全文获取类型
收费全文 | 289562篇 |
免费 | 28468篇 |
国内免费 | 18213篇 |
学科分类
工业技术 | 336243篇 |
出版年
2024年 | 1606篇 |
2023年 | 5278篇 |
2022年 | 10769篇 |
2021年 | 14111篇 |
2020年 | 10349篇 |
2019年 | 7744篇 |
2018年 | 8592篇 |
2017年 | 9829篇 |
2016年 | 8812篇 |
2015年 | 12645篇 |
2014年 | 15478篇 |
2013年 | 18669篇 |
2012年 | 21380篇 |
2011年 | 22488篇 |
2010年 | 20030篇 |
2009年 | 19328篇 |
2008年 | 18945篇 |
2007年 | 18064篇 |
2006年 | 16888篇 |
2005年 | 14203篇 |
2004年 | 9804篇 |
2003年 | 7598篇 |
2002年 | 6878篇 |
2001年 | 6209篇 |
2000年 | 5646篇 |
1999年 | 4851篇 |
1998年 | 3692篇 |
1997年 | 3089篇 |
1996年 | 2843篇 |
1995年 | 2314篇 |
1994年 | 1862篇 |
1993年 | 1374篇 |
1992年 | 1110篇 |
1991年 | 838篇 |
1990年 | 617篇 |
1989年 | 522篇 |
1988年 | 400篇 |
1987年 | 267篇 |
1986年 | 229篇 |
1985年 | 140篇 |
1984年 | 124篇 |
1983年 | 105篇 |
1982年 | 92篇 |
1981年 | 92篇 |
1980年 | 97篇 |
1979年 | 46篇 |
1977年 | 25篇 |
1976年 | 26篇 |
1959年 | 35篇 |
1951年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
在铝材生产中,熔炼、铸造工序是能源与资源消耗多的工序,因此,节约资源、降低烧损与能耗有着重要意义。降低能耗还可以相应地减少温室气体与有害、有毒物质排放,对环保有利。中国当前铝合金熔炼铸造能源与资源节约的主要措施:调整加工用锭坯供应结构,大幅提高电解铝厂供应的锭坯,由2013年供应的42%提高到"十三五"末的65%-70%;加快走出去的力度,到国外去办铝厂,将在国外生产的铝合金锭坯运回来,争取2020年出口的铝材与铝制品全部以进口锭坯加工,这是最大的资源与能源节约;加强废铝回收与有效再生利用;加强创新,大力采用新装备、新技术与新工艺;加强管理,精心操作,管理中还有较大的能源与资源节约潜力。 相似文献
2.
3.
大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。 相似文献
4.
Effects of different carbon sources and C/N values on nonvolatile taste components of Pleurotus eryngii 下载免费PDF全文
Wen Li Xiaobei Li Yan Yang Feng Zhou Yanfang Liu Shuai Zhou Hailong Yu 《International Journal of Food Science & Technology》2015,50(11):2360-2366
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels. 相似文献
5.
6.
7.
Rectangular section control technology(RSCT)was introduced to achieve high-precision profile control during silicon steel rolling.The RSCT principle and method were designed,and the whole RSCT control strategy was developed.Specifically,RSCT included roll contour design,rolling technology optimization,and control strategy development,aiming at both hot strip mills(HSMs)and cold strip mills(CSMs).Firstly,through the high-performance variable crown(HVC)work roll optimization design in the upper-stream stands and the limited shifting technology for schedule-free rolling in the downstream stands of HSMs,a hot strip with a stable crown and limited wedge,local spot,and single wave was obtained,which was suitable for cold rolling.Secondly,an approximately rectangular section was obtained by edge varying contact(EVC)work roll contour design,edge-drop setting control,and closed loop control in the upper-stream stands of CSMs.Moreover,complex-mode flatness control was realized by coordinating multiple shape-control methods in the downstream stands of CSMs.In addition,the RSCT approach was applied in several silicon-steel production plants,where an outstanding performance and remarkable economic benefits were observed. 相似文献
8.
Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface. 相似文献
9.
10.