present study provides an initial examination under
experimental conditions with both responses and reinforcers measured along continuous dimensions.
Materials and methods Cocaine-maintained responding was studied in rats under a novel, hold-down schedule of reinforcement wherein the duration
of the response was directly related to the magnitude of the reinforcer. These conditions were established by activating the
syringe pump when the lever was pressed down and turning the pump off when the lever was released. The concentration of cocaine
available in the syringe was varied across sessions.
Results Cocaine self-administration was readily maintained under these conditions and remained stable across sessions. Responding
was concentration dependent, with the number of responses and total duration of the response inversely related to concentration,
and overall session intake of cocaine was stable across concentrations. In general, the duration of the responses were less
than 0.5 s and did not vary as a function of concentration.
Conclusions Stability of responding under these schedule conditions was acquired quickly. This schedule of reinforcement may be useful
for comparing across drug classes, can be extended for use with other types of responses and reinforcers, and may be more
representative of the natural world where response-reinforcer contingencies are more likely to be experienced along continuous,
rather than discrete, dimensions.
Drake Morgan and Yu Liu contributed equally to this publication. 相似文献
992.
Kamalneet Kaur Vinod Kumar Vikas Beniwal Vikas Kumar Neeraj Kumar Vishal Sharma Sundeep Jaglan 《Medicinal chemistry research》2016,25(10):2237-2249
In search of a new class of biologically active agents, some novel oxazolidinone-thiazole hybrids 4a–m have been synthesized and characterized on the basis of a combined use of infrared, NMR (1H, 13C) spectroscopy, mass spectrometry and elemental analysis. All compounds were evaluated for their antimicrobial, antioxidant and ultraviolet mediated DNA damage protective activity. Among the series, compound 4i emerged as the most potent antimicrobial agent, particularly, against Bacillus subtilis, Candida albicans and Saccharomyces cerevisiae in comparison to the standard drugs, Ciprofloxacin (antibacterial) and Amphotericin-B (antifungal). Other promising antimicrobial agents including the compounds 4f–h. In addition, all compounds 4a–m were found to show very high DNA damage protecting ability under ultraviolet irradiation. The antioxidant study revealed that the compounds 4d and 4j were found as the most potent antioxidants as compared to ascorbic acid, a reference compound considered in the study. 相似文献
993.
Woo JS 《Archives of pharmacal research》2007,30(6):778-784
Granisetron is a selective 5-HT3 receptor antagonist that is used therapeutically for the prevention of vomiting and nausea associated with emetogenic cancer chemotherapy. Although forms of the drug are commercially available for intravenous and oral dosage, there is a need for intranasal delivery formulations in specific patient populations in which the use of these dosage forms may be unfeasible and/or inconvenient. A rapid and specific high-performance liq uid chromatography method with mass spectrometric detection (LC-MS) was developed and validated for the analysis of granisetron in plasma after nasal administration in rats. Granisetron was separated in a reverse-phase C-18 column without interference from other components of plasma. This method involves a rapid assay for the determination of granisetron in a small volume of plasma with a run time of 12 min using ondansetron as an internal standard. Data were acquired in the electrospray ionization (ESI) mode with positive ion detection and application of single ion recording (SIR). Granisetron and ondansetron were detected at m/z values of 313.2 and 294.2, respectively. The method described was found to be suitable for the analysis of all samples collected during preclinical pharmacokinetic investigations of granisetron in rats after nasal administration. To date, the first pharmacokinetic study after intranasal administration of granisetron was performed and some pharmacokinetic parameters were presented in this paper. Granisetron was found to be well absorbed through nasal route and the bioavailability of this drug following nasal administration was comparable with that of intravenous administration. 相似文献
994.
Ali Najafi Ehsan Motaghi Mohammad Javad Hosseini Masoumeh Ghasemi-Pirbaluti 《Inflammopharmacology》2017,25(1):137-145
Ulcerative colitis is a chronic recurrent disease with incomplete treatment options. The current article evaluated the effect of sodium valproate on acetic acid-induced ulcerative colitis in rats. Rats were randomly distributed into six groups including Sham group, colitis control group, sodium valproate treatment groups (50, 100 and 300 mg/kg, i.p.) and dexamethasone-treatment group. Dexamethasone was used as a reference drug. Colitis was induced by intracolonic instillation of 2 mL of 3% acetic acid solution. The efficacy of sodium valproate was evaluated by macroscopical and histopathological scoring systems, hematocrit measurement as well as biochemical analysis including myeloperoxidase (MPO) and pro-inflammatory cytokines assessment. Sodium valproate, particularly with doses of 100 and 300 mg/kg significantly improved weight loss, and macroscopic damage, reduced ulcer area, colon weight, microscopic colitis index and elevated hematocrit level. Biochemical experiments showed elevated levels of colonic MPO activity, interleukin 1β (IL-1β), interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) in colitis control group. Treatment with sodium valproate at the doses of 100 and 300 mg/Kg) decreased the MPO activity and colonic concentrations of IL-1β, IL-6 and TNF-α. The results provide evidence that sodium valproate has a protective effect in acetic acid-induced ulcerative colitis which might be due to its anti-inflammatory activities, and it may be useful in patients with ulcerative colitis. 相似文献
995.
