全文获取类型
收费全文 | 193416篇 |
免费 | 24849篇 |
国内免费 | 24169篇 |
专业分类
电工技术 | 19409篇 |
技术理论 | 8篇 |
综合类 | 13608篇 |
化学工业 | 39122篇 |
金属工艺 | 7564篇 |
机械仪表 | 12268篇 |
建筑科学 | 8593篇 |
矿业工程 | 2262篇 |
能源动力 | 5980篇 |
轻工业 | 14469篇 |
水利工程 | 2458篇 |
石油天然气 | 4187篇 |
武器工业 | 1962篇 |
无线电 | 31062篇 |
一般工业技术 | 20644篇 |
冶金工业 | 4174篇 |
原子能技术 | 2788篇 |
自动化技术 | 51876篇 |
出版年
2024年 | 1106篇 |
2023年 | 3636篇 |
2022年 | 6513篇 |
2021年 | 7561篇 |
2020年 | 7191篇 |
2019年 | 6461篇 |
2018年 | 6035篇 |
2017年 | 8112篇 |
2016年 | 8818篇 |
2015年 | 10024篇 |
2014年 | 9862篇 |
2013年 | 12890篇 |
2012年 | 14771篇 |
2011年 | 16567篇 |
2010年 | 11810篇 |
2009年 | 11610篇 |
2008年 | 12859篇 |
2007年 | 14248篇 |
2006年 | 13617篇 |
2005年 | 11649篇 |
2004年 | 9809篇 |
2003年 | 7637篇 |
2002年 | 5819篇 |
2001年 | 4382篇 |
2000年 | 3645篇 |
1999年 | 2976篇 |
1998年 | 2471篇 |
1997年 | 1915篇 |
1996年 | 1492篇 |
1995年 | 1259篇 |
1994年 | 1089篇 |
1993年 | 851篇 |
1992年 | 699篇 |
1991年 | 556篇 |
1990年 | 476篇 |
1989年 | 342篇 |
1988年 | 267篇 |
1987年 | 169篇 |
1986年 | 160篇 |
1985年 | 228篇 |
1984年 | 191篇 |
1983年 | 142篇 |
1982年 | 183篇 |
1981年 | 91篇 |
1980年 | 89篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1959年 | 18篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
2-[N-甲基-N-(2-吡啶基)氨基] 乙醇制备条件的优化 总被引:1,自引:0,他引:1
2-[N-甲基-N-(2-吡啶基)氨基]乙醇是合成罗格列酮(Rosighitazone)的一种中间体,罗格列酮是新型噻唑烷二酮类胰岛素增敏剂,通过两轮优化设计,实验室小试得到了较好的反应条件.为工业化生产提供了基础数据。 相似文献
993.
994.
Degree of crosslinking and mechanical properties of crosslinked poly(vinyl alcohol) beads for use in solid-phase organic synthesis 总被引:1,自引:0,他引:1
The limited swellability in polar media of the commonly used polystyrene/divinylbenzene (PS-DVB) support materials for solid-phase organic synthesis has led to the development of novel, highly swellable hydrophilic gels designed for use in aqueous or polar media. Poly(vinyl alcohol) beads crosslinked with epichlorohydrin (PVA-EP) were prepared by a two-step inverse-suspension polymerization method. While it is known that the morphology of the resulting beads can be controlled by the ratio of EP versus PVA as well as by the pre-crosslinking time, the actual degree of crosslinking of the beads and their mechanical properties remain unknown. It is therefore the purpose of this study to evaluate the actual degree of crosslinking of beads prepared with different quantities of crosslinker in the feed by spectroscopic (Raman, nuclear magnetic resonance) and chemical (functional group loading) methods. The mechanical properties of these swollen PVA-EP beads will be evaluated by single-bead unconfined compression in solvents such as water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF) and compared to model PS-DVB beads commonly used for solid phase synthesis. 相似文献
995.
