首页 | 官方网站   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   3114篇
  免费   210篇
  国内免费   20篇
医药卫生   3344篇
  2023年   25篇
  2022年   23篇
  2021年   78篇
  2020年   40篇
  2019年   87篇
  2018年   91篇
  2017年   72篇
  2016年   80篇
  2015年   67篇
  2014年   95篇
  2013年   169篇
  2012年   186篇
  2011年   183篇
  2010年   125篇
  2009年   95篇
  2008年   151篇
  2007年   153篇
  2006年   117篇
  2005年   132篇
  2004年   108篇
  2003年   111篇
  2002年   97篇
  2001年   69篇
  2000年   65篇
  1999年   68篇
  1998年   78篇
  1997年   60篇
  1996年   47篇
  1995年   33篇
  1994年   36篇
  1993年   37篇
  1992年   32篇
  1991年   48篇
  1990年   39篇
  1989年   42篇
  1988年   44篇
  1987年   44篇
  1986年   41篇
  1985年   43篇
  1984年   21篇
  1983年   14篇
  1982年   23篇
  1980年   15篇
  1979年   12篇
  1978年   12篇
  1977年   14篇
  1976年   15篇
  1975年   12篇
  1974年   14篇
  1969年   13篇
排序方式: 共有3344条查询结果,搜索用时 15 毫秒
31.
New optical scheme for a polarimetric-based glucose sensor   总被引:1,自引:0,他引:1  
A new optical scheme to detect glucose concentration in the aqueous humor of the eye is presented. The ultimate aim is to apply this technique in designing a new instrument for, routinely and frequently, noninvasively monitoring blood glucose levels in diabetic patients without contact (no index matching) between the eye and the instrument. The optical scheme exploits the Brewster reflection of circularly polarized light off of the lens of the eye. Theoretically, this reflected linearly polarized light on its way to the detector is expected to rotate its state of polarization, owing to the presence of glucose molecules in the aqueous humor of a patient's eye. An experimental laboratory setup based on this scheme was designed and tested by measuring a range of known concentrations of glucose solutions dissolved in water. (c) 2004 Society of Photo-Optical Instrumentation Engineers.  相似文献   
32.
We tested the survival of the Wa strain of human rotavirus on the hands of volunteers and also studied infectious virus transfer between animate and inanimate (stainless steel disks) surfaces. The virus was diluted in a 10% suspension of feces, and 10 microliters (1 X 10(3) to 4 X 10(4) PFU) was placed on each of the four fingerpads of the left hand. One milliliter of 20% tryptose phosphate broth in Earle balanced salt solution was used for virus elution from each fingerpad, and the hands were disinfected with 70% ethanol before they were washed with an antiseptic soap and water. At 20, 60, and 260 min after inoculation, approximately 57, 43, and 7%, respectively, of the input infectious virus could be recovered. For virus transfer, the inoculum (2 X 10(4) to 8 X 10(4) PFU) was allowed to dry, and the donor surface was kept in contact with the recipient surface for 10 s at a pressure of approximately 1 kg/cm2. At 20 and 60 min after virus inoculation, 16.1 and 1.8%, respectively, of the input infectious virus could be transferred from the contaminated hand to a clean disk; when a clean hand was pressed against a contaminated disk, virus transfer was 16.8 and 1.6%, respectively. Contact between a contaminated and a clean hand 20 and 60 min after virus inoculation resulted in the transfer of 6.6 and 2.8%, respectively, of the input infectious virus. These findings indicate the potential vehicular role for human hands in the spread of rotaviral infections.  相似文献   
33.
The aim of this study was to determine the blood protein changes during different stages of pregnancy and to compare with prepregnancy diestrus in ewes. A total of 90 blood samples were taken from ten Makuii ewes (the native sheep breed in Iran) at diestrus and on days 8, 14, 28, 45, 60, 90, 125, and 145 of pregnancy. Serum protein electrophoresis of samples exhibited four fractions: albumin, α, β, and γ fractions in Makuii ewes, which in α- and γ-globulin bands were divided to α1 and α2; and γ1 and γ2, respectively. The mean concentrations (in gram per deciliter) of total serum proteins, albumin, α1-, α2-, β-, γ1-, and γ2-globulin at diestrus period were 7.03, 3.77, 0.18, 0.74, 0.41, 1.56, and 0.41, respectively. Those values fluctuated nonsignificantly throughout gestation until the 125th day of pregnancy. Thereafter, a significant decrease (p < 0.01) in serum protein levels occurred at the 145th day of pregnancy compared to prepregnancy and other gestational time points. It was concluded that blood protein levels declined sharply during late gestation when the nutrient demands of the fetus were maximal.  相似文献   
34.
Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy is a rare recessive autoimmune disorder caused by a defect in a single gene called AIRE (autoimmune regulator). Characteristics of this disease include a variable combination of autoimmune endocrine tissue destruction, mucocutaneous candidiasis and ectodermal dystrophies. The development of Aire-knockout mice has provided an invaluable model for the study of this disease. The aim of this review is to briefly highlight the strides made in APECED research using these transgenic murine models, with a focus on known roles of Aire in autoimmunity. The findings thus far are compelling and prompt additional areas of study which are discussed.  相似文献   
35.
Human IgE and IgG antibody responsiveness to the short ragweed-pollen allergen Amb a V (formerly known as Ra5) has been found to be strongly associated with HLA-D specificities Dw2 and DR2 in ragweed-allergic white individuals. To study the molecular basis of these associations, restriction fragment length polymorphism (RFLP) mapping was performed on a group of 45 white ragweed-allergic patients with full-length HLA-DR beta, DQ beta, and DQ alpha cDNA probes. The data on 41 of these subjects were used for the purposes of statistical analysis. With the DR beta probe, we found that the presence of three polymorphic restriction fragments correlated with responsiveness to Amb a V and with the DR2 specificity, namely, a 6.5 kb Eco RI fragment, a 9.4 kb Hind III fragment, and a 2.2 kb Hind III fragment. The presence of four fragments detected with the DQ beta probe correlated with responsiveness to Amb a V and with Dw2 specificity: a 2.3 kb Eco RI fragment, a 13.0 kb Pst I fragment, a 2.9 kb Taq I fragment, and a 5.2 kb Eco RV fragment. The DR beta Eco RI 6.5 kb and the DQ beta Eco RI 2.3 kb fragments were studied in detail; the concordant presence of these fragments was even more strongly associated with responsiveness to Amb a V. Fifteen of 17 responders had both fragments, whereas only one of 24 nonresponders had both fragments (p = 5 x 10(-7). This is the first time that such an association has been found between a person's immune response to a well-defined antigen and a set of HLA class II DNA restriction fragments.  相似文献   
36.
Levin  DC; Gardiner  GA  Jr 《Radiology》1987,164(3):675-680
For many years, atherosclerotic coronary artery lesions have been described by angiographers only in terms of location and degree of narrowing. However, it has become apparent that coronary stenoses generally have distinct morphologic features that can be recognized at angiography and that allow them to be classified as either "simple" or "complex" plaques. Complex plaques are those characterized by ulcerated or ruptured surfaces, subintimal hemorrhage, superimposed partially occluding thrombi, recanalized thrombi, or some combination. Pathologic studies have shown a very high frequency of these lesions at sites of total thrombotic occlusion of coronary arteries. Clinical and angiographic studies have demonstrated a high frequency of such lesions in living patients with both unstable angina and acute myocardial infarction. The presence of complex stenoses has also been found to increase the risk of future myocardial infarction. Plaque morphology thus appears to significantly affect the prognosis of patients with coronary disease and should be carefully evaluated in interpretation of all coronary angiograms.  相似文献   
37.
The excretion, tissue distribution, and binding of [14C]-formaldehyde were studied at different time intervals in male rats following a single intraperitoneal injection of 72 mg CH2O (14.7 Ci)/ kg body weight. Within 30 min, 10% of the total dose was recovered in expired air as14CO2 and by the end of 72 hr, 41% of the administered dose was eliminated through expired air. The total elimination of14CH2O activity in urine and feces in 72 hr was 15%. Erythrocytes retained significant amounts of radioactivity, even at the end of 72 hr. Substantial levels of radioactivity were detected in most tissues one hr after administration, indicating a fast absorption and rapid distribution. Subcellular fractionation of the tissues showed that the highest levels of relative percent binding was in the microsomal fraction, whereas cytosol fractions contained lowest levels of bound radioactivity. DNA, RNA, protein and lipid fractions of liver and spleen tissues showed significantly elevated levels of14C-incorporation as compared to other tissues. Thein vivo incorporation of14C-activity showed an increased association of14CH2O with RNA in all the tissues. The maximum registration of radioactivity in RNA was at 48 hr after administration. Significantly higher amounts of14C-activity were registered in DNA of all tissues. The maximum registration of radiolabel in DNA of most tissues was at 12 hr after the14CH2O administration. The liver DNA showed maximal levels at 3 hr with a second peak at 48 hr.Substantial amounts of bound radioactivity in nucleic acids of all the tissues were observed even 72 hr after dosing. The relationship between macromolecular association and formaldehyde toxicity has been discussed.  相似文献   
38.
