全文获取类型
收费全文 | 47379篇 |
免费 | 7902篇 |
国内免费 | 8417篇 |
专业分类
化学 | 22916篇 |
晶体学 | 749篇 |
力学 | 2309篇 |
综合类 | 812篇 |
数学 | 3716篇 |
物理学 | 13567篇 |
无线电 | 19629篇 |
出版年
2024年 | 213篇 |
2023年 | 932篇 |
2022年 | 1591篇 |
2021年 | 1749篇 |
2020年 | 1645篇 |
2019年 | 1473篇 |
2018年 | 1352篇 |
2017年 | 1650篇 |
2016年 | 1703篇 |
2015年 | 2122篇 |
2014年 | 2620篇 |
2013年 | 3300篇 |
2012年 | 3795篇 |
2011年 | 3820篇 |
2010年 | 3233篇 |
2009年 | 3423篇 |
2008年 | 3746篇 |
2007年 | 3472篇 |
2006年 | 3327篇 |
2005年 | 2929篇 |
2004年 | 2284篇 |
2003年 | 1808篇 |
2002年 | 1692篇 |
2001年 | 1507篇 |
2000年 | 1488篇 |
1999年 | 1166篇 |
1998年 | 710篇 |
1997年 | 602篇 |
1996年 | 642篇 |
1995年 | 556篇 |
1994年 | 505篇 |
1993年 | 443篇 |
1992年 | 396篇 |
1991年 | 295篇 |
1990年 | 261篇 |
1989年 | 259篇 |
1988年 | 219篇 |
1987年 | 157篇 |
1986年 | 122篇 |
1985年 | 91篇 |
1984年 | 88篇 |
1983年 | 64篇 |
1982年 | 49篇 |
1981年 | 51篇 |
1980年 | 36篇 |
1979年 | 19篇 |
1974年 | 7篇 |
1965年 | 20篇 |
1964年 | 10篇 |
1957年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
基于DOCSIS标准的增强型基线保密性接口(BPI+)采用56bit DES加密分组数据,采用二密钥三重DES加密通信量加密密钥。这种多重加密技术的应用为HFC网络的数据传输提供了相当于或更好于专线级的网络安全与加密性能。 相似文献
2.
介绍两个表连接的几种常用方式和不同方式的内部机制.在比较3种不同表连接方式的优缺点基础上,选择一种好的方式来优化表连接,以提高查询速度,并结合中国邮政报刊发行系统数据库开发中遇到的生产实际,分析3种表连接方式的优劣. 相似文献
3.
The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004 相似文献
4.
Nylon‐6/glass‐fiber (GF)/liquid‐crystalline‐polymer (LCP) ternary blends with different viscosity ratios were prepared with three kinds of nylon‐6 with different viscosities as matrices. The rheological behaviors of these blends were characterized with capillary rheometry. The morphology was observed with scanning electron microscopy and polarizing optical microscopy. This study showed that although LCP did not fibrillate in binary nylon‐6/LCP blends, LCP fibrillated to a large aspect ratio in some ternary blends after GF was added. The addition of 5 wt % LCP significantly reduced the melt viscosity of nylon‐6/GF blends to such an extent that some nylon‐6/GF/LCP blends had quite low viscosities, not only lower than those of neat resins and nylon‐6/GF blends but also lower than those of corresponding nylon‐6/LCP blends. The mutual influence of the morphology and rheological properties was examined. The great reduction of the melt viscosity was considered the result of LCP fibrillation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1619–1627, 2004 相似文献
5.
Based on the complexation between proteins and Cu(II) coupled with the time-resolved chemiluminescence (CL) technique, a highly sensitive and quantitative assay for measuring proteins in solution is described. The complexes of proteins with Cu(II) have a strongly catalytic effect on the luminol-H2O2 CL reaction. Because the CL emission produced by the complexes is much more long-lived than that by Cu(II), the CL signals originating from proteins can be easily identified and measured with a time-resolved technique. On this basis, bovine albumin fraction V (BAF V) can be quantitatively determined in the range of 0.01 - 5.0 microg/ml with a detection limit of 5.8 ng/ml. The results show that the proposed assay exhibits a small variation in the response values for the same amount of different proteins, as compared to the Lowry as well as Bradford assays. The CL assay has also been studied for the detection of immobilized proteins. 相似文献
6.
A hybrid cluster complex, formed by chelating a chromogenic ligand to a [2Fe-2S] cluster, sensitively exhibited differential colorimetric responses towards Hg2+, Cd2+, Cr3+, Pb2, Sn2+, Cu2+, Zn2+, Fe3+ and Co2+ in water at physiological pH. Speciation of some of these metal elements, such as Cr(III) and Sn(IV), was also studied by UV/Vis absorption. 相似文献
7.
8.
The complete and incomplete aggregation-annihilation processes are investigated with the method of generating function, and the scale exponents are obtained exactly. We find that the scale exponents of incomplete aggregation-annihilation process are different from the previous exponents obtained by different methods. The time dependence of the total number of clusters and the total mass of clusters are analytically obtained. 相似文献
9.
10.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献