全文获取类型
收费全文 | 24751篇 |
免费 | 1467篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 449篇 |
综合类 | 60篇 |
化学工业 | 4983篇 |
金属工艺 | 686篇 |
机械仪表 | 579篇 |
建筑科学 | 1113篇 |
矿业工程 | 137篇 |
能源动力 | 451篇 |
轻工业 | 3222篇 |
水利工程 | 228篇 |
石油天然气 | 31篇 |
无线电 | 1794篇 |
一般工业技术 | 5895篇 |
冶金工业 | 2606篇 |
原子能技术 | 217篇 |
自动化技术 | 3789篇 |
出版年
2023年 | 264篇 |
2022年 | 199篇 |
2021年 | 506篇 |
2020年 | 398篇 |
2019年 | 405篇 |
2018年 | 760篇 |
2017年 | 760篇 |
2016年 | 836篇 |
2015年 | 692篇 |
2014年 | 885篇 |
2013年 | 1746篇 |
2012年 | 1164篇 |
2011年 | 1390篇 |
2010年 | 1154篇 |
2009年 | 1060篇 |
2008年 | 1191篇 |
2007年 | 1188篇 |
2006年 | 838篇 |
2005年 | 697篇 |
2004年 | 607篇 |
2003年 | 588篇 |
2002年 | 593篇 |
2001年 | 466篇 |
2000年 | 410篇 |
1999年 | 391篇 |
1998年 | 892篇 |
1997年 | 666篇 |
1996年 | 487篇 |
1995年 | 364篇 |
1994年 | 328篇 |
1993年 | 302篇 |
1992年 | 197篇 |
1991年 | 167篇 |
1990年 | 165篇 |
1989年 | 143篇 |
1988年 | 160篇 |
1987年 | 125篇 |
1986年 | 112篇 |
1985年 | 221篇 |
1984年 | 212篇 |
1983年 | 140篇 |
1982年 | 150篇 |
1981年 | 172篇 |
1980年 | 143篇 |
1979年 | 127篇 |
1978年 | 127篇 |
1977年 | 123篇 |
1976年 | 156篇 |
1975年 | 116篇 |
1974年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
81.
JL Banyer S Goldwurm L Cullen B van der Griend A Zournazi DJ Smit LW Powell EC Jazwinska 《Canadian Metallurgical Quarterly》1998,9(3):235-239
We have examined acetaminophen (paracetamol) dosing for outpatient management of posttonsillectomy pain in children. Forty children, 5-15 years of age, undergoing tonsillectomy and their parents were randomly assigned to use a scheduled administration of acetaminophen in weight appropriate doses, 60 mg.kg-1.24h-1 orally, 90 mg.kg-1.24h-1 rectally, or to use acetaminophen 'as needed' according to present standards (control group). Postoperative pain was assessed by the child using the poker chip tool for the first three days after discharge. The prevalence of pain amongst all the children was high. The second day after discharge 22%-64% of the children in the study group and 36%-73% of the children in the control group rated severe pain. Recommended dose ranges of acetaminophen do not provide sufficient pain relief in children following tonsillectomy. Further studies are required to determine, whether higher doses of acetaminophen or analgesics with different analgesic properties will lead to improved analgesia in children following tonsillectomy. 相似文献
82.
Bernd Stöckel 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(10):2131-2148
A two beam interferometer in the Martin-Puplett configuration is used to determine the complex dielectric constant at 300 GHz of teflon, TPX-plastics, SPECTRALON and paraffin waxes with melting temperatures of 48° C and 72° C, respectively. The design of the quasi-optical system leads to a constant beam diameter at the power detector independent of path delay and frequency. The power detector signal is recorded not only along one period but over about 50 periods. A spectrum estimation routine allows to determine more exactly amplitude and phase angle of the signal. A basic problem is noticed: imperfect detector and source match cause harmonic distortion of the power detector signal. The effects on processing the loss tangent and the invalidation are shown. Finally loss tangent and dielectric constant are determined indirectly by optimizing an equivalent microwave circuit using a commercial available microwave design system to take multiple reflections and losses in consideration. 相似文献
83.
F F?ndrich AM Waaga J Schr?der E Schweizer A Schmid S Jacob HH Wacker P Schroeder 《Canadian Metallurgical Quarterly》1995,27(2):1553-1554
84.
Ö. Jonsson T. Larsson M. Rönnqvist 《Structural and Multidisciplinary Optimization》1994,7(1-2):103-111
An efficient and commonly used approach to structural optimization is to solve a sequence of approximate design problems that are constructed iteratively. As is well-known, a major part of the computational burden of this scheme lies in the sensitivity analysis needed to state the approximate problems. We propose a possibility for reducing this burden by streamlining the calculations in a combined approximation and duality scheme for structural optimization. The difference between this scheme and the traditional one is that, instead of calculating all the constraint gradients to state an approximate design problem explicitly, linear combinations of these gradients are generated as they are needed during the solution of the approximate problem by the dual method. We show, by analysing some typical scenarios of problem characteristics, that this rearrangement of the calculations may be a computationally viable alternative to the traditional scheme. An advantage of streamlining the calculations is that there is no need to incorporate an active set strategy in the scheme, as is usually done, since all the design constraints may be taken into consideration without any loss of computational efficiency. This may, clearly, enhance the practical rate of convergence of the overall approximation scheme. Moreover, the proposed rearrangement of the calculations may make it computationally viable to apply iterative equation solvers to the structural analysis problem. Numerical results with direct as well as iterative equation solvers show that the streamlined scheme is a feasible and promising approach to structural optimization. 相似文献
85.
