全文获取类型
收费全文 | 1479篇 |
免费 | 62篇 |
国内免费 | 5篇 |
专业分类
化学 | 1173篇 |
晶体学 | 15篇 |
力学 | 16篇 |
数学 | 78篇 |
物理学 | 264篇 |
出版年
2022年 | 15篇 |
2021年 | 12篇 |
2020年 | 31篇 |
2019年 | 25篇 |
2018年 | 20篇 |
2017年 | 8篇 |
2016年 | 30篇 |
2015年 | 29篇 |
2014年 | 41篇 |
2013年 | 99篇 |
2012年 | 77篇 |
2011年 | 108篇 |
2010年 | 47篇 |
2009年 | 46篇 |
2008年 | 85篇 |
2007年 | 89篇 |
2006年 | 86篇 |
2005年 | 63篇 |
2004年 | 62篇 |
2003年 | 54篇 |
2002年 | 42篇 |
2001年 | 35篇 |
2000年 | 22篇 |
1999年 | 24篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 20篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 12篇 |
1974年 | 6篇 |
1973年 | 13篇 |
排序方式: 共有1546条查询结果,搜索用时 15 毫秒
111.
Utilization of a metalloligand, ([Cu(2,4-pydca)2(H2O)].2Et3NH) (1) (2,4-pydca = pyridine-2,4-dicarboxylate), as a building unit provides a novel porous coordination polymer, ([ZnCu(2,4-pydca)2(H2O)3(DMF)].DMF)n (2), in which the Zn(II) ion at the node of the network acts as a linker and the Cu(II) ion in the channel wall is available for guest-coordination. 相似文献
112.
Yamashita M Yamamoto Y Akiba Ky Nagase S 《Angewandte Chemie (International ed. in English)》2000,39(22):4055-4058
113.
Single crystals of amylose V complexes with the 81 helical configuration can be obtained from aqueous solutions of amylose by using α-naphthol as a complexing agent. Morphological observations suggest that the differences in crystallization behavior among the α-naphthol complex and other complexes with alcohols are due to differences in solubility of the complexes in water. Electron diffraction studies indicate a two-dimensional tetragonal unit cell with a = b = 22.9 Å. It is deduced that the space group providing a satisfactory arrangement of two helices is one of the enantiomorphs P41212 and P43212. From x-ray diffraction it was found that the c axis spacing of the α-naphthol complex is equivalent to that in 61 and 71 helical amylose crystals. Consequently, the geometry of the helical configuration requires an integral number of glucose residues per turn. The true helical diameters of the n-butanol, isopropanol, and α-naphthol complexes were calculated from experimental data. The ratio was 6:7:8 and indicated that the helix of the α-naphthol complex has eight glucose residues per turn. The diversity of helical configurations in V amylose crystals is discussed. 相似文献
114.
115.
Four three-coordinate arylpalladium amido complexes with a single hindered phosphine were isolated and structurally characterized. Each possessed a T-shaped geometry. Several of these complexes possessed true three-coordinate structures that lacked any additional coordination by ligand C-H bonds. All of the three-coordinate complexes underwent reductive elimination to form the corresponding triarylamine. A comparison of the rate of reaction of the three-coordinate compounds demonstrated that the rate of elimination from the pentaphenylferrocenyl di-tert-butylphosphine complex were the fastest. A comparison of the rates of reactions between three-coordinate and four-coordinate complexes showed that the rates were much faster from the three-coordinate complexes. 相似文献
116.
The straightforward methodology for the construction of chiral arene-fused-piperidine motifs using a highly enantioselective addition of 2-trityloxymethylaryllithiums to cyclic and acyclic nitroalkenes has been developed. The versatility of the process was highlighted by the first asymmetric synthesis of a dopamine D1 full agonist, A-86929. 相似文献
117.
Hozumi N Yamashita R Lee CK Nagao M Kobayashi K Saijo Y Tanaka M Tanaka N Ohtsuki S 《Ultrasonics》2004,42(1-9):717-722
The authors have proposed a new type of ultrasonic microscopy for biological tissue characterization. The system is driven by a nanosecond pulse voltage, the generated acoustic wave being reflected at the front and rear side of the sliced tissue. In this report, a time-frequency analysis was applied to determine the sound speed thorough the tissue. Frequency dependence of sound speed was obtained with a myocardium of a rat sliced into 10 microm. As the reflected waveform had a significant amount of oscillating component, the waveform was once subjected to the deconvolution process. As the result, two reflections were clearly separated in time domain. Then these two reflections were separately analyzed by time-frequency analysis. Each reflection was extracted by using a proper window function. Phase angles of these reflections at the same frequency were compared. A sound speed micrograph at an arbitrary frequency in between 50 and 150 MHz was successfully obtained. A tendency was found that the sound speed slightly increases with frequency. 相似文献
118.
Kato S Matsumoto T Ishi-i T Thiemann T Shigeiwa M Gorohmaru H Maeda S Yamashita Y Mataka S 《Chemical communications (Cambridge, England)》2004,(20):2342-2343
Novel donor-pi-bridge-acceptor-pi-bridge-donor (D-pi-A-pi-D) type 2,1,3-benzothiadiazole fluorescent dyes connected to the N,N-diarylamino terminus via various type pi-conjugate spacers exhibits large two-photon absorption cross-sections and high fluorescent quantum yields in orange-red color. 相似文献
119.
A laser terahertz-emission microscope (LTEM) system is proposed and developed for inspecting electrical faults in integrated circuits (IC). We test a commercial operational amplifier while the system is operating. Two-dimensional terahertz-emission images of the IC chip are clearly observed while the chip is scanned with a femtosecond laser. When one of the interconnection lines is cut, the damaged chip has a LTEM image different from that of normal chips. The results indicate that the LTEM system is a potential tool for IC inspection. 相似文献
120.
We investigated adsorbed states of CO on Pt(997) at 11 K using infrared reflection absorption spectroscopy. At 11 K, thermal migration is suppressed and thus the initial chemisorption at terrace sites and step sites is controlled by the transient mobility of the adsorbing molecule. The initial occupation ratio between atop CO on the terrace and atop CO at the step is directly determined to be 3.6:1. With a simple isotropic migration model, we estimated the mean lateral displacement from the first impact point to the initial chemisorption site to be 6.8 A. We also discuss the origin of transient mobility of CO on metal surfaces. 相似文献