全文获取类型
收费全文 | 813篇 |
免费 | 36篇 |
国内免费 | 22篇 |
专业分类
耳鼻咽喉 | 1篇 |
儿科学 | 39篇 |
妇产科学 | 3篇 |
基础医学 | 62篇 |
口腔科学 | 9篇 |
临床医学 | 62篇 |
内科学 | 223篇 |
皮肤病学 | 3篇 |
神经病学 | 5篇 |
特种医学 | 313篇 |
外科学 | 48篇 |
综合类 | 19篇 |
预防医学 | 23篇 |
眼科学 | 3篇 |
药学 | 31篇 |
中国医学 | 1篇 |
肿瘤学 | 26篇 |
出版年
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 8篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 8篇 |
2012年 | 13篇 |
2011年 | 19篇 |
2010年 | 12篇 |
2009年 | 19篇 |
2008年 | 14篇 |
2007年 | 36篇 |
2006年 | 16篇 |
2005年 | 15篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 17篇 |
1998年 | 46篇 |
1997年 | 42篇 |
1996年 | 57篇 |
1995年 | 43篇 |
1994年 | 33篇 |
1993年 | 39篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 31篇 |
1988年 | 35篇 |
1987年 | 28篇 |
1986年 | 25篇 |
1985年 | 39篇 |
1984年 | 20篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1975年 | 14篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有871条查询结果,搜索用时 31 毫秒
101.
Alkylureas are capable of inhibiting sickling in vitro and the gelation of solutions of hemoglobin S at concentrations between 0.05 and 0.1 M with increasing effectiveness that is directly proportional to the length of the alkyl chain (butyl greater than propyl greater than ethyl greater than methyl). 6The inhibitory effect is independent of pH between 6.5 and 7.5 and is a process driven by entropy. The alkylureas at concentrations of 0.1 M have minimal effects on several erythrocyte functions. Oxygen equilibria, osmotic fragility, reduced glutathione content, and glutathione reductase activity are totally unaffected, while pyruvic kinase activity is decreased only by butylurea by about 20%, and glucose-6-phosphate dehydrogenase activity is decreased progressively to a maximum of 30% in direct proportion to the length of the alkyl chain. Alkylureas not only inhibit sickling but are also capable of desickling erythrocytes that have been maintained in the deoxygenated state. They have little effect on several erythrocyte functions at antisickling concentrations, but their toxicity must be evaluated before they can be examined as potential therapeutic agents for the treatment or prevention of acute episodes in sickle cell anemia. 相似文献
102.
Signal transduction and the regulation of actin conformation during myeloid maturation: studies in HL60 cells 总被引:2,自引:0,他引:2
Maturation of human myeloid cells is associated with quantitative and qualitative changes in protein kinase C (PKC) and increases in N-formyl- L-methionyl-L-leucyl-L-phenylalanine (FMLP) receptors, actin, and actin regulatory proteins. We have studied the actin responses and cell shape changes caused by FMLP and its second messenger pathways in HL60 cells undergoing neutrophilic maturation. In uninduced cells, the PKC activators 12-O-tetradecanoyl phorbol-13-acetate (TPA), bryostatin, and 1-oleyl-2-acetylglycerol (OAG) resulted in 15% to 30% decreases in F- actin, whereas FMLP had no effect. Ionomycin had no effect on actin but did cause a 10-fold increase in intracellular calcium. Cells grown for 24 hours in 1% dimethyl sulfoxide (DMSO) acquired the ability to polymerize actin in response to FMLP and ionomycin. TPA continued to cause a decrease in F-actin at 24 hours, but caused an increase in F- actin at 48 to 72 hours of maturation. The PKC inhibitor 1-5- isoquinolinesulfonyl 2-methylpiperazine (H7) partially blocked the F- actin increase caused by TPA in induced cells, but had no effect on the decrease in F-actin caused by TPA in uninduced cells or the increase in F-actin seen in FMLP-treated neutrophils. F-actin rich pseudopods developed following TPA or FMLP stimulation of induced HL60 cells; in uninduced cells neither agent caused pseudopod formation but TPA caused a dramatic loss of surface ruffles. The ability of FMLP and ionomycin to elicit a neutrophil-like actin response in HL60 cells within 24 hours after DMSO treatment shows that the actin regulatory mechanism is mature by that time. The inability of ionomycin to increase F-actin in uninduced cells supports the view that calcium increases alone are insufficient for actin polymerization. The longer maturation time required for HL60 cells to develop an actin polymerization response to TPA compared with FMLP, coupled with the inability of H7 to block the FMLP-mediated F-actin increase in neutrophils, suggests that the F- actin increase caused by FMLP is not mediated solely by PKC. Lastly, the TPA-induced F-actin decrease and shape changes in uninduced HL60 cells, and the longer time required for a "mature" response to TPA, may reflect immaturity in the PKC isoenzyme pattern rather than immaturity of the actin regulatory mechanism. 相似文献
103.
