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   217篇
  免费   6篇
  国内免费   50篇
工业技术   273篇
  2022年   5篇
  2021年   2篇
  2020年   2篇
  2018年   3篇
  2017年   6篇
  2015年   4篇
  2014年   4篇
  2013年   8篇
  2012年   7篇
  2011年   31篇
  2010年   3篇
  2009年   5篇
  2008年   4篇
  2007年   4篇
  2006年   3篇
  2005年   2篇
  2004年   4篇
  2003年   6篇
  2001年   5篇
  2000年   4篇
  1999年   11篇
  1998年   32篇
  1997年   9篇
  1996年   25篇
  1995年   10篇
  1994年   5篇
  1993年   4篇
  1992年   6篇
  1991年   4篇
  1990年   2篇
  1989年   9篇
  1988年   12篇
  1987年   5篇
  1986年   3篇
  1985年   2篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1980年   1篇
  1979年   1篇
  1978年   3篇
  1977年   1篇
  1976年   2篇
  1975年   1篇
  1974年   2篇
  1969年   1篇
  1967年   1篇
  1962年   1篇
  1961年   1篇
  1960年   1篇
排序方式: 共有273条查询结果,搜索用时 15 毫秒
11.
Seventy-two clinically anxious children, aged 7 to 14 years, were randomly allocated to clinic-based, cognitive-behavior therapy, the same treatment partially delivered via the Internet, or a wait-list control (WL). Children in the clinic and clinic-plus-Internet conditions showed significantly greater reductions in anxiety from pre- to posttreatment and were more likely to be free of their anxiety diagnoses, compared with the WL group. Improvements were maintained at 12-month follow-up for both therapy conditions, with minimal difference in outcomes between interventions. The Internet treatment content was highly acceptable to families, with minimal dropout and a high level of therapy compliance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
12.
13.
1. Age-matched (3-4 months old) male, heterozygous, hypertensive, transgenic ((mRen-2)27) rats (abbreviated to TG rats) and the normotensive control animals (homozygous, Hannover Sprague-Dawley rats (abbreviated to SD rats), were chronically instrumented for the assessment of regional haemodynamic responses to continuous lipopolysaccharide (LPS) infusion (150 microg kg(-1) h(-1), i.v.) 2. The early (1-2 h) hypotension in SD rats (-11+/-3 mmHg; n=7) was significantly less than that in TG rats (-35+/-3 mmHg; n=8), but by 24 h mean arterial blood pressure (MAP) in both strains of rat was not different from the pre-LPS value (SD rats: baseline, 108+/-3 mmHg; 24 h LPS, 112+/-4 mmHg; TG rats: baseline, 171+/-2 mmHg; 24 h LPS, 169+/-3 mmHg). At this stage in the SD rats there was a renal vasodilatation (delta vascular conductance, 29+/-10 [kHz mmHg(-1)]10(3)) but not in TG rats (delta vascular conductance 2+/-3[kHz mmHg(-1)]10(3)). 3. Co-infusion of LPS and the non-selective endothelin receptor antagonist, SB 209670 (600 microg kg(-1) bolus, 600 microg kg(-1) h(-1)) between 24 and 31 h in SD rats caused a fall in MAP of 16+/-2 mmHg accompanied by hindquarters vasodilatation (delta vascular conductance 11+/-3 (kHz mmHg(-1))10(3)). In TG rats, under the same conditions, the fall in MAP was -60+/-6 mmHg, and there were renal, mesenteric and hindquarters vasodilatations (delta vascular conductance, 23+/-5, 32+/-7, and 14+/-4 (kHz mmHg(-1))10(3), respectively). All effects, except the hindquarters vasodilatation, were greater in TG than in SD rats. 4. In TG rats infused with LPS alone for 31 h, between 24 and 31 h the fall in MAP was -17+/-4 mmHg, and the changes in renal, mesenteric and hindquarters vascular conductances were 5+/-3, -4+/-5, and 12+/-4 (kHz mmHg(-1)10(3), respectively. 5. Administration of the angiotensin (AT1)-receptor antagonist, losartan (10 mg kg(-1), i.v.) following co-infusion of LPS and SB 209670 between 24 and 31 h caused similar falls in MAP in SD and TG rats (-12+/-3 and -14+/-4 mmHg, respectively). 6. These results, together with previous findings, are consistent with a relative enhancement of the contribution of endothelin to the maintenance of cardiovascular status in endotoxaemic TG rats, particularly through a mesenteric vasoconstrictor action.  相似文献   
14.
