全文获取类型
收费全文 | 24911篇 |
免费 | 919篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 330篇 |
综合类 | 38篇 |
化学工业 | 5666篇 |
金属工艺 | 383篇 |
机械仪表 | 482篇 |
建筑科学 | 1315篇 |
矿业工程 | 100篇 |
能源动力 | 621篇 |
轻工业 | 1897篇 |
水利工程 | 236篇 |
石油天然气 | 71篇 |
无线电 | 1832篇 |
一般工业技术 | 4513篇 |
冶金工业 | 4574篇 |
原子能技术 | 197篇 |
自动化技术 | 3608篇 |
出版年
2023年 | 214篇 |
2022年 | 360篇 |
2021年 | 568篇 |
2020年 | 338篇 |
2019年 | 432篇 |
2018年 | 536篇 |
2017年 | 463篇 |
2016年 | 634篇 |
2015年 | 561篇 |
2014年 | 752篇 |
2013年 | 1425篇 |
2012年 | 1171篇 |
2011年 | 1515篇 |
2010年 | 1081篇 |
2009年 | 1015篇 |
2008年 | 1155篇 |
2007年 | 1092篇 |
2006年 | 950篇 |
2005年 | 774篇 |
2004年 | 747篇 |
2003年 | 665篇 |
2002年 | 570篇 |
2001年 | 436篇 |
2000年 | 368篇 |
1999年 | 407篇 |
1998年 | 761篇 |
1997年 | 562篇 |
1996年 | 451篇 |
1995年 | 417篇 |
1994年 | 377篇 |
1993年 | 365篇 |
1992年 | 271篇 |
1991年 | 196篇 |
1990年 | 270篇 |
1989年 | 261篇 |
1988年 | 216篇 |
1987年 | 227篇 |
1986年 | 227篇 |
1985年 | 265篇 |
1984年 | 225篇 |
1983年 | 223篇 |
1982年 | 207篇 |
1981年 | 196篇 |
1980年 | 170篇 |
1979年 | 193篇 |
1978年 | 165篇 |
1977年 | 186篇 |
1976年 | 240篇 |
1975年 | 160篇 |
1974年 | 124篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
This paper highlights the role of the faculty member in recruiting students currently enrolled in B.S. programs in engineering and the sciences into full-time pursuit of a graduate-level engineering degree. The faculty member is demonstrated to be in a unique position to influence such students, providing strong counterforces to a confluence of attitudes and pressures experienced during the B.S. experience which effectively create a barrier to full-time engineering graduate study. We analyze this barrier via the method of force field analysis, and demonstrate that effective recruitment into full-time graduate study must be based on a four-fold strategy of education, expectations, improved B.S. experience and better control of the B.S. environment. Approaches to implement these strategies are discussed. 相似文献
132.
A statistical study of the particle shape and size of pure V2O5 and TiO2, and samples of coprecipitated V2O5---TiO2 catalysts with different V/Ti ratios, has been performed. They were also characterized by XRD, EDAX, SEM and XPS. The results showed that pure vanadium pentoxide is compose by large square or needle-shaped particles, while pure titanium dioxide has small and rounded ones. VTiO samples presented an area and shape, depending on the V/Ti ratio.
These results and the spectroscopical characterization conducted to a particle model of the catalysts. Those VOTi samples with high V/Ti ratio would have large V2O5 crystals acting as support of a V/TiO2 solid solution. In contrast, those samples with a low V/Ti ratio, would have the solid solution supporting vanadium pentoxide crystals. 相似文献
133.
134.
135.
136.
Thomas G. OConnor Jonathan A. Dantzig 《Metallurgical and Materials Transactions B》1994,25(3):443-457
A three-dimensional mathematical model has been developed to compute the thermomechanical state in the mold of thin-slab continuous
casters. The thin-slab mold differs from those used in conventional slab casters in that the upper portion of the broad side
walls defines a funnel-shaped chamber which allows the nozzle to be submerged into the liquid metal. The chamber converges
with distance down the mold, reducing to the rectangular cross section of the finished casting near the mold exit. The new
mold, along with casting speeds up to 6 m/min, allows slabs to be cast 50–60 mm thick, compared with 150 to 350 mm in conventional
continuous slab casting. However, the mold shape and high casting speed lead to higher mold temperatures and shorter mold
life than are found in conventional slab casters. In this article, we develop mathematical models of the process to determine
the role of various process parameters in determining the mold life. Finite-element analysis is used to determine the temperatures
in the mold and cast slab, and these data are then used in an elastic-viscoplastic analysis to investigate the deformation
of the mold wall in service. Cyclic inelastic strains up to 1.75 Pct are found in a region below the meniscus along the funnel
edge. These large strains result from the combination of locally high temperatures coupled with geometric restraint of the
mold. The deformation leads to short mold life because of thermal fatigue cracking of the mold. The computed locations and
time to failure of the mold in fatigue agree very well with observations of the appearance of mold surface cracks in an operating
caster. The models are also used to develop an improved mold design.
Formerly Research Assistant, Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 相似文献
137.
Any soft tissue swelling beneath the deep fascia should be considered a sarcoma until proven otherwise. As the most important factor in the primary treatment of these cancers is the adequacy of the primary surgical resection, it is vital to diagnose these malignant tumours pre-operatively. The modern treatment of soft tissue sarcomas may involve all modalities, but the most important aspect of treatment of a primary localised sarcoma is wide excisional surgery preserving limb function. Radiotherapy is a vital adjunct in high-grade tumours, or in tumours whose resectability is limited either by size or anatomical proximity to vital structures. Apart from a few chemosensitive sarcomas, the role of chemotherapy is limited to treatment of metastatic disease where documented response rates are no greater than 30%. As 50% of patients with high-grade sarcomas will die from metastatic disease, improvements in survival rates will only come from improvements in response to systemic therapy. No controlled trials have shown any survival benefit for adjuvant chemotherapy, although a recent meta-analysis of published data has shown a trend to increased survival at two years. Multicentre randomised trials are ongoing. The prognosis of these lesions is highly variable, but is intimately related to the anatomical site (i.e., resectability), and also the grade and size of the tumour. 相似文献
138.
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
139.
Yan Shuicheng Wang Huan Liu Jianzhuang Tang Xiaoou Thomas S. Huang 《Frontiers of Computer Science in China》2007,1(4):407-412
The techniques for image analysis and classification generally consider the image sample labels fixed and without uncertainties.
The rank regression problem studied in this paper is based on the training samples with uncertain labels, which often is the
case for the manual estimated image labels. A core ranking model is designed first as the bilinear fusing of multiple candidate
kernels. Then, the parameters for feature selection and kernel selection are learned simultaneously by maximum a posteriori
for given samples and uncertain labels. The provable convergency Expectation Maximization (EM) method is used for inferring
these parameters in an iterative manner. The effectiveness of the proposed algorithm is finally validated by the extensive
experiments on age ranking task and human tracking task. The popular FG-NET and the large scale Yamaha aging database are
used for the age estimation experiments, and our algorithm outperforms those state-of-the-art algorithms ever reported by
other interrelated literatures significantly. The experiment result of human tracking task also validates its advantage over
conventional linear regression algorithm.
A short version of this paper appeared in ICME07. 相似文献
140.