全文获取类型
收费全文 | 1412篇 |
免费 | 97篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 17篇 |
综合类 | 2篇 |
化学工业 | 658篇 |
金属工艺 | 18篇 |
机械仪表 | 38篇 |
建筑科学 | 40篇 |
矿业工程 | 5篇 |
能源动力 | 44篇 |
轻工业 | 91篇 |
水利工程 | 9篇 |
石油天然气 | 6篇 |
无线电 | 118篇 |
一般工业技术 | 175篇 |
冶金工业 | 187篇 |
原子能技术 | 4篇 |
自动化技术 | 98篇 |
出版年
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 107篇 |
2018年 | 122篇 |
2017年 | 57篇 |
2016年 | 52篇 |
2015年 | 16篇 |
2014年 | 118篇 |
2013年 | 57篇 |
2012年 | 58篇 |
2011年 | 82篇 |
2010年 | 53篇 |
2009年 | 45篇 |
2008年 | 56篇 |
2007年 | 49篇 |
2006年 | 60篇 |
2005年 | 42篇 |
2004年 | 39篇 |
2003年 | 25篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 30篇 |
1999年 | 16篇 |
1998年 | 31篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 5篇 |
1970年 | 5篇 |
排序方式: 共有1510条查询结果,搜索用时 140 毫秒
1.
<正>最近,陶氏公司在2019上海国际车展期间介绍了一系列应对汽车行业新挑战的创新产品和解决方案,帮助汽车厂商化挑战为机遇。以"创新为你,续写经典"为主题,陶氏公司从用户体验出发,与车企紧密合作,为消费者提供"声、形、味"俱佳的驾乘体验。陶氏聚氨酯业务部大中华区销售总监陈飞介绍说:"当今汽车行业面临众多挑战,安全性、轻量化、舒适性和环保性要求不断推 相似文献
2.
PA Grace 《Canadian Metallurgical Quarterly》1997,166(3):152-156
PURPOSE: To examine the management and possible causes of primary valve malfunction of the Krupin eye valve with disk. METHODS: The authors reviewed the results of 113 patients undergoing implantation of the Krupin eye valve with disk and identified eight patients with primary valve malfunction requiring surgical revision. RESULTS: Valve revision involved manipulation (n = 1 case), explantation of the malfunctioning valve and implantation of a new valve (n = 2), and amputation of the valve (n = 5). Six of eight patients had final intraocular pressures of < 21 mmHg on one or no medications at a mean interval of 15.9 months (range 5-36) after surgical revision. Transient postoperative hypotony was noted in three patients and chronic hypotony with loss of light perception in one patient. One explanted valve was examined and found to have partially fused leaflets. CONCLUSIONS: Surgical revision in cases of primary valve malfunction of the Krupin eye valve with disk may be accomplished relatively safely with an acceptable level of postoperative complications. The etiology of primary valve malfunction may be related to the sterilization process and prolonged storage before implantation. 相似文献
3.
John R. Grace 《加拿大化工杂志》1986,64(3):353-363
An attempt is made to extend schemes for classifying the behaviour of gas—solid contacting modes and other two-phase systems. The regime diagram approach of Reh (1971) is modified and extended to cover the operating regions of common reactors and contactors where a gas flows upwards through a bed of solids including fixed and moving packed beds, conventional fluidized beds, circulating beds, spouted beds, and pneumatically conveyed suspensions. New boundaries are proposed between groups A and B and between groups B and D of the Geldart (1972, 1973) powder classification scheme. These boundaries reflect more recent data and allow the classification scheme to be used for gases other than air and for temperatures and pressures other than atmospheric. 相似文献
4.
Melatonin deacetylase, an enzyme activity recently discovered in the Xenopus laevis retina, regulates local melatonin levels. The deacetylase occurs in retina, retinal pigment epithelium, and skin, all sites of melatonin action, and is widely distributed among vertebrates. We have solubilized the enzyme from Xenopus retina and pigment epithelium using nonionic detergents, and have developed a specific enzyme assay. We have characterized the enzyme and now report that the deacetylase is relatively specific for melatonin and is inhibited by the melatonin precursor N-acetylserotonin and the product of the deacetylase, 5-methoxytryptamine. Inhibition of deacetylase activity by eserine (physostigmine) suggests a relationship between deacetylase and cholinesterase activities. However, among a variety of cholinesterase inhibitors tested, only eserine inhibits the deacetylase. Furthermore, eserine is much less potent as an inhibitor of the deacetylase than the cholinesterases, and purified cholinesterases failed to deacetylate melatonin. We also show that melatonin deacetylase and aryl acylamidase (an enzyme related to cholinesterases) activities are differentially extractable from Xenopus ocular tissues, and that they exhibit different pH optima and inhibition profiles. Our results provide an initial characterization of the Xenopus retinal melatonin deacetylase, and indicate that deacetylase activity is distinct from cholinesterase and aryl acylamidase activities. 相似文献
5.
