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   980篇
  免费   27篇
  国内免费   6篇
耳鼻咽喉   9篇
儿科学   24篇
妇产科学   30篇
基础医学   87篇
口腔科学   9篇
临床医学   60篇
内科学   205篇
皮肤病学   62篇
神经病学   86篇
特种医学   29篇
外科学   220篇
综合类   2篇
预防医学   24篇
眼科学   8篇
药学   94篇
肿瘤学   64篇
  2022年   8篇
  2021年   11篇
  2020年   5篇
  2019年   15篇
  2018年   5篇
  2016年   7篇
  2015年   15篇
  2014年   21篇
  2013年   17篇
  2012年   40篇
  2011年   34篇
  2010年   5篇
  2009年   15篇
  2008年   27篇
  2007年   33篇
  2006年   43篇
  2005年   26篇
  2004年   36篇
  2003年   27篇
  2002年   25篇
  2001年   30篇
  2000年   31篇
  1999年   28篇
  1998年   15篇
  1997年   10篇
  1996年   15篇
  1995年   8篇
  1994年   9篇
  1993年   16篇
  1992年   48篇
  1991年   38篇
  1990年   47篇
  1989年   31篇
  1988年   47篇
  1987年   30篇
  1986年   24篇
  1985年   19篇
  1984年   21篇
  1983年   20篇
  1982年   8篇
  1980年   8篇
  1979年   12篇
  1977年   9篇
  1976年   8篇
  1974年   7篇
  1972年   7篇
  1971年   7篇
  1970年   5篇
  1969年   7篇
  1968年   8篇
排序方式: 共有1013条查询结果,搜索用时 15 毫秒
11.
Polymerizations of malealdehyde were carried out with alkalimetal alkoxides, AlEt3, pyridine, AlEt3? TiCl4 and BF3OEt2 as catalysts. All the polymers obtained with other catalysts than AlEt3 and AlEt3? TiCl4 were composed only of the cyclized unit (dialkoxydihydrofuran ring) (> 95%) and the 1.2-addition structure (< 5%). IR spectra of the polymers obtained with AlEt3 and AlEt3? TiCl4 catalysts were suggestive of the presence of five-membered lactone rings which may occur as a result of termination by hydride transfer. The steric structure (cis vs. trans) of the dialkoxydihydrofuran ring in polymer was inferred from the comparison of the IR spectra of the polymer with those of the isomeric dialkoxydihydrofurans in the 800 cm?1 region. Anionic catalysts gave higher contents of the cis configuration, while coordinated anionic catalysts gave comparable amounts of the cis and trans structures.  相似文献   
12.
T Tominaga  Y Yogo  T Kitamura  Y Aso 《Virology》1992,186(2):736-741
JC virus DNAs derived from the urine of nonimmunosuppressed individuals generally contain an archetypal regulatory region which may have generated various regulatory regions of JC virus from from the brain with progressive multifocal leukoencephalopathy (PML). In this study, we examined whether JC virus persisting in normal human kidney tissue contains the archetypal regulatory region. Renal medulla, cortex, and tumor from 32 patients bearing renal tumors were screened for JC virus DNA by blot hybridization. Viral DNA was detected in the medulla in 13 cases (41%), in the cortex in 2 cases (6%), but not at all from the tumor. A number of viral DNA-positive specimens (8 from the medulla and 2 from the cortex) were used to amplify and sequence viral regulatory regions by polymerase chain reaction. Structures of the regulatory regions from all the specimens were, with a few nucleotide variations, identical with that of the archetypal region which was previously detected in the JC virus DNA from urine. This finding supports the hypothesis that the JC virus associated with PML evolved from the archetypal JC virus during persistence in human hosts. Furthermore, we present evidence that renal JCV is replicating and that progeny virions are excreted into the urine.  相似文献   
13.