报道了以磷钨钼杂多酸掺杂聚苯胺为催化剂,通过丁醛和乙二醇反应合成了丁醛乙二醇缩醛。系统考察了醛醇物质的量比、催化剂用量以及反应时间诸因素对产品收率的影响。确定适宜的工艺条件为n(丁醛)∶n(乙二醇)=1∶1.5,催化剂的质量为反应物料总质量的0.8%,反应时间1.0 h。在此反应条件下,丁醛乙二醇缩醛的收率可达71.1%。 相似文献
996.
Several low‐powered gas plasmas were employed to treat a biomedical poly(ester)urethane using the treatment gases of CO2, O2, NH3, and SO2 with different treatment time (2, 5, 10, and 15 min). The changes of the physical and chemical characteristics of the biopolymer surface were studied. Surface morphology was evaluated by scanning probe microscopy, which showed increased roughness of the surface after plasma treatment. The wettability of the surface was examined by static water contact angle (SCA) measurements, which presented that there was a decrease of SCA in all plasma treatments compared with the untreated surface and that each gas plasma had an optimum treatment time accompanied by a minimum contact angle. X‐ray photoelectron spectroscopy indicated the changes of the surface functional groups. The data demonstrated that CO2 and O2 plasmas resulted in the incorporation of oxygen‐containing groups, while NH3 plasma resulted in the combination of nitrogen‐containing groups, and SO2 plasma resulted in the formation of sulfur‐containing groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1273–1282, 2006 相似文献
997.
998.
Miscibility has been investigated in blends of poly(butylene succinate) (PBSU) and poly(vinyl phenol) (PVPh) by differential scanning calorimetry in this work. PBSU is miscible with PVPh as shown by the existence of single composition dependent glass transition temperature over the entire composition range. In addition, the polymer–polymer interaction parameter, obtained from the melting depression of PBSU using the Nishi–Wang equation, is composition dependent, and its value is always negative. This indicates that PBSU/PVPh blends are thermodynamically miscible in the melt. Preliminary morphology study of PBSU/PVPh blends was also studied by optical microscopy (OM). OM experiments show the spherulites of PBSU become larger with the PVPh content, indicative of a decrease in the nucleation density, and the coarseness of PBSU spherulites increases too with increasing the PVPh content in the blends. 相似文献
999.
The thermal conductivity of a filler and the thermal conductivity of a composite made from that filler influence the heat‐transfer process during melt processing. The heat‐transfer process from the melt to the mold wall becomes an important factor in developing the skin–core morphology. These aspects were examined in this study. The thermal conductivity of polypropylene–filler composites was estimated with a standard model for various fillers such as calcium carbonate, talc, silica, wollastonite, mica, and carbon fibers. The rate of cooling under given conditions, including the melting temperature, mold wall temperature, mass of the composite, and filler content, was estimated with standard heat‐transfer equations. The time to attain the crystallization temperature for polypropylene was evaluated with a regression method with differential temperature steps. The crystallization curves were experimentally determined for the different fillers, and from them, the induction period for the onset of crystallization was estimated. These observations were correlated with the expected trends from the aforementioned formalism. The excellent fit of the curves showed that in all these cases, the thermal conductivity of the filler and composite played a dominant role in controlling the onset of the crystallization process. However, the nucleation effects became important in the later stages after the crystallization temperature was attained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2994–2999, 2003 相似文献
1000.
漆酶改善分离木素和OCC纸浆特性的研究 总被引:2,自引:0,他引:2
应用漆酶处理纤维素酶分离酶解木素和OCC(Old corrugated containers)纸浆,结果表明:木素在漆酶处理过程中会发生降解,经漆酶处理后再经加热处理会使木素发生聚合,木素降解主要发生在高分子量木素部分,而聚合作用主要发生在低分子量木素之间;木素经漆酶处理后,酚羟基的含量略有增加,这是由于在漆酶处理木素的过程中,木素不但发生酚氧自由基的离域现象,而且还有高分子量的木素发生降解产生了新的酚羟基;经不同用量的漆酶处理的OCC纸浆手抄片的湿环压指数和湿抗指数与对照样相比均有明显提高,特别是漆酶用量为24 U/g时,湿环压指数达到4.1 N.m/g,提高了41%。经不同用量的漆酶处理的OCC纸浆干环压强度和干抗张强度与对照样相比略有提高,但提高的幅度不大。 相似文献