全文获取类型
收费全文 | 5494篇 |
免费 | 598篇 |
专业分类
系统科学 | 1076篇 |
理论与方法论 | 276篇 |
现状及发展 | 891篇 |
研究方法 | 3篇 |
综合类 | 3846篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 728篇 |
2017年 | 732篇 |
2016年 | 431篇 |
2015年 | 30篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 258篇 |
2011年 | 952篇 |
2010年 | 814篇 |
2009年 | 455篇 |
2008年 | 509篇 |
2007年 | 762篇 |
2006年 | 4篇 |
2005年 | 44篇 |
2004年 | 122篇 |
2003年 | 150篇 |
2002年 | 56篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 2篇 |
1991年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1962年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有6092条查询结果,搜索用时 0 毫秒
981.
The rate constants for the hydrogen donation of three 3-aryl-benzofuranone compounds with tert-butoxyl radicals have been cal-culated through laser flash photolysis (LFP) technique, which were used to evaluate the hydrogen donating abilities of those 3-aryl-benzofuranone compounds. The antioxidant activities of those 3-aryl-benzofuranone compounds in polypropylene (PP) have been studied using the oxidation induction time (OIT) of PP stabilized by those 3-aryl-benzofuranone compounds too. It has been found t... 相似文献
982.
The equatorial Pacific underwent a significant climate transition during the late Pliocene, which is characterized by cooling of global sea surface temperatures (SSTs) and formation of a marked SST gradient between the eastern and western equatorial Pacific. Moreover, this transition was nearly synchronous with the late Pliocene Northern Hemisphere glaciation. Probing the relationship among solar insolation, low and high latitude processes is the key to unravel the mechanism of this climate transition. A se... 相似文献
983.
S-wave velocity of the crust around Tianshan Mountains inverted from seismic ambient noise tomography 总被引:1,自引:0,他引:1
We process ambient noise data from seismic stations deployed in central Asia to determine the crustal shear wave velocity structure beneath the Tianshan Mountians and surrounding area. About 748 inter-station Rayleigh wave empirical Green’s functions have been recovered to estimate the phase velocity dispersions over periods from 6 to 50 s using the image transformation technique. Results show that for short periods (6–20 s), the distribution of Rayleigh wave phase velocities is generally consistent with surface geology, with high velocities corresponding to mountain ranges and low velocities to sedimentary basins. Along two profiles, which trend from NE-SW and NW-SE, the shear wave velocity shows a pair of high velocity anomalies dipping in opposite directions beneath the Tianshan Mountains. At shallow depths, those high velocity anomalies roughly correlate with areas where the mountain front and the surrounding basin are connected. The profiles also show a narrow zone beneath the Tianshan Mountains, which may represent a route for the upwelling from upper mantle. Those observations suggest that the underthrusting of the Tarim Basin and Kazakh Shield combine with the weakness of the crust, which is heated by the upwelling from upper mantle, may play an important role on the reactivation of the Tianshan Mountains associated with the India-Eurasia collision. 相似文献
984.
Fluid and melt inclusions in mantle xenoliths are thought as direct samples to study mantle liquids. Here we apply Raman mi- crospectroscopy and microthermometry to fluid/melt inclusions in lherzolite xenoliths in Qiaoshan basalts, a Miocene volcano in Linqu, Shandong Province, eastern China. These inclusions include (1) early CO2 fluid inclusions, (2) early carbonate melt inclu-sions, (3) late CO2 fluid inclusions, and (4) late silicate melt inclusions. Among the early CO2 fluid inclusions, most consist of... 相似文献
985.
We thank Cheng et al. for their interest in our paper “On linking climate to Chinese dynastic change: Spatial and temporal variations of of monsoonal rain” [1]. Our paper was written largely as a response to the suggestion made by Zhang P Z, et al. [2] that climate has a key role in affecting chapters of Chinese cultural history (e.g. the demise of the Tang, Yuan and Ming dynasties).
........... 相似文献
........... 相似文献
986.
Raman spectroscopy has been widely used to identify the physical properties of carbon nanotubes (CNTs), and to assess their func-tionalization as well as orientation. Recently, Raman spectroscopy has become a powerful tool to characterize the interfacial properties between CNTs and polymer matrices. This review provides an overview of micro-Raman spectroscopy of CNTs and its application in studying CNT reinforced polymer composites. Based on the specific Raman band shifts relating to the mechanical deformation of CNTs, Raman scattering can be used to evaluate the interactions between the CNTs and the surrounding polymer in the composites, and to detect the phase transitions of the polymer, and investigate the local stress state as well as the Young’s modulus of the CNTs. Moreover, we also review the current progress of Raman spectroscopy in various CNT macroarchitectures (such as films, fibers as well as composite fibers). The microscale structural deformation of CNT macroarchitectures and strain transfer factors from macroscale architectures to microscale structures are inferred. Based on an in situ Raman-tensile test, we further predict the Young’s modulus of the CNT macroarchitectures and reveal the dominating factors affecting the mechanical performances of the CNT macroarchitectures 相似文献
987.
In this paper, based on the verifiable pair and identity-based threshold cryptography, a novel identity-based (ID-based) threshold
decryption scheme (IDTDS) is proposed, which is provably secure against adaptive chosen ciphertext attack under the computational
bilinear Diffie-Hellman (CBDH) problem assumption in the random oracle. The pubic checkability of ciphertext in the IDTDS
is given by simply creating a signed ElGamal encryption instead of a noninteractive zero-knowledge proof. Furthermore, we
introduce a modified verifiable pairing to ensure all decryption shares are consistent. Our scheme is more efficient in verification
than the schemes considered previously. 相似文献
988.
Lianru Zhang Junjie Chen Siyang Song Zhonghui Zheng Yaojian Huang 《武汉大学学报:自然科学英文版》2010,15(5):444-448
The interaction between acetylgliotoxin and human serum albumin (HSA) has been studied by spectroscopic method. Acetylgliotoxin
quenches the intrinsic fluorescence of HSA in a static quenching procedure. The binding of acetylgliotoxin to HSA causes a
slight conformational change of HSA. The binding constants at different temperatures as well as enthalpy change and entropy
change, are calculated according to relevant fluorescent data and Van’t Hoff equation. The hydrogen bond is a predominant
intermolecular force for stabilizing the complex, which is in conformity with the results of molecular modeling study. 相似文献
989.
In this paper,a Littlewood-Paley function characterization of the spaces L p(R),1
相似文献
990.
For the problem of track correlation failure under the influence of sensor system deviation in wireless sensor networks, a
new track correlation method which is based on relative positional relation chart matching is proposed. This method approximately
simulates the track correlation determination process using artificial data, and integrally matches the relative position
relation between multiple targets in the common measuring space of various sensors in order to fulfill the purpose of multi-target
track correlation. The simulation results show that this method has high correlation accuracy and robustness. 相似文献