全文获取类型
收费全文 | 30423篇 |
免费 | 3021篇 |
国内免费 | 3368篇 |
专业分类
化学 | 6893篇 |
晶体学 | 121篇 |
力学 | 1574篇 |
综合类 | 658篇 |
数学 | 19705篇 |
物理学 | 7861篇 |
出版年
2024年 | 30篇 |
2023年 | 283篇 |
2022年 | 504篇 |
2021年 | 686篇 |
2020年 | 662篇 |
2019年 | 744篇 |
2018年 | 721篇 |
2017年 | 866篇 |
2016年 | 834篇 |
2015年 | 703篇 |
2014年 | 1344篇 |
2013年 | 2458篇 |
2012年 | 1300篇 |
2011年 | 1684篇 |
2010年 | 1487篇 |
2009年 | 1912篇 |
2008年 | 2133篇 |
2007年 | 2212篇 |
2006年 | 1870篇 |
2005年 | 1737篇 |
2004年 | 1408篇 |
2003年 | 1484篇 |
2002年 | 1337篇 |
2001年 | 1045篇 |
2000年 | 1085篇 |
1999年 | 1003篇 |
1998年 | 959篇 |
1997年 | 772篇 |
1996年 | 580篇 |
1995年 | 404篇 |
1994年 | 430篇 |
1993年 | 271篇 |
1992年 | 243篇 |
1991年 | 197篇 |
1990年 | 155篇 |
1989年 | 147篇 |
1988年 | 140篇 |
1987年 | 120篇 |
1986年 | 85篇 |
1985年 | 148篇 |
1984年 | 99篇 |
1983年 | 61篇 |
1982年 | 92篇 |
1981年 | 55篇 |
1980年 | 50篇 |
1979年 | 54篇 |
1978年 | 56篇 |
1977年 | 41篇 |
1976年 | 31篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
János B. Czirok Ákos Tarcsay Pál D. Mezei András Simon László Balázs 《Supramolecular chemistry》2013,25(10-12):722-728
The size limit of substituents allowing O-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R1 on the conformational inversion was investigated by means of 1H NMR. The rotational isomerisation of the parent (R1 = H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies. 相似文献
993.
《代数通讯》2013,41(7):3519-3527
Abstract Let G and A be finite groups such that (|G|, |A|) = 1. Let K be an algebraically closed field with Char K = 0. Denote by K α G the twisted group algebra of G over K with factor set α. In this paper we prove that if A acts homogeneously on K α G, then there exists an action of A on G, and there is a one-to-one correspondence between the set of A-invariant irreducible K α G-modules and the set of irreducible K α C G (A)-modules. 相似文献
994.
Shui FENG 《Frontiers of Mathematics in China》2021,16(2):381
Residual allocation models (RAMs) arise in many subjects including Bayesian statistics, combinatorics, ecology, finance, information theory, machine learning, and population genetics. In this paper, we give a brief review of RAM and presents a few examples where the model arises. An extended discussion will focus a concrete model, the GEM distribution, and its ordered analogue, the Poisson-Dirichlet distribution. The paper concludes with a discussion of the GEM process. 相似文献
995.
《Journal of Macromolecular Science: Physics》2013,52(4-6):1091-1104
The influence of cooling rate from the melt on the polymorphism and crystallinity is investigated as a function of isotacticity and stereo-defect distribution in polypropylenes. Detailed analysis of wide angle x-ray diffraction patterns shows that crystallinity in the materials used is nearly independent of the experimental cooling rates (0.5–40°C/min). At high cooling rates, the materials exist mainly in the α-phase, whereas the amount of the γ-phase increases at the lower cooling rates. With an increasing amount of stereo-defects, this cooling-rate dependence of the polymorphism is enhanced. The effect of different stereo-defect distributions, as observed in metallocene-(random) and Ziegler–Natta (blocklike) derived isotactic polypropylenes, was investigated. The formation of the γ-phase is more prevalent in materials with a random defect distribution compared to the materials in which the stereo-defects have a blocklike distribution. The crystallinity decreases more rapidly as a function of the tacticity in the random defect-distributed materials. 相似文献
996.
In this paper, we construct a new class of finite groups whose common divisor graphs are complete graphs, while there is no prime dividing all the nontrivial degrees. 相似文献
997.
In this paper, for a kind of risk models with heavy-tailed and delayed claims, we derive the asymptotics of the infinite-time ruin probability and the uniform asymptotics of the finite-time ruin probability. The numerical simulation results are also presented. The results of theoretical analysis and numerical simulation
show that the influence of the delay for the claim payment is nearly negligible to the ruin probability when the initial capital and running-time are all large. 相似文献
998.
We develop a methodology for the estimation of extreme loss event probability and the value at risk, which takes into account both the magnitudes and the intensity of the extreme losses. Specifically, the extreme loss magnitudes are modeled with a generalized Pareto distribution, whereas their intensity is captured by an autoregressive conditional duration model, a type of self‐exciting point process. This allows for an explicit interaction between the magnitude of the past losses and the intensity of future extreme losses. The intensity is further used in the estimation of extreme loss event probability. The method is illustrated and backtested on 10 assets and compared with the established and baseline methods. The results show that our method outperforms the baseline methods, competes with an established method, and provides additional insight and interpretation into the prediction of extreme loss event probability. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
999.
We introduce the concept of a pentagonal geometry as a generalization of the pentagon and the Desargues configuration, in the same vein that the generalized polygons share the fundamental properties of ordinary polygons. In short, a pentagonal geometry is a regular partial linear space in which for all points x, the points not collinear with the point x, form a line. We compute bounds on their parameters, give some constructions, obtain some nonexistence results for seemingly feasible parameters and suggest a cryptographic application related to identifying codes of partial linear spaces. 相似文献
1000.
The present paper proposes an evolutionary credibility model that describes the joint dynamics of mortality through time in several populations. Instead of modeling the mortality rate levels, the time series of population-specific mortality rate changes, or mortality improvement rates are considered and expressed in terms of correlated time factors, up to an error term. Dynamic random effects ensure the necessary smoothing across time, as well as the learning effect. They also serve to stabilize successive mortality projection outputs, avoiding dramatic changes from one year to the next. Statistical inference is based on maximum likelihood, properly recognizing the random, hidden nature of underlying time factors. Empirical illustrations demonstrate the practical interest of the approach proposed in the present paper. 相似文献