全文获取类型
收费全文 | 622992篇 |
免费 | 7147篇 |
国内免费 | 1925篇 |
专业分类
电工技术 | 11390篇 |
综合类 | 464篇 |
化学工业 | 94399篇 |
金属工艺 | 25078篇 |
机械仪表 | 19584篇 |
建筑科学 | 14008篇 |
矿业工程 | 3583篇 |
能源动力 | 16719篇 |
轻工业 | 49271篇 |
水利工程 | 6652篇 |
石油天然气 | 12855篇 |
武器工业 | 28篇 |
无线电 | 72341篇 |
一般工业技术 | 124843篇 |
冶金工业 | 115857篇 |
原子能技术 | 14214篇 |
自动化技术 | 50778篇 |
出版年
2021年 | 5350篇 |
2020年 | 4122篇 |
2019年 | 5184篇 |
2018年 | 8958篇 |
2017年 | 8882篇 |
2016年 | 9596篇 |
2015年 | 6088篇 |
2014年 | 10095篇 |
2013年 | 29069篇 |
2012年 | 16205篇 |
2011年 | 21993篇 |
2010年 | 17625篇 |
2009年 | 20063篇 |
2008年 | 20555篇 |
2007年 | 20233篇 |
2006年 | 18032篇 |
2005年 | 16411篇 |
2004年 | 15471篇 |
2003年 | 15313篇 |
2002年 | 14742篇 |
2001年 | 14554篇 |
2000年 | 13726篇 |
1999年 | 14182篇 |
1998年 | 35749篇 |
1997年 | 25316篇 |
1996年 | 19537篇 |
1995年 | 14650篇 |
1994年 | 13020篇 |
1993年 | 12909篇 |
1992年 | 9503篇 |
1991年 | 9070篇 |
1990年 | 8978篇 |
1989年 | 8701篇 |
1988年 | 8430篇 |
1987年 | 7204篇 |
1986年 | 7170篇 |
1985年 | 8132篇 |
1984年 | 7576篇 |
1983年 | 6899篇 |
1982年 | 6445篇 |
1981年 | 6564篇 |
1980年 | 6174篇 |
1979年 | 6027篇 |
1978年 | 6150篇 |
1977年 | 7015篇 |
1976年 | 9047篇 |
1975年 | 5398篇 |
1974年 | 5070篇 |
1973年 | 5203篇 |
1972年 | 4424篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Malignant bone pain: pathophysiology and treatment 总被引:1,自引:0,他引:1
S Mercadante 《Canadian Metallurgical Quarterly》1997,69(1-2):1-18
2-acetyl aminofluorene (AAF) reacts in acidic conditions with nitrous fume yielding N-nitroso-AAF (N-NO-AAF), as previously described, that exerts more toxic and mutagenic effects than its parental compound. In this study, the effect of sodium nitrite (NaNO2) on the tumorigenicity of AAF in rats fed with AAF and NaNO2 was observed. Wistar rats were divided into five groups: group I served as control; group II were treated with NaNO2 (0.3%); group III was given 0.02% AAF alone; groups IV and V received both AAF and NaNO2 (0.2 and 0.3% respectively) in their diet for 12 weeks. At the end of the experiment, all rats in groups III, IV and V developed early stage phenomena of hepatocellular carcinoma, including hepatomegaly with variable-sized foci and neoplastic nodules. Severe damage was observed in the rats treated with AAF and NaNO2. Feeding of AAF (0.02%) for 3 months elevated the levels of c-Fos, c-Jun and c-Myc proteins in the rat livers. The AAF-induced c-Jun, c-Fos and c-Myc expressions were significantly magnified (P < 0.001) by NaNO2. These data confirmed that the strengthening of AAF-induced hepatocarcinogenesis by NaNO2 should be associated with its enhancing effect on the AAF-induced increases in the expressions of c-Jun, c-Fos and c-Myc. 相似文献
84.
For part I see, ibid., p. 134, 1998. The basic approach outlined in the previous article is applied to the difficult problem of computing the optical modes of a vertical-cavity surface-emitting laser. The formulation utilizes a finite difference equation based upon the lowest order term of an infinite series solution of the scalar Helmholtz equation in a local region. This difference equation becomes exact in the one-dimensional (1-D) limit, and is thus ideally suited for nearly 1-D devices such as vertical-cavity lasers. The performance of the resulting code is tested on both a simple cylindrical cavity with known solutions and an oxide-confined vertical-cavity laser structure, and the results compared against second-order-accurate code based upon Crank-Nicolson differencing 相似文献
85.
We present the design of E-kernel, an embedding kernel on the Victor V256 message-passing partitionable multiprocessor, developed for the support of program mapping and network reconfiguration. E-kernel supports the embedding of a new network topology onto Victor's 2D mesh and also the embedding of a task graph onto the 2D mesh network or the reconfigured network. In the current implementation, the reconfigured network can be a line or an even-size ring, and the task graphs meshes or tori of a variety of dimensions and shapes or graphs with similar topologies. For application programs having these task graph topologies and that are designed according to the communication model of E-kernel, they can be run without any change on partitions connected by the 2D mesh, line, or ring. Further, E-kernel attempts the communication optimization of these programs on the different networks automatically, thus making both the network topology and the communication optimization attempt completely transparent to the application programs. Many of the embeddings used in E-kernel are optimal or asymptotically optimal (with respect to minimum dilation cost). The implementation of E-kernel translated some of the many theoretical results in graph embeddings into practical tools for program mapping and network reconfiguration in a parallel system. E-kernel is functional on Victor V256. Measurements of E-kernel's performance on V256 are also included 相似文献
86.
87.
88.
S. Otakulov 《Cybernetics and Systems Analysis》1994,30(3):458-462
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 172–176, May–June, 1994 相似文献
89.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information
technologies and systems by the Ukrainian State Committee, of Science and Technology. 相似文献
90.
The study presents a hypothesis on how randomness could be simulated by human subjects. Three sources of deviation from randomness are predicted: (1) the preferred application of overlearned production schemata for producing sequences of digits, (2) a wrong concept of randomness, and (3) the impossibility to monitor for redundancies of higher- than those of first-order. Deviations of random generation of digits produced by healthy subjects, patients with chronic frontal lobe damage, and patients with Parkinson's disease from random sequences produced by a computer program can be explained by the differential influence of these factors. Whereas incorrect concepts of randomness and limits on monitoring capacity distinguished all sequences produced by humans from actual random sequences, persistence on a single production strategy distinguished brain-damaged patients from controls. Random generation of digits appears to be a theoretically transparent and clinically useful test of executive function. 相似文献