全文获取类型
收费全文 | 29294篇 |
免费 | 4732篇 |
国内免费 | 3609篇 |
专业分类
化学 | 12995篇 |
晶体学 | 346篇 |
力学 | 1897篇 |
综合类 | 402篇 |
数学 | 7724篇 |
物理学 | 14271篇 |
出版年
2024年 | 62篇 |
2023年 | 285篇 |
2022年 | 596篇 |
2021年 | 681篇 |
2020年 | 862篇 |
2019年 | 804篇 |
2018年 | 765篇 |
2017年 | 868篇 |
2016年 | 1130篇 |
2015年 | 999篇 |
2014年 | 1398篇 |
2013年 | 2825篇 |
2012年 | 1555篇 |
2011年 | 1947篇 |
2010年 | 1668篇 |
2009年 | 1938篇 |
2008年 | 1985篇 |
2007年 | 1979篇 |
2006年 | 1841篇 |
2005年 | 1681篇 |
2004年 | 1397篇 |
2003年 | 1425篇 |
2002年 | 1262篇 |
2001年 | 991篇 |
2000年 | 996篇 |
1999年 | 864篇 |
1998年 | 696篇 |
1997年 | 609篇 |
1996年 | 562篇 |
1995年 | 424篇 |
1994年 | 400篇 |
1993年 | 322篇 |
1992年 | 296篇 |
1991年 | 249篇 |
1990年 | 157篇 |
1989年 | 175篇 |
1988年 | 128篇 |
1987年 | 98篇 |
1986年 | 94篇 |
1985年 | 116篇 |
1984年 | 92篇 |
1983年 | 39篇 |
1982年 | 72篇 |
1981年 | 54篇 |
1980年 | 39篇 |
1979年 | 46篇 |
1978年 | 24篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
121.
王筑娟 《数学的实践与认识》2006,36(11):217-222
讨论Dx广义正定阵的问题,给出了Dx广义正定阵的一些等价性的刻划,同时还讨论了Dx广义正定阵的若干性质. 相似文献
122.
123.
A. Shaporenko A. Terfort M. Grunze M. Zharnikov 《Journal of Electron Spectroscopy and Related Phenomena》2006
Analysis of photoemission spectra of complex thioaromatic self-assembled monolayers (SAMs) requires the knowledge and understanding of such spectra for the basic systems. Keeping this goal in mind, synchrotron-based high-resolution X-ray photoelectron spectroscopy was used to characterize SAMs formed from the simplest thioaromatic compounds, namely thiophenol, 1,1′-biphenyl-4-thiol and 1,1′;4′,1″-terphenyl-4-thiol on evaporated Au(1 1 1) and Ag(1 1 1) substrates. The acquired S 2p and C 1s spectra were analyzed in terms of fine structure and initial and final state effects in the photoemission process. The assignment of the individual spectral features was considered in detail. Conclusions on quality and chemical and structural homogeneity of the investigated SAMs were derived. 相似文献
124.
Ultrathin epitaxial Fe films on Cu(1 0 0) with perpendicular magnetization have been used as templates for the preparation of FCC Fe/Cu/Fe trilayers. The magnetic anisotropy and the coupling of these films have been studied by in-situ magneto optical Kerr effect measurements and Kerr microscopy. The magnetic coupling of both Fe layers is found to be dominated by magnetostatic interaction. Adsorbate-induced spin reorientation in the top layer also causes spin reorientation in the bottom layer. The governing role of the Fe-vacuum interface for the magnetism of the whole trilayer is demonstrated. 相似文献
125.
