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   216504篇
  免费   15844篇
  国内免费   752篇
耳鼻咽喉   2391篇
儿科学   5688篇
妇产科学   4439篇
基础医学   28041篇
口腔科学   4740篇
临床医学   20620篇
内科学   45946篇
皮肤病学   2833篇
神经病学   20803篇
特种医学   7128篇
外国民族医学   13篇
外科学   33776篇
综合类   3558篇
现状与发展   2篇
一般理论   293篇
预防医学   19757篇
眼科学   4545篇
药学   14812篇
  1篇
中国医学   380篇
肿瘤学   13334篇
  2023年   873篇
  2022年   1434篇
  2021年   3511篇
  2020年   2170篇
  2019年   3481篇
  2018年   4096篇
  2017年   3323篇
  2016年   3519篇
  2015年   4169篇
  2014年   6234篇
  2013年   9015篇
  2012年   13382篇
  2011年   14607篇
  2010年   8265篇
  2009年   7453篇
  2008年   13857篇
  2007年   14716篇
  2006年   14183篇
  2005年   14638篇
  2004年   14070篇
  2003年   13116篇
  2002年   12654篇
  2001年   2153篇
  2000年   1729篇
  1999年   2256篇
  1998年   2929篇
  1997年   2492篇
  1996年   2269篇
  1995年   1990篇
  1994年   1811篇
  1993年   1693篇
  1992年   1394篇
  1991年   1308篇
  1990年   1176篇
  1989年   1105篇
  1988年   1154篇
  1987年   1148篇
  1986年   1122篇
  1985年   1194篇
  1984年   1550篇
  1983年   1537篇
  1982年   1845篇
  1981年   1682篇
  1980年   1595篇
  1979年   877篇
  1978年   1031篇
  1977年   994篇
  1976年   875篇
  1975年   724篇
  1974年   708篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
This study investigated whether feeding different wheat varieties to laying hens could influence colonization with the intestinal spirochaete Brachyspira intermedia. Fifty ISA-Brown laying hens were divided into two groups. One group were fed a laying-hen diet formulated with wheat variety Westonia, and one were fed the diet incorporating variety Stilleto. Each group was divided into 15 hens experimentally infected with B. intermedia and 10 uninfected controls. The 30 infected hens were housed in individual cages in one room, and the controls were similarly housed in another room. Following administration of cultures of B. intermedia strain HB60 by crop-tube over 3 days, cloacal swabs were taken for spirochaete culture every 3 to 4 days. The water content of caecal faeces, and egg production and body weight were measured weekly. The hens were killed after 4 weeks, the caeca cultured for spirochaetes and the viscosity of the ileal contents measured. A total of 48/120 (40%) of the excreta samples from infected hens fed Westonia contained B. intermedia, compared with 21/120 (17.5%) for Stiletto (P = 0.0002). The ileal viscosity of hens fed Westonia also was higher (P = 0.048), but viscosity was not clearly related to the non-starch polysaccharide (NSP) content of the wheats. Westonia had a slightly higher total NSP content than Stiletto, but the ratio of soluble to insoluble NSP was lower. Infected hens developed wetter excreta, but neither infection nor diet altered egg production. In conclusion, the wheat variety can influence colonization with B. intermedia, apparently through diet-related alterations in the intestinal microenvironment.  相似文献   
992.
