全文获取类型
收费全文 | 47107篇 |
免费 | 3692篇 |
国内免费 | 3230篇 |
专业分类
化学 | 39831篇 |
晶体学 | 236篇 |
力学 | 1125篇 |
综合类 | 369篇 |
数学 | 3565篇 |
物理学 | 8903篇 |
出版年
2024年 | 73篇 |
2023年 | 487篇 |
2022年 | 1015篇 |
2021年 | 1081篇 |
2020年 | 1275篇 |
2019年 | 1292篇 |
2018年 | 1134篇 |
2017年 | 1568篇 |
2016年 | 1858篇 |
2015年 | 1702篇 |
2014年 | 1910篇 |
2013年 | 2761篇 |
2012年 | 2918篇 |
2011年 | 2563篇 |
2010年 | 2301篇 |
2009年 | 2761篇 |
2008年 | 2349篇 |
2007年 | 2678篇 |
2006年 | 2385篇 |
2005年 | 2245篇 |
2004年 | 1913篇 |
2003年 | 1539篇 |
2002年 | 1454篇 |
2001年 | 1050篇 |
2000年 | 1101篇 |
1999年 | 990篇 |
1998年 | 947篇 |
1997年 | 903篇 |
1996年 | 824篇 |
1995年 | 870篇 |
1994年 | 675篇 |
1993年 | 601篇 |
1992年 | 471篇 |
1991年 | 497篇 |
1990年 | 427篇 |
1989年 | 359篇 |
1988年 | 468篇 |
1987年 | 434篇 |
1986年 | 335篇 |
1985年 | 319篇 |
1984年 | 324篇 |
1983年 | 176篇 |
1982年 | 287篇 |
1981年 | 235篇 |
1980年 | 178篇 |
1979年 | 178篇 |
1978年 | 50篇 |
1976年 | 15篇 |
1975年 | 9篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
工程施工中运输网络优化方案 总被引:5,自引:0,他引:5
施工工地运输方案的优化设计可以归结为 :按施工期要求设计运输线路或验证已有线路通行能力 ,计算总线路中影响提高流量的关键路段 ,取得最小费用最大流 .本文运用图论理论这一数学工具把实际问题抽象为有向网络 ,进而建立数学模型 .此方法理论上严密 ,解题步聚直观清晰 ,对水利、公路、水路、铁路等其它运输系统有普遍意义 . 相似文献
82.
Mean value in invexity analysis 总被引:1,自引:0,他引:1
In this paper, a generalization of the mean value theorem is considered in the case of functions defined on an invex set with respect to η (which is not necessarily connected). 相似文献
83.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献
84.
85.
86.
The association of complex formation with static quenching in CT systems was investigated. Evaluation of the data made evident
that the inner filter effect must be allowed for. Time-resolved and temperature-dependent stationary measurements of fluorescence
led to the separation of dynamic and static quenching components. The static quenching constant is discussed with respect
to the equilibrium constant of complex formation determined by absorption spectroscopy. 相似文献
87.
A highly selective solid phase extraction sorbent for pre-concentration of sameridine made by molecular imprinting 总被引:5,自引:0,他引:5
Summary A novel approach to solid phase extraction, based on the use of a highly selective molecularly imprinted polymer, is presented.
The versatility of this type of sorbent for solid phase extraction was demonstrated in a model batch-wise pre-concentration
of sameridine prior to gas chromatography. Problems associated with leakage of remaining imprint molecules during the desorption
phase could be eliminated by the use of a close structural analogue of sameridine as the imprint species. It was found that
a major benefit of the imprinted polymer was its specificity, which lead to distinctly cleaner chromatographic traces and
ability to improve sensitivity by extracting sameridine from larger sample volumes. 相似文献
88.
Modified Stern-Volmer equation is obeyed by bovine serum albumin (BSA)-iodide system showing selective quenching of tryptophanyl
fluorescence of BSA. The fraction of accessible protein fluorescence is 0.56 and the effective Stern-Volmer constant is 290
M-1 at pH 7.4 in 0.005 M phosphate buffer at 25°C. Collisional quenching is operative both in the BSA -I−1 system and the model system, tryptophan-I−1. It is supported by the observed relationship between the ratio of quenching rate constants (k
q
) and diffusion coefficients and alsok
q
with bulk viscosity. 相似文献
89.
本文系统研究了MFX体系中Eu3+荧光光谱特征,着重讨论了X-,M2+及杂质缺陷(主要为O2-)对Eu3+发光的影响. 相似文献
90.
A method employing a wide pore polymeric reversed phase column has been developed for the separation of most of the chlorophylls and related compounds previously described as occurring in marine microalgae. The high selectivity toward molecular shape of this kind of stationary phase has enabled compounds of very similar structure, such as chlorophylls c1, c2 and Mg-divinylpheoporphyrin a5 monomethyl ester, and chlorophyll a and the phytol-substituted chlorophyll c-like pigments, which commonly coelute on monomeric bonded phases, to be resolved in a single run. Some of these pigments, formerly thought to be a single compound, have, in fact, been demonstrated to be groups of two or more. The method has been successfully applied to both algal cultures and natural sea water samples. When visible light absorbance detection was used, the method proved suitable for separation of various carotenoids. 相似文献