全文获取类型
收费全文 | 41276篇 |
免费 | 4159篇 |
国内免费 | 2437篇 |
专业分类
电工技术 | 3066篇 |
技术理论 | 2篇 |
综合类 | 3050篇 |
化学工业 | 6627篇 |
金属工艺 | 2071篇 |
机械仪表 | 2198篇 |
建筑科学 | 3631篇 |
矿业工程 | 1397篇 |
能源动力 | 1036篇 |
轻工业 | 3975篇 |
水利工程 | 842篇 |
石油天然气 | 2249篇 |
武器工业 | 388篇 |
无线电 | 4909篇 |
一般工业技术 | 4695篇 |
冶金工业 | 1648篇 |
原子能技术 | 494篇 |
自动化技术 | 5594篇 |
出版年
2024年 | 280篇 |
2023年 | 892篇 |
2022年 | 1669篇 |
2021年 | 2090篇 |
2020年 | 1703篇 |
2019年 | 1331篇 |
2018年 | 1463篇 |
2017年 | 1565篇 |
2016年 | 1391篇 |
2015年 | 1903篇 |
2014年 | 2325篇 |
2013年 | 2768篇 |
2012年 | 3069篇 |
2011年 | 3176篇 |
2010年 | 2620篇 |
2009年 | 2412篇 |
2008年 | 2301篇 |
2007年 | 2175篇 |
2006年 | 2077篇 |
2005年 | 1700篇 |
2004年 | 1105篇 |
2003年 | 939篇 |
2002年 | 831篇 |
2001年 | 766篇 |
2000年 | 834篇 |
1999年 | 812篇 |
1998年 | 653篇 |
1997年 | 531篇 |
1996年 | 513篇 |
1995年 | 409篇 |
1994年 | 377篇 |
1993年 | 251篇 |
1992年 | 225篇 |
1991年 | 170篇 |
1990年 | 125篇 |
1989年 | 120篇 |
1988年 | 69篇 |
1987年 | 47篇 |
1986年 | 46篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 9篇 |
1980年 | 18篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1966年 | 1篇 |
1959年 | 9篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Single-crystalline 3C-SiC nanowires have been synthesized in large scale through a one-step autoclave route by the reaction of SiCl4, (C5H5)2Fe and metallic Na at 500 °C. Electron microscopy investigations show that the nanowires have typical diameters of 15-50 nm, lengths up to several tens of micrometers and grow along the [111] direction. The possible growth mechanism of the nanowires is discussed. 相似文献
32.
Magnesiumandmagnesiumalloyshavebeenin vestigatedashydrogenstoragematerialsforseveralde cadesbecausefarmorehydrogenbyweightcanbestoredinthemthaninmostoftheothercurrentlyknownhydrogenstoragealloys .Moreover ,thehighnaturalabundanceofMg ,itslightmassandenviron mentalcompatibilitypotentiallymakemagnesiumoneofthemostprospectivecandidatesforfuturehydrogenstoragematerials .Unfortunately ,thepracticalappli cationofMganditsalloyshasbeenlimitedonlytocertainstoragedevicebecauseoftheirpoorhydriding dehydr… 相似文献
33.
Mushroom-like ZnO microcrystals have been prepared via a solution calcination route, using Zn(NO3)2 as Zn source in the absence of any surfactants, templates or catalysts. This is the first example to prepare mushroom-like crystals as semiconductors, which are expected to show particular physical properties. The ZnO products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectrum measurements. A suitable concentration of Zn(NO3)2 solution was important for the growth of the mushroom-like products. The reported synthetic procedure is straightforward and inexpensive, and thus can be readily adopted to produce large quantities of mushroom-like ZnO microcrystals. 相似文献
34.
35.
PRO——一种新的地震资料处理方法 总被引:2,自引:0,他引:2
PRO(影像的参数展开)技术是由俄罗斯地球物理学家开发的一种崭新的地震资料处理技术。本文从PRO基本原理入手,简单介绍了PRO的速度分析原理。PRO速度分析和成像均以信号的椭圆展开和参数展开为基础,其中参数展开方法考虑波型转换、介质的横向不均匀造成传播速度的变化。该技术抛开了传统共中心点叠加的思想,从根本上解决了以CMP方法为基础的传统地震处理技术遇到的困难。通过模型与实例分析对比,PRO比传统CMP方法更优越。 相似文献
36.
