首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   34069篇
  免费   331篇
  国内免费   302篇
化学   13741篇
晶体学   282篇
力学   1576篇
综合类   12篇
数学   10065篇
物理学   9026篇
  2023年   57篇
  2022年   139篇
  2021年   199篇
  2020年   171篇
  2019年   162篇
  2018年   1307篇
  2017年   1549篇
  2016年   934篇
  2015年   759篇
  2014年   691篇
  2013年   952篇
  2012年   3479篇
  2011年   2718篇
  2010年   2035篇
  2009年   1752篇
  2008年   892篇
  2007年   909篇
  2006年   877篇
  2005年   4684篇
  2004年   4108篇
  2003年   2445篇
  2002年   652篇
  2001年   351篇
  2000年   132篇
  1999年   230篇
  1998年   158篇
  1997年   131篇
  1996年   92篇
  1995年   86篇
  1994年   88篇
  1993年   53篇
  1992年   194篇
  1991年   180篇
  1990年   158篇
  1989年   126篇
  1988年   120篇
  1987年   82篇
  1986年   61篇
  1985年   61篇
  1984年   50篇
  1983年   39篇
  1982年   41篇
  1979年   43篇
  1978年   40篇
  1976年   85篇
  1975年   42篇
  1974年   46篇
  1973年   55篇
  1972年   44篇
  1966年   37篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
992.
To bridge the gap between laboratory-scale studies and commercial applications, mass production of high quality graphene is essential. A scalable exfoliation strategy towards the production of graphene sheets is presented that has excellent yield (ca. 75 %, 1–3 layers), low defect density (a C/O ratio of 21.2), great solution-processability, and outstanding electronic properties (a hole mobility of 430 cm2 V−1 s−1). By applying alternating currents, dual exfoliation at both graphite electrodes enables a high production rate exceeding 20 g h−1 in laboratory tests. As a cathode material for lithium storage, graphene-wrapped LiFePO4 particles deliver a high capacity of 167 mAh g−1 at 1 C rate after 500 cycles.  相似文献   
993.
994.
We consider an almost Hermitian manifold and apply the conformal change of metric to its holomorphic curvature tensor. In such a way we find that the generalized Bochner curvature tensor can be expressed as a linear combination of B 1, B 2, and B 3 such that (6.4) holds. Each of the tensors B 1, B 2, B 3 is conformally invariant and satisfies the condition (1.2) of K?hler type.  相似文献   
995.
Phase shifts and resonance parameters can be obtained from finite-volume lattice spectra for interacting pairs of particles, moving with non-zero total momentum. We present a simple derivation of the method that is subsequently applied to obtain the ?Ц? and ??K phase shifts in the sectors with total isospin I = 0 and I = 1/2 , respectively. Considering different total momenta, one obtains extra data points for a given volume that allow for a very efficient extraction of the resonance parameters in the infinite-volume limit. Corrections due to the mixing of partial waves are provided. We expect that our results will help to optimize the strategies in lattice simulations, which aim at an accurate determination of the scattering and resonance properties.  相似文献   
996.
997.
998.
Thermodynamic integration (TI) for computing marginal likelihoods is based on an inverse annealing path from the prior to the posterior distribution. In many cases, the resulting estimator suffers from high variability, which particularly stems from the prior regime. When comparing complex models with differences in a comparatively small number of parameters, intrinsic errors from sampling fluctuations may outweigh the differences in the log marginal likelihood estimates. In the present article, we propose a TI scheme that directly targets the log Bayes factor. The method is based on a modified annealing path between the posterior distributions of the two models compared, which systematically avoids the high variance prior regime. We combine this scheme with the concept of non-equilibrium TI to minimise discretisation errors from numerical integration. Results obtained on Bayesian regression models applied to standard benchmark data, and a complex hierarchical model applied to biopathway inference, demonstrate a significant reduction in estimator variance over state-of-the-art TI methods.  相似文献   
999.
1000.
Donor–acceptor Stenhouse adducts (DASAs) are playing an outstanding role as innovative and versatile photoswitches. Until now, all the efforts have been spent on modifying the donor and acceptor moieties to modulate the absorption energy and improve the cyclization and reversion kinetics. However, there is a strong dependence on specific structural modifications and a lack of predictive behavior, mostly owing to the complex photoswitching mechanism. Here, by means of a combined experimental and theoretical study, the effect of chemical modification of the π-bridge linking the donor and acceptor moieties is systematically explored, revealing the significant impact on the absorption, photocyclization, and relative stability of the open form. In particular, a position along the π-bridge is found to be the most suited to redshift the absorption while preserving the cyclization. However, thermal back-reaction to the initial isomer is blocked. These effects are explained in terms of an increased acceptor capability offered by the π-bridge substituent that can be modulated. This strategy opens the path toward derivatives with infra-red absorption and a potential anchoring point for further functionalization.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号