全文获取类型
收费全文 | 6433篇 |
免费 | 1297篇 |
国内免费 | 1089篇 |
专业分类
化学 | 5028篇 |
晶体学 | 173篇 |
力学 | 402篇 |
综合类 | 67篇 |
数学 | 715篇 |
物理学 | 2434篇 |
出版年
2024年 | 33篇 |
2023年 | 218篇 |
2022年 | 382篇 |
2021年 | 346篇 |
2020年 | 393篇 |
2019年 | 369篇 |
2018年 | 299篇 |
2017年 | 259篇 |
2016年 | 333篇 |
2015年 | 384篇 |
2014年 | 395篇 |
2013年 | 487篇 |
2012年 | 599篇 |
2011年 | 555篇 |
2010年 | 365篇 |
2009年 | 370篇 |
2008年 | 424篇 |
2007年 | 381篇 |
2006年 | 321篇 |
2005年 | 290篇 |
2004年 | 189篇 |
2003年 | 185篇 |
2002年 | 184篇 |
2001年 | 160篇 |
2000年 | 144篇 |
1999年 | 119篇 |
1998年 | 85篇 |
1997年 | 75篇 |
1996年 | 90篇 |
1995年 | 66篇 |
1994年 | 55篇 |
1993年 | 48篇 |
1992年 | 39篇 |
1991年 | 28篇 |
1990年 | 31篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1968年 | 1篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有8819条查询结果,搜索用时 15 毫秒
91.
Yang Liu Ning Wu Lihua Geng Yang Yue Quanbin Zhang Jing Wang 《Molecules (Basel, Switzerland)》2022,27(6)
Nowadays, natural polysaccharides-based hydrogels have achieved promising results as dressings to promote skin healing. In the present study, we prepared a novel hydrogel nanocomposite with poly(vinyl alcohol) (PVA) and sulfated heterosaccharide (UF), named UPH. The SEM results showed that the UPH had dense porous structures with a high porosity and a specific surface area. The UPH had a good swelling property, which can effectively adsorb exudate and keep the wound moist. The in vitro experiments results showed that the UPH was non-cytotoxic and could regulate the inflammatory response and promote the migration of fibroblasts significantly. The phenotypic, histochemistry, and Western blot analyses showed UPH treatment accelerated the wound healing and recovery of skin tissue at wound sites in a C57BL/6 mouse model. Furthermore, the UPH could promote the inflammation process to onset earlier and last shorter than that in a normal process. Given its migration-promoting ability and physicochemical properties, the UPH may provide an effective application for the treatment and management of skin wounds. 相似文献
92.
Jiong Zhou Hongliang Ma Minjian Zhong Guoqing Xu Zhongyue Yue Zhengming He 《Journal of magnetism and magnetic materials》2006
Polycrystalline BaCoxZrxFe11.5−2xO18.25 samples with 0?x?0.6 ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:11.5. The cationic site preferences of Co2+ and Zr4+ in Co–Zr substituted Ba ferrite were investigated by magnetic measurements and X-ray diffractometer (XRD) analysis. The coercivity Hc was decreasing with increasing Co–Zr substitution. The datum showed that the max coercive force (Hc) was obtained when substitution of 0.2, while the best saturation magnetizations (Ms) was obtained when substitution of 0.4. 相似文献
93.
Effects of the strain relaxation of an AlGaN barrier layer induced by various cap layers on the transport properties in AlGaN/GaN heterostructures 总被引:1,自引:0,他引:1 下载免费PDF全文
The strain relaxation of an AlGaN barrier layer may be influenced by a thin cap layer above, and affects the transport properties of AlGaN/GaN heterostructures. Compared with the slight strain relaxation found in AlGaN barrier layer without cap layer, it is found that a thin cap layer can induce considerable changes of strain state in the AlGaN barrier layer. The degree of relaxation of the AlGaN layer significantly influences the transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures. It is observed that electron mobility decreases with the increasing degree of relaxation of the AlGaN barrier, which is believed to be the main cause of the deterioration of crystalline quality and morphology on the AlGaN/GaN interface. On the other hand, both GaN and AlN cap layers lead to a decrease in 2DEG density. The reduction of 2DEG caused by the GaN cap layer may be attributed to the additional negative polarization charges formed at the interface between GaN and AlGaN, while the reduction of the piezoelectric effect in the AlGaN layer results in the decrease of 2DEG density in the case of AlN cap layer. 相似文献
94.
