全文获取类型
收费全文 | 12198篇 |
免费 | 1692篇 |
国内免费 | 1399篇 |
专业分类
化学 | 8229篇 |
晶体学 | 147篇 |
力学 | 870篇 |
综合类 | 95篇 |
数学 | 1424篇 |
物理学 | 4524篇 |
出版年
2024年 | 35篇 |
2023年 | 174篇 |
2022年 | 297篇 |
2021年 | 343篇 |
2020年 | 393篇 |
2019年 | 356篇 |
2018年 | 319篇 |
2017年 | 305篇 |
2016年 | 469篇 |
2015年 | 455篇 |
2014年 | 587篇 |
2013年 | 814篇 |
2012年 | 901篇 |
2011年 | 967篇 |
2010年 | 652篇 |
2009年 | 712篇 |
2008年 | 752篇 |
2007年 | 722篇 |
2006年 | 682篇 |
2005年 | 627篇 |
2004年 | 493篇 |
2003年 | 392篇 |
2002年 | 347篇 |
2001年 | 327篇 |
2000年 | 286篇 |
1999年 | 317篇 |
1998年 | 327篇 |
1997年 | 266篇 |
1996年 | 265篇 |
1995年 | 224篇 |
1994年 | 244篇 |
1993年 | 161篇 |
1992年 | 150篇 |
1991年 | 131篇 |
1990年 | 139篇 |
1989年 | 84篇 |
1988年 | 80篇 |
1987年 | 87篇 |
1986年 | 82篇 |
1985年 | 71篇 |
1984年 | 48篇 |
1983年 | 33篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
微乳液介质—1—(2—吡啶偶氮)—2—萘酚光度法测定汽油中环烷酸铁的含量 总被引:8,自引:2,他引:8
本研究了微乳液为介质时,铁与1-(2-吡啶偶氮)-2-萘酚(PAN)的显色反应。选择730nm处为测定波长,ε为1.4×10^4L.mol^-^1.cm^-^1,铁量在0-50μg/25ml范围内符合比耳定律,该法适用于汽油中环烷酸铁的测定。 相似文献
92.
93.
Liu GD Zhong TS Huang SS Shen GL Yu RQ 《Fresenius' Journal of Analytical Chemistry》2001,370(8):1029-1034
A renewable amperometric immunosensor based on the sol-gel technique has been constructed by dispersing graphite, complement 3 (C3) antiserum, and sol-gel at low temperature. The prepared immunosensor is rigid, porous, and has a renewable external surface. A competitive binding assay has been used to determine C3 in human serum with the aid of C3 labeled with horseradish peroxidase. The enzyme-labeled antigen can readily diffuse toward the encapsulated antibody, which retains its binding properties. The experimental conditions for the assay with the biocomposite, including the loading of C3 antiserum in the biocomposite, the amount of labeled C3 in incubation solution, incubation time, and temperature, have been optimized. Using C3 labeled with horseradish peroxidase, and o-AP as the substrate, amperometric detection at -150 mV (relative to the SCE) results in a linear detection range of 1.17-35.1 microg mL(-1), with a detection limit of 0.56 microg mL(-1). Serum samples have been assayed and the results demonstrate the feasibility of the proposed immunosensor for clinical analysis. The surface of the immunosensor can be renewed simply by polishing to obtain a fresh immunocomposite ready to use in a new competitive assay. 相似文献
94.
Fang-Mo Chang Chen-Chia Huang Shin-Ming Shen Sun-I Chen 《Journal of Thermal Analysis and Calorimetry》1995,44(2):405-417
The effects of various burning rate catalysts on thermal decomposition of cured glycidyl azide polymer (GAP)-ammonium perchlorate (AP) propellants have been studied by means of thermal analysis and a modified vacuum stability test (MVST). Four types of iron-containing catalysts examined in this paper are catocene, ferrocenecarboxaldehyde (FCA), ferrocene, and ferric oxide. Results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) revealed that the catalysts play an important role in the decomposition of both AP and GAP. The peak decomposition temperature (T m) of DTA curves and onset decomposition temperature (T o) of TG patterns considerably shifted to a lower temperature as the concentration of catalysts increased in the propellants. The endothermic temperature of AP, however, is unaffected by the presence of burning rate catalysts in all cases. The activation energy of decomposition of the propellants in range of 80 to 120°C is determined, based on the MVST results. 相似文献
95.