A signal intensity based maximum-likelihood (ML) target location estimator that uses quantized data is proposed for wireless sensor networks (WSNs). The signal intensity received at local sensors is assumed to be inversely proportional to the square of the distance from the target. The ML estimator and its corresponding Crameacuter-Rao lower bound (CRLB) are derived. Simulation results show that this estimator is much more accurate than the heuristic weighted average methods, and it can reach the CRLB even with a relatively small amount of data. In addition, the optimal design method for quantization thresholds, as well as two heuristic design methods, are presented. The heuristic design methods, which require minimum prior information about the system, prove to be very robust under various situations 相似文献
37.
对苯二甲酸精制技术的研究进展 总被引:7,自引:0,他引:7
综述了对苯二甲酸精制技术的研究进展,对几种主要的精制方法进行了对比,并指出了对苯二甲酸精制技术的发展趋势。 相似文献
38.
39.
Dystrophin is a plasma membrane-associated cytoskeletal protein of the spectrin superfamily. The dystrophin cytoskeleton has been first characterized in muscle. Muscular 427 kDa dystrophin binds to subplasmalemmal actin filaments via its amino-terminal domain. The carboxy-terminus of dystrophin binds to a plasma membrane anchor, beta-dystroglycan, which is associated on the external side with the extracellular matrix receptor, alpha-dystroglycan, that binds to the basal lamina proteins laminin-1, laminin-2, and agrin. In the muscle, the dystroglycan complex is associated with the sarcoglycan complex that consists of several glycosylated, integral membrane proteins. The absence or functional deficiency of the dystrophin cytoskeleton is the cause of several types of muscular dystrophies including the lethal Duchenne muscular dystrophy (DMD), one of the most severe and most common genetic disorders of man. The dystrophin complex is believed to stabilize the plasma membrane during cycles of contraction and relaxation. Muscular dystrophin and several types of dystrophin variants are also present in extramuscular tissues, e.g. in distinct regions of the central nervous systems including the retina. Absence of dystrophin from these sites is believed to be responsible for some extramuscular symptoms of DMD, e.g. mental retardation and disturbances in retinal electrophysiology (reduced b-wave in electroretinograms). The reduced b-wave in electroretinograms indicated a disturbance of neurotransmission between photoreceptors and ON-bipolar cells. At least two different dystrophin variants are present in photoreceptor synaptic complexes. One of these dystrophins (Dp260) is virtually exclusively expressed in the retina. In the neuroretina, dystrophin is found in significant amounts in the invaginated photoreceptor synaptic complexes. At this location dystrophin colocalizes with dystroglycan. Agrin, an extracellular ligand of alpha-dystroglycan, is also present at this location whereas the proteins of the sarcoglycan complex appear to be absent in photoreceptor synaptic complexes. Dystrophin and dystroglycan are located distal from the ribbon-containing active synaptic zones where both proteins are restricted to the photoreceptor plasma membrane bordering on the lateral sides of the synaptic invagination. In addition, some neuronal profiles of the postsynaptic complex also contain dystrophin and beta-dystroglycan. These profiles appear to belong at least in part to projections of the photoreceptor terminals into the postsynaptic dendritic complex. In view of the abnormal neurotransmission between photoreceptors and ON-bipolar cells in DMD patients the dystrophin/beta-dystroglycan-containing projections of photoreceptor presynaptic terminals into the postsynaptic dendritic plexus might somehow modify the ON-bipolar pathway. Another retinal site associated with dystrophin/beta-dystropglycan is the plasma membrane of Müller cells where dystrophin/beta-dystroglycan appear to be present at particular high concentrations. At this location the dystrophin/dystroglycan complex may play a role in the attachment of the retina to the vitreous, and, under pathological conditions, in traction-induced retinal detachment. 相似文献
40.