为解决光导开关耐受场强的提高问题,研制了2种体结构光导开关,并进行了实验研究。两种开关均由半绝缘GaAs材料制成,一种尺寸为10.0 mm×10.0 mm×0.6 mm,电极位于10.0 mm×10.0 mm面上相对位置,电极直径6 mm;另一种尺寸为15.0 mm×15.0 mm×3.0 mm,8 mm直径电极位于15.0 mm×15.0 mm面上相对位置。测试了第1种开关在不同半高宽脉冲加载电压下的击穿电压,结果表明其最大耐受电压达7.6 kV,击穿电场127 kV/cm。对第2种结构测试了开关在直流加载条件下的暗态伏安特性并进行了触发实验,结果表明在15 kV工作电压下,其放电最大电流超过3.5 kA。 相似文献
95.
为了测量材料在高温甚至超高温下的力学性能,采用数字图像相关方法,并研究其在高温下的最优成像。采取不同的散斑制作方法,同时加入不同颜色的高温漆,在不同的温度节点,外加不同光源及相应的滤波片,采集并观察图像是否具有良好的对比度。普通的单色光源在800℃以后会逐渐失效,无法获取图像,而紫外光在1 200℃时依然可以获取较好的图像,且直接利用试件本身颜色作为底色效果更佳。采用紫外光照明可以实现DIC在高温环境下的测量。同时利用黑色或者蓝色散斑直接喷涂在试件上有着最佳的对比度,要优于常规的散斑制作方法。 相似文献
96.
97.
利用原位还原法成功制备了尺寸均一、超薄完整金壳包覆的NaYF4:Yb,Er@SiO2@Au(NSA)纳米结构,其XRD、TEM、EDX、HRTEM-HAADF、Mapping及吸收光谱表征结果表明,SiO2壳及纳米金壳的平均厚度分别约为5 nm和2 nm。在980 nm连续激光激发下,系统研究了核壳结构的上转换荧光强度与氯金酸浓度的依赖关系。稳态光谱结果显示,NSA与仅SiO2包覆样品(NS)相比Er3+的红绿荧光强度均增强了~2.8倍。通过分析上转换荧光动力学过程及利用FDTD方法模拟,讨论了表面等离激元增强上转换荧光的机制。 相似文献
98.
99.
Keitaro Tezuka Yue Jin Shan Kenji Ohoyama 《Journal of Physics and Chemistry of Solids》2007,68(11):2133-2137
Chromium(II) sulfide, Y2CrS4, prepared by a solid-state reaction of Y2S3 and CrS, showed an antiferromagnetic transition at 65 K. The neutron diffraction patterns at 10 and 90 K were both well refined with the space group Pca21. At 90 K, cell parameters were a=12.5518(13) Å, b=7.5245(8) Å, and c=12.4918(13) Å. At 10 K, magnetic peaks were observed, which could be indexed on the same unit cell. Magnetic moments of chromium ions were parallel to the b-axis and antiferromagnetically ordered in each set of the 4a sites. 相似文献
100.
In this paper, time-varying photoconductivity (PC) and the photoluminescence (PL) of different complexes were studied. Due to thick polymer layer hindering light penetrating into porous silicon (PS) layer, intrinsic PS luminescence in polymer/PS system disappeared. The physical origin of PL may be related to the recombination mechanisms involving surface defect states such as silicon oxide, siloxene. Due to carrier transfer controlled by different energy barrier, different devices prepared from different doped Si wafer showed opposite current-voltage characteristic. 相似文献