全文获取类型
收费全文 | 1354篇 |
免费 | 21篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 108篇 |
金属工艺 | 15篇 |
机械仪表 | 27篇 |
建筑科学 | 29篇 |
矿业工程 | 1篇 |
能源动力 | 10篇 |
轻工业 | 106篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 58篇 |
一般工业技术 | 162篇 |
冶金工业 | 756篇 |
原子能技术 | 7篇 |
自动化技术 | 91篇 |
出版年
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 24篇 |
2013年 | 28篇 |
2012年 | 22篇 |
2011年 | 43篇 |
2010年 | 46篇 |
2009年 | 20篇 |
2008年 | 25篇 |
2007年 | 22篇 |
2006年 | 28篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 30篇 |
1998年 | 229篇 |
1997年 | 143篇 |
1996年 | 99篇 |
1995年 | 42篇 |
1994年 | 32篇 |
1993年 | 47篇 |
1992年 | 10篇 |
1991年 | 21篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 6篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 26篇 |
1976年 | 56篇 |
1975年 | 10篇 |
1973年 | 5篇 |
1971年 | 7篇 |
1970年 | 5篇 |
排序方式: 共有1379条查询结果,搜索用时 31 毫秒
1.
Sensory activity mediates regulation of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway, in the rodent olfactory bulb. The current studies established for the first time primary cultures of neonatal mouse olfactory bulb expressing TH and tested whether L-type calcium channels mediate the activity-dependent regulation of the dopamine phenotype. After 1 d in vitro (DIV), a small population of TH-immunostained neurons that lacked extensive processes could be demonstrated. After an additional 2 DIV in serum-free medium, the number of TH neurons had doubled, and they exhibited long interdigitating processes. Membrane depolarization for 48 hr with 50 mM KCl produced a further 2.4-fold increase in the number of TH-immunoreactive neurons compared with control cultures. Increased TH neuron number required at least 36 hr of exposure to KCl. Forskolin, which increases intracellular cAMP levels, induced a 1.5- to 1.6-fold increase in the number of TH-immunostained neurons. Combined treatment with KCl and forskolin was not additive. Nifedipine, an L-type calcium channel blocker, completely prevented the depolarization-mediated increase in TH expression but did not block the response to forskolin. Treatment with Bay K8644, an L-type calcium channel agonist, also significantly increased the number of TH-expressing neurons. Depolarization also induced alterations in neuritic outgrowth, resulting in a stellate versus an elongate morphology that, in contrast, was not prevented by nifedipine. These results are the first demonstration that in vitro, as in vivo, depolarization increases TH expression in olfactory bulb and that L-type calcium channels mediate this activity-dependent regulation of the dopamine phenotype. 相似文献
2.
3.
This article describes a study of delamination growth along 0 °/0 °, 0 °/ 5 °, ± 5 °, and 0 °/90 ° interfaces sandwiched between unidirectional carbon fibre/epoxy composite material. Relationships between damage criticality, growth rate and acoustic emission activity for delamination growth have been studied and the transferability of results from laboratory coupons to composite structural elements has been examined. Two types of coupon tests, conventional delamination beams and rigidly loaded single edge notched strips, have been compared for different mode ratios. Comparative tests have been made on buckling-induced delamination in plates. A graphite crack gauge has been used to measure delamination length and growth rate, ranging from 0.05–2000 m/s. Damage growth was also followed using visual, ultrasonic C-scan, X-ray radiography, macro-video and acoustic emission measurements. Empirical evaluations of interlaminar toughness for delamination beams are made using the Irwin-Kies relation. Unstable growth is analysed using elasto-dynamic moving finite elements. Bucklinginduced delamination is analysed using plate/shell FE methods with growth/remeshing algorithms. 相似文献
4.
OBJECTIVE: To evaluate the discrepancy index between the clinical and histological diagnosis and the prevalence of epithelial dysplasia and carcinoma in 45 patients with potentially malignant epithelial oral lesions (PMEL). PATIENTS AND METHODS: We submitted 45 patients with PMEL to clinical examination and obtained a biopsy from each. The results of histological diagnosis were compared to the clinical diagnosis. RESULTS: Clinical diagnosis showed that the most common PMEL was leukoplakia followed by lichen planus and by actinic cheilitis associated with leukoplakia. The most common site was the buccal mucosa. Histological diagnosis revealed that 46.7% of the PMEL were lichen planus. The discrepancy index between clinical and histological diagnosis was 24.4%. The higher discrepancy index occurred among leukoplakias. The prevalence of epithelial dysplasia and carcinoma was 17.8%. CONCLUSIONS: We conclude that all PMEL should be submitted to a microscopic analysis because the discrepancy between clinical and histological diagnosis was present in a quarter of these lesions. Otherwise, the epithelial dysplasia and carcinoma were more frequent in the leukoplakias. 相似文献
5.
6.
7.
We report on compound formation in the system HgCdTeO. Samples were prepared by solid state reaction of mixtures of the binary oxide components. Specific phases were identified and characterized by X-ray and microprobe techniques. For some of these compounds small single crystals could be prepared and structural data of which are reported. Three groups of phases could be distinguished, most of them being of low symmetry, with Te in +4, +6, and in mixed oxidation states. The monotellurites HgTeO3 and CdTeO3 are structurally different and exhibit a large miscibility gap, whereas for the di-tellurites complete solid solution between CdTe2O5 and HgTe2O5 was found. As to the tellurates, phases with the compositions MTeO4 and M3Te2O9 (M = Hg, Cd) have been prepared. The Cd3Te2O9-structure is stabilized by 30 mole% Hg. Another tellurate, monoclinic Hg2TeO4, was found to be isomorphous to the respective selenate and sulfate and is identical with the mineral magnolite. The interaction of Te2O5 with the metal oxides led to the formation of mixed valence compounds with both Te(+4) and Te(+6) of the types M2Te2O7 and MTe2O6. 相似文献
8.
9.
10.
J Cremer G Steinhoff M Karck T Ahnsell M Brandt OE Teebken D Hollander A Haverich 《Canadian Metallurgical Quarterly》1997,12(5):753-758
OBJECTIVE: Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery. METHODS: A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored. RESULTS: The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min). CONCLUSIONS: Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning. 相似文献