全文获取类型
收费全文 | 10223篇 |
免费 | 416篇 |
国内免费 | 51篇 |
专业分类
电工技术 | 189篇 |
综合类 | 33篇 |
化学工业 | 1333篇 |
金属工艺 | 176篇 |
机械仪表 | 273篇 |
建筑科学 | 633篇 |
矿业工程 | 17篇 |
能源动力 | 280篇 |
轻工业 | 654篇 |
水利工程 | 68篇 |
石油天然气 | 40篇 |
武器工业 | 3篇 |
无线电 | 1767篇 |
一般工业技术 | 1676篇 |
冶金工业 | 1504篇 |
原子能技术 | 53篇 |
自动化技术 | 1991篇 |
出版年
2023年 | 54篇 |
2022年 | 108篇 |
2021年 | 157篇 |
2020年 | 110篇 |
2019年 | 140篇 |
2018年 | 208篇 |
2017年 | 200篇 |
2016年 | 242篇 |
2015年 | 207篇 |
2014年 | 246篇 |
2013年 | 601篇 |
2012年 | 534篇 |
2011年 | 602篇 |
2010年 | 458篇 |
2009年 | 492篇 |
2008年 | 587篇 |
2007年 | 537篇 |
2006年 | 514篇 |
2005年 | 412篇 |
2004年 | 320篇 |
2003年 | 330篇 |
2002年 | 282篇 |
2001年 | 246篇 |
2000年 | 243篇 |
1999年 | 254篇 |
1998年 | 521篇 |
1997年 | 323篇 |
1996年 | 254篇 |
1995年 | 218篇 |
1994年 | 139篇 |
1993年 | 146篇 |
1992年 | 107篇 |
1991年 | 80篇 |
1990年 | 69篇 |
1989年 | 67篇 |
1988年 | 62篇 |
1987年 | 58篇 |
1986年 | 51篇 |
1985年 | 76篇 |
1984年 | 47篇 |
1983年 | 31篇 |
1982年 | 49篇 |
1981年 | 42篇 |
1980年 | 35篇 |
1979年 | 38篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 48篇 |
1975年 | 21篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We present a two-sorted algebra, called aPeirce algebra, of relations and sets interacting with each other. In a Peirce algebra, sets can combine with each other as in a Boolean algebra, relations can combine with each other as in a relation algebra, and in addition we have both a set-forming operator on relations (the Peirce product of Boolean modules) and a relation-forming operator on sets (a cylindrification operation). Two applications of Peirce algebras are given. The first points out that Peirce algebras provide a natural algebraic framework for modelling certain programming constructs. The second shows that the so-calledterminological logics arising in knowledge representation have evolved a semantics best described as a calculus of relations interacting with sets. 相似文献
42.
Performance model of interactive video-on-demand systems 总被引:5,自引:0,他引:5
Li V.O.K. Wanjiun Liao Xiaoxin Qiu Wong E.W.M. 《Selected Areas in Communications, IEEE Journal on》1996,14(6):1099-1109
An interactive video-on-demand (VoD) system allows users to access video services, such as movies, electronic encyclopedia, interactive games, and educational videos from video servers on a broadband network. This paper develops a performance evaluation tool for the system design. In particular, a user activity model is developed to describe the usage of system resources, i.e., network bandwidth and video server usage, by a user as it interacts with the service. In addition, we allow batching of user requests, and the effect of such batching is captured in a batching model. Our proposed queueing model integrates both the user activity and the batching model. This model can be used to determine the requirements of network bandwidth and video server and, hence, the trade-off in communication and storage costs for different system resource configurations 相似文献
43.
HS Wong 《Canadian Metallurgical Quarterly》1997,38(11):459-464
44.
A genetic algorithm for multiple molecular sequence alignment 总被引:1,自引:0,他引:1
MOTIVATION: Multiple molecular sequence alignment is among the most important and most challenging tasks in computational biology. The currently used alignment techniques are characterized by great computational complexity, which prevents their wider use. This research is aimed at developing a new technique for efficient multiple sequence alignment. APPROACH: The new method is based on genetic algorithms. Genetic algorithms are stochastic approaches for efficient and robust searching. By converting biomolecular sequence alignment into a problem of searching for optimal or near-optimal points in an 'alignment space', a genetic algorithm can be used to find good alignments very efficiently. RESULTS: Experiments on real data sets have shown that the average computing time of this technique may be two or three orders lower than that of a technique based on pairwise dynamic programming, while the alignment qualities are very similar. AVAILABILITY: A C program on UNIX has been written to implement the technique. It is available on request from the authors. 相似文献
45.
