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   269008篇
  免费   5194篇
  国内免费   2270篇
电工技术   5902篇
技术理论   5篇
综合类   1594篇
化学工业   43469篇
金属工艺   11506篇
机械仪表   8129篇
建筑科学   7137篇
矿业工程   1922篇
能源动力   5856篇
轻工业   26555篇
水利工程   3069篇
石油天然气   6289篇
武器工业   307篇
无线电   29041篇
一般工业技术   50365篇
冶金工业   47614篇
原子能技术   5696篇
自动化技术   22016篇
  2021年   2849篇
  2020年   1954篇
  2019年   2382篇
  2018年   3670篇
  2017年   3673篇
  2016年   4016篇
  2015年   3164篇
  2014年   5021篇
  2013年   11994篇
  2012年   8240篇
  2011年   10784篇
  2010年   8622篇
  2009年   9169篇
  2008年   9930篇
  2007年   10004篇
  2006年   8858篇
  2005年   7767篇
  2004年   6907篇
  2003年   6433篇
  2002年   6417篇
  2001年   6490篇
  2000年   6078篇
  1999年   6035篇
  1998年   12986篇
  1997年   9651篇
  1996年   7364篇
  1995年   5603篇
  1994年   5147篇
  1993年   5009篇
  1992年   3972篇
  1991年   3796篇
  1990年   3849篇
  1989年   3792篇
  1988年   3555篇
  1987年   3029篇
  1986年   3059篇
  1985年   3418篇
  1984年   3337篇
  1983年   3080篇
  1982年   2710篇
  1981年   2914篇
  1980年   2654篇
  1979年   2846篇
  1978年   2742篇
  1977年   2848篇
  1976年   3694篇
  1975年   2458篇
  1974年   2294篇
  1973年   2326篇
  1972年   1986篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
52.
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   
53.
54.
55.
Using the fear-potentiated startle paradigm in rats, 4 experiments examined whether the inhibitory effect of a feature is evident after its offset following serial feature-negative discrimination training (A+ and X-->A-). When startle probes were presented shortly after the offset of X on X-->A test trials, the inhibitory properties of X were observed immediately after its offset. Furthermore, trace reinforcement of X (X-->+), but not delay reinforcement (X+), disrupted the ability of X to inhibit fear-potentiated startle on X-->A trials. Trace conditioning to X was also retarded after A+ and X-->A- training. These results suggest that the inhibitory properties of the serially trained feature are present after its offset and raise the possibility that either temporal information regarding nonreinforcement or poststimulus attributes of X acquire inhibitory properties.  相似文献   
56.
The ability voluntarily to stabilize the head in space during lateral rhythmic oscillations (0.59+/-0.09 Hz) of the trunk has been investigated during microgravity (microG) and normal gravity (nG) conditions (parabolic flights). Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, during phases of either microG or nG. The main result was that head orientation with respect to vertical may be stabilized about the roll axis under microG with, as well as without vision, despite the reduction in vestibular afferent and muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as was previously reported. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may in fact be organized on the basis of either dynamic vestibular afferents or a short-term memorized postural body schema.  相似文献   
57.
58.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
59.
The water sorption behaviour of several cross-linked gelatin-based systems were investigated and compared. The systems were gelatin, gelatin/ethyleneglycol, gelatin/polyoxypropylenediamine, and gelatin/polyethylene oxide. For all the systems, an increased water gain was obtained by raising the concentration of the second component, while the swelling was reduced by an increase of the cross-linking density. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
60.
OBJECTIVE: To estimate the frequency of perioperative morbidities in patients who underwent anesthesia and a surgical procedure with no preoperative laboratory testing. MATERIAL AND METHODS: We conducted an electronic database search of medical records of 56,119 patients who underwent surgical or diagnostic procedures and anesthesia at Mayo Clinic Rochester in 1994 and found 5,120 who had no laboratory tests done within 90 days before the procedure. From this group, we randomly selected 1,044 patients (87 from each month) to document the absence of preoperative tests, the presence of preexisting disease (by organ system), the type of anesthetic agent, and the outcomes and tests intraoperatively and postoperatively. RESULTS: The 1,044 patients ranged in age from 0 to 95 years (median age, 21). No deaths or major perioperative morbidities occurred (0.0%; exact 95% confidence interval, 0.00 to 0.35%). Although 10 patients underwent blood typing and screening for antibodies immediately preoperatively, no blood transfusions were necessary. Intraoperatively, 17 laboratory tests and 1 electrocardiogram were obtained, and 3 results were abnormal. Postoperatively, 42 blood tests and 2 electrocardiographic procedures were performed. Five of the 42 blood tests showed abnormal results (hemoglobin levels in 3, serum sodium in 1, and arterial blood gases in 1). One electrocardiogram showed normal findings, and the other revealed normal results except for premature ventricular contractions. No laboratory test done intraoperatively or postoperatively was found to change surgical or medical management substantially. One patient who had unanticipated blood loss during an outpatient procedure was admitted to the hospital for observation. CONCLUSION: All 1,044 patients, 97% of whom were relatively healthy, with no recent laboratory testing safely underwent anesthesia and an operation. We conclude that patients who have been assessed by history and physical examination and determined to have no preoperative indication for laboratory tests can safely undergo anesthesia and operation with tests obtained only as indicated intraoperatively and post-operatively. Current anesthetic and medical practices rapidly identify perioperative indications for laboratory evaluation as they arise.  相似文献   
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