全文获取类型
收费全文 | 1198篇 |
免费 | 52篇 |
国内免费 | 16篇 |
专业分类
化学 | 836篇 |
晶体学 | 4篇 |
力学 | 40篇 |
数学 | 167篇 |
物理学 | 219篇 |
出版年
2022年 | 48篇 |
2021年 | 48篇 |
2020年 | 44篇 |
2019年 | 43篇 |
2018年 | 31篇 |
2017年 | 33篇 |
2016年 | 73篇 |
2015年 | 34篇 |
2014年 | 43篇 |
2013年 | 117篇 |
2012年 | 87篇 |
2011年 | 72篇 |
2010年 | 63篇 |
2009年 | 42篇 |
2008年 | 51篇 |
2007年 | 57篇 |
2006年 | 49篇 |
2005年 | 45篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 28篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 2篇 |
1967年 | 2篇 |
1938年 | 3篇 |
排序方式: 共有1266条查询结果,搜索用时 15 毫秒
101.
Understanding CHF is of an upmost importance in many industries, especially in the design and operation of boilers, nuclear power plants, cryogenic systems, etc. Due to safety issues related to the nuclear power plants, and the adaptation of CHF as the limiting criterion of power generation, it is important to understand the mechanisms of CHF relevant to nuclear systems operation. Moreover, CHF is expected to occur during transients than steady-state conditions. Therefore, knowledge of transient CHF is of great importance for the safety evaluation of nuclear reactors under transient condition. In this paper, the existing CHF experimental and modeling studies are discussed in order to understand the phenomena leading to CHF. Also, the effect of transient conditions on CHF for nuclear fuels has been evaluated. 相似文献
102.
M. K. Kullab B. A. Al-Bataina A. M. Ismail K. M. Abumurad 《Radiation measurements》2001,34(1-6):361-364
Previously calibrated passive detectors (CR-39) and an active radon device (Radon Monitor RM3) were used to study seasonal variation of radon-222 concentration levels inside and outside specific locations in Jordan. The study sites were located in an area that used to be an old phosphate mine. We found that the maximum value of radon concentration in air inside the dwellings, as measured by the passive dosimeters, was 1532.9 Bq/m3 during the winter season, and the minimum one was 46.3 Bq/m3 during fall season. While the highest and lowest readings of the active monitor were 892 and 4 Bq/m3 during fall and summer seasons, respectively. The radon concentration in soil ranges from 0.2 kBq/m3 in spring to 37.8 kBq/m3 in fall. 相似文献
103.
104.
105.
106.
The structure of the 2-thiazolylazosalicylic acid molecule, TAS, has been determined by means of quantum SCF-CI calculations. The ionization potential and the electron affinity of TAS molecule were calculated to have the values 9.057 and 2.56 eV respectively. The solvation energies in different solvents, and the bond orders of the TAS molecule were calculated for the neutral state, the oxidized form (the cation) and the reduced form (the anion). Mixed solvent studies were carried out with TAS and 2-benzothiazolylazosalicylic acid (BTAS), using polar solvents (EtOH and MeOH) to confirm the formation of a solvent-solute complex. The azo group in the TAS molecule nas a considerable contribution in the SCFLUMO; thus cathodic reduction has been focused on the azo group and was verified experimentally by cathodic reduction. 相似文献
107.
Amand Faessler M. Ismail N. Ohtsuka M. Rashdan W. Wadia 《Zeitschrift für Physik A Hadrons and Nuclei》1987,326(4):501-508
A recent approach for calculating both the real and imaginary parts of the ion-ion potential has been modified to produce the ground state properties of separate nuclei. This approach is used to study both the energy and orientation dependence of the optical potential between two U nuclei adopting the sudden and adiabatic approximations. 相似文献
108.
Ismail A. Haj Waseem Hafiz Muhammad Ishtiaq Muhammad Jamal Sajjad Shaukat Khan Majid 《International Journal of Theoretical Physics》2021,60(5):1720-1741
International Journal of Theoretical Physics - Most of the enciphering structures are based on the transformation of mediums by describing the strict criteria. The presented article is based on... 相似文献
109.
Muhammad Shabbir Paul R. Raithby Lynne H. Thomas Hammad Ismail Faiza Arshad 《Journal of Coordination Chemistry》2017,70(14):2463-2478
Four novel ON donor Schiff bases (E)-3-((4-phenoxyphenylimino)methyl)benzene-1,2-diol (HL1),(E)-3-((4-(4-biphenyloxy)phenyliminomethyl)benzene-1,2-diol (HL2), (E)-3-((4-naphthoxyphenylimino)methyl)benzene-1,2-diol (HL3), (E)-3-((4-(2-naphthoxy)phenylimino)methyl)benzene-1,2-diol (HL4) and their copper(II) complexes bis((E)-3-((4-phenoxyphenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L1)2) bis((E)-3-((4-(4-biphenyloxy)phenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L2)2), bis((E)-3-((4-naphthoxyphenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L3)2), bis((E)-3-((4-(2-naphthoxy)phenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L4)2) have been synthesized and characterized by spectroscopic (FTIR, NMR, UV–visible) and elemental analysis. The crystal structures of HL1, HL2, HL3, and HL4 have been determined, which reveal intramolecular N-H?O (HL1, HL2, HL3, and HL4) hydrogen bonds in the solid state. Keto-amine and enol-imine tautomerism is exhibited by the Schiff bases in solid and solution states. The Schiff bases and their copper(II) complexes have been screened for their biological activities. In antimicrobial assays (antibacterial and antifungal), HL4 showed promising results against all strains through dual inhibition property while the rest of the compounds showed activity against selective strains. On the other hand, in cytotoxic, DPPH, and inhibition of hydroxyl (OH) free radical-induced DNA damage assays, the results were found significantly correlated with each other, i.e. the ligands HL1 and HL2 showed moderate activity while their complexes Cu(L1)2 and Cu(L2)2 exhibited prominent increase in activity. As the results of these assays are supporting each other, it represents the strong positive correlation and antioxidant nature of investigated compounds. 相似文献
110.
Mohamed Abass Mostafa M. Ismail Wafaa R. Abdel-Monem Aisha S. Mayas 《Chemical Papers》2010,64(1):72-83
Reactivity of 2-hydroxy-4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde (I) towards N- and C-nucleophiles was described. A series of new enaminones II–III, Schiff’s base IV, and hydrazinomethylenediketones V–VIII and X were prepared in good yields. Cyclization of compounds X was achieved by an action of acetic acid to give pyrazolo[3,4-d]pyrido[1,2-a]pyrimidines XI. Base catalyzed Knoevenagel condensation of aldehyde I with some active methyl and methylene compounds led to a series of chalcone-like derivatives XII, XV, XVII, XX, XXIII, XXV, XXVII, XXIX, XXXI, XXXII, and XXXV, in fair yields. Cyclization of enones XII, XV, and XX with hydrazine gave novel heterocyclyl substituted pyrazoles XIII, XVII, and XXI, respectively. Pyrano[2,3-d]pyrido[1,2-a]pyrimidine-2,5-diones XXXIII, XXXIV, and XXXVI derivatives were obtained via cyclization of their respective enone derivatives. 相似文献