全文获取类型
收费全文 | 87558篇 |
免费 | 6948篇 |
国内免费 | 3649篇 |
专业分类
电工技术 | 4751篇 |
技术理论 | 12篇 |
综合类 | 5513篇 |
化学工业 | 15159篇 |
金属工艺 | 5115篇 |
机械仪表 | 5325篇 |
建筑科学 | 7201篇 |
矿业工程 | 2515篇 |
能源动力 | 2621篇 |
轻工业 | 5569篇 |
水利工程 | 1516篇 |
石油天然气 | 6079篇 |
武器工业 | 595篇 |
无线电 | 9410篇 |
一般工业技术 | 10888篇 |
冶金工业 | 4437篇 |
原子能技术 | 957篇 |
自动化技术 | 10492篇 |
出版年
2024年 | 344篇 |
2023年 | 1487篇 |
2022年 | 2415篇 |
2021年 | 3389篇 |
2020年 | 2675篇 |
2019年 | 2296篇 |
2018年 | 2626篇 |
2017年 | 2875篇 |
2016年 | 2574篇 |
2015年 | 3287篇 |
2014年 | 4302篇 |
2013年 | 5163篇 |
2012年 | 5514篇 |
2011年 | 5948篇 |
2010年 | 5198篇 |
2009年 | 4959篇 |
2008年 | 4813篇 |
2007年 | 4687篇 |
2006年 | 4817篇 |
2005年 | 4173篇 |
2004年 | 2753篇 |
2003年 | 2492篇 |
2002年 | 2207篇 |
2001年 | 2059篇 |
2000年 | 2171篇 |
1999年 | 2406篇 |
1998年 | 1921篇 |
1997年 | 1567篇 |
1996年 | 1435篇 |
1995年 | 1257篇 |
1994年 | 1033篇 |
1993年 | 740篇 |
1992年 | 588篇 |
1991年 | 441篇 |
1990年 | 397篇 |
1989年 | 272篇 |
1988年 | 240篇 |
1987年 | 148篇 |
1986年 | 132篇 |
1985年 | 92篇 |
1984年 | 69篇 |
1983年 | 42篇 |
1982年 | 44篇 |
1981年 | 31篇 |
1980年 | 26篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
姜建国 《信息安全与通信保密》2006,(2):20-22
研究意义和应用前景信息系统的安全威胁成为日益受到关注的严重问题。涉密内网虽然与因特网物理隔离,仍同样面临着漏洞、蠕虫、病毒、木马和后门等威胁。涉密信息可以通过文件共享、木马、邮件等方式被泄露,也可能被非授权用户登录访问,还可能通过外设(如:USB、光 相似文献
22.
23.
Polymer networks in which poly(propylene imine) dendrimers (Astramol?) are connected to each other by linear polytetrahydrofuran (polyTHF) segments, were prepared by two methods. The first method was a one‐step procedure in which bifunctionally living polyTHF, obtained by initiation of the THF polymerization with trifluoromethane sulfonic anhydride (triflic anhydride), was reacted with an amino‐dendrimer. This reaction was very fast but did not allow formation of the end products. The second method was a two‐step procedure. In a first step, living polyTHF, prepared with acryloyloxybutyl triflate as initiator, was grafted on an amino‐dendrimer, to form a star‐like, acrylate‐terminated polyTHF multi‐macromonomer with the dendrimer as core. In a second step, networks were obtained by Michael addition between the acrylate end‐groups and unreacted amino‐groups of the dendrimer. This cross‐linking reaction occurred spontaneously upon heating of the solution of the multi‐macromonomer with gelation times varying from a few minutes to a few hours, depending on the temperature and the composition of the prepolymers. With this method it was possible to prepare networks in the form of coatings or films. © 2003 Society of Chemical Industry 相似文献
24.
蒋协治 《石油化工腐蚀与防护》2006,23(4):63-64
采用自行研制的水力旋流器进行了降低酸性油酸值的工业实验。实验表明,水力旋流器可将酸值为13.3 mgKOH/g的酸性油酸值降至12 mgKOH/g左右,从而能满足工业生产要求,沉降时间大为缩短。 相似文献
25.
介绍了数字信号处理器ADSP21XX芯片的特点以及实现FFT(快速离散付里叶变换)的方法,给出了ADSP21XX的C和汇编混合编程的特点及技巧。 相似文献
26.
27.
D Sternberg A Peled E Shezen O Abramsky W Jiang F Bertolero D Zipori 《Canadian Metallurgical Quarterly》1996,2(1):29-38
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay. 相似文献
28.
对菱镁矿在固体燃料燃烧过程中的固硫特性进行了理论研究,所得结论对进一步将菱镁矿作为固体燃料燃烧过程中的固硫剂具有非常重要的意义。 相似文献
29.
Norton NBD 200 silicon nitride ceramics were implanted with sodium to a dose of 7.0×1015cm-2 at 72 keV (1 at% peak sodium content at 100 nm). The sodium-implanted samples were further implanted with aluminium to 7.3×1015cm-2 at 87 keV (1 at% peak aluminium content at 100 nm). The implanted and unimplanted samples were oxidized in 1 atm dry oxygen
at 1100 and 1300°C for 2–6 h. Profilometry and scanning electron microscopy measurements indicated that sodium implantation
led to up to a two-fold increase in the oxidation rate of silicon nitride. The sodium effect was effectively neutralized when
aluminium was co-implanted. The opposite effects of sodium and aluminium on the oxidation resistance of silicon nitride can
be attributed to their different roles in modifying the structure and properties of the oxide formed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
30.