全文获取类型
收费全文 | 72549篇 |
免费 | 17034篇 |
国内免费 | 1231篇 |
学科分类
工业技术 | 90814篇 |
出版年
2024年 | 91篇 |
2023年 | 463篇 |
2022年 | 687篇 |
2021年 | 1332篇 |
2020年 | 2263篇 |
2019年 | 3851篇 |
2018年 | 3897篇 |
2017年 | 4404篇 |
2016年 | 4712篇 |
2015年 | 5046篇 |
2014年 | 5324篇 |
2013年 | 6893篇 |
2012年 | 4718篇 |
2011年 | 4609篇 |
2010年 | 4514篇 |
2009年 | 4391篇 |
2008年 | 3885篇 |
2007年 | 3715篇 |
2006年 | 3505篇 |
2005年 | 3087篇 |
2004年 | 2558篇 |
2003年 | 2361篇 |
2002年 | 2278篇 |
2001年 | 1977篇 |
2000年 | 2022篇 |
1999年 | 1472篇 |
1998年 | 1132篇 |
1997年 | 900篇 |
1996年 | 870篇 |
1995年 | 711篇 |
1994年 | 585篇 |
1993年 | 540篇 |
1992年 | 377篇 |
1991年 | 283篇 |
1990年 | 258篇 |
1989年 | 208篇 |
1988年 | 154篇 |
1987年 | 127篇 |
1986年 | 106篇 |
1985年 | 83篇 |
1984年 | 72篇 |
1983年 | 48篇 |
1982年 | 42篇 |
1981年 | 37篇 |
1980年 | 41篇 |
1979年 | 22篇 |
1977年 | 26篇 |
1976年 | 21篇 |
1973年 | 18篇 |
1970年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
High‐performance shape‐memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft‐segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape‐recovery ratios higher than 80%. In dynamic mechanical testing, the glass‐transition behavior clearly depended on the soft‐segment arrangement: random copolymers had only one glass‐transition peak, whereas block copolymers showed two separate glass‐transition peaks. Overall, the control of the soft‐segment arrangement plays a vital role in the development of high‐performance shape‐memory polyurethane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2410–2415, 2004 相似文献
992.
Kwang‐Pill Lee Anantha Iyengar Gopalan See‐Hee Lee Ali Md Showkat Young Chang Nho 《应用聚合物科学杂志》2006,102(4):3912-3918
Conducting polydiphenylamine was used to encapsulate silica nanoparticles through the oxidative polymerization of diphenylamine in the presence of ultrasonic irradiation. The polymerization was performed in the presence of sodium lauryl sulfate as a surfactant. Experiments performed in the absence of ultrasound clearly demonstrated that the application of ultrasonication played multiple roles in the preparation of a composite of polydiphenylamine with silica nanoparticles. Ultrasonication dispersed the silica nanoparticles, converted sodium lauryl sulfate to lauryl alcohol, and augmented the dispersion of the silica‐nanoparticle/polydiphenylamine composite in an organic medium. Silica‐nanoparticle/polydiphenylamine composites were also prepared in the absence of ultrasound and/or sodium lauryl sulfate. The silica‐nanoparticle/polydiphenylamine composites were characterized with Fourier trans form infrared spectroscopy, ultraviolet–visible/near‐infrared spectroscopy, and thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3912–3918, 2006 相似文献
993.
通过结构设计和负荷计算,研制出适合于实验室使用的以钼丝为电热体,电熔镁砂或镁铝尖晶石为沪芯材料,H2-N2混合气体为保护气氛和最高使用温度达1950℃的内挂式氢气钼丝炉。 相似文献
994.
Shen TJ; Ho NT; Zou M; Sun DP; Cottam PF; Simplaceanu V; Tam MF; Bell DA Jr; Ho C 《Protein engineering, design & selection : PEDS》1997,10(9):1085-1097
A hemoglobin expression system in Escherichia coli is described. In order
to produce authentic human hemoglobin, we need to co-express both
methionine aminopeptidase and globin genes under the control of a strong
promoter. We have constructed three plasmids, pHE2, pHE4 and pHE7, for the
expression of human normal adult hemoglobin and a plasmid, pHE9, for the
expression of human fetal hemoglobin, in high yields. The globin genes can
be derived from either synthetic genes or human globin cDNAs. The extra
amino-terminal methionine residues of the expressed globins can be removed
by the co-expressed methionine aminopeptidase. The heme is inserted
correctly into the expressed alpha- globin from our expression plasmids. A
fraction (approximately 25%) of the heme is not inserted correctly into the
expressed beta- or gamma- globin. However, the incorrectly inserted hemes
can be converted into the correct conformation by carrying out a simple
oxidation-reduction process on the purified hemoglobin molecule. We have
investigated the functional properties of the expressed hemoglobins by
measuring their oxygen-binding properties and their structural features by
obtaining their 1H-NMR spectra. Our results show that authentic human
normal adult and fetal hemoglobins can be produced from our expression
plasmids in E. coli and in high yields. Our expression system allows us to
design and to produce any recombinant hemoglobins needed for our research
on the structure-function relationship in hemoglobin.
