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   87916篇
  免费   6547篇
  国内免费   3972篇
耳鼻咽喉   392篇
儿科学   1543篇
妇产科学   930篇
基础医学   14327篇
口腔科学   1760篇
临床医学   7211篇
内科学   15263篇
皮肤病学   1169篇
神经病学   8198篇
特种医学   1384篇
外国民族医学   15篇
外科学   5436篇
综合类   14747篇
现状与发展   22篇
预防医学   5033篇
眼科学   1051篇
药学   11216篇
  13篇
中国医学   2850篇
肿瘤学   5875篇
  2024年   644篇
  2023年   1039篇
  2022年   2394篇
  2021年   3223篇
  2020年   2681篇
  2019年   2225篇
  2018年   2196篇
  2017年   2497篇
  2016年   2860篇
  2015年   3236篇
  2014年   5376篇
  2013年   6038篇
  2012年   5683篇
  2011年   6338篇
  2010年   5025篇
  2009年   4936篇
  2008年   5055篇
  2007年   4891篇
  2006年   4363篇
  2005年   4073篇
  2004年   3380篇
  2003年   2867篇
  2002年   2198篇
  2001年   1883篇
  2000年   1623篇
  1999年   1391篇
  1998年   1306篇
  1997年   1131篇
  1996年   964篇
  1995年   774篇
  1994年   745篇
  1993年   625篇
  1992年   534篇
  1991年   503篇
  1990年   420篇
  1989年   332篇
  1988年   321篇
  1987年   299篇
  1986年   264篇
  1985年   374篇
  1984年   330篇
  1983年   219篇
  1982年   254篇
  1981年   197篇
  1980年   171篇
  1979年   115篇
  1978年   95篇
  1977年   83篇
  1976年   78篇
  1975年   58篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
目的:研究睾丸局部感染后支持细胞免疫调节功能与锌指蛋白265(zinc finger protein265,ZNF265)的变化情况。方法:以溶脲脲原体(Ureaplasma urealyticum,UU)体内感染支持细胞后,分别在感染1、2、3周时间段运用RT-PCR、免疫组化和流式细胞术(FCM)方法比较感染组与对照组间ZNF265、IL-1α、IL-6、TGF-β和FasL的mRNA及蛋白水平的表达变化情况。结果:与对照组相比,体内感染处理后2周后支持细胞的ZNF-265表达下降,3周后又升高;TGF-β和FasL从感染2周开始表达上升,一直至3周仍处于上升趋势;感染2周IL-1α和IL-6表达分别上升;3周后则分别下降。结论:ZNF265在支持细胞被UU感染后会产生表达变化。  相似文献   
952.
Objective To explore the relationship between total bile acid(TBA)concentration and fetal pulmonary surfactant in intrahepatic cholestasis of pregnancy(ICP).Methods Fifry five patients with ICP(ICP group)who received cesarean section from April 2008 to February 2010 in Second Xiangya Hospital,Central South University,were recruited.The general conditions of the neonates within 7 days after birth in ICP group were recorded.Those with fetal distress,neonatal asphyxia,or neonatal respiratory distress syndrome were referred as pathological neonates, others were referred as normal neonates. Over the same period, 23 healthy gravidas were recruited as control group. Enzymatic method was used to detect the TBA concentrations in maternal blood, cord blood and amniotic fluid. ELISA was employed to measure the urfactant protein A (SP-A) concentration in cord blood. High performance liquid chromatography system was used to detect the concentrations of phesphatidylcholine (PC),phosphatidylinositol (PI),lysophosphatidylcholine ( LPC), and sphingomyelin(SM) in amniotic fluid. Results ( 1 ) The concentrations of TBA in maternal blood, cord blood and amniotic fluid were ( 30. 1 ± 7.9 ), (9. 3± 3. 3 ) and (4. 4 ± 1.5 ) mmol/L in ICP group, (4. 8 ± 2. 2), (4. 9 ± 0. 9) and ( 1.4 v 1.1 ) mmol/L in control group, respectively. The differences between the two groups were significant ( P < 0. 05 ). ( 2 ) The SP-A concentration in cord blood in ICP group was ( 29. 5 ± 6. 4 ) μg/L, significantly higher than that in control group, which was ( 22. 6 ± 7. 4 )μg/L ( P< 0. 05 ). ( 3 ) There were 20 pathological neonates and 35 normal neonates in ICP group. In pathological neonates, the concentrations of TBA and SP-A in cord blood were (10.9 ± 2.2) mmol/L,(37.0 ± 5.9 ) μg/L, respectively; and were ( 8.0 ± 2. 8 ) mmol/L, ( 26. 7 ± 4. 8 ) μg/L in normal neonates. The differences were significant (P< 0. 05 ). (4) There was a positive correlation between TBA concentration in cord blood and in maternal blood ( r1 = 0. 706, P<0. 05 ). The TBA concentration in cord blood was positively correlated with SP-A concentration as well ( r3 = 0. 494,P < 0. 05 ). (5) The PC and PI concentrations in amniotic fluid were (65.4 ± 7.2) mg/L and ( 3. 8 ± 0. 6 ) mg/L in ICP group, ( 69. 7 ±3.7) mg/L and (4. 3 ± 0. 7 ) mg/L in control group, respectively. The differences were significant (P <0. 