JF Weel RW van der Hulst Y Gerrits GN Tytgat A van der Ende J Dankert 《Canadian Metallurgical Quarterly》1996,34(9):2158-2162
Combination therapies that include metronidazole (MTZ) are the most successful therapies used in eradicating Helicobacter pylori. In this study, the prevalence and the relevance of heterogeneity in susceptibility to MTZ among H. pylori populations of 156 patients were evaluated. The results of this study show that 37 patients (24%) were infected with MTZ-resistant H. pylori (MIC > or = 8 micrograms/ml). Furthermore, 33% (52 of 156) of the patients were found to be infected with H. pylori populations heterogeneous for their susceptibility to MTZ. The reassessment of the MICs of MTZ for these 52 H. pylori populations revealed MTZ resistance in 28 of them, increasing the number of MTZ-resistant H. pylori populations among the 156 patients to 65 (42%). Out of 20 isolates, 2 (10%) heterogeneous in their susceptibility to MTZ also appeared to be heterogeneous at the genome level as determined by randomly amplified polymorphic DNA fingerprinting. In conclusion, the results show the limitations and risk of possible misinterpretations when only a single colony, picked from the primary H. pylori populations isolated from patients, is analyzed for its susceptibility to MTZ. 相似文献
86.
Dr.-Ing. Ch. Dörnemann Prof. Dr.-Ing. E. Handschin 《Electrical Engineering (Archiv fur Elektrotechnik)》1992,76(1):33-40
Übersicht Der Betriebszustand eines Verteilungsnetzes wird durch die Strombelastung aller Betriebsmittel beschrieben. Mit Hilfe einer statischen Estimationsmethode werden aus einzelnen Messungen und der Kenntnis der Verbrauchsdaten typische Verbraucherkurven (TVK) berechnet, die das elektrische Verhalten verschiedener Verbrauchergruppen widerspiegeln. Auf dieser Basis ist eine betriebsmittelbezogene Lastmodellierung an beliebigen Betriebsmitteln in Abhängigkeit der Verbraucherzusammensetzung unter Berücksichtigung externer Einflüsse wie der Temperatur möglich. Die so gewonnenen Belastungsverläufe erlauben eine Beschreibung des Netzzustands in den Verteilungsnetzen.
Bus load modelling in distribution systems
Contents The operating state of a distribution system is determined by the bus load current. Based on individual substation measurements and the load composition typical load curves are calculated using statistical estimation theory. These typical load curves describe the electrical behaviour of the different load types (e.g. household, storage heating, commerce etc.). As soon as the typical load curves are determined it is possible to calculate the bus load current in any substation taking external influences such as temperature into consideration. The bus load current serve as load models which completely describe the operating state of the distribution system.相似文献
87.
88.
H Sánchez T Fester S Kloska W Schr?der W Schuster 《Canadian Metallurgical Quarterly》1996,15(9):2138-2149
The discovery of disrupted rps19 genes in Arabidopsis mitochondria prompted speculation about the transfer to the nuclear compartment. We here describe the functional gene transfer of rps19 into the nucleus of Arabidopsis. Molecular cloning and sequence analysis of rps19 show that the nuclear gene encodes a long N-terminal extension. Import studies of the precursor protein indicate that only a small part of this extension is cleaved off during import. The larger part of the extension, which shows high similarity to conserved RNA-binding domains of the RNP-CS type, became part of the S19 protein. In the Escherichia coli ribosome S19 forms an RNA-binding complex as heterodimer with S13. By using immuno-analysis and import studies we show that a eubacterial-like S13 protein is absent from Arabidopsis mitochondria, and is not substituted by either a chloroplastic or a cytosolic homologue of this ribosomal protein. We therefore propose that either a highly diverged or missing RPS13 has been functionally replaced by an RNP domain that most likely derived from a glycine-rich RNA-binding protein. These results represent the first case of a functional replacement of a ribosomal protein by a common RNA-binding domain and offer a new view on the flexibility of biological systems in using well-adapted functional domains for different jobs. 相似文献
89.
The compression of a paper web in a calender nip has been simulated using the finite element method. The mechanical properties of the paper were allowed to vary in the thickness and machine directions of the web. This was done in order to model the influence of temperature gradients as well as density variations (due to the presence of fibre floes) on the deformation behaviour in the nip. Paper was assumed to be an elastic-plastic material exhibiting strain hardening. The yielding behaviour was governed by the Drucker-Prager yield condition. Simulations of the deformation behaviour when paper was subjected to a temperature gradient, clearly revealed that the deformation gradually became more concentrated towards the surface layers as the temperature of the surface increased. This is in accordance with experimental results which indicate that temperature-gradient calendering promotes the surface properties, whereas the bulk of the structure is preserved. Modelling the deformation behaviour of a structure containing density variations reveals that the paper may contain an inhomogeneous strain distribution after unloading, i.e. after passage through the nip. 相似文献
90.
A general numerical model is described for the dissolution kinetics of spherical particles in binary systems for any combination of first order reactions at the particle-matrix interface and long distance diffusion within the matrix. The model is applicable to both finite and infinite media and handles both complete and partial particle dissolution. It is shown that interfacial reactions can have a strong effect on the dissolution kinetics, the solute concentration at the particle-matrix interface and the solute concentration profile in the matrix. 相似文献