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   11881篇
  免费   713篇
  国内免费   65篇
耳鼻咽喉   140篇
儿科学   491篇
妇产科学   265篇
基础医学   1714篇
口腔科学   737篇
临床医学   1057篇
内科学   2584篇
皮肤病学   339篇
神经病学   1125篇
特种医学   316篇
外科学   1495篇
综合类   55篇
一般理论   4篇
预防医学   831篇
眼科学   228篇
药学   716篇
中国医学   66篇
肿瘤学   496篇
  2023年   108篇
  2022年   214篇
  2021年   394篇
  2020年   239篇
  2019年   325篇
  2018年   406篇
  2017年   280篇
  2016年   388篇
  2015年   429篇
  2014年   504篇
  2013年   658篇
  2012年   911篇
  2011年   906篇
  2010年   503篇
  2009年   469篇
  2008年   701篇
  2007年   770篇
  2006年   605篇
  2005年   566篇
  2004年   552篇
  2003年   430篇
  2002年   422篇
  2001年   134篇
  2000年   92篇
  1999年   91篇
  1998年   75篇
  1997年   74篇
  1996年   63篇
  1995年   53篇
  1994年   39篇
  1993年   52篇
  1992年   58篇
  1991年   50篇
  1990年   46篇
  1989年   44篇
  1988年   30篇
  1987年   34篇
  1986年   19篇
  1985年   34篇
  1984年   30篇
  1983年   28篇
  1982年   24篇
  1981年   20篇
  1980年   27篇
  1979年   21篇
  1977年   19篇
  1976年   20篇
  1975年   21篇
  1931年   23篇
  1923年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
: Accelerated fractionation was used to shorten overall treatment time to increase locoregional control and cause-specific survival.

: Eighty-eight patients with cancer of the esophagus ineligible for surgery were entered in the study between 1986 and 1993. Neoadjuvant chemotherapy was given to 64% of patients. Accelerated radiotherapy using the concomitant boost technique delivered a median dose of 65 Gy in a median overall treatment time of 32 days.

: The 3-year acturial local control rate in patients with T1, T2, and T3 tumors was 71%, 42%,and 33%, respectively. The 3-year cause-specific survival rates were 40%, 22%, and 6%, respectively. Sixteen percent of patients experienced Grafe 3 esophagitis. Late toxicity included esophageal stenosis and pulmonary fibrosis in 8% and 9% of the patients, respectively. Multivariate analysis demonstrated that T stage and overall treatment time were prognostic factors for cause-specific survival. T stage and neoadjuvant chemotherapy were independent prognostic factors for locoregional control.

: These findings suggest that accelerated giben in an overall treatment time of <35 days might be beneficial for easy-stage cancer of the esophagus. Neoadjuvant chemotherapy is not recommended, as it was a significant adverse prognostic factor in the multivariate analysis for local control. Accelerated fractionation can be carried out with modeate acure and late toxicity.  相似文献   

102.
103.
OBJECTIVE: To acquire data on pediatric nosocomial infections (NIs), which are associated with substantial morbidity and mortality and for which data are scarce. DESIGN: Prevalence survey and evaluation of a new comorbidity index. SETTING: Seven Swiss pediatric hospitals. PATIENTS: Those hospitalized for at least 24 hours in a medical, surgical, intensive care, or intermediate care ward. RESULTS: Thirty-five NIs were observed among 520 patients (6.7%; range per hospital, 1.4% to 11.8%). Bacteremia was most frequent (2.5 per 100 patients), followed by urinary tract infection (1.3 per 100 patients) and surgical-site infection (1.1 per 100 patients; 3.2 per 100 patients undergoing surgery). The median duration until the onset of infection was 19 days. Independent risk factors for NI were age between 1 and 12 months, a comorbidity score of 2 or greater, and a urinary catheter. Among surgical patients, an American Society of Anesthesiologists (ASA) score of 2 or greater was associated with any type of NI (P = .03). Enterobacteriaceae were the most frequent cause of NI, followed by coagulase-negative staphylococci; viruses were rarely the cause. CONCLUSIONS: This national prevalence survey yielded valuable information about the rate and risk factors of pediatric NI. A new comorbidity score showed promising performance. ASA score may be a predictor of NI. The season in which a prevalence survey is conducted must be considered, as this determines whether seasonal viral infections are observed. Periodic prevalence surveys are a simple and cost-effective method for assessing NI and comparing rates among pediatric hospitals.  相似文献   
104.
