全文获取类型
收费全文 | 9164篇 |
免费 | 865篇 |
国内免费 | 783篇 |
专业分类
化学 | 3408篇 |
晶体学 | 69篇 |
力学 | 2835篇 |
综合类 | 95篇 |
数学 | 2465篇 |
物理学 | 1940篇 |
出版年
2024年 | 14篇 |
2023年 | 99篇 |
2022年 | 154篇 |
2021年 | 172篇 |
2020年 | 227篇 |
2019年 | 200篇 |
2018年 | 209篇 |
2017年 | 285篇 |
2016年 | 307篇 |
2015年 | 258篇 |
2014年 | 392篇 |
2013年 | 648篇 |
2012年 | 489篇 |
2011年 | 543篇 |
2010年 | 432篇 |
2009年 | 533篇 |
2008年 | 487篇 |
2007年 | 509篇 |
2006年 | 445篇 |
2005年 | 508篇 |
2004年 | 417篇 |
2003年 | 403篇 |
2002年 | 360篇 |
2001年 | 284篇 |
2000年 | 264篇 |
1999年 | 253篇 |
1998年 | 220篇 |
1997年 | 226篇 |
1996年 | 154篇 |
1995年 | 183篇 |
1994年 | 145篇 |
1993年 | 125篇 |
1992年 | 94篇 |
1991年 | 108篇 |
1990年 | 80篇 |
1989年 | 60篇 |
1988年 | 85篇 |
1987年 | 74篇 |
1986年 | 78篇 |
1985年 | 56篇 |
1984年 | 43篇 |
1983年 | 18篇 |
1982年 | 57篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献
52.
S.V. Astashkin F.A. Sukochev 《Journal of Mathematical Analysis and Applications》2007,336(2):1231-1258
We catalogue all Marcinkiewicz function and sequence spaces with the Banach-Saks property and present necessary and sufficient conditions for a wide subclass of spaces to possess the p-Banach-Saks property, 1<p<∞. We apply our results to several open problems. 相似文献
53.
平衡规划问题的熵函数方法及其在混合交通流中的应用 总被引:1,自引:0,他引:1
将参变极值问题的极大熵函数方法应用到求解平衡规划问题中,通过先验分布信息和Kullback熵概念,给出了平衡规划问题基于Kullback熵表示的熵函数求解方法,并将平衡规划的极大熵函数方法应用于求解混合交通平衡分配问题. 相似文献
54.
In this paper we study higher Chow groups of smooth, projective surfaces over a field k of characteristic zero, using some new Hodge theoretic methods which we develop for this purpose. In particular we investigate the subgroup of CH
r+1 (X,r) with r = 1,2 consisting of cycles that are supported over a normal crossing divisor Z on X. In this case, the Hodge theory of the complement forms an interesting variation of mixed Hodge structures in any geometric deformation of the situation. Our main result is a structure theorem in the case where X is a very general hypersurface of degree d in projective 3-space for d sufficiently large and Z is a union of very general hypersurface sections of X. In this case we show that the subgroup of CH
r+1 (X,r) we consider is generated by obvious cycles only arising from rational functions on X with poles along Z. This can be seen as a generalization of the Noether–Lefschetz theorem for r = 0. In the case r = 1 there is a similar generalization by Müller-Stach, but our result is more precise than it, since it is geometric and not only cohomological. The case r = 2 is entirely new and original in this paper. For small d, we construct some explicit examples for r = 1 and 2 where the corresponding higher Chow groups are indecomposable, i.e. not the image of certain products of lower order groups. In an appendix Alberto Collino constructs even more indecomposable examples in CH
3 (X,2) which move in a one-dimensional family on the surface X.Contribution to appendix. 相似文献
55.
56.
A. V. Kravtsov 《Computational Mathematics and Mathematical Physics》2007,47(11):1875-1884
A linear problem of parametric oscillations of a low-viscous two-layer fluid in a closed vessel partially filled with a porous medium is studied. An asymptotic solution is constructed on the basis of combined application of boundary functions and averaging methods. Approximate formulas for boundaries of instability domains in the case of subharmonic and harmonic resonances are derived. 相似文献
57.
Chang-jian Zhao 《中国科学A辑(英文版)》2007,50(9):1347-1360
In this paper, we first introduce a concept of L
p
-dual Quermassintegral sum function of convex bodies and establish the polar projection Minkowski inequality and the polar
projection Aleksandrov-Fenchel inequality for L
p
-dual Quermassintegral sums. Moreover, by using Lutwak’s width-integral of index i, we establish the L
p
-Brunn-Minkowski inequality for the polar mixed projection bodies. As applications, we prove some interrelated results.
This work was partially supported by the National Natural Science Foundation of China (Grant No. 10271071), Zhejiang Provincial
Natural Science Foundation of China (Grant No. Y605065) and Foundation of the Education Department of Zhejiang Province of
China (Grant No. 20050392) 相似文献
58.
Bianchi type-III magnetized cosmological model when the field of gravitation is governed by either a perfect fluid or cosmic
string is investigated in Rosen’s [1] bimetric theory of gravitation. To complete determinate solution, the condition, viz.,
A=(BC)
n
, where n is a constant, between the metric potentials is used. We have assumed different equations of state for cosmic string [2]
for the complete solution of the model. Some physical and geometrical properties of the exhibited model are discussed and
studied. 相似文献
59.
用核磁共振对非晶态中B3+离子的微观结构进行了测定,结合Raman光谱的研究,对Li2O-B2O3-P2O5系统非晶态的性能(电导率、密度等)在P2O5/B2O3比约等于1时产生极值的原因从理论上作了阐明。 相似文献
60.
Analytical approach is presented to the isoperimetric type problems of finding convex figures separated by current hyperplanes. 相似文献