Let G be a graph and let Pm(G) denote the number of perfect matchings of G.We denote the path with m vertices by Pm and the Cartesian product of graphs G and H by G×H. In this paper, as the continuance of our paper [W. Yan, F. Zhang, Enumeration of perfect matchings of graphs with reflective symmetry by Pfaffians, Adv. Appl. Math. 32 (2004) 175-188], we enumerate perfect matchings in a type of Cartesian products of graphs by the Pfaffian method, which was discovered by Kasteleyn. Here are some of our results:1. Let T be a tree and let Cn denote the cycle with n vertices. Then Pm(C4×T)=∏(2+α2), where the product ranges over all eigenvalues α of T. Moreover, we prove that Pm(C4×T) is always a square or double a square.2. Let T be a tree. Then Pm(P4×T)=∏(1+3α2+α4), where the product ranges over all non-negative eigenvalues α of T.3. Let T be a tree with a perfect matching. Then Pm(P3×T)=∏(2+α2), where the product ranges over all positive eigenvalues α of T. Moreover, we prove that Pm(C4×T)=[Pm(P3×T)]2. 相似文献
126.
R. Thomas conjectured, 20 years ago, that the presence of a positive circuit in the interaction graph of a dynamical system is a necessary condition for the presence of several stable states. Recently, E. Remy et al. stated and proved the conjecture for Boolean dynamical systems. Using a similar approach, we generalize the result to discrete dynamical systems, and by focusing on the asynchronous dynamics that R. Thomas used in the course of his analysis of genetic networks, we obtain a more general variant of R. Thomas’ conjecture. In this way, we get a necessary condition for genetic networks to lead to differentiation. 相似文献
127.
关于矩阵和算子迹的一组不等式 总被引:1,自引:1,他引:0
周其生 《数学的实践与认识》2006,36(3):252-256
给出关于半正定矩阵迹和正算子迹的一组不等式,得到与邱贤忠关于实数的不等式的类似结果. 相似文献
128.
We study the four-directional traffic flow on a two-dimensional lattice. In the case of discrete densities, we assume equal number of vehicles in each lane. Except for the minimum density, the gridlock emerges swiftly. Two kinds of gridlock have been observed. The global gridlock dominates the system when the density is twice the minimum value. At higher densities, the system is pervaded by local gridlocks. We also analyze the time evolution of average speed. In the case of continuous densities, the vehicle numbers vary from lane to lane. The global gridlock is then destroyed by the fluctuations; while the local gridlock can still be observed. 相似文献
129.
Andreas Lüttge 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):248-259
The dependence of dissolution rates on the difference of Gibbs free energy is of critical importance for our understanding of crystal dissolution, reactive flow models and their applications to a variety of environmentally related problems. Here, we review experimental data generated with mineral powders and single crystals to develop a better understanding of apparent inconsistencies between otherwise internally consistent data sets. Additional information from direct surface observations and measurements with vertical scanning interferometry (VSI) and atomic force microscopy (AFM) of albite dissolution at 25, 150 and 185 °C may shed new light on this old but unsolved question. Our discussion is based on the importance of etch pit development, its ΔG dependence, and the pits’ role as a source for steps and step movement in the dissolution process. Results indicate that reaction history may be of critical importance in determining the overall reaction mechanism and its rate. Different rates are observed for systems having otherwise identical ΔGr acquired from increasing versus decreasing disequilibrium positions.
In this context, we finally discuss the validity of the common application of transition state theory (TST) to elementary and overall reactions governing the dissolution process. In this discussion of crystal dissolution, we contrast TST applications with a stochastic, many-body treatment that has led to the development of a stepwave model. This discussion also focuses on the controversy caused by the rivalry between surface adsorption models and a probabilistic model that seeks to incorporate the full three-dimensional crystal structure. 相似文献
130.
q变形对相干态的相位概率分布特性 总被引:2,自引:0,他引:2
通过推广Pegg和Barnett的相位算符和相位态到q变形的双模情况, 应用数值计算
研究了q变形对相干态的相位概率分布特性. 结果表明, q变形对相干态的相位概率分布受到相位参数、q参数和参数│ξ│的调节, 从而反映出不同的量子相干特性. 相似文献