全文获取类型
收费全文 | 42056篇 |
免费 | 5509篇 |
国内免费 | 5851篇 |
专业分类
化学 | 31889篇 |
晶体学 | 602篇 |
力学 | 1950篇 |
综合类 | 441篇 |
数学 | 4861篇 |
物理学 | 13673篇 |
出版年
2024年 | 115篇 |
2023年 | 651篇 |
2022年 | 1223篇 |
2021年 | 1335篇 |
2020年 | 1404篇 |
2019年 | 1445篇 |
2018年 | 1229篇 |
2017年 | 1233篇 |
2016年 | 1743篇 |
2015年 | 1827篇 |
2014年 | 2219篇 |
2013年 | 3060篇 |
2012年 | 3469篇 |
2011年 | 3742篇 |
2010年 | 2722篇 |
2009年 | 2619篇 |
2008年 | 2938篇 |
2007年 | 2685篇 |
2006年 | 2406篇 |
2005年 | 2075篇 |
2004年 | 1674篇 |
2003年 | 1371篇 |
2002年 | 1328篇 |
2001年 | 1135篇 |
2000年 | 949篇 |
1999年 | 843篇 |
1998年 | 689篇 |
1997年 | 569篇 |
1996年 | 604篇 |
1995年 | 504篇 |
1994年 | 474篇 |
1993年 | 420篇 |
1992年 | 381篇 |
1991年 | 334篇 |
1990年 | 295篇 |
1989年 | 217篇 |
1988年 | 202篇 |
1987年 | 147篇 |
1986年 | 168篇 |
1985年 | 178篇 |
1984年 | 121篇 |
1983年 | 79篇 |
1982年 | 76篇 |
1981年 | 59篇 |
1980年 | 57篇 |
1979年 | 62篇 |
1978年 | 41篇 |
1976年 | 40篇 |
1974年 | 42篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Earth-orbiting spacecraft often contain solar arrays or antennas supported by a preloaded mast. Due to weight and cost considerations, the supporting structures of the spacecraft appendages are made extremely light and flexible. Therefore, it is essential to investigate the influence of all physical and structural parameters on the dynamic behavior of the overall structure. The governing equation of motion and its general solution for the preloaded mast are developed. Furthermore, the mass moment of inertia of the mast subjected to bending vibrations is included in the governing equation of motion to investigate its influence on determining the circular frequencies. To verify the developed formulations, a finite element technique was implemented. The accuracy and limitation of the technique on calculating the circular frequencies are discussed. Although the study described in this paper primarily focuses on the mast for the space station solar arrays, the developed formulations and techniques can be applied to any large and flexible beam in zero gravity. 相似文献
122.
Y. Jao W. L. Cheng H. J. Chen C. C. Shaeh C. C. Huang Y. M. Lin 《Journal of Radioanalytical and Nuclear Chemistry》1995,194(2):411-417
This study was performed under the joint TRMC/INER program for the determination of low level85Kr and133Xe concentrations in the environmental air samples. Based on cryogenic adsorption of krypton and xenon on charcoal followed by chromatographic separation from other gases, the85Kr and133Xe recovered from 200 liters of atmospheric air can be determined by either on-line gas flow proportional counter or liquid scintillation counting. The recovery yields of krypton and xenon examined by using85Kr and133Xe tracers were nearly 100%. The minimum detectable activity of85Kr and133Xe by gas flow proportional counting is about 7.40 Bq. The method is satisfactory for environmental monitoring applications under abnormal conditions of nuclear facilities. However, for lower level environmental85Kr and133Xe measurements, the liquid scintillation counting method can be applied due to their extremely low detection limits (i.e. 0.107 Bq and 0.093 Bq for85Kr and133Xe, respectively). Using this method, the measurable limits of concentrations are 0.535 Bq/m3 and 0.466 Bq/m3 for85Kr and133Xe, respectively. 相似文献
123.
