全文获取类型
收费全文 | 20429篇 |
免费 | 1512篇 |
国内免费 | 531篇 |
专业分类
电工技术 | 648篇 |
技术理论 | 1篇 |
综合类 | 1737篇 |
化学工业 | 3960篇 |
金属工艺 | 472篇 |
机械仪表 | 753篇 |
建筑科学 | 1819篇 |
矿业工程 | 418篇 |
能源动力 | 378篇 |
轻工业 | 2203篇 |
水利工程 | 267篇 |
石油天然气 | 319篇 |
武器工业 | 73篇 |
无线电 | 917篇 |
一般工业技术 | 3321篇 |
冶金工业 | 961篇 |
原子能技术 | 138篇 |
自动化技术 | 4087篇 |
出版年
2024年 | 87篇 |
2023年 | 287篇 |
2022年 | 371篇 |
2021年 | 577篇 |
2020年 | 598篇 |
2019年 | 609篇 |
2018年 | 562篇 |
2017年 | 670篇 |
2016年 | 743篇 |
2015年 | 744篇 |
2014年 | 1240篇 |
2013年 | 1274篇 |
2012年 | 1443篇 |
2011年 | 1647篇 |
2010年 | 1242篇 |
2009年 | 1246篇 |
2008年 | 1022篇 |
2007年 | 1227篇 |
2006年 | 1024篇 |
2005年 | 834篇 |
2004年 | 729篇 |
2003年 | 634篇 |
2002年 | 542篇 |
2001年 | 412篇 |
2000年 | 337篇 |
1999年 | 318篇 |
1998年 | 276篇 |
1997年 | 229篇 |
1996年 | 170篇 |
1995年 | 184篇 |
1994年 | 125篇 |
1993年 | 112篇 |
1992年 | 86篇 |
1991年 | 65篇 |
1990年 | 67篇 |
1989年 | 76篇 |
1988年 | 78篇 |
1987年 | 46篇 |
1986年 | 43篇 |
1985年 | 58篇 |
1984年 | 73篇 |
1983年 | 89篇 |
1982年 | 90篇 |
1981年 | 29篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1959年 | 5篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this paper we consider a conservative discretization of the two-dimensional incompressible Navier–Stokes equations. We propose an extension of Arakawa’s classical finite difference scheme for fluid flow in the vorticity–stream function formulation to a high order discontinuous Galerkin approximation. In addition, we show numerical simulations that demonstrate the accuracy of the scheme and verify the conservation properties, which are essential for long time integration. Furthermore, we discuss the massively parallel implementation on graphic processing units. 相似文献
32.
F. Comte 《时间序列分析杂志》1996,17(1):19-36
Abstract. Some general properties of long memory continuous time processes are recalled or proved. Methods of simulation are studied. A comparison with the usual discrete time autoregressive fractionally integrated moving-average filter is made and illustrations are provided. Then, two methods of estimation of the parameters of such a model from a discrete sample are studied, both theoretically and empirically, with Monte Carlo experiments. 相似文献
33.
纳米SiO2粉体的制备与研究 总被引:1,自引:0,他引:1
纳米SiO2粉体的制备是以硅酸钠和盐酸为原料,添加适宜的稳定剂(非离子表面活性剂)和分散剂,在适宜的pH值和温度下,采用化学沉淀法合成。研究表明,要得到性能优良纳米的SiO2粉体,最佳工艺条件为:温度20~40℃,pH=6,反应液质量浓度P1=20g/L,P2=1.20g/L,反应时间15min。结果表明:制备的纳米SiO2粒径30~50nm,比表面积大,分散性好,质量优良,可达到产业化的生产。 相似文献
34.
《Journal of Systems Architecture》2014,60(10):783-795
Complex systems on chip containing dozens of processing resources with critical communication requirements usually rely on the use of networks on chip (NoCs) as communication infrastructure. NoCs provide significant advantages over simpler infrastructures such as shared busses or point to point communication, including higher scalability, more efficient energy management, higher bandwidth and lower average latency. Applications running on NoCs with more than 10% of bandwidth usage attest that the most significant portion of message latencies refers to buffered packets waiting to enter the NoC, whereas the latency portion that depends on the packet traversing the NoC is sometimes negligible. This work presents an adaptive routing architecture, named Monitored NoC (MoNoC), which is based on a traffic monitoring mechanism and the exchange of high priority control packets. This method enables to adapt paths by choosing less congested routes. Practical experiments show that the proposed path adaptation is a fast process, enabling to transmit packets with smaller latencies, up to 9 times smaller, by using non-congested NoC regions. 相似文献
35.
