全文获取类型
收费全文 | 589833篇 |
免费 | 6757篇 |
国内免费 | 1726篇 |
专业分类
电工技术 | 10850篇 |
综合类 | 543篇 |
化学工业 | 90294篇 |
金属工艺 | 23428篇 |
机械仪表 | 18778篇 |
建筑科学 | 12920篇 |
矿业工程 | 3246篇 |
能源动力 | 15566篇 |
轻工业 | 48310篇 |
水利工程 | 6123篇 |
石油天然气 | 11451篇 |
武器工业 | 44篇 |
无线电 | 67483篇 |
一般工业技术 | 116142篇 |
冶金工业 | 111675篇 |
原子能技术 | 13278篇 |
自动化技术 | 48185篇 |
出版年
2021年 | 5301篇 |
2020年 | 3965篇 |
2019年 | 5141篇 |
2018年 | 8745篇 |
2017年 | 8744篇 |
2016年 | 9360篇 |
2015年 | 5895篇 |
2014年 | 9851篇 |
2013年 | 27893篇 |
2012年 | 15772篇 |
2011年 | 21400篇 |
2010年 | 17031篇 |
2009年 | 19071篇 |
2008年 | 19709篇 |
2007年 | 19577篇 |
2006年 | 17563篇 |
2005年 | 15602篇 |
2004年 | 14806篇 |
2003年 | 14599篇 |
2002年 | 14172篇 |
2001年 | 13920篇 |
2000年 | 13173篇 |
1999年 | 13603篇 |
1998年 | 34143篇 |
1997年 | 23654篇 |
1996年 | 18255篇 |
1995年 | 13773篇 |
1994年 | 12088篇 |
1993年 | 12076篇 |
1992年 | 8957篇 |
1991年 | 8349篇 |
1990年 | 8489篇 |
1989年 | 8044篇 |
1988年 | 7706篇 |
1987年 | 6750篇 |
1986年 | 6685篇 |
1985年 | 7599篇 |
1984年 | 7061篇 |
1983年 | 6377篇 |
1982年 | 5906篇 |
1981年 | 6053篇 |
1980年 | 5710篇 |
1979年 | 5512篇 |
1978年 | 5532篇 |
1977年 | 6231篇 |
1976年 | 8096篇 |
1975年 | 4794篇 |
1974年 | 4512篇 |
1973年 | 4666篇 |
1972年 | 3922篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A value-based test is presented for economic screening of electric utility demand-side management (DSM) programs. The widely used least cost test is valid if the programs do not alter the amount or value of energy services provided to customers. But, in general, DSM programs have such effects and, as a result, the value consumers receive is changed. A more general economic efficiency test, the most value test, provides a practical method for considering the effects of DSM on customer value. The version presented allows for multiple load periods and can account for rate impacts on several customer classes. Four typical DSM programs are evaluated as illustrations 相似文献
992.
993.
OBJECTIVE: To compare the efficacy and toxicity of three patient-controlled analgesia (PCA) morphine regimens. DESIGN: A prospective, randomized, pilot study of three PCA morphine regimens: (1) 1 mg with 6-minute lockout (n = 10), (2) 2 mg with 12-minute lockout (n = 12), and (3) 2 mg with 20-minute lockout (n = 12). SETTING: Large teaching institution. PARTICIPANTS: Thirty-four patients undergoing cholecystectomy or hysterectomy. MAIN OUTCOME MEASURES: Pain scores (0 = no pain, 1 = mild pain, 2 = moderate pain, 3 = severe pain), sedation scores, analgesic consumption, and patient attempts (patient activation of PCA device) and injections (doses actually delivered) were evaluated using analysis of covariance. Distribution of pain and sedation scores and adverse effects were assessed using Fisher's exact test. RESULTS: Data on 24 patients were evaluable. Six patients withdrew for poor pain control (2 in group 1, 1 in group 2, and 3 in group 3). Three other patients withdrew because of adverse effects and 1 withdrew because of pump problems. Mean morphine consumption did not differ significantly among the groups. Distribution of pain and sedation scores and the number of patients with nausea were similar across treatment groups. The mean injection to attempt ratio was significantly smaller in group 3 (0.71 +/- 0.11) compared with groups 1 and 2 (0.9 +/- 0.06 and 0.83 +/- 0.09, respectively; p = 0.001). Adverse events occurred similarly among treatment groups. CONCLUSIONS: No significant differences in the efficacy or toxicity of the three morphine PCA regimens were identified. 相似文献
994.
