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   4275篇
  免费   271篇
  国内免费   115篇
耳鼻咽喉   18篇
儿科学   177篇
妇产科学   201篇
基础医学   508篇
口腔科学   94篇
临床医学   451篇
内科学   818篇
皮肤病学   81篇
神经病学   394篇
特种医学   544篇
外国民族医学   1篇
外科学   338篇
综合类   67篇
一般理论   4篇
预防医学   374篇
眼科学   36篇
药学   291篇
中国医学   2篇
肿瘤学   262篇
  2021年   42篇
  2020年   36篇
  2019年   65篇
  2018年   61篇
  2017年   35篇
  2016年   45篇
  2015年   67篇
  2014年   74篇
  2013年   123篇
  2012年   142篇
  2011年   137篇
  2010年   113篇
  2009年   104篇
  2008年   122篇
  2007年   182篇
  2006年   126篇
  2005年   159篇
  2004年   105篇
  2003年   103篇
  2002年   100篇
  2001年   126篇
  2000年   125篇
  1999年   113篇
  1998年   132篇
  1997年   127篇
  1996年   141篇
  1995年   82篇
  1994年   89篇
  1993年   96篇
  1992年   78篇
  1991年   94篇
  1990年   79篇
  1989年   112篇
  1988年   87篇
  1987年   116篇
  1986年   103篇
  1985年   132篇
  1984年   85篇
  1983年   65篇
  1982年   49篇
  1981年   45篇
  1980年   58篇
  1979年   50篇
  1978年   46篇
  1977年   48篇
  1976年   62篇
  1975年   50篇
  1973年   30篇
  1972年   32篇
  1969年   26篇
排序方式: 共有4661条查询结果,搜索用时 15 毫秒
81.
DNA isolated from skin epitheliomas containing papovavirus induced lymphomas within four to eight weeks in 40 to 50 per cent of newborn Syrian hamsters injected. This DNA effect was eliminated by DNase but not by RNase and was not induced by DNA preparations of transplanted epitheliomas or the induced lymphomas. Lymphomas were similarly induced by cellfree filtrates from certain human tumors such as gastric carcinomas and ovarian tumors. Little or no lymphoma effects were observed following injections with filtrates derived from normal human or animal tissues or human blood. The lymphomas induced by DNA and human tumors were transmissible by cell-free filtrates to newborn Syrian hamsters; however, successful serial passage, like the primary lymphomas induced by the DNA preparations, depended upon the use of a newborn hamster from a special breeding colony of hamsters.  相似文献   
82.
International Journal of Legal Medicine - The recently developed probabilistic genotyping software package MaSTR™ (SoftGenetics LLC) was used to develop statistical weight estimates for a...  相似文献   
83.
Friend murine erythroleukemia (MEL) cells provide an early erythroid precursor model that can be induced to terminally differentiate in cell culture and has been used to study erythroid differentiation as well as multistage tumorigenesis. During the chemically induced differentiation of MEL cells, expression of the c-myb protooncogene is downregulated in a biphasic fashion and forced expression of c-myb is able to block the differentiation process, suggesting that c-myb activity may be limiting for differentiation in MEL cells. We have recently produced stable transfectants in the C19 MEL cell line that carry a dominant interfering myb allele (MEnT) under the control of an inducible mouse metallothionein I (MTH) promoter. Upon inducing expression of MEnT, transfected cells enter a differentiation program and begin to produce alpha-globin mRNA, assemble hemoglobin, and stop proliferating. Differential display was used to compare mRNA expression between parental C19 MEL cells induced to differentiate with hexamethylene bisacetamide (HMBA) and stable transfectants induced to differentiate via expression of MEnT to identify potential Myb target promoters. We identified six candidate cDNAs in this fashion and present evidence that two of these represent genes that are dependent on c-Myb activity for maximal expression in MEL cells.  相似文献   
84.
