全文获取类型
收费全文 | 4329篇 |
免费 | 290篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 69篇 |
综合类 | 5篇 |
化学工业 | 954篇 |
金属工艺 | 81篇 |
机械仪表 | 67篇 |
建筑科学 | 177篇 |
矿业工程 | 7篇 |
能源动力 | 149篇 |
轻工业 | 333篇 |
水利工程 | 33篇 |
石油天然气 | 15篇 |
无线电 | 374篇 |
一般工业技术 | 912篇 |
冶金工业 | 724篇 |
原子能技术 | 35篇 |
自动化技术 | 688篇 |
出版年
2023年 | 59篇 |
2022年 | 103篇 |
2021年 | 171篇 |
2020年 | 123篇 |
2019年 | 122篇 |
2018年 | 145篇 |
2017年 | 132篇 |
2016年 | 151篇 |
2015年 | 122篇 |
2014年 | 200篇 |
2013年 | 280篇 |
2012年 | 244篇 |
2011年 | 313篇 |
2010年 | 210篇 |
2009年 | 188篇 |
2008年 | 207篇 |
2007年 | 188篇 |
2006年 | 165篇 |
2005年 | 112篇 |
2004年 | 127篇 |
2003年 | 82篇 |
2002年 | 91篇 |
2001年 | 46篇 |
2000年 | 33篇 |
1999年 | 66篇 |
1998年 | 105篇 |
1997年 | 84篇 |
1996年 | 55篇 |
1995年 | 50篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 29篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 35篇 |
1980年 | 20篇 |
1979年 | 28篇 |
1978年 | 25篇 |
1977年 | 22篇 |
1976年 | 34篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 17篇 |
排序方式: 共有4623条查询结果,搜索用时 31 毫秒
21.
22.
R Albrecht TC Awes C Baktash P Beckmann F Berger R Bock G Claesson G Clewing L Dragon A Eklund RL Ferguson A Franz S Garpman R Glasow HA Gustafsson HH Gutbrod J Idh P Jacobs K Kampert BW Kolb P Kristiansson IY Lee H Loehner I Lund FE Obenshain A Oskarsson I Otterlund T Peitzmann S Persson F Plasil AM Poskanzer M Purschke H Ritter S Saini R Santo HR Schmidt T Siemiarczuk SP Sorensen E Stenlund ML Tincknell GR Young 《Canadian Metallurgical Quarterly》1991,44(6):2736-2752
23.
MG Fehlings T Errico P Cooper V Benjamin T DiBartolo 《Canadian Metallurgical Quarterly》1993,32(2):198-207; discussion 207-8
Although occipitocervical fusion is frequently used for instability of the upper cervical spine and the occipitocervical articulation, most currently used techniques have one or more of the following disadvantages: the necessity for sublaminar wires, the use of occipital screws, a fixed angle of instrumentation, or the necessity for routine postoperative halo immobilization. Moreover, many reported techniques are associated with a high rate of nonunion or instrumentation failure. We present our experience with a technically simple method of obtaining rigid occipitocervical arthrodesis using a 5-mm malleable rod that is fixed to the skull by a pair of wires passed through four suboccipital burr holes. Segmental spinal fixation is achieved with Wisconsin interspinous wires and is occasionally supplemented with sublaminar wires. Supplemental autogenous bone graft is used in all cases. A cervical collar is routinely used for postoperative immobilization. The results of treatment were retrospectively reviewed in 16 patients with an average age of 49.4 years (range, 9-69). Mean follow-up was 24 months (range, 12-36 mo). The indication for fusion was instability of the occiput-C1-C2 complex as a result of Chiari malformation, rheumatoid disease, skull base tumor resection, basilar invagination, ankylosing spondylitis, Down's syndrome, cervical laminectomy, and trauma. The average number of levels fused was 5.4 (range, O-C3 to O-T3). Successful occipitocervical arthrodesis was achieved in all but one of the surviving patients. The single patient with a pseudarthrosis was successfully managed with supplemental bone grafting and halo immobilization. There were two deaths from medical complications in chronically ill patients. Other complications included one postoperative instrumentation loosening, one myocardial infarction, and one superficial occipital decubitus. In conclusion, rodding and segmental interspinous wiring is an effective, technically simple method of obtaining rigid occipitocervical fixation, which obviates the need for bulky orthoses. 相似文献
24.