Concerning the classification of ventilators, Elam (1958), Faireley (1959), and Hunter (1961) reported some simple ones such as pressure limited, volume limited, pressure preset, or volume preset models. Mapleson (1969) also classified them by the generating force or cycling together with the above-mentioned types.The latest ventilators applicable to patients with respiratory failure usually have some cut-off function at high airway pressures as a safety measure. Therefore, all of them belong to the pressure limited type. Some ventilators are of two types such as the time cycled and pressure cycled type.Therefore, we attempted to classify ventilators into four groups, i.e. the time cycled, volume cycled, pressure cycled and selective time-pressure cycled types according to the fundamental mode of ventilator function, the so-called change of cycling from inspiration to expiration. Each group was further divided into subgroups according to preset dials such as respiratory rate, I/E ratio, inspiration time, expiration time, tidal volume, flow rate and airway pressure.By this method, fifty one ventilators on the market in Japan can be classified without overlapping. Although this classification seems complex, it will be of use in selecting ventilators by emphasizing preset dials according to the users needs, ability or both.(Goto Y, Takahashi K, Harada J et al.: A consideration on the new classification of latest lung ventilators. J Anesth 1: 178–182, 1987)  相似文献   
14.
Rats with bladder tumor induced by BBN were treated by intravesical instillation of 0.8 mg of (2"R)-4'-O-tetrahydropyranyladriamycin (THP) (9 rats) or adriamycin (ADM) (8 rats) dissolved in 0.2 ml of distilled water. Thirty minutes later, the bladder was removed surgically. Rats without the tumor received the same treatment of THP (8 rats) or ADM (9 rats). THP and ADM infiltrations to the normal bladder tissue and the tumor were estimated by the use of the photonic microscope system, since both drugs were known to emit characteristic fluorescence. It was found that infiltration of THP to the tumor tissue was more prominent in amounts and deeper than that of ADM, while smaller amounts of THP infiltrated into the normal mucosa compared to ADM. The fact might explain the clinical finding that THP instilled intravesically in half a concentration of ADM showed the same effect on the tumor as ADM. Subsequently, tissue concentrations of THP and ADM were estimated by high performance liquid chromatography. Either THP or ADM was instilled intravesically for 30 minutes to 6 rats with bladder tumor. Similarly, either THP or ADM was instilled in 5 rats without the tumors. Contrary to the result of the photonic microscope system, the tissue concentration of THP was not different from that of ADM not only in the tumor tissues but also in the normal bladder ones. Furthermore, the tissue concentration of both drugs in the normal bladder was higher than that in the bladder tumor.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
15.
Purpose. The effect of the molecular weight of dextran on the molecular mobility and protein stability of freeze-dried serum -globulin (BGG) formulations was studied. The stabilizing effect of higher molecular weight dextran is discussed in relation to the molecular mobility of the formulations. Methods. The molecular mobility of freeze-dried BGG formulations containing dextrans of various molecular weights was determined based on the free induction decay of dextran and water protons measured by proton NMR. The protein stability of the formulations was determined at temperatures ranging from 20 to 70°C by size exclusion chromatography. Results. Changes in the molecular mobility of freeze-dried formulations that occurred at temperatures below the glass transition temperature could be detected as the molecular mobility-changing temperature (Tmc), at which dextran protons started to exhibit a Lorentzian relaxation decay due to higher mobility in addition to a Gaussian relaxation decay. Tmc increased as the molecular weight of dextran increased. The proportion of dextran protons which exhibited the higher mobility relaxation process (Phm) at temperatures above Tmc decreased as the molecular weight of dextran increased. Protein stability was closely related to molecular mobility. The temperature dependence of the denaturation rate changed at around Tmc, and denaturation in the microscopically liquidized state decreased as Phm decreased with increasing molecular weight of dextran. Conclusions. The effect of the molecular weight of dextran on the protein stability of freeze-dried BGG formulations could be explained in terms of the parameters obtained by 1H-NMR such as Tmc and Phm. These parameters appear to be useful in preformulation and stability prediction of freeze-dried formulations.  相似文献   
16.
