全文获取类型
收费全文 | 2411篇 |
免费 | 73篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 125篇 |
综合类 | 4篇 |
化学工业 | 634篇 |
金属工艺 | 67篇 |
机械仪表 | 65篇 |
建筑科学 | 61篇 |
能源动力 | 77篇 |
轻工业 | 167篇 |
水利工程 | 6篇 |
石油天然气 | 4篇 |
无线电 | 221篇 |
一般工业技术 | 468篇 |
冶金工业 | 344篇 |
原子能技术 | 62篇 |
自动化技术 | 192篇 |
出版年
2023年 | 11篇 |
2022年 | 28篇 |
2021年 | 40篇 |
2020年 | 19篇 |
2019年 | 12篇 |
2018年 | 40篇 |
2017年 | 25篇 |
2016年 | 43篇 |
2015年 | 47篇 |
2014年 | 60篇 |
2013年 | 117篇 |
2012年 | 99篇 |
2011年 | 139篇 |
2010年 | 88篇 |
2009年 | 117篇 |
2008年 | 132篇 |
2007年 | 113篇 |
2006年 | 80篇 |
2005年 | 100篇 |
2004年 | 86篇 |
2003年 | 81篇 |
2002年 | 64篇 |
2001年 | 69篇 |
2000年 | 54篇 |
1999年 | 53篇 |
1998年 | 117篇 |
1997年 | 83篇 |
1996年 | 56篇 |
1995年 | 43篇 |
1994年 | 53篇 |
1993年 | 50篇 |
1992年 | 32篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 38篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1974年 | 7篇 |
1973年 | 3篇 |
排序方式: 共有2497条查询结果,搜索用时 15 毫秒
41.
An automatic optical through-hole inspection system for ultrahigh density printed wiring boards (PWBs) using leakage light detection has been developed. To detect the dim leakage light emitted from the through-hole defect, we enhanced the sensitivity of the light detector 150 times using a microchannel plate tube. However, the tube caused two problems: stray light sensing and image distortion. To solve these problems, we optically isolated the sensing optics and developed a distortion correction method. We have developed a prototype system that can detect a defect as small as 100 m. 相似文献
42.
Mio Yamaguchi Kiyoshi Takagi Koki Narita Yasuhiro Miki Yoshiaki Onodera Minoru Miyashita Hironobu Sasano Takashi Suzuki 《International journal of molecular sciences》2021,22(4)
Chemokines secreted from stromal cells have important roles for interactions with carcinoma cells and regulating tumor progression. C-C motif chemokine ligand (CCL) 5 is expressed in various types of stromal cells and associated with tumor progression, interacting with C-C chemokine receptor (CCR) 1, 3 and 5 expressed in tumor cells. However, the expression on CCL5 and its receptors have so far not been well-examined in human breast carcinoma tissues. We therefore immunolocalized CCL5, as well as CCR1, 3 and 5, in 111 human breast carcinoma tissues and correlated them with clinicopathological characteristics. Stromal CCL5 immunoreactivity was significantly correlated with the aggressive phenotype of breast carcinomas. Importantly, this tendency was observed especially in the CCR3-positive group. Furthermore, the risk of recurrence was significantly higher in the patients with breast carcinomas positive for CCL5 and CCR3 but negative for CCR1 and CCR5, as compared with other patients. In summary, the CCL5-CCR3 axis might contribute to a worse prognosis in breast cancer patients, and these findings will contribute to a better understanding of the significance of the CCL5/CCRs axis in breast carcinoma microenvironment. 相似文献
43.
44.
Natsuhiko Kuratomi Shinichi Takano Mitsuharu Fukasawa Shinya Maekawa Makoto Kadokura Hiroko Shindo Ei Takahashi Sumio Hirose Yoshimitsu Fukasawa Satoshi Kawakami Hiroshi Hayakawa Hitomi Takada Natsuko Nakakuki Ryoh Kato Tatsuya Yamaguchi Yasuhiro Nakayama Hiromichi Kawaida Hiroshi Kono Taisuke Inoue Tetsuo Kondo Daisuke Ichikawa Nobuyuki Enomoto 《International journal of molecular sciences》2021,22(6)
New biomarkers are needed to further stratify the risk of malignancy in intraductal papillary mucinous neoplasm (IPMN). Although microRNAs (miRNAs) are expected to be stable biomarkers, they can vary owing to a lack of definite internal controls. To identify universal biomarkers for invasive IPMN, we performed miRNA sequencing using tumor-normal paired samples. A total of 19 resected tissues and 13 pancreatic juice samples from 32 IPMN patients were analyzed for miRNA expression by next-generation sequencing with a two-step normalization of miRNA sequence data. The miRNAs involved in IPMN associated with invasive carcinoma were identified from this tissue analysis and further verified with the pancreatic juice samples. From the tumor-normal paired tissue analysis of the expression levels of 2792 miRNAs, 20 upregulated and 17 downregulated miRNAs were identified. In IPMN associated with invasive carcinoma (INV), miR-10a-5p and miR-221-3p were upregulated and miR-148a-3p was downregulated when compared with noninvasive IPMN. When these findings were further validated with pancreatic juice samples, miR-10a-5p was found to be elevated in INV (p = 0.002). Therefore, three differentially expressed miRNAs were identified in tissues with INV, and the expression of miR-10a-5p was also elevated in pancreatic juice samples with INV. MiR-10a-5p is a promising additional biomarker for invasive IPMN. 相似文献
45.
