全文获取类型
收费全文 | 22640篇 |
免费 | 3959篇 |
国内免费 | 3236篇 |
专业分类
化学 | 16174篇 |
晶体学 | 326篇 |
力学 | 1468篇 |
综合类 | 216篇 |
数学 | 2599篇 |
物理学 | 9052篇 |
出版年
2024年 | 105篇 |
2023年 | 488篇 |
2022年 | 837篇 |
2021年 | 844篇 |
2020年 | 1012篇 |
2019年 | 996篇 |
2018年 | 879篇 |
2017年 | 831篇 |
2016年 | 1173篇 |
2015年 | 1173篇 |
2014年 | 1359篇 |
2013年 | 1779篇 |
2012年 | 2130篇 |
2011年 | 2132篇 |
2010年 | 1538篇 |
2009年 | 1455篇 |
2008年 | 1686篇 |
2007年 | 1409篇 |
2006年 | 1230篇 |
2005年 | 979篇 |
2004年 | 810篇 |
2003年 | 621篇 |
2002年 | 651篇 |
2001年 | 502篇 |
2000年 | 441篇 |
1999年 | 463篇 |
1998年 | 320篇 |
1997年 | 249篇 |
1996年 | 255篇 |
1995年 | 220篇 |
1994年 | 189篇 |
1993年 | 173篇 |
1992年 | 154篇 |
1991年 | 143篇 |
1990年 | 133篇 |
1989年 | 97篇 |
1988年 | 72篇 |
1987年 | 53篇 |
1986年 | 42篇 |
1985年 | 56篇 |
1984年 | 40篇 |
1983年 | 29篇 |
1982年 | 23篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Whereas the thermospray mass spectra of most compounds consist of only the pseudo-molecular ion with little fragmentation, the thermospray mass spectra of arteether (a cyclic endoperoxide) and its metabolites are relatively complex. Assignments of structures to individual fragments from normal spectra was particularly ambiguous because of uncertainties as to which fragments arose from ammonium ion or methanol adducts. In this study, these assignments could be resolved through the comparison of the regular spectrum with the deuterium-exchange spectrum (in an ND4O2CCH3–CD3OD–D2O mobile phase) achieved using ‘sandwiched slug’ injection technique. The mass spectra of arteether and four of its metabolites all showed [M + ND4]+ pseudo-molecular ions with greater than 91% H/D exchange, indicating a high efficiency with a minimal use of deuterated mobile phase. Most fragments showed H/D exchange rates in the 70–90% range and the isotope shift of individual spectral lines (ΔM) was found to be extremely useful in determining the structure of the fragment. 相似文献
142.
借助定量金相、扫描电子显微镜、透射电子显微镜等微观分析手段对钨质量分数为93%的钨合金在15~50GPa冲击压力下微观结构响应性态进行了考察,发现了一些钨合金所特有的现象,即钨颗粒与粘结相交界处出现成分迁移,新相析出;并结合断口分析,探讨了钨合金在冲击作用下发生断裂的微观特征与韧脆转化间的关系及其物理本质。 相似文献
143.
Hongyu Liu Xinhui Guo Juncheng Chen Aobo Song Gu Jin Qizhi Yao Jiao Li Lingling Li 《大学化学》1986,35(12):221-226
This paper introduces an experiment about waste liquid recovery and effect evaluation in laboratory. Through this experiment, the basic operations of crystal preparation, chemical analysis and instrumental analysis are further consolidated. At the same time, it allows students to experience a series of possible problems of condition selection and control in the process of waste liquid treatment. We hope to improve the students' ability to analyze and solve problems, enhance their interest in learning, and strengthen their humanistic education. 相似文献
144.