Sickle erythrocyte-endothelial interactions in microcirculation: the role of von Willebrand factor and implications for vasoocclusion 总被引:1,自引:0,他引:1
To determine the role of von Willebrand factor (vWF) in adhesion of sickle (SS) erythrocytes in microvascular flow conditions, we have perfused the ex vivo mesocecum vasculature of the rat with desmopressin, an analogue of vasopressin that causes the release of endothelial vWF. Analysis of vWF in the venous effluent of the isolated vasculature showed mainly the presence of extra-large molecular weight forms characteristic of endothelial vWF, which in the presence of desmopressin showed an average increase of 54%. Also, desmopressin induced a significant increase in adhesion of washed oxygenated (oxy) unseparated SS erythrocytes, accompanied by a persistent microvascular obstruction and a pronounced increase in the peripheral resistance (PRU). In contrast, infusion of SS deformable discocytes (SS2) in desmopressin-perfused vasculature resulted in a significant adhesion but not in persistent vasoocclusion, showing that SS2 discocytes alone are not sufficient for microvascular obstruction. Furthermore, SS4 erythrocytes (dense discocytes and irreversibly sickled erythrocytes) caused a persistent microvascular blockage and a significantly higher PRU than SS2 discocytes. However, the increase in PRU for SS4 erythrocytes following desmopressin treatment was 50% less compared with a corresponding increase for SS2 discocytes over the control values, which showed a smaller effect of desmopressin on the hemodynamic behavior of SS4 dense erythrocytes. Incubation of desmopressin-treated vasculature with anti-vWF antibodies resulted in a pronounced decrease in adhesion and significantly improved hemodynamic behavior of SS cells. Also, in untreated vasculature, similarly incubated with anti-vWF antibodies, there was almost complete inhibition of adhesion. Under the described perfusion conditions, antibodies to fibronectin and thrombospondin, as well as incubation of SS erythrocytes with anti-vWF antibodies did not affect adhesion. These results are compatible with a model for SS vasoocclusion in which extra- large vWF-mediated adhesion of deformable SS erythrocytes is the first step followed by an accelerated entrapment of dense SS erythrocytes. 相似文献
104.
Storb R; Prentice RL; Banaji M; Witherspoon RP; Sullivan KM; Stewart P; Sanders JE; Mason M; Doney K; Deeg J; Clift RA; Buckner CD; Appelbaum FR; Thomas ED 《Blood》1983,61(4):672-675
The present study in patients with aplastic anemia was undertaken to determine whether exposure of recipients to donor blood products 24 hr before preparation with cyclophosphamide (1) enhanced the rate of sustained engraftment of marrow from HLA-identical siblings as suggested by animal experiments, (2) increased the rejection rate, in particular in transfused patients who may already have been exposed to donor antigens by blood products, or (3) was of no relevance to the outcome of transplantation of marrow from HLA-identical siblings. One- hundred fifty-five patients were studied, of whom 78 received blood products from the marrow donor 24 hr before cyclophosphamide and 77 did not. A binary logistic regression analysis was applied to the data, simultaneously considering five previously known risk factors for rejection. Results showed that preceding transfusion of donor blood products had neither a significant beneficial nor detrimental effect on the incidence of sustained engraftment. 相似文献
105.
