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   575篇
  免费   31篇
  606篇
  2023年   1篇
  2022年   8篇
  2021年   12篇
  2020年   8篇
  2019年   12篇
  2018年   17篇
  2017年   23篇
  2016年   29篇
  2015年   27篇
  2014年   39篇
  2013年   42篇
  2012年   50篇
  2011年   51篇
  2010年   25篇
  2009年   38篇
  2008年   23篇
  2007年   29篇
  2006年   31篇
  2005年   37篇
  2004年   27篇
  2003年   31篇
  2002年   26篇
  2001年   3篇
  1999年   3篇
  1998年   4篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
排序方式: 共有606条查询结果,搜索用时 15 毫秒
291.
Diffuse large B-cell lymphoma is the commonest histological type of malignant lymphoma, and remains incurable in many cases. Developing more efficient immunotherapy strategies will require better understanding of the disorders of immune responses in cancer patients. NKT (natural killer-like T) cells were originally described as a unique population of T cells with the co-expression of NK cell markers. Apart from their role in protecting against microbial pathogens and controlling autoimmune diseases, NKT cells have been recently revealed as one of the key players in the immune responses against tumors. The objective of this study was to evaluate the frequency of CD3(+)/CD16(+)CD56(+) cells in the peripheral blood of 28 diffuse large B-cell lymphoma (DLBCL) patients in correlation with clinical and laboratory parameters. Median percentages of CD3(+)/CD16(+)CD56(+) were significantly lower in patients with DLBCL compared to healthy donors (7.37% vs. 9.01%, p = 0.01; 4.60% vs. 5.81%, p = 0.03), although there were no differences in absolute counts. The frequency and the absolute numbers of CD3(+)/CD16(+)CD56(+) cells were lower in advanced clinical stages than in earlier ones. The median percentage of CD3(+)/CD16(+)CD56(+) cells in patients in Ann Arbor stages 1-2 was 5.55% vs. 3.15% in stages 3-4 (p = 0.02), with median absolute counts respectively 0.26 G/L vs. 0.41 G/L (p = = 0.02). The percentage and absolute numbers of CD3(+)/CD16(+)CD56(+) cells were significantly higher in DL -BCL patients without B-symptoms compared to the patients with B-symptoms, (5.51% vs. 2.46%, p = 0.04; 0.21 G/L vs. 0.44 G/L, p = 0.04). The percentage of CD3(+)/CD16(+)CD56(+) cells correlated adversely with serum lactate dehydrogenase (R= -445; p 〈 0.05) which might influence NKT count. These figures suggest a relationship between higher tumor burden and more aggressive disease and decreased NKT numbers. But it remains to be explained whether low NKT cell counts in the peripheral blood of patients with DLBCL are the result of their suppression by the tumor cells, or their migration to affected lymph nodes or organs.  相似文献   
292.
This study analyzed the effects of L-arginine and non-specific nitric oxide (NO) synthase blocker (L-NAME) on structural and metabolic changes in experimental ischemia/reperfusion injury in the rat. Histopathological evaluation of rat tissues after reperfusion was also performed. The animals were divided into four groups: [1] nonischemic control, [2] ischemia 4 hrs/repefusion 30, 60, 120 min, [3] ischemia/reperfusion after L-arginine administration, [4] ischemia/reperfusion, after L-arginine, and L-NAME. L-arginine (500 mg/kg) and L-NAME (75 micromol/rat/day) were administrated orally for 5 days before experiment. Concentrations of free radicals, CD-62P, CD-54 and malonyl dialdehyde (MDA) in tissues, and MDA and NO levels in sera were determined. Free radical levels significantly increased in reperfused skeletal muscle, small and large intestines. In large bowel, reperfusion increased MDA levels and evoked a rise of endotoxin level while NO levels decreased. Histological studies showed an increase in the number of lymphocytes in both intestines. Administration of L-arginine reduced leukocyte adherence associated with ischemia-repefusion injury, decreased the levels of free radicals and MDA in the examined tissues, and inhibited the release of endotoxins into blood. L-arginine-treated animals showed higher serum NO levels and reduced leukocyte bowel infiltration. Concomitant L-NAME administration reduced serum NO and tissue free radical [corrected] levels, but did not affect intestinal leukocyte infiltration. L-arginine could ameliorate intestinal ischemia/reperfusion injury and constitute a possible protective mechanism by decreasing neutrophil-endothelial interactions, stimulating free radical scavenging and reducing lipid peroxidation.  相似文献   
293.
