全文获取类型
收费全文 | 1313篇 |
免费 | 61篇 |
国内免费 | 31篇 |
专业分类
化学 | 1015篇 |
晶体学 | 17篇 |
力学 | 39篇 |
综合类 | 1篇 |
数学 | 109篇 |
物理学 | 224篇 |
出版年
2024年 | 11篇 |
2023年 | 13篇 |
2022年 | 30篇 |
2021年 | 88篇 |
2020年 | 58篇 |
2019年 | 47篇 |
2018年 | 56篇 |
2017年 | 37篇 |
2016年 | 56篇 |
2015年 | 42篇 |
2014年 | 55篇 |
2013年 | 93篇 |
2012年 | 99篇 |
2011年 | 102篇 |
2010年 | 61篇 |
2009年 | 47篇 |
2008年 | 57篇 |
2007年 | 61篇 |
2006年 | 54篇 |
2005年 | 53篇 |
2004年 | 35篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1985年 | 5篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 8篇 |
排序方式: 共有1405条查询结果,搜索用时 62 毫秒
161.
Disposal of untreated industrial effluents is drastically deteriorating the quality of underground water. Research work has been conducted to analyze the effect of disposal of urea plant effluent on the quality of ground water of the District Mianwali Daudkhail, Pakistan. For this purpose the effluent and ground water samples were analyzed for pH, TDS, TSS, Cl, F, COD, BOD, Fe, Zn, Pb, Cu, Cr, Cd, Mn, and As. Results obtained were compared with WHO and NEQS standards for drinking and effluent emission limits, respectively. Moreover, effluent samples were also evaluated for irrigation purposes and results compared with criteria recommended for irrigation water. Results showed though the effluents were according to the standards given by National Environmental Quality Standards (NEQS) for liquid emission and fit for irrigation purposes, the quality of underground water was below standard due to having a higher quantity of total dissolved solids than permissible. 相似文献
162.
本文在文[1],[2]的基础上,进一步讨论了算子超等距膨胀的性质,证明了T∈L(H)可超等距膨胀的充分必要条件是T≌P_H M|_H,或者T≌∑■ P_H M|_H这里M是Bergman位移,H∈LatM~*。 相似文献
163.
164.
165.
We calculate the action and the topological charge of classical solutions in two-dimensional euclidean grassmannian σ models (for both generic and special solutions). We show that all the above non-instanton or non-anti-instanton solutions are unstable. We also find solutions of the Dirac equation describing fermions in the background of these grassmannian fields, and we exhibit relations between these fermionic solutions and those of the associated Hilbert-Riemann problem. 相似文献
166.
167.
R.M. Saleh J.M. Abd El Kader A.A. El Hosary A.M. Shams El Din 《Journal of Electroanalytical Chemistry》1975,62(1):297-310
The dissolution of Cu in solutions of HNO3 of different concentrations has been studied by the thermometric method. Starting from the initial temperature, Ti, the temperature—time curves exhibit an induction period followed by a rapid rise in temperature to a maximum value, Tm, attained t min after the start of the reaction. Tm increases and t decreases with increase of the acid concentration, M. ΔT (i.e.Tm ? Ti) and the reaction number (R.N. = (Tm ? Ti)/t) vary with M according to: ΔT = k(M ? M0) and R.N. = A1Mn, where k, M0, A1 and n are constants.The effect of varying concentrations of HCl, H2SO4 and H3PO4 on the R.N. of Cu in 3.5 M HNO3 was examined. Small amounts of these acids lower the R.N. (inhibition) due to the displacement of an active species on the surface of the metal by the anion of the acid. Larger additions of the acids accelerate dissolution. The concentration at which the added acid changes from corrosion-inhibitor to accelerator varies as HCl < H2SO4 < H3PO4. This sequence is considered to parallel the strength of adsorption of the respective anions. The results of experiments with salt additions confirm this view; all salts act only as dissolution-retardants. Calculations pertaining to the effect of the various ions on the R.N. support the conclusion that the dissolution of Cu in HNO3 is autocatalytic in nature, and depends on the [H+]/[NO3?] ratio.Cu does not dissolve in air-free, cold HCl. Attack takes place, however, in the presence of KNO3. Under these conditions attack is of the pitting- rather than the general type. The temperature rises suddenly after an incubation period, which decreases in length with increase of the amount of the added salt.Proof of the involvement of HNO2 in the autocatalytic cycle of Cu dissolution in HNO3 is obtained from the results of urea additions to the solution. 相似文献
168.