The use of type I interferon (IFN), in combination with ribvirin, to treat chronic hepatitis C virus (HCV) infection has many drawbacks that prevent widespread application, ultimately leading to a significant unmet clinical need. Potential improvements in IFN therapy through targeted delivery, molecular alteration, and combination with other agents are ongoing in an attempt to decrease adverse effects and increase efficacy. In this report, the HCV replicon cell culture system was used to assess potential synergistic antiviral effects of multiple IFN species when administered in combination. Quantitative analysis of HCV replicon RNA by TaqMan (PE Applied Biosystems, Foster City, CA) and qualitative analysis of HCV protein expression were used to measure the antiviral efficacy of individual and combination IFN treatments, and synergistic responses of IFN combinations were determined through statistical analysis of the TaqMan results. We found that when administered simultaneously, type I/II IFN combinations (IFN-alpha2b + IFN-gamma or IFN-beta + IFN-gamma) resulted in dramatic antiviral synergy, whereas a type I/I combination (IFN-alpha2b + IFN-beta) demonstrated a slightly antagonistic profile. The synergistic effect is likely due to differential cell surface receptors and signaling pathways employed by types I and II IFNs. Conversely, all type I IFN species bind the same receptor and signal through similar pathways, possibly accounting for the nearly additive response observed. In support of this hypothesis, IFN treatment resulted in differential induction of Stat1 phosphorylation at Tyr 701. In conclusion, simultaneous type I/II IFN combination treatment may allow an overall decreased effective IFN dose, which may reduce the side effect profiles that hinder current therapy.  相似文献   
993.
Muscle tissue transplantation applied to regain or dynamically assist contractile functions is known as 'dynamic myoplasty'. Success rates of clinical applications are unpredictable, because of lack of endurance, ischemic lesions, abundant scar formation and inadequate performance of tasks due to lack of refined control. Electrical stimulation is used to control dynamic myoplasties and should be improved to reduce some of these drawbacks. Sequential segmental neuromuscular stimulation improves the endurance and closed-loop control offers refinement in rate of contraction of the muscle, while function-controlling stimulator algorithms present the possibility of performing more complex tasks. An acute feasibility study was performed in anaesthetised dogs combining these techniques. Electrically stimulated gracilis-based neo-sphincters were compared to native sphincters with regard to their ability to maintain continence. Measurements were made during fast bladder pressure changes, static high bladder pressure and slow filling of the bladder, mimicking among others posture changes, lifting heavy objects and diuresis. In general, neo-sphincter and native sphincter performance showed no significant difference during these measurements. However, during high bladder pressures reaching 40 cm H(2)O the neo-sphincters maintained positive pressure gradients, whereas most native sphincters relaxed. During slow filling of the bladder the neo-sphincters maintained a controlled positive pressure gradient for a prolonged time without any form of training. Furthermore, the accuracy of these maintained pressure gradients proved to be within the limits set up by the native sphincters. Refinements using more complicated self-learning function-controlling algorithms proved to be effective also and are briefly discussed. In conclusion, a combination of sequential stimulation, closed-loop control and function-controlling algorithms proved feasible in this dynamic graciloplasty-model. Neo-sphincters were created, which would probably provide an acceptable performance, when the stimulation system could be implanted and further tested. Sizing this technique down to implantable proportions seems to be justified and will enable exploration of the possible benefits.  相似文献   
994.
The Toll-like receptor (TLR) system is responsible for the recognition of infectious agents leading to initiation of the primary innate, and later adaptive, immune response. Genetic technologies have enabled the discovery of new factors involved in these systems, their genetic manipulation and the global analyses of their effects on gene expression. Furthermore, this increased understanding has resulted in the need to reassess our preconceptions about the functions of well-known molecules. For example, type I interferons (IFNs), which were discovered as antiviral proteins, are now known to be produced in response to TLR activation by many pathogens, including bacteria. Should we be surprised? Has the inflammatory response unexpectedly highjacked the body's antiviral system? Or are we too easily blinkered by preconceptions from how a compound was discovered?  相似文献   
995.
