全文获取类型
收费全文 | 18124篇 |
免费 | 702篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 215篇 |
综合类 | 18篇 |
化学工业 | 3764篇 |
金属工艺 | 322篇 |
机械仪表 | 403篇 |
建筑科学 | 1006篇 |
矿业工程 | 49篇 |
能源动力 | 501篇 |
轻工业 | 1675篇 |
水利工程 | 120篇 |
石油天然气 | 56篇 |
武器工业 | 1篇 |
无线电 | 1586篇 |
一般工业技术 | 3065篇 |
冶金工业 | 3029篇 |
原子能技术 | 189篇 |
自动化技术 | 2848篇 |
出版年
2023年 | 157篇 |
2022年 | 296篇 |
2021年 | 460篇 |
2020年 | 341篇 |
2019年 | 365篇 |
2018年 | 425篇 |
2017年 | 389篇 |
2016年 | 491篇 |
2015年 | 423篇 |
2014年 | 521篇 |
2013年 | 1075篇 |
2012年 | 856篇 |
2011年 | 1116篇 |
2010年 | 766篇 |
2009年 | 821篇 |
2008年 | 862篇 |
2007年 | 758篇 |
2006年 | 702篇 |
2005年 | 591篇 |
2004年 | 485篇 |
2003年 | 436篇 |
2002年 | 420篇 |
2001年 | 295篇 |
2000年 | 317篇 |
1999年 | 347篇 |
1998年 | 733篇 |
1997年 | 476篇 |
1996年 | 393篇 |
1995年 | 287篇 |
1994年 | 269篇 |
1993年 | 266篇 |
1992年 | 182篇 |
1991年 | 154篇 |
1990年 | 136篇 |
1989年 | 135篇 |
1988年 | 123篇 |
1987年 | 115篇 |
1986年 | 113篇 |
1985年 | 138篇 |
1984年 | 133篇 |
1983年 | 116篇 |
1982年 | 90篇 |
1981年 | 101篇 |
1980年 | 86篇 |
1979年 | 96篇 |
1978年 | 87篇 |
1977年 | 115篇 |
1976年 | 138篇 |
1975年 | 79篇 |
1974年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
Summary We introduce a very simple model for thermally activated atomic migration on a lattice, and several techniques to handle it. For thermodynamical systems, the model can be used for simulating decomposition paths taking into account relevant metallurgical features. Close to equilibrium, the simplest mean-field approximation of the model can be linearized with respect to the departure from equilibrium; one then gets a microscopic interpretation of classical phenomenological coefficients, such as mobility, interfacial transfer coefficient, rate constants for the coupled relaxation of concentration and order fields. Further away from the equilibrium, the nonlinearities can be taken into account in a consistent way. For driven alloys, i.e. alloys submitted to external forcing, forced atomic migration is added to the model and new features emerge: the model is supported by several experimental results some of which confirmed its predictions a posteriori. 相似文献
84.
In farm animals as in human, reproduction is affected by changes in the level of energetic balance. The main factors that link metabolism and reproduction, like insulin, IGFs, glucose, FFA, leptin and NPY, act on hypothalamo-pituitary axis as well as on gonads by directly altering gametogenesis. 相似文献
85.
Communication between patients with breast cancer and health care providers. Determinants and implications 总被引:1,自引:0,他引:1
C Lerman M Daly WP Walsh N Resch J Seay A Barsevick L Birenbaum T Heggan G Martin 《Canadian Metallurgical Quarterly》1993,72(9):2612-2620
BACKGROUND: This study evaluated the perceptions of patients with breast cancer of their medical interactions with providers. The determinants and psychological consequences of communication problems also were examined. METHODS: Ninety-seven patients with Stage I or II breast cancer completed a set of validated questionnaires before initiating postoperative therapy. Data on psychological distress were collected at baseline and 3-month follow-up, and multivariate models were fit to explain the relationship between pretreatment communication problems and subsequent psychological distress. Data on clinical variables were abstracted from medical records. RESULTS: A substantial proportion of patients (84%) reported difficulties communicating with the medical team. Communication problems were more common among patients who were less optimistic about their disease and had less assertive coping styles. Patient-reported communication problems were associated with increased anxiety, depression anger, and confusion at the 3-month follow-up. The association between communication problems and mood disturbance remained significant, although small, after adjusting for baseline mood disturbance, demographic, clinical, and coping style variables. CONCLUSION: Interventions that enhance communication between patients with breast cancer and their providers may improve patients' psychological adjustment to treatment. Conversely, interventions that lower distress and modify coping style may enhance communication. 相似文献
86.
Tindall C.E. Martin J.P. Morrow D.J. Calvert P.A.J. 《Energy Conversion, IEEE Transaction on》1996,11(3):539-546
The use of small alternators, other than for standby purposes, is increasing and this has focused attention on the reliability and utility of the parameters normally quoted for such machines. Test procedures are described and methods used for parameter estimation discussed, with particular emphasis on the difficulties presented by small brushless machines 相似文献
87.
Reduction of optical proximity effects (OPE), at deep uv wavelength of 248nm, caused by the variation of stepper lens operating conditions is investigated. It is shown that many of these effects, which increase as the Rayleigh limit is approached, can be minimised, and in many cases eliminated, by suitable choice of lens numerical aperture (NA) and partial coherence (sigma, σ).
Application of these results should enable the user of advanced wafer steppers to carry out high resolution lithography with a minimum of time consuming optical proximity correction (OPC). 相似文献
88.
L Martin 《Canadian Metallurgical Quarterly》1997,75(2):174-177
The present study describes the influence of cataract on high-pass resolution perimetry results. Twenty-five otherwise healthy patients were examined before and after cataract surgery. Their preoperative visual acuities ranged from 0.1 to 0.8 and their mean resolution thresholds from 3.9 to 12.3 dB. Both elevated mean thresholds and local visual fields defects were observed. In patients with low-grade cataract, i.e. preoperative visual acuity 0.3 to 0.65, the mean improvement in perimetric results after operation was approximately 1 dB. In patients with higher degrees of lens opacity, visual acuity 0.1 to 0.25, the difference between pre- and postoperative perimetry results showed a wide range, 1.4-6.2 dB. In conclusion, cataract induced different types of visual field defects. The general threshold increase due to low-grade cataract (VA > or = 0.3) could be compensated for by subtracting 1 dB from the measured value. 相似文献
89.
A. Martin D. Gutschick N. I. Jaeger G. Schulz-Ekloff H. Miessner B. Lücke 《Catalysis Letters》1994,27(1-2):119-130
In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol. 相似文献
90.
More than one hundred samples of European beers have been investigated by the new SNIF-NMR method which is based on 2H NMR at the natural abundance level and enables site-specific natural isotope fractionation factors in ethanol to be determined. The relative (R) and absolute (D/H)i, parameters are shown to be characteristic of the country where the beers are brewed and the observed variations are explained in terms of cereal composition, water resource, and manufacturing processing (fermentation, yeast, temperature cycle). These new parameters find analytical and mechanistic applications in the identification of a beer and in the investigation of a fermentation process. 相似文献