首页 | 官方网站   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   2328篇
  免费   6篇
工业技术   2334篇
  2023年   1篇
  2021年   6篇
  2020年   2篇
  2019年   4篇
  2018年   5篇
  2017年   2篇
  2016年   1篇
  2015年   4篇
  2014年   1篇
  2013年   11篇
  2012年   3篇
  2011年   3篇
  2010年   4篇
  2009年   6篇
  2008年   2篇
  2007年   1篇
  2006年   3篇
  2005年   4篇
  2004年   5篇
  2003年   4篇
  2002年   4篇
  2001年   2篇
  2000年   1篇
  1999年   78篇
  1998年   767篇
  1997年   384篇
  1996年   244篇
  1995年   144篇
  1994年   106篇
  1993年   145篇
  1992年   23篇
  1991年   26篇
  1990年   27篇
  1989年   23篇
  1988年   29篇
  1987年   38篇
  1986年   20篇
  1985年   11篇
  1983年   6篇
  1982年   4篇
  1981年   9篇
  1980年   28篇
  1979年   3篇
  1978年   2篇
  1977年   27篇
  1976年   102篇
  1975年   5篇
  1955年   1篇
  1954年   1篇
  1938年   1篇
排序方式: 共有2334条查询结果,搜索用时 533 毫秒
91.
Intracerebroventricular administration of neuropeptide Y to normal rats induces a syndrome characterised by obesity, hyperinsulinaemia, insulin resistance and over expression of the adipose tissue ob gene. Little is known about the effect of circulating neuropeptide Y on glucose metabolism, insulin secretion and leptin. We therefore aimed to evaluate the effect of an intravenous infusion of neuropeptide Y on glucose disposal, endogenous glucose production, whole body glycolytic flux, and glucose storage as assessed during euglycaemic hyperinsulinaemic clamp. In addition, the insulin-stimulated glucose utilisation index in individual tissues was measured by the 2-deoxy-[1-3H]-glucose technique. The effect of neuropeptide Y on insulin secretion was evaluated by hyperglycaemic clamp. Infusion did not induce any change in endogenous glucose production during basal conditions or at the end of the clamp. Glucose disposal was significantly increased in the rats given neuropeptide Y compared with controls (27.8 +/- 1.3 vs 24.3 +/- 1.6 mg x min(-1) x kg(-1); p < 0.05) as was the glycolytic flux (18.9 +/- 1.6 vs 14.4 +/- 0.8 mg x min(-1) x kg(-1); p < 0.05), while glucose storage was comparable in the two groups. In skeletal muscle, the glucose utilisation index was increased significantly in rats given neuropeptide Y. The glucose utilisation index in subcutaneous and epididimal adipose tissue was not significantly different between the two groups. Plasma leptin was significantly increased by hyperinsulinaemia, but was not affected by neuropeptide Y infusion. Both the early and late phase of the insulin response to hyperglycaemia were significantly reduced by neuropeptide Y. In conclusion neuropeptide Y infusion may increase insulin-induced glucose disposal in normal rats, accelerating its utilisation through the glycolytic pathway. Neuropeptide Y reduces both phases of the insulin response to hyperglycaemia.  相似文献   
92.
We have identified a member of the VEGF family by computer-based homology searching and have designated it VEGF-D. VEGF-D is most closely related to VEGF-C by virtue of the presence of N- and C-terminal extensions that are not found in other VEGF family members. In adult human tissues, VEGF-D mRNA is most abundant in heart, lung, skeletal muscle, colon, and small intestine. Analyses of VEGF-D receptor specificity revealed that VEGF-D is a ligand for both VEGF receptors (VEGFRs) VEGFR-2 (Flk1) and VEGFR-3 (Flt4) and can activate these receptors. However. VEGF-D does not bind to VEGFR-1. Expression of a truncated derivative of VEGF-D demonstrated that the receptor-binding capacities reside in the portion of the molecule that is most closely related in primary structure to other VEGF family members and that corresponds to the mature form of VEGF-C. In addition, VEGF-D is a mitogen for endothelial cells. The structural and functional similarities between VEGF-D and VEGF-C define a subfamily of the VEGFs.  相似文献   
93.
Most abdominal aortic aneurysms (AAA) and thoracoabdominal aortic aneurysms (TAAA) are asymptomatic and are found on physical exam or incidentally during radiological studies for other indications. These aneurysms are repaired primarily because their risk of rupture increases geometrically as the size exceeds 5 cm. The potential morbidity of intraoperative visceral and spinal ischemia involved with TAAA repair may be reduced with various adjunctive maneuvers.  相似文献   
94.
Mutation of thymidylate synthase N229(177) to alanine results in an essentially inactive enzyme, yet it leads to formation of a stable ternary complex. The kinetics of N229(177)A show that kcat for Escherichia coli is reduced by 200-fold while the Km for dUMP is increased 200-fold and the Km for folate increased by tenfold versus the wild-type enzyme. The crystal structures of N229(177)A in complex with dUMP and CB3717, and in complex with dUMP alone are determined at 2.4 A, and 2.5 A resolution. These structures identify the covalently bound ternary complex and show how N229(177)A traps an intermediate, and so becomes inactive in a later step of the reaction. Since the smaller alanine side-chain at N229(177)A does not directly sterically impair binding of ligands, the structures implicate, and place quantitative limits on the involvement of the structured water network in the active site of thymidylate synthase in both catalysis and in determining the binding affinity for dUMP (in contrast, the N229(177)V mutation in Lactobacillus casei has minimal effect on activity).  相似文献   
95.
