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   2070篇
  免费   107篇
  国内免费   17篇
化学   1588篇
晶体学   12篇
力学   31篇
综合类   16篇
数学   235篇
物理学   312篇
  2023年   18篇
  2022年   11篇
  2021年   36篇
  2020年   44篇
  2019年   52篇
  2018年   36篇
  2017年   25篇
  2016年   54篇
  2015年   52篇
  2014年   54篇
  2013年   115篇
  2012年   148篇
  2011年   146篇
  2010年   77篇
  2009年   92篇
  2008年   159篇
  2007年   136篇
  2006年   134篇
  2005年   135篇
  2004年   114篇
  2003年   85篇
  2002年   91篇
  2001年   25篇
  2000年   29篇
  1999年   23篇
  1998年   25篇
  1997年   22篇
  1996年   18篇
  1995年   11篇
  1994年   12篇
  1993年   10篇
  1992年   9篇
  1991年   4篇
  1990年   15篇
  1989年   11篇
  1988年   10篇
  1987年   9篇
  1986年   6篇
  1985年   22篇
  1984年   17篇
  1983年   13篇
  1982年   13篇
  1981年   16篇
  1980年   15篇
  1979年   9篇
  1978年   5篇
  1977年   8篇
  1976年   6篇
  1975年   4篇
  1974年   5篇
排序方式: 共有2194条查询结果,搜索用时 109 毫秒
961.
A new molecule-based magnetic material [Mn2(Saloph)2(μ-OH)][Ni(bdt)2](CH3CN)2 was prepared by the metathesis of [Mn(Saloph)(H2O)(ClO4)] (S = 2) and TBA[Ni(bdt)2] (S = 1/2). In the crystal, [Ni(bdt)2]? anions form square lattices which are separated from each other by the layers of antiferromagnetically coupled binuclear cations [Mn2(Saloph)2(μ-OH)]+. The magnetic susceptibility of the material coincides with the sum of the S = 2 van Vleck dimer model and S = 1/2 Heisenberg ferromagnetic square lattice model with 2J = ?92.4 and +4.5 K, respectively. The origin of the ferromagnetic interaction can be explained by the T-shaped intermolecular overlap mode of SOMOs which spreads to the ends of [Ni(bdt)2]? molecules.  相似文献   
962.
Polyethersulfone membranes are widely used for ultrafiltration and microfiltration especially in the dairy industry, but they are believed to degrade when exposed to the sodium hypochlorite solution that is used to sanitize the processing equipment. Such membranes were exposed to sodium hypochlorite for up to 25,000 ppm-day at 55 °C, and pH 9 and 12. Mechanical properties as measured by dynamic mechanical analysis and tensile strength did not change greatly, but surface properties measured by FTIR-ATR, field emission scanning electron microscopy and associated energy dispersive X-ray spectroscopy detected significant changes in the surface. Surface pitting was observed and was found to be most severe at pH 9. It was thought that pitting was the likely cause of degradation in performance of the membranes and that pits could act as stress raisers leading to cracking.  相似文献   
963.
A thermal neutron-sensitive liposome has been developed focusing on irradiation site-specific-controlled release of a medicine. We recommended a 10B-borocaptate dimer as a detonator of liposome in expectation of effects of low-energy heavy ions produced by 10B(n, α)7Li reaction. As a result, an X-ray-sensitive liposome incorporating the detonator was vulnerable enough to release an anticancer agent, carboplatin, at a dose/dose–rate near clinical use. These results reveal, moreover, that the liposomes are also applicable to a heavy-ion beam.  相似文献   
964.
Journal of Statistical Physics - The emergence of deterministic and irreversible macroscopic behavior from deterministic and reversible microscopic dynamics is understood as a result of the law of...  相似文献   
965.
966.
967.
968.
Numerical Algorithms - We construct approximate Fekete point sets for kernel-based interpolation by maximising the determinant of a kernel Gram matrix obtained via truncation of an orthonormal...  相似文献   
969.
We consider solving large sparse symmetric singular linear systems. We first introduce an algorithm for right preconditioned minimum residual (MINRES) and prove that its iterates converge to the preconditioner weighted least squares solution without breakdown for an arbitrary right‐hand‐side vector and an arbitrary initial vector even if the linear system is singular and inconsistent. For the special case when the system is consistent, we prove that the iterates converge to a min‐norm solution with respect to the preconditioner if the initial vector is in the range space of the right preconditioned coefficient matrix. Furthermore, we propose a right preconditioned MINRES using symmetric successive over‐relaxation (SSOR) with Eisenstat's trick. Some numerical experiments on semidefinite systems in electromagnetic analysis and so forth indicate that the method is efficient and robust. Finally, we show that the residual norm can be further reduced by restarting the iterations.  相似文献   
970.
Inclusion compounds of a dipeptide, (S)-threonyl-(S)-phenylglycine (Thr-Phg), with several aliphatic alcohols were easily prepared by grinding them in a mortar. Thr-Phg molecules arranged in antiparallel to construct a sheet, and guest alcohols were accommodated in a chiral pocket between the sheets. 3-Butyn-2-ol and 2-butanol were included with moderate enantioselectivity, 57% ee (R) and 49% ee (R), respectively. The role of the hydroxy group of Thr-Phg is not only to construct the unique pocket but also to capture guest alcohols by hydrogen bonding.  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