全文获取类型
收费全文 | 40515篇 |
免费 | 3240篇 |
国内免费 | 2127篇 |
专业分类
电工技术 | 3315篇 |
技术理论 | 2篇 |
综合类 | 2330篇 |
化学工业 | 12439篇 |
金属工艺 | 1898篇 |
机械仪表 | 1323篇 |
建筑科学 | 1831篇 |
矿业工程 | 704篇 |
能源动力 | 1178篇 |
轻工业 | 5156篇 |
水利工程 | 1779篇 |
石油天然气 | 2168篇 |
武器工业 | 268篇 |
无线电 | 2971篇 |
一般工业技术 | 2784篇 |
冶金工业 | 1483篇 |
原子能技术 | 552篇 |
自动化技术 | 3701篇 |
出版年
2024年 | 134篇 |
2023年 | 586篇 |
2022年 | 2009篇 |
2021年 | 2673篇 |
2020年 | 1139篇 |
2019年 | 1037篇 |
2018年 | 965篇 |
2017年 | 1158篇 |
2016年 | 1383篇 |
2015年 | 1477篇 |
2014年 | 2114篇 |
2013年 | 2203篇 |
2012年 | 2572篇 |
2011年 | 3062篇 |
2010年 | 2163篇 |
2009年 | 2377篇 |
2008年 | 2164篇 |
2007年 | 2409篇 |
2006年 | 2227篇 |
2005年 | 1813篇 |
2004年 | 1561篇 |
2003年 | 1340篇 |
2002年 | 1132篇 |
2001年 | 960篇 |
2000年 | 764篇 |
1999年 | 703篇 |
1998年 | 524篇 |
1997年 | 497篇 |
1996年 | 451篇 |
1995年 | 428篇 |
1994年 | 378篇 |
1993年 | 246篇 |
1992年 | 205篇 |
1991年 | 174篇 |
1990年 | 162篇 |
1989年 | 127篇 |
1988年 | 91篇 |
1987年 | 57篇 |
1986年 | 73篇 |
1985年 | 48篇 |
1984年 | 49篇 |
1983年 | 33篇 |
1982年 | 39篇 |
1981年 | 31篇 |
1980年 | 36篇 |
1979年 | 34篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 650 毫秒
51.
A highly transparent and thermally stable copolymer of 1‐adamantyl methacrylate and styrene
下载免费PDF全文
![点击此处可从《Polymer International》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Thermal and optical properties of copolymers of 1‐adamantyl methacrylate (AdMA) and styrene (St) prepared by free radical polymerization in the bulk are investigated. The copolymer forms an azeotrope when the composition is AdMA/St = 55/45 mol%. The glass transition temperature and decomposition temperature of the azeotropic copolymer are 170 and ca 340 °C, respectively. The refractive index increases nonlinearly with St content from 1.522 to 1.591. The light scattering loss at 633 nm is 28.1 dB km?1, which is less than half of that of polystyrene. The total optical loss including molecular vibrational absorption, which is evaluated using a copolymer‐based optical fiber, is 292–645 dB km?1 at 500–700 nm. These values correspond to transmittances of 86–93% for a 1 m optical path length. © 2014 Society of Chemical Industry 相似文献
52.
The aim of this paper is to assess the closeness of agreement between results of ELISA and LC-MS/MS methods for determination of aflatoxin B1 in corn and aflatoxin M1 in milk. Samples of corn (n=100) and milk (n=250) were simultaneously analyzed using ELISA and LC-MS/MS methods, after the severe drought that affected Serbia in summer 2012 resulting in occurrence of aflatoxin B1 in corn and aflatoxin M1 in milk. Regression analysis showed higher level of agreement between aflatoxin B1 samples (R2=0.994), compared to aflatoxin M1 samples (R2=0.920). However, both techniques were satisfactory in meeting the requirements for official control purposes. 相似文献
53.
Bengü Ergüden 《Yeast (Chichester, England)》2019,36(2):99-105
The correct separation of chromosomes during mitosis is necessary to prevent genetic instability and aneuploidy, which are responsible for cancer and other diseases, and it depends on proper centrosome duplication. In a recent study, we found that Smy2 can suppress the essential role of Mps2 in the insertion of yeast centrosome into the nuclear membrane by interacting with Eap1, Scp160, and Asc1 and designated this network as SESA (S my2, E ap1, S cp160, A sc1). Detailed analysis showed that the SESA network is part of a mechanism which regulates translation of POM34 mRNA. Thus, SESA is a system that suppresses spindle pole body duplication defects by repressing the translation of POM34 mRNA. In this study, we performed a genome-wide screening in order to identify new members of the SESA network and confirmed Dhh1 as a putative member. Dhh1 is a cytoplasmic DEAD-box helicase known to regulate translation. Therefore, we hypothesized that Dhh1 is responsible for the highly selective inhibition of POM34 mRNA by SESA. 相似文献
54.
The fission yeast Schizosaccharomyces pombe is an important model organism for the study of fundamental questions in eukaryotic cell and molecular biology. A plethora of cellular processes are membrane associated and/or dependent on the proper functioning of cellular membranes. Phospholipids are not only the basic building blocks of cellular membranes; they also serve as precursors to numerous signaling molecules. In this review, we describe the biosynthetic pathways leading to major S. pombe phospholipids, how these pathways are regulated, and what is known about degradation and turnover of fission yeast phospholipids. This review also addresses the synthesis, regulation and the role of water-soluble phospholipid precursors. The last chapter of the review is devoted to the use of S. pombe for the biotechnological production of value-added lipid molecules. 相似文献
55.