We describe results from a survey designed to assess patterns of communication within families shortly after an individual receives results of BRCA1 and BRCA2 mutation carrier status. Shortly after disclosure of BRCA1 and BRCA2 genetic test results, the proband was contacted by phone to administer the post disclosure survey. Questions asked included whether they had shared their results with their siblings or adult children, if there were difficulties in communicating the test results, and if there was any distress associated with the sharing of results. A total of 162 women who have received results from BRCA1 and BRCA2 genetic testing participated in the survey. The probands shared their results more often with their female than their male relatives (P < 0.001). Probands who had tested positive for a mutation in the BRCA1 or BRCA2 gene shared their results more often with their relatives than did probands who were not carriers (P = 0.002). Probands reported more often that their siblings rather than their adult children had difficulties understanding the results (P = 0.001). The probands who were carriers more often reported having difficulties explaining their results to their relatives (P < 0.001) and their relatives were upset on hearing the result more often than were the relatives of probands who were not carriers (P < 0.001). The probands who were carriers reported more often that they were upset explaining their results to their relatives than did the probands who were not carriers (P < 0.001). Individuals are disclosing their test results to their relatives. Probands who are BRCA1- or BRCA2-positive are more likely to experience difficulty and distress with the communication of their test results to family members.  相似文献   
996.
997.
998.
We investigated anaerobic threshold (< theta(L)) gas exchange kinetics and maximal oxygen uptake (VO2,max) among older men with reduced left ventricular end-diastolic filling (LVDF). Ten men (mean age, 73 years) with LVDF impairment and low fitness, but without other cardiovascular dysfunction were studied. Treatments compared to control included: 5 days, high intensity exercise training protocol; 5 days, calcium channel blockade (240 mg verapamil); 21 days, detraining/washout; and 5 days, combined treatments. Results indicated no changes in resting left ventricular systolic function with any treatment. Significant resting diastolic function changes included increased early:late flow velocity (control, 0.87; training, 1.28; verapamil, 1.32), and a decreased isovolumic relaxation time (control, 0.10 s; training, 0.08 s; verapamil, 0.08 s). The combined treatments were not additive. Sub-threshold oxygen uptake kinetics (tauVO2, s) were significantly faster following either training or verapamil (tauVO2,control, 62+/-12; tauVO2,training, 44+/-9; tauVO2,verapamil, 48+/-10) and combined treatments (tauVO2, 41+/- 8). V O2,max (ml kg(-1) min(-1)) was significantly increased (control, 21.8+/-2.2; training, 27.3+/-2.2; verapamil, 25.2+/-3.4; combined treatments, 26.9+/-2.3). Increasing ventricular preload with either exercise training or calcium channel blockade was coincident with faster tauVO2 and increased VO2,max.  相似文献   
999.
Hypertrichosis lanuginosa (without gingival hyperplasia) is described in a mother and son; the latter also had photophobia, infantile genitalia, growth retardation, hypotension, low IQ and dental abnormalities (hyperdontia, permanence of deciduous and delayed eruption of permanent teeth). Both have normal dermatoglyphics. Some clinical findings are discussed. The presence of this syndrome in a mother and son supports an autosomal mode of inheritance (with variable expressivity). Hypertrichosis lanuginosa is a pure monomultidysplasia and may be classified with the tricho-odontic sub-group of the ectodermal dysplasias.  相似文献   
1000.
Spectral karyotyping of prostate cell lines LNCaP, DU145, PC3, and 22RV demonstrated structural chromosome rearrangements involving the distal long arm of chromosome 4. In all but 22RV, these are nonreciprocal translocations between chromosomes 4 and 10. In 22RV, an apparently reciprocal t(2q;4q) is seen. Fluorescence in situ hybridization analysis of the chromosome 4 translocation breakpoints demonstrated that deletions were associated with all of the translocations, resulting in a net loss of chromosome material. Overlapping deletions in 4q28 approximately 34 were seen in LNCap, DU145, and 22RV, which defined an approximately 4.5-megabase pair common region of deletion. The deletion in PC3 was more proximal on 4q, involving the 4q21 approximately q26 region. A meta analysis of high-resolution definition of losses of chromosome material from published studies demonstrates that loss of 4q material may occur in at least 50% of primary tumors. This analysis defines a series of genes in the critical 4q region, which is potentially associated with prostate tumor development.  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