全文获取类型
收费全文 | 168369篇 |
免费 | 7062篇 |
国内免费 | 3337篇 |
专业分类
电工技术 | 5126篇 |
技术理论 | 9篇 |
综合类 | 6816篇 |
化学工业 | 26657篇 |
金属工艺 | 9109篇 |
机械仪表 | 8167篇 |
建筑科学 | 9174篇 |
矿业工程 | 2545篇 |
能源动力 | 3554篇 |
轻工业 | 8452篇 |
水利工程 | 2697篇 |
石油天然气 | 4866篇 |
武器工业 | 495篇 |
无线电 | 19419篇 |
一般工业技术 | 27158篇 |
冶金工业 | 7266篇 |
原子能技术 | 1080篇 |
自动化技术 | 36178篇 |
出版年
2024年 | 330篇 |
2023年 | 1327篇 |
2022年 | 2311篇 |
2021年 | 3140篇 |
2020年 | 2359篇 |
2019年 | 2048篇 |
2018年 | 16330篇 |
2017年 | 15537篇 |
2016年 | 12061篇 |
2015年 | 3539篇 |
2014年 | 4238篇 |
2013年 | 5253篇 |
2012年 | 8297篇 |
2011年 | 14716篇 |
2010年 | 12973篇 |
2009年 | 10115篇 |
2008年 | 11075篇 |
2007年 | 12020篇 |
2006年 | 4758篇 |
2005年 | 5323篇 |
2004年 | 3873篇 |
2003年 | 3645篇 |
2002年 | 2718篇 |
2001年 | 2116篇 |
2000年 | 2461篇 |
1999年 | 2619篇 |
1998年 | 2435篇 |
1997年 | 1914篇 |
1996年 | 1786篇 |
1995年 | 1455篇 |
1994年 | 1228篇 |
1993年 | 892篇 |
1992年 | 670篇 |
1991年 | 566篇 |
1990年 | 410篇 |
1989年 | 367篇 |
1988年 | 328篇 |
1987年 | 175篇 |
1986年 | 166篇 |
1985年 | 112篇 |
1984年 | 99篇 |
1983年 | 63篇 |
1982年 | 60篇 |
1981年 | 54篇 |
1980年 | 39篇 |
1968年 | 45篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
81.
Cyclic oxidation response of multiphase niobium-based alloys 总被引:4,自引:0,他引:4
Kwai S. Chan 《Metallurgical and Materials Transactions A》2004,35(2):589-597
Cyclic oxidation tests were performed on multiphase Nb-based alloys containing silicide, Laves, and Nb solid solution phases.
In particular, the oxidation resistance of six alloys with various compositions (Nb, Ti, Hf, Cr, Ge, and Si) and microstructures
was characterized by thermal cycling from ambient temperature to a peak temperature that ranges from 900 °C to 1400 °C. Weight
change data were obtained and the corresponding spalled oxides were collected and identified by X-ray diffraction. The results
indicated that Nb-based alloys formed a mixture of CrNbO4, Nb2O5, and Nb2O5 · TiO2, with possibly small amounts of SiO2 or GeO2. The oxidation resistance was improved when CrNbO4 formed instead of Nb2O5 and Nb2O5 · TiO2. These results were used to assess the influence of microstructure and composition on the oxidation resistance of multiphase
Nb-based alloys. 相似文献
82.
83.
Jürgen Schönbeçk 《NTM》2004,12(2):80-99
Thomas Fincke (January 6th, 1561–April 24th, 1656), born in Flensburg (Germany), was one of the very most important and significant scientists in Denmark during the
seventeenth century, a mathematician and astrologer and physician in the beginning of modern science, a representative of
humanism and an influentual academic organizer. He studied in Strasbourg (since 1577) and Padua (since 1583) and received
his M.D. in Basel (1587), he practised as a physician throughout his life (since 1587 or 1590) and became a professor at Copenhagen
(1591). But he was best known because of his Geometriae rotundi libri XIIII (1583), a famous book on plane and spherical trigonometry, based not on Euclid but on Petrus Ramus. In this influentual work,
in which Fincke introduced the terms tangent and secant and probable first noticed the Law of Tangents and the so-called Newton-Oppel-Mauduit-Simpson-Mollweide-Gauss-formula,
he showed himself to be „abreast of the mathematics of his time“.