Intramolecular general base catalysis by the imidazolyl group was found in the hydrolyses of endo-5-[4;(5')-imidazolyl]-bicyclo[2.2.1]hept-endo-2-yl trans-cinnamate and endo-5-[4'(5')-imidazolyl]bicyclo[2.2.2]oct-endo-2-yl trans-cinnamate in which the imidazolyl and trans-cinnamoyl groups are bound in close proximity to each other by rigid bicyclic rings. The rate constants for the intramolecular general base-catalyzed hydrolyses at 60 degrees are 6.4 X 10(-7) sec-1 for the former and 1.8 X 10(-7) sec-1 for the latter and the deuterium oxide solvent isotope effects are 3.0 for both. On the other hand, no intramolecular catalytic participation of the imidazolyl group was observed in the hydrolyses of the endo-exo isomers, exo- 5-[4'(5')-imidazolyl]bicyclo[2.2.1]hept-endo-2-yl trans-cinnamate and endo-5[4'(5')-imidazolyl]bicyclo[2.2.2]oct-exo-2-yl trans-cinnamate, in which the imidazolyl groups are located far from the trans-cinnamoyl groups. Intramolecular general base-catalyzed hydrolyses by the imidazolyl groups in endo-5[4'(5')-imidazolyl]bicyclo[2.2.1]hept-endo-2-yl trans-cinnamate and endo-5-[4'(5')-imidazolyl]bicyclo[2.2.2]oct-endo-2-yl trans-cinnamate can serve as models of serine esterase-catalyzed hydrolyses.  相似文献   
85.
BACKGROUND: In type 1 diabetic patients with nephropathy, tight blood pressure control has been shown to prevent the progression of the disease. Up until now, self-monitoring, ambulatory and office blood pressure values have not been compared in these patients. Thus, we have evaluated blood pressure values obtained in the office by a physician and at home by self-monitoring with those measured under ambulatory conditions in these patients. Additionally, for blood pressure self-monitoring, three different devices (the sphygmomanometer, upper-arm oscillometer and wrist oscillometer) were compared. METHODS: Twenty-one treated hypertensive type 1 diabetic patients [age 45+/-9 years, duration of diabetes 33+/-12 years (mean+/-SD)] with overt diabetic nephropathy participated in this study. At both baseline and the end of the study, daytime ambulatory blood pressure measurement was performed. Office blood pressure was measured at baseline. Additionally, all the patients measured their blood pressure over a 3-week period using each of the three different devices, in random order, for 1 week. RESULTS: The mean office blood pressure values (135+/-21/85+/-12mmHg) were higher than both the ambulatory (131+/-23/80+/-12, P<0.05) and self-monitoring values (130+/-14/78+/-10; P<0.05 for systolic and P<0.02 for diastolic values). The difference between the ambulatory and self-monitoring values were not statistically significant. Diastolic blood pressure values measured with the oscillometric wrist device showed a trend towards higher values when compared to those measured with the sphygmomanometer and with the oscillometric upper-arm device (P=0.065 for diastolic values). CONCLUSION: Office blood pressure measurements may over-estimate blood pressure in patients with type 1 diabetes and diabetic nephropathy. Because the oscillometric wrist device tends to over-estimate diastolic values, upper-arm devices should be preferred for blood pressure self-monitoring in these patients.  相似文献   
86.
A phase III prospective randomized multicenter study was performed to determine whether quinine could improve the response rate of poor-risk acute leukemias (ALs) to standard chemotherapy including a multidrug resistance (MDR)-related cytotoxic agent. The rationale of the study was based on the negative prognostic value of MDR phenotype in ALs and the ability of quinine to reverse this phenotype both in vitro and ex vivo. Three hundred fifteen patients (median age, 49 years; range, 16 to 65) with relapsed (n = 108) or refractory (n = 32) acute myeloblastic leukemia (AML), relapsed (n = 27) or refractory (n = 9) acute lymphoblastic leukemia (ALL), secondary AL (n = 22) or blastic transformation of myelodysplastic syndrome ([MDS] n = 74) or myeloproliferative syndrome ([MPS] n = 43) were randomly assigned to receive mitoxantrone ([MXN] 12 mg/m2/d, days 2 to 5) and cytarabine ([Ara-C] 1 g/m2/12 h, days 1 to 5) alone or in combination with quinine (30 mg/kg/d, days 1 to 5; continuous intravenous infusion beginning 24 hours before MXN infusion). Side effects of quinine were observed in 56 of 161 quinine-treated patients and disappeared in all but four cases after one or two 20% dose decreases. Sera from quinine-treated patients showed increased MXN uptake in an MDR-positive cell line compared with matched sera obtained before quinine infusion. Quinine induced a significant increase in the incidence of nausea, vomiting, mucositis, and cardiac toxicity. A complete response (CR) was observed in 85 of 161 patients (52.8%) from the quinine-treated group versus 70 of 154 patients (45.5%) in the control group (P = .19). The most important differences between quinine and control group CR rates were observed in patients with refractory AMLs and blastic transformation of MDS and MPS. The CR rate was higher in P-glycoprotein-positive cases, although the difference was not significant. Failure of the regimen due to blastic persistence or blast number increase was higher in the control group (61 of 154 patients) than in the quinine group (45 of 161, P = .04). Early death was observed in eight cases (four in each arm) and death in aplasia in 27 cases (20 in quinine group v seven in control group, P = .01). The significant increase of toxicity in the quinine arm could have masked the clinical benefit of MDR reversion in poor- risk ALs.  相似文献   
87.
