全文获取类型
收费全文 | 431496篇 |
免费 | 6060篇 |
国内免费 | 1395篇 |
专业分类
电工技术 | 7775篇 |
综合类 | 336篇 |
化学工业 | 65394篇 |
金属工艺 | 16951篇 |
机械仪表 | 14035篇 |
建筑科学 | 9118篇 |
矿业工程 | 2215篇 |
能源动力 | 12051篇 |
轻工业 | 32967篇 |
水利工程 | 4522篇 |
石油天然气 | 8013篇 |
武器工业 | 22篇 |
无线电 | 50252篇 |
一般工业技术 | 87501篇 |
冶金工业 | 81555篇 |
原子能技术 | 9306篇 |
自动化技术 | 36938篇 |
出版年
2022年 | 2858篇 |
2021年 | 4560篇 |
2020年 | 3524篇 |
2019年 | 4460篇 |
2018年 | 7574篇 |
2017年 | 7504篇 |
2016年 | 8031篇 |
2015年 | 5146篇 |
2014年 | 8123篇 |
2013年 | 22130篇 |
2012年 | 12947篇 |
2011年 | 16715篇 |
2010年 | 13358篇 |
2009年 | 14800篇 |
2008年 | 15121篇 |
2007年 | 14764篇 |
2006年 | 13070篇 |
2005年 | 11671篇 |
2004年 | 11063篇 |
2003年 | 10899篇 |
2002年 | 10283篇 |
2001年 | 10058篇 |
2000年 | 9464篇 |
1999年 | 9872篇 |
1998年 | 26184篇 |
1997年 | 18022篇 |
1996年 | 13645篇 |
1995年 | 10029篇 |
1994年 | 8772篇 |
1993年 | 8867篇 |
1992年 | 6227篇 |
1991年 | 5872篇 |
1990年 | 5808篇 |
1989年 | 5449篇 |
1988年 | 5182篇 |
1987年 | 4541篇 |
1986年 | 4401篇 |
1985年 | 4931篇 |
1984年 | 4528篇 |
1983年 | 4079篇 |
1982年 | 3767篇 |
1981年 | 3863篇 |
1980年 | 3564篇 |
1979年 | 3393篇 |
1978年 | 3408篇 |
1977年 | 4026篇 |
1976年 | 5459篇 |
1975年 | 2895篇 |
1974年 | 2710篇 |
1973年 | 2789篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
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
53.
54.
55.
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
56.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period 相似文献
57.
A novel class of narrow-band tunable wavelength filters is proposed and evaluated. Wavelength selectivity of the proposed filters Is derived from the finite time response of an optical nonlinearity. The nonlinearity is gain saturation in semiconductor optical amplifier structures. The filters are shown to have very narrow passbands tunable over the entire semiconductor gain bandwidth. The key to filter implementation is a device configuration in which the wave-mixing products can be isolated from the amplified inputs. Three integrated optics compatible configurations are considered and shown to have high filter throughputs 34 to 180% and subangstrom bandwidths 相似文献
58.
V. A. Arzamastsev N. L. Sardaev A. S. Kochergin 《Metal Science and Heat Treatment》1996,38(11):477-479
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described. 相似文献
59.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized 相似文献
60.
A. A. Konstantinov N. V. Kurenkov A. B. Malinin T. E. Sazonova S. V. Sepman 《Atomic Energy》1989,67(3):696-698
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989. 相似文献