05 ). The concentration of LPC in amniotic fluid in ICP group was (4. 8 ±0. 9) mg/L, significantly higher than that in control group (P<0. 05), which was (4. 2 ±0. 6) mg/L. The concentration of SM in amniotic fluid was (3.5±0. 8) mg/L in ICP group, (4. 0 ± 0. 5 ) mg/L in control group, with no significant difference ( P>0. 05 ). (6) The ratio of PC/LPC in ICP group ( 14. 2± 3. 2 ) was significantly lower than that in control group ( 16. 9 ± 2. 5 ) ( P< 0. 05 ). ( 7 ) The TBA concentration in cord blood was negatively correlated with PC and PI concentrations (r1 = -0. 561, r2 = -0. 407, P < 0. 05 ), and had no correlation with LPC concentration (r3 = 0. 260, P> 0. 05). Conclusions ( 1 ) The fetal TBA concentrations in both cord blood and amniotic fluid of patients with ICP was higher than those of healthy gravidas, they were also positively correlated with maternal TBA concentration. (2) ICP resulted in the change of fetal pulmonary surfactant and this change was associated with TBA concentrations in both cord blood and amniotic fluid.  相似文献   
953.
954.
Cat and rat experiments show that the protein fraction isolated from blood serum of the Greenland seal has a protective activity against motion sickness. This activity is comparable to that of the classical vestibuloprotector scopolamine and is greater than that of diprazine. Radioligand assay of the receptor binding showed that the serum protein fraction has the highest affinity for α2-adrenoceptors, μ-opioid, and benzodiazepine receptors. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol 117, N o 4, pp. 444–445, April, 1994  相似文献   
955.
OBJECTIVE: This study was undertaken to assess the left ventricular mass (LV Mass) and systolic and diastolic functions of the left ventricle in children with protein energy malnutrition (PEM). METHODOLOGY: Thirty children, aged between 2 months and 2 years with PEM (four kwashiorkor, seven marasmic- kwashiorkor, 19 marasmus), and 17 healthy, age-matched children, using Doppler echocardiography were studied. RESULTS: The mean LV Mass in the patients was lower than that in the controls (14.5 +/- 5.2 vs 19.8 +/- 4.7 g, P < 0.05). However, the LV Mass/body surface area was not different in the patients with PEM and in the control group (52 +/- 9.2 vs 53.9 +/- 8.2g/m(2), P > 0.05), indicating that LV Mass was reduced in proportion to decrease in body size in malnutrition. Left ventricular septal and posterior wall thickness in PEM were also lower than that in the controls, and the most significant reduction in the LV Mass, septal and posterior wall thickness were found in the kwashiorkor group. Cardiac output was reduced in proportion to decrease in body size in the patient group (1.6 +/- 0.5 vs 2.1 +/- 0.8 L/min, P < 0.05), therefore cardiac index was not significantly different between the patients and the control subjects (5.9 +/- 1.4 vs 5.7 +/- 1.6 L/min/m(2), P > 0.05). Systolic function indices including ejection fraction, fractional shortening, and diastolic function indices were not significantly different in the groups. CONCLUSIONS: We demonstrated that LV Mass and cardiac output were reduced in proportion to decrease in body size in patients with PEM, and LV systolic and diastolic functions were preserved in atrophic hearts.  相似文献   
956.
957.
基质金属蛋白酶-1、2在异位内膜组织中的表达   总被引:6,自引:0,他引:6  
目的 :探讨基质金属蛋白酶 1(MMP 1)和MMP 2在子宫内膜异位症发生发展中的作用。方法 :采用免疫组化链霉菌抗生物素蛋白 过氧化物酶染色法 (S P法 )检测子宫内膜异位症 5 1例的异位内膜和在位内膜中MMP 1、2的表达 ;并用银染法观察嗜银网状纤维的完整性及细胞外基质的崩解情况。正常子宫内膜为对照组。结果 :在异位内膜组织中MMP 1、2均呈高表达状态 ,与正常子宫内膜和子宫内膜异位症在位内膜 ,差异有高度显著性 (P <0 .0 0 1) ,而且失去二者在内膜组织中表达的周期性变化。但在子宫内膜异位症在位内膜与正常子宫内膜之间没有差别 (P >0 .0 5 )。银染结果显示 :MMP 1的局部表达 (尤其间质中的表达 )与嗜银纤维网的完整性呈负相关 (P <0 .0 1)。在巧克力囊肿异位灶间质中 ,MMP 1、2的染色强度较紫蓝色结节灶中增强 ,二者的表达与异位灶的活性相关 (P <0 .0 5 ) ;但二者的表达强度与子宫内膜异位症的严重程度无明显的相关性 (P>0 .0 5 )。结论 :异位内膜组织中MMP 1、2过度表达 ,使异位内膜组织具有更强的侵袭力 ,可能在子宫内膜异位症的发生发展中起重要作用。  相似文献   
958.
