全文获取类型
收费全文 | 6782篇 |
免费 | 113篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 314篇 |
综合类 | 5篇 |
化学工业 | 1198篇 |
金属工艺 | 203篇 |
机械仪表 | 148篇 |
建筑科学 | 105篇 |
矿业工程 | 2篇 |
能源动力 | 176篇 |
轻工业 | 465篇 |
水利工程 | 33篇 |
石油天然气 | 7篇 |
无线电 | 642篇 |
一般工业技术 | 1189篇 |
冶金工业 | 1867篇 |
原子能技术 | 131篇 |
自动化技术 | 422篇 |
出版年
2023年 | 29篇 |
2022年 | 61篇 |
2021年 | 111篇 |
2020年 | 53篇 |
2019年 | 52篇 |
2018年 | 77篇 |
2017年 | 68篇 |
2016年 | 83篇 |
2015年 | 80篇 |
2014年 | 101篇 |
2013年 | 220篇 |
2012年 | 200篇 |
2011年 | 273篇 |
2010年 | 192篇 |
2009年 | 205篇 |
2008年 | 221篇 |
2007年 | 226篇 |
2006年 | 225篇 |
2005年 | 200篇 |
2004年 | 182篇 |
2003年 | 172篇 |
2002年 | 179篇 |
2001年 | 165篇 |
2000年 | 139篇 |
1999年 | 173篇 |
1998年 | 690篇 |
1997年 | 426篇 |
1996年 | 311篇 |
1995年 | 217篇 |
1994年 | 213篇 |
1993年 | 169篇 |
1992年 | 91篇 |
1991年 | 99篇 |
1990年 | 91篇 |
1989年 | 81篇 |
1988年 | 74篇 |
1987年 | 61篇 |
1986年 | 70篇 |
1985年 | 85篇 |
1984年 | 54篇 |
1983年 | 63篇 |
1982年 | 43篇 |
1981年 | 56篇 |
1980年 | 56篇 |
1979年 | 31篇 |
1978年 | 26篇 |
1977年 | 57篇 |
1976年 | 58篇 |
1975年 | 31篇 |
1973年 | 24篇 |
排序方式: 共有6907条查询结果,搜索用时 15 毫秒
101.
The configurational sequences of 1,2-unit in a series of hydrogenated syndiotactic 1,2-polybutadienes were determined in relation to the sequence distribution of 1,2- and 1,4-units on the basis of the 13C-n.m.r. signal assignment of the methyl carbons. The observed triad distributions of 1,2- and 1,4-units and configurational distributions of the 1,2-unit are in good agreement with the calculated distributions from transition probabilities. The number average sequence lengths of the 1,2-unit and the 1,2-unit in the racemic addition are 5.7 to 8.0 and 4.1 to 5.4, respectively. From the extrapolation of the plot of the number average sequence length against the crystallinity of the starting 1,2-polybutadienes, the minimum sequence length for crystallization is estimated to be 3.7 for the 1,2-unit in the racemic addition. 相似文献
102.
Pressure effects on the low temperature state of the α-(BEDT-TTF)2MHg(SCN)4 organic conductor family
X. Chen J. S. Brooks S. Valfells G. J. Athas S. J. Klepper M. Tokumoto N. Kinoshita H. Anzai Y. Tanaka 《Synthetic Metals》1995,70(1-3)
Systematic magnetotransport measurements as a function of hydrostatic pressure have been made on four members of the α-(BEDT-TTF)2MHg(SCN)4 organic conductor family (M = K, Tl, Rb, NH4). Applied pressure above about 6 Kbar removes the density wave state for M = K, Tl, and Rb. For M = NH4 the superconducting state is removed with pressure as dTc/dP = − 0.25 K/Kbar. In all cases the Shubnikov de Haas oscillation frequency increases with pressure, including the β orbit (which involves the entire Brillouin zone), and new orbits involving very small fractions of the Fermi surface are formed. 相似文献
103.
We analyzed the copper corrosion products that formed during a month in summer and a month in winter at three sites in Tokyo using several analytical techniques. The X-ray diffraction patterns revealed that cuprite Cu2O and posnjakite Cu4SO4(OH)6·H2O formed on copper exposed in summer. By contrast, only cuprite was found in winter exposed copper. The X-ray fluorescence results indicated that the amounts of sulfur and chlorine on the copper plates exposed in summer were much greater than those in winter. This could be explained by the change in particulate sulfate and sea salt concentrations. Depth profiling analysis by Auger electron spectroscopy revealed that the oxide layer formed in summer was thicker than that in winter. This difference in oxide layer thickness could have been due to the differences in temperature, relative humidity, and the amount of sulfur and chlorine on the copper plate. 相似文献
104.
