全文获取类型
收费全文 | 18040篇 |
免费 | 2133篇 |
国内免费 | 994篇 |
专业分类
电工技术 | 1114篇 |
综合类 | 1242篇 |
化学工业 | 2692篇 |
金属工艺 | 794篇 |
机械仪表 | 850篇 |
建筑科学 | 1308篇 |
矿业工程 | 352篇 |
能源动力 | 397篇 |
轻工业 | 2362篇 |
水利工程 | 387篇 |
石油天然气 | 469篇 |
武器工业 | 139篇 |
无线电 | 2070篇 |
一般工业技术 | 1833篇 |
冶金工业 | 2360篇 |
原子能技术 | 172篇 |
自动化技术 | 2626篇 |
出版年
2024年 | 144篇 |
2023年 | 401篇 |
2022年 | 778篇 |
2021年 | 1095篇 |
2020年 | 851篇 |
2019年 | 637篇 |
2018年 | 622篇 |
2017年 | 770篇 |
2016年 | 698篇 |
2015年 | 984篇 |
2014年 | 1147篇 |
2013年 | 1345篇 |
2012年 | 1312篇 |
2011年 | 1414篇 |
2010年 | 1175篇 |
2009年 | 950篇 |
2008年 | 954篇 |
2007年 | 836篇 |
2006年 | 741篇 |
2005年 | 530篇 |
2004年 | 327篇 |
2003年 | 285篇 |
2002年 | 278篇 |
2001年 | 261篇 |
2000年 | 165篇 |
1999年 | 168篇 |
1998年 | 677篇 |
1997年 | 408篇 |
1996年 | 237篇 |
1995年 | 175篇 |
1994年 | 140篇 |
1993年 | 146篇 |
1992年 | 34篇 |
1991年 | 48篇 |
1990年 | 46篇 |
1989年 | 56篇 |
1988年 | 37篇 |
1987年 | 40篇 |
1986年 | 29篇 |
1985年 | 21篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 24篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 26篇 |
1976年 | 77篇 |
1968年 | 4篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Wu Ting M. Badaye T. Morishita N. Koshizuka S. Tanaka 《Journal of Superconductivity》1996,9(6):637-645
Recently, superconducting Nd1Ba2Cu3Oy (Ndl23) thin films with high superconducting transition temperature (T
c) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half-integer number of thec-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. This result is supported byI-V STS measurements. The surface morphology of the Nd123 thin films is compared with that of thec-axis-oriented Y1Ba2Cu3Sy thin films. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films. 相似文献
22.
23.
吕汀 《常州信息职业技术学院学报》2006,5(2):12-14
静电复印机是常用的办公设备,复印时要将不同规格的复印纸装入纸盒,经常需要操作者对纸盒进行调整。从使用者的角度讲,要用最小的力气、最简便的方法来完成对机器的操纵。这就需要考虑进行人性化设计。纸盒调整主要有自动监测纸盒尺寸的功能和纸盒内侧挡板(导纸板)的调整。对比不同品牌和不同机型复印机的纸盒设计,可看出人性化设计对方便操作者使用的重要性,也为购买机器时提供了借鉴。 相似文献
24.
25.
26.
Thirty-two consecutive patients with haematological disorders, in need of a permanent central venous catheter (CVC) were randomly allocated to have their CVC bandages (Tegaderm) changed once (OAW, n = 20) or twice (TAW, n = 19) a week. The two randomization arms were balanced in respect of age, sex, and underlying disease. The exit site of the CVC was inspected daily through the transparent bandage and erythema was noted. If severe erythema occurred, daily wet gauze dressings were applied. Samples for bacterial cultures were taken from the exit site of the CVC at every change of bandages. There was no difference in complications leading to removal of the CVC between the two groups (7/20 OAW vs. 7/19 TAW) or in CVC survival-time (P = 0.4). However, the OAW group had more positive CVC tip cultures (OAW 11/14 vs. TAW 2/9; P < 0.05) and a tendency to: (i) more extra dressings (P = 0.08); (ii) more cultures from the exit skin site showing high numbers of colony forming units (P = 0.07); (iii) shorter time to first exit site infection (P = 0.09); and (iv) more Gram-positive septicaemias (P = 0.08). Both clinical and bacteriological data in this study indicate that changing transparent polyurethane CVC bandages twice a week is superior to once a week. 相似文献
27.