A novel monoclonal antibody to 6 beta-hydroxycortisol (6 beta-OHC) was generated and incorporated into an antigen-coated indirect enzyme-linked immunosorbent assay (ELISA) using 6 beta-OHC-protein conjugate as the steroid-coating antigen. The monoclonal antibody is specific to 6 beta-OHC and 6 beta-OHC-3-carboxymethyloxime. Cross-reactivity with other structurally related steroids such as cortisol, cortisone, and 6 beta-hydroxycortisone was less than 10%. Two different clones (clone 5C1 and 19F) of the monoclonal anti-6 beta-OHC antibody have been developed, each with slightly different sensitivity and specificity. The sensitivity of the MAb clones was not significantly improved when compared to the rabbit polyclonal antibodies in this study, but still within the accepted detection limit for 6 beta-OHC in both human and laboratory animals. The assay had a detection limit of 200 ng/ml, an intraassay variation of 6.4% and an interassay variation of 7.3%. The application of the anti-6 beta-OHC-MAb-based-ELISA was tested by measuring the urinary output of 6 beta-OHC in human before and after enzyme induction by rifampicin treatment. The mean 24-h urine output of 6 beta-OHC in human subjects was 485 +/- 100 micrograms and 1478 +/- 281 micrograms before and after rifampicin administration, respectively. In conclusion, the monoclonal anti-6 beta-OHC antibody developed in this study has the required specificity and sensitivity as an alternative method for measuring urinary 6 beta-OHC in the detection of enzyme induction or enzyme inhibition of CYP3A in humans and laboratory animals. 相似文献
46.
47.
48.
TY Chen ST Lee TN Lui CW Wong YS Yeh WC Tzaan SY Hung 《Canadian Metallurgical Quarterly》1997,48(5):435-40; discussion 441
BACKGROUND: Controversy surrounds the treatment of traumatic central cord syndrome (TCCS), as there are strong advocates for nonsurgical treatment for most patients. However, conservative treatment has been shown to yield a longer period of discomfort from pain and weakness in certain cases. METHODS: In a retrospective review of 114 patients presenting with acute or chronic TCCS from 1988-94, four different age groups were separately observed under different treatments. Motor and sensory recovery were assessed. RESULTS: Better results were achieved in younger patients, with or without radiographic abnormalities, and in patients with clinically correlated encroaching cord lesions who received early surgical decompression. CONCLUSIONS: Surgical intervention for TCCS must be addressed with careful clinical and radiographic survey. Removal of offending lesions in the subacute period results in significant motor and sensory improvement in short-term and long-term follow-up. 相似文献
49.
The problem of joint estimation of time delay and Doppler shift is considered from the point of view of the Wigner distribution of the signal. A very efficient method of obtaining the optimum signal with minimum estimation error based on the convexity of the design region is developed. Practical applications, however, require the signal to satisfy other constraints which present complications in acquiring the optimum signal. A design approach based on the method of simulated annealing is suggested to solve for the optimum signal under constraints. The performance of the signals so obtained is evaluated and compared with that of signals obtained by synthesis 相似文献
50.
The effects of chronic injection of U50,488H (trans-3,4-dichloro-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeacetamidel++ +), a selective kappa opioid agonist, on the properties of the binding sites of tritiated U69593 [(5 alpha,7 alpha,8 beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro (4,5)dec-8-yl)benzeneacetamide], another selective kappa opioid agonist, and mechanical responses to U50,488H of the heart were studied. Rats received injection twice a day with U50,488H for 4 days. Binding studies on the crude membrane homogenates revealed that there was no change in maximum binding, but a significant increase in Kd after the treatment, indicating that the number of kappa binding sites remained unchanged whereas the affinity of the binding sites to kappa-agonist decreased. The study on the mechanical responses to U50,488H in the isolated perfused heart preparation showed that although the agonist at 10(-6) M caused MR2266 reversible reductions in heart rate and force of contraction as well as ventricular ectopic beat in the heart of rats in the control group, its effects were absent in the U50,488H-treated group, indicating the development of tolerance to the mechanical effects of U50,488H on the heart. The results indicate that the development of tolerance to the mechanical effects of a kappa-agonist after chronic treatment with the agonist was not accompanied by down-regulation, but only a slight and significant reduction in affinity of kappa binding sites in the rat heart. 相似文献