3 cases of seronegative synovitis syndrome were reported. Two elderly women and one man presented with symmetrical polysynovitis of acute onset involving most of their appendicular joints and flexor digitorum tendons associated with pitting edema of the dorsum of both hands and both feet. Rheumatoid factor was absent from serum samples in all and no radiologically evident erosions developed. All the three patients had a benign course and the disease resolved completely within 2-18 months after the onset. None had deformities, erosions and/or relapse after being followed for 22-34 months. Literatures on this syndrome were reviewed. 相似文献
995.
Schmidt Frank L.; Law Kenneth; Hunter John E.; Rothstein Hannah R.; Pearlman Kenneth; McDaniel Michael 《Canadian Metallurgical Quarterly》1993,78(1):3
Using a large database, this study examined 3 refinements of validity generalization procedures: (1) a more accurate procedure for correcting the residual standard deviation (SD) for range restriction to estimate SDp, (2) use of r? instead of study-observed rs in the formula for sampling error variance, and (3) removal of non-Pearson rs. The 1st procedure does not affect the amount of variance accounted for by artifacts. The addition of the 2nd and 3rd procedures increased the mean percentage of validity variance accounted for by artifacts from 70 to 82%, a 17% increase. The cumulative addition of all 3 procedures decreased the mean SDp estimate from .150 to .106, a 29% decrease. Six additional variance-producing artifacts were identified that could not be corrected for. In light of these it was concluded that the obtained estimates of mean SDp and mean validity variance accounted for were consistent with the hypothesis that the true mean SDp value is close to zero. These findings provide further evidence against the situational specificity hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
996.
The memory of hamsters (Mesocricetus auratus) for the flank scent of older male hamsters was investigated in a series of habituation experiments. In 2 types of habituation tasks (Exps 1 and 2), male hamsters habituated to the flank scent of 1 male and then increased their level of investigation to that of a novel male; similar results were obtained when the intervals between trials ranged from 1 sec to 2 days. When the test trial was 10 or 21 days after habituation (Exp 3), males discriminated between familiar and novel flank scents at 10 days but not at 21 days. The results demonstrate recognition of familiar and unfamiliar individual odors and excellent memory for these differences. Habituation techniques yield extremely robust results and may be useful for investigations of other aspects of individual signatures. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
Effect of sliding speed on adhesive wear of binary Al-Si alloys 总被引:2,自引:0,他引:2
998.
45 patients with occlusive peripheral vascular disease were examined by MR angiography in a retrospective study. A FISP 3D sequence was used by acquiring a rephased and a dephased data set. The individual slices were post-processed by using a maximum-intensity-projection algorithm. The MRA results of the popliteal and tibioperoneal arteries were compared to conventional or digital angiography. In comparing these techniques MR angiography cannot be accepted for pre- and postoperative staging of patients with occlusive peripheral vascular disease. In future new MRA techniques may be useful in postoperative staging of patients with peripheral vascular stenosis. 相似文献
999.
We report 11 patients having revision of total hip arthroplasty using massive structural allografts for failure due to sepsis and associated bone loss. All patients had a two-stage reconstruction and the mean follow-up was 47.8 months (24 to 72). Positive cultures were obtained at the first stage in nine of the 11 patients, with Staphylococcus epidermidis being the most common organism. The other two patients had draining sinuses with negative cultures. There was no recurrence of infection in any patient. The mean increase in the modified Harris hip score was 45 and all the grafts appeared to have united to host bone. Two patients required additional procedures, but only one was related to the allograft. Complications included an incomplete sciatic nerve palsy and one case of graft resorption. Our results support the use of massive allografts in failed septic hip arthroplasty in which there is associated bone loss. 相似文献
1000.
Over 2000 electrocution deaths were identified among U.S. construction workers from 1980 to 1991, with the highest mean annual crude mortality rate (2.5 per 100,000 people), and second highest mean age-adjusted rate (2.7 per 100,000 people) of all industries. Although the crude fatality rates showed a downward trend, construction workers are still about four times more likely to be electrocuted at work than are workers in all industries combined. Nearly 40% of the 5083 fatal electrocutions in all industries combined occurred in construction, and 80% were associated with industrial wiring, appliances, and transmission lines. Electrocutions ranked as the second leading cause of death among construction workers, accounting for an average of 15% of traumatic deaths in the industry from 1980 to 1991. The study indicates that the workers most at risk of electrical injury are male, young, nonwhite, and electricians, structural metal workers, and laborers. The most likely time of injury is 11 a.m. to 3 p.m. from June to August. Focusing prevention on these populations and characteristics through better methods of worker and supervisor electrical safety training, use of adequate protective clothing, and compliance with established procedures could minimize the average annual loss of 168 U.S. construction workers. 相似文献