全文获取类型
收费全文 | 3908篇 |
免费 | 3篇 |
专业分类
化学工业 | 36篇 |
金属工艺 | 1篇 |
机械仪表 | 1篇 |
建筑科学 | 1篇 |
能源动力 | 1篇 |
轻工业 | 2篇 |
石油天然气 | 2篇 |
一般工业技术 | 3篇 |
冶金工业 | 3860篇 |
自动化技术 | 4篇 |
出版年
2023年 | 1篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2007年 | 1篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 7篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 107篇 |
1998年 | 1153篇 |
1997年 | 699篇 |
1996年 | 448篇 |
1995年 | 219篇 |
1994年 | 222篇 |
1993年 | 213篇 |
1992年 | 17篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 41篇 |
1986年 | 52篇 |
1985年 | 37篇 |
1984年 | 3篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 25篇 |
1980年 | 53篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 111篇 |
1976年 | 258篇 |
1975年 | 7篇 |
1964年 | 1篇 |
1955年 | 5篇 |
1954年 | 2篇 |
排序方式: 共有3911条查询结果,搜索用时 32 毫秒
991.
DS Chiu JF Oram RC LeBoeuf CE Alpers KD O''Brien 《Canadian Metallurgical Quarterly》1997,17(11):2350-2358
Human extracellular superoxide dismutase (hEC-SOD) is a secreted tetrameric protein involved in protection against oxygen free radicals. Because EC-SOD is too large a protein for structural determination by multidimensional NMR, and attempts to crystallize the protein for X-ray structural determination have failed, the three-dimensional structure of hEC-SOD is unknown. This means that alternative strategies for structural studies are needed. The N-terminal domain of EC-SOD has already been studied using the fusion protein FusNN, comprised of the 49 N-terminal amino acids from hEC-SOD fused to human carbonic anhydrase (HCAII). The N-terminal domain in this fusion protein forms a well-defined three-dimensional structure, which probably contains alpha-helical elements and is responsible for the tetramerization of the protein. In this work, we have extended the studies, using site-directed mutagenesis in combination with size-exclusion chromatography, CD, and fluorescence spectroscopy, to investigate the nature of the tetrameric interaction. Our results show that the hydrophobic side of a predicted amphiphatic alpha-helix (formed by residues 14-32) in the N-terminal domain is essential for the subunit interaction. 相似文献
992.
Effect of alpha-tocopherol succinate on free radical and lipid peroxidation levels in BL6 melanoma cells 总被引:1,自引:0,他引:1
Numerous studies have proposed a radical or oxidant involvement in a number of degenerative diseases such as cancer. This has led to suggestions that the supplementation of antioxidants such as alpha-tocopherol (vitamin E) may function to reduce the growth of cancer. In this study, a nonmalignant Monkey kidney (LLCMK) and a malignant Murine melanoma (BL6-F10) cell line were supplemented with varying levels of alpha-Tocopherol acid succinate (vitamin E succinate) ranging from 1 to 10 microg/ml. BL6-F10 cells supplemented with 5, 7, and 10 microg/ml vitamin E succinate, showed significant decreases in cell proliferation, and this decrease was accompanied by a concomitant increase rather than a decrease in the levels of free radicals and lipid peroxidation. LLCMK cells supplemented with 1-10 microg/ml vitamin E succinate showed no significant increase or decrease in growth, while the levels of lipid peroxidation were shown to be insignificantly elevated at 5, 7, and 10 microg/ml vitamin E succinate. Free radical levels in LLCMK cells were significantly decreased at 1 microg/ml vitamin E succinate, while at 3, 5, 7, and 10 microg/ml supplementary vitamin E succinate, free radical levels increased compared to the 1 microg/ml group, but not compared to control cultures. These results suggest that the inhibitory effects of vitamin E succinate on BL6-F10 cell growth in vitro is not a consequence of its antioxidant properties, but may, in fact, be due to one or more of its other potential roles within the cells, such as the regulation of cellular enzyme activities involved in growth. 相似文献
993.
