全文获取类型
收费全文 | 3206篇 |
免费 | 205篇 |
国内免费 | 50篇 |
专业分类
耳鼻咽喉 | 33篇 |
儿科学 | 104篇 |
妇产科学 | 55篇 |
基础医学 | 281篇 |
口腔科学 | 36篇 |
临床医学 | 378篇 |
内科学 | 744篇 |
皮肤病学 | 130篇 |
神经病学 | 119篇 |
特种医学 | 260篇 |
外科学 | 304篇 |
综合类 | 60篇 |
预防医学 | 172篇 |
眼科学 | 131篇 |
药学 | 403篇 |
中国医学 | 18篇 |
肿瘤学 | 233篇 |
出版年
2021年 | 37篇 |
2020年 | 22篇 |
2019年 | 36篇 |
2018年 | 40篇 |
2017年 | 57篇 |
2016年 | 48篇 |
2015年 | 85篇 |
2014年 | 90篇 |
2013年 | 144篇 |
2012年 | 133篇 |
2011年 | 145篇 |
2010年 | 132篇 |
2009年 | 123篇 |
2008年 | 141篇 |
2007年 | 143篇 |
2006年 | 133篇 |
2005年 | 138篇 |
2004年 | 94篇 |
2003年 | 109篇 |
2002年 | 104篇 |
2001年 | 90篇 |
2000年 | 78篇 |
1999年 | 80篇 |
1998年 | 109篇 |
1997年 | 87篇 |
1996年 | 89篇 |
1995年 | 63篇 |
1994年 | 73篇 |
1993年 | 62篇 |
1992年 | 43篇 |
1991年 | 30篇 |
1990年 | 33篇 |
1989年 | 60篇 |
1988年 | 54篇 |
1987年 | 48篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 25篇 |
1980年 | 14篇 |
1979年 | 36篇 |
1978年 | 28篇 |
1977年 | 18篇 |
1976年 | 29篇 |
1975年 | 21篇 |
1974年 | 21篇 |
1973年 | 22篇 |
1971年 | 14篇 |
排序方式: 共有3461条查询结果,搜索用时 15 毫秒
101.
Kevin Chiou Erin Hollanger Tarek Agag Hatsuo Ishida 《Macromolecular chemistry and physics.》2013,214(14):1629-1635
Isocyanate functional benzoxazine (NCO‐4HBA‐a) is used for coupling with hydroxyl‐group‐containing molecules. Glycerol is used in a model reaction to study the urethane bonds formed between the NCO‐4HBA‐a and the glycerol's hydroxyl groups. The model supports a reaction between NCO‐4HBA‐a and poly(vinyl alcohol) (PVA), which leads to an improved char yield, determined by thermogravimetric analysis. Glycerol‐based benzoxazine is also an attractive benzoxazine synthesized from the products of biofuel production. Upon functionalization with benzoxazine and subsequent thermal treatment, the hydroxyl‐containing polymer gains thermal stability shown by improved char yield of polybenzoxazine cross‐linked PVA.
102.
Hsiao SH Wang WC Yang SH Lee CY Chang SM Lin SK Chiou KR 《The American journal of cardiology》2008,101(4):536-541
The objective of this study was to develop tissue Doppler parameters that could be used to differentiate right ventricular (RV) volume overload from RV pressure overload. The RV-pressure-overload group consisted of 40 patients with severe pulmonary hypertension, and the RV-volume-overload group consisted of 40 patients who had an atrial septal defect without evidence of right-to-left shunt, significant pulmonary hypertension, or Eisenmenger's complex. Another 40 healthy subjects were enrolled and served as a control group. Routine echocardiography and tissue Doppler imaging were performed. RV myocardial performance index was determined based on data collected during tissue Doppler imaging over the lateral tricuspid annulus. In patients with RV pressure overload, tissue Doppler parameters showed characteristically lower systolic velocity over the tricuspid annulus (RV myocardial systolic wave [Sm]) and longer isovolumic relaxation time (RV-IVRT). Nevertheless, in patients with RV volume overload, RV-Sm increased significantly, but early-diastolic velocity over tricuspid annulus was relatively low. In conclusion, RV-MPI, RV-Sm/early-diastolic velocity over tricuspid annulus, and RV-IVRT/RV-Sm were all useful to differentiate RV pressure overload from volume overload, although RV-IVRT/RV-Sm was the best parameter, with excellent sensitivity and specificity. 相似文献
103.