The iron phases present in an electrostatic precipitator ash, an uncooled ash deposit and a cooled superheater ash deposit from Hazelwood Power Station, Australia, burning Morwell brown coal has been examined using Mössbauer spectroscopy. The principal iron phase in the precipitator ash and the uncooled ash deposit from a hot gas offtake was calcium aluminoferrite (Ca2Fe2 ? xAlxO5). Minor amounts of hematite (α-Fe2O3) and magnetite (Fe3O4) were also detected in the precipitator ash. The cooled superheater ash deposit contained a (Mg, Fe, Al) oxide spinel as the primary iron phase; small quantities of hematite were also detected in this deposit close to the heat exchanger interface. The formation of these iron phases has been rationalized on the basis of the average composition of coal delivered to the power station and supplementary ash chemistry data obtained from other techniques. The evidence suggests that the calcium aluminoferrite in the precipitator ash is derived from inorganic constituents (distributed throughout the coal organic matrix) and the hematite and magnetite are of mineral origin (discrete particles). 相似文献
36.
The reductive alkylation of Illinois No. 6 coal has been carried out using potassium and naphthalene in tetrahydrofuran and methyl-13C and butyl-1 -13C iodides to alkylate the resultant polyanion. The soluble products of the reductive alkylation reaction were isolated by extraction and chromatography. Proton and carbon n.m.r. spectra were recorded. The intense resonance signal at δ3.95 which appears in the proton n.m.r. spectra of Illinois No. 6 coal butylated with unenriched butyl iodide is split into a doublet by the 13C nuclei. Similar results were obtained for the methylation products. The chemical shift and coupling interaction establish that aryl ethers are a very important constituent of the alkylated coal. The carbon n.m.r. spectra of the coal alkylated with 13C-enriched alkyl iodides are intense. The resonances of the C-alkylation products appear in a single broad band with a maximum intensity in spectral regions compatible with the formation of the reductive alkylation products of certain polynuclear aromatic hydrocarbons or the base-catalysed alkylation of certain benzylic carbon atoms. The resonances of the N -alkylation products appear in two distinct bands. These resonances are tentatively assigned to amines produced as a result of reductive alkylation of heterocyclic compounds. The resonances of the 0-alkylation products appear in three distinct bands which can be assigned to alkyl aryl ethers, alkyl aryl ethers with substituents at the adjacent positions, and to alkyl carboxylates. The ratio of ethers to carboxylates in the soluble alkylation products was determined to be 7.8 for butylation and 8.0 for methylation. The Chromatographic fractions contain different amounts of C-, N-, and 0-alkylation products. This finding suggests that the coal structure is not highly uniform. 相似文献
37.
38.
Mohammed Mahfooz Khan 《Fuel》1982,61(6):553-556
This Paper deals with a comparative study on the use of gel permeation chromatography (g.p.c.) and vapour pressure osmometry (v.p.o.) to obtain molecular weight data for the hexane-soluble fractions of three H-coal liquids. The use of two types of column packing materials, polyvinylacetate and styrene-divinylbenzene copolymer gels, is described. A successful, preparative use of the polyvinylacetate gel to fractionate the hexane-soluble fraction of H-coal liquid, atmospheric still overhead (ASO), has been established. Molecular weight data obtained by v.p.o. for the benzene-soluble fraction and the pyridine-soluble fraction of the three H-coal liquids are reported. Solvent extraction has been utilized also to find the amount of oil, asphaltenes and asphaltols in the three H-coal liquids. 相似文献
39.
A. N. Gent 《The Journal of Adhesion》1987,23(2):115-122
Three new methods are discussed for measuring the work Ga, required to detach unit area of an adhering material from a substrate. The first is a simple modification of the Outwater double-torsion test for long rectangular plates, bonded together. This method is suitable for evaluating aluminum-epoxy bonds, for example, or the transverse strength of fibrous composites. The second is a pull-off test for long strips adhering to a rigid surface. It seems suitable for adhesive tapes and laminates. The third is a reconsideration of the “blister” test for films and coatings, in which a circular debond at the interface is made to grow by internal pressure. The relation obtained between pull-off force F for a strip, or blow-off pressure P for a layer, takes the unusual form:
F4 (or P4) ∞ KG3a
where K is the tensile stiffness of the detaching layer. This dependence arises from the non-linear (cubic) relation between load or pressure and deflection in these configurations. Nevertheless, the product Fθ, where θ is the angle of detachment of a strip, or Py, where y is the height of a “blister”, give direct measures of the strength of adhesion Ga, independent of the stiffness of the adhering material and of the extent of detachment. 相似文献
F4 (or P4) ∞ KG3a
where K is the tensile stiffness of the detaching layer. This dependence arises from the non-linear (cubic) relation between load or pressure and deflection in these configurations. Nevertheless, the product Fθ, where θ is the angle of detachment of a strip, or Py, where y is the height of a “blister”, give direct measures of the strength of adhesion Ga, independent of the stiffness of the adhering material and of the extent of detachment. 相似文献
40.
杨从麇 《重庆电力高等专科学校学报》2010,15(4):69-71
分析体育课教学中的主要任务、教材内容、教学方法、成绩考核等几个问题,并对此进行初步的研究和探讨,提出改革意见和措施,以改善体育课的教学效果。 相似文献