Chen L.R. Benjamin S.D. Smith P.W.E. Sipe J.E. 《Quantum Electronics, IEEE Journal of》1998,34(11):2117-2129
We discuss theoretical and experimental studies on the propagation of ultrashort pulses through fiber Bragg gratings. We also consider several applications in optical communications to be found by combining ultrashort pulses and fiber Bragg gratings: a multiwavelength source for wavelength-division-multiplexed systems and a means for implementing optical code-division multiple access 相似文献
25.
Low-temperature-grown GaAs (LT-GaAs) is a promising material for all-optical switching devices due to its outstanding optical characteristics. In this paper, we outline a simplified model we have developed to describe the dynamics of the carriers in this material. We also report the results of a series of measurements that we have performed to characterize the optical properties of the material. Specifically, we present the first measurements of the two-photon absorption coefficient and the refractive index changes as a function of the growth and annealing temperatures in LT-GaAs. Finally, we show how our model can be used to optimize the material for applications in all-optical switching 相似文献
26.
27.
The object of this paper is to demonstrate the usefulness of the transalkylation reaction for determining chemical structural features of products derived from coal. For example, the method is applied to derivatized coals, coals modified by thermolysis, and materials physically or chemically separated from coals. Data are presented for the pyridine soluble and insoluble parts of two coals, an O-methylated coal, a Birch reduced coal, a solvent refined coal, and a coke. Similarities and differences in chemical make-up of these materials are discussed. 相似文献
28.
29.
Brent M. Phares Glenn A. Washer Dennis D. Rolander Benjamin A. Graybeal Mark Moore 《Canadian Metallurgical Quarterly》2004,9(4):403-413
Routine inspection is the most common form of highway bridge inspection to satisfy the requirements of the National Bridge Inspection Standards. The accuracy and reliability of documentation generated during these inspections are critical to the allocation of Department of Transportation construction, maintenance, and rehabilitation resources. Routine inspections are typically completed using only the visual inspection technique and rely heavily on subjective assessments made by bridge inspectors. In light of this, and given the fact that visual inspection may have other limitations that influence its reliability, the Federal Highway Administration initiated an investigation to examine the reliability of visual inspection as it is currently applied to bridges in the United States. This paper will summarize results from this study related to the accuracy and reliability of routine inspection documentation. A number of important conclusions were developed from the experimental study. Generally, it was found that all structural condition documentation is collected with significant variability. Specifically, 95% of primary element condition ratings for individual bridge components will vary within two rating points of the average and only 68% will vary within one point. Documentation generally collected to support condition ratings also has significant variability as exemplified by the number and types of field notes and photographs taken by inspectors. With respect to the use of element-level inspections, it was found that element usage was generally consistent with the Commonly Recognized Element Guide. However, there is significant variability in the condition state assignments of those elements and in some cases the condition states are not applied correctly to particular elements. 相似文献
30.
Conducted prolonged tests of male Long-Evans rats' penile responses outside the context of copulation (ex copula) to facilitate analysis of these penile components of copulatory behavior. Penile erections and flips were evoked for 1 hr following penile sheath retraction (SR), and Ss were retested for 30 min after a rest interval of 5 min to 4 hr. The number of penile responses declined sharply over the course of 1 hr. Following a 5-min rest, there was little likelihood of additional responses. Within 2 hrs, some measures of penile response potential approached their original high asymptotes: other measures were still depressed after the 4-hr rest. In control tests, the penile sheath was unretracted (SU) during the 1st 60 min, and hence few or no penile responses occurred. This condition caused no reduction in the number of erections and flips in the subsequent 30-min SR test; hence, the reduction in response to potential during and after SR tests was due to the responses displayed, not to the conditions of restraint. Ejaculation occurred frequently in the SU condition but rarely in SR tests. These results suggest that SR may normally inhibit ejaculation in ex copula tests and during copulation. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献