Alice Maurer Prof. Dr. Florian P. Seebeck 《Chembiochem : a European journal of chemical biology》2020,21(20):2908-2911
Ergothioneine has emerged as a crucial cytoprotectant in the pathogenic lifestyle of Mycobacterium tuberculosis. Production of this antioxidant from primary metabolites may be regulated by phosphorylation of Thr213 in the active site of the methyltransferase EgtD. The structure of mycobacterial EgtD suggests that this post-translational modification would require a large-scale change in conformation to make the active-site residue accessible to a protein kinase. In this report, we show that, under in vitro conditions, EgtD is not a substrate of protein kinase PknD. 相似文献
56.
Yingli Li Shaoying Zhang Yu Dong 《International Journal of Food Science & Technology》2021,56(1):115-125
Ethylene continues to be a major factor influencing quality of European pears during storage. Although research has been done on the effect of pre-harvest 1-methylcyclopropene (1-MCP) on physiological characteristics in pears, a full understanding of cultivar response and antioxidant metabolism remains elusive. Spraying 1-MCP on ‘Bartlett’ and ‘d’Anjou’ pears was studied with respect to physiology, storage and eating quality, disorders, and antioxidant properties at two harvest date (H1 and H2) during storage and ripening. Treatment with 1-MCP extended the harvest window of ‘Bartlett’ and ‘d’Anjou’ pears 3 and 4 days, respectively, without reducing storage or eating quality. Treatment with 1-MCP reduced ethylene production (EPR) and respiration rates (RR), maintained fruit firmness and green colour during storage and retarded development of desirable melting texture in both cultivars. Additionally, 1-MCP lowered the incidence of disorders by alleviating membrane lipid peroxidation, retaining high total flavonoids (TF) and antioxidant capacity, and enhancing superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity in both cultivars. Overall, pre-harvest 1-MCP applications could extend storage time of ‘Bartlett’ and ‘d’Anjou’ pears to 5 and 6 months, respectively, at −1.1 ± 0.5 °C, by reducing ethylene synthesis and enhancing antioxidant metabolism. 相似文献
57.
1-read/1-write (1R1W) register file (RF) is a popular memory configuration in modern feature rich SoCs requiring significant amount of embedded memory. A memory compiler is constructed using the 8T RF bitcell spanning a range of instances from 32 b to 72 Kb. An 8T low-leakage bitcell of 0.106 μm2 is used in a 14 nm FinFET technology with a 70 nm contacted gate pitch for high-density (HD) two-port (TP) RF memory compiler which achieves 5.66 Mb/mm2 array density for a 72 Kb array which is the highest reported density in 14 nm FinFET technology. The density improvement is achieved by using techniques such as leaf-cell optimization (eliminating transistors), better architectural planning, top level connectivity through leaf-cell abutment and minimizing the number of unique leaf-cells. These techniques are fully compatible with memory compiler usage over the required span. Leakage power is minimized by using power-switches without degrading the density mentioned above. Self-induced supply voltage collapse technique is applied for write and a four stack static keeper is used for read Vmin improvement. Fabricated test chips using 14 nm process have demonstrated 2.33 GHz performance at 1.1 V/25 °C operation. Overall Vmin of 550 mV is achieved with this design at 25 °C. The inbuilt power-switch improves leakage power by 12x in simulation. Approximately 8% die area of a leading 14 nm SoC in commercialization is occupied by these compiled RF instances. 相似文献
58.
1,5-己二烯交联烯烃聚合物的合成及其抗剪切稳定性 总被引:1,自引:0,他引:1
以金属配合物为催化剂、1,5-己二烯为交联剂,采用本体聚合法合成了交联超高相对分子质量烯烃类聚合物(简称交联聚合物)。用傅里叶变换红外光谱、核磁共振、凝胶渗透色潜表征交联聚合物的结构和相对分子质量。用旋转黏度计和超声波仪研究了1,5-己二烯用量对交联聚合物溶液表观黏度的影响及交联聚合物的相对分子质量对交联聚合物溶液抗剪切稳定性的影响。实验结果表明,在最佳聚合条件(单体80mL、助催化剂0.4mL、CS-1催化剂0.090g、1,5-己二烯0.40mL、0℃、24 b)下所合成的交联聚合物的重均相对分子质量为7.7×106,数均相对分子质量3.6×106。加入少量1,5-己二烯能提高交联聚合物的抗剪切能力,同时也能提高交联聚合物的相对分子质量。交联聚合物的相对分子质量越大,抗剪切稳定性越好。1,5-己二烯用量约为0.1 mL时(单体40 mL),交联聚合物溶液的表观黏度达到最大值(16.8 mPa·s)。 相似文献
59.
结合经过校正后的适合于本地无线环境的OKUMURA-HATA传播模型,建立起一种新的本地化基于1x EV—DO系统数据业务吞吐量分析的覆盖预测仿真模型,可应用于1xEV—DO系统的网络规划及系统性能分析。 相似文献
60.
番禺30-1砂岩强水驱气藏储层非均质性研究 总被引:7,自引:5,他引:2
针对垂向非均质性严重且边底水能量强的番禺30-1气田面临的潜在开发问题,通过岩心分析及测井二次解释,对其夹层特征及储层非均质性等进行了研究,划分出19个流动单元并定量描述了各流动单元的特征参数,建立了该气田的精细地质模型。综合评价表明,新建的地质模型具有较高的精度,为该气藏合理开发提供了坚实的地质基础。 相似文献