FUNDAMENTALS AND OBJECTIVE: Multiple sclerosis (MS) is the prototype of demyelinating disease, but recently, it has been shown that the existence of axonal lesions contribute to irreversible central nervous system damage in this disease. Tau proteins are considered to be important for maintaining the stability of axonal microtubules involved in the mediation of fast axonal transport of synaptic constituents. There have been reports of increased cerebrospinal fluid (CSF) tau concentrations in patients with MS, and it has been suggested that this could be a marker of axonal damage. The objective of the present study was to elucidate whether CSF tau levels could be a marker of MS activity. PATIENT AND METHODS: We measured tau concentrations in the CSF of 20 patients with MS (nine in the first, seven in the second, one in the fourth exacerbation, and three patients with chronic progressive course) and 32 age- and sex-matched controls, using a specific enzyme-linked immunosorbent assay method. RESULTS: The CSF tau concentrations of patients with MS did not differ from those of controls, and they were not correlated with age at onset and duration of the disease. CONCLUSION: CSF tau concentrations are not a marker of MS activity.  相似文献   
959.
A cell type-specific green fluorescent protein (GFP) expression system in rat cortical primary cultures has been developed for the fluorescence labeling of brain cells. Lipid-mediated transfection (lipofection) was employed, allowing the establishment of a convenient efficient system for the analysis of individual cells. To achieve cell type-specific labeling, GFP expression vectors containing the rat neuron-specific enolase (NSE) gene promoter, human glial fibril acidic protein (GFAP) gene promoter, human elongation factor (EF-1alpha) gene promoter, or human cytomegalovirus (CMV) immediate early promoter were constructed, and their specificities examined. Vectors containing the CMV or GFAP promoter resulted primarily in GFP expression in astrocytes, while those containing the EF1-alpha or NSE promoter resulted primarily in GFP expression in neurons. This labeling system was applied to the morphological analysis of living neurons and to cell type-selective calcium imaging. Confocal microscopy revealed that individual GFP-expressing neurons had processes, which were longer than 500 microm and bore spine-like protrusions. A calcium-indicating GFP variant, yellow cameleon (YC2.1), was expressed in the same system, and cell type-selective calcium imaging performed. On pharmacological stimulation, YC2.1-expressing neurons responded to depolarizing stimuli, but not to the metabotropic glutamate receptor agonist, trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (tACPD), while astrocytes responded only to tACPD.  相似文献   
960.
Since Pb(2+) substitutes for Ca(2+) in essential steps leading to exocytosis, we have investigated whether Ca(2+) and Pb(2+) induce exocytosis through similar pathways. Vesicular catecholamine release was measured from dexamethasone-differentiated PC12 cells using carbon fiber microelectrode amperometry. Effects of drugs known to modulate PKC (PMA, staurosporine), calcineurin (cyclosporin A), calmodulin (W7), and CaM kinase II (KN-62) activity were investigated in intact and in ionomycin-permeabilized PC12 cells. Activation of PKC and inhibition of calmodulin decrease the frequency of exocytotic events evoked by high K(+) stimulation in intact cells. In addition, inhibition of calmodulin enhances the frequency of basal exocytosis from intact cells. Activation of PKC and inhibition of calcineurin enhance the frequency of basal exocytosis in intact as well as in ionomycin-permeabilized cells. Inhibition of PKC and of CaM kinase II cause no significant effects. None of the treatments has a significant effect on vesicle contents. The combined results indicate that PKC and calcineurin enhance and inhibit exocytosis through direct effects on the exocytotic machinery, whereas calmodulin and CaM kinase II exert indirect effects only. Conversely, Pb(2+)-evoked exocytosis in permeabilized cells is strongly reduced by inhibition of CaM kinase II, but is not sensitive to modulation of PKC and calcineurin activity. Inhibition of calmodulin only reduces the delay to onset of Pb(2+)-evoked exocytosis. Synaptotagmin I- and II-deficient PC12-F7 cells exhibit vesicular catecholamine release following depolarization or superfusion with Pb(2+). However, the frequency of exocytosis and the contents of vesicles released are strongly reduced as compared to PC12 cells. It is concluded that Ca(2+)-evoked exocytosis is modulated mainly by PKC and calcineurin, whereas Pb(2+)-evoked exocytosis is mainly modulated by CaM kinase II.  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