全文获取类型
收费全文 | 37545篇 |
免费 | 2035篇 |
国内免费 | 57篇 |
专业分类
电工技术 | 254篇 |
综合类 | 40篇 |
化学工业 | 8481篇 |
金属工艺 | 745篇 |
机械仪表 | 702篇 |
建筑科学 | 1151篇 |
矿业工程 | 76篇 |
能源动力 | 1236篇 |
轻工业 | 6639篇 |
水利工程 | 361篇 |
石油天然气 | 170篇 |
武器工业 | 2篇 |
无线电 | 1691篇 |
一般工业技术 | 5581篇 |
冶金工业 | 7253篇 |
原子能技术 | 252篇 |
自动化技术 | 5003篇 |
出版年
2024年 | 73篇 |
2023年 | 296篇 |
2022年 | 765篇 |
2021年 | 1068篇 |
2020年 | 749篇 |
2019年 | 910篇 |
2018年 | 1240篇 |
2017年 | 1203篇 |
2016年 | 1277篇 |
2015年 | 1043篇 |
2014年 | 1383篇 |
2013年 | 2610篇 |
2012年 | 2100篇 |
2011年 | 2371篇 |
2010年 | 1833篇 |
2009年 | 1808篇 |
2008年 | 1626篇 |
2007年 | 1462篇 |
2006年 | 1138篇 |
2005年 | 955篇 |
2004年 | 933篇 |
2003年 | 811篇 |
2002年 | 734篇 |
2001年 | 524篇 |
2000年 | 517篇 |
1999年 | 589篇 |
1998年 | 2412篇 |
1997年 | 1580篇 |
1996年 | 1102篇 |
1995年 | 614篇 |
1994年 | 517篇 |
1993年 | 550篇 |
1992年 | 208篇 |
1991年 | 195篇 |
1990年 | 164篇 |
1989年 | 184篇 |
1988年 | 162篇 |
1987年 | 147篇 |
1986年 | 121篇 |
1985年 | 172篇 |
1984年 | 113篇 |
1983年 | 101篇 |
1982年 | 109篇 |
1981年 | 121篇 |
1980年 | 113篇 |
1979年 | 58篇 |
1978年 | 59篇 |
1977年 | 185篇 |
1976年 | 342篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
182.
A method for reconstitution of membrane proteins into unilamellar liposomes is described. The model enzyme was the F0F1 ATP synthase from mitochondria when in complex or free from its inhibitor protein. The enzymes were first solubilized with either of two detergents, i.e., n-dodecyl-beta-D maltoside or lauryldimethylamine oxide. After solubilization, the enzymes were passed through a column of Sepharose-AH using an ADP/sodium cholate selective elution buffer. The enzymes recovered from the column were subsequently passed through a centrifuge column of Sephadex G-50 fine. The eluate contained liposomes in which the F0F1 complex (with and without inhibitor protein) had been reconstituted. The reconstituted enzymes were capable of hydrolyzing ATP with formation of electrochemical H+ gradients. They also catalyzed the ATP-Pi exchange reactions. Thus the F0F1 complex which is formed by 18 subunits can be rapidly reconstituted into liposomes in a fully functional state. Moreover the data show that the interactions between the enzyme and its inhibitor protein are not perturbed in the reconstitution procedure. 相似文献
183.
Orestes E. Alarcón Ricardo E. medrano Pcter P. Gillis 《Metallurgical and Materials Transactions A》1994,25(5):961-968
To fully characterize the mechanical behavior of ceramics, it is useful to study their response to both tensile and bending
tests. In this investigation, a quantitative comparison is made between tensile and bending results from (circularly) cylindrical
glass rods of borosilicate glass and of fused silica. These experimental results show that in each material, the Weibull exponentm is approximately the same for both types of test. The fractured samples clearly showed that all failures initiated at surface-located
flaws. The stress level at which the probability of fracture in tension equals 50 Pct was determined; the maximum tensile
stress for 50 Pct probability of fracture in bending was also determined. The ratio of these two stresses was predicted previously
from simple, theoretical considerations based upon the applicability of the Weibull function and on the distribution of defects
in the specimens. This theoretical result is inconsistent with the experimental observations in view of the fractography.
Therefore, it is concluded that failure in the materials tested is not satisfactorily described by Weibull statistics. 相似文献
184.
