全文获取类型
收费全文 | 177830篇 |
免费 | 16970篇 |
国内免费 | 12306篇 |
专业分类
化学 | 95151篇 |
晶体学 | 1860篇 |
力学 | 12111篇 |
综合类 | 679篇 |
数学 | 43577篇 |
物理学 | 53728篇 |
出版年
2024年 | 353篇 |
2023年 | 2074篇 |
2022年 | 3712篇 |
2021年 | 3989篇 |
2020年 | 4223篇 |
2019年 | 4015篇 |
2018年 | 13275篇 |
2017年 | 12803篇 |
2016年 | 10610篇 |
2015年 | 5764篇 |
2014年 | 6379篇 |
2013年 | 8143篇 |
2012年 | 12920篇 |
2011年 | 19430篇 |
2010年 | 11988篇 |
2009年 | 12021篇 |
2008年 | 12961篇 |
2007年 | 14288篇 |
2006年 | 5806篇 |
2005年 | 5941篇 |
2004年 | 5126篇 |
2003年 | 4836篇 |
2002年 | 3635篇 |
2001年 | 2476篇 |
2000年 | 2241篇 |
1999年 | 2217篇 |
1998年 | 1938篇 |
1997年 | 1708篇 |
1996年 | 1761篇 |
1995年 | 1485篇 |
1994年 | 1315篇 |
1993年 | 1095篇 |
1992年 | 953篇 |
1991年 | 841篇 |
1990年 | 703篇 |
1989年 | 560篇 |
1988年 | 436篇 |
1987年 | 395篇 |
1986年 | 392篇 |
1985年 | 308篇 |
1984年 | 231篇 |
1983年 | 189篇 |
1982年 | 167篇 |
1981年 | 116篇 |
1980年 | 105篇 |
1979年 | 70篇 |
1978年 | 56篇 |
1973年 | 42篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
本文讨论了每个元都有幂等元作为右单位元的左消半群与幂单半群N的Schuzenberger积M◇N的ρ类,证明了这种半群M与N的Schuzenberger积M◇N的ρ类是右E一半适合半群和弱E-headged半群. 相似文献
12.
Chris Hope 《The Journal of the Operational Research Society》2003,54(11):1167-1176
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points. 相似文献
13.
14.
Dominique Fourdrinier William E. Strawderman 《Annals of the Institute of Statistical Mathematics》2003,55(4):803-816
We consider estimation of loss for generalized Bayes or pseudo-Bayes estimators of a multivariate normal mean vector, θ. In
3 and higher dimensions, the MLEX is UMVUE and minimax but is inadmissible. It is dominated by the James-Stein estimator and by many others. Johnstone (1988,
On inadmissibility of some unbiased estimates of loss,Statistical Decision Theory and Related Topics, IV (eds. S. S. Gupta and J. O. Berger), Vol. 1, 361–379, Springer, New York) considered the estimation of loss for the usual
estimatorX and the James-Stein estimator. He found improvements over the Stein unbiased estimator of risk. In this paper, for a generalized
Bayes point estimator of θ, we compare generalized Bayes estimators to unbiased estimators of loss. We find, somewhat surprisingly,
that the unbiased estimator often dominates the corresponding generalized Bayes estimator of loss for priors which give minimax
estimators in the original point estimation problem. In particular, we give a class of priors for which the generalized Bayes
estimator of θ is admissible and minimax but for which the unbiased estimator of loss dominates the generalized Bayes estimator
of loss. We also give a general inadmissibility result for a generalized Bayes estimator of loss.
Research supported by NSF Grant DMS-97-04524. 相似文献
15.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
16.
Liuman Ou Guilie Luo Yiping Li 《Journal of Mathematical Analysis and Applications》2003,283(2):534-548
In this paper, we consider an autonomous predator-prey Lotka-Volterra system in which individuals in the population may belong to one of two classes: the immatures and the matures, the age to maturity is represented by a time delay. By using eigenvalue analysis, principal term analyze method, reduction to absurdity, and iterative method, we obtain some simple conditions for global asymptotic stability of the unique positive equilibrium point. Moreover, a condition that the prey population in the system get extinction and the predator population in the system get permanence will be obtained. Meanwhile the theorems extend the corresponding conclusions in which there have no two stage structures. 相似文献
17.
Florin Ambro 《manuscripta mathematica》2003,111(1):43-49
We prove a precise inversion of adjunction formula for the log variety (ℂ
d
+1,X), where X is a non-degenerate hypersurface. As a corollary, the minimal log discrepancies of non-degenerate normal hypersurface singularities
are bounded by dimension.
Received: 17 September 2002 / Revised version: 22 November 2002
Published online: 14 February 2003
Current address: DPMMS, CMS, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, England. e-mail: f.ambro@dpmms.cam.ac.uk
Mathematics Subject Classification (2000): Primary 14B05; Secondary 14M25, 52B20 相似文献
18.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
19.
20.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献