目的:合成双-对二甲氨基苯甲醛缩二胺类希夫碱,并对其抗菌活性进行研究。方法:以对二甲氨基苯甲醛和二胺类为原料,经缩合反应,制得4种相应希夫碱。结果:结构经元素分析、红外光谱、核磁共振谱确定,4种化合物均未见文献报道,抗菌活性测试表明,它们具有一定抗菌活性。结论:乙酸是催化剂,对缩合反应有利,希夫碱化合物具有一定抗菌活性。  相似文献   
39.
This study reports the first evaluation of sperm hyaluronan binding assay (HBA) for predicting the fertility of Nili-Ravi buffalo bulls in relation to standard parameters of sperm quality. Cryopreserved semen doses of low (n = 6), medium (n = 3) and high fertility (n = 8) bulls based on their respective return rates were used. Significantly, more spermatozoa bound to hyaluronan from the most fertile bulls (57.15% ± 1.44) compared with medium (42.46% ± 1.08) and low fertility bulls (29.70% ± 0.78). A strongly positive correlation (r = .824, p < .01) was found between HBA and fertility that predicts a 67.9% variability (r2 = .679, p < .01) in fertility. HBA was also strongly positively correlated with sperm viability (r = .679, p < .01) followed by their live/dead ratio (r = .637, p < .01), uncapacitated spermatozoa (r = .631, p < .01), normal apical ridge (r = .459, p < .01), motility (r = .434, p < .01), mature spermatozoa with low residual histones (r = .364, p < .01), high plasma membrane integrity (r = .316, p < .01) and nonfragmented DNA levels (r = .236, p < .05). It was negatively correlated with spermatozoa having reacted acrosome (r = −.654, p < .01). A fertility model built using a combination of sperm HBA and either sperm livability or viability predicts, respectively, 86.1% (r2 = .861, p < .01) and 85.9% (r2 = .859, p < .01) variability in buffalo bull fertility. In conclusion, sperm HBA may prove to be a single robust predictor of Nili-Ravi buffalo bull fertility.  相似文献   
40.
IntroductionThe human immunodeficiency virus 1 (HIV‐1) pandemic is characterized by numerous distinct sub‐epidemics (clusters) that continually fuel local transmission. The aims of this study were to identify active growing clusters, to understand which factors most influence the transmission dynamics, how these vary between different subtypes and how this information might contribute to effective public health responses.MethodsWe used HIV‐1 genomic sequence data linked to demographic factors that accounted for approximately 70% of all new HIV‐1 notifications in New South Wales (NSW). We assessed differences in transmission cluster dynamics between subtype B and circulating recombinant form 01_AE (CRF01_AE). Separate phylogenetic trees were estimated using 2919 subtype B and 473 CRF01_AE sequences sampled between 2004 and 2018 in combination with global sequence data and NSW‐specific clades were classified as clusters, pairs or singletons. Significant differences in demographics between subtypes were assessed with Chi‐Square statistics.ResultsWe identified 104 subtype B and 11 CRF01_AE growing clusters containing a maximum of 29 and 11 sequences for subtype B and CRF01_AE respectively. We observed a > 2‐fold increase in the number of NSW‐specific CRF01_AE clades over time. Subtype B clusters were associated with individuals reporting men who have sex with men (MSM) as their transmission risk factor, being born in Australia, and being diagnosed during the early stage of infection (p < 0.01). CRF01_AE infections clusters were associated with infections among individuals diagnosed during the early stage of infection (p < 0.05) and CRF01_AE singletons were more likely to be from infections among individuals reporting heterosexual transmission (p < 0.05). We found six subtype B clusters with an above‐average growth rate (>1.5 sequences / 6‐months) and which consisted of a majority of infections among MSM. We also found four active growing CRF01_AE clusters containing only infections among MSM. Finally, we found 47 subtype B and seven CRF01_AE clusters that contained a large gap in time (>1 year) between infections and may be indicative of intermediate transmissions via undiagnosed individuals.ConclusionsThe large number of active and growing clusters among MSM are the driving force of the ongoing epidemic in NSW for subtype B and CRF01_AE.  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-23

京公网安备 11010802026262号