全文获取类型
收费全文 | 3489篇 |
免费 | 600篇 |
国内免费 | 552篇 |
专业分类
化学 | 2859篇 |
晶体学 | 54篇 |
力学 | 164篇 |
综合类 | 49篇 |
数学 | 454篇 |
物理学 | 1061篇 |
出版年
2024年 | 4篇 |
2023年 | 36篇 |
2022年 | 51篇 |
2021年 | 72篇 |
2020年 | 106篇 |
2019年 | 145篇 |
2018年 | 120篇 |
2017年 | 94篇 |
2016年 | 178篇 |
2015年 | 192篇 |
2014年 | 213篇 |
2013年 | 249篇 |
2012年 | 264篇 |
2011年 | 297篇 |
2010年 | 231篇 |
2009年 | 226篇 |
2008年 | 295篇 |
2007年 | 261篇 |
2006年 | 225篇 |
2005年 | 202篇 |
2004年 | 179篇 |
2003年 | 190篇 |
2002年 | 232篇 |
2001年 | 189篇 |
2000年 | 109篇 |
1999年 | 80篇 |
1998年 | 45篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1936年 | 4篇 |
排序方式: 共有4641条查询结果,搜索用时 31 毫秒
981.
A novel method for preparation of hydrogen peroxide biosensor was presented based on immobilization of hemoglobin (Hb) on carbon‐coated iron nanoparticles (CIN). CIN was firstly dispersed in a chitosan solution and cast onto a glassy carbon electrode to form a CIN/chitosan composite film modified electrode. Hb was then immobilized onto the composite film with the cross‐linking of glutaraldehyde. The immobilized Hb displayed a pair of stable and quasireversible redox peaks and excellent electrocatalytic reduction of hydrogen peroxide (H2O2), which leading to an unmediated biosensor for H2O2. The electrocatalytic response exhibited a linear dependence on H2O2 concentration in a wide range from 3.1 μM to 4.0 mM with a detection limit of 1.2 μM (S/N=3). The designed biosensor exhibited acceptable stability, long‐term life and good reproducibility. 相似文献
982.
Theoretical Study on the Intermolecular Interactions between 1,1‐Diamino‐2,2‐Dinitroethylene and H2O
The density functional method was applied to the study of 1,1‐diamino‐2,2‐dinitroethylene (Fox‐7)/H2O dimer. All the possible dimers ( 1, 2 and 3 ), as well as the monomers, were fully optimized with the DFT method at the B3LYP/6‐311++G** level. The basis set superposition errors (BSSE) are 4.62, 4.07 and 3.45 kJ/mol, and the zero point energy (ZPE) corrections for the interaction energies are 7.94, 5.66 and 6.40 kJ/mol for 1, 2 and 3 , respectively. Dimer 1 is the most stable, judged by binding energy. After BSSE and ZPE corrections, the greatest corrected intermolecular interaction energy of dimer 1 was predicted to be ?29.36 kJ/mol. The charge redistribution mainly occurs on the adjacent N–H··· O atoms and N–O··· H atoms between submolecules. The oxygen in the nitro group acts as a moderate hydrogen acceptor as compared to water oxygen. Based on the statistical thermodynamic method, the standard thermodynamic functions, heat capacities (C0P), entropies (S0T) and thermal corrections to enthalpy (H0T), and the changes of thermodynamic properties on going from monomer to dimer over the temperature range 200.00‐700.00 K were predicted. It is energetically or thermodynamically favorable for Fox‐7 to bind with H2O and to form dimer 1 at room temperature. 相似文献
983.
984.
碳纳米管性质奇特、用途广泛[1]。目前制备碳纳米管薄膜的方法主要有电弧放电法[2]、催化裂解[3]、及真空过滤碳纳米管悬浮液制备“巴基管纸”(Buckypaper)[4]等。本文采用镀镍基板催化裂解低碳烷烃法制备碳纳米管薄膜,考察了镀膜时间、蚀刻和氨水处理等条件对碳纳米管薄膜产物形貌的影响。1 实验部份1 1 镀膜与后处理采用离子溅射法在硅酸盐基板上镀镍,镀镍电流7 5mA,镀镍时间分别为2min、15min、30min、45min或60min;对镀镍基板再进行蚀刻(蚀刻电流7 5mA,蚀刻时间2min)或用氨水浸泡处理(含NH325%,超声振荡30min),然后烘干备用。1 … 相似文献
985.