Z. P. Hu Z. X. Shen L. Qin S. H. Tang M. H. Kuok G. Q. Xu K. F. Mok H. H. Huang 《Journal of Molecular Structure》1995,356(3):163-168
The high-pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) single crystals and polycrystalline CuTCNQ are presented in this paper. TCNQ shows a phase transition at 22 kbar, a pressure higher than reported earlier. CuTCNQ undergoes a first order phase transition at 30 kbar, which is characterized by the abrupt disappearance of all the Raman bands. 相似文献
96.
Mujie Yang Xiaojun Zhang Jianfu Li Zhiquan Shen 《Journal of polymer science. Part A, Polymer chemistry》1992,30(1):63-69
The study of rare earth coordination catalysts for polymerization of 1-octene has been successfully carried out for the first time. Some features and kinetic behavior of polymerization of 1-octene by Nd(naph)3–AIEt3 catalyst system in tetrachloro-methane are described. The overall polymerization activation energy Ea measured was 74.5 kJ/mol and the rate equation could be expressed as Rp = kp [Nd] [M] (kp = 3.21 × 10?3 L/mol s, at 50°C). The catalytic activity of various rare earth elements in Ln (naph)3 and ligands in NdL3 for the polymerization was compared. A 1-octene oligomer with double bonds was obtained. It is either a white or pale yellow waxy semi-solid. Its number-average molecular weight is about 103 and the molecular weight distribution is less than 2. 相似文献
97.
98.
Wei Ge ZHANG Ying Hua JIN Ping QI Kai BAO Jin Guang LIN Nai Li WANG Xin Shen YAO 《中国化学快报》2006,17(1):9-11
Erythromycin has been extensively used in the treatment of bacterial infections for over 50 years1. In addition to the antimicrobial effect, the quite unique antiinflammatory activity of the erythromycin derivatives has attracted much attention as new the… 相似文献
99.
Polynuclear mixed‐valent nickel oxide and nickel hexacyanoferrate hybrid film was prepared on glassy carbon electrode by multiple scan cyclic voltammetry. The film growth was monitored using electrochemical quartz crystal microbalance (EQCM). The cyclic voltammogram of the nickel hexacyanoferrate film is characterized by single redox couple whereas nickel oxide/nickel hexacyanoferrate hybrid film exhibits two redox couples. Cyclic voltammetric features suggest that the charge transfer process in both films resembles that of surface‐confined redox species. In stronger basic solution (pH ≥9), nickel hexacyanoferrate film was gradually converted into nickel oxide film during potentiodynamic cycling. The peak potential of nickel oxide redox couple moved into more negative side with increasing pH of contacting solution whereas the peak potential of nickel hexacyanoferrate redox couple remains the same. Electrocatalytic behavior of hybrid film coated electrodes toward ascorbic acid, hydrazine and hydroxylamine was investigated using cyclic voltammetry technique. Analytical application of nickel oxide/nickel hexacyanoferrate hybrid film electrode was tested in amperometry and flow injection analysis. 相似文献
100.
A first-principle method has been successfully developed for the prediction of pKa values of aromatic heterocyclic compounds in DMSO solution with a precision of 1.1 pKa units. Comparison of theoretical results and experimental data (where available) also shows excellent consistency. Armed with this useful approach, the pKa values for a series of aromatic heterocycles were calculated in DMSO. Moreover, a discussion of the relationships between hydrogen acidities and molecular structures is conducted for the first time (determinants of C-H acidities, substituent effects, and some practical use of dehydrometalation). These statistics could be useful for synthetic chemists to design proper routes for introduction of aromatic heterocyclic moiety, especially when dehydrometalation reactions are used. 相似文献