An engineered fusion protein containing two tandem lactose permease molecules (permease dimer) exhibits high transport activity and is used to test the phenomenon of negative dominance. Introduction of the mutation Glu-325-->Cys into either the first or the second half of the dimer results in a 50% decrease in activity, whereas introduction of the mutation into both halves of the dimer abolishes transport. Lactose transport by permease dimer is completely inactivated by N-ethylmaleimide; however, 40-45% activity is retained after N-ethylmaleimide treatment when either the first or the second half of the dimer is replaced with a mutant devoid of cysteine residues. The observations demonstrate that both halves of the fusion protein are equally active and suggest that each half may function independently. To test the possibility that oligomerization between dimers might account for the findings, a permease dimer was constructed that contains two different deletion mutants that complement functionally when expressed as untethered molecules. Because this construct does not catalyze lactose transport to any extent whatsoever, it is unlikely that the two halves of the dimer interact or that there is an oligomeric interaction between dimers. The approach is consistent with the contention that the functional unit of lactose permease is a monomer. 相似文献
185.
Solution of temperature fields in hydrodynamics bearings by the numerical network method 总被引:1,自引:0,他引:1
Solution to the 2-D steady-state nonlinear heat conduction equation, involving cylindrical coordinates, applied to a plain bearing by a simple and versatile numerical technique based on network method is presented in this work. These advantages of the technique are necessary for the status evaluation of industrial machines during operation because time and computing resources are limited. The pressure field in the fluid is previously solved from the Reynolds equation by finite element method. The main difficulty is associated with the exponential dependency of the viscosity on temperature. The proposed model is very efficient and requires negligible computing times. Solutions are very close to the experimental and numerical results of other researchers. 相似文献
186.
RM Martín‐Aranda E Ortega‐Cantero ML Rojas‐Cervantes MA Vicente‐Rodríguez MA Baares‐Muoz 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(2):234-238
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry 相似文献
187.
Paulo S. André António L. Teixeira Armando N. Pinto Lara P. Pellegrino Berta B. Neto José F. Rocha Joäo L. Pinto Paulo N. Monteiro 《ETRI Journal》2006,28(2):257-259
In this letter, we will evaluate the performance degradation of a 40 km high‐speed (40 Gb/s) optical system, induced by optical fiber variations of the chromatic dispersion induced by temperature changes. The chromatic dispersion temperature sensitivity will be estimated based on the signal quality parameters. 相似文献
188.
The aim of this study was to determine the tocopherol contents of wine by-products including grape seed, pomace (seed, skin and stem) and bagasse (skin and stem) by using two different extraction methods in order to evaluate the possibilities of them as natural non-polar antioxidants. Cold extraction appeared to give more tocopherol contents in seeds than hot extraction. But hot extraction was found more suitable for pomace and bagasse. α-Tocopherol was the most abundant tocopherol in the grape seed, pomace and bagasse. Although γ- and δ-tocopherols were found in the samples with low concentrations, β-tocopherol was not detected in the samples. Kalecik karası had the highest α and total tocopherol compared to the other cultivars. On the other hand, hot extracted bagasse in all cultivars gave the highest tocopherol contents. As a conclusion, wine by-products, a large scale wastes, can be evaluated both to get natural tocopherol source and to obtain economical gain. 相似文献
189.
Bei der Model Driven Architecture (MDA) bilden Modelle die zentralen Elemente des Softwareentwicklungsprozesses. Ziel ist es, plattformspezifische Modelle möglichst automatisiert aus plattformunabhängigen Modellen abzuleiten. Dadurch soll der Aufwand der Softwareentwicklung verringert und die Adaptierung an neue Technologien erleichtert werden.*Vorschläge an Prof. Dr. Frank Puppe oder Dieter Steinbauer Alle „Aktuellen Schlagwörter“ seit 1988 finden Sie unter: www.ai-wuerzburg.de/as 相似文献
190.
Disassembly sequence planning in a disassembly cell context 总被引:2,自引:0,他引:2
In this paper a two-phase approach is proposed for determining the optimal disassembly sequence when the disassembly system has a cellular configuration. Operations are first grouped into cells based on the resources they require with the goal of minimizing machine acquisition costs. The aim is to group together those operations that use similar equipment in order to achieve good utilization levels of such equipment. A maximum cell size may be imposed. Once the cells have been formed and the operations have been assigned to them, a metaheuristic algorithm (namely GRASP) is used to search for the disassembly sequence for each product that leads to the minimum number of intercellular movements. To account for uncertainty regarding the condition in which the product may arrive, each disassembly task is assumed to be required with a certain probability, regardless of the other tasks. AND/OR precedence relations among the disassembly tasks are also considered. The proposed approach is illustrated on a randomly generated disassembly problem. 相似文献