全文获取类型
收费全文 | 121631篇 |
免费 | 14800篇 |
国内免费 | 4290篇 |
专业分类
电工技术 | 3250篇 |
技术理论 | 2篇 |
综合类 | 5128篇 |
化学工业 | 40533篇 |
金属工艺 | 12165篇 |
机械仪表 | 3109篇 |
建筑科学 | 6255篇 |
矿业工程 | 2724篇 |
能源动力 | 2473篇 |
轻工业 | 18079篇 |
水利工程 | 1404篇 |
石油天然气 | 2976篇 |
武器工业 | 561篇 |
无线电 | 7078篇 |
一般工业技术 | 22049篇 |
冶金工业 | 5835篇 |
原子能技术 | 854篇 |
自动化技术 | 6246篇 |
出版年
2024年 | 528篇 |
2023年 | 2593篇 |
2022年 | 4314篇 |
2021年 | 6963篇 |
2020年 | 4746篇 |
2019年 | 4331篇 |
2018年 | 4743篇 |
2017年 | 5688篇 |
2016年 | 6845篇 |
2015年 | 7402篇 |
2014年 | 8196篇 |
2013年 | 9295篇 |
2012年 | 7734篇 |
2011年 | 8063篇 |
2010年 | 5796篇 |
2009年 | 6092篇 |
2008年 | 5221篇 |
2007年 | 6682篇 |
2006年 | 6753篇 |
2005年 | 5422篇 |
2004年 | 4331篇 |
2003年 | 3895篇 |
2002年 | 3049篇 |
2001年 | 2051篇 |
2000年 | 1871篇 |
1999年 | 1321篇 |
1998年 | 1051篇 |
1997年 | 901篇 |
1996年 | 739篇 |
1995年 | 622篇 |
1994年 | 505篇 |
1993年 | 363篇 |
1992年 | 346篇 |
1991年 | 294篇 |
1990年 | 351篇 |
1989年 | 324篇 |
1988年 | 137篇 |
1987年 | 114篇 |
1986年 | 112篇 |
1985年 | 131篇 |
1984年 | 129篇 |
1983年 | 73篇 |
1982年 | 92篇 |
1981年 | 41篇 |
1980年 | 82篇 |
1966年 | 26篇 |
1964年 | 37篇 |
1962年 | 65篇 |
1959年 | 23篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献
72.
针对某在建矿山深井开拓方案探索需求,通过对胶带运输系统发展应用情况介绍和胶带运输系统运输特性影响因素分析,并结合深井开拓胶带斜井方案与竖井加胶带斜井方案投资经济性比较,以及对胶带运输系统在运行过程中关键问题的分析和讨论,得出随着胶带运输技术的不断发展,在大规模深井开拓中,胶带斜井开拓将大有可为,为冶金矿山深井开拓方案选择提供决策支持。 相似文献
73.
Norfariza Jamaluddin David C. Stuckey Arbakariya B. Ariff 《Critical reviews in food science and nutrition》2018,58(14):2453-2465
ABSTRACTBacteriocin is a proteinaceous biomolecule produced by bacteria (both Gram-positive and Gram-negative) that exhibits antimicrobial activity against closely related species, and food-borne pathogens. It has recently gained importance and attracted the attention of several researchers looking to produce it from various substrates and bacterial strains. This ushers in a new era of food preservation where the use of bacteriocin in food products will be an alternative to chemical preservatives, and heat treatment which are understood to cause unwanted side effects, and reduce sensory and nutritional quality. However, this new market depends on the success of novel downstream separation schemes from various types of crude feedstocks which are both effective and economic. This review focuses on the downstream separation of bacteriocin from various sources using both conventional and novel techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted. 相似文献
74.
75.
通过河南省渑池地区含锂铝土矿(岩)层工艺矿物学分析,查明铝土矿的物质组成、嵌布特征、伴生锂分布特征和赋存状态,为矿产综合利用提供理论依据。结果显示:该铝土矿Al2O3含量为54.8%,铝硅比值(A/S)为2.6,铝土矿层和粘土岩层中Li2O含量均高于伴生锂边界品位,粘土岩中锂更为富集;矿物组成除一水硬铝石之外,主要是以集合体形态产出的粘土矿物。采用稀酸解析、选矿测试和电子探针分析锂的赋存状态,查明矿石中锂主要是以类质同象置换形式赋存在伊利石和高岭石等粘土矿物中;选矿富锂尾矿中Li2O可富集到0.57%左右,是锂综合回收利用的重点研究对象。 相似文献
76.
采用动态平衡法,在293.15~332.80 K、常压下,测定了双季戊四醇(DPE)在水+(甲醇、乙醇、异丙醇)三种混合溶剂中的溶解度数据。结果表明:DPE在不同质量分数的水+(甲醇、乙醇、异丙醇)混合溶剂中的溶解度随体系温度升高而增大;同一温度下,其在所选取溶剂体系中的溶解度随着甲醇、乙醇或异丙醇质量分数的增大而先增大后减小。λh方程、两参数方程与Apelblat方程均能够对所测定的溶解度数据进行较好的关联;通过修正的van’t Hoff方程计算得到DPE在所选取溶剂体系中Δsol H 0、Δsol S 0和Δsol G 0均大于零,表明DPE在所选取溶剂体系中的溶解过程为吸热、熵增的非自发过程。 相似文献
77.