To understand better the wide-spread pharmaceutical use of non-ionic surfactant Tween 80 (TW), the colloidal properties of the surfactant alone and in combinations with the common phospholipid, phosphatidylcholine (PC), were studied. Static and dynamic light scattering revealed that TW solubilises PC at TW/PC approximately 2.75/1 mol/mol and that TW micelle disintegration occurs on time-scale of 2.5 min, independent of amphipath concentration. This is up to nearly 300-times faster than the TW caused dissolution of PC containing unilamellar vesicles. The apparent dissolution time of TW/PC mixed aggregates, in contrast, decelerates from >700 min to <5 min upon increasing starting total amphipath concentration, with thermal activation energy > or =24 (< or =80) kJ mol(-1). The aggregate dissolution rate in highly concentrated TW/PC suspensions reflects the dissolved polysorbate-aggregate exchange rate (approximately 6.7 x 10(-3)s(-1)) rather than TW flip-flop rate across a bilayer (>0.2 min(-1)). PC solubilisation proceeds linearly with the square-root of time, and is kinetically governed by the speed of surfactant diffusion through the bulk (D approximately 2.8 x 10(-11)m2 s(-1)). Creation of small Tween-phosphatidylcholine mixed micelles is typically preceded by pre-solubilisation structures, first in the form of deformable, strongly fluctuating, bilayer vesicles and then of elongated, presumably thread-like, mixed micelles. TW/PC mixed micelles become smaller with growing surfactant/lipid molar ratio, whereas TW/PC mixed vesicles become more and more leaky with increasing surfactant concentration. Our results highlight the molecular and kinetic aspects of polysorbate-membrane interactions and provide a rationale for the popularity of Tween surfactants in pharmaceutical products: such surfactants can solubilise fatty molecules and bilayer membranes but need quite a long time for this, which is available in pharmaceutical preparations but normally not in vivo; this makes Tweens relatively efficient and safe. Furthermore, our data could help design better ultra-deformable mixed lipid-surfactant vesicles for the non-invasive transdermal drug delivery across the skin.  相似文献   
105.
We describe herein the structural optimization of new piperamide analogues, designed from two natural prototypes, piperine 1 and piperdardine 2, obtained from Piper tuberculatum Jacq. (Piperaceae). Molecular modeling studies using semiempirical AM1 method were made in order to establish rational modifications to optimize them by molecular simplification. The targeted compounds (10) and (11) were respectively obtained using benzaldehyde (12) and para-anisaldehyde (13) as starting materials. 1H NMR spectra showed that the target compounds were diastereoselectively obtained as the (E)-isomer, the same geometry of the natural prototypes. These new synthetic amides presented significant hypotensive effects in cardiovascular essays using in vivo methodologies. Compound 11 (N-[5-(4′-methoxyphenyl)-2(E)-pentenoyl]thiomorpholine) showed a potency 10,000 times greater than its prototype 5, evidencing an optimization of the molecular architecture for this class of hypotensive drug candidates.  相似文献   
106.
Carriers for non-invasive administration of biologically important antioxidant enzymes Cu,Zn-superoxide dismutase (SOD) and catalase (CAT) were developed. Solubilisation and permeabilities of various soybean phosphatidylcholine/sodium cholate (SPC/NaChol) mixtures, mainly in the form of lipid bilayers, focussing on system properties relevant for non-invasive enzyme delivery were investigated in this work. Static and dynamic light scattering measurements gave information on the behaviour of the systems containing up to 40 mM NaChol and 30.6-1.2 mM SPC in the final suspension. The average size of such mixed aggregates was in the 100-200 nm range. Suspension turbidity decreased by 50% upon increasing nominal molar detergent/lipid ratio to NaChol/SPC = 7 and 1.25, in case of SPC = 1.2 and 19.6 mM, respectively. The effective NaChol/SPC molar ratio in bilayers saturated with the detergent was found to be: R(e)(sat) = 0.70 +/- 0.01; bilayer solubilisation point corresponded to R(e)(sol) = 0.97 +/- 0.02, independently of enzyme loading. Vesicles became very permeable to SOD when membrane bound NaChol concentration exceeded 13.7 mM, in case of total starting lipid concentration of 138 mM diluted to SPC = 19.6 mM. Specifically, we measured a 50% loss of SOD from the vesicles with an aggregate-associated molar detergent ratio NaChol/SPC approximately 0.7, which is near the saturation but well below the solubilisation limit. Calcein efflux from such vesicles was compared with SPC/NaChol/SOD mixed aggregates. Our results should contribute to the future design of vesicle mediated transdermal delivery of antioxidant enzymes.  相似文献   
107.