Trauma centers are now being perceived as financial burdens because of recent changes in trauma reimbursement for the Medicare Prospective Payment System population and the perception that collection rates are lower among trauma patients. We examined the demographic and clinical factors associated with the collection experience in a series of 114 trauma patients transferred by helicopter from the accident site to an inner-city trauma center. Factors affecting payment at 30, 60, 90, and 180 days included patient age, insurance class, and discharge status. While not as high as the collection rate for the facility as a whole, we found an average 71.2% collection rate for trauma patients at 180 days. As long as trauma reimbursement continues to be cost based for nonMedicare patients, collection rates remain an important consideration in determining the financial viability of trauma centers.  相似文献   
88.
Summary Tumor samples from 74 patients with gynecologic malignancies including breast cancer were processed in a soft agar colony-forming assay. None of the samples resulted in a pure single cell suspension. Of the 10 samples meeting our criteria of evaluability for chemosensitivity testing, only 5 samples showed in vitro sensitivity to any drug. Of the 3 evaluable correlations between in vitro and in vivo results, 2 were correct. Due to the low rate of evaluable samples the assay has only limited value in the assignment of chemotherapeutic drugs for patients treated at our institution.This work was supported in part by the Gesellschaft zur Bekämpfung der Krebskrankheiten Nordrhein-Westfalen  相似文献   
89.
This article comprises the development and validation of a protocol for the qualitative analysis of 61 phase I synthetic cannabinoid metabolites in urine originating from 29 synthetic cannabinoids, combining solid‐phase extraction (SPE) utilizing a reversed phase silica‐based sorbent (phenyl) with liquid chromatography–tandem mass spectrometry (LC?MS/MS). Validation was performed according to the guidelines of the German Society of Toxicological and Forensic Chemistry. Sufficient chromatographic separation was achieved within a total runtime of 12.3 minutes. Validation included specificity and selectivity, limit of detection (LOD), recovery and matrix effects, as well as auto‐sampler stability of processed urine samples. LOD ranged between 0.025 ng/mL and 0.5 ng/mL in urine. Recovery ranged between 43% and 97%, with only two analytes exhibiting recoveries below 50%. However, for those two analytes, the LODs were 0.05 ng/mL in urine. In addition, matrix effects between 81% and 185% were determined, whereby matrix effects over 125% were observed for 10 non‐first‐generation synthetic cannabinoid metabolites. The developed method enables the rapid and sensitive detection of synthetic cannabinoid metabolites in urine, complementing the spectrum of existing analytical tools in forensic case work. Finally, application to 61 urine samples from both routine and autopsy case work yielded one urine sample that tested positive for ADB‐PINACA N‐pentanoic acid.  相似文献   
90.
Functional magnetic resonance imaging (fMRI) is an extensively used method for the investigation of normal and pathological brain function. In particular, fMRI has been used to characterize spatiotemporal hemodynamic response to pharmacological challenges as a non-invasive readout of neuronal activity. However, the mechanisms underlying regional signal changes are yet unclear. In this study, we use a meta-analytic approach to converge data from microdialysis experiments with relative cerebral blood volume (rCBV) changes following acute administration of neuropsychiatric drugs in adult male rats. At whole-brain level, the functional response patterns show very weak correlation with neurochemical alterations, while for numerous brain areas a strong positive correlation with noradrenaline release exists. At a local scale of individual brain regions, the rCBV response to neurotransmitters is anatomically heterogeneous and, importantly, based on a complex interplay of different neurotransmitters that often exert opposing effects, thus providing a mechanism for regulating and fine tuning hemodynamic responses in specific regions.  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