全文获取类型
收费全文 | 193827篇 |
免费 | 23949篇 |
国内免费 | 23978篇 |
专业分类
电工技术 | 18583篇 |
技术理论 | 8篇 |
综合类 | 13428篇 |
化学工业 | 40471篇 |
金属工艺 | 7690篇 |
机械仪表 | 12154篇 |
建筑科学 | 8807篇 |
矿业工程 | 2207篇 |
能源动力 | 6183篇 |
轻工业 | 14452篇 |
水利工程 | 2485篇 |
石油天然气 | 4259篇 |
武器工业 | 1941篇 |
无线电 | 30884篇 |
一般工业技术 | 20888篇 |
冶金工业 | 4298篇 |
原子能技术 | 3265篇 |
自动化技术 | 49751篇 |
出版年
2024年 | 1059篇 |
2023年 | 3568篇 |
2022年 | 6402篇 |
2021年 | 7342篇 |
2020年 | 7005篇 |
2019年 | 6372篇 |
2018年 | 5940篇 |
2017年 | 8040篇 |
2016年 | 8706篇 |
2015年 | 9842篇 |
2014年 | 9524篇 |
2013年 | 12765篇 |
2012年 | 14447篇 |
2011年 | 16356篇 |
2010年 | 11723篇 |
2009年 | 11558篇 |
2008年 | 12826篇 |
2007年 | 14220篇 |
2006年 | 13616篇 |
2005年 | 11650篇 |
2004年 | 9879篇 |
2003年 | 7743篇 |
2002年 | 5927篇 |
2001年 | 4471篇 |
2000年 | 3721篇 |
1999年 | 3142篇 |
1998年 | 2600篇 |
1997年 | 2108篇 |
1996年 | 1682篇 |
1995年 | 1371篇 |
1994年 | 1223篇 |
1993年 | 918篇 |
1992年 | 734篇 |
1991年 | 608篇 |
1990年 | 516篇 |
1989年 | 369篇 |
1988年 | 291篇 |
1987年 | 184篇 |
1986年 | 175篇 |
1985年 | 231篇 |
1984年 | 200篇 |
1983年 | 139篇 |
1982年 | 193篇 |
1981年 | 97篇 |
1980年 | 95篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 25篇 |
1976年 | 15篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The insecticidal nonprotein amino acid S-(-carboxyethyl)-cysteine (S-CEC) is the major free amino acid in the seeds of severalCalliandra spp. where it accounts for up to 2.9 % of dry weight. Lesser amounts of other related S-containing amino acids and an array of nonprotein imino acids derived from pipecolic acid are other constituents. High concentrations of imino acids, which also show insecticidal activity, are maintained in the mature leaves, but sulfur compounds are lacking. In this study the disappearance of S-CEC from the germinating seeds and young seedlings ofC. rubescens was monitored over time. After 10 weeks, S-CEC continues to be found in high concentrations in the stems and new leaves. As young leaves mature, sulfur compounds quickly decrease in concentration. Traces of S-CEC are found in new leaves of plants up to nine months after germination. Whether high concentration of S-CEC in young leaves is due to transportation from the seed or de novo synthesis is unclear. The ecological implications are discussed. 相似文献
992.
介绍了一种测定废水中LAS浓度的新方法。克服了常规方法亚甲基蓝比色法要绘制标准曲线,操作过程复杂等局限性。该方法测定过程简单,结果准确,标准偏差为1.4l,变异系数为3.92%。 相似文献
993.
994.
Gas hold-up, mixing intensity of dispersion characterised by exchange flows between adjacent impellers and a volumetric mass transfer coefficient are presented for 18 impeller configurations in triple-impeller vessel of inner diameter . Rushton Turbines, six Pitched Blade impellers pumping down and hydrofoil impellers Techmix 335 (Techmix co., Czech republic) pumping up or down and their combinations were used. aqueous solution was used as a liquid phase, which represents non-coalescent batches. Gas hold-ups and volumetric mass transfer coefficients are presented for individual configurations as functions of specific power dissipated and superficial gas velocity. The regression of the mass transfer coefficients shows large standard deviation (30%). The power number included to the regression to express the impeller configuration effect did not improve the standard deviation significantly (23%). The impeller configurations with low power number (less than unity) provide higher dispersion mixing intensities, while the impeller configurations with high power number provide better mass transfer performance. 相似文献
995.
