全文获取类型
收费全文 | 4992篇 |
免费 | 87篇 |
国内免费 | 9篇 |
学科分类
工业技术 | 5088篇 |
出版年
2023年 | 22篇 |
2022年 | 47篇 |
2021年 | 75篇 |
2020年 | 26篇 |
2019年 | 53篇 |
2018年 | 51篇 |
2017年 | 32篇 |
2016年 | 55篇 |
2015年 | 58篇 |
2014年 | 68篇 |
2013年 | 170篇 |
2012年 | 136篇 |
2011年 | 193篇 |
2010年 | 154篇 |
2009年 | 146篇 |
2008年 | 165篇 |
2007年 | 152篇 |
2006年 | 158篇 |
2005年 | 115篇 |
2004年 | 116篇 |
2003年 | 140篇 |
2002年 | 101篇 |
2001年 | 123篇 |
2000年 | 99篇 |
1999年 | 159篇 |
1998年 | 551篇 |
1997年 | 365篇 |
1996年 | 258篇 |
1995年 | 148篇 |
1994年 | 142篇 |
1993年 | 137篇 |
1992年 | 76篇 |
1991年 | 64篇 |
1990年 | 67篇 |
1989年 | 62篇 |
1988年 | 59篇 |
1987年 | 37篇 |
1986年 | 53篇 |
1985年 | 45篇 |
1984年 | 47篇 |
1983年 | 31篇 |
1982年 | 43篇 |
1981年 | 33篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1978年 | 23篇 |
1977年 | 34篇 |
1976年 | 44篇 |
1975年 | 17篇 |
1973年 | 23篇 |
排序方式: 共有5088条查询结果,搜索用时 15 毫秒
991.
In the pathogenesis of Parkinson's disease and senile dementia of the Alzheimer type, free radicals might play a role. Fat-soluble vitamins are a kind of anti-oxidative substance. Therefore, fat-soluble vitamins, such as vitamin E, may be useful in treatment of Parkinson's disease and senile dementia of the Alzheimer type. However, it is still unclear whether the concentration of vitamin E in the blood or in the brain tissue, in patients with Parkinson's disease or with of the senile dementia Alzheimer type, is higher than or the same as that in normal subjects. Furthermore, although the effectiveness of vitamin E in the treatment of Parkinson's disease has been reported, the usefulness of vitamin E is still obscure. Further study will be necessary, in order to clarify the role of fat-soluble vitamins in the treatment of Parkinson's disease and senile dementia of the Alzheimer type. 相似文献
992.
993.
Algorithms for Extracting Correct Critical Points and Constructing Topological Graphs from Discrete Geographical Elevation Data 总被引:12,自引:0,他引:12
Shigeo Takahashi Tetsuya Ikeda Yoshihisa Shinagawa Tosiyasu L. Kunii Minoru Ueda 《Computer Graphics Forum》1995,14(3):181-192
Researchers in the fields of computer graphics and geographical information systems (GISs) have extensively studied the methods of extracting terrain features such as peaks, pits, passes, ridges, and ravines from discrete elevation data. The existing techniques, however, do not guarantee the topological integrity of the extracted features because of their heuristic operations, which results in spurious features. Furthermore, there have been no algorithms for constructing topological graphs such as the surface network and the Reeb graph from the extracted peaks, pits, and passes. This paper presents new algorithms for extracting features and constructing the topological graphs using the features. Our algorithms enable us to extract correct terrain features; i.e., our method extracts the critical points that satisfy the Euler formula, which represents the topological invariant of smooth surfaces. This paper also provides an algorithm that converts the surface network to the Reeb graph for representing contour changes with respect to the height. The discrete elevation data used in this paper is a set of sample points on a terrain surface. Examples are presented to show that the algorithms also appeal to our visual cognition. 相似文献
994.