Male, Long Evans rats (350-450 g) were anaesthetized and had pulsed Doppler probes and intravascular catheters implanted to allow monitoring of regional (renal, mesenteric and hindquarters) haemodynamics in the conscious state. Our main objectives were to:- assess the effects of administering human recombinant tumour necrosis factor (TNF)-alpha and human recombinant interleukin-1 (IL-1)beta, alone and together; determine the influence of pretreatment with a mixture of antibodies to TNF-alpha and IL-1beta on responses to co-administration of the cytokines; ascertain if pretreatment with a mixture of the antibodies to TNF-alpha and IL-1beta had any influence on the responses to lipopolysaccharide (LPS). TNF-alpha (10, 100 and 250 microg kg(-1), in separate groups, n=3, 9 and 8, respectively) caused tachycardia (maximum delta, +101+/-9 beats min(-1)) and modest hypotension (maximum delta, -10+/-2 mmHg), accompanied by variable changes in renal and mesenteric vascular conductance, but clear increases in hindquarters vascular conductance; only the latter were dose-related (maximum delta, +6+/-6, +27+/-9, and +61+/-12% at 10, 100 and 250 microg kg(-1), respectively). IL-1beta (1, 10, and 100 microg kg(-1) in separate groups, n = 8, 8 and 9, respectively) evoked changes similar to those of TNF-alpha (maximum delta heart rate, +69+/-15 beats min(-1); maximum delta mean blood pressure, -14+/-2 mmHg; maximum delta hindquarters vascular conductance, +49+/-17%), but with no clear dose-dependency. TNF-alpha (250 microg kg(-1)) and IL-1beta (10 microg kg(-1)) together caused tachycardia (maximum delta, +76+/-15 beats min(-1)) and hypotension (maximum A, -24+/-2 mmHg) accompanied by increases in renal, mesenteric and hindquarters vascular conductances (+52+/-6%, +23+/-8%, and +52+/-11%, respectively). Thereafter, blood pressure recovered, in association with marked reductions in mesenteric and hindquarters vascular conductances (maximum delta, -50+/-3% and -58+/-3%, respectively). Although bolus injection of LPS (3.5 mg kg(-1)) caused an initial hypotension (maximum delta, -27+/-11 mmHg) similar to that seen with co-administration of the cytokines, it did not cause mesenteric or hindquarters vasodilatation, and there was only a slow onset renal vasodilatation. The recovery in blood pressure following LPS was less than after the cytokines, and in the former condition there was no mesenteric vasoconstriction. By 24 h after co-administration of TNF-alpha and IL-1beta or after bolus injection of LPS, the secondary reduction in blood pressure was similar (-16+/-2 and -13+/-3 mmHg, respectively), but in the former group the tachycardia (+117+/-14 beats min(-1)) and increase in hindquarters vascular conductance (+99+/-21%) were greater than after bolus injection of LPS (+54+/-16 beats min ' and +439%, respectively). Pretreatment with antibodies to TNF-alpha and IL-1beta (300 mg kg(-1)) blocked the initial hypotensive and mesenteric and hindquarters vasodilator responses to co-administration of the cytokines subsequently. However, tachycardia and renal vasodilatation were still apparent. Premixing antibodies and cytokines before administration prevented most of the effects of the latter, but tachycardia was still present at 24 h. Pretreatment with antibodies to TNF-alpha and IL-1beta before infusion of LPS (150 microg kg(-1) h(-1) for 24 h) did not affect the initial fall in blood pressure, but suppressed the hindquarters vasodilatation and caused a slight improvement in the recovery of blood pressure. However, pretreatment with the antibodies had no effect on the subsequent cardiovascular sequelae of LPS infusion. the results indicate that although co-administration of TNF-alpha and IL-1beta can evoke cardiovascular responses which, in some respects, mimic those of LPS, and although antibodies to the cytokines can suppress most of the cardiovascular effects of the cytokines, the antibodies have little influence on the haemodynamic responses to LPS, possibly because, during infusion of LPS, the sites of production and local action of endogenous cytokines, are not accessible to exogenous antibodies.  相似文献   
15.
Multivariate curve resolution is proposed for the study of complex chemical reactions monitored by two-dimensional (2D) NMR spectroscopy. In particular, in this work, multivariate curve resolution is applied to the study of the reaction between (15)N-labeled cisplatin and the amino acid-nucleotide hybrid (Phac-Met-linker-p(5')dG). At several stages of the reaction, 2D [(1)H,(15)N] HSQC NMR spectra were acquired and stored in data matrices. In a first step, multivariate curve resolution was applied to analyze individually each one of these 2D spectra, allowing the resolution of the corresponding (1)H and (15)N one-dimensional correlation spectra. In a second step, the whole set of 2D spectra recorded along the reaction were simultaneously analyzed by multivariate curve resolution, allowing the resolution of the kinetic concentration profiles and of the pure 2D NMR spectra of each of the species detected along the reaction. Results finally obtained confirmed previously postulated reaction mechanisms involving the existence of two monofunctional adducts and of two bifunctional adducts, with the structure of one of them not completely resolved.  相似文献   
16.
Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic and debilitating disease characterized by unexplained physical fatigue, cognitive and sensory dysfunction, sleeping disturbances, orthostatic intolerance, and gastrointestinal problems. People with ME/CFS often report a prodrome consistent with infections. Using regression, Bayesian and enrichment analyses, we conducted targeted and untargeted metabolomic analysis of plasma from 106 ME/CFS cases and 91 frequency-matched healthy controls. Subjects in the ME/CFS group had significantly decreased levels of plasmalogens and phospholipid ethers (p < 0.001), phosphatidylcholines (p < 0.001) and sphingomyelins (p < 0.001), and elevated levels of dicarboxylic acids (p = 0.013). Using machine learning algorithms, we were able to differentiate ME/CFS or subgroups of ME/CFS from controls with area under the receiver operating characteristic curve (AUC) values up to 0.873. Our findings provide the first metabolomic evidence of peroxisomal dysfunction, and are consistent with dysregulation of lipid remodeling and the tricarboxylic acid cycle. These findings, if validated in other cohorts, could provide new insights into the pathogenesis of ME/CFS and highlight the potential use of the plasma metabolome as a source of biomarkers for the disease.  相似文献   
17.
In the last few years, the critical current densities of long commercially available REBa2Cu3O7?x (RE-123, where RE represents Y or a rare earth element) coated conductors have reached values of 250 A/cm-width at 77 K and zero applied field. Even higher values of 600 A/cm-w (77 K, B = 0) have been demonstrated in shorter lengths. The attractive features of the use of these high-Tc superconductors (HTS) are operation temperatures above 20 K and/or magnetic fields higher than those envisaged for the ITER TF coils. Possible operation conditions for HTS fusion magnets have been studied taking into consideration the possible further improvements of RE-123 coated conductors. Investigations of stability and quench behavior indicate that stability is not a problem, whereas quench detection and protection need attention. Because of the high currents necessary for fusion magnets, many tapes need to be assembled into a transposed conductor. The qualification of HTS conductors for fusion magnets would require their test at magnetic fields of 11 T and currents well above 10 kA. The possibilities to test straight HTS conductor samples in SULTAN have been considered. For a test at 4.5 K, only the development of a low resistance joint between the HTS conductor under test and the NbTi transformer of SULTAN would be necessary. Tests up to 20 K would require that the HTS sample is connected with the NbTi transformer by a conduction-cooled HTS bus bar of large thermal resistance similar to the HTS module of a current lead. HTS conductor tests at temperatures around 50 K would be possible with modified cryogenics.  相似文献   
18.
低碳钢冷脆特性参量——临界缺口(裂缝)尺寸的研究   总被引:2,自引:0,他引:2  
李道明  姚枚 《金属学报》1988,24(6):432-438
本文研究了缺口尺寸对低碳钢低温断裂行为的影响,分析了断裂载荷谷值所对应的温度T_C~*(称为冷脆特征温度)附近的断裂特征,结合工程设计特点,提出了冷脆临界缺口(裂缝)尺寸α_C及其特征值α_C~*的概念,推荐作为控制冷脆的一个基本特性参量。文中推导出了α_C及α_C~*的数学表达式,该式的可行性得到了静载及疲劳载荷条件下模拟试验数据的验证。  相似文献   
19.
俞学节 《金属学报》1984,20(1):41-146
用透射电镜研究了两种结构钢的断裂行为与显微组织的关系。结果表明,回火后准解理断口的出现和消失与Fe_3C的析出和聚集密切相关:经250℃回火时析出ε碳化物,呈现单一韧窝断口,回火温度超过350℃时,有Fe_3C析出,这时出现准解理断口,而于450℃回火后达最大比例。在550℃回火后,60Si2Mn钢因Fe_3C聚集,准解理断口消失,又变成单一韧窝断口,37SiMnCrNiMoV钢Fe_3C聚集的倾向小,经550℃回火后仍有少量准解理断口保留下来。观察试样上由负荷产生的残留显微裂纹发现,它们常沿孪晶马氏体的内孪晶界及板条马氏体的条界发展,因此认为这两种脆化了的界面是准解理的解理面,而Fe_3C沿这类界面析出并呈连续分布是导致界面脆化的原因。  相似文献   
20.
In aquatic environments, chemical cues are believed to be associated with prey response to predation risk, yet few basic cue compositions are known despite the pronounced ecological and evolutionary significance of such cues. Previous work indicated that negatively-charged ions of m/z 501 are possibly a kairomone that induces anti-predator responses in amphibian tadpoles. However, work described here confirms that this specific ion species m/z 501.2886 is produced by injured tadpoles, exhibits increased spectral intensity with higher tadpole biomass, and is not produced by starved predators. These results indicate the anion is an alarm cue released from tadpoles. High resolution mass spectrometry (HR-MS) revealed a unique elemental composition for [M-H]?, m/z 501.2886, of C26H45O7S? which could not be determined in previous studies using low resolution instruments. Collision induced dissociation of m/z 501 ions formed product ions of m/z 97 and m/z 80, HSO4? and SO3?, respectively, showing the presence of sulfate. Green frog tadpoles, Lithobates clamitans, exposed to the m/z 501 anion or sodium dodecyl sulfate exhibited similar anti-predator responses, suggesting organic sulfate is a tadpole behavior modifier.  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