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   130154篇
  免费   31039篇
  国内免费   22598篇
化学   85545篇
晶体学   1676篇
力学   8682篇
综合类   407篇
数学   16457篇
物理学   71024篇
  2024年   494篇
  2023年   1791篇
  2022年   2042篇
  2021年   2402篇
  2020年   3067篇
  2019年   3479篇
  2018年   3166篇
  2017年   3602篇
  2016年   4697篇
  2015年   4823篇
  2014年   5207篇
  2013年   7880篇
  2012年   9151篇
  2011年   10819篇
  2010年   12435篇
  2009年   12592篇
  2008年   6860篇
  2007年   6087篇
  2006年   5602篇
  2005年   5283篇
  2004年   5530篇
  2003年   4492篇
  2002年   4162篇
  2001年   4169篇
  2000年   3413篇
  1999年   3697篇
  1998年   3117篇
  1997年   2899篇
  1996年   3250篇
  1995年   3530篇
  1994年   3464篇
  1993年   3366篇
  1992年   2985篇
  1991年   2527篇
  1990年   2134篇
  1989年   2162篇
  1988年   2075篇
  1987年   1371篇
  1986年   1388篇
  1985年   1058篇
  1984年   1110篇
  1983年   457篇
  1982年   971篇
  1981年   778篇
  1980年   793篇
  1979年   544篇
  1978年   536篇
  1977年   638篇
  1976年   1050篇
  1972年   536篇
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
41.
Photoactivated chemotherapy (PACT) has appealing merits over traditional chemotherapy as well as photodynamic therapy (PDT) by virtue of its spatial and temporal control on drug activity and oxygen-independent mechanisms of action. However, the short photoactivation wavelengths, e.g., visible light–activated Ru(II)-based PACT agents, limit the clinical application severely. In this work, a facile construction of supramolecular nanoparticles from a poly(ethylene glycol) (PEG)-modified [Ru(dip)2(py-SO3)]+ (abbreviated as Ru-PEG, dip = 4,7-diphenyl-1,10-phenanthroline, py-SO3 = pyridine-2-sulfonate) and 1,3-phenylenebis(pyren-1-ylmethanone) (BP) is shown. While Ru-PEG may undergo photoinduced ligand dissociation and release anticancer species of [Ru(dip)2(H2O)2]2+, BP has extremely large two-photon absorption cross sections (δ2) in the NIR region and intense fluorescence over the wavelengths where Ru-PEG has strong absorption. Thus, two-photon excitation of BP followed by an efficient Förster resonance energy transfer (FRET) from BP to Ru-PEG may lead to a potent inactivation against cisplatin-resistant cancer cells and 3D multicellular tumor spheroids (MCTSs). The residue fluorescence of BP also allows the cellular uptake of the particles to be visualized. This work provides a universal and convenient strategy to realize theranostic PACT in the ideal phototherapeutic window of 650–900 nm.  相似文献   
42.
Wu  Xuze  Sun  Yu  Wang  Yu  Chen  Yu 《Nonlinear dynamics》2020,99(3):1937-1958
Nonlinear Dynamics - Oblique collisions are more likely to happen in the realistic translational joint with clearance, compared to the full front impacts. It can be a quite demanding task to...  相似文献   
43.
44.
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.  相似文献   
45.
Crystallography Reports - A cobalt coordination polymer, {[Co(L1)2(H2O)2] · (HCOO)2 · H2O}n, where L1 is a bis(4-(1H-imidazol-1-yl)phenyl)methanone, has been synthesized and characterized...  相似文献   
46.
International Journal of Theoretical Physics - Gram matrices arise naturally in the consideration of pair-wise overlap of a family of vectors or quantum pure states, and play an important role in...  相似文献   
47.
48.
The satisfiability (SAT) problem is a core problem in computer science. Existing studies have shown that most industrial SAT instances can be effectively solved by modern SAT solvers while random SAT instances cannot. It is believed that the structural characteristics of different SAT formula classes are the reasons behind this difference. In this paper, we study the structural properties of propositional formulas in conjunctive normal form (CNF) by the principle of structural entropy of formulas. First, we used structural entropy to measure the complex structure of a formula and found that the difficulty solving the formula is related to the structural entropy of the formula. The smaller the compressing information of a formula, the more difficult it is to solve the formula. Secondly, we proposed a λ-approximation strategy to approximate the structural entropy of large formulas. The experimental results showed that the proposed strategy can effectively approximate the structural entropy of the original formula and that the approximation ratio is more than 92%. Finally, we analyzed the structural properties of a formula in the solution process and found that a local search solver tends to select variables in different communities to perform the next round of searches during a search and that the structural entropy of a variable affects the probability of the variable being flipped. By using these conclusions, we also proposed an initial candidate solution generation strategy for a local search for SAT, and the experimental results showed that this strategy effectively improves the performance of the solvers CCAsat and Sparrow2011 when incorporated into these two solvers.  相似文献   
49.
We report theoretical studies of electron impact triple differential cross sections of two bio-molecules,pyrimidine and tetrahydrofurfuryl alcohol,in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of-5°,-10°,and-15°.Present multi-center distorted-wave method well describes the experimental data,which was obtained by performing(e,2e)experiment.The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential,which must be considered when the low energy electron interacts with DNA analogues.  相似文献   
50.
Ding  Q.  Yao  M.  Wu  Sh.  Zeng  M.  Xue  N.  Wu  D.  Xu  J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the...  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