Khan Tahir Ali Hasan Syed Sirajul Varkey Saji P. Rather Manzoor Ahmad Jahan Nafees Shakir Mohammad 《Transition Metal Chemistry》1997,22(1):4-8
A new class of tetraiminetetraamide macrocyclic (Ph4[20]tetraene, N8O4, and Ph6[20]tetraene, N8O4) complexes have been prepared through the metal ion controlled reaction of 1,2-diphenylethane-1,2-dione dihydrazone (DPEDDH) with succinic acid [ML1X2] or phthalic acid [ML2X2] [M=Mn, Co, Ni, Cu or Zn; X=Cl or NO3]. The structures of the complexes have been elucidated on the basis of i.r, 1H-n.m.r, e.p.r. and electronic spectral data and conductance, as well as magnetic, properties. An octahedral geometry is assigned for all the complexes, involving coordination of the all-imine nitrogens. 相似文献
169.
Syed Ashfaq Nabi Rifaqat AliKhan Rao Ahsan Rasheed Siddiqui 《Fresenius' Journal of Analytical Chemistry》1982,311(5):503-506
Summary Stannic selenoarsenate samples have been prepared by adding a mixture which is 0.05 M in sodium arsenate and 0.05 M in sodium selenite to a 0.05 M solution of stannic chloride in different volume ratios at pH 1. Its ion-exchange properties, pH titration curves and X-ray pattern were studied. Adsorption behaviour of 24 metal ions in different solvent systems has been examined. The analytical importance of this material has been demonstrated by achieving the following binary and ternary separations: Hg2+-Cd2+, Co2+-Fe3+, Cu2+-Fe3+, Hg2+-Zn2+-Al3+, Hg2+-Cu2+-Al3+, Hg2+-Ni2+-Al3+, Hg2+-Zn2+-Fe3+ and Hg2+-Ni2+-Fe3+. A comparison of the ion-exchange properties of this material has also been made with some other tin(IV) based ion-exchangers.
Synthese, Ionenaustauscher-Eigenschaften und analytische Anwendungen von Zinn-Selenoarsenat: Vergleich mit anderen Heteropolysalzen
Zusammenfassung Zinn-Selenoarsenat wurde durch Mischen von 0,05 M Natriumarsenat-, 0,05 M Natriumselenitund 0,05 M Zinn(IV)-Chlorid-Lösungen bei pH 1 in verschiedenen Verhältnissen hergestellt. Die Ionenaustauscher-Eigenschaften, pH-Titrationskurven sowie Röntgendiagramme wurden untersucht und das Adsorptionsverhalten von 24 Metallionen in verschiedenen Lösungsmittelsystemen geprüft. Die analytische Verwertbarkeit wurde an Hand der folgenden Trennungsmöglichkeiten gezeigt: Hg2+-Cd2+, Co2+-Fe3+, Cu2+-Fe3+, Hg2+-Zn2+-Al3+, Hg2+-Cu2+-Al3+, Hg2+-Ni2+-Al3+, Hg2+-Zn2+-Fe3+, Hg2+-Ni2+-Fe3+. Vergleiche mit anderen Ionenaustauschern auf Zinn(IV)-Basis werden ebenfalls beschrieben.相似文献
170.
Excitation functions for a number of proton groups for the reactions 23Na(d, p)24Na and 27Al(d, p)28Al were measured in the energy range Ed = 1.5 to 3.0 MeV. The angular distributions for a number of proton groups were measured at a number of deuteron energies below 3.0 MeV for the three reactions 12C(d, p)13C, 23Na(d, p)24Na and 27Al(d, p)28Al. The theory of deuteron stripping reactions at incident energies below the Coulomb barrier has been considered. A closed analytical form for the differential cross-section has been obtained considering three cases according to the incident deuteron and outgoing proton energies. An attempt has been made to fit the angular distribution measurements at a number of deuterons bombarding energies accordingly. 相似文献