全文获取类型
收费全文 | 3216篇 |
免费 | 48篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 45篇 |
综合类 | 9篇 |
化学工业 | 334篇 |
金属工艺 | 58篇 |
机械仪表 | 43篇 |
建筑科学 | 36篇 |
矿业工程 | 8篇 |
能源动力 | 36篇 |
轻工业 | 166篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 233篇 |
一般工业技术 | 378篇 |
冶金工业 | 1609篇 |
原子能技术 | 48篇 |
自动化技术 | 249篇 |
出版年
2023年 | 13篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 20篇 |
2016年 | 41篇 |
2015年 | 26篇 |
2014年 | 41篇 |
2013年 | 100篇 |
2012年 | 72篇 |
2011年 | 102篇 |
2010年 | 86篇 |
2009年 | 73篇 |
2008年 | 71篇 |
2007年 | 71篇 |
2006年 | 51篇 |
2005年 | 64篇 |
2004年 | 58篇 |
2003年 | 42篇 |
2002年 | 48篇 |
2001年 | 42篇 |
2000年 | 28篇 |
1999年 | 71篇 |
1998年 | 520篇 |
1997年 | 260篇 |
1996年 | 202篇 |
1995年 | 125篇 |
1994年 | 115篇 |
1993年 | 95篇 |
1992年 | 36篇 |
1991年 | 50篇 |
1990年 | 47篇 |
1989年 | 55篇 |
1988年 | 40篇 |
1987年 | 23篇 |
1986年 | 30篇 |
1985年 | 40篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1978年 | 17篇 |
1977年 | 41篇 |
1976年 | 109篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1973年 | 19篇 |
排序方式: 共有3266条查询结果,搜索用时 15 毫秒
991.
KA Metwally M Dukat CT Egan C Smith A DuPre CB Gauthier K Herrick-Davis M Teitler RA Glennon 《Canadian Metallurgical Quarterly》1998,41(25):5084-5093
Spiperone (1) is a widely used pharmacological tool that acts as a potent dopamine D2, serotonin 5-HT1A, and serotonin 5-HT2A antagonist. Although spiperone also binds at 5-HT2C receptors, it is one of the very few agents that display some (ca. 1000-fold) binding selectivity for 5-HT2A versus 5-HT2C receptors and, hence, might serve as a useful template for the development of novel 5-HT2A antagonists if the impact of its various substituent groups on binding was known. In the present investigation we focused on the 1, 3,8-triazaspiro[4.5]decanone portion of spiperone and found that replacement of the N1-phenyl group with a methyl group only slightly decreased affinity for cloned rat 5-HT2A receptors. However, N1-methyl derivatives displayed significantly reduced affinity for 5-HT1A, 5-HT2C, and dopamine D2 receptors. Several representative examples were shown to behave as 5-HT2 antagonists. As such, N1-alkyl analogues of spiperone may afford entry into a novel series of 5-HT2A-selective antagonists. 相似文献
992.
993.
P. Kumar D. Gospodaric P. Bauer 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2007,11(10):923-941
The process of mutation has been studied extensively in the field of biology and it has been shown that it is one of the major
factors that aid the process of evolution. Inspired by this a novel genetic algorithm (GA) is presented here. Various mutation
operators such as small mutation, gene mutation and chromosome mutation have been applied in this genetic algorithm. In order to facilitate the implementation of the above-mentioned mutation operators
a modified way of representing the variables has been presented. It resembles the way genetic information is coded in living
beings. Different mutation operators pose a challenge as regards the determination of the optimal rate of mutation. This problem
is overcome by using adaptive mutation operators. The main purpose behind this approach was to improve the efficiency of GAs
and to find widely distributed Pareto-optimal solutions. This algorithm was tested on some benchmark test functions and compared
with other GAs. It was observed that the introduction of these mutations do improve the genetic algorithms in terms of convergence
and the quality of the solutions. 相似文献
994.
By applying lock-in thermography imaging, light-beam-induced current imaging, electron-beam-induced current imaging at different
stages of sample preparation, and infrared light microscopy in transmission mode, the physical nature of the dominant material-induced
shunts in multicrystalline solar cells made from p-type silicon material has been investigated. It turns out that these shunts are due to silicon carbide (SiC) filaments, which
grow preferentially in grain boundaries and cross the whole cell. These filaments are highly n-type doped, like the emitter layer on the surface of the cells. They are electrically connected both with the emitter and
with the back contact, thereby producing internal shunts in the solar cell.
The text was submitted by the authors in English. 相似文献
995.
