全文获取类型
收费全文 | 135497篇 |
免费 | 8575篇 |
国内免费 | 15684篇 |
专业分类
化学 | 109821篇 |
晶体学 | 1675篇 |
力学 | 4265篇 |
综合类 | 1068篇 |
数学 | 13894篇 |
物理学 | 29033篇 |
出版年
2024年 | 229篇 |
2023年 | 1240篇 |
2022年 | 3155篇 |
2021年 | 2806篇 |
2020年 | 3646篇 |
2019年 | 3400篇 |
2018年 | 3108篇 |
2017年 | 4373篇 |
2016年 | 4850篇 |
2015年 | 4124篇 |
2014年 | 5133篇 |
2013年 | 10541篇 |
2012年 | 9062篇 |
2011年 | 7680篇 |
2010年 | 6472篇 |
2009年 | 8590篇 |
2008年 | 8356篇 |
2007年 | 8955篇 |
2006年 | 8018篇 |
2005年 | 6898篇 |
2004年 | 6304篇 |
2003年 | 5224篇 |
2002年 | 6114篇 |
2001年 | 3808篇 |
2000年 | 3614篇 |
1999年 | 3333篇 |
1998年 | 2930篇 |
1997年 | 2353篇 |
1996年 | 2122篇 |
1995年 | 1980篇 |
1994年 | 1753篇 |
1993年 | 1423篇 |
1992年 | 1322篇 |
1991年 | 1007篇 |
1990年 | 819篇 |
1989年 | 759篇 |
1988年 | 634篇 |
1987年 | 546篇 |
1986年 | 427篇 |
1985年 | 356篇 |
1984年 | 379篇 |
1983年 | 186篇 |
1982年 | 306篇 |
1981年 | 236篇 |
1980年 | 235篇 |
1979年 | 223篇 |
1978年 | 191篇 |
1977年 | 132篇 |
1976年 | 124篇 |
1973年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Luigi Ambrosone Lucia Costantino Gerardino D'errico Vincenzo Vitagliano 《Journal of colloid and interface science》1997,190(2):286
The densities and viscosities of binary aqueous mixtures of poly(ethylenoxide)hexanols [C6H13(OCH2CH2)mOH, C6Em] (m= 3, 4, and 5) have been studied in the micellar composition range. For the same surfactants the self-diffusion coefficients in mixtures with heavy water have been determined by the spin-echo pulsed field gradient method. The volumetric data are interpreted by means of the phase separation model, and values of the CMC, volume change, and standard free energy change of micellization are obtained. From the viscosity data the hydration numbers of the surfactant hydrophilic head in the micellar state are computed; they are in agreement with those obtained from HDO self-diffusion data. The surfactant self-diffusion data are used to calculate the apparent micelle radius and the aggregation number. The micellization parameters obtained for the different surfactants are compared and discussed. 相似文献
992.
Magnetic field-induced orientation of a chiral side chain liquid crystalline polyacrylate(P-11) was studied by using IR dichroism. For the investigated P-11, it has been shown thatthe magnetic alignment takes place over the entire temperature range between its meltingpoint and clearing point and the orientation level is strongly temperature-dependent, thedevelopment with time of the magnetic orieatation follows an exponeotial-type relation,and the smectic phase state influences the thermal relaxation process in the absence of themagnetic field. 相似文献
993.
Summary The simultaneous stereospecific assay of four stereoisomers of diltiazem hydrochloride in bulk drug and aqueous solution was
developed using HPLC on a Chiralcel OF column. The four isomers were quantitated with good precision by the internal standard
method. The chiral inversion of (+)-cis-diltiazem hydrochloride in vitro, stability of its (2S, 3S) configuration in the solid
and aqueous states was examined by HPLC. Chiral inversion of (+)-cis-diltiazem hydrochloride was not observed in the solid
state, and its (2S, 3S) configuration was stable to heat, humidity and light. Chiral inversion of (+)-cis-diltiazem hydrochloride
(2S, 3S) was observed in aqueous solution under UV, but not in aqueous solution stored at 80°C for 5h nor under visible light
for 10 h. The (+)-cis-diltiazem hydrochloride (2S, 3S) epimerized to (+)-trans-diltiazem hydrochloride (2R, 3S) with a half-life
of 5h in aqueous solution under UV but the reverse chiral inversion of (+)-trans-diltiazem hydrochloride (2R, 3S) to (+)-cis-diltiazem
hydrochloride (2S, 3S) was not observed. 相似文献
994.
