全文获取类型
收费全文 | 15602篇 |
免费 | 3160篇 |
国内免费 | 4311篇 |
专业分类
化学 | 11327篇 |
晶体学 | 551篇 |
力学 | 1036篇 |
综合类 | 454篇 |
数学 | 2521篇 |
物理学 | 7184篇 |
出版年
2024年 | 22篇 |
2023年 | 205篇 |
2022年 | 553篇 |
2021年 | 544篇 |
2020年 | 632篇 |
2019年 | 611篇 |
2018年 | 588篇 |
2017年 | 771篇 |
2016年 | 649篇 |
2015年 | 854篇 |
2014年 | 942篇 |
2013年 | 1279篇 |
2012年 | 1290篇 |
2011年 | 1333篇 |
2010年 | 1202篇 |
2009年 | 1216篇 |
2008年 | 1325篇 |
2007年 | 1179篇 |
2006年 | 1125篇 |
2005年 | 1004篇 |
2004年 | 790篇 |
2003年 | 732篇 |
2002年 | 816篇 |
2001年 | 815篇 |
2000年 | 642篇 |
1999年 | 407篇 |
1998年 | 158篇 |
1997年 | 146篇 |
1996年 | 135篇 |
1995年 | 114篇 |
1994年 | 73篇 |
1993年 | 110篇 |
1992年 | 89篇 |
1991年 | 80篇 |
1990年 | 64篇 |
1989年 | 80篇 |
1988年 | 67篇 |
1987年 | 44篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 46篇 |
1983年 | 44篇 |
1982年 | 45篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
由“从正则分布出发,在小涨落近似下得出的能量涨落分布公式”求得的能量涨落的二次矩与直接由正则分布求得的二次矩完全相同,但分别由二求得的高次矩并不完全相同。 相似文献
82.
Dashan Huang Yoshitaka Kai Frank J. Fabozzi Masao Fukushima 《European Journal of Operational Research》2007
This paper presents a model for optimally designing a collateralized mortgage obligation (CMO) with a planned amortization class (PAC)-companion structure using dynamic cash reserve. In this structure, the mortgage pool’s cash flow is allocated by rule to the two bond classes such that PAC bondholders receive substantial prepayment protection, that protection being provided by the companion bondholders. The structure we propose provides greater protection to the PAC bondholders than current structures during periods of rising interest rates when this class of bondholders faces greater extension risk. We do so by allowing a portion of the cash flow from the collateral to be reserved to meet the PAC’s scheduled cash flow in subsequent periods. The greater protection is provided by the companion bondholders exposure to interest loss. To tackle this problem, we transform the problem of designing the optimal PAC-companion structure into a standard stochastic linear programming problem which can be solved efficiently. Moreover, we present an extended model by considering the quality of the companion bond and by relaxing the PAC bondholder shortfall constraint. Based on numerical experiments through Monte Carlo simulation, we show the utility of the proposed model. 相似文献
83.
84.
在电流及温度分布满足“不变性”原理的基础上,本文分析了等离子体中心热区的能量平衡,求出了电子热传导系数,根据实验数据拟合出HL-1装置电子热传导系数的定标关系为X_e=6.8(n_(eq1))~(-1.2)。此关系与其他托卡马克装置的结果类似。 相似文献
85.
Photoluminescence spectra of a series of MBE-grown Hg1-xCdxTe samples with the same mole fraction of about x≈0.39 have been measured at different temperatures from 5 to 100 K. By aid of the temperature and exciting laser power dependence of photoluminescence peak energy and relative intensity, as well as of the comparison with other measurements, four main structures dominating in the photoluminescence spectra are attributed to band to band, DoX, AoX and DoAo transitions. A deep donor state level located at about 8.5meV below the bottom of the conduction band has been observed and is determined to be due to the arsenic-occupied mercury vacancies. Two acceptor levels located at about 14.5 meV and about 31.5 meV above the top of the valance band have also been found from the measuements, which are identified as the mercury vacancies and As in anion site, respectively. 相似文献
86.
MicrostructureEvolutioninLaserRSCo-baseMetastableAlloyWANGAnan;CHENGShunqi;GUOZhiyao(KunmingUniversityofScienceandTechnology,... 相似文献
87.
Cytologic and embryologic studies on the reproductive pattern of male sterility line C1001 in rice (Oryza saliva L.) indicated that several types of apomixis were discovered in partial strains of male sterility line C1001 in rice. Under a fully separate condition, two possible apomixis embryogenesis ways in the ovules were observed: One way was that the embryo was initiated from the somatic cells of the ovules, and then pushed against the embryo sac to develop into a mature embryo. The other way was that the embryo was from the unfertilized egg cell or one of synergids, and then developed into a mature embryo in the form of haploid parthenogenesis without forming endosperm. Besides, the antipodal cells migrated in the embryo sac, and their cytoplasm became thin and vacuolated while mitosis was taking place, giving rise to a multicellular structure or a group of large cells each containing several nuclei. This paper also discusses the significance and patterns of apomixis in rice C1001. 相似文献
88.
有限维路代数的K_1群 总被引:1,自引:0,他引:1
本文通过计算有限维路代数k△的单位群和单位群的阿贝尔化,完全刻划了 任意域上有限维路代数的K1群. 相似文献
89.
In this paper we apply linear control theory to study the effect of various inventory policies on order and inventory variability, which are key drivers of supply chain performance. In particular, we study a two-echelon supply chain with a stationary demand pattern under the influence of three inventory policies: an inventory-on-hand policy that bases orders on the visible inventory at an installation, an installation-stock policy that bases orders on the inventory position (on-hand plus on-order inventory) at an installation, and an echelon-stock policy that bases orders on the inventory position at that installation and all downstream installations. We prove analytically that the inventory-on-hand policy is unstable in practical settings, confirming analytically what has been observed in experimental settings and in practice. We also prove that the installation-stock and echelon-stock policies are stable and analyze their effect on order and inventory fluctuation. Specifically, we show the general superiority of the echelon-stock in our setting and demonstrate analytically the effect of forecasting parameters on order and inventory fluctuations, confirming the results in other research. 相似文献
90.