Randle C. Johnson M.D. Major USAF MC Michael H. Bleshman M.D. James W. DeFord M.D. 《Diseases of the colon and rectum》1978,21(7):510-513
Summary We have presented an unusual case of benign lymphoid hyperplasia, which manifested as a cecal deformity in a 15-year-old boy.
The clinical manifestation may have been related to partial occlusion of the appendiceal orifice. In future cases of benign
lymphoid hyperplasia, colonoscopy may be diagnostic, and if it is used for continuing observation, may avert unnecessary surgical
procedures in children and young adults. 相似文献
104.
LTC Lawrence F. Johnson MC USA LTC Tom R. Demeester MC USA MAJ Roger C. Haggitt MC USA 《Digestive diseases and sciences》1978,23(6):498-509
Exposure of the distal esophageal mucosa to acid gastric juice was quantitated by 24-hr pH monitoring in 100 individuals and was correlated with morphologic data derived from esophageal biopsies. The degree of acid exposure to the distal esophagus correlated directly with increases in both relative and absolute length of the subepithelial papillae and to relative basal zone hyperplasia. Both papillary length and basal zone hyperplasia decreased after antireflux surgery had reduced acid exposure to normal. Reflux in the recumbent position resulted in prolonged exposure of the mucosa to acid because of poor acid clearing from the esophagus. This caused longer papillae than did upright reflux, where there were more frequent reflux episodes, but with rapid acid clearance. The presence of a hiatal hernia was associated with longer papilae, lower DES pressure, increased reflux frequency, and prolonged recumbent acid clearance. Twenty-four hour pH monitoring correlated better with papillary length than did symptoms or other clinical measures of gastroesophageal reflux. 相似文献
105.
Platelet alpha-granule and plasma membrane share two new components: CD9 and PECAM-1 总被引:1,自引:2,他引:1
CD9 (p24) and PECAM1 (CD31) antigens are well-defined components of the platelet plasma membrane. Both are integral glycoproteins (GPs) implicated in the adhesive and aggregative properties of human platelets. In the present report, we have investigated their subcellular localization using immunoelectron microscopy. The monospecificity of the two polyclonal antibodies used was confirmed by immunoblotting. On normal resting platelets, immunolabeling for CD9 and PECAM1 was found lining the plasma membrane and the luminal face of the open canalicular system. Some labeling was also consistently found on the alpha-granule limiting membrane. This was confirmed by double labeling experiments in which fibrinogen and von Willebrand factor (vWF) were used as alpha-granule markers. CD9 and PECAM-1 were found lining the membrane of the same granules that contained fibrinogen and vWF in their matrix. CD9 and PECAM-1 thus appear to have an intracellular distribution identical to GPIIb-IIIa, a major aggregation platelet receptor. To rule out a cross-reactivity of the two polyclonal antibodies with GPIIb/IIIa, we studied PECAM1 and CD9 expression on the platelets from a patient with type I Glanzmann's thrombasthenia whose platelets are devoid of GPIIb/IIIa. The same pattern of labeling was observed for both antigens as for normal platelets. Normal platelets were further observed after stimulation by agonists that either fail to induce (ADP) or induce granule secretion (thrombin). After treatment with ADP, platelets changed shape and centralized their granules; the plasma membrane immunolabeling remained unchanged; and gold particles were still found decorating the periphery of the centralized alpha- granules. After thrombin treatment, alpha-granules fused with the platelet membrane and secretion occurred. A significant increase of labeling was then observed on the platelet surface. From these results we conclude that the alpha-granule membrane contains two additional receptors in common with the plasma membrane. This suggests that alpha- granule membrane receptors may originate from a dual mechanism: direct targeting from the Golgi complex in megakaryocytes (for alpha-granule- specific receptors such as P-selectin) or by endocytosis from the plasma membrane (for proteins distributed in the two compartments). 相似文献
106.
