全文获取类型
收费全文 | 330790篇 |
免费 | 5089篇 |
国内免费 | 743篇 |
专业分类
电工技术 | 6473篇 |
综合类 | 598篇 |
化学工业 | 51733篇 |
金属工艺 | 10653篇 |
机械仪表 | 9216篇 |
建筑科学 | 9096篇 |
矿业工程 | 959篇 |
能源动力 | 9106篇 |
轻工业 | 32733篇 |
水利工程 | 2716篇 |
石油天然气 | 3729篇 |
武器工业 | 8篇 |
无线电 | 41254篇 |
一般工业技术 | 62287篇 |
冶金工业 | 60498篇 |
原子能技术 | 5621篇 |
自动化技术 | 29942篇 |
出版年
2021年 | 2785篇 |
2019年 | 2530篇 |
2018年 | 4083篇 |
2017年 | 3862篇 |
2016年 | 4118篇 |
2015年 | 3057篇 |
2014年 | 5089篇 |
2013年 | 15530篇 |
2012年 | 8378篇 |
2011年 | 11488篇 |
2010年 | 8858篇 |
2009年 | 10048篇 |
2008年 | 10614篇 |
2007年 | 10516篇 |
2006年 | 9352篇 |
2005年 | 8548篇 |
2004年 | 8410篇 |
2003年 | 8071篇 |
2002年 | 7831篇 |
2001年 | 7914篇 |
2000年 | 7512篇 |
1999年 | 7895篇 |
1998年 | 18291篇 |
1997年 | 13312篇 |
1996年 | 10474篇 |
1995年 | 8222篇 |
1994年 | 7520篇 |
1993年 | 7212篇 |
1992年 | 5519篇 |
1991年 | 5225篇 |
1990年 | 5153篇 |
1989年 | 4994篇 |
1988年 | 4846篇 |
1987年 | 4080篇 |
1986年 | 4188篇 |
1985年 | 4935篇 |
1984年 | 4459篇 |
1983年 | 4196篇 |
1982年 | 3777篇 |
1981年 | 3920篇 |
1980年 | 3591篇 |
1979年 | 3585篇 |
1978年 | 3361篇 |
1977年 | 3975篇 |
1976年 | 5038篇 |
1975年 | 2904篇 |
1974年 | 2758篇 |
1973年 | 2763篇 |
1972年 | 2290篇 |
1971年 | 2012篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
121.
122.
123.
124.
125.
The solvent-dependent polymorphism of the active pharmaceutical ingredient (API) carbamazepine is interpreted from calculations of the solid-state and API-solvent intermolecular interactions. These simulations suggested that apolar solute-solute interactions could be disrupted by apolar solvents. In contrast, the polar solute-solute interactions were found to be easily disrupted by polar and protic solvents. This is consistent with experimental observations that the crystallization of the metastable form II is more dominant in apolar solvents. The Mercury program remains the gold standard in terms of usability; however, further expansion into more complex simulation techniques could make this package of even greater use in pharmaceutical manufacturing workflows. 相似文献
126.
Radiochemistry - Leaching of uranium and REEs with oxalic acid from the Egyptian Abu-Tartur phosphate rock (PR) was studied. The effect exerted on the leaching process by oxalic acid concentration,... 相似文献
127.
Interactions of hexamethylenetetramine ligand in atom transfer radical polymerization initiated by activator generated by electron transfer were studied. Polymerization of methyl methacrylate was done using two-step experimental procedure in 2 L emulsion batch reactor at 50, 60, and 80°C. The selection of reactant ratios was quite challenging for a reactor of this size. Replicate runs were conducted for data reproducibility purpose. Gravimetry method and gel permeation chromatography were used to determine monomer conversion, Mn, and PDI of polymer samples. PMMA produced was also characterized by means of dynamic light scattering, Fourier-transform infrared spectroscopy and nuclear Magnetic Resonance spectroscopy. Results showed high monomer conversion up to 93% and Mn ranging 243–274 kg/mol with PDI from 1.45 to 1.60. Besides, combining HMTA with sodium dodecyl sulfate, an anionic surfactant, a well-controlled polymer with a lower Mn of 201 kg/mol and PDI of 1.56 was obtained in 3 hr reaction time. 相似文献
128.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献
129.
Electrodewatering is a technique in which pressure dewatering is combined with electrokinetic effects to realize an improved solid/liquid separation and hence increased filter cake dry matter contents. In order to be energy efficient, it is shown that sludge should be dewatered by pressure dewatering to a high extent prior to electric field application, and a sufficient contact time for the electric field must be guaranteed. In order to realize these goals, a bench- and pilot-scale diaphragm filter press suited for electrodewatering were constructed for treatment of sewage and other types of sludges. It was shown that electrodewatering of sludge is a feasible technique, especially for biological sludge types. Other types of sludge are less suited for electrodewatering because of the restricted improvements that can be realized in cake dry matter content and the high electric energy consumption. Furthermore, it was shown in pilot-scale tests that the use of a diaphragm filter press with electrodewatering facilities was very well suited to deliver dry filter cakes of sewage sludge at a moderate energy consumption. Depending on local market prices for investment, operating and sludge disposal costs, this technology may therefore lead to important savings in the sludge management process. 相似文献
130.
A. A. Salem S. R. Kalidindi R. D. Doherty S. L. Semiatin 《Metallurgical and Materials Transactions A》2006,37(1):259-268
Novel experiments were conducted to elucidate the effect of deformation twinning on the mechanical response of high-purity
α-titanium deformed at room temperature. Orientation-imaging microscopy (OIM), microhardness, and nanohardness evaluations
were employed in conjunction with optical microscopy and quasi-static compression testing to obtain insight into the deformation
mechanisms. Hardness measurements revealed that the newly formed deformation twins were harder than the matrix. This observation
is perhaps the first experimental evidence for the Basinski mechanism for hardening associated with twinning, arising from
the transition of glissile dislocations to a sessile configuration upon the lattice reorientation by twinning shear. This
work also provided direct evidence for two competing effects of deformation twinning on the overall stress-strain response:
(1) hardening via both a reduction of the effective slip length (Hall-Petch effect) and an increase in the hardness of twinned regions (Basinski
mechanism) and (2) softening due to the lattice reorientation of the twinned regions. 相似文献