N Corva?a P Tournier TN Nguyen JF Haeuw UF Power H Binz C Andréoni 《Canadian Metallurgical Quarterly》1997,176(3):560-569
The polypeptide of aa 130-230 of the G protein (G2Na) of respiratory syncytial virus (RSV) was fused to BB, the albumin-binding region of streptococcal G protein, producing BBG2Na, which induced protective immune responses in rodent models. Evaluation of the immune response in mice immunized with BBG2Na in the adjuvant alhydrogel revealed high amounts of interleukin (IL)-5 and some IL-4 in splenocytes restimulated in vitro. This is compatible with a Th2 response. The activation of the Th2 pathway in such mice was further supported by the detection of IL-5 and G2Na-specific IgE in vivo. Of interest, in contrast to immunization with formalin-inactivated RSV, immunization of mice with BBG2Na followed by intranasal RSV challenge did not lead to increased production of IL-5- or G2Na-specific IgE. However, IgG1- and IgG2a-specific antibodies were boosted. These results demonstrate that the Th2 pathway is not enhanced by RSV challenge in BBG2Na-immunized mice. 相似文献
994.
L Guillevin JF Cordier F Lhote P Cohen B Jarrousse I Royer P Lesavre C Jacquot P Bindi P Bielefeld JF Desson F Détrée A Dubois E Hachulla B Hoen D Jacomy C Seigneuric D Lauque M Stern M Longy-Boursier 《Canadian Metallurgical Quarterly》1997,40(12):2187-2198
OBJECTIVE: To investigate the effectiveness and side effects of oral versus pulse cyclophosphamide (CYC) in combination with corticosteroids (CS) in the treatment of systemic Wegener's granulomatosis (WG). METHODS: Patients with newly diagnosed systemic WG were enrolled in a prospective, randomized trial. At the time of diagnosis, prior to randomization, every patient received a daily injection of methylprednisolone for 3 days, followed by daily oral prednisone (1 mg/kg/day) and a 0.7-gm/m2 pulse of CYC. Patients were then randomly assigned to receive either prednisone plus intravenous pulse CYC (group A) or prednisone plus oral CYC (group B) as first-line treatment. CYC was given for at least 1 year and was then progressively tapered and discontinued. RESULTS: Fifty patients were included in the study: 27 in group A and 23 in group B. At 6 months, 24 group A patients (88.9%) were in remission, versus 18 group B patients (78.3%). At the end of the trial, 18 group A patients (66.7%) and 13 group B patients (56.5%) were in remission. In group A, 66.7% of the patients experienced side effects, versus 69.6% in group B. Infectious side effects were significantly more frequent in group B (69.6%) than in group A (40.7%) (P < 0.05). The incidence of Pneumocystis carinii pneumonia was higher in oral CYC-treated patients (30.4%) than in pulse CYC-treated patients (11.1%). Nine group A patients (33.3%) and 10 group B patients (43.5%) died. Actuarial curves showed that relapses were significantly more frequent in group A (59.2%) than in group B (13%) (P = 0.02). CONCLUSION: Our results indicate that pulse CYC is as effective as oral CYC in achieving initial remission of WG and is associated with fewer side effects and lower mortality. However, in the long term, treatment with pulse CYC does not maintain remission or prevent relapses as well as oral CYC. 相似文献
995.
The outcome was studied in 100 patients with adult-onset primary ankylosing spondylitis (AS). After a mean disease duration of 16 yr, 51.5% of the patients were employed in full-time work. Cessation of work occurred at a mean disease duration of 15.6 yr, and was significantly associated with female sex, low levels of education, acute anterior uveitis, 'bamboo spine' and the co-existence of non-rheumatic diseases. Functional outcome was studied by analysing activities of daily living, and revealed similar findings in males and females. Most of the loss of function occurred during the first 10 yr of disease, and correlated significantly with the occurrence of peripheral arthritis, spinal X-ray changes of AS and development of 'bamboo spine'. After > 20 yr of disease, > 80% of the patients still complained of daily pain and stiffness, and > 60% reported daily use of drugs. 相似文献
996.
