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   33272篇
  免费   865篇
  国内免费   67篇
电工技术   366篇
综合类   35篇
化学工业   6815篇
金属工艺   876篇
机械仪表   637篇
建筑科学   1845篇
矿业工程   247篇
能源动力   1037篇
轻工业   2786篇
水利工程   336篇
石油天然气   207篇
武器工业   2篇
无线电   2170篇
一般工业技术   5238篇
冶金工业   6649篇
原子能技术   322篇
自动化技术   4636篇
  2022年   198篇
  2021年   393篇
  2020年   338篇
  2019年   402篇
  2018年   496篇
  2017年   516篇
  2016年   525篇
  2015年   464篇
  2014年   738篇
  2013年   2146篇
  2012年   1250篇
  2011年   1601篇
  2010年   1175篇
  2009年   1267篇
  2008年   1448篇
  2007年   1470篇
  2006年   1264篇
  2005年   1178篇
  2004年   1061篇
  2003年   1032篇
  2002年   1035篇
  2001年   644篇
  2000年   617篇
  1999年   580篇
  1998年   605篇
  1997年   506篇
  1996年   605篇
  1995年   548篇
  1994年   534篇
  1993年   535篇
  1992年   488篇
  1991年   324篇
  1990年   439篇
  1989年   426篇
  1988年   379篇
  1987年   427篇
  1986年   384篇
  1985年   515篇
  1984年   493篇
  1983年   445篇
  1982年   464篇
  1981年   445篇
  1980年   355篇
  1979年   366篇
  1978年   329篇
  1977年   311篇
  1976年   268篇
  1975年   318篇
  1974年   243篇
  1973年   279篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
Serendipitous events have been shown to affect the careers of prominent counseling psychologists. Why should this seem surprising? Unplanned events affect everyone's career. The surprise is due to the widespread but unfounded assumption that career decisions should be the logical outcome of a "true reasoning" process. Counseling psychologists need to (a) broaden their view so that the reluctance to make an occupational commitment in the face of unpredictable future events can be celebrated as open-mindedness, not denigrated as indecisiveness, (b) teach clients that unplanned events are a normal and expected part of the career development process, and (c) teach clients how to generate unplanned events that contribute to a more satisfying life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
62.
63.
64.
65.
66.
Studied Minnesota Multiphasic Personality Inventory (MMPI) profiles of 362 patients with acute and chronic low back pain (LBP) for replicable homogeneous subgroups using 3 cluster-analysis procedures. Two normal and 3 clinically elevated profile subgroups were identified. The 2 normal subgroups were characterized by relatively normal musculoskeletal condition and were least disabled but differed from each other in duration of pain, presence of physical abnormalities, and daily functioning. The most pathologic profile subgroup consisted largely of acute-pain patients whose musculoskeletal condition and daily functioning were similar to those of the normal subgroups. Patients in the 3 abnormal MMPI subgroups were exposed to more LBP physical-risk factors in the workplace. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
67.
A method for the rapid, simultaneous determination of protein, fat, carbohydrate, non-protein nitrogen and total solids in milk and liquid dairy products by infrared reflectance spectroscopy is presented. The method is calibrated against known standards obtained by conventional, time-consuming wet chemical methods but, once calibrated, can be operated routinely by non-skilled personnel. The method is sensitive and accurate down to 0·5% w/v and can be applied to most liquid samples without any need for prior preparation.  相似文献   
68.
Investigated the similarity of reference effects for different delay conditions by testing the independence of reference and delay effects in 4 experiments, using 5 young adult observers. The critical independence property was whether the spatial variables (displacement separation from the visual reference) combined independently of the temporal variable (delay). This kind of independence did not hold for displacement discrimination at delays of 50 msec and 2,000 msec. When a test for the independence property was conducted at delays of 500 msec and 4,000 msec, observers reported no perceived movement. For these longer delays, the property was satisfied. These results are discussed using the general concept of a psychophysical mechanism. Such a mechanism combines the effects of several stimulus variables into a single mediating representation. By this analysis, at least 2 mechanisms must mediate the reference effect on displacement discrimination, one for delays of 200 msec and less and another for delays of 500 msec and more. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
69.
A ring of ultrasonic sensors mounted on a mobile robot is used to map a room. The sensors are modelled with an arc model: the object causing the reflection lies on an arc with radius equal to the range and arc angle equal to twice the beam angle. By fusing sensing with motion, a surface is displayed as a sequence of arcs. In this paper, the algorithm for obtaining outline segments from the arcs is presented.  相似文献   
70.
In order for quantitative applications to make full use of the ever-increasing number of Earth observation satellite systems, data from the various imaging sensors involved must be on a consistent radiometric scale. This paper reports on an investigation of radiometric calibration errors due to differences in spectral response functions between satellite sensors when attempting cross-calibration based on near-simultaneous imaging of common ground targets in analogous spectral bands, a commonly used post-launch calibration methodology. Twenty Earth observation imaging sensors (including coarser and higher spatial resolution sensors) were considered, using the Landsat solar reflective spectral domain as a framework. Scene content was simulated using spectra for four ground target types (Railroad Valley Playa, snow, sand and rangeland), together with various combinations of atmospheric states and illumination geometries. Results were obtained as a function of ground target type, satellite sensor comparison, spectral region, and scene content. Overall, if spectral band difference effects (SBDEs) are not taken into account, the Railroad Valley Playa site is a “good” ground target for cross calibration between most but not all satellite sensors in most but not all spectral regions investigated. “Good” is defined as SBDEs within ± 3%. The other three ground target types considered (snow, sand and rangeland) proved to be more sensitive to uncorrected SBDEs than the RVPN site overall. The spectral characteristics of the scene content (solar irradiance, surface reflectance and atmosphere) are examined in detail to clarify why spectral difference effects arise and why they can be significant when comparing different imaging sensor systems. Atmospheric gas absorption features are identified as being the main source of spectral variability in most spectral regions. The paper concludes with recommendations on spectral data and tools that would facilitate cross-calibration between multiple satellite sensors.  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