全文获取类型
收费全文 | 94135篇 |
免费 | 7894篇 |
国内免费 | 4082篇 |
专业分类
电工技术 | 5737篇 |
技术理论 | 2篇 |
综合类 | 5758篇 |
化学工业 | 14763篇 |
金属工艺 | 5040篇 |
机械仪表 | 5360篇 |
建筑科学 | 6793篇 |
矿业工程 | 1826篇 |
能源动力 | 2815篇 |
轻工业 | 7150篇 |
水利工程 | 1808篇 |
石油天然气 | 3822篇 |
武器工业 | 674篇 |
无线电 | 12725篇 |
一般工业技术 | 12377篇 |
冶金工业 | 4944篇 |
原子能技术 | 1054篇 |
自动化技术 | 13463篇 |
出版年
2024年 | 310篇 |
2023年 | 1304篇 |
2022年 | 2598篇 |
2021年 | 3625篇 |
2020年 | 2466篇 |
2019年 | 2108篇 |
2018年 | 2376篇 |
2017年 | 2773篇 |
2016年 | 2487篇 |
2015年 | 3432篇 |
2014年 | 4514篇 |
2013年 | 5983篇 |
2012年 | 6249篇 |
2011年 | 7035篇 |
2010年 | 6091篇 |
2009年 | 5937篇 |
2008年 | 5820篇 |
2007年 | 5553篇 |
2006年 | 5292篇 |
2005年 | 4322篇 |
2004年 | 2980篇 |
2003年 | 2481篇 |
2002年 | 2479篇 |
2001年 | 2118篇 |
2000年 | 1985篇 |
1999年 | 2027篇 |
1998年 | 2004篇 |
1997年 | 1694篇 |
1996年 | 1520篇 |
1995年 | 1256篇 |
1994年 | 1008篇 |
1993年 | 838篇 |
1992年 | 657篇 |
1991年 | 493篇 |
1990年 | 414篇 |
1989年 | 332篇 |
1988年 | 285篇 |
1987年 | 195篇 |
1986年 | 167篇 |
1985年 | 148篇 |
1984年 | 109篇 |
1983年 | 77篇 |
1982年 | 82篇 |
1981年 | 63篇 |
1980年 | 59篇 |
1979年 | 55篇 |
1978年 | 43篇 |
1977年 | 43篇 |
1976年 | 63篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
131.
M Beltramo N Stella A Calignano SY Lin A Makriyannis D Piomelli 《Canadian Metallurgical Quarterly》1997,277(5329):1094-1097
Anandamide, an endogenous ligand for central cannabinoid receptors, is released from neurons on depolarization and rapidly inactivated. Anandamide inactivation is not completely understood, but it may occur by transport into cells or by enzymatic hydrolysis. The compound N-(4-hydroxyphenyl)arachidonylamide (AM404) was shown to inhibit high-affinity anandamide accumulation in rat neurons and astrocytes in vitro, an indication that this accumulation resulted from carrier-mediated transport. Although AM404 did not activate cannabinoid receptors or inhibit anandamide hydrolysis, it enhanced receptor-mediated anandamide responses in vitro and in vivo. The data indicate that carrier-mediated transport may be essential for termination of the biological effects of anandamide, and may represent a potential drug target. 相似文献
132.
Coplanar waveguide-fed uniplanar bow-tie antenna 总被引:3,自引:0,他引:3
Yu-De Lin Syh-Nan Tsai 《Antennas and Propagation, IEEE Transactions on》1997,45(2):305-306
The design of coplanar waveguide (CPW)-fed bow-tie antenna for the 2.4-GHz ISM band is described. A coplanar waveguide-to-coplanar strips (CPW-to-CPS) balun is used to obtain the balanced feed line for the printed bow-tie. An analysis method based on the mixed potential integral equation method is used to characterize the input characteristics of the bow-tie antenna. The numerical results obtained are in good agreement with the experimental data. Through experiments with bow-tie antennas of various extended angles, the bow-tie antenna with a 90° extended angle exhibits the widest bandwidth in the desired frequency band which has a bandwidth of 17% for a VSWR <1.5:1 相似文献
133.
