全文获取类型
收费全文 | 1862篇 |
免费 | 50篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 136篇 |
综合类 | 3篇 |
化学工业 | 365篇 |
金属工艺 | 25篇 |
机械仪表 | 29篇 |
建筑科学 | 43篇 |
矿业工程 | 3篇 |
能源动力 | 62篇 |
轻工业 | 143篇 |
水利工程 | 27篇 |
无线电 | 219篇 |
一般工业技术 | 337篇 |
冶金工业 | 300篇 |
原子能技术 | 67篇 |
自动化技术 | 161篇 |
出版年
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 9篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 9篇 |
2016年 | 28篇 |
2015年 | 23篇 |
2014年 | 31篇 |
2013年 | 68篇 |
2012年 | 55篇 |
2011年 | 85篇 |
2010年 | 73篇 |
2009年 | 68篇 |
2008年 | 76篇 |
2007年 | 71篇 |
2006年 | 67篇 |
2005年 | 66篇 |
2004年 | 70篇 |
2003年 | 57篇 |
2002年 | 53篇 |
2001年 | 50篇 |
2000年 | 41篇 |
1999年 | 44篇 |
1998年 | 122篇 |
1997年 | 82篇 |
1996年 | 66篇 |
1995年 | 43篇 |
1994年 | 33篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 33篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 26篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 16篇 |
1975年 | 17篇 |
1973年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有1920条查询结果,搜索用时 15 毫秒
31.
Almost all polymer processing operations involve moving and shaping the polymer as a melt and then cooling it, usually quite rapidly, to a solid state. In order to develop models for such processes we have begun systematic studies in non-isothermal rheology; here we interpret the results in the context of melt spinning. Theoretical predictions of stress vs distance from the spinneret were calculated from generalized (non-isothermal) viscoelastic theory and compared with Dees' melt spinning data on high density polyethylene. Despite certain experimental and theoretical difficulties, the agreement is good. Surprisingly, an additional theoretical curve, based on a simple Trouton viscosity, also gave a reasonable approximation over much of the distance, despite the transient nature of the flow. To understand this phenomenon further, a more tractable theoretical problem was studied in detail; the problem, of constant elongational flow (? = constant) in the presence of a constant rate of temperature change (dT/dt = constant). The results depend on two dimensionless groupings; the first is the usual product of a relaxation time and ?; the second involves the ratio of normalized dT/dt to ?. When the second group is large, a quasi-viscous state exists. The melt spinning data for the HDPE may be near this state. 相似文献
32.
33.
Summary Spontaneous copolymerizations of cyclic acyl phosphonite (SPO) and phosphite (SPI) with an electron-deficient vinyl monomer
such as methyl acrylate (MA), methyl vinyl ketone (MVK), and acrolein (AL), gave the corresponding alternating copolymers.
These copolymerizations took place without added initiator and proceeded through zwitterion intermediates. Copolymer structures
1a, 1b, 2 and 3 have been established, all of which were derived in a regiospecific manner of ambident anions. The scheme of the copolymerizations
is presented. 相似文献
34.
Summary The ring-opening polymerization of 2-phenyl-1,3,-6,2-trioxaphosphocane (4), an eight-membered cyclic phosphonite, has been investigated. Cationic initiators of PhCH2-Cl and MeOTf gave polymers, whereas anionic and radical initiators did not yield polymer. The structure of polymer was examined by IR, 1H, 31P, and 31C NMR spectroscopy of polymers and elemental analysis as well as the alkaline hydrolysis products. The polymer consisted of two different units, i.e., the major part is the normal phosphinate structure 5 and the minor part is the isomerized unit 6 in 7% with PhCH2Cl initiation and in 34% with MeOTf initiator. The difference in nature of propagating species from these two initiators are discussed in connection with their reactivities.On leave from the Institute of Chemistry, Academia Sinica, Beijing, China 相似文献
35.