Mitchell PL; Clutterbuck RD; Powles RL; De Lord C; Morilla R; Hiorns LR; Titley J; Catovsky D; Millar JL 《Blood》1996,87(11):4797-4803
Human interleukin-4 (huIL-4) has been shown to inhibit the growth in vitro of cells from patients with acute lymphoblastic leukemia (ALL). With the aim of determining whether this cytokine might be useful in the treatment of patients with ALL, the effects of huIL-4 on human B- cell precursor ALL engrafted in severe combined immunodeficient (SCID) mice were examined. The inhibition of [3H] thymidine uptake of primary ALL cells by huIL-4 was maintained following engraftment and passage of leukemia in SCID mice. Five of seven xenograft leukemias showed significant inhibition in vitro by huIL-4 at concentrations as low as 0.5 ng/mL; furthermore, huIL-4 counteracted the proliferative effects of IL-7. When used to treat two human leukemias engrafted in SCID mice, huIL-4 200 microgram/kg/d, as a continuous 14-day subcutaneous infusion, suppressed the appearance of circulating lymphoblasts and extended survival of mice by 39% and 108%, respectively, the first demonstration of IL-4 activity against human leukemia in vivo. The mean steady-state huIL-4 level in mouse plasma during the infusion was 1.46 ng/mL (SEM +/- 0.14 ng/mL), which was similar to concentrations found to be effective in vitro. ALL cells obtained from mice relapsing after huIL-4 treatment continued to show inhibition by the cytokine in vitro. These data suggest that IL-4 may be useful in the treatment of patients with ALL. 相似文献
106.
BACKGROUND: The prognostic significance of proteinuria in older people is not well defined. We examined the associations between proteinuria and incident coronary heart disease, cardiovascular mortality, and all-cause mortality in older people.SUBJECTS AND METHODS: Casual dipstick proteinuria was determined in 1,045 men (mean [+/- SD] age 68 +/- 7 years) and 1,541 women (mean age 69 +/- 7 years) attending the 15th biennial examination of the Framingham Heart Study. Participants were divided by grade of proteinuria: none (85.3%), trace (10.2%), and greater-than-trace (4.5%). Cox proportional hazards analyses were used to determine the relations of baseline proteinuria to the specified outcomes, adjusting for other risk factors, including serum creatinine level.RESULTS: During 17 years of follow-up, there were 455 coronary heart disease events, 412 cardiovascular disease deaths, and 1,214 deaths. In men, baseline proteinuria was associated with all-cause mortality (hazards ratio [HR] = 1.3, 95% confidence interval [CI] 1.0 to 1.7 for trace proteinuria; HR = 1.3, 95% CI 1.0 to 1.8 for greater-than-trace proteinuria; P for trend = 0.02). In women, trace proteinuria was associated with cardiovascular disease death (HR = 1. 6, 95% CI 1.1 to 2.4), and all-cause mortality (HR = 1.4, 95% CI 1.1 to 1.7).CONCLUSION: Proteinuria is a significant, although relatively weak, risk factor for all-cause mortality in men and women, and for cardiovascular disease mortality in women. 相似文献
107.