Hiroyuki Sato Hernán Aguirre Kiyoshi Tanaka 《Annals of Mathematics and Artificial Intelligence》2013,68(4):197-224
In this work, we analyze variable space diversity of Pareto optimal solutions (POS) and study the effectiveness of crossover and mutation operators in evolutionary many-objective optimization. First we examine the diversity of variables in the true POS on many-objective 0/1 knapsack problems with up to 20 items (bits), showing that variables in POS become noticeably diverse as we increase the number of objectives. We also verify the effectiveness of conventional two-point and uniform crossovers, Local Recombination that selects mating parents based on proximity in objective space, and two-point and uniform crossover operators which Controls the maximum number of Crossed Genes (CCG). We use NSGA-II, SPEA2, IBEA ??+? and MSOPS, which adopt different selection methods, and many-objective 0/1 knapsack problems with $n=\{100,250,500,750,\mbox{1,000}\}$ items (bits) and m?=?{2,4,6,8,10} objectives to verify the search performance of each crossover operator. Simulation results reveal that Local Recombination and CCG operators significantly improve search performance especially for NSGA-II and MSOPS, which have high diversity of genes in the population. Also, results show that CCG operators achieve higher search performance than Local Recombination for m?≥?4 objectives and that their effectiveness becomes larger as the number of objectives m increases. In addition, the contribution of CCG and mutation operators for the solutions search is analyzed and discussed. 相似文献
105.
Daiji Noda Makoto Tanaka Kazuma Shimada Wataru Yashiro Atsushi Momose Tadashi Hattori 《Microsystem Technologies》2008,14(9-11):1311-1315
X-ray imaging is a very important technology in the fields of medical, biological, inspection, material science, etc. However, it is not enough to get the clear X-ray imaging with low absorbance. We have produced a diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. In this X-ray Talbot interferometer, diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we succeeded to fabricate a high aspect ratio diffraction grating with a pitch of 8 μm and small area using a deep X-ray lithography technique. We discuss that the diffraction gratings having a narrow pitch and an large effective area to obtain imaging size of practical use in medical application. If the pitch of diffraction gratings were narrow, it is expected high resolution imaging for X-ray Talbot interferometer. We succeeded and fabricated the diffraction grating with pitch of 5.3 μm, Au height of 28 μm and an effective area of 60 × 60 mm2. 相似文献
106.
Yasunobu Hitaka Yoshito Tanaka Yutaka Tanaka Ken Ichiryu 《Artificial Life and Robotics》2009,14(4):494-497
A tripod parallel mechanism consists of three links of fixed length and a rigid platform, and these are connected by revolute
joints. The platform can achieve sixdegrees-of-freedom (6-DOF) motion by the coordinated movement of the bottom ends of the
three links on a horizontal plane. This mechanism has advantages over the more common six extendible parallel manipulators.
It has a much larger work space and a simple structure. In this article, we show that the vector analysis for this tripod
parallel mechanism and the derivation of the positions of the three bottom ends of the links in an arbitrary attitude of platform
can be found by inverse kinematics and the conditions of geometrical constraint. Then, by a numerical simulation, the trajectories
of the bottom ends of the three links are shown. 相似文献
107.
A data-driven design method for a cascade control system is proposed. The cascade control system consists of inner and outer loops, where the control interval of the outer loop is an integer multiple of the inner loop; hence, the system is a dual-rate system. In the proposed method, controllers in the inner and outer loops are designed based on one-shot data. In such a dual-rate cascade system, since the controllers are designed using different data-rate signals, the lifting technique is applied to align the dual-rate data. To show its effectiveness, the proposed method is compared with a conventional single-rate cascade control method, and numerical simulations and experiments are presented to examine servo and regulation performance. 相似文献
108.
Optical Properties of Self‐Assembled Cellulose Nanocrystals Films Suspended at Planar–Symmetrical Interfaces 下载免费PDF全文
Blaise L. Tardy Mariko Ago Jiaqi Guo Maryam Borghei Tero Kämäräinen Orlando J. Rojas 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(47)
Hierarchically structured materials comprising rod‐like, chiral, nanoparticles are commonly encountered in nature as they can form assemblies with exceptional optical and mechanical characteristics. These include cellulose nanocrystals (CNCs), which have a large potential for the fabrication of bioinspired materials mimicking those advanced properties. Fine‐tuning the optomechanical properties of assemblies obtained from CNCs hinges on the transformations from suspensions of liquid crystals to long‐range order in the dry state. So far, associated transitions have been studied using trivial interfaces such as planar substrates. Such transitions are explored as they evolve onto meshed supports. The meshed substrate offers a complex topology, as is encountered in nature, for the formation of CNCs films. The CNCs self‐assembly occurs under confinement and support of the framework bounding the mesh openings. This leads to coexisting suspended and supported nanoparticle layers exhibiting nematic and/or chiral nematic order. Optical microscopy combined with crossed polarizers indicate that the formation of the suspended films occurs via intermediate gelation or kinetic arrest of CNCs across the mesh's open areas. The formation of self‐standing, ultrathin films of CNCs with tunable optical properties, such as selective reflections in the visible range (structural color), is demonstrated by using the presented simple and scalable approach. 相似文献
109.
110.