全文获取类型
收费全文 | 119786篇 |
免费 | 25408篇 |
国内免费 | 7522篇 |
专业分类
化学 | 115374篇 |
晶体学 | 933篇 |
力学 | 5164篇 |
综合类 | 450篇 |
数学 | 9975篇 |
物理学 | 20820篇 |
出版年
2024年 | 486篇 |
2023年 | 4648篇 |
2022年 | 3003篇 |
2021年 | 4331篇 |
2020年 | 7253篇 |
2019年 | 6317篇 |
2018年 | 3955篇 |
2017年 | 2641篇 |
2016年 | 9057篇 |
2015年 | 9230篇 |
2014年 | 9257篇 |
2013年 | 10752篇 |
2012年 | 9125篇 |
2011年 | 6969篇 |
2010年 | 8007篇 |
2009年 | 7747篇 |
2008年 | 5989篇 |
2007年 | 4949篇 |
2006年 | 3971篇 |
2005年 | 3672篇 |
2004年 | 3127篇 |
2003年 | 2624篇 |
2002年 | 3204篇 |
2001年 | 2434篇 |
2000年 | 2235篇 |
1999年 | 1435篇 |
1998年 | 931篇 |
1997年 | 862篇 |
1996年 | 909篇 |
1995年 | 851篇 |
1994年 | 739篇 |
1993年 | 757篇 |
1992年 | 603篇 |
1991年 | 487篇 |
1990年 | 441篇 |
1989年 | 337篇 |
1988年 | 365篇 |
1987年 | 314篇 |
1985年 | 276篇 |
1984年 | 262篇 |
1977年 | 331篇 |
1976年 | 393篇 |
1975年 | 490篇 |
1974年 | 496篇 |
1973年 | 304篇 |
1972年 | 387篇 |
1971年 | 361篇 |
1970年 | 547篇 |
1969年 | 420篇 |
1968年 | 458篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
物理实验课程考核、评估体系初探 总被引:4,自引:0,他引:4
对物理实验课程考核、评估方法进行了探讨,提出了物理实验课程考核、评估体系及实施细则.重点介绍了体系中的核心部分——正规的物理实验课程考试. 相似文献
132.
Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO4) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO4 compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO4 and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO4 compound was mainly due to the crosslinking induced by coordination between CN and Cu2+. The increasing extent of E′ increased with the rise of CuSO4 content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (Ea) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007 相似文献
133.
Tracy Huziak‐Clark Stephen J. Van Hook Julie Nurnberger‐Haag Lena Ballone‐Duran 《School science and mathematics》2007,107(8):311-324
This article focuses on the impact a collaborative project between university graduate fellows and K‐12 classroom teachers had on improved pedagogy in the classroom and in the future at the university. Nine teams participated in a yearlong professional development project to improve pedagogy and communication skills of the participants. This study shows that the participants, the fellows and the K‐12 teacher partners, made changes in planning, implementation, and even motivation for using inquiry‐based methods in their classroom. External observations of the teams further support the individuals' claims of improved pedagogy using inquiry and impact on student conceptual understanding. The Horizon Classroom Observation instrument was used for these observations. The teams showed an overall increase in scores, as well as overall effective and exemplarily implementation of their planning. The program design, the implementation, and the results of this three‐year study will be elaborated in this article. 相似文献
134.
135.
In this paper, we discuss the local and global existence ofweak solutions for some hyperbolicparabolic systems modellingchemotaxis. 相似文献
136.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
137.
In general, we will use the numerical differentiation when dealing with the differential equations. Thus the differential equations can be transformed into algebraic equations and then we can get the numerical solutions. But as we all have known, the numerical differentiation process is very sensitive to even a small level of errors. In contrast it is expected that on average the numerical integration process is much less sensitive to errors. In this paper, based on the Sinc method we provide a new method using Sinc method incorporated with the double exponential transformation based on the interpolation of the highest derivatives (SIHD) for the differential equations. The error in the approximation of the solution is shown to converge at an exponential rate. The numerical results show that compared with the exiting results, our method is of high accuracy, of good convergence with little computational efforts. It is easy to treat nonhomogeneous mixed boundary condition for our method, which is unlike the traditional Sinc method. 相似文献
138.
This work reports a new synthetic approach for single‐phase TiO2 nanomaterials by solvothermal treatment of titanium tetrachloride in acetone at 80–110 °C. Small, uniform, and yet size‐tunable (5–10 nm) anatase titania nanocrystallites were obtained using a low concentration of TiCl4 in acetone (i.e., at molar ratios of TiCl4/acetone ≤ 1:15) in the temperature range of 80–110 °C, while rutile nanofibers were synthesized using a high concentration of TiCl4 (e.g., TiCl4/acetone = 1:10) at 110 °C. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
139.
胡锦涛主席在全国科技大会上提出的,坚持走中国特色自主创新道路,建设创新型国家的口号,正在激励全国各族人民为实现我国中长期发展目标而奋斗.如何理解、实践这个口号,把每个行业、每个领域建设成创新型子系统,从而使整个国家有效地向着创新型国家目标发展,是13亿中国人民共同的任务,是历史赋予当代炎黄子孙的使命。我们必须在深入学习、研究理解胡锦涛主席关于“坚持走中国特色的自主创新道路,为建设创新型国家而奋斗”重要讲话的基础上,对本专业领域的创新型发展提出奋斗目标,作出科学规划。为此,我们就此主题谈一些想法,以期引起物理学界和教育界的朋友们深入思考、研究。 相似文献
140.
X.C. Li J. Wu K. Xu A.Q. Liu J.T. Lin 《Applied Physics A: Materials Science & Processing》2007,89(2):327-332
This paper presents the theoretical model and the optimization method to suppress the sidelobes of side-coupled photonic crystal
filters. Numerical verification shows a good agreement between the theoretical method and the finite-difference time-domain
simulation, but the theoretic method does not involve the time-consuming computation. The theoretical method also presents
a better physical image for choosing the critical parameters, such as the quality factor, phase shift and the number of resonators.
Based on the theoretical model, two optimization methods (chirp and cascading) are proposed to deeply suppress the sidelobes.
They also show more flexibility in controlling the bandwidth and steepness of the roll-off in the filter.
PACS 42.70.Qs 相似文献