全文获取类型
收费全文 | 13387篇 |
免费 | 2067篇 |
国内免费 | 1856篇 |
专业分类
化学 | 10328篇 |
晶体学 | 191篇 |
力学 | 673篇 |
综合类 | 129篇 |
数学 | 1546篇 |
物理学 | 4443篇 |
出版年
2024年 | 24篇 |
2023年 | 199篇 |
2022年 | 339篇 |
2021年 | 414篇 |
2020年 | 463篇 |
2019年 | 505篇 |
2018年 | 406篇 |
2017年 | 429篇 |
2016年 | 621篇 |
2015年 | 666篇 |
2014年 | 755篇 |
2013年 | 911篇 |
2012年 | 1154篇 |
2011年 | 1292篇 |
2010年 | 879篇 |
2009年 | 772篇 |
2008年 | 931篇 |
2007年 | 821篇 |
2006年 | 801篇 |
2005年 | 677篇 |
2004年 | 536篇 |
2003年 | 489篇 |
2002年 | 474篇 |
2001年 | 389篇 |
2000年 | 333篇 |
1999年 | 339篇 |
1998年 | 246篇 |
1997年 | 216篇 |
1996年 | 175篇 |
1995年 | 167篇 |
1994年 | 146篇 |
1993年 | 109篇 |
1992年 | 111篇 |
1991年 | 125篇 |
1990年 | 79篇 |
1989年 | 49篇 |
1988年 | 59篇 |
1987年 | 48篇 |
1986年 | 38篇 |
1985年 | 35篇 |
1984年 | 15篇 |
1983年 | 26篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
81.
本文针对单件小批量生产系统 ,建立了模糊优化的动态随机投入产出模型 ,同时给出了该模型的递推解法 ,并用此模型对某单件小批企业在生产计划期的商品量进行了规划 相似文献
82.
83.
84.
A novel copolymer, poly(N‐hexyl‐3,7‐phenothiazylene‐1,2‐ethenylene‐2,6‐pyridylene‐1,2‐ethenylene) ( P3 ), containing N‐hexyl‐3,7‐phenothiazylene and 2,6‐pyridylene chromophores was synthesized to investigate the effect of protonation, metal complexation, and chemical oxidation on its absorption and photoluminescence (PL). Poly(N‐hexyl‐3,8‐iminodibenzyl‐1,2‐ethenylene‐1,3‐phenylene‐1,2‐ethenylene) and poly(N‐hexyl‐3,7‐phenothiazylene‐1,2‐ethenylene‐1,3‐phenylene‐1,2‐ethenylene) ( P2 ), consisting of 1,3‐divinylbenzene alternated with N‐hexyl‐3,8‐iminodibenzyl and N‐hexyl‐3,7‐phenothiazylene, respectively, were also prepared for comparison. Electrochemical investigations revealed that P3 exhibited lower band gaps (2.34 eV) due to alternating donor and acceptor conjugated units (push–pull structure). The absorption and PL spectral variations of P3 were easily manipulated by protonation, metal chelation, and chemical oxidation. P3 displayed significant bathochromic shifts when protonated with trifluoroacetic acid in chloroform. The complexation of P3 with Fe3+ led to a significant absorption change and fluorescence quenching, and this implied the coordination of ferric ions with the 2,6‐pyridylene groups in the backbone. Moreover, both phenothiazylene‐containing P2 and P3 showed conspicuous PL quenching with a slight redshift when oxidized with NOBF4. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1272–1284, 2004 相似文献
85.
Guosong Wu Xiaoqin Zeng Wenbin Ding Xingwu Guo Shoushan Yao 《Applied Surface Science》2006,252(20):7422-7429
Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO2 and Al2O3 as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiOx film as well as the AlOx film. In the electrochemical corrosion test, the AlOx coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiOx coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate. 相似文献
86.
Chen-liang Li Jin-ping Zeng 《应用数学学报(英文版)》2007,23(1):79-90
We consider several synchronous and asynchronous multisplitting iteration schemes for solving aclass of nonlinear complementarity problems with the system matrix being an H-matrix.We establish theconvergence theorems for the schemes.The numerical experiments show that the schemes are efficient forsolving the class of nonlinear complementarity problems. 相似文献
87.
海藻酸钠/大豆蛋白共混凝胶微球的结构 总被引:4,自引:1,他引:3
利用钙离子交联海藻酸钠/大豆分离蛋白共混溶液,制得海藻酸钠/大豆分离蛋共混凝胶微球.结果表明,海藻酸钠和大豆分离蛋白质量配比的不同以及各组分间相互作用的变化,微球呈现不同的微观结构.将微球干燥后置于水中溶胀,微球的尺寸无法回复到干燥前的尺寸,这是由于真空干燥处理使水分子挥发,促进微球内组分间形成了强的氢键作用所致.此外,用碱处理该共混微球,发现由于大豆分离蛋白溶解以及部分钙离子被置换析出,微球塌陷且内部形成了大孔. 相似文献
88.
89.
90.