Transforming growth factor-beta1: differential effects on multiple myeloma versus normal B cells 总被引:7,自引:4,他引:7
Urashima M; Ogata A; Chauhan D; Hatziyanni M; Vidriales MB; Dedera DA; Schlossman RL; Anderson KC 《Blood》1996,87(5):1928-1938
Interleukin-6 (IL-6), a product of bone marrow stromal cells (BMSCs), is a growth factor for multiple myeloma (MM) cells. Transforming growth factor-beta1 (TGF-beta1) is also produced by BMSCs and can regulate IL- 6 secretion by several tissues, including BMSCs. The present study was designed to characterize in vitro tumor growth regulation by TGF-beta1 in MM. Sorted CD38+CD45RA- MM cells secreted significantly more TGF- beta1 (8.2 +/- 2.0 ng/mL) than peripheral blood mononuclear cells (P < .001), splenic B cells (P < .001), and CD40 ligand (CD40L) pretreated B cells (P < .05). TGF-beta1 secretion by MM-BMMCs (3.8 +/- 0.9 ng/mL) was significantly greater than by N-BMMCs (1.2 +/- 0.1 ng/mL, P < .001). MM-BMSCs also secreted significantly more TGF-beta1 (6.6 +/- 2.5 ng/mL, n = 11) than N-BMSCs (4.4 +/- 0.6 ng/mL, P < .02, n = 10) and N- BMSC lines (3.9 +/- 0.2 ng/mL, P < .02, n = 6). TGF-beta1 secretion was correlated with IL-6 secretion in MM-BMSCs. Anti-TGF-beta1 monoclonal antibody both blocked IL-6 secretion by BMSCs and inhibited the increments in IL-6 secretion by BMSCs induced by MM cell adhesion. Moreover, exogenous TGF-beta1 upregulated IL-6 secretion by MM-BMSCs, normal BMSCs, and CD38+ CD45RA- MM cells, as well as tumor cell proliferation. This is in contrast to the inhibitory effect of TGF- beta1 on proliferation and Ig secretion of normal splenic B cells. Finally, retinoblastoma proteins (pRB) are constitutively phosphorylated in MM cells; TGF-beta1 either did not alter or increased pRB phosphorylation. pRB are dephosphorylated in splenic B cells and phosphorylated in CD40L triggered B cells in contrast to its effects on MM cells, TGF-beta1 decreased phosphorylation of pRB in CD40L treated B cells. These results suggest that TGF-beta1 is produced in MM by both tumor cells and BMSCs, with related tumore cell growth. Moreover, MM cell growth may be enhanced by resistance of tumor cells to the inhibitory effects of TGF-beta1 on normal B-cell proliferation and Ig secretion. 相似文献
108.
Surface shield: device to reduce personnel radiation exposure 总被引:2,自引:0,他引:2
Young AT; Morin RL; Hunter DW; Nelson KL; Cardella JF; Castaneda-Zuniga WR; Amplatz K 《Radiology》1986,159(3):801-803
A simple device is described that can reduce personnel exposure from scatter radiation by up to 75%. The device consists of an oblong piece of shielding (0.75-mm lead equivalent) that is taped to the side of the patient during percutaneous renal stone removal and other interventional procedures. Contrary to other shields and barriers, this does not interfere with access to the patient. Scatter exposure data from phantom studies are presented and the rationale for surface shielding discussed. 相似文献
109.
Common bile duct stones: reassessment of criteria for CT diagnosis 总被引:17,自引:0,他引:17
To evaluate the specificity of previously suggested computed tomographic (CT) criteria for diagnosing common bile duct (CBD) stones, CT scans of 38 patients with CBD stones were compared with scans of 32 patients with carcinoma obstructing the CBD and 28 nonobstructed patients. The CBD stone was directly visualized as a target sign or densely calcified structure in 29 of 38 patients with stones (76%); one with carcinoma showed a similar target sign. A rim of increased density in the distal CBD was found without accompanying target sign in six patients with stones (16%), compared with 12 with carcinoma (38%) and 15 nonobstructed patients (54%). Irregular intraluminal densities without a detectable target sign were noted in four patients with stones (11%), compared with eight with carcinoma (25%) and nine nonobstructed patients (32%). Abrupt termination of the CBD without a mass was more common as an isolated finding in patients with carcinoma (31%) than in patients with stones (13%). CT is accurate in detecting CBD stones in certain patient populations, but direct visualization of the stone is required. 相似文献
110.