The present study was undertaken to investigate the effectsof transforming growth factor (TGF)-1 on ovarian steroidogenesisin immature or moderately mature porcine granulosa cells invitro. TGF-1 (0.01–10 ng/ml) significantly attenuatedprogesterone release from the basal and follicle stimulatinghormone-stimulated porcine granulosa cells, and significantlyincreased DNA synthesis. TGF-1 also significantly increasedthe extracellular accumulation of cyclic AMP, but did not changethe production of inositol phosphate or the intracellular calciumconcentration in these cells. Thus, TGF-1 appears to have adirect effect on porcine granulosa cell function, regulatingthe differential synthesis of progesterone mainly via the intracellularsignal transduction of the cyclic AMP—protein kinase Apathway. This growth factor may play a physiologically significantrole in controlling differentiation of immature and moderatelymature porcine granulosa cells via an autocrine/paracrine mechanism.  相似文献   
17.
The pathophysiology of altitude-related disorders in untrained trekkers has not been clarified. In the present study, the effects of workload on cardiovascular parameters and regional cerebral oxygenation were studied in untrained trekkers at altitudes of 2700 m and 3700 m above sea level. We studied 6 males and 4 females at each altitude, and their average ages were 31.3+/-7.1 y at 2700 m and 31.2+/-6.8 y at 3700 m, respectively. The resting values of heart rate and mean blood pressure were not significantly different at 2700 m and 3700 m than at sea level. However, increases in these values after exercise were more prominent at high altitudes (heart rate increase = 51.6% at 2700 m and 70.4% at 3700 m; mean blood pressure increase: 19.0% at 2700 m and 17.2% at 3700 m). In addition, post-exercise blood lactate concentration was significantly higher at 3700 m than at sea level or at 2700 m (i.e., 7.6 mM at 3700 m, 3.8 mM at 2700 m, and 4.17 mM at 0 m, respectively). Exercise induced an acute reduction in the arterial oxygen saturation value (SpO2) at 2700 m and 3700 m (i.e., 11.2% reduction at 2700 m and 9.4% at 3700 m), whereas no changes were observed at sea level. The resting values of regional oxygen saturation (rSO2)--measured by a near infra-red spectrophotometer at sea level, 2700 m, and 3700 m-were nearly identical. Exercise at sea level did not reduce this value. In contrast, we observed a decrease in rSO2 after subjects exercised at 2700 m and 3700 m (i.e., 26.9% at 2700 m and 48.1% at 3700 m, respectively). The rSO2 measured 2 min and 3 min after exercise at 3700 m was significantly higher than the preexercise value. From these observations, we concluded that alterations in cardiovascular parameters were apparent only after an exercise load occurred at approximately 3000 m altitude. Acute reduction in cerebral regional oxygen saturation might be a primary cause of headache and acute mountain sickness among unacclimatized trekkers.  相似文献   
18.
19.
20.
Diagnoses recorded in the chapter E of Minimum Data Set (MDS) were analyzed in patients requiring care admitted in a geriatric hospital in Sapporo, Japan. They were classified as: A-diseases causing care-requiring conditions, B-their symptoms, and C-coexisting diseases requiring no care. Orthopedic diseases were not analyzed because they were not adequately recorded in MDS system. Class A diagnoses varied, but only five diagnoses were responsible for 3% or more of the total patients who required care. They were 1) Alzheimer's disease (AD), 2) Parkinson's disease, 3) dementia other than AD without neurological symptoms, 4) dementia other than AD with sequelae of stroke, and 5) sequelae of stroke without dementia. These diagnoses pooled represented over 90% of all patients. "Diagnoses and symptoms" in MDS were useful to 1) describe medical problems briefly in a predetermined format, 2) evaluate urgent or unstable conditions separately from stable diagnoses and symptoms, and 3) use common information by various professions, but have difficulties because 1) preselected diagnoses were few and unsuited to practices in Japan, 2) it is impossible to record a previous disease in the past that initiated the process leading to the present disabilities, and 3) it is also impossible to record the severities of the diseases and symptoms.  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