相似文献
995.
本文在高温烧成的高铝强化瓷坯体配方的基础上,加入烧滑石和骨粉(磷酸钙),得到了可以中温烧成的强化瓷,并对此进行了分析讨论。 相似文献
996.
Structured dispersion particles suitable for pressure sensitive adhesives (PSA) were synthesized via swelling polymerization technique (EP 359562). Particles consisting of poly(n‐butyl acrylate) copolymerized with different types of carboxylic acids were used as seeds. The final particles were synthesized by swelling polymerization process, using 6 wt % styrene or 6 wt % methyl methacylate. The resulting particle morphology was analyzed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). From previous works (Coll Surf A 2001, 183–185, 725–737; J Appl Polym Sci 2004, 91, 2610–2623) where two‐step emulsion polymerization was used on similar particles, it is expected that the particle morphology is affected by the polarity of the monomer used for swelling polymerization because of the phase compatibility (thermodynamic parameter). In this work, the seed particles used were always of a glass transition temperature (Tg) below polymerization temperature. The diffusion of the growing polymer chains from the swelling polymerization is therefore mainly affected by their own Tg and the influence of the carboxy groups on the chain length of the entering radicals (kinetic parameter). The different morphologies of the single particles are discussed qualitatively. The effects of reaction parameters are compared with the results given in the previous work. The structure of the corresponding dispersion films was characterized using AFM. Correlations to macroscopic properties such as the cohesive strength and peel adhesion to different substrates are discussed. The results are also compared with the application properties of the corresponding unmodified particles, statistical copolymers, and to blends with small sized PMMA or PS particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1444–1455, 2006 相似文献
997.
Ranjit Prasad Vanja Pasanovic‐Zujo Rahul K. Gupta Ferenc Cser Sati N. Bhattacharya 《Polymer Engineering and Science》2004,44(7):1220-1230
Shear and extensional rheological measurements were conducted in conjunction with laser light scattering (LLS) on ethylene‐vinyl acetate copolymer (EVA) nanocomposites. The materials were prepared by melt‐mixing EVA and commercially acquired layered silicates. Wide Angle X‐Ray Scattering (WAXS) was used to ascertain the degree of layer swelling. This could be attributed to the intercalation of polymer chains into the interlayer of the silicates. The nanocomposites prepared were determined to be predominantly intercalated in nature. In shear rheological tests, the nanocomposites exhibited an increase in viscoelastic properties compared to the pure EVA. The extent of this property enhancement was not as pronounced as had been reported in many instances with respect to other polymer nanocomposites. This could be attributed to the absence of a network structure normally observed in an exfoliated system. The extensional rheological tests showed an increase in extensional flow properties. This was confirmed by the LLS, which indicated that the filled systems had higher deformability than the unfilled one. Polym. Eng. Sci. 44:1220–1230, 2004. © 2004 Society of Plastics Engineers. 相似文献
998.
The effects of poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), sodium polyacrylate (NaPA), poly(ethylene glycol) (PEG), pectin (P), and carboxymethyl cellulose (CMC) on the corrosion of cadmium in a 0.5M hydrochloric acid (HCl) solution were studied with both electrochemical impedance spectroscopy and Tafel plot techniques. Measurements were carried out at cathodic, open‐circuit, and anodic potentials. All the investigated polymers had inhibitory effects on both the cathodic (except for NaPA, P, and CMC) and anodic processes, with a predominant anodic inhibiting action. However, NaPA, P, and CMC exhibited a slight cathodic inhibiting action only at higher polymer concentrations. This behavior may be attributed to the very weak adsorbability of the polymers on the cathodic sites. Because PVA and PEG had hydroxy groups, there could be bridging between the polymer and the surface, resulting in an inhibiting effect in the HCl solution. However, PVA had much greater adsorbability on the surface than PEG at the anodic potential. The adsorption of most of the polymers obeyed a Temkin adsorption isotherm, and this indicated indicating that the main process of inhibition was adsorption. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 866–871, 2003 相似文献
999.
1000.