在多项选择题测验分数等于真实分数和猜测分数之和的假设模型下,本文得到了一个多项选择题测验信度的理论公式,并由此给出了测验信度的估计方法。最后,通过两个例子,说明了本文提出的方法在测验信度分析中的应用,并将这种方法与教育测量中常用的库德——理查逊方法(Kuder-Richardson)进行了比较 相似文献
124.
添加剂在氧化铈抛光中的作用机理的探索 总被引:2,自引:0,他引:2
本文在试验基础上,对添加剂在氧化铈抛光中作用机理—提高氧化铈抛光效率的机理和防止玻璃抛光表面腐蚀的机理作了探索,指出在一定的抛光工艺条件下,每一种添加剂对于一定品位的氧化铈和一定牌号的光学玻璃有一最佳的加入量。 相似文献
125.
126.
Ying Guang Shi 《Constructive Approximation》1994,10(4):439-450
In this paper we give a theorem of Grünwald-type for (0, 1,...,m-1) Hermite-Fejér interpolation (m=2, 4,...), which extends the famous result for a strongly normal system of nodes in the casem=2 given by Grünwald in [1]. 相似文献
127.
Ying Lung-an 《Numerical Methods for Partial Differential Equations》1991,7(4):317-338
A viscosity-splitting scheme for the initial boundary value problems of the Navier-Stokes equations is considered. In the scheme, the Stokes equation is solved in conjunction with a nonhomogeneous boundary condition which connects the tangent flow with a no-slip flow. Convergence is proved. 相似文献
128.
Tumor cells transduced with herpes simplex virus thymidine kinase gene have been intensively applied to the field of positron emission tomography via imaging of its substrate. As a pilot synthesis approach, a facile preparation of 5‐[125I] iodoarabinosyl uridine starting from commercially available uridine is reported herein. 相似文献
129.
Yanlin Huang Kiwan Jang Wanxue Zhao Eunjin Cho Ho Sueb Lee Xigang Wang Dake Qin Ying Zhang Chanfang Jiang Hyo Jin Seo 《Journal of solid state chemistry》2007,180(12):3325-3332
Usually, Sm2+ ions could be reduced by heating the materials in reducing atmospheres. Exposure to ionizing radiations is also known to cause Sm3+→Sm2+ conversion. In this work, BaBPO5 doped with the samarium ion was prepared by high temperature solid-state reaction. Sm2+ ions were obtained by two different reduction methods, i.e., heating in H2 reduced atmosphere and X-ray irradiation. The measurements of X-ray diffraction (XRD), and scanning electron microscope (SEM) were investigated. It is found that the conversion of Sm3+→Sm2+ is very efficient in BaBPO5 hosts after X-ray irradiation. Sm2+ ions under these two reduction methods exhibit different characteristics that were studied by measurements of luminescence and decay. The results showed that the luminescence properties of Sm2+ ions in BaBPO5 were highly dependent on the sample preparation conditions. 相似文献
130.
Three novel zinc complexes [Zn(dbsf)(H2O)2] ( 1 ), [Zn(dbsf)(2,2′‐bpy)(H2O)]·(i‐C3H7OH) ( 2 ) and [Zn(dbsf)(DMF)] ( 3 ) (H2dbsf = 4,4′‐dicarboxybiphenyl sulfone, 2,2′‐bpy = 2,2′‐bipyridine, i‐C3H7OH = iso‐propanol, DMF = N,N‐dimethylformamide) were first obtained and characterized by single crystal X‐ray crystallography. Although the results show that all the complexes 1–3 have one‐dimensional chains formed via coordination bonds, unique three‐dimensional supramolecular structures are formed due to different coordination modes and configuration of the dbsf2? ligand, hydrogen bonds and π–π interactions. Iso‐propanol molecules are in open channels of 2 while larger empty channels are formed in 3 . As compared with emission band of the free H2dbsf ligand, emission peaks of the complexes 1–3 are red‐shifted, and they show blue emission, which originates from enlarging conjugation upon coordination. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献