Increasing evidence demonstrates that ultraviolet A radiation (UVA) contributes to photoaging, which results in the accumulation of massive amounts of abnormal elastic material in the dermis of photoaged skin. To study UVA-induced photoaging in an in vivo system, we utilized a line of transgenic mice containing the human elastin promoter linked to a chloramphenicol acetyl transferase reporter gene. Our prior work demonstrates promoter activation in response to ultraviolet B radiation (UVB), UVA, and psoralen plus ultraviolet A radiation in the skin of these mice. The addition of psoralen (8-MOP) prior to administration of UVA results in substantial increases in promoter activation, as compared with UVA alone. To demonstrate the utility of these mice as a model of UVA-induced photodamage, we administered four lotions to the skin of our transgenic mice that included: a sunscreen containing octyl methoxycinnamate and benzophenone-3 with a sun protection factor (SPF) of 15, the UVA filter butyl methoxydibenzoylmethane, the SPF 15 sunscreen and the UVA filter together, and the lotion vehicle alone. Following sunscreen administration, mice received a single psoralen plus ultraviolet A radiation treatment. All sunscreens decreased chloramphenicol acetyl transferase activity with the SPF 15 sunscreen, the UVA filter, and the combination SPF 15 sunscreen and UVA filter, resulting in increasing degrees of protection against psoralen plus ultraviolet A radiation. These results demonstrate that this model functions as a rapid and sensitive model of UVA photodamage for the identification and comparison of compounds that protect against UVA-induced photoaging.  相似文献   
96.
Twenty-one antimicrobial agents were incorporated individually into Frey's agar to evaluate their inhibitory activities against 86 isolates of avian mycoplasmas recently detected in Taiwan. Among them, 45 and 37 isolates were found positive with Mycoplasma gallisepticum and Mycoplasma synoviae fluorescent antibody conjugate, respectively. Twenty-one other isolates were unable to be identified by the above 2 conjugates. All of the field isolates were highly sensitive (with MIC50 < 1 microgram/ml) to enrofloxacin, gentamicin, myplabin, tiamutin and tylosin. However, those field isolates were highly resistant (with MIC50 > 32 micrograms/ml) to apramycin, chlortetracycline (CTC), erythromycin (ER), flumequine (FI), nalidixic acid (NA), oxolinic acid (OA), oxytetracycline (OTC) and spiramycin (SP). The inhibitory activities of the antibiotics which possessed an MIC90 of 50 micrograms/ml or less against local isolates were, in decreasing order, enrofloxacin (< 0.004 microgram/ml), gentamicin (1.53 micrograms/ml), tiamutin (1.81 micrograms/ml), tylosin (3.2 micrograms/ml), streptomycin (SM; 12.0 micrograms/ml), colistin (13.1 micrograms/ml), chloramphenicol (14.0 micrograms/ml), spectinomycin (15.0 micrograms/ml), myplabin (16.0 micrograms/ml), spiramycin (30.0 micrograms/ml), minocycline (32.0 micrograms/ml). The MIC90 of OA, CTC, SM, FI, SP, OTC, ER or NA was greater than 50 micrograms/ml; which work poorly in the control of mycoplasmoses. Since the antibiotic control policy is quite loose in Taiwan, many antimicrobial agents are often freely used in clinics, with a resulting gradual decrease in the inhibitory activity to the avian mycoplasmas.  相似文献   
97.
98.
Psychiatric workers facing redeployment completed questionnaire measures of stressors, resources (locus of control and perceived social support), coping, well-being, and negative affectivity, at baseline (N = 109) and 1 year later (loss of 7 participants). Regression analyses of the baseline data suggested that as stressors increased, so did avoidance coping, but less so for those high in internality or perceived social support. Problem-focused coping was bolstered by internality and emotion-focused coping by perceived social support. Other regression analyses, with a longitudinal aspect, suggested that stressors had a deleterious effect on well-being. Problem- and emotion-focused coping had beneficial effects, whereas avoidance coping had a (delayed) deleterious effect. These effects of coping were predominantly main and not buffering effects.  相似文献   
99.
100.
Mechanism of suppression of cell-mediated immunity by measles virus   总被引:2,自引:0,他引:2  
The mechanisms underlying the profound suppression of cell-mediated immunity (CMI) accompanying measles are unclear. Interleukin-12 (IL-12), derived principally from monocytes and macrophages, is critical for the generation of CMI. Measles virus (MV) infection of primary human monocytes specifically down-regulated IL-12 production. Cross-linking of CD46, a complement regulatory protein that is the cellular receptor for MV, with antibody or with the complement activation product C3b similarly inhibited monocyte IL-12 production, providing a plausible mechanism for MV-induced immunosuppression. CD46 provides a regulatory link between the complement system and cellular immune responses.  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-23

京公网安备 11010802026262号