全文获取类型
收费全文 | 3798篇 |
免费 | 64篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 73篇 |
综合类 | 8篇 |
化学工业 | 579篇 |
金属工艺 | 76篇 |
机械仪表 | 40篇 |
建筑科学 | 141篇 |
矿业工程 | 13篇 |
能源动力 | 34篇 |
轻工业 | 323篇 |
水利工程 | 12篇 |
石油天然气 | 9篇 |
无线电 | 198篇 |
一般工业技术 | 361篇 |
冶金工业 | 1725篇 |
原子能技术 | 17篇 |
自动化技术 | 257篇 |
出版年
2019年 | 27篇 |
2018年 | 29篇 |
2017年 | 26篇 |
2016年 | 48篇 |
2015年 | 38篇 |
2014年 | 37篇 |
2013年 | 145篇 |
2012年 | 61篇 |
2011年 | 94篇 |
2010年 | 68篇 |
2009年 | 79篇 |
2008年 | 77篇 |
2007年 | 83篇 |
2006年 | 85篇 |
2005年 | 83篇 |
2004年 | 76篇 |
2003年 | 73篇 |
2002年 | 68篇 |
2001年 | 42篇 |
2000年 | 42篇 |
1999年 | 94篇 |
1998年 | 369篇 |
1997年 | 259篇 |
1996年 | 167篇 |
1995年 | 99篇 |
1994年 | 106篇 |
1993年 | 106篇 |
1992年 | 55篇 |
1991年 | 49篇 |
1990年 | 49篇 |
1989年 | 69篇 |
1988年 | 65篇 |
1987年 | 49篇 |
1986年 | 49篇 |
1985年 | 55篇 |
1984年 | 54篇 |
1983年 | 53篇 |
1982年 | 42篇 |
1981年 | 44篇 |
1980年 | 43篇 |
1979年 | 35篇 |
1978年 | 44篇 |
1977年 | 49篇 |
1976年 | 74篇 |
1975年 | 38篇 |
1974年 | 30篇 |
1973年 | 26篇 |
1972年 | 36篇 |
1971年 | 29篇 |
1966年 | 29篇 |
排序方式: 共有3866条查询结果,搜索用时 471 毫秒
1.
2.
3.
4.
OL Lopez RP Brenner JT Becker RF Ulrich F Boller ST DeKosky 《Canadian Metallurgical Quarterly》1997,48(6):1521-1525
We examined whether either psychotic features (e.g., delusions and hallucinations) or EEG abnormalities are associated with more rapid progression of Alzheimer's disease (AD). AD patients with psychosis have exhibited more EEG abnormalities than those without psychosis, and both abnormal EEG and psychosis have been noted to be predictors of functional and cognitive decline in AD. Ninety-five probable AD patients participating in a longitudinal study of dementia had an EEG and a semistructured psychiatric interview at baseline. Using EEG spectral analysis, we classified records as normal/abnormal based on the parasagittal mean frequency. Patients with abnormal EEGs were more functionally (e.g., Blessed Rating Scale for activities of daily living) and cognitively (e.g., Mini-Mental State) impaired than patients with normal EEG. AD patients with psychosis were only more functionally impaired than patients without psychosis. A two-factor analysis showed no interaction between abnormal EEG and psychosis. In addition, using a Cox proportional hazard model adjusted for age and education, the presence of an abnormal EEG or psychotic symptom at study entry was associated with higher risk of reaching severe cognitive and functional impairment during follow-up. Neither abnormal EEG nor the presence of psychosis predicted death. These results indicate that both abnormal EEG and psychosis are independent predictors of disease progression but not of physical survival. 相似文献
5.
Somatic hypermutation of the immunoglobulin variable genes during germinal reactions might permit the expansion of B-cell clones with unwanted (e.g. autoreactive) specificity. Here, Ernst Lindhout and colleagues propose three antigen-specific checkpoints that ensure the appropriate antigen specificity of activated B cells is maintained by regulating the activation, selection and further differentiation of B cells. 相似文献
6.
N Delanty MP Reilly D Pratico JA Lawson JF McCarthy AE Wood ST Ohnishi DJ Fitzgerald GA FitzGerald 《Canadian Metallurgical Quarterly》1997,95(11):2492-2499
BACKGROUND: Myocardial reperfusion is believed to be associated with free radical injury. However, indexes of oxidative stress in vivo have been limited by their poor specificity and sensitivity. Isoprostanes are stable products of arachidonic acid formed in a nonenzymatic, free radical-catalyzed manner. We have developed a sensitive and specific assay for one of these compounds, 8-epi prostaglandin (PG) F2 alpha. METHODS AND RESULTS: To address its utility as an index of oxidative stress during coronary reperfusion, we measured urinary levels by gas chromatography/mass spectrometry in a canine model of coronary thrombolysis, in patients with acute myocardial infarction treated with thrombolytic therapy, and in patients after elective coronary artery bypass surgery. Urinary 8-epi PGF2 alpha was unchanged after circumflex artery occlusion in a canine model of coronary thrombolysis (n = 13; 437.2 +/- 56.4 versus 432.7 +/- 55.2 pmol/mmol creatinine) but increased significantly (P < .05) immediately after reperfusion (553.8 +/- 64.7 pmol/mmol). Urinary levels were increased (P < .001) in patients (n = 12) with acute myocardial infarction given lytic therapy (265.8 +/- 40.8 pmol/mmol) compared with age-matched control subjects (n = 20; 91.5 +/- 11.8 pmol/mmol) and patients with stable coronary disease (n = 20; 95.7 +/- 6.3 pmol/mmol). Preoperative levels rose from 113.2 +/- 11.8 to 248.2 +/- 86.3 pmol/mmol at 30 minutes into revascularization to 332.2 +/- 82.6 pmol/mmol by 15 minutes after global myocardial reperfusion (P < .05) and dropped to 181.2 +/- 50.4 pmol/mmol at 30 minutes and 120.2 +/- 9.9 pmol/mmol at 24 hours after bypass surgery (n = 5). Corresponding changes in spin adduct formation, found with electron paramagnetic resonance, were noted in 2 patients. CONCLUSIONS: These data support the hypothesis that free radical generation occurs during myocardial reperfusion. Measurement of isoprostane production may serve as a noninvasive index of oxidative stress. 相似文献
7.
8.
9.
Hans-Jürgen Odenthal Herbert Pfeifer Ina Lemanowicz Rainer Gorissen 《Metallurgical and Materials Transactions B》2002,33(2):163-172
The present work describes quantitative digital particle image velocimetry measurements of a full-scale water model of a thin
slab mold. Different casting speeds and two submerged entry nozzles with one and two outlet ports have been investigated.
The flow pattern of the single-port nozzle shows a counterclockwise-rotating double vortex that is nearly steady-state but
leads to high stationary surface waves. The flow jets out of the two-port nozzle oscillate and produce a transient flow pattern
with low wave amplitudes. The amplitudes for the one-port nozzle show a linear variation with the volumetric flow rate. The
experimental results lead to a good interpretation of the flow phenomena and are used to validate steady-state numerical simulations
with the commercial program, CFX, on the basis of the Reynolds equations. To describe anisotropic turbulence effects, the
Reynolds stress model (RSM) is used for the flat single-port nozzle and the standard k-ɛ model for the mold flow. The calculated mean velocities and wave amplitudes, predicted from pressure distribution at the
water surface, are generally in the consensus of the experimental data.
An erratum to this article is available at . 相似文献
10.