全文获取类型
收费全文 | 23494篇 |
免费 | 4610篇 |
国内免费 | 4110篇 |
专业分类
化学 | 10872篇 |
晶体学 | 457篇 |
力学 | 1009篇 |
综合类 | 564篇 |
数学 | 1620篇 |
物理学 | 7203篇 |
无线电 | 10489篇 |
出版年
2024年 | 125篇 |
2023年 | 488篇 |
2022年 | 916篇 |
2021年 | 968篇 |
2020年 | 1022篇 |
2019年 | 800篇 |
2018年 | 816篇 |
2017年 | 980篇 |
2016年 | 1000篇 |
2015年 | 1312篇 |
2014年 | 1541篇 |
2013年 | 1878篇 |
2012年 | 2062篇 |
2011年 | 2073篇 |
2010年 | 1712篇 |
2009年 | 1674篇 |
2008年 | 1830篇 |
2007年 | 1707篇 |
2006年 | 1556篇 |
2005年 | 1465篇 |
2004年 | 1037篇 |
2003年 | 799篇 |
2002年 | 744篇 |
2001年 | 778篇 |
2000年 | 678篇 |
1999年 | 407篇 |
1998年 | 207篇 |
1997年 | 184篇 |
1996年 | 143篇 |
1995年 | 117篇 |
1994年 | 127篇 |
1993年 | 129篇 |
1992年 | 121篇 |
1991年 | 91篇 |
1990年 | 90篇 |
1989年 | 105篇 |
1988年 | 75篇 |
1987年 | 54篇 |
1986年 | 49篇 |
1985年 | 47篇 |
1984年 | 42篇 |
1983年 | 43篇 |
1982年 | 36篇 |
1981年 | 49篇 |
1980年 | 25篇 |
1979年 | 26篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1974年 | 13篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
数字散斑干涉技术在振动分析中的应用 总被引:2,自引:0,他引:2
首次将相移技术应用于频闪数字散斑干涉计量中,对物体的振动进行了定量分析.实验证明,这种方法有广泛的实用价值.另外,介绍了一套自动分析系统,讨论了各参数对测量结果的影响. 相似文献
32.
In the present study, proteins and glycoproteins of mouse embryos at 2-cell,morula and blastocyst stages were analyzed.The techniques of ~(35)S-Met incorporation,ConA antiserum-precipitating ConA-binding proteins, mini-2D-electrophoresis, fluorography,video densitometer scanning and the computer-lmage system were used for analyses.Results of the investigations indicated that proteins and glycoproteins were synthesized by the embryos in a gradual increase manner from 2-cell to blastocyst. A relatively large amount of glycoproteins was synthesized during the morula and blastocyst stages.Two specific small glycoproteins respectively with molecular weights about 6500 and 9000 and PIs at 5.0 and 6.5 were apparently synthesized in the blastocyst but not in the 2-cell or the morula. 相似文献
33.
34.
35.
Effects of Substrate Temperature on Helium Content and Microstructure of Nanocrystalline Titanium Films 下载免费PDF全文
Helium-charged nanocrystalline titanium films have been deposited by HeAr magnetron co-sputtering. The effects of substrate temperature on the helium content and microstructure of the nanocrystalline titanium films have been studied. The results indicate that helium atoms with a high concentration are evenly incorporated in the deposited titanium films. When the substrate temperature increases from 60℃ to 350℃ while the other deposition'parameters are fixed, the helium content decreases gradually from 38.6 at.% to 9.2at.%, which proves that nanocrystalline Ti films have a great helium storage capacity. The 20 angle of the Bragg peak of (002) crystal planes of the He-charged Ti film shifts to a lower angle and that of (100) crystal plane is unchanged as compared with that of the pure Ti film, which indicates that the lattice parameter c increases and a keeps at the primitive value. The grain refining and helium damage result in the diffraction peak broadening. 相似文献
36.
Based on the theory of calculus of variation, some suffcient conditions are given for some Euler-Lagrangcequations to be equivalently represented by finite or even infinite many Hamiltonian canonical equations. Meanwhile,some further applications for equations such as the KdV equation, MKdV equation, the general linear Euler Lagrangeequation and the cylindric shell equations are given. 相似文献
37.
KANG Zihua WANG Mingwei QIAN Jiamei RAO Jun LI Xiujuan ZHENG Tieliu WANG Xuehua 《核工业西南物理研究院年报(英文版)》2004,(1):73-76
Lower hybrid wave (LHW), electro cyclotron (EC) and neutral beam injection (NBI) etc. are the important methods of auxiliary heating. They would be devoted to the HL-2A tokamak step by step. In order to satisfy the debug of each system and the need of the experiment, the system should be equipped with high voltage pulse power (HVPP) according to the requirement. 相似文献
38.
L. K. Seah U. S. Dinish S. K. Ong Z. X. Chao V. M. Murukeshan 《Optics & Laser Technology》2004,36(5):371-376
Imaging of latent fingerprints using time-resolved (TR) method offers a broader platform to eliminate the unwanted background emission. In this paper, a novel TR imaging technique is demonstrated and implemented, which facilitates the detection of latent fingerprints with nanosecond resolution. Simulated experiments were carried out with two overlapping fingerprints treated with two fluorescent powders having different lifetimes in nanosecond range. The dependence of the fluorescence emission intensity in nanosecond resolution of TR imaging is also revealed. 相似文献
39.
多目标半定规划的互补弱鞍点和G-鞍点最优性条件 总被引:1,自引:0,他引:1
对于含矩阵函数半定约束和多个目标函数的多目标半定规划问题,给出Lagrange函数在弱有效意义下的互补弱鞍点和Geofrrion恰当有效意义下的G-鞍点的定义及其等价定义.然后,在较弱的凸性条件下,利用含矩阵和向量约束的择一性定理,建立多目标半定规划的互补弱鞍点和G-鞍点充分必要条件. 相似文献
40.
溶胶-凝胶生物玻璃多孔材料显微结构和生物活性的扫描电镜及红外光谱分析 总被引:13,自引:0,他引:13
本文利用溶胶.凝胶法制备了CaO-P2O5-SiO,系统生物活性玻璃,并以其为原料制备了用于骨修复及骨组织工程支架的块状生物活性材料。利用体外实验方法(invitro)结合x射线衍射(XRD)、扫描电子显微镜(SEM)和傅立叶变换红外光谱分析(FTIR)技术对不同烧结工艺制备的材料结构、晶相和生物活性的影响进行了分析研究。研究表明,经800℃和1100℃烧结5min的两种材料均有硅磷酸钙Ca5(PO4)2SjO4微晶相析出。烧结温度越高,析出微晶相的体积比例越大,材料的生物活性则越低。在模拟生理溶液中碳酸羟基磷灰石(HCA)只在烧结体中的玻璃颗粒表面形成,而在其硅磷酸钙Ca5(PO4)2SiO4微晶相表面未发现HCA形成。 相似文献