全文获取类型
收费全文 | 13191篇 |
免费 | 691篇 |
国内免费 | 428篇 |
出版年
2023年 | 223篇 |
2022年 | 338篇 |
2021年 | 369篇 |
2020年 | 346篇 |
2019年 | 434篇 |
2018年 | 424篇 |
2017年 | 277篇 |
2016年 | 275篇 |
2015年 | 346篇 |
2014年 | 723篇 |
2013年 | 987篇 |
2012年 | 529篇 |
2011年 | 791篇 |
2010年 | 508篇 |
2009年 | 608篇 |
2008年 | 636篇 |
2007年 | 639篇 |
2006年 | 567篇 |
2005年 | 542篇 |
2004年 | 483篇 |
2003年 | 393篇 |
2002年 | 351篇 |
2001年 | 239篇 |
2000年 | 203篇 |
1999年 | 223篇 |
1998年 | 170篇 |
1997年 | 166篇 |
1996年 | 153篇 |
1995年 | 198篇 |
1994年 | 126篇 |
1993年 | 134篇 |
1992年 | 106篇 |
1991年 | 108篇 |
1990年 | 86篇 |
1989年 | 79篇 |
1988年 | 77篇 |
1987年 | 74篇 |
1986年 | 72篇 |
1985年 | 120篇 |
1984年 | 160篇 |
1983年 | 107篇 |
1982年 | 135篇 |
1981年 | 123篇 |
1980年 | 103篇 |
1979年 | 90篇 |
1978年 | 98篇 |
1977年 | 83篇 |
1976年 | 70篇 |
1975年 | 59篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
Ford LT Berg JD 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2003,798(1):111-115
A non-extraction high-performance liquid chromatographic (HPLC) method has been developed for the determination of 6-methylthioguanine (6-MTG), as part of the determination of thiopurine S-methyltransferase activity (TPMT) in erythrocytes. Erythrocyte lysate is added to a glass vial containing substrates and incubation buffer, which is then sealed for the rest of the analysis. Enzyme incubation, sample preparation, and analysis are then undertaken without further sample-handling steps. The need for a solvent extraction step has been overcome by heating the incubate to 85 degrees C to stop the enzyme reaction. The heat inactivation step precipitates protein which upon centrifugation forms a thin film in the bottom of the glass vial enabling the supernatant to be injected directly onto the HPLC system. The assay shows excellent precision and recovery with a within-batch imprecision giving a co-efficient of variation of 2.9% (mean=41.5 nmol 6-MTG/gHb/h, n=10) and 5.1% (mean=12.6 nmol 6-MTG/g Hb/h, n=10). The between-batch imprecision gives a co-efficient of variation of 8.2% (mean=11.1 nmol 6-MTG/gHb/h, n=11) and 7.3% (mean=41.0 nmol 6-MTG/gHb/h, n=16). Determination of the TPMT activity in 120 people shows a range of enzyme activity of 11.3-63.8 nmol 6-MTG/gHb/h with a mean and median activity of 34.8 and 34.2 nmol 6-MTG/gHb/h, respectively. TPMT is increasingly used in clinical practice to ensure optimisation of treatment with thioguanine drugs. This direct HPLC method minimises sample-handling, reduces inherent imprecision, the possibility of laboratory error and with the potential for further automation, makes it ideal for use in a regional referral laboratory. 相似文献
992.
993.
994.
Excessive increase of serum interleukin 6 jeopardizes host defense against multi-bacterial infection 总被引:1,自引:0,他引:1
Serum interleukin 6 (IL-6) is elevated among patients who have undergone surgery, trauma, and thermal injury. It is well known that the greater the increase of serum IL-6, the higher the incidence of post-injury morbidity and mortality is. However, it has not been determined whether the physiological effects of IL-6 increase the rate of morbidity and mortality or if IL-6 is just a bystander that only indicates the severity of the injury. To elucidate this, we planned to investigate the effect of IL-6 on a multi-bacterial infection, one of the most frequent post-injury complications. CDF1 male mice were administered recombinant human IL-6 (hIL-6) continuously at a dose of 0, 1, or 10 microg/day. The mice then underwent cecal ligation without puncture that induced slow multi-bacterial infection. The survival rate of mice receiving 10 microg/day of hIL-6 was significantly lower (38.5%) than the rate of those receiving 0 (83.3%) or 1 (92.3%) microg/day of hIL-6. The result of this study showed that only excessive increases in serum IL-6, to levels that were observed among patients who underwent severe injury or extensive surgery with high incidence of post-injury infection, jeopardize the host's defense against bacterial infection. 相似文献
995.