相似文献
84.
Sorin Manolache Petru Eles Zebo Peng 《International journal of parallel programming》2007,35(2):125-156
As feature sizes shrink, transient failures of on-chip network links become a critical problem. At the same time, many applications
require guarantees on both message arrival probability and response time. We address the problem of transient link failures
by means of temporally and spatially redundant transmission of messages, such that designer-imposed message arrival probabilities
are guaranteed. Response time minimisation is achieved by a heuristic that statically assigns multiple copies of each message
to network links, intelligently combining temporal and spatial redundancy. Concerns regarding energy consumption are addressed
in two ways. First, we reduce the total amount of transmitted messages, and, second, we minimise the application response
time such that the resulted time slack can be exploited for energy savings through voltage reduction. The advantages of the
proposed approach are guaranteed message arrival probability and guaranteed worst case application response time. 相似文献
85.
The method of preirradiation grafting of acrylic acid and methacrylic acid onto polyethylene films was studied. The trapped radicals and hydroperoxides or diperoxides appeared to be able to induce graft polymerization. Mohr's salt was added to depress homopolymerization. The influences of crystallinity, dosage, and storage period on the grafting behavior were investigated from the viewpoint of practical application. At elevated temperature, the degree of grafting increased rapidly with reaction time initially, and then leveled off to the value of final percent grafting. Dosage and storage periods had greater extent of influence on the final percent grafting of LDPE than on that of HDPE. Electrical properties, transport properties, and mechanical properties were measured to compare the differences between acrylic-acid-and methacrylic-acid-grafted copolymer films. It was found that the properties of methacrylic-acid-grafted copolymer film was superior to those of acrylic-acid-grafted copolymer film, especially in electrical conductivity. The KOH diffusion test confirmed that grafting occurred not only on the surface but also in the interior of the polymer matrix, and the grafting is believed to proceed from the surface to the interior of the matrix. 相似文献
86.
A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25°C and 325°C
was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal
cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6·10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction
behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements. 相似文献
87.
Yung Ting Liang-Chiang Chen Chun-Chung Li Jeng-Lin Huang 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(4):847-853
A new type of piezoelectric linear motor incorporating a traveling wave has been developed. The linear motor is comprised of a stator and a carriage. The stator design, which consists of a meander-line structure and gear teeth mounted on the meander-line structure, is the focus of this article. The meander-line structure is constructed with bimorph actuators arranged in a line. These actuators are driven by two phased sets of alternating current (ac) in order to generate a traveling wave. The traveling wave is transferred to the gear teeth, by which the carriage is driven. Modeling of the stator is derived by use of a strain energy method. The performance of various materials is evaluated by analytical and experimental methods. The analytical and the experimental results are quite approximate. Modal analysis is investigated using ANSYS. Appropriate modes associated with ultrasonic levels of resonant frequency are selected to obtain desired motion and to enhance the output performance. Surface speed for various applied input voltage are studied and indicate a nearly linear relationship. The stator in combination with the carriage makes up the linear motor. 相似文献
88.
An optimum power metal-oxide-semiconductor field effect transistor (MOSFET) width technique is proposed for enhancing the efficiency characteristics of switching DC-DC converters. By implementing a one-cycle buck DC-DC converter, it is demonstrated that the dynamic power MOSFET width controlling technique has a much improved power reduction whether the load current is light or heavy. The maximum efficiency of the buck converter is ~92% with a 3% efficiency improvement for the heavy load condition. The efficiency is further improved by ~16% for the light load condition as a result of the power reduction from the large power MOSFET transistors. Also proposed is a new error-correction loop circuit to enable a better load regulation than that of previous designs. Compared with the adaptive gate driver voltage technique, the optimum power MOSFET width can achieve a significant improvement in power saving. It is also superior to the low-voltage-swing MOSFET gate drive technique for switching DC-DC converters 相似文献
89.
Nicolas Clauvelin Basile Audoly Sébastien Neukirch 《Scientific Modeling and Simulation》2007,14(1):95-101
The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. 相似文献
90.