全文获取类型
收费全文 | 7654篇 |
免费 | 443篇 |
国内免费 | 609篇 |
专业分类
化学 | 291篇 |
晶体学 | 9篇 |
力学 | 128篇 |
综合类 | 90篇 |
数学 | 1883篇 |
物理学 | 863篇 |
综合类 | 5442篇 |
出版年
2024年 | 39篇 |
2023年 | 114篇 |
2022年 | 236篇 |
2021年 | 213篇 |
2020年 | 148篇 |
2019年 | 190篇 |
2018年 | 136篇 |
2017年 | 228篇 |
2016年 | 201篇 |
2015年 | 219篇 |
2014年 | 385篇 |
2013年 | 434篇 |
2012年 | 381篇 |
2011年 | 478篇 |
2010年 | 395篇 |
2009年 | 438篇 |
2008年 | 384篇 |
2007年 | 523篇 |
2006年 | 452篇 |
2005年 | 378篇 |
2004年 | 348篇 |
2003年 | 329篇 |
2002年 | 272篇 |
2001年 | 232篇 |
2000年 | 250篇 |
1999年 | 183篇 |
1998年 | 189篇 |
1997年 | 153篇 |
1996年 | 123篇 |
1995年 | 70篇 |
1994年 | 86篇 |
1993年 | 69篇 |
1992年 | 59篇 |
1991年 | 68篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 33篇 |
1987年 | 34篇 |
1986年 | 17篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1974年 | 3篇 |
排序方式: 共有8706条查询结果,搜索用时 137 毫秒
51.
52.
设D是一个Jordan,Г为其边界,并设Г满足Aльпер条件。本文得到了一种基于Fejer点的有理型插值算子对于f(z)∈C(Г)的一致逼近阶。 相似文献
53.
Marlies Gerber 《Geometriae Dedicata》2003,98(1):123-160
We establish some criteria for the existence or nonexistence of focal points near closed geodesics on surfaces. These criteria are in terms of the curvature of the manifold along the closed geodesic and the average values of the partial derivatives of the curvature in the direction perpendicular to the geodesic. Our criteria lead to a new family of examples of surfaces with no focal points. We also show that if S is a compact surface with no focal points and an inequality relating the curvature of the surface to the curvature of the horocycles holds, then the horocycles (considered as curves in S) are uniformly C
2+Lipschitz. 相似文献
54.
通过解读《普通高等学校本科教学工作水平评估方案(试行)》中的两个观测点——“课外科技文化活动”和“学生的创新精神与实践能力”,探讨了重庆文理学院近年来在这些观测点所做的努力.以此证明,开展课外科技文化活动是培养大学生创新能力的重要途径. 相似文献
55.
The combination of the optical diagnostics and image processing technique has produced various methods of practical measurement in engineering. The measurement of size and velocity of droplets in fuel spray is one typical example. In general, the spray is a complicated and three-dimensional two-phase flow; therefore multi-dimensional field measurement of the spray field is indispensable. In the present paper, a technique of simultaneous measurement of droplet size and three-components of velocity is proposed and applied to spray issuing from the swirl nozzle as a practical application. The focused image of glare points is captured by a stereoscopic arrangement, and droplet size and the three-components of velocity are evaluated from the doublet image. Fundamental optical arrangements to capture the image of the glare points with a stereo view are established, and the feasibility and the accuracy of the technique are confirmed. © 2004 The Optical Society of Japan 相似文献
56.
基于Karhunen-Loève变换和小波谱特征矢量量化的三维谱像数据压缩 总被引:1,自引:1,他引:0
提出了基于Karhunen Lo埁ve变换的小波谱特征矢量量化三维谱像数据压缩方法耍幔颍瑁酰睿澹?Lo埁ve变换 /小波变换 /小波谱特征矢量量化方法应用了Karhunen Lo埁ve变换的消除谱相关性优良性能 ,应用二维小波变换消除空间相关性 ,在小波变换域内应用二维集分割嵌入块编码和一维谱特征矢量量化对三维谱像数据压缩 ,获得较高的压缩性能。实验结果表明 :Karhunen Lo埁ve变换 /小波变换 /小波谱特征矢量量化编码比Karhunen Lo埁ve变换 /小波变换 /改进对块零树编码和Karhunen Lo埁ve变换 /小波变换 /快速矢量量化编码方法在同样压缩比条件下 ,峰值信噪比提高 2dB和 1dB以上 ,而速度提高了 1.5和 8倍 ,整体压缩性能有较大的提高 相似文献
57.
This paper deals with two mixed nonlinear boundary value problems depending on a parameter λ. For each of them we prove the existence of at least three generalized solutions when λ lies in an exactly determined open interval. Usefulness of this information on the interval is then emphasized by means of some consequences. Our main tool is a very recent three critical points theorem stated in [Topol. Methods Nonlinear Anal. 22 (2003) 93-104]. 相似文献
58.
Support vector machine (SVM), developed by Vapnik et al., is a new and promising technique for classification and regression and has been proved to be competitive with the best available learning machines in many applications. However, the classification speed of SVM is substantially slower than that of other techniques with similar generalization ability. A new type SVM named projected SVM (PSVM), which is a combination of feature vector selection (FVS) method and linear SVM (LSVM), is proposed in present paper. In PSVM, the FVS method is first used to select a relevant subset (feature vectors, FVs) from the training data, and then both the training data and the test data are projected into the subspace constructed by FVs, and finally linear SVM(LSVM) is applied to classify the projected data. The time required by PSVM to calculate the class of new samples is proportional to the count of FVs. In most cases, the count of FVs is smaller than that of support vectors (SVs), and therefore PSVM is faster than SVM in running. Compared with other speeding-up techniques of SVM, PSVM is proved to possess not only speeding-up ability but also de-noising ability for high-noised data, and is found to be of potential use in mechanical fault pattern recognition. 相似文献
59.
在环境中创造建筑的自我,就是以客观环境制约条件和人文环境背景为基础,探索有个性和特色的建筑形态.从“建筑环境协调、建筑文脉意象”等视角,提出了“顺应协调、对比协调、历史文脉、建筑文脉、自然文脉”等5种在环境中创造建筑特色的设计手法. 相似文献
60.
A. A. Kuznetsova V. I. Mikhailenko A. Yu. Popovskii 《Journal of Applied Spectroscopy》2004,71(5):648-653
Two types of absorption centers, one being related to monomers and the other to dimers, have been revealed by the method of statistical analysis of the normalized absorption spectra of a superthin interlayer of nitrobenzene of variable thickness formed on activated surfaces of quartz and barium fluoride and measured for different thicknesses of the interlayer. On a decrease in the interlayer thickness the concentration of dimers increases. 相似文献