28.
多人决策的一类相对均衡解 总被引:1,自引:0,他引:1
本文分析由于决策人偏好不同而引起决策差异的多人多目标决策问题,提出了这类决策问题的一类相对均衡解的概念和求取方法。相对均衡解以决策群体偏好的加权集结为基础,能最大程度地反映每个决策人的偏好。文中研究相对均衡解的SWT求取方法,并给出了求解的步骤。 相似文献
29.
This is a study of the differences in the risk factors for being either hepatitis B surface antigen positive [HBsAg(+)] or antibody to hepatitis C virus positive [Anti-HCV(+)] in A-Lein, a rural area in southern Taiwan, an area which also has a high hepatoma mortality rate. Three hundred eighty-five patients age > or =40 years participated in hepatoma screening at the A-Lein Community Health Center during 1995. Those who were HBsAg(-) and anti-HCV(-) or had coinfection of HBsAg(+) and anti-HCV(+) were excluded, leaving 293 patients: 109 HBsAg(+) and 184 anti-HCV(+). The anti-HCV(+) patients had a lower socioeconomic status (as defined by level of education and type of occupation) and were older than HBsAg(+) patients (P < 0.05). Those with higher alanine aminotransferase levels (ALT) also had a higher anti-HCV(+) to HBsAg(+) odds ratio (OR), and a dose response relationship was found, P < 0.0001. Anti-HCV(+) patients were more likely than HBsAg(+) patients to have a spouse who shared the infection, OR = 5.11; 95% CI, 2.30-11.28. Anti-HCV(+) patients were more likely than HBsAg(+) patients to have had blood transfusions (OR = 2.66; 95% CI, 1.20-5.89), frequent medical injections (OR = 2.64; 95% CI, 1.62-4.31), or injections by non-licensed medical providers (OR = 1.91; 95% CI, 1.18-3.09). Multiple logistic regression analysis showed that the significant factors for anti-HCV(+) patients vs. HBsAg(+) patients are drinking habit (OR = 3.45; 95% CI, 1.02-11.60), age (OR = 6.33; 95% CI, 2.93-13.68), and frequent medical injections (OR = 2.88; 95% CI, 1.65-5.03). The transmission of hepatitis C in A-Lein is closely related to low socioeconomic status, age, alcohol abuse, spouses being anti-HCV(+), and frequent medical injections, especially from non-licensed medical providers, including both pharmacists and those with no medical licensing whatsoever. These nonlicensed medical providers sometimes reuse needles to save money, which is a likely route of infection. 相似文献
30.
The present study was undertaken to evaluate the postoperative relapse from the period of unwiring to 1 year postoperatively and its correlation to the amount of mandibular setback and change in vertical dimension after mandibular bilateral sagittal split osteotomy. Twenty-seven patients were evaluated cephalometrically by the time preoperatively, 6 weeks, 6 months and 1 year postoperatively. It was found that 1) the average amount of mandibular setback at pogonion point, 6 weeks postoperatively, is 7.6mm backward and 1.9mm downward, 2) the average amount of horizontal relapse at pogonion point, 6 months and 1 year postoperatively, are 1.9mm and 2.3mm respectively. 86% of the horizontal relapse, 1 year postoperatively, occurs in the first 6 months after removal of intermaxillary fixation, 3) the average amount of vertical relapse at pogonion point, 6 months and 1 year postoperatively, are 0.9mm and 1.1mm upward. 82% of the vertical relapse, 1 year postoperatively, occurs in the first 6 months after removal of intermaxillary fixation, 4) the amount of 1 year postoperatively horizontal relapse is significantly correlated both with the amount of horizontal mandibular set back and vertical downward change (r = 0.58, 0.67, p < 0.001), whereas the amount of vertical relapse is with the vertical downward change only, but horizontal setback isn't. 相似文献