全文获取类型
收费全文 | 1711篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 27篇 |
综合类 | 1篇 |
化学工业 | 127篇 |
金属工艺 | 19篇 |
机械仪表 | 20篇 |
建筑科学 | 25篇 |
矿业工程 | 2篇 |
能源动力 | 13篇 |
轻工业 | 66篇 |
水利工程 | 6篇 |
石油天然气 | 2篇 |
无线电 | 128篇 |
一般工业技术 | 137篇 |
冶金工业 | 1004篇 |
原子能技术 | 4篇 |
自动化技术 | 142篇 |
出版年
2021年 | 11篇 |
2020年 | 4篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 43篇 |
2012年 | 23篇 |
2011年 | 40篇 |
2010年 | 30篇 |
2009年 | 25篇 |
2008年 | 39篇 |
2007年 | 28篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 53篇 |
1998年 | 275篇 |
1997年 | 176篇 |
1996年 | 106篇 |
1995年 | 81篇 |
1994年 | 58篇 |
1993年 | 69篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 32篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 31篇 |
1976年 | 80篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有1723条查询结果,搜索用时 31 毫秒
1.
H.W. Choi C.W. Jeon M.D. Dawson 《Photonics Technology Letters, IEEE》2004,16(1):33-35
The fabrication and performance of an InGaN light-emitting diode (LED) array based on a microring device geometry is reported. This design has been adopted in order to increase the surface area for light extraction and to minimize losses due to internal reflections and reabsorption. Electrical characteristics of these devices are similar to those of a conventional large-area LED, while the directed light extraction proves to be superior. In fact, these devices are found to be more efficient when operated at higher currents. This may be attributed to improved heat sinking due to the large surface area to volume ratio. The potential applications of these devices are also discussed. 相似文献
2.
We develop a characterization for m-fault-tolerant extensions, and for optimal m-fault-tolerant extensions, of a complete multipartite graph. Our formulation shows that this problem is equivalent to an interesting combinatorial problem on the partitioning of integers. This characterization leads to a new procedure for constructing an optimal m-fault-tolerant extension of any complete multipartite graph, for any m⩾0. The proposed procedure is mainly useful when the size of the graph is relatively small, because the search time required is exponential. This exponential search, however, is not always necessary. We prove several necessary conditions that help us, in several cases, to identify some optimal m-fault-tolerant extensions without performing any search 相似文献
3.
Geoffrey M. Eggert Paul R. Dawson Kapil K. Mathur 《International journal for numerical methods in engineering》1991,31(6):1031-1054
A forming model based on a viscoplastic flow formulation is derived which includes the effects of small elastic strains. A significant feature of the formulation is its reliance on the dominant inelastic material characteristics in the formation of the stiffness matrix for large strain problems. The resultant non-linear system of equations is solved by an adaptive descent method which combines the rapid convergence of Newton's method near the solution with the robustness of a method of successive approximations. The use of the adaptive descent method effectively extends the viscoplastic flow formulations into the nearly rate-insensitive range of behaviours exhibited, for example, by metals at low temperature, where slow convergence of the non-linear solution algorithm has traditionally hampered their use. 相似文献
4.
On the learning control of a robot manipulator 总被引:1,自引:0,他引:1
D. M. Dawson Z. Qu J. F. Dorsey F. L. Lewis 《Journal of Intelligent and Robotic Systems》1991,4(1):43-53
This paper derives a learning control law to achieve trajectory following for a robot manipulator. The controller consists of two parts, a computed torque servo for the rigid body terms that can be modelled and a learning law for the unmodelled dynamics. An advantage of this method is that bounds can be assigned to the position and velocity tracking errors. 相似文献
5.