The involvement of the proinflammatory cytokines, interleukin 8 (IL-8) and 6 (IL-6), was studied during the first 72 h of acute invasive gastroenteritis. Study population included 33 infants and young children aged six months to six years and seven age-matched controls. As a group, patients with acute invasive gastroenteritis had an increased serum level of IL-8 and IL-6 as compared with healthy controls (p < 0.002 and p < 0.001, respectively). Subjects were then divided into two groups based on stool cultures (proven and non-proven bacterial cultures). Patients with bacterial-proven acute invasive gastroenteritis tended to have increased IL-8 serum concentrations (p < 0.07) as compared with those with non-proven bacterial etiologies and IL-6 levels were only detected in subjects with positive bacterial cultures (p < 0.05). When dividing each sub-group into early and late blood drawing with respect to disease onset, no statistical differences were found in each group but subjects with bacterial-proven etiologies had significant higher IL-6 levels as compared with non-proven etiologies at the two time points (p < 0.019 and p < 0.015, respectively).In conclusion, the proinflammatory cytokines, IL-6 and IL-8, are involved in acute invasive gastroenteritis. The difference in IL-6, and to a lesser degree IL-8, between proven and non-proven bacterial etiologies, needs further investigation. 相似文献
996.
Immunohistochemical localization of leukemia inhibitory factor, interleukins 1 and 6 at the primary implantation site in the rhesus monkey 总被引:8,自引:0,他引:8
Blastocyst implantation and placentation involve localized inflammatory type of responses at and around the site of nidation. In the present study, the likely involvement of inflammatory cytokines, namely, leukemia inhibitory factor (LIF), interleukins 1 alpha and 1 beta (IL-1alpha and IL-1beta) and IL-6 at the primary implantation site of the rhesus monkey was examined immunocytochemically during lacunar (n=6) and villous (n=8) stages of gestation. Trophoblast cells and extraembryonic mesenchymal cells were immunopositive for LIF and IL-1alpha. The distribution of IL-1beta and IL-6 in trophoblast cells was low in lacunar stage samples, however, a higher degree of immunopositivity for IL-6 was observed in villous stage samples. Decidual cells were immunopositive for all the cytokines studied. In lacunar stage samples, plaque cells adjacent to implanted nidus were immunopositive for all the cytokines examined, and the degree of their immunoprecipitation increased, except that of IL-1beta, during the villous stage. Luminal and glandular epithelial cells were immunopositive for LIF, IL-1alpha, IL-1beta and IL-6 in lacunar and in villous stage samples. LIF immunopositivity was detected in endothelial cells of blood vessels within and below chorionic plate and cytotrophoblast shell, while vascular smooth muscle cells were positive for all the cytokines studied. The temporo-spatial characteristics of LIF, IL-1alpha, IL-1beta and IL-6 protein expressions in primary implantation sites of the rhesus monkey suggest that these pro-inflammatory cytokines play specific roles in regulating trophoblast cell proliferation, differentiation, invasion and associated maternal tissue remodelling during early gestation. 相似文献
997.
Ham D 《Cell biology international》2003,27(8):675-687
Although the Man-6-P-independent lysosomal sorting of prosaposin, a precursor of four saposins (A, B, C, and D) is not understood, a protein/lipid interaction is considered. Immunocytochemical analysis revealed that each single saposin linked to the C-terminus of prosaposin and to secretory albumin, drives the chimeric protein to lysosomes in COS-7 cells. Quantitative image analysis demonstrated that saposins are targeted with different efficiency (P<0.05) and in a less smooth manner than the precursor. Despite a very close homology, the charge distribution at the surface of 3D comparative models between saposins appeared different. Western blotting monitored prosaposin in cells also as a di- or trimeric form, whereas the chimeric saposins as monomeric. This implies that each amphipathic saposin-like motif may be a part of the overall structural requirements for binding of the precursor to the membrane lipids of transport vesicle. The crystal structure of saposin B demonstrating two dimeric units for lipid binding supports current findings. 相似文献
998.
