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   15194篇
  免费   2526篇
  国内免费   1670篇
化学   11271篇
晶体学   193篇
力学   813篇
综合类   73篇
数学   1537篇
物理学   5503篇
  2024年   16篇
  2023年   309篇
  2022年   323篇
  2021年   482篇
  2020年   627篇
  2019年   622篇
  2018年   560篇
  2017年   495篇
  2016年   717篇
  2015年   746篇
  2014年   943篇
  2013年   1185篇
  2012年   1382篇
  2011年   1480篇
  2010年   1061篇
  2009年   906篇
  2008年   1045篇
  2007年   951篇
  2006年   839篇
  2005年   727篇
  2004年   543篇
  2003年   457篇
  2002年   427篇
  2001年   305篇
  2000年   301篇
  1999年   236篇
  1998年   218篇
  1997年   191篇
  1996年   171篇
  1995年   143篇
  1994年   184篇
  1993年   126篇
  1992年   125篇
  1991年   96篇
  1990年   90篇
  1989年   84篇
  1988年   44篇
  1987年   31篇
  1986年   34篇
  1985年   29篇
  1984年   22篇
  1983年   11篇
  1982年   15篇
  1981年   7篇
  1980年   17篇
  1976年   10篇
  1975年   7篇
  1974年   8篇
  1973年   7篇
  1967年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A theoretical investigation of the H2O + HCNO reaction, which is carried out by means of CCSD(T)/6‐311G(d,p)//B3LYP/6‐311G(d,p)+ZPVE computational method to determine a set of reasonable pathways, there are seven product pathways, P i with i = 1 , 2 , …, 7 are involved. It is shown that P 1 (H2O + NCOH), P 2 (CO + NH2 + OH), P 4 (HCN + HO2 + H), and P 6 (CO + NH2OH) are the major product channels; and P 7 (HOC + H2 + NO) is the minor product channels, whereas the other channels for P 3 (HNO + HCOH) and P 5 (HNO + H2CO) are very minor, the minor product channels. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011  相似文献   
992.
A series of novel pyrazole amides J1 , J2 , J3 , J4 , J5 , J6 , J7 , J8 , J9 , J10 , J11 , J12 , J13 , J14 , J15 containing an α‐aminophosphonate moiety were synthesized and subsequently characterized by spectral (IR, 1H‐, 13C‐, 31P‐, and 19F‐NMR) data and elemental analysis. The racemic sample of J1 was further separated into its enantiomers under normal‐phase condition on two immobilized polysaccharide‐based chiral stationary phases (Chiralpak IA and Chiralpak IC). The synthesized compounds revealed certain degree of antiviral activity in the bioassay. The title compounds ( J3 , J10 , and J12 ) showed some curative activities (39.9%, 41.8%, 50.1%, respectively) against tobacco mosaic virus at 0.5 mg/mL. J. Heterocyclic Chem., 00 , 00 (2011).  相似文献   
993.
994.
1 引 言 对于一阶常微分方程 y'=f(t,y).(1) 的数值解法,目前常用的主要有两类方法:单步法和线性多步法(Linear Multistep Methods,LMM).  相似文献   
995.
Ir(ppy)2(VPHD) (ppy=2-phenyl pyridine, VPHD=6-(4-vinylphenyl)-2,4-hexanedione) was copolymerized with methyl methacrylate (MMA). The copolymer had high quantum yield of 52.3±0.5% in dilute ethyl acetate solution, and the yield increased around 45% than that of the iridium monomer. The maximum emission peaks for the copolymers shifted from 515 to 489 nm while the iridium complex content was less than 0.005 mol% in the feed. The blue emission at 489 nm and the green emission at 520 nm were analyzed by Lorenz function. They are attributed to 1MLCT and 3MLCT emissions, respectively.  相似文献   
996.
An oxidative rearrangement of cyclic tertiary a-hydroxy allylsilanes has been carried out in refluxing ClCH2CH2Cl with pyridinium chlorochromate(PCC).The reaction provides a convenient method to synthesize cyclicβ-silylenones in modest to excellent yields.  相似文献   
997.
998.
999.
Consider a risk model with two correlated classes of insurance business and a constant force of interest. We assume that the correlation comes from a common shock and that the claim-size distribution is heavy-tailed. Under this setting, we investigate the tail behavior of the sum of the two correlated classes of discounted aggregate claims. We obtain the uniform asymptotic formulas for some subclass of subexponential distributions.  相似文献   
1000.
A series of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole‐based polymers such as poly[1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole] ( PTPT ), poly[1,4‐(2,5‐bis(octyloxy)phenylene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PPTPT ), and poly[2,5‐(3‐octylthiophene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PTTPT ) were synthesized and characterized. The new polymers were readily soluble in common organic solvents and the thermogravimetric analysis showed that the three polymers are thermally stable with the 5% degradation temperature >379 °C. The absorption maxima of the polymers were 478, 483, and 485 nm in thin film and the optical band gaps calculated from the onset wavelength of the optical absorption were 2.15, 2.20, and 2.13 eV, respectively. Each of the polymers was investigated as an electron donor blending with PC70BM as an electron acceptor in bulk heterojunction (BHJ) solar cells. BHJ solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC70BM/TiOx/Al configurations. The BHJ solar cell with PPTPT :PC70BM (1:5 wt %) showed the power conversion efficiency (PCE) of 1.35% (Jsc = 7.41 mA/cm2, Voc = 0.56 V, FF = 33%), measured using AM 1.5G solar simulator at 100 mW/cm2 light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010  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