Assuming that bat-detection is the primary function of moth ears, the ears of moths that are no longer exposed to bats should be deaf to echolocation call frequencies. To test this, we compared the auditory threshold curves of 7 species of Venezuelan day-flying moths (Notodontidae: Dioptinae) to those of 12 sympatric species of nocturnal moths (Notodontidae: Dudusinae, Noctuidae and Arctiidae). Whereas 2 dioptines (Josia turgida, Zunacetha annulata) revealed normal ears, 2 (J. radians, J. gopala) had reduced hearing at bat-specific frequencies (20-80 kHz) and the remaining 3 (Thirmida discinota, Polypoetes circumfumata and Xenorma cytheris) revealed pronounced to complete levels of high-frequency deafness. Although the bat-deaf ears of dioptines could function in other purposes (e.g., social communication), the poor sensitivities of these species even at their best frequencies suggest that these moths represent a state of advanced auditory degeneration brought about by their diurnal life history. The phylogeny of the Notodontidae further suggests that this deafness is a derived (apomorphic) condition and not a retention of a primitive (pleisiomorphic), insensitive state. 相似文献
6.
Gag rules-clauses in managed care contracts that prevent physicians from disclosing information that the plan may find disparaging, but that could relate directly to the patient's health-have recently been the subject of ethical condemnation and legislative prohibition. Another serious problem in managed care contracts, trade secrets, or guidelines and quality assurance mechanisms that are imposed on physicians while their origins are shrouded in proprietary secrecy, have by contrast received little attention. Responses to these ethical challenges to the physician's integrity must involve individual physicians, managed care organizations, professional organizations, and public policymakers. 相似文献
7.
The structural gene for V antigen (lcrV) is known to be encoded within the lcrGVH-yopBD operon of the approximately 70-kb low-calcium-response or Lcr plasmid of Yersinia pestis. This 37-kDa monomeric peptide was reported to provide active immunity in mice, suppress inflammatory cytokines, and regulate expression of the low calcium response (Lcr+). Here we describe pVHB62, encoding a polyhistidine-V antigen fusion peptide (Vh) and linked LcrH. Vh underwent degradation from both the C terminus and N terminus during classical chromatographic fractionation but remained intact within two compartments during Ni2+ affinity chromatography. The first was homogeneous, capable of active immunization (mouse intravenous 50% lethal dose, > 10(7) bacteria), and stable at 4 degrees C. The second remained bound to the affinity column but could be eluted as a mixture of Vh, LcrH, and low-molecular-weight material by application of 6 M guanidine HCl. This mixture was dialyzed, denatured in 8 M urea, and again applied to the affinity column, which then hound Vh but not LcrH. The latter was recovered and renatured, and low-molecular-weight material was removed by biochemical fractionation. The resulting homogeneous LcrH bound protein AN antigen fusion peptide but not protein A in a sandwich enzyme-linked immunosorbent assay, and this reaction was inhibited by Vh. These observations indicate that LcrH normally binds V antigen in bacterial cytoplasm and suggest that only free LcrH down-regulates expression of the low calcium response. 相似文献
8.
What ethical concerns regarding the application of new antidementia compounds are pertinent to the best interests of patients with Alzheimer's disease and their caregivers? Based on collected preliminary anecdotal accounts, these concerns are important and should be considered carefully by clinicians, researchers, and families. 相似文献
9.
10.
R Fitzpatrick J Dawson M Boulton J McLean G Hart M Brookes 《Canadian Metallurgical Quarterly》1994,44(379):80-82
BACKGROUND: Primary care has an important role to play in the prevention and management of the human immunodeficiency virus (HIV). It has been suggested that homosexual men experience a variety of problems in relation to primary care. AIM: As part of a larger study, it was decided to examine the extent to which a sample of homosexually active men experienced difficulties in general practice and whether they consulted their general practitioner for problems related to HIV or the acquired immune deficiency syndrome (AIDS). METHOD: Homosexual men were recruited for interview in 1991-92 from a variety of sources including genitourinary clinics and homosexual organizations. RESULTS: Of 623 men registered with a general practitioner 44% had not informed their general practitioner of their sexual orientation and 44% of the 77 men who were HIV antibody positive, as confirmed by the study, had not informed their general practitioner of this fact. Men who viewed their practice as unsympathetic towards homosexual men were less likely to have informed their general practitioner of their sexual orientation or HIV status. The majority of men (87%) nevertheless viewed primary care as an appropriate source of HIV/AIDS advice. CONCLUSION: There is considerable scope for improvement in the acceptability of general practice to homosexual men. 相似文献