AbstractDifferent drying methods (spray drying (SD), vacuum drying (VD), microwave vacuum drying (MVD), and infrared vacuum drying (IFVD)) were applied in order to compare the hygroscopicity behavior of chicken powders. The hygroscopicity curves and glass transition temperature were used to evaluate the influence of ambient humidity and temperature on moisture absorption of powders. The results showed that the chicken powder dried by MVD had the lowest moisture absorption, followed by IFVD, VD, and SD. The hygroscopicity of SD chicken powders was different from other three kinds of chicken powders due to the physical properties of particles and the changes of protein secondary structure as detected by the Fourier transform-infrared spectrometer. For the three vacuum drying methods, the difference of protein secondary structure was the main reason of differences in hygroscopicity. Although MVD chicken powders were slightly inferior to SD chicken powders in taste, MVD chicken powders were the best in terms of smell and color as suggested by instrumental sensory parameter evaluations. It was found that MVD had a positive effect on reducing moisture absorption and maintaining sensory quality of chicken powders. 相似文献
78.
《Ceramics International》2020,46(7):9240-9248
The effects of Sr2+ substitution for Ba2+ on phase structure, microstructure, dielectric and electric properties for Ba4-xSrxSmFe0.5Nb9.5O30 (x = 0, 1, 2, 3 and 4) ceramics were systematically researched. X-ray diffraction patterns show that Ba4-xSrxSmFe0.5Nb9.5O30 (x = 0, 1, 2 and 3) ceramics are tetragonal tungsten bronze compound with a space group of P4bm, while the sample for x = 4 is an orthorhombic structure compound. The result can be corroborated by the analysis of Raman spectroscopy. As the Sr2+ contents increase from 0 to 3, the full width at half maximum of Raman lines of all samples increase gradually, indicating that the degree of lattice distortion increase. All tetragonal tungsten bronze ceramics exhibited a broad permittivity peaks, accompanied by frequency dispersion, indicating all samples are relaxor. The electrical properties of BSSFN ceramics were further studied by complex impedance spectroscopy. XPS spectrum shows that Fe2+ and Fe3+ coexist in Ba4-xSrxSmFe0.5Nb9.5O30 ceramics, and their proportion varies with the concentration of Sr2+. 相似文献
79.
通过对紫金山东南矿段铜钼(金)矿床地质矿化特征分析,指出铜钼矿化带主要赋存于花岗闪长斑岩的内外接触带,处于似斑状花岗闪长斑岩的上部,金矿化带赋存在表生氧化带的英安玢岩、隐爆角砾岩中。经过对矿石的组构特征、矿物生成顺序等特征分析,将矿床的成矿演化过程分为斑岩热液期、高硫化浅成低温热液期、表生氧化期三个主要矿化期次,进一步将斑岩热液期分为黑云母-钾长石化阶段、石英-绢云母化阶段、碳酸盐化阶段三个阶段;高硫化浅成低温热液期分为地开石化阶段、明矾石化阶段、硅化阶段三个阶段。研究结果为进一步研究矿床成因提供了依据。 相似文献
80.
Rong Zhang Hailong Hu Hai Chen Siqi Li Cheng Ying Shuai Huang Qingting Liu Xudong Fu Shengfei Hu Ching-Ping Wong 《应用聚合物科学杂志》2020,137(39):49186
Recently, thermal interface materials (TIMs) are in great demands for modern electronics. For mechanically mixed polymer composite TIMs, the thermal conductivity and the mechanical properties are generally lower than expected values due to the sharply increased viscosity and poor filler dispersion. This work shows that addition of a small amount of polyester-based hyperbranched polymer (HBP) avoided the trade-off in mechanically mixed ABS/hexagonal boron nitride (h-BN) composites. After adding 0.5 wt% HBP, the maximum h-BN content in the composites increased from 50 to 60 wt%. The out-of-plane, in-plane thermal conductivity, and tensile strength of ABS/h-BN with 50 wt% h-BN were 0.408, 0.517 W/mK, and 18 MPa, respectively, and were increased to 0.729, 0.847 W/mK, and 32 MPa by adding 0.5 wt% HBP, while 0.972, 1.12 W/mK, and 29.5 MPa were achieved for ABS/h-BN/HBP with 60 wt% h-BN. The morphological and rheological results proved that these enhancements are due to the improved h-BN dispersion by decreasing viscosity of composites during mixing. Theoretical modeling based on the modified effective medium theory confirmed such results and showed that the interfacial thermal resistance also decreased slightly. Thus, this work demonstrates a facile and scalable method for simultaneously improving the thermal conductivity and mechanical properties of thermoplastic-based TIMs. 相似文献