全文获取类型
收费全文 | 88341篇 |
免费 | 6970篇 |
国内免费 | 8560篇 |
专业分类
化学 | 29606篇 |
晶体学 | 455篇 |
力学 | 7860篇 |
综合类 | 1726篇 |
数学 | 38315篇 |
物理学 | 25909篇 |
出版年
2023年 | 704篇 |
2022年 | 1309篇 |
2021年 | 1557篇 |
2020年 | 1692篇 |
2019年 | 1994篇 |
2018年 | 1750篇 |
2017年 | 2086篇 |
2016年 | 2372篇 |
2015年 | 2010篇 |
2014年 | 3217篇 |
2013年 | 5814篇 |
2012年 | 3585篇 |
2011年 | 4312篇 |
2010年 | 3801篇 |
2009年 | 5276篇 |
2008年 | 5635篇 |
2007年 | 5887篇 |
2006年 | 5329篇 |
2005年 | 4629篇 |
2004年 | 4170篇 |
2003年 | 4127篇 |
2002年 | 3786篇 |
2001年 | 3132篇 |
2000年 | 3070篇 |
1999年 | 2768篇 |
1998年 | 2597篇 |
1997年 | 2111篇 |
1996年 | 1856篇 |
1995年 | 1619篇 |
1994年 | 1474篇 |
1993年 | 1255篇 |
1992年 | 1224篇 |
1991年 | 931篇 |
1990年 | 755篇 |
1989年 | 667篇 |
1988年 | 612篇 |
1987年 | 473篇 |
1986年 | 396篇 |
1985年 | 478篇 |
1984年 | 474篇 |
1983年 | 233篇 |
1982年 | 393篇 |
1981年 | 430篇 |
1980年 | 335篇 |
1979年 | 336篇 |
1978年 | 249篇 |
1977年 | 221篇 |
1976年 | 174篇 |
1974年 | 118篇 |
1973年 | 118篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
31.
32.
分析学生对二氧化碳的3个典型学科认知障碍,以“二氧化碳的捕捉”为情境,通过“尝试捕捉二氧化碳”“谁在捕捉二氧化碳”“捕捉背后的原理”等3个主要环节,实现对学科认知障碍的突破,展示了一种新的中考复习教学思路。 相似文献
33.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but ) nonlinearities. 相似文献
34.
35.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming. 相似文献
36.
37.
38.
《Physics letters. A》2020,384(35):126904
Exploring the evolution of cooperation has been one of the most challenging topics and attracted increasing attention in various realms. Hereby, we institute an analytic model where the relationship between the common benefits and contributions is the typical saturation nonlinearity. We investigate the evolutionary dynamics of cooperation with and without consensual incentives respectively. The population always evolves to full defection when the incentives are absent. Cooperation, however, can be promoted by consensual incentives when the degree of cooperators' preferences for incentives is great. There exists an intermediate amount of resources at which the positive effect of consensual incentives on cooperation is minimized. Furthermore, there is a U-shape relationship between the degree of cooperators' preference for an incentive and the evolution of cooperation. A greater basin of full cooperation can be induced when the cooperators' preference for reward is more pronounced than that for punishment. 相似文献
39.
Norbornene derivatives from a metal‐free,strain‐promoted cycloaddition reaction: New building blocks for ring‐opening metathesis polymerization reactions 下载免费PDF全文
Christopher E. Hobbs Binhong Lin Thomas Malinski 《Journal of polymer science. Part A, Polymer chemistry》2015,53(20):2357-2362
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362 相似文献
40.
采用DIS数字信息化系统,对不同浓度的蓝墨水溶液在激光光源照射下的透射平均照度及照度分布图像进行实验研究,得到了平均照度值随溶液浓度变化的规律。对不同颜色塑料膜片对白炽灯光源透过照度值及照度分布图像进行实验研究得到及其相关之规律。 相似文献