全文获取类型
收费全文 | 61753篇 |
免费 | 1978篇 |
国内免费 | 2931篇 |
专业分类
系统科学 | 2211篇 |
丛书文集 | 2219篇 |
教育与普及 | 1911篇 |
理论与方法论 | 205篇 |
现状及发展 | 307篇 |
研究方法 | 192篇 |
综合类 | 59606篇 |
自然研究 | 11篇 |
出版年
2024年 | 298篇 |
2023年 | 654篇 |
2022年 | 996篇 |
2021年 | 1182篇 |
2020年 | 784篇 |
2019年 | 333篇 |
2018年 | 594篇 |
2017年 | 682篇 |
2016年 | 781篇 |
2015年 | 1562篇 |
2014年 | 2201篇 |
2013年 | 2083篇 |
2012年 | 2435篇 |
2011年 | 2871篇 |
2010年 | 2790篇 |
2009年 | 3080篇 |
2008年 | 3471篇 |
2007年 | 3325篇 |
2006年 | 2751篇 |
2005年 | 2749篇 |
2004年 | 1967篇 |
2003年 | 1959篇 |
2002年 | 2040篇 |
2001年 | 2117篇 |
2000年 | 1918篇 |
1999年 | 2911篇 |
1998年 | 2397篇 |
1997年 | 2421篇 |
1996年 | 2292篇 |
1995年 | 1895篇 |
1994年 | 1752篇 |
1993年 | 1454篇 |
1992年 | 1262篇 |
1991年 | 1197篇 |
1990年 | 963篇 |
1989年 | 920篇 |
1988年 | 734篇 |
1987年 | 434篇 |
1986年 | 258篇 |
1985年 | 81篇 |
1984年 | 19篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1969年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
341.
Fuzzy metric and convergences based on the symmetric difference 总被引:1,自引:0,他引:1
342.
The vibrational energy transfer from highly vibrationally excited CO to H2O molecules is studied by time-resolved Fourier transform infrared emission spectroscopy (TR FTIR). Following the 193 nm laser
photolysis of CHBr3 and O2 the secondary reactions generate CO(v). The infrared emission of CO(v → v−1) is detected by TR FTIR. The excitation of H2O molecules is not observed. By the method of the spectral simulation and the differential technique, 8 rate constants for
CO(v)/H2O system are obtained: (1.7 ±0.1), (3.4 ±0.2), (6.2 ±0.4), (8.0 ±1.0), (9.0 ±2.0), (12 ±3), (16 ±4) and (18 ±7) (1013cm3 · molecule-1· s-1). At least two reasons lead to the efficient energy transfer. One is the contributions of the rotational energy to the vibational
energy defect and the other is the result of the complex collision. With the SSH andab initio calculations, the quenching mechanism of CO(v) by H2O is suggested. 相似文献
343.
A type of recurring relations on syndrome series is presnted. After some important theorems are established, an algorithm for computing a minimal polynomial set is presented. Finally an algorithm for determining the unknown syndromes with incorporating α majority scheme is presented. 相似文献
344.
Determination of tectonic background for sedimentary basin from sandstone geochemistry 总被引:2,自引:0,他引:2
The chemical composition of sedimentary rocks is mainly controlled by source rocks. Through examining chemical composition
of terrigenous rocks, the tectonic evolution of a sedimentary basin can be modeled. The Turpan Basin belongs to a continental
sedimentary basin and its source rocks are derived from the upper continental crust. 相似文献
345.
346.
A new calculation method was discussed to treat the Hückel Hamiltonian of any fullerene with a certain point group symmetry. This method was applied to calculating the electronic energy levels of icosahedral fullerenes C\-n(I\-h: n=60h 2, 0相似文献
347.
The shear-wave splitting was analyzed on the deep seismic sounding profile crossing the Dabieshan area. The direction difference
between Sg and SmS fast wave polarization indicates that the modem regional tectonic stress field in the Dabieshan area exists
only in uppcr crust, while the crack alignment caused by the Triassic collision between the North China and the Yangtze blocks
had been preserved in mid-lower curst. 相似文献
348.
Identification and classification of subspecies of Asian cultivated rice and their hybrids 总被引:2,自引:0,他引:2
Xiangkun Wang Renhua Li Chuanqing Sun Zichao Li Hongwei Cai Xinli Sun 《科学通报(英文版)》1998,43(22):1864-1864
Having reviewed the major classification systems proposed by various scholars across the world, it is found thatindica andjaponica underO. sativa L. are two major directions thoroughly differentiated from the Asian cultivated rice, forming the framework of the classification
structure. A system withindica andjaponica as the only two subspecies is therefore reiterated. There are various ways to determine the indica-japonica identity of hybrid
rice, but the “combined morphological trait index” (CMT index) method is more efficient and easier to handle, although the
isozyme analysis, molecular marker analysis and grain quality assay methods are also feasible. 相似文献
349.
Carbon isotope anomaly in marbles associated with eclogites from the Dabie Mountains 总被引:1,自引:0,他引:1
This is a report of carbon isotope anomaly in marbles associated with the UHP eclogites from the Dabie Mountains. The results
place constraints on the degree of crust-mantle interaction during the UHP metamorphism. 相似文献
350.
Ming Tan Dongsheng Liu Hua Zhong Xiaoguang Qin Hongchun Li Shusen Zhao Tieying Li Jinbo Lu Xiangyang Lu 《科学通报(英文版)》1998,43(6):506-506
Within the East Asian monsoon zone the change in oxygen isotope of Holocene stalagmite is mainly related to monsoon rain rather than to temperature. And carbon isotope can be taken as a comprehensive signal which contains the natural information and the information of anthropogenic activity. Isotopic analysis is also compared with the annual layer records. 相似文献