A. V. Kazakova N. D. Kushch L. I. Buravov E. B. Yagubskii S. V. Simonov L. V. Zorina S. S. Khasanov R. P. Shibaeva E. Canadell J. Yamada M. Umemiya 《Russian Chemical Bulletin》2007,56(1):49-55
New radical cation salts based on 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) with copper(II) metal complex anions, β-(BDA-TTP)4Cu2Cl6 and (BDA-TTP)2CuCl4, were synthesized and structurally characterized. Single crystals were prepared by electrochemical oxidation of BDA-TTP under
galvanostatic conditions. X-ray diffraction study demonstrated that the salts have a layered structure, in which the conducting
BDA-TTP layers alternate with the [Cu2Cl6]2− or [CuCl4]2− anions. Both salts show the semiconductor-type temperature dependence of the conductivity.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 48–54, January, 2007. 相似文献
995.
以紫外光谱、荧光光谱、粘度法和凝胶电泳方法研究了全反式维甲酸合钇(Ⅲ)配合物与DNA的作用。结果表明,该配合物能在生理条件下比配体和金属离子更有效地切割质粒DNA,体系离子强度和pH值的变化对配合物的切割活性有较大影响,自由基捕捉剂的加入不影响配合物的切割活性。该配合物对DNA的切割可能通过水解机理进行。该配合物可使DNA的粘度增加,使EB-DNA体系的荧光强度和DNA溶液的紫外吸收强度降低。据此推断,该配合物主要以嵌入方式与DNA作用。 相似文献
996.
Affinity Chromatography of Insulin with a Heptapeptide Ligand Selected from Phage Display Library 总被引:1,自引:0,他引:1
A heptapeptide phage display library was screened with insulin to find its ligands for affinity chromatography. The peptide was synthesized and coupled to EAH Sepharose 4B (5.4 mol mL–1 bed). Then, insulin chromatography was carried out with mobile phases of different pH values and by the addition of urea and ethylene glycol. It was found that electrostatic interactions were predominant for the affinity binding, and hydrogen bonding might also contribute somewhat to the affinity. Finally, frontal analysis was performed and the dynamic binding capacity of the affinity column for insulin at 50% breakthrough was estimated at 60.6 mg mL–1 bed, which was about two times higher than the theoretical binding capacity of the monomeric insulin. The result suggests that insulin was bound in dimer state in a stoichiometric relationship with the coupled peptide, indicating the high binding efficiency of the peptide ligand for insulin. 相似文献
997.
聚硅氧烷涂敷的反相高效液相色谱固定相 总被引:5,自引:1,他引:5
用甲基乙烯基聚硅氧烷涂敷于硅烷化的微粒硅胶上,制备出一种新型的涂敷型反相高效液相色谱固定相。该固定相对极性、非极性和碱性化合物均有良好的分离能力,峰对称性好。对其恶性循环 了考察,连续使用三个月后,固定相的碳量和色谱性能仍保持不变。 相似文献
998.
N-[2(3)-Hydroxyalkylj-4-thiazolidinones have been synthesized by the reaction of 2(3)-vinyloxyalkylamines with mercaptoacetic acid in 24–69 % yield. The structure of the compounds obtained was supported by (R and1H NMR spectroscopic data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 677–679, March, 1996. 相似文献
999.
Hiromu Hayashi 《Catalysis Surveys from Japan》1999,3(1):43-52
Additive telluromolybdates, MoO3·2TeO2 and MIIO·TeO2·MoO3 (MIITeMoO6; MII = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO2–MoO3, and crystalline Te2MoO7 was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO6 revealed the layer structure quite different from that of the reference Te2MoO7, but tellurium was again located adjacent to molybdenum linked through lattice oxygen. 相似文献
1000.