全文获取类型
收费全文 | 48132篇 |
免费 | 4617篇 |
国内免费 | 4410篇 |
专业分类
化学 | 30483篇 |
晶体学 | 517篇 |
力学 | 8223篇 |
综合类 | 308篇 |
数学 | 6250篇 |
物理学 | 11378篇 |
出版年
2024年 | 57篇 |
2023年 | 492篇 |
2022年 | 1067篇 |
2021年 | 1255篇 |
2020年 | 1531篇 |
2019年 | 1388篇 |
2018年 | 1305篇 |
2017年 | 1551篇 |
2016年 | 1735篇 |
2015年 | 1639篇 |
2014年 | 2061篇 |
2013年 | 3365篇 |
2012年 | 2570篇 |
2011年 | 3007篇 |
2010年 | 2381篇 |
2009年 | 3001篇 |
2008年 | 2786篇 |
2007年 | 2844篇 |
2006年 | 2541篇 |
2005年 | 2295篇 |
2004年 | 2328篇 |
2003年 | 1868篇 |
2002年 | 2133篇 |
2001年 | 1366篇 |
2000年 | 1183篇 |
1999年 | 1002篇 |
1998年 | 959篇 |
1997年 | 840篇 |
1996年 | 853篇 |
1995年 | 770篇 |
1994年 | 738篇 |
1993年 | 569篇 |
1992年 | 580篇 |
1991年 | 373篇 |
1990年 | 313篇 |
1989年 | 279篇 |
1988年 | 289篇 |
1987年 | 220篇 |
1986年 | 183篇 |
1985年 | 189篇 |
1984年 | 175篇 |
1983年 | 77篇 |
1982年 | 178篇 |
1981年 | 139篇 |
1980年 | 133篇 |
1979年 | 162篇 |
1978年 | 110篇 |
1977年 | 76篇 |
1976年 | 71篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
71.
基于校园网的实验管理系统的设计 总被引:2,自引:1,他引:1
主要讨论了应用实验室管理系统的必要性,并从用户需求分析、系统总体设计、功能模块的设计等方面对B/S实验室管理系统的开发进行了详细的阐述。 相似文献
72.
Amine boranes bearing hydrophobic substituents were used to reduce aryl ketones in competition with a methyl ketone. Their high stability in protic solvents combined with their ease of preparation made amine boranes useful compounds in the study of hydrophobically directed selective reductions. Several characteristics of the reducing agent were found to be important in determining the reaction selectivity, including available hydrocarbon surface area, degree of fluorination, and proximity of the hydrophobic group to the active hydrides. 相似文献
73.
All-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity
Fei Wang 《Optics Communications》2006,257(2):334-339
A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme. 相似文献
74.
75.
Cosmic dust and our origins 总被引:1,自引:0,他引:1
J Mayo Greenberg 《Surface science》2002,500(1-3):793-822
The small solid particles in the space between the stars provide the surfaces for the production of many simple and complex molecules. Processes involving the effects of ultraviolet irradiation of the thin (hundredth micron) mantles are shown to produce a wide range of molecules and ions also seen in comets. Some of the more complex ones inferred from laboratory experiments are expected to play an important role in the origin of life. An outline of the chemical evolution of interstellar dust as observed and as studied in the laboratory is presented. Observations of comets are shown to provide substantial evidence for their being fluffy aggregates of interstellar dust as it was in the protosolar nebula, i.e. the interstellar cloud which collapsed to form the solar system. The theory that comets may have brought the progenitors of life to the earth is summarized. 相似文献
76.
77.
78.
79.
We introduce a new scheme for the future application of Real-coded Lattice Gas (RLG) to the numerical simulation of suspended solid objects in a fluctuating fluid environment. The reproduction of Brownian motion for a single solid object is verified through the Gaussian distribution of its displacements. The effectiveness of the solid–solid interaction model is also confirmed in an N-body simulation. 相似文献
80.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献