首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   293660篇
  免费   4380篇
  国内免费   885篇
电工技术   5476篇
综合类   358篇
化学工业   43901篇
金属工艺   10904篇
机械仪表   9165篇
建筑科学   7971篇
矿业工程   1186篇
能源动力   7397篇
轻工业   25461篇
水利工程   2947篇
石油天然气   4015篇
武器工业   72篇
无线电   36999篇
一般工业技术   55623篇
冶金工业   52536篇
原子能技术   5657篇
自动化技术   29257篇
  2021年   2669篇
  2020年   1953篇
  2019年   2619篇
  2018年   4195篇
  2017年   4189篇
  2016年   4507篇
  2015年   3016篇
  2014年   5020篇
  2013年   13530篇
  2012年   8095篇
  2011年   10765篇
  2010年   8501篇
  2009年   9286篇
  2008年   10325篇
  2007年   10248篇
  2006年   9255篇
  2005年   8470篇
  2004年   7960篇
  2003年   7744篇
  2002年   7334篇
  2001年   7115篇
  2000年   6667篇
  1999年   6803篇
  1998年   14773篇
  1997年   10805篇
  1996年   8611篇
  1995年   6939篇
  1994年   6198篇
  1993年   6047篇
  1992年   5005篇
  1991年   4476篇
  1990年   4416篇
  1989年   4139篇
  1988年   3928篇
  1987年   3504篇
  1986年   3358篇
  1985年   4011篇
  1984年   3775篇
  1983年   3327篇
  1982年   3117篇
  1981年   3212篇
  1980年   3012篇
  1979年   2900篇
  1978年   2731篇
  1977年   3156篇
  1976年   3747篇
  1975年   2502篇
  1974年   2473篇
  1973年   2469篇
  1972年   1966篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
14 medicated hypertensive, 15 nonmedicated mild hypertensive, 39 normotensive, and 13 hypotensive adults participated in a 1–2 hr laboratory experiment that assessed each S's symptoms, moods, and estimates of systolic blood pressure (SBP) relative to actual SBP levels. Several self-reports and autonomic measures were collected during and after each of 22 tasks. Within-S correlations indicated that all Ss could estimate SBP at levels greater than chance. Further, 68% of the Ss evidenced at least 1 significant symptom–SBP correlation. Although medicated hypertensives believed they could estimate their BP more accurately than other groups, they were actually no more accurate than the other Ss. They also evidenced far fewer empirically derived symptom–SBP and emotion–SBP correlations than any other group. Overall, blood pressure (BP) beliefs were largely inaccurate. If these erroneous beliefs can be eliminated, Ss may be able to estimate BP fluctuations more accurately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
42.
We report the results of the first national survey of psychologists in private practice regarding their participation in peer consultation groups. The sample (71% return) was drawn from 800 randomly selected psychologists listed in the National Register of Health Service Providers in Psychology. We found that 23% of the sample currently belonged to peer consultation groups, and 24% had belonged in the past. Of those not currently in groups, 61% expressed the desire to belong if one were available. There were virtually no significant demographic differences between current members and nonmembers. We examined the following group characteristics: formation, length of existence, size, membership, leadership, theoretical orientation, range of experience, time and place, content, and group process. Groups tended to be small, informal, and leaderless; however, we found great variation among groups on all dimensions. Findings also showed a high degree of satisfaction with membership. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
43.
The paper proposes a structure for quality-of-service (QoS)-centered service level agreements (SLA), and a framework for their real-time management in multiservice packet networks. The SLA is structured to be fair to both parties, the service provider and their customer. The SLA considered here are for QoS assured delivery of aggregate bandwidth from ingress to egress nodes; however, the control and signaling is for the more granular flows or calls. A SLA monitoring scheme is presented in which revenue is generated by the admission of flows into the network, and penalty incurred when flows are lost in periods when the service provider is not SLA compliant. In the SLA management scheme proposed, the results of a prior off-line design are used, in conjunction with measurements taken locally at ingress nodes, to classify the loading status of routes. The routing and resource management are based on virtual partitioning and its supporting mechanism of bandwidth protection. The effectiveness of SLA management is measured by the robustness in performance in the presence of substantial diversity in actual traffic conditions. A simulation testbed called D'ARTAGNAN has been built from which we report numerical results for a case study. The results show that the SLA management scheme is robust, fair and efficient over a broad range of traffic conditions  相似文献   
44.
45.
This study contrasted six subscales of the Brief Psychiatric Rating Scale (BPRS) to determine their sensitivity to psychosocial treatment outcome. An expanded version of the BPRS was administered to 216 clients on admission to a day program. The subscale measuring hostility and suspiciousness discriminated at intake clients who were therapeutically discharged from clients who did not complete the program and predicted discharge status after the investigators controlled for the effects of demographic variables. Significant reductions in scores were obtained on five subscales for a subset of clients to whom the BPRS was readministered before discharge. The results support the use of the expanded BPRS as an evaluative tool in psychosocial rehabilitation programs.  相似文献   
46.
The energy expenditure and heart rate of five Shetland ponies were measured during transport and compared with the values recorded while they were at rest and walking. Secondary aims of the study were to investigate whether there was any correlation between heart rate and energy expenditure and whether different orientations affected the values to different degrees. The measurements were recorded at one-minute intervals while the ponies were at rest, walking and being transported in four different orientations, on journeys lasting 30 minutes. There were significant increases (P < 0.001) in both heart rate and energy expenditure during transport which were similar to those associated with walking, and there was a strong correlation between the two measurements. There was no conclusive evidence that orientation affected the measurements, but it appeared that rear facing transport might have had the least effect.  相似文献   
47.
48.
Purified cell-envelope polyphosphatase as well as polyphoshatase activities of cytosol and isolated vacuoles, of nuclei and mitochondria of the yeast Saccharomyces cerevisiae were compared. The polyphosphatases of cell envelope and cytosol are similar, the polyphosphatases of nuclei, vacuoles and mitochondria differ in their kinetic properties, substrate specificity, requirements in divalent cations and in some effector actions both from these and from each other.  相似文献   
49.
50.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号