The harmonic and anharmonic frequencies of fundamental vibrations in formaldehyde and water were successfully estimated using the B3LYP Kohn-Sham limit. The results obtained with polarization- and correlation-consistent basis sets were fitted with a two-parameter formula. Anharmonic corrections were obtained by a second order perturbation treatment (PT2). We compared the performance of the PT2 scheme on the two title molecules using SCF, MP2 and DFT (BLYP, B3LYP, PBE and B3PW91 functionals) methods combined with polarization consistent pc-n (n = 0, 1, 2, 3, 4) basis sets, Dunning’s basis sets (aug)-cc-pVXZ where X = D, T, Q, 5, 6 and Pople’s basis sets up to 6-311++G(3df,2pd). The influence of SCF convergence level and density grid size on the root mean square of harmonic and anharmonic frequency deviations from experimental values was tested. The wavenumber of formaldehyde CH2 anharmonic asymmetric stretching mode is very sensitive to grid size for large basis sets; this effect is not observed for harmonic modes. BLYP-calculated anharmonic frequencies consistently underestimate observed wavenumbers. On the basis of formaldehyde anharmonic frequencies, we show that increasing the Pople basis set size does not always lead to improved agreement between anharmonic frequencies and experimental values.  相似文献   
294.
The netrin family of secreted proteins provides migrational cues in the developing central nervous system. Recently, netrins have also been shown to regulate diverse processes beyond their functions in the brain, incluing the ochrestration of inflammatory events. Particularly netrin-1 has been implicated in dampening hypoxia-induced inflammation. Here, we hypothesized an anti-inflammatory role of endogenous netrin-1 in acute kidney injury (AKI). As homozygous deletion of netrin-1 is lethal, we studied mice with partial netrin-1 deletion (Ntn-1(+/-) mice) as a genetic model. In fact, Ntn-1(+/-) mice showed attenuated Ntn-1 levels at baseline and following ischemic AKI. Functional studies of AKI induced by 30 min of renal ischemia and reperfusion revealed enhanced kidney dysfunction in Ntn-1(+/-) mice as assessed by measurements of glomerular filtration, urine flow rate, urine electrolytes, serum creatinine and creatinine clearance. Consistent with these findings, histological studies indicated a more severe degree kidney injury. Similarly, elevations of renal and systemic inflammatory markers were enhanced in mice with partial netrin-1 deficiency. Finally, treatment of Ntn-1(+/-) mice with exogenous netrin-1 restored a normal phenotype during AKI. Taking together, these studies implicate endogenous netrin-1 in attenuating renal inflammation during AKI.  相似文献   
295.
296.
297.
Two intramolecular interactions, i.e., (1) hydrogen bond and (2) substituent effect, were analyzed and compared. For this purpose, the geometry of 4- and 5-X-substituted salicylaldehyde derivatives (X = NO2, H or OH) was optimized by means of B3LYP/6-311 + G(d,p) and MP2/aug-cc-pVDZ methods. The results obtained allowed us to show that substituents (NO2 or OH) in the para or meta position with respect to either OH or CHO in H-bonded systems interact more strongly than in the case of di-substituted species: 4- and 3-nitrophenol or 4- and 3-hydroxybenzaldehyde by ∼31%. The substituent effect due to the intramolecular charge transfer from the para-counter substituent (NO2) to the proton-donating group (OH) is ∼35% greater than for the interaction of para-OH with the proton-accepting group (CHO). The total energy of H-bonding for salicylaldehyde, and its derivatives, is composed of two contributions: ∼80% from the energy of H-bond formation and ∼20% from the energy associated with reorganization of the electron structure of the systems in question.  相似文献   
298.
Based on a previously identified HCV replication (replicase) inhibitor 1, SAR efforts were conducted around the pyrimidine core to improve the potency and pharmacokinetic profile of the inhibitors. A benzothiazole moiety was found to be the optimal substituent at the pyrimidine 5-position. Due to potential reactivity concern, the 4-chloro residue was replaced by a methyl group with some loss in potency and enhanced rat in vivo profile. Extensive investigations at the C-2 position resulted in identification of compound 16 that demonstrated very good replicon potency, selectivity and rodent plasma/target organ concentration. Inhibitor 16 also demonstrated good plasma levels and oral bioavailability in dogs, while monkey exposure was rather low. Chemistry optimization towards a practical route to install the benzothiazole moiety resulted in an efficient direct C-H arylation protocol.  相似文献   
299.
300.
This study was conducted in order to identify quantitative trait loci (QTLs) for the in vitro culture response of winter rye (Secale cereale L.) immature embryos and immature inflorescences. A genetic linkage map comprising 67 SSRs, 9 ISSRs, 13 SAMPLs, 7 RAPDs, 2 SCARs and one EST marker was created based on the analyses of 102 recombinant inbred lines from the cross between lines L318 (which has a good response in tissue cultures) and L9 (which is unable to regenerate plants from somatic tissues and anthers). The map spans 979.2 cM, and the average distance between markers is 9.9 cM. Two characteristics were evaluated: callus induction (CI) and somatic embryogenesis ability (SE). They were expressed as the percentage of immature embryos/inflorescences producing callus (designated ECI/ICI) and the percentage of explants producing somatic embryos (ESE/ISE). All the analysed traits showed continuous variation in the mapping population but a non-normal frequency distribution. We identified nine putative QTLs controlling the tissue culture response of rye, explaining up to 41.6% of the total phenotypic variation: two QTLs for ECI — eci-1, eci-2; 4 for ESE — ece-1, ese-2, ese-3, ese-4; 2 for ICI — ici-1, ici2; and 1 for ISE — ise-1. They were detected on chromosomes 1R, 4R, 5R, 6R and 7R.  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