Atom transfer radical polymerization of n‐butyl methacrylate (BMA) was conducted in an aqueous dispersed system with different kinds of copper complexes. The partitioning behavior of the copper complexes, including CuCl/4,4′‐di(5‐nonyl)‐2,2′‐bipydine (dNbpy), CuCl2/dNbpy, CuCl/2,2′‐bipydine (bpy), CuCl2/bpy, CuCl/bis(N,N′‐dimethylaminoethyl)ether (bde), and CuCl2/bde between the monomer (BMA), and water was studied in detail with ultraviolet‐visible spectroscopy. The results show that with a less hydrophobic ligand, such as bpy or bde, most of the Cu(I) or the Cu(II) complexes migrated from the BMA phase to the aqueous phase, the atom transfer equilibrium was destroyed, and the polymerization was nearly not controlled; it converted to classical emulsion polymerization. As to the very hydrophobic ligand dNbpy, although the partitioning study of the copper complexes indicated that not all the copper species were restricted to the organic phase, the linear correlation between the molecular weight and the monomer conversion and the narrow polydispersities confirmed that the polymerization was still quite well controlled. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3175–3179, 2003 相似文献
996.
制备了HDI(1,6-己二异氰酸酯)型聚酯聚氨酯/聚(甲基丙烯酸甲酯-甲基丙烯酸-β羟乙酯)(HDI-PU/P(MMA-HEMA))互穿网络胶粘剂,研究了接枝剂甲基丙烯酸-β羟乙酯(HEMA)用量对其形态、性能与分子结构的影响。结果表明,接枝剂HEMA可使分散相接枝到连续相中形成复合网络,从而改善其界面的相容性,提高其胶液粘度和初粘力,并可广泛作为制鞋工业用胶。 相似文献
997.
Yinzhong Guo Vijay M. Mannari Pulin Patel John L. Massingill 《Journal of Coatings Technology and Research》2006,3(4):327-331
A series of soybean oil phosphate ester polyols (SOPEP) was prepared by reaction of fully epoxidized soybean oil with phosphoric
acid and simultanoeous hydrolysis in the presence of a polar solvent. The polyols were characterized by determination of acid
value, oxirane number, hydroxyl value, molecular weight (GPC), and FTIR spectra. These polyols with varying amounts of acid
phosphate groups could be self-emulsified to form aqueous dispersions after neutralization with organic base. These aqueous
dispersion showed varying degrees of stability and their appearance ranged from opaque dispersions to translucent to clear
solutions. Waterborne coating compositions were prepared using these aqueous dispersions as principal components and their
thermally cured film properties were studied. it was found that by careful selection and formulation, SOPEPs can be successfully
used for low-VOC waterborne coating formulations. SOPEPs with 3.5% phosphate ester content showed visibly superior corrosion
resistance properties. 相似文献
998.
车联网在生活中扮演着越来越重要的角色,它可以有效地防止交通拥堵从而减少交通事故。然而,在车联网中总是有非法车辆试图接入车联网并发布虚假消息。此外,现有方案多数存在计算效率低下的问题。针对上述存在的问题进行了研究,提出了一种车联网中基于雾计算和多TA的条件隐私保护认证方案。在保护车辆用户身份的条件下实现了车辆、雾节点、TA三者之间的身份认证,且在车辆追踪阶段可以还原车辆用户的真实身份,从而实现条件隐私保护。雾计算的使用降低了方案的计算和通信开销,同时多TA模型的使用也解决了单TA单点故障的问题。安全性证明和性能分析的结果表明该方案是安全且高效的。最后对当前方案进行了总结以及对未来研究作出了展望。 相似文献
999.
报道了TGS晶体的溶液状态及其快速生长的实验结果。发现了pH为2.52的溶液是实现快速生长的最佳溶液,利用快速旋转叶片来加速溶液对流,对于截面积为40mm×40 mm的(010)面,其生长速度达到了5mm/d,对快速生长的TGS晶体的性能研究表明:其热电和介电性能也发生了一些变化。 相似文献
1000.
标量乘法是椭圆曲线密码算法中最核心的运算,其运算速度影响着整个密码体制的实现效率。首先,详细地介绍了Edwards曲线的基本概念。其次,为了提高标量乘法的运算速度,针对椭圆曲线标量乘算法进行了研究,引入了一种可以用来计算连续倍点2◢△mP◣的算法CDA。为了提高CDA的计算效率,提出了将标量◢k◣表示为4-NNAF形式以减少◢k◣的长度,再结合CDA计算标量乘法可以有效地减少运算量。最后根据算法的运算量分析和具体例子得出,减少标量◢k◣长度后的计算效率提高了13%以上。为了进一步加快运算速度,又提出了对CDA中乘法运算和模逆运算采用并行结构来减少标量乘法的运算次数。计算结果表明,并行后的计算效率提高了36%以上。 相似文献