Color image retrieval based on hidden Markov models 总被引:1,自引:0,他引:1
In this correspondence, a new approach to retrieving images from a color image database is proposed. Each image in the database is represented by a two-dimensional pseudo-hidden Markov model (2-D PHMM), which characterizes the chromatic and spatial information about the image. In addition, a flexible pictorial querying method is used, by which users can paint the rough content of the desired images in a query picture. Image matching is achieved by comparing the query picture with each 2-D PHMM in the database. Experimental results show that the proposed approach is indeed effective. 相似文献
134.
BACKGROUND: To determine the best cutoff values of aspartate aminotransferase (AST) and alanine amino-transferase (ALT) in detecting viral hepatitis C infection among patients of continuous ambulatory peritoneal dialysis (CAPD). METHODS: 90 (44 male and 46 female) CAPD patients and 526 adult controls (266 male, 260 female) were enrolled. Serum AST and ALT were measured by an auto-analyser monthly. Serum HBsAg was examined using a RIA method and anti-HCV by an second-generation EIA method. The best cutoff values of AST and ALT for detecting viral hepatitis were obtained from the ROC (receiver-operating characteristic) curve. RESULTS: The prevalence of anti-HCV(+) was significantly higher in CAPD patients (16.7%) than in normal controls (4.9%), while that of HBsAg(+) was similar in both groups. CAPD patients had significantly lower levels of serum aminotransferases compared to normal controls. Mean AST were 23.8 IU/l in normal control and 18.8 IU/l in the CAPD patients (P < 0.001). Mean ALT were 21.9 IU/l in normal controls and 15.3 IU/l in the CAPD patients (P < 0.001). CAPD patients with HCV infection had higher serum AST and ALT levels than those without. However, HBV infection did not cause significant serum aminotransferase elevation in patients. The conventional cutoff values of AST (40 IU/l) and ALT (40 IU/l) for detecting viral hepatitis yielded only a sensitivity of 27.3 and 18.2% respectively; on the contrary, our revised cutoff values of AST (24 IU/l) and ALT (17 IU/l) had better sensitivities (AST, 72.7%; ALT, 63.6%). For serial aminotransferase values, the sensitivity of AST and ALT for detecting HCV were 36.4 and 27.3% by conventional criteria, and were both 81.8%, by our newly revised criteria. CONCLUSIONS: Serum aminotransferase cutoff values should be modified for screening viral hepatitis in a CAPD population. Our new cutoff criteria had important clinical implications in providing benefits of earlier detection and possible prevention from chronic hepatic deteriorations. 相似文献
135.
Horng-Dar Lin 《Circuits and Devices Magazine, IEEE》1995,11(4):25-31
Identifies the basic technological components of multimedia communications. Among these technologies, multimedia processing and transmission already benefit heavily from VLSI advances. in fact, these two technologies could not have matured without special-purpose VLSI chips. We have examined basic processing required in these technologies and some VLSI architectures. The focus has been on standard-compliant VLSI chips, because the eventual goal of communications is to allow everyone to reach others without constraints. There are still a number of evolving standards, which means that we might witness yet another wave of VLSI chips for multimedia communications 相似文献
136.
本文用计算机数字模拟方法研究了电活性分子多层Z型L-B膜修饰电极的循环伏安行为。计算了电极与修饰L-B膜分子第一层之间的电荷转移速度常数K_o,L-B膜分子层间的电荷转移速度常数k_i;对峰电位差△E_p及阳极峰面积Q的影响,以及在不同条件下各层分子的氧化态分数随扫描时间的变化。为研究和设计电活性分子修饰电极的实际体系提供了大量数据和信息。 相似文献
137.
演绎数据库管理系统DEDBMS是工程数据库管理系统EDBMS/2中的一个子系统。本文着重介绍其产生式语言用户界面、工作流程及功能特点。DEDBMS系统的开发,使EDBMS/2不仅具有工程数据据管理功能,而且具有数据演绎和知识处理能力,从而成为CAD/CAM系统集成化和智能化的有力支撑工具。 相似文献
138.
本文提出新型布线算法,集李氏迷宫法与线搜索法的长处为一体,以饱和带法进行动态排序,以线搜索法确定借孔位置,然后用李氏法进行单层布线,获得最佳路径,从而达到线型好,布通率高的效果。 相似文献
139.
140.