全文获取类型
收费全文 | 64310篇 |
免费 | 6351篇 |
国内免费 | 3328篇 |
学科分类
工业技术 | 73989篇 |
出版年
2024年 | 122篇 |
2023年 | 969篇 |
2022年 | 1614篇 |
2021年 | 2582篇 |
2020年 | 1927篇 |
2019年 | 1672篇 |
2018年 | 1754篇 |
2017年 | 1988篇 |
2016年 | 2049篇 |
2015年 | 2774篇 |
2014年 | 3357篇 |
2013年 | 3992篇 |
2012年 | 4312篇 |
2011年 | 4750篇 |
2010年 | 4270篇 |
2009年 | 3868篇 |
2008年 | 3899篇 |
2007年 | 3575篇 |
2006年 | 3592篇 |
2005年 | 3074篇 |
2004年 | 2252篇 |
2003年 | 2144篇 |
2002年 | 2362篇 |
2001年 | 1975篇 |
2000年 | 1607篇 |
1999年 | 1388篇 |
1998年 | 1122篇 |
1997年 | 930篇 |
1996年 | 836篇 |
1995年 | 736篇 |
1994年 | 625篇 |
1993年 | 456篇 |
1992年 | 347篇 |
1991年 | 275篇 |
1990年 | 192篇 |
1989年 | 158篇 |
1988年 | 129篇 |
1987年 | 76篇 |
1986年 | 57篇 |
1985年 | 42篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
探讨长治市手足口病(HFMD)与气象因素的关联关系.利用Apriori关联规则算法挖掘不同气象因素组合引发手足口病的频繁程度.长治市手足口病的周高发、中等发病率与前一周的平均水汽压、气温具有显著相关性.而周低发病率与前一周的气温(最低、平均)、降水量存在显著相关性.长治市手足口病周发病率与气象因素存在一定的关联性,应根据气象条件进行流行风险评估,及时采取相应的防控措施. 相似文献
33.
L.H. Jin G.Q. Liu X.Y. Xu G.F. Jiao H.L. Zheng Q.B. Hao S.N. Zhang C.S. Li P.X. Zhang 《Ceramics International》2021,47(3):3299-3305
Bi2Sr2CaCu2Ox (Bi-2212) precursor powders were synthesized by the oxalate freeze drying (OFD) method. In comparison with the traditional method, the novel method could shorten the processing steps and thus improve the fabrication efficiency of precursor powder. The phase, microstructure and superconducting properties of Bi-2212 precursor powders and wires were characterized by X-ray diffraction, scanning electron microscopy and four-probe method, respectively. The thermal behavior, surface area and particle size of powders were also discussed. The results indicated that large surface area and small particle size might improve the reactivity and uniformity of powders. These properties were beneficial for the rapid and homogeneous formation of Bi-2212. High-purity crystallized Bi-2212 powders without Bi-2201 and alkaline-earth cuprates phases could be achieved. Furthermore, multi-filamentary Bi-2212 wires with OFD powders showed good microstructures without noticeable pores and large secondary particles. Therefore, high engineering critical current densities (Je) of 1619 A/mm2 and critical current densities (Jc) of 7039 A/mm2 were obtained in Bi-2212 wires at 4.2K, self field. It indicated that the oxalate freeze drying method would be a potential candidate for the mass production of high performance Bi-2212 wires. 相似文献
34.
采用直流磁控溅射和后退火氧化工艺在p型GaAs单晶衬底上成功制备了n-VO_2/pGaAs异质结,研究了不同退火温度和退火时间对VO_2/GaAs异质结性能的影响,并分析其结晶取向、化学组分、膜层质量以及光电特性。结果表明,在退火时间2 h和退火温度693 K下能得到相变性能最佳的VO_2薄膜,相变前后电阻变化约2个数量级。VO_2/GaAs异质结在308 K、318 K和328 K温度下具有较好的整流特性,对应温度下的阈值跳变电压分别为6.9 V、6.6 V和6.2 V,该结果为基于VO_2相变特性的异质结光电器件的设计与应用提供了可行性。 相似文献
35.
以海蜇为原料,采用盐酸-胃蛋白酶法提取胶原蛋白,并通过聚丙烯酰胺凝胶电泳(SDS-Polyacrylamide gel electrophoresis,SDS-PAGE)、紫外光谱(UV-visible spectroscopy,UV)、氨基酸分析、红外光谱(Fourier-transform infrared spectroscopy,FTIR)、圆二色谱(Circular dichroism,CD)以及扫描电镜(Scanning electron microscope,SEM)对其结构特性进行了系统全面的研究。结果显示,海蜇胶原蛋白在135 kDa左右有一条α-链,在245 kDa以上有一条β-链和γ-链,紫外吸收峰在233 nm处,符合I型胶原蛋白的特征,其亚基组成可能为[α1(I)]3。海蜇胶原蛋白中含量最高的氨基酸为甘氨酸,占氨基酸总量的25.99%,且含有15.94%的亚氨基酸。红外光谱和圆二色谱均表明海蜇胶原蛋白分子排布紧凑,具有主要由氢键构成的完整三螺旋结构。扫描电镜结果显示海蜇胶原蛋白具有多层聚集、以纤维为主的无规则网状结构。 相似文献
36.
Shuai Yang Yun Lu Yangang Guo Baofeng Guo Lei Chen Miao Jin 《Ceramics International》2021,47(5):6562-6572
Alumina inclusions in commercial as-cast 2.25Cr1Mo0.25V aluminum deoxidized steel exhibited a feature of porous structure. In order to investigate the crushing characteristics of alumina inclusion during hot working, a series of alumina blocks with different porosity whose properties are similar to the alumina inclusions in ingots were prepared using spark plasma sintering. The crushing behavior of alumina blocks during hot compression with quasi-static load was studied. A prediction model of compressive strength of alumina inclusions considering apparent porosity was established on basis of hyperbolic sine Arrhenius equation. A novel crushing mode diagram for alumina inclusions characterized by Z parameter was proposed. The crushing mechanism of alumina inclusions under different deformation parameters was clarified by fracture characteristics. The results showed that the hot compression process of alumina presented a typical brittle fracture, the compressive strength was more sensitive to deformation conditions at lower apparent porosity as compared with the conditions of higher apparent porosity. With the increase of Z, the crushing mode of alumina inclusions gradually changed from intergranular fracture to transgranular fracture. 相似文献
37.
38.
39.
基于数据安全考虑,对具有自主知识产权和可控数据平台的国内BIM建模软件(BIMMAKE)进行应用、分析和总结.通过在中国科学院脑认知功能图谱与类脑智能交叉研究平台项目上进行施工模型创建、钢筋节点深化、精确配模并指导施工和模型轻量化等应用,总结自主知识产权软件的应用步骤、应用方法. 相似文献
40.
Xiao-juan Li Yi-xiang Xu Xiang Li Zhi-jiang Jin Jin-yuan Qian 《International Journal of Hydrogen Energy》2021,46(7):5537-5547
Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers. 相似文献