TiO2 nanotubes: Self-organized electrochemical formation, properties and applications 总被引:2,自引:0,他引:2
J.M. Macak H. Tsuchiya A. Ghicov K. Yasuda R. Hahn S. Bauer P. Schmuki 《Current Opinion in Solid State & Materials Science》2007,11(1-2):3-18
The present paper gives an overview and review on self-organized TiO2 nanotube layers and other transition metal oxide tubular structures grown by controlled anodic oxidation of a metal substrate. We describe mechanistic aspects of the tube growth and discuss the electrochemical conditions that need to be fulfilled in order to synthesize these layers. Key properties of these highly ordered, high aspect ratio tubular layers are discussed. In the past few years, a wide range of functional applications of the layers have been explored ranging from photocatalysis, solar energy conversion, electrochromic effects over using the material as a template or catalyst support to applications in the biomedical field. A comprehensive view on state of the art is provided. 相似文献
996.
A. Bauer J. Bentner M. Aprili M. Della Rocca C. Strunk 《Journal of Low Temperature Physics》2007,147(3-4):431-439
Superconducting loops containing a π-junction are predicted to show a spontaneous magnetic moment in zero external magnetic
field. In order to confirm this longstanding prediction experimentally, we performed magnetization measurements on individual
mesoscopic superconducting niobium loops with a ferromagnetic (PdNi) π-junction. The loops are prepared on top of the active
area of a micro Hall-sensor based on high mobility GaAs/AlGaAs heterostructures. We observe switching of the loop between
different magnetization states at very low-magnetic fields, which is asymmetric for positive and negative sweep direction.
This is evidence for a spontaneous current induced by the intrinsic phase shift of the π-junction. In addition, the presence
of the spontaneous current at zero applied field is directly revealed by an increase of the magnetic moment with decreasing
temperature, which results in a half integer flux quantization in the loop at low temperatures.
This work is dedicated to H. von L?hneysen on the occasion of his 60th birthday. 相似文献
997.
BACKGROUND: Clinical improvement in photodamaged skin after carbon dioxide (CO2) laser resurfacing is thought to result in part from thermal collagen shrinkage. The presence of such collagen has not been unequivocally demonstrated. To identify and characterize the morphological features of collagen after CO2 laser exposure, we irradiated ex vivo human facial skin and bovine calcaneus tendon with microsecond domain pulsed CO2 laser energy and examined specimens for histopathological and ultrastructural changes in collagen. OBSERVATIONS: In dermis and tendon, 3 zones of collagen structure were apparent on electron microscopy. The first, most superficial zone demonstrated loss of collagen structure. The second zone consisted of admixed normal collagen fibers and thickened collagen fibers. Zone 3 consisted of normal-appearing collagen fibers. CONCLUSIONS: Ultrastructural examination of irradiated collagen revealed distinct morphological zones of denatured collagen fibers. Partially denatured fibers had an increased diameter consistent with lineal shrinkage. Zonal distinction was undetectable by light microscopy. Ultrastructurally, the zones of denatured collagen located above the normal fibers correlated with the zone of altered material seen on light microscopy. These findings suggest that collagen fiber shrinkage does occur after pulsed CO2 laser irradiation and that this phenomenon contributed, at least in part, to the immediate tissue contraction observed clinically. 相似文献
998.
999.
The indications for conservative and surgical management of fractures of the thoracolumbar spine are reviewed, based upon the morphology of the lesions, which is assessed by meticulous analysis of radiographs, CT scan and in some cases MRI. The author advocates using the AO classification, which considers several subtypes of fractures: compression fractures, distraction fractures and fractures with multidirectional displacement. The indication for treatment is based upon morphological analysis of the lesions, while other factors such as the general condition of the patient or the locally available surgical environment must also be taken into consideration. Up to 50% of thoracolumbar fractures can benefit from surgical management, with posterior or anterior stabilisation, the latter performed through thorascoscopy in selected cases. 相似文献
1000.
C. Dreyer Dr. rer. nat. J. Schneider Dr. rer. nat. K. Göcks B. Beuster M. Bauer Prof. Dr. sc. nat. N. Keil H. Yao Prof. Dr. C. Zawadzki O. Radmer 《e & i Elektrotechnik und Informationstechnik》2003,120(6):178-185
Within this paper the development of special polymers for their use in integrated optics is shown exemplarily for selected optical devices (thermooptical switches and arrayed waveguide gratings). Emphasis is put on long-range data transfer in a wavelength region around 1,550 µm. Fluorinated polyacrylates, polycyanurates and triazine-containing reactive polymers were investigated. 相似文献