全文获取类型
收费全文 | 339159篇 |
免费 | 3702篇 |
国内免费 | 533篇 |
专业分类
化学 | 167921篇 |
晶体学 | 5212篇 |
力学 | 15453篇 |
综合类 | 12篇 |
数学 | 51148篇 |
物理学 | 103648篇 |
出版年
2020年 | 2357篇 |
2019年 | 2479篇 |
2018年 | 11575篇 |
2017年 | 12403篇 |
2016年 | 8985篇 |
2015年 | 4336篇 |
2014年 | 4929篇 |
2013年 | 12066篇 |
2012年 | 13373篇 |
2011年 | 22589篇 |
2010年 | 14226篇 |
2009年 | 14020篇 |
2008年 | 19523篇 |
2007年 | 22708篇 |
2006年 | 8638篇 |
2005年 | 14521篇 |
2004年 | 10416篇 |
2003年 | 9686篇 |
2002年 | 7361篇 |
2001年 | 7138篇 |
2000年 | 5788篇 |
1999年 | 4157篇 |
1998年 | 3270篇 |
1997年 | 3117篇 |
1996年 | 3287篇 |
1995年 | 2911篇 |
1994年 | 2865篇 |
1993年 | 2655篇 |
1992年 | 3318篇 |
1991年 | 3146篇 |
1990年 | 3131篇 |
1989年 | 3080篇 |
1988年 | 3115篇 |
1987年 | 3092篇 |
1986年 | 2945篇 |
1985年 | 3794篇 |
1984年 | 3769篇 |
1983年 | 2992篇 |
1982年 | 3081篇 |
1981年 | 3150篇 |
1980年 | 2874篇 |
1979年 | 3224篇 |
1978年 | 3207篇 |
1977年 | 3227篇 |
1976年 | 3120篇 |
1975年 | 2809篇 |
1974年 | 2782篇 |
1973年 | 2779篇 |
1972年 | 1868篇 |
1968年 | 1948篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Y Sonoda K Ichinose T Yoshimura Y Sato T Sasaki 《Chemical & pharmaceutical bulletin》1991,39(1):100-103
Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity. 相似文献
172.
The problem of the vector and axial-vector dominance of weak interactions within the framework of the quark model of superconductivity type is discussed. 相似文献
173.
174.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献
175.
176.
177.
178.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
179.
180.
Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献