996.
997.
Sequential effects of cadmium on genotoxicity and lipoperoxidation in <Emphasis Type="Italic">Vicia faba</Emphasis> roots 总被引:1,自引:0,他引:1
Kinetics of stress responses to Cd exposure (50, 100 and 200 μM) expanding from 12 to 48 h were studied in roots of hydroponically
cultivated-Vicia faba seedlings. The heavy metal induced toxicity symptoms and growth arrest of Vicia roots gradually to the Cd concentration and duration of the treatment. The intracellular oxidative stress was evaluated with
the H2O2 production. The H2O2 content increased gradually with the sequestered Cd and root growth inhibition. Lipid peroxidation—evidenced by malondialdehyde
(MDA) content and Evans blue uptake—and genotoxicity—evidenced by mitotic index (MI) and micronuclei (MCN) values—were concomitantly
investigated in root tips. By 12 h, root meristematic cells lost 15% of their mitotic activity under 50 or 100 μM Cd treatment
and 50% under 200 μM Cd treatment and led cells with MCN, while the MDA content and Evans blue absorption were not affected.
The loss of membrane integrity occurred subsequently by 24 h. The increase in MDA content in root cells treated with 50, 100
and 200 μM Cd was significantly higher than the control. By 48 h, the MDA content increased 134, 178 or 208% in root cells
treated with 50, 100 and 200 μM Cd, respectively. The Evans blue absorption was also affected by 24 h in roots when treated
with 200 μM Cd and gradually increase by 48 h with the Cd concentration of the treatment. The decrease of mitotic activity
triggered by 12 h was even higher by 24 h and the MI reduced to 44, 56 or 80% compared to the control in the three different
Cd concentrations tested. The different kinetics of early in vivo physiological and cytogenetic responses to Cd might be relevant
to the characterization of its toxicity mechanisms in disrupting primarily the mitosis process. 相似文献
998.
PURPOSE: To compare higher order wavefront aberrations in eyes implanted with acrylic aspherical intraocular lenses (IOLs) with a modified prolate anterior surface with conventional acrylic spherical IOLs by using the optical path difference method. METHODS: In a nonrandomized parallel cohort investigation, 36 eyes of 31 patients implanted with aspherical IOLs (Tecnis ZA9003) and 37 eyes of 23 age-matched patients implanted with spherical IOLs (SENSOR AR40e) were evaluated with a wavefront analyzer (OPD-Scan II) preoperatively and 1 month after surgery. The higher order aberrations for a 4.0-mm pupil diameter were expanded into Zernike's polynomial expression. Coma aberration, spherical aberration, and total higher order aberrations were evaluated as root mean square values. RESULTS: Postoperatively, coma and total higher order aberrations of spherical and aspherical IOLs significantly improved in both eyes. Spherical aberration improved in eyes with aspherical IOLs only (P < 0.01). CONCLUSION: After implantation of acrylic aspherical IOLs, postoperative higher order aberrations were not necessarily lower than after implantation of acrylic spherical IOLs, but compared with levels following implantation of acrylic spherical IOLs, a significant reduction in spherical aberration was achieved. 相似文献
999.
Shimada H Yuzawa M Hirose T Nakashizuka H Hattori T Kazato Y 《Japanese journal of ophthalmology》2008,52(4):282-288
PURPOSE: To compare the pathological findings between multifocal choroiditis with panuveitis (MCP) and punctate inner choroidopathy (PIC). METHODS: Fourteen eyes of 14 patients clinically diagnosed as having MCP or PIC who underwent surgical excision of choroidal neovascularization (CNV) were studied. Immunohistochemical findings of the excised CNV in MCP (eight eyes) and PIC (six eyes) cases were compared. Antibodies against vascular endothelial growth factor (VEGF), CD68, CD3, and CD20 were used as primary antibodies. RESULTS: Expression of VEGF and CD68 in the CNV was observed in all MCF and PIC cases. In three of eight eyes with MCP, intraocular inflammatory findings were found clinically, while immunohistochemical study demonstrated infiltration of CD20-positive B lymphocytes in the CNV. No B lymphocyte infiltration was found in the six eyes with PIC. No differences in pathological findings were found between the five MCP eyes without intraocular inflammation and the six PIC eyes, with all eyes showing no B lymphocyte infiltration. CONCLUSIONS: In MPC cases showing clinical inflammatory findings, infiltration of B lymphocytes was also observed histopathologically, suggesting that the presence of inflammatory cells in the anterior chamber or vitreous body clinically is an indicator of active inflammatory CNV. However, this study clarifies that MCP eyes without intraocular inflammation and PIC eyes are not different in histopathological findings. 相似文献
1000.
Monika Maria Biernat Jolanta Rusiecka-Ziółkowska Elżbieta Piątkowska Iwona Helemejko Paweł Biernat Grażyna Gościniak 《Japanese journal of ophthalmology》2018,62(6):628-633