Summary The ring-opening polymerization of deoxophostone 5, a five-membered cyclic phosphinite, has been studied. Some cationic initiators gave polymer whereas anionic and radical initiators as well as metal chloride (Lewis acid) catalysts did not yield polymer. The polymer consisted of a phosphine oxide repeating unit 6. The polymerization proceeded via the Arbuzov-type reaction. The reduction of polymer 6 with a HSiCl3/Et3N system gave polyphosphine 7. 相似文献
36.
Copoly(amide-ethers) containing two types of tertiary amine units were made as antistatic modifiers for poly(ethylene terephthalate) (PET) fibers. The filaments of the copolymers were melt-spun and reacted with three alkylating agents in order to quaternize the tertiary amine into a sulfo-betaine, a carbobetaine, and an ammonium ion. The apparent electric resistivity of the filaments was greatly reduced by this reaction, being in the range of 106 to 108 Ω/cm. However, because these quaternized copolymers incurred decomposition during blend spinning with PET, a blend PET fiber containing one type of copoly(amide-ether) was melt-spun and subjected to quaternization of the amino groups as well as to surface crosslinking with various alkylating and epoxy agents. The quaternized blend fibers obtained showed improved antistatic properties compared with the original blend fiber. Particularly, the fibers crosslinked with epoxy compounds were found to have the best antistatic properties that had ever been attained with this type of modification. The antistatic properties were retained even after dyeing, because both hydrophilic and ionic groups had been effectively immobilized on the surface. Since this quaternization and crosslinking could be conducted on-line with spinning and drawing within a short reaction time, this modification technique is called “spin-finishing method”, which should be superior to the conventional methods in terms of cost performance and productivity. 相似文献
37.
Summary A binary system of a palladium complex as catalyst and zinc alkoxide as initiator conducted a novel ring-opening polymerization of cyclic carbonate, i. e., 5,5-dimethyl-4-ethenyl-1,3-dioxan-2-one. The polymerization proceeded along with releasing carbon dioxide to produce the corresponding polyether. The -allylpalladium complex generated from the monomer with the catalyst is the key intermediate for this new polymerization. The propagating end is zinc alkoxide, which nucleophilically attacks the monomer activated as the -allylpalladium complex in the propagation. 相似文献
38.
Summary The synthesis of poly(-thiophenediyl)benzylidene (PTB) with high molecular weight is described. Number-average degrees of polymerization reached about 74. The characterizations of the polymer was investigated by 1H-NMR, 13C-NMR, IR, and UV-VIS spectra. The polymer with well-defined structure and high molecular weight was obtained by polymerization at low temperature and in polar solvent. This polymer was thermally stable and a thermal decomposition took place at 391°C under nitrogen and at 370°C under air. The glass transformation temperature was 117°C and this PTB was nonfusible. 相似文献
39.
Takeo Hattori Atsushi Shigemori Jun-Ichi Mohri Masahiro Yoshimura Shigeyuki Somiya 《Journal of the American Ceramic Society》1982,65(9):c142-c142
Powder compacts of synthetic mica (fluorphlogopite) encapsulated in a boro–silicate glass tube were isostatically hot–pressed in a Roy–Tuttle–type pressure vessel. Synthetic mica was sintered to a density of 2.60 g/cm3 (91.2% of theoretical density) without additives under 98 MPa of water at 800°C for 45 min. 相似文献
40.
The electron-microscopic visualization of acrylic rubber dispersed in a heterogeneous structural resin composition consisting of a rubber-modified two-phase plastic comprising essentially a butyl acrylate rubber phase and an acrylonitrile–styrene copolymer phase, respectively, has been accomplished. This procedure consists of the following: The molded resin specimen is treated with hydrazine hydrate solution to produce the acrylic acid hydrazides. Allow the treated specimen to soak in osmium tetroxide solution. The acrylic rubber may be indirectly fixed and stained. Some micrographs of ultrathin sections of two or three resin compositions, cut by an ultramicrotome, are presented. 相似文献