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   564篇
  免费   29篇
化学   376篇
晶体学   3篇
力学   15篇
数学   70篇
物理学   129篇
  2023年   2篇
  2022年   16篇
  2021年   24篇
  2020年   15篇
  2019年   23篇
  2018年   17篇
  2017年   19篇
  2016年   24篇
  2015年   18篇
  2014年   25篇
  2013年   43篇
  2012年   44篇
  2011年   37篇
  2010年   26篇
  2009年   24篇
  2008年   33篇
  2007年   20篇
  2006年   27篇
  2005年   23篇
  2004年   16篇
  2003年   7篇
  2002年   12篇
  2001年   10篇
  1999年   4篇
  1997年   7篇
  1996年   2篇
  1995年   7篇
  1994年   5篇
  1993年   3篇
  1992年   3篇
  1991年   2篇
  1989年   4篇
  1988年   5篇
  1986年   2篇
  1985年   2篇
  1982年   2篇
  1980年   4篇
  1979年   2篇
  1978年   3篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
  1973年   2篇
  1971年   2篇
  1961年   1篇
  1948年   4篇
  1947年   2篇
  1939年   1篇
  1935年   1篇
  1934年   2篇
排序方式: 共有593条查询结果,搜索用时 687 毫秒
31.
Research on Chemical Intermediates - Magnetic separable nanoparticles-decorated N-heterocyclic carbene complex with copper (MNP[1-Methyl benzimidazole]NHC@Cu) has been prepared by covalent grafting...  相似文献   
32.
Bergenia (Saxifragaceae) genus is native to central Asia and encompasses 32 known species. Among these, nine are of pharmacological relevance. In the Indian system of traditional medicine (Ayurveda), “Pashanabheda” (stone breaker) is an elite drug formulation obtained from the rhizomes of B. ligulata. Bergenia species also possess several other biological activities like diuretic, antidiabetic, antitussive, insecticidal, anti-inflammatory, antipyretic, anti-bradykinin, antiviral, antibacterial, antimalarial, hepatoprotective, antiulcer, anticancer, antioxidant, antiobesity, and adaptogenic. This review provides explicit information on the traditional uses, phytochemistry, and pharmacological significance of the genus Bergenia. The extant literature concerned was systematically collected from various databases, weblinks, blogs, books, and theses to select 174 references for detailed analysis. To date, 152 chemical constituents have been identified and characterized from the genus Bergenia that belong to the chemical classes of polyphenols, phenolic-glycosides, lactones, quinones, sterols, tannins, terpenes, and others. B. crassifolia alone possesses 104 bioactive compounds. Meticulous pharmacological and phytochemical studies on Bergenia species and its conservation could yield more reliable compounds and products of pharmacological significance for better healthcare.  相似文献   
33.

α-Amylase and α-Glucosidase are important therapeutic targets for type II diabetes. The present focus of our study is to elucidate the hypoglycemic activity of novel compounds through in vitro and in silico studies. Here, we synthesized the nitro acridines (3a–3c), amino acridines (4a–4c), and nitro phenylquinoline (3d) and amino phenylquinoline (4d) using a multi-step reaction protocol in good yields. All the above derivatives were screened for molecular docking, α-Amylase and α-Glucosidase inhibitory activities utilizing acarbose as standard drug. In silico studies were performed to explore the binding ability of compounds with the active site of α-Amylase and α-Glucosidase enzymes. The in vitro antihyperglycemic report of 3c exhibits the maximum inhibitory activity with IC50 values of 200.61?±?9.71 μmol/mL and 197.76?±?8.22 μmol/mL against α-Amylase and α-Glucosidase, respectively. Similarly, the compound 3a exhibits IC50 values of 243.78?±?13.25 μmol/mL and 296.57?±?10.66 μmol/mL, and 4c exhibits IC50 values of 304.28?±?3.51 μmol/mL and 278.86?±?3.24 μmol/mL with a significant p?<?0.05 in both enzyme inhibitions. In addition, the presence of diverse functional moieties in synthesized compounds may provide a strong inhibitory action against the abovementioned enzymes compared with standard acarbose inhibition (IC50, 58.74?±?3.68 μmol/mL and 49.39?±?4.94 μmol/mL). Also, the docking studies provided an excellent support for our in vitro studies. The outcome of these studies recommends that the tested compounds might be treated as potential inhibitors for the starch hydrolyzing enzymes in type II diabetes.

  相似文献   
34.
Titania (TiO2) and barium titanate (BaTiO3) were synthesized using three different dicarboxylates, which included oxalate, malate and tartarate. These powders were characterized by X-ray powder diffraction, scanning electron micrographs, BET specific surface area and particle size distribution. Their properties depended to a great extent on the nature of the precursor. The titania and barium titanate powders obtained from the tartarate precursor were found to be good for slip casting. Slips of these oxides with different solids contents were prepared at different pH values using both distilled water and ethanol as the dispersing agent and also with and without deflocculant. The rheological behaviors of the suspensions were then determined, and the slip, green and sedimentation bulk densities were measured. The minimum viscosities were observed at pH 8.2 for the TiO2–water and pH 10.2 for the BaTiO3–water system.  相似文献   
35.
We present a new method for resolving combinatorial ambiguities that arise in multi-particle decay chains at hadron colliders where the assignment of visible particles to the different decay chains has ambiguities. Our method, based on selection cuts favoring high transverse momentum and low invariant mass pairings, is shown to be significantly superior to the more traditional hemisphere method for a large class of decay chains, producing an increase in signal retention of up to a factor of 2. This new method can thus greatly reduce the combinatorial ambiguities of decay chain assignments.  相似文献   
36.
37.
38.
The complexes [MHCl(CO)(PPh3)3] (M = Ru or Os) readily undergo substitution at the site trans to the hydride ligand to afford phosphinite-, phosphonite-, or phosphite-containing products [MHCI(CO)(PPh3)2L] [L = P(OR)Ph2, P(OR)2Ph or P(OR)3 respectively; R = Me or Et]. The ruthenium complexes alone undergo further substitution to afford complex cations [RuH(CO)(PPh3)nL4?n]+ [n = 2, L = P(OMe)3; n = 1, L = P(OR)3; n = 0, L = P(OR)2Ph or P(OR)Ph2] which were isolated and characterised as their tetraphenylborate salts. Synthesis of the cationic complexes [IrHL5][BPh4]2 [L = P(OR)3, R = Me or Et] is also reported. Stereochemical assignments based on NMR data are given, and second order 31P and high field 1H NMR patterns are analysed.  相似文献   
39.
We present a phenomenological analysis of backward photoproduction in terms of the recently proposed kinematic cut model. The cut fills in the dip at u ≈ −0.15 without having to invoke the Nγ trajectory. Good agreement with the data is obtained in the scattering region; the extrapolation to the nucleon pole is unsatisfactory.  相似文献   
40.
Different physicochemical properties such as solubilities, densities, viscosities, and electrical conductivities of calcium sulfate dihydrate in aqueous calcium chloride solutions have been measured at 30°C to examine the ionic interactions in the system. Density values have been used to calculate the mean apparent molar volumes of ternary mixtures. Viscosity values have been analyzed using different empirical equations and the experimental values of viscosity were combined with conductivity values to get the Walden product. The experimental data have been fitted by a polynomial equation for least-squares analysis to obtain the coefficients and the standard errors. Results have been examined in the light of the structure making or structure breaking effect of the various ions present in the solution.  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