The intrinsic deprotonation constant (pK(a(2))(int)) and the intrinsic ion exchange constants (pK(Me(+))(int)) of Li(+), Na(+), and K(+) on SiO(2) were uniquely determined at 30 degrees C by using the potentiometric titration data, the Gouy-Chapman-Stern-Grahame (GSCG) model for the structure of the electrical double-layer (edl) and the double-extrapolation method. The values of these constants were pK(a(2))(int) = 6.57, pK(Li(+))(int) = pK(Na(+))(int) = pK(K(+))(int) = 5.61. The chemical meaning of intrinsic equilibrium constants and the equality in the values of pK(Li(+))(int), pK(Na(+))(int) and pK(K(+))(int) were discussed. 相似文献
145.
Yan-Qing Wang Hong-Mei Zhang Gen-Cheng Zhang Wei-Hua Tao Shu-He Tang 《Journal of Molecular Structure》2007,830(1-3):40-45
The feature of brucine binding to human serum albumin (HSA) was investigated via fluorescence and UV/vis absorption spectroscopy. The results revealed that brucine caused the fluorescence quenching of HSA by the formation of brucine–HSA complex. The hydrophobic interaction plays a major role in stabilizing the complex; the binding site number n and apparent binding constant KA, corresponding thermodynamic parameters the free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) at different temperatures were calculated. The distance r between donor (HSA) and acceptor (brucine) was obtained according to fluorescence resonance energy transfer. The effect of brucine on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy and UV/vis absorption spectroscopy. 相似文献
146.
An easily prepared and highly efficient monodentate phosphoramidite ligand derived from BINOL, (S)-2,2'-O,O-(1,1'-binaphthyl)-dioxo-N,N-diethylphospholidine, was examined in the hydrogenation of both enamides and alpha-dehydroamino acid derivatives. The catalyst provided remarkably high enantioselectivities (up to 99.6% ee for enamides and >99.9% ee for alpha-dehydroamino acid derivatives). 相似文献
147.
Xin Sheng Li Yan Xin Chen Yao Jun Zhang Chun Xin Ji Qin Xin 《Reaction Kinetics and Catalysis Letters》1996,58(2):391-396
Hydrogen adsorption-desorption over Mo2N has been studied using a temperature-programmed technique. It is revealed that hydrogen on Mo2N exhibits very high mobility leading to migration of the surface hydrogen into the sublayer and bulk of the sample or the reverse. The surface hydrogen species are preferentially formed when adsorption is carried out below 573 K. On increasing the adsorption temperature to above 573 K, the quantity of hydrogen species located in the sublayer or/and bulk of the Mo2N sample increases significantly. 相似文献
148.
Du Jinzhou Dong Wenming Wang Xiangke Tao Zuyi 《Journal of Radioanalytical and Nuclear Chemistry》1996,203(1):31-36
The effect of different solid components of calcareous soil on the retention of Sr was investigated by using batch technique and selective extraction method. The sorption and desorption isotherms of Sr on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001 M CaCl2. It was found that all isotherms are linear and that the sorption of Sr on the calcareous soil can be described by a reversible sorption process and the sorption mechanism is mainly ion exchange. 相似文献
149.
Ju Tao LIU Xiao Hong WANG Jing Fu LIU Faculty of Chemistry Northeast Normal University Changchun 《中国化学快报》2004,15(7):859-862
A novel vanadate decamer, involving all vanadium atoms present in +5 oxidation and one formhydroxamic acid dimer cation readical, has been synthesized. The single-crystal X-ray diffraction shows that the orange crystal is formed in the triclinic system, space group Pi, a = 8. 4960 (17), b = 10.447 (2), c = 11.299 (2) A, α= 68. 82 (3)°,β= 87.35 (3)°, γ = 66.97(3)°. V = 855. 3(3) A3, Z = 8, R1 = 0. 0857, wR2=0. 2551. X-ray crystallographic and packing in superlattice studies showed that the crystal structure was constructed by electrostatic attraction of O-H…O hydrogen bonds between formhydroxamic acid dimer cation and decavanadate polyanion. Formhydroxamic acid dimer is got through controlling the condition of the reaction using formhydroxamic acid. 相似文献
150.