全文获取类型
收费全文 | 161585篇 |
免费 | 2122篇 |
国内免费 | 541篇 |
专业分类
化学 | 89799篇 |
晶体学 | 2439篇 |
力学 | 6381篇 |
综合类 | 4篇 |
数学 | 16500篇 |
物理学 | 49125篇 |
出版年
2021年 | 1364篇 |
2020年 | 1578篇 |
2019年 | 1730篇 |
2018年 | 2007篇 |
2017年 | 1972篇 |
2016年 | 3127篇 |
2015年 | 2103篇 |
2014年 | 2883篇 |
2013年 | 6911篇 |
2012年 | 5863篇 |
2011年 | 7151篇 |
2010年 | 4835篇 |
2009年 | 4757篇 |
2008年 | 6599篇 |
2007年 | 6293篇 |
2006年 | 6179篇 |
2005年 | 5670篇 |
2004年 | 5031篇 |
2003年 | 4562篇 |
2002年 | 4427篇 |
2001年 | 5766篇 |
2000年 | 4137篇 |
1999年 | 3245篇 |
1998年 | 2262篇 |
1997年 | 2366篇 |
1996年 | 2234篇 |
1995年 | 2059篇 |
1994年 | 2022篇 |
1993年 | 1822篇 |
1992年 | 2298篇 |
1991年 | 2368篇 |
1990年 | 2195篇 |
1989年 | 2139篇 |
1988年 | 2119篇 |
1987年 | 2132篇 |
1986年 | 1952篇 |
1985年 | 2438篇 |
1984年 | 2447篇 |
1983年 | 1942篇 |
1982年 | 1968篇 |
1981年 | 1796篇 |
1980年 | 1777篇 |
1979年 | 2063篇 |
1978年 | 2140篇 |
1977年 | 2081篇 |
1976年 | 2013篇 |
1975年 | 1884篇 |
1974年 | 1873篇 |
1973年 | 1899篇 |
1972年 | 1246篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed. 相似文献
72.
A systematic study on the electrochemical behavior of diosmin in Britton-Robinson buffer (pH 2.0-10.0) at a glassy carbon electrode (GCE) was made. The oxidation process of the drug was found to be quasi-reversible with an adsorption-controlled step. The adsorption stripping response was evaluated with respect to various experimental conditions, such as the pH of the supporting electrolyte, the accumulation potential and the accumulation time. The observed anodic peak current at +0.73 V vs. Ag/AgCl reference electrode increased linearly over two orders of magnitude from 5.0x10(-8) M to 9.0x10(-6) M. A limit of detection down to 3.5x10(-8) M of diosmin at the GCE was achieved with a mean recovery of 97+/-2.1%. Based on the electrochemical data, an open-circuit accumulation step in a stirred sample solution of BR at pH 3.0 was developed. The proposed method was successfully applied to the determination of the drug in pharmaceutical formulations. The results compared favorably with the data obtained via spectrophotometric and HPLC methods. 相似文献
73.
74.
The development of a tool for calculating resonances and bound states in three-body systems described by a single-potential
energy surface is reported. The method has been applied to the antiprotonic helium, doubly excited states in helium, the 11Li nuclear halo, the NeICl van der Waals molecule, and the recently found FHD reaction complex.
Received November 26, 2001; accepted for publication November 28, 2001 相似文献
75.
The buffer extracts (3S) of sclerotia of Sclerotinia sclerotiorum IFO 9395 contained mitogenic substance(s) to murine splenocytes (Shinohara et al. Chem. Pharm. Bull., 38, 2219 (1990)). Although the native 3S was slightly mitogenic, heating of 3S induced significant mitogenic activity. To isolate the mitogen, we separated 3S by ion-exchange and gel filtration chromatographies. The isolated mitogen, named sclerogen, has a molecular mass of 32 kilodaltons (kDa) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the isoelectric point (pI) of 5.9 by chromatofocusing. Sclerogen was significantly mitogenic in vitro against murine splenocytes after heat denaturation, and also showed the augmentation of the primary mixed lymphocyte reaction (MLR) in vitro. However, sclerogen did not show the activation of an alternative pathway of complement and hemagglutination activity. These results suggest that sclerogen is a unique mitogen which differs from lectins and shows mitogenicity after heat denaturation. 相似文献
76.
77.
We study matter-wave solitons in Bose-Einstein condensates of ultracold gaseous atoms with spin degrees of freedom and present a class of exact solutions based on the inverse scattering method. The one-soliton solutions are classified with respect to the spin states. We analyze collisional effects between solitons in the same or different spin state(s), which reveals a very interesting possibility: we can manipulate the spin dynamics by controlling the parameters of colliding solitons. 相似文献
78.
79.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
80.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献