To further our knowledge of the structure-function relationship and mechanism of action of the Clostridium perfringens enterotoxin (CPE), a series of recombinant CPE (rCPE) species containing N- and C-terminal CPE deletion fragments was constructed by recombinant DNA approaches. Each rCPE species was characterized for its ability to complete the first four early steps in the action of CPE, putatively ordered as specific binding, a postbinding physical change to bound CPE, large-complex formation, and induction of alterations in small-molecule membrane permeability. These studies demonstrated that (i) at least 44 amino acids can be removed from the N terminus of CPE without loss of cytotoxicity, (ii) removal of the first 53 amino acids from the N terminus of CPE produces a fragment that appears to be noncytotoxic because it cannot undergo the post-binding physical change step in CPE action, (iii) removal of as few as five amino acids from the C terminus of CPE produces a noncytotoxic fragment lacking receptor binding activity, and (iv) a fragment lacking the first 44 N-terminal amino acids of native CPE formed twice as much large complex and was twice as cytotoxic as native CPE. From these structure-function results, it appears that the minimum-size cytotoxic CPE fragment comprises approximately residues 45 to 319 of native CPE. Results from these deletion fragment studies have also contributed to our understanding of CPE action by (i) independently supporting previous suggestions that binding, the postbinding physical change step, and large-complex formation represent important steps in CPE cytotoxicity and (ii) providing independent evidence confirming the putative sequential order of these early events in CPE action. 相似文献
997.
K Haack U Moebius MV Knebel Doeberitz C Herfarth HK Schackert JF Gebert 《Canadian Metallurgical Quarterly》1997,8(11):1395-1401
Myocardial ischemia identified by ambulatory electrocardiography (AECG), exercising treadmill testing, (ETT), or 12-lead electrocardiogram at rest is associated with an adverse prognosis, but the effect of improving these ischemic manifestations by treatment on outcome is unknown. The Asymptomatic Cardiac Ischemia Pilot (ACIP) study was a National Heart, Lung, and Blood Institute funded study to determine the feasibility of conducting a large-scale prognosis study and to assess the effect of 3 treatment strategies (angina-guided strategy, AECG ischemia-guided strategy, and revascularization strategy) in reducing the manifestations of ischemia as indicated by AECG and ETT. The study cohort for this database study consisted of 496 randomized patients who performed the AECG, ETT, and 12-lead electrocardiogram at rest at both the qualifying and week 12 visits. The effect of modifying ischemia by treatment on the incidence of cardiac events (death, myocardial infarction, coronary revascularization procedure, or hospitalization for an ischemic event) at 1 year was examined. In the 2 medical treatment groups (n = 328) there was an association between the number of ambulatory electrocardiographic ischemic episodes at the qualifying visit and combined cardiac events at 1 year (p = 0.003). In the AECG ischemia-guided patients there was a trend associating greater reduction in the number of ambulatory electrocardiographic ischemia episodes with a reduced incidence of combined cardiac events (r = -0.15, p = 0.06). In the revascularization strategy patients this association was absent. In the medical treatment patients the exercise duration on the baseline ETT was inversely associated with an adverse prognosis (p = 0.02). The medical treatment strategies only slightly improved the exercise time and the exercise duration remained of prognostic significance. In the revascularization group strategy patients this association was absent. Thus, myocardial ischemia detected by AECG and an abnormal ETT are each independently associated with an adverse cardiac outcome in patients subsequently treated medically. 相似文献
998.
999.
1000.
JF Doz M Gavagnach E Ros LL Gracia M Romaguera C Borrell 《Canadian Metallurgical Quarterly》1996,17(9):585-589
The effects of paraquat on rat brain were studied. Activities of complex I (NADH: ubiquinone oxidoreductase) in mitochondrial electron transport system, lipid peroxidation and the amount of catecholamines in rat brain were measured after acute paraquat exposure. Complex I activities were significantly lower and lipid peroxides were higher in the brains of a paraquat-treated group than in those of a control group. Lipid peroxide in rat serum, however, did not increase after paraquat exposure. A study of the time dependency of paraquat effects disclosed that mitochondrial complex I activities in rat brain as well as those in rat lung and liver gradually decreased prior to the appearance of respiratory dysfunction. As compared to controls, the dopamine in rat striatum was significantly lower in the paraquat-treated group. These results suggest that paraquat after crossing the blood-brain barrier might be reduced to the radical in rat brain, which may damage the brain tissue, especially dopaminergic neurons in striatum. We therefore propose that cerebral damage should be taken into consideration on paraquat exposure. Patients may therefore need to be followed up after exposure to high doses of paraquat. 相似文献