K. Nishio M. Fujimoto O. Ando H. Ono T. Murayama 《Journal of Applied Electrochemistry》1996,26(4):425-429
Polypyrrole was chemically synthesized using various oxidizing reagents and examined as a positive electrode material. Physical properties, morphologies and electrochemical characteristics of polypyrrole were greatly influenced by the oxidizing reagent used for polymerization. In general, polypyrrole with a smaller particle size and a larger specific surface area showed better discharge performance than that with a larger particle size and a smaller specific surface area. Polypyrrole was also synthesized on various conducting and nonconducting substrates using Fe(C104)3 as an oxidizing reagent. By using PP nonwoven fabric as a substrate material, a high discharge capacity of 72 mA h g–1 was obtained. Polypyrrole synthesized on only one side of PP nonwoven fabric was able to be used as an electrode. 相似文献
46.
Uniaxial drawing experiments of the polystyrene films plasticized by a sorption of compressed CO2 gas at pressures up to about 18 MPa were carried out with strain rates ε of 0.0290 and 0.0079 s?1. The drawing was performed successfully with draw ratio λ up to 4 at the temperatures of 308.15, 318.15, 328.15, and 338.15 K. The Hermans orientation function f of the drawn samples was determined from the dichroic ratio measured by an infrared spectrophotmeter. While f value increases with increasing ε or λ, it decreases with increasing CO2 pressure or temperature. © 1995 John Wiley & Sons, Inc. 相似文献
47.
Oxygen self-diffusion coefficients for single-crystal MgO-Al2 O3 spinels previously determined for crushed particles were recalculated using the microscopic suface area of the sample, as was done for alumina. The corrected results agree well with those of Reddy and Cooper . 相似文献
48.
Tsutomu Osawa Masashi Ando Saori Sakai Tadao Harada Osamu Takayasu 《Catalysis Letters》2005,105(1-2):41-45
The role of acetic acid added to the reaction media for the enantio-differentiating hydrogenation of methyl acetoacetate over
a (R,R)-tartaric acid-in-situ-modified nickel catalyst was studied from the viewpoint of the hydrogenation rate during repeated
runs. The hydrogenation of methyl acetoacetate on the “enantio-differentiating sites” of a tartaric acid-modified nickel catalyst
was specifically accelerated by the acetic acid added to the reaction media to increase the enantio-differentiating ability
of the catalyst. In order to increase the enantio-differentiating ability, the addition of acetic acid to the reaction media
was required in each run during the repeated use of the catalyst. 相似文献
49.
Interaction of cation-exchange membrane with polycation I. Poly(N-methyl-4-vinylpyridinium chloride)
We elucidated the effect of the molecular weight of poly(N-methyl-4-vinylpyridinium chloride) (PMVP) on its adsorbed or ion-exchanged amount on the cation-exchange membrane and the preferntial permselectivity of the membrane for sodium ion to calcium ion. The amount of the adsorbed or ion-exchanged PMVP increases with time and then attains to a definite value at a definite concentration. Also, the ultimate value increases with increasing the concentration of PMVP. When the molecular weight of PMVP is 3090, the ratio of the pyridinium groups of PMVP ion-exchanged with the sulfonic acid groups on the membrane surface to the total pyridinium groups of the cohered PMVP is in the range of 70–80%. The relative transport number of calcium ions to sodium ions(PNaCa) decreases with increasing the amount of adsorbed or ion-exchanged PMVP and the numbe rof non-ion-exchanged pyridinium groups of PMVP and the number of non-ion-exchanged pyridinium groups of PMVP on the membrane surface. The smaller the molecular weight of PMVP, the more the adsorbed or ion-exchanged amount and the more preferable the permselectivity for sodium ion. 相似文献
50.
Momoji Kubo Tsuguo Kubota Changho Jung Minako Ando Satoshi Sakahara Kenji Yajima Kotaro Seki Rodion Belosludov Akira Endou Seiichi Takami Akira Miyamoto 《Catalysis Today》2004,89(4):479-493
Recently, we introduced a concept of combinatorial chemistry to computational chemistry and proposed a new method called “combinatorial computational chemistry”, which enables us to perform a theoretical high-throughput screening of catalysts. In the present paper, we reviewed our recent application of our combinatorial computational chemistry approach to the design of new catalysts for high-quality transportation fuels. By using our combinatorial computational chemistry techniques, we succeeded to predict new catalysts for methanol synthesis and Fischer–Tropsch synthesis. Moreover, we have succeeded in the development of chemical reaction dynamics simulator based on our original tight-binding quantum chemical molecular dynamics method. This program realizes more than 5000 times acceleration compared to the regular first-principles molecular dynamics method. Electronic- and atomic-level information on the catalytic reaction dynamics at reaction temperatures significantly contributes the catalyst design and development. Hence, we also summarized our recent applications of the above quantum chemical molecular dynamics method to the clarification of the methanol synthesis dynamics in this review. 相似文献