Aller MI Jones A Merlo D Paterlini M Meyer AH Amtmann U Brickley S Jolin HE McKenzie AN Monyer H Farrant M Wisden W 《Genesis (New York, N.Y. : 2000)》2003,36(2):97-103
The cerebellum maintains balance and orientation, refines motor action, stores motor memories, and contributes to the timing aspects of cognition. We generated two mouse lines for making Cre recombinase-mediated gene disruptions largely confined to adult cerebellar granule cells. For this purpose we chose the GABA(A) receptor alpha6 subunit gene, whose expression marks this cell type. Here we describe mouse lines expressing Cre recombinase generated by 1) Cre knocked into the native alpha6 subunit gene by homologous recombination in embryonic stem cells; and 2) Cre recombined into an alpha6 subunit gene carried on a bacterial artificial chromosome (BAC) genomic clone. The fidelity of Cre expression was tested by crossing the mouse lines with the ROSA26 reporter mice. The particular alpha6BAC clone we identified will be valuable for delivering other gene products to cerebellar granule cells. 相似文献
999.
Ng TB Liu F Lu Y Cheng CH Wang Z 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,136(2):109-115
A number of compounds were isolated from the medicinal plant Aster tataricus including shionone, epifriedelinol, quercetin, kaempferol, scopoletin, emodin, aurantiamide acetate and 1,7-dihydroxy-6-methyl-anthraquinone. The compounds were compared with regard to their ability in inhibiting hemolysis of rat erythrocytes induced by 2'-2' azobis (2-amidinopropane) dihydrochloride, lipid peroxidation using the FeSO(4)-ascorbic acid system, and generation of superoxide radicals using a phenazine methosulfate-nicotinamide adenine dinucleotide system. The effects on the Fe-bleomycin-induced DNA damage reflected pro-oxidant activity. Quercetin and kaempferol were most potent in inhibiting hemolysis, lipid peroxidation and superoxide radical generation. Scopoletin and emodin were similar to quercetin and kaempferol in inhibiting superoxide radical generation and second to them in inhibiting lipid peroxidation. Aurantiamide acetate exhibited some inhibitory activity toward superoxide radical generation. 1,7-dihydroxy-6-methyl-anthraquinone exerted an inhibitory activity only on superoxide radical generation. Shionone and epifriedelinol did not display any antioxidant activity. Quercetin and kaempferol, but not the remaining compounds, exhibited some pro-oxidant activity. 相似文献
1000.
Coal mining causes health problems, such as pneumoconiosis. We have previously shown that prevalence of pneumoconiosis in workers from various coalmine regions positively correlates with levels of bioavailable iron (BAI) in the coals from that region. In the present study, the nature of reactive oxygen species formed by BAI in the coals and its mechanisms of the induction of biological responses were investigated. Human lung epithelial cell line, A549 cells, were used to examine the induction of interleukin-6 (IL-6), a pro-inflammatory cytokine, which is known to play a crucial role in the development of pneumoconiosis. We found that levels of IL-6 protein as well as its mRNA were significantly increased in the cells treated for 24 h with 20 microg/cm2 of the BAI-containing Pennsylvania (PA) coal; for example we observed 6.7-fold increase in IL-6 protein. Levels of IL-6 protein in cells treated with the Utah (UT) coal containing low-BAI were only 1.9-fold of the control levels. The enhancing effect on the IL-6 by the PA coal was similar to that caused by hydrogen peroxide. Superoxide dismutase (SOD), catalase (CAT), and N-acetyl-L-cysteine (NAC) all had inhibitory effects on the PA coal-induced IL-6 formation. However, CAT had the least protective effect as compared to SOD and NAC. Our results indicate that BAI in the PA coal may induce IL-6 through both ferryl species (via iron autoxidation) and hydroxyl radicals (via the Fenton/Haber Weiss reactions). 相似文献