Analysis of exercise-induced R wave amplitude changes in detection of coronary artery disease in asymptomatic men with left bundle branch block 总被引:1,自引:0,他引:1
Gregory S. Uhl USAF MC Major J.Andrew C. Hopkirk MRCP RAF Squadron Leader 《The American journal of cardiology》1979,44(7):1247-1250
The exercise electrocardiograms of 44 asymptomatic men with acquired left bundle branch block were analyzed for changes in R wave amplitude. Results were correlated with findings on selective coronary angiography. There were two subgroups: 7 men with significant angiographic coronary artery disease (Group I) and 37 with normal coronary angiograms (Group II). Exercise induced an increase in R wave amplitude in all seven men with coronary artery disease but in only 10 of the 37 men without significant coronary artery disease. This criterion thus had a sensitivity of 100 percent but a poor specificity of 73 percent, a predictive value of 41 percent and an accuracy rate of 77 percent for the diagnosis of coronary artery disease. The greater the increase in R wave amplitude the greater was the likelihood of some degree of left ventricular dysfunction as measured by wall motion abnormalities and elevated left ventricular end-diastolic pressure. The increase in R wave amplitude with exercise appears to be a sensitive test in identifying coronary artery disease in asymptomatic men with acquired left bundle branch block. 相似文献
107.
Dandan He Jiachi Chiou Zhenling Zeng Lanping Liu Xiaojie Chen Li Zeng Edward Wai Chi Chan Jian-Hua Liu Sheng Chen 《Antimicrobial agents and chemotherapy》2015,59(10):5976-5983
A variety of CTX-M-type extended-spectrum β-lactamases (ESBLs), including hybrid ones, have been reported in China that are uncommon elsewhere. To better characterize the substrate profiles and enzymatic mechanisms of these enzymes, we performed comparative kinetic analyses of both parental and hybrid CTX-M enzymes, including CTX-M-15, -132, -123, -64, -14 and -55, that are known to confer variable levels of β-lactam resistance in the host strains. All tested enzymes were susceptible to serine β-lactamase inhibitors, with sulbactam exhibiting the weakest inhibitory effects. CTX-M-55, which differs from CTX-M-15 by one substitution, A77V, displayed enhanced catalytic activity (kcat/Km) against expanded-spectrum cephalosporins (ESCs). CTX-M-55 exhibits higher structure stability, most likely by forming hydrophobic interactions between A77V and various key residues in different helices, thereby stabilizing the core architecture of the helix cluster, and indirectly contributes to a more stable active site conformation, which in turn shows higher catalytic efficiency and is more tolerant to temperature change. Analyses of the hybrids and their parental prototypes showed that evolution from CTX-M-15 to CTX-M-132, CTX-M-123, and CTX-M-64, characterized by gradual enhancement of catalytic activity to ESCs, was attributed to introduction of different substitutions to amino acids distal to the active site of CTX-M-15. Similarly, the increased hydrolytic activities against cephalosporins and sensitivity to β-lactamase inhibitors, clavulanic acid and sulbactam, of CTX-M-64 were partly due to the amino acids that were different from CTX-M-14 and located at both the C and N termini of CTX-M-64. These data indicate that residues distal to the active site of CTX-Ms contributed to their enhanced catalytic activities to ESCs. 相似文献
108.
109.
110.
Kuo LJ Chiou JF Tai CJ Chang CC Kung CH Lin SE Hung CS Wang W Tam KW Lee HC Liang HH Chang YJ Wei PL 《International journal of colorectal disease》2012,27(5):613-621