Makoto Ishiguro Katsufumi Ohmuro Yukito Saitoh Yuuta Takahashi Jun Watanabe Tsutomu Arai Yoji Ito Keiji Mihayashi 《Journal of the Society for Information Display》2012,20(11):598-603
We have successfully developed a quarter‐wave retardation film (QWF) for wide viewing angle 3D liquid crystal displays (3D‐LCDs) that provides high luminance, low crosstalk, low color change, and low head‐tilt‐angle dependency. It was found that the out‐of‐plane retardation (Rth) of the QWF in the LCD needs to be close to 0 nm in order to improve the 3D display properties at an off‐axis position and that the in‐plane retardation (Re) needs to be adjusted from 120 to 130 nm to achieve low color change with head tilting. We adopted a coating process for making our QWF because of its potential for retardation control. 3D‐LCDs with this QWF whose Rth was nearly zero had high performance and allowed off‐axis other than on‐axis. 相似文献
995.
996.
997.
This paper presents a method for describing and reasoning about the behavior of VLSI circuits within the framework of Extended Temporal Logic. For a reasoning method, an “ω-graph approach” is proposed which is useful in verifying the validity of a design. Not only verification but also other reasoning about circuit properties, such as unknown signal identification, can be treated in a unified way by this ω-graph approach. This approach has been studied as a basis of an expert system for the authors’ VLSI CAD system. 相似文献
998.
Takayuki Shibata Yoichi Takahashi Takahiro Kawashima Toshio Kubota Mamoru Mita Takashi Mineta Eiji Makino 《Microsystem Technologies》2008,14(9-11):1359-1365
In order to fabricate polymer-based microstructures with feature sizes on the order of micrometers, we have been developing a microimprint technology with a fine nickel (Ni) mold instead of a conventional photolithography technique. The Ni mold was successfully fabricated by electroforming using a positive thick photoresist microstructure patterned on a silicon substrate as a replication master. The photoresist microstructure with excellent edge quality can be obtained under irradiation with single wavelength (g line) selected from a high-pressure mercury lamp. In addition, its sidewall angle in the range of 65° to 84° can be controlled precisely by varying the distance between a photomask and a photoresist surface. On the structured photoresist master, Ni was electroplated up to a thickness of about 110 μm, and then removed from the master. In this process, two-step electroplating at different current densities was carried out in order to prevent deformation of the photoresist master due to stress generated in a Ni electrodeposit. With the Ni mold, fine patterns with a width of 10 or 30 μm and a depth of 24 μm were almost completely transferred to polymetric materials (PMMA). The geometrical dimensions of the fabricated PMMA microstructures were found to be only about 10% reduction against the Ni mold. 相似文献
999.
Polyethylene reactor powders prepared under different conditions were characterized using transmission electron microscopy, 1H nuclear magnetic resonance and X-ray diffraction techniques. The molecular weight of the polyethylene reactor powders was around 1 × 105. A unique domain morphology, quite different from the usual melt- or solution-crystallized lamellar structure, was observed, independent of polymerization temperature (Tpoly). Annealing of reactor powders caused the aggregation of these crystalline domains, due to the significant molecular motion of the amorphous chains, before melting. The critical temperature was 20 °C higher than each Tpoly, and corresponded to the temperature at the active catalyst site producing the chain growth. The morphologies of powders prepared at the lower Tpoly contained smaller crystals that exhibited a constrained monoclinic form. In contrast, only usual orthorhombic crystals of larger size were found within the powder prepared at the higher Tpoly. These results suggest that the competitive processes of chain propagation and crystal growth upon polymerization may lead to unique variations of the crystalline and amorphous phases, but with similar intermediate components in the phase that connects them. 相似文献
1000.
Structural evolution in the X-ray amorphous precursors to La2 Sn2 O7 and La2 Ti2 O7 is examined using IR and Raman spectroscopy. These precursors are prepared by rapid coprecipitation from mixed aqueous solutions of the corresponding metal chlorides. Rapid coprecipitation from an SnCl2− 6 and La3+ -containing aqueous solution yields microcrystalline particles of SnO2 · n H2 O and La(OH)3 , which instantaneously interconnect to form an ultimate, complex colloid particle. The Ti(OH)2+ 2 and La3+ in the other solution system coprecipitate into a different, complex colloid (an unidentified phase), which is definitely not a mixed dispersion of single-component colloids. A comparative examination of the vibrational spectra of the coprecipitates heated to various temperatures indicates that the SnO2 and anatase phases develop in the respective precursors before crystallization of the desired double oxides. Crystallization itself can be attributed to a solid-state reaction among the various microcrystallites of each single-metal oxide in a gel particle of the precursor. 相似文献