In this work, the method of isotope dilution thermal ionization mass spectrometry able to trace to SI was developed to accurately measure trace amount of Cd, Pb, Zn and Cu in sediment, rice, wine, and human serum samples for interlaboratory comparisons. The research focuses on how to apply the primary method correctly, uncertainty evaluation of measurement results, and how to achieve the meaning of traceability to SI by using ID-TIMS. As a result, the measurement results of Cu and Zn in the human serum 1 and 2 with 0.94, 0.83 and 0.49% combined uncertainty, respectively, were accepted by EC-JRC-IRMM as the certified values of the serum samples. The measurement results of Cd and Pb in CCQM-K13 and CCQM-K24 with 3.96, 1.62 and 1.03% combined uncertainty, respectively, are within the degrees of the equivalence. These comparisons at the highest level of measurement are proof that traceability of chemical measurement can be achieved as the traceability chain of ID-TIMS established in this work was used. 相似文献
986.
Chemistry is the force to transform nature. To let people have a proper understanding of chemistry, this popular science teaching team, based on the previously Finding Chemistry in Detective Conan, select creatively words from the lyrics of influential pop songs, such as "blue and white porcelain" and "bubble", as the hot problems for chemistry popular science teaching; based on the chemistry topic of each part, seven interactive episodes of popular science are designed, which are rich in content and popular with readers. 相似文献
987.
LC/MS3‐Guided biotransformation of p‐coumaric acid (=(2E)‐3‐(4‐hydroxyphenyl)prop‐2‐enoic acid; CA) with H2O2/Momordica charantia peroxidase at pH 5.0 and 45° in the presence of acetone has resulted in the isolation of three CA trimers, triCA1 ( 1 ), triCA2 (trans‐ 2 ), and triCA3 (cis‐ 2 ), and seven CA dimers, diCA1–diCA7, i.e., 3 – 9 , among which seven (triCA1–triCA3 and diCA1–diCA4) are new compounds and three (diCA5–diCA7) are known compounds. The structures were established by 2D‐NMR such as HSQC, HMBC, and NOESY measurements. The possible mechanism for the formation of the products is also discussed (Schemes 1–3). This is the first time that the biotansformation of p‐coumaric acid catalyzed by peroxidase in vitro was achieved. Compounds triCA3 (cis‐ 2 ), diCA1 ( 3 ), diCA5 ( 7 ), and diCA7 ( 9 ) exhibit a stronger antioxidative activity than the parent CA. 相似文献
988.
研究了超声波作用下烯醇硅醚的环丙化反应(Simmons-Smith反应),发现在超声波和CuCl共同作用下,锌粉能有效地被活化。三甲基硅氧基环丙烷类化合物的产率可达56%~78%。同时,还研究了超声波功率、反应温度、溶剂、反应时间等对环丙化反应的影响。 相似文献
989.
高效液相色谱-串联质谱法测定香肠中硝基呋喃代谢物 总被引:1,自引:0,他引:1
高效液相色谱法与串联质谱联用法应用于香肠中硝基呋喃代谢物的测定.试样在稀盐酸溶液中同时加入一定量的衍生试剂邻硝基苯甲醛后,在37 ℃放置过夜使其中与蛋白质结合的硝基呋喃代谢物水解并衍生化.将此溶液的酸度调节至pH 7.0~7.5后,以3 000 r·min-1的转速离心10 min,分出上层清液,用乙酸乙酯萃取.所得萃取液用作HPLC-MS/MS测定.在电喷雾正离子条件下,用多离子反应监测模式,以外标法对萃取液中对经衍生化后的各硝基呋喃代谢物进行定量.在0.5~10 μg·kg-1范围内进行标准加入回收试验,4种硝基呋喃代谢物的回收率在77.3%~90.7%之间,测定值的相对标准偏差小于9%.测得方法的检出限(S/N=3)为:0.10 μg·kg-1对呋喃唑酮、呋喃它酮及呋喃西林的代谢物和0.20 μg·kg-1对呋喃妥因代谢物. 相似文献
990.
De Cong HU Qiong LIU Hui Bi XU Hai Rong CUI Si Wang YU Xiao Da YANG Kui WANG 《中国化学快报》2005,16(10):1347-1350
Selenium(Se)is well known for its cancer-preventive function1.In our previous work,silkworm pupas from Ziyang county of Shanxi Province,one of the two largest Se-rich areas in China,was found to have Se content215times higher than that from Luoyang which is a normal region in China2.Meanwhile,Se-rich amino acids extracted from Ziyang pupas could efficiently induce the apoptosis of human hepatoma cells SMMC-7721.In order to find out the effective component responsible for this carcinostat… 相似文献