全文获取类型
收费全文 | 33134篇 |
免费 | 866篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 367篇 |
综合类 | 35篇 |
化学工业 | 6834篇 |
金属工艺 | 858篇 |
机械仪表 | 622篇 |
建筑科学 | 1842篇 |
矿业工程 | 248篇 |
能源动力 | 1025篇 |
轻工业 | 2763篇 |
水利工程 | 335篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2150篇 |
一般工业技术 | 5195篇 |
冶金工业 | 6643篇 |
原子能技术 | 322篇 |
自动化技术 | 4618篇 |
出版年
2022年 | 196篇 |
2021年 | 386篇 |
2020年 | 332篇 |
2019年 | 400篇 |
2018年 | 488篇 |
2017年 | 509篇 |
2016年 | 520篇 |
2015年 | 463篇 |
2014年 | 736篇 |
2013年 | 2132篇 |
2012年 | 1242篇 |
2011年 | 1590篇 |
2010年 | 1172篇 |
2009年 | 1263篇 |
2008年 | 1438篇 |
2007年 | 1469篇 |
2006年 | 1257篇 |
2005年 | 1173篇 |
2004年 | 1053篇 |
2003年 | 1024篇 |
2002年 | 1033篇 |
2001年 | 634篇 |
2000年 | 616篇 |
1999年 | 575篇 |
1998年 | 599篇 |
1997年 | 499篇 |
1996年 | 606篇 |
1995年 | 548篇 |
1994年 | 537篇 |
1993年 | 534篇 |
1992年 | 488篇 |
1991年 | 321篇 |
1990年 | 438篇 |
1989年 | 425篇 |
1988年 | 379篇 |
1987年 | 426篇 |
1986年 | 382篇 |
1985年 | 519篇 |
1984年 | 495篇 |
1983年 | 450篇 |
1982年 | 465篇 |
1981年 | 445篇 |
1980年 | 354篇 |
1979年 | 366篇 |
1978年 | 331篇 |
1977年 | 308篇 |
1976年 | 270篇 |
1975年 | 319篇 |
1974年 | 245篇 |
1973年 | 280篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
81.
82.
Ph.D.John B. Durkee II 《Metal Finishing》2003,101(6):126-129
83.
84.
Rosen James C.; Grubman James A.; Bevins Thomas; Frymoyer John W. 《Canadian Metallurgical Quarterly》1987,6(6):581
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
85.
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
86.
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
87.
Philip John McKerrow 《Robotics and Autonomous Systems》1993,11(3-4):205-211
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
88.
Impacts of spectral band difference effects on radiometric cross-calibration between satellite sensors in the solar-reflective spectral domain 总被引:2,自引:0,他引:2
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
89.
Considering the critical contribution of your rectifier to the safe, effective, and reliable operation of your electrocoating process, the selection and maintenance of the optimum unit for your operation is time well spent. 相似文献
90.