1. The presence of dye coupling between striatal neurons was investigated using in vivo intracellular recording and dye injection in adult rats. In 17% of the cases in which a single striatal neuron was injected with Lucifer yellow, more than one labeled neuron was recovered. In control rats, this dye coupling was observed only between single pairs of medium spiny neurons and only when the neuron injected exhibited the Type II response profile as defined by paired-pulse stimulation of corticostriatal afferents. 2. After intravenous administration of the D1/D2 agonist apomorphine at a behaviorally effective dose (i.e., 0.1-0.3 mg/kg), an increase in the incidence (from 17% to 82% of injected cells) and extent (from 2 cells to 3-7 cells labeled per injection) of dye coupling was observed. This effect was mediated by D2 receptor stimulation because administration of the D2 agonist quinpirole caused similar alterations in the incidence and extent of dye coupling (66% coupled). In contrast, administration of the D1 agonist SKF 38393 or the D1 antagonist SCH 23390 did not result in any significant alteration in dye coupling. 3. In control rats, the entire somatodendritic regions of dye-coupled neurons were found to be localized within single matrix compartments of the striatum. However, after intravenous administration of apomorphine or quinpirole, clusters of dye-coupled neurons were found to extend across the patch/matrix boundary. Moreover, dye coupling was observed after injecting cells exhibiting either the Type I or the Type II response profile. 4. In response to D2 receptor stimulation, both the extent and the pattern of coupling between striatal neurons is altered, resulting in direct coupling between neurons that are otherwise functionally and anatomically segregated in the control animal. 相似文献
6.
The performance of two distributed channel assignment algorithms which use coexistence etiquettes for point to point links are considered by the authors. It has been found that selecting channels prior to transmission at the transmitter as opposed to the receiver, supports greater offered traffic with the additional advantage of a less complex protocol 相似文献
7.
Incubation of intact platelets from Sinclair(S-1) miniature swine with32P-labeled lysophosphatidylcholine (lyso PC) indicated the presence of an active lysophospholipase with a pH optimum of 8.0
for hydrolysis of the substrate. However, lyso PC was incorporated into the membrane phosphatidylcholines by the acyltransferase
pathway upon addition of ATP, Mg++ and CoA to the platelet suspension. These results suggest that intact platelets are able to resist the cytotoxic effects
of lyso PC in plasma, and the phospholipids in platelet membranes are not readily affected by the lipid environment of the
plasma. The acyltransfer reaction apparently is saturated with endogenous free fatty acids since arachidonic acid added exogenously
did not further enhance the incorporation activity. Neither the acyltransferase nor the lysophospholipase activity was affected
by Ca++, but divalent metal ions such as Zn++ inhibited the lysophospholipase activity. Cholesterol but not cholesteryl esters elicited a biphasic effect on both enzymes,
stimulating at low concentration but inhibiting at a cholesterol to lyso PC ratio greater than 1. Serum albumin inhibited
the lysophospholipase but gave a small biphasic effect to the acyltransferase. 相似文献
8.
本文用不热形变栅状直丝化学气相沉积(CVD)法生长金刚石膜,在Si及WC-Co硬质合金衬底上金刚石膜晶面显露规律随衬底温度和甲烷浓度而异,经适当表面处理及选择合适的工艺条件,当生长初期衬底上就呈现出良好晶形的沉积膜,衬底与膜之间的粘结力能得到提高。Raman谱分析表明此膜仅具有特征金刚石1332cm ̄(-1)峰,通过SEM观察揭示出盒刚石膜可在表面、侧面及棱上生长,并与衬底有良好的联结。 相似文献
9.
Microstructural and dielectric properties of the Pb x Ba 0.5 _x —Sr0.5 TiO3 system have been studied. It is found that this system forms a solid solution in the entire composition range (0.0≤ x ≤0.5) and is cubic for the x = 0, 0.1, and 0.2 compositions and tetragonal for other compositions. Measurements of the dielectric constant as a function of temperature reveal that this material is ferroelectric at room temperature for the x > 0.2 compositions and has a broad paraelectric-ferroelectric transition region. No shift in the dielectric maxima was noted; however, there is a slight spread in the dielectric constant with frequency for the x = 0.4 composition. A quantitative model to mathematically analyze the effect of composition fluctuations on the dielectric broadening for a ternary system is presented. Transmission electron microscopic studies reveal the presence of 90° ferroelectric domains oriented along the {01 } planes for the x = 0.3 and 0.4 compositions. 相似文献
10.