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   987篇
  免费   24篇
  国内免费   4篇
化学   745篇
晶体学   15篇
力学   7篇
数学   28篇
物理学   220篇
  2023年   4篇
  2022年   9篇
  2021年   19篇
  2020年   20篇
  2019年   20篇
  2018年   11篇
  2017年   9篇
  2016年   19篇
  2015年   20篇
  2014年   20篇
  2013年   41篇
  2012年   50篇
  2011年   51篇
  2010年   40篇
  2009年   24篇
  2008年   60篇
  2007年   66篇
  2006年   67篇
  2005年   55篇
  2004年   55篇
  2003年   41篇
  2002年   30篇
  2001年   20篇
  2000年   24篇
  1999年   15篇
  1998年   14篇
  1997年   15篇
  1996年   10篇
  1995年   6篇
  1994年   10篇
  1993年   9篇
  1992年   19篇
  1991年   9篇
  1990年   8篇
  1989年   7篇
  1988年   6篇
  1987年   14篇
  1986年   10篇
  1985年   10篇
  1984年   11篇
  1983年   8篇
  1982年   7篇
  1981年   8篇
  1980年   7篇
  1979年   7篇
  1978年   6篇
  1977年   5篇
  1976年   7篇
  1973年   3篇
  1971年   4篇
排序方式: 共有1015条查询结果,搜索用时 31 毫秒
91.
Results are presented of a detailed study of the effects of high-temperature 4-MeV neutron irradiation on the performance degradation of Si pin photodiodes together with the radiation-induced defects, observed by deep level transient spectroscopy. The degradation of the device performance and the introduction rate of the lattice defects decrease with increasing sample temperature during irradiation. For a 250°C irradiation, the reduction of the reverse current is only 20% of the starting value. This result suggests that the creation and recovery of the radiation damage proceeds simultaneously at high temperatures. Carbon-related complex as hole capture levels is also mainly responsible for the device degradation for high-temperature neutron irradiation.  相似文献   
92.
93.
A simple approach for determining a liquid structure using X-ray scattering data, in which a liquid structure is uniquely evaluated without construction of any plausible structure models, has been applied to liquid acetonitrile, acetone and cyclohexane. For a pair of molecules, a given point within a molecule is located at the origin with a given molecular orientation. The site of the given point of another molecule is defined by the polar coordinates and the molecular orientation is treated by three Eulerian angles. These parameters are optimized by a non-linear least-squares calculation applied to X-ray scattering data. The reliability of the method was examined by determining the liquid structure of polar acetonitrile and the obtained intermolecular interatomic distances are in good agreement with the previously reported values. The method was then successfully applied to the determination of the liquid structure of acetone and cyclohexane. Especially for nonpolar cyclohexane, the construction of a variety of plausible structural models is very difficult. It was revealed that acetone has an ordered liquid arrangement similar to that found in its crystal, although the intermolecular distances in liquid acetone are different from those in the crystal. On the other hand, the liquid structure of cyclohexane is disordered.  相似文献   
94.
Polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) was successfully synthesized through the combination of metallocene catalysis with living radical polymerization. Terminally hydroxylated polyethylene, prepared by ethylene/allyl alcohol copolymerization with a specific zirconium metallocene/methylaluminoxane/triethylaluminum catalyst system, was treated with 2‐bromoisobutyryl bromide to produce terminally esterified polyethylene (PE‐Br). With the resulting PE‐Br as an initiator for transition‐metal‐mediated living radical polymerization, methyl methacrylate polymerization was subsequently performed with CuBr or RuCl2(PPh3)3 as a catalyst. Then, PE‐b‐PMMA block copolymers of different poly(methyl methacrylate) (PMMA) contents were prepared. Transmission electron microscopy of the obtained block copolymers revealed unique morphological features that depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50–100‐nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix. Moreover, the PE‐b‐PMMA block copolymers effectively compatibilized homopolyethylene and homo‐PMMA at a nanometer level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3965–3973, 2003  相似文献   
95.
The sera of diabetic patients showed an inverse correlation (r = -0.67, n = 57) between free gliclazide (oral hypoglycemic drug) level and the fructosamine value. The binding capacity of the primary binding site for gliclazide in the albumin molecule was increased from 4.5 x 10(-4) to 8.0 x 10(-4) M-1 by glycation of albumin, but not that of the secondary binding site (1.2 x 10(-4) M-1). This suggests that the glycation of albumin increases its total binding capacity for gliclazide, resulting in a low free gliclazide level. Therefore, a low hypoglycemic activity of the drug is observed when it is administered to diabetic patients with hyperglycemia.  相似文献   
96.
Photoredox catalytic functions of water-soluble vinyl copolymers with pendant porphyrin or metalloporphyrin dimers were investigated. With FRA-L-ascorbic acid in aqueous solution, a vinyl copolymer bearing Mg-porphyrin dimer linked with the shortest N,N′-methylenebisamide bridge was found to have a remarkable accelerating effect under illumination of visible light as compared with that bearing Mg-porphyrin monomer and other copolymers with longer dimer bridges as well as vinyl copolymers bearing porphyrin dimers and monomer. A copolymer bearing Zn-porphyrin dimer was much inferior to that bearing monomer. Copolymers with other metals such as Co(II), Ni(II), and Cu(II) were almost inert.  相似文献   
97.
Volume reduction(N), tritium retention factor (R), tritium concentration factor(Z) and apparent separation factor(beta) were measured on the large and small electrolytic cell systems. The relative variation of R was smaller than that of Z. So, it is recommended to use R in calculation of tritium concentrations in water samples. Furthermore, it was empirically revealed that R can be obtained only from N if a reliable beta-value is previously known. Therefore, it is possible to obtain R without electrolysis of the tritium standard solution. Taking into account the above facts, the so-called non-spike analysis of tritium, in which electrolytic enrichment and liquid scintillation counting are combined, becomes practicable.  相似文献   
98.
99.
Recently, thermally activated delayed fluorescence (TADF) materials have received increasing attention as effective emitters for organic light‐emitting diodes (OLEDs). However, most of them are usually employed as dopants in a host material. In this report, carbazole dendrimers with a triphenyl‐s‐triazine core are reported, which are the first solution‐processable, non‐doped, high‐molecular‐weight TADF materials. The dendrimers were obtained by a new and facile synthetic route using the tert‐butyldimethylsilyl moiety as a protecting group. All dendrimers showed TADF in toluene. Measurements of the temperature‐dependent luminescence lifetime revealed that spin‐coated neat films also showed TADF with moderate quantum yields. OLED devices incorporating these dendrimers as spin‐coated emitting layers gave external quantum efficiencies of up to a 3.4 %, which suggests that this device is harvesting triplet excitons. This result indicates that carbazole dendrimers with attached acceptors are potential TADF materials owing to their polarized electronic structure (with HOMO–LUMO separation).  相似文献   
100.
A treatment of cobalt oxide supported gold nanoparticles (Au/Co3O4) under syngas atmosphere effectively generated a cobalt carbonyl-like active species in the reaction vessel. The preparation of Au/Co3O4 was quite simple and the in situ generated cobalt species could be used as a stable and easy handling alternative for dicobalt octacarbonyl without bothersome purification prior to use. The reactions, which are sensitive to the purity of the dicobalt octacarbonyl, such as the alkoxycarbonylation of epoxides and the Pauson-Khand reaction, smoothly progressed with Au/Co3O4.  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