108.
CO2 adsorption on bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on pyridinic N3-doped graphene (PNG) was investigated by employing the density functional theory. First, the interaction of Co13 and Cu13 with PNG was analyzed by spin densities, interaction energies, charge transfers, and HUMO-LUMO gaps. According to the interaction energies, the Co13 nanocluster was adsorbed more efficiently than Cu13 on the PNG. The charge transfer indicated that the Co13 nanocluster donated more charges to the PNG nanoflake than the Cu13 nanocluster. The HUMO-LUMO gap calculations showed that the PNG improved the chemical reactivity of both Co13 and Cu13 nanoclusters. When the CO2 was adsorbed on the bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on the PNG, it experienced a bond elongation and angle bending in both systems. In addition, the charge transfer from the nanoclusters to the CO2 molecule was observed. This study proved that Co13/PNG and Cu13/PNG composites are adequate candidates for CO2 adsorption and activation.  相似文献   
109.
Background/objectiveAlthough many therapeutic approaches use energy conservation, only a few effectively report the steps involved. Thus, it is intended to identify energy conservation practices to be organized in flexible and adaptable stages.MethodsA scoping review was carried out, whose search strategies were applied in seven databases (CINAHL, Cochrane Library, Portal BVS, PsycINFO, PubMed, Scopus, and Web of Science) following guidelines by Arksey and O’Malley on the Rayyan software. Searches were carried out from January 2010 to December 2020. Inclusion of refered publications with different study designs, participation of adults with or by demands of energy conservation, joint protection, and control of fatigue and/or pain. Exclusion of productions without an occupational therapist or involving merely pharmacological or surgical therapeutic strategies.Results653 articles were identified, after the selection and eligibility steps, 30 articles were full review, 18 articles were included and 635 excluded. Energy conservation studies have been increasingly focusing on neurological and systemic diseases, especially regarding symptoms of fatigue and pain. The findings were arranged in six strategies whose interventions are essentially based on guidelines and setting goals for patients, client-centered approach. Merely supervised interventions are less frequent. The number of sessions is closed, but the duration of treatment is not yet.ConclusionsThe signs of pain and fatigue are confirmed as indicators of energy conservation strategies, this delivery can be condensed from planning and organization, priorities, activity analysis, balance between activity and rest, outsourcing of tasks and physical/environmental adaptation.Trial Registration, OSF https://osf.io/rsyq4.  相似文献   
110.
The early diagnosis of and intervention in vitamin B12 deficiency in exclusively breastfed infants by mothers with low vitamin B12 is crucial in preventing possible irreversible neurologic damage, megaloblastic anemia, and failure to thrive. We assess the usefulness of the early detection of asymptomatic B12 deficiency related to acquired conditions and highlight the importance of monitoring serum vitamin B12 levels during pregnancy. We describe demographic, clinical, dietary, and biochemical data, including the evolution of a vitamin B12 deficiency’s functional biomarkers. We enrolled 12 newborns (5 males) with an age range of 1–2 months old that were exclusively breastfed and asymptomatic. These cases were referred to our metabolic unit due to alterations in expanded newborn screening: high levels of methylmalonic acid and/or total homocysteine (tHcy). All mothers were under a vegetarian diet except three who had abnormal B12 absorption, and all presented low or borderline serum B12 level and high plasma levels of tHcy. Supplementation with oral vitB12 re-established the metabolic homeostasis of the mothers. In infants, therapy with an intramuscular injection of 1.0 mg hydroxocobalamin led to the rapid normalization of the metabolic pattern, and a healthy outcome was observed. Acquired B12 deficiency should be ruled out before proceeding in a differential diagnosis of cobalamin metabolism deficits, methylmalonic acidemia, and homocystinuria.  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