全文获取类型
收费全文 | 95026篇 |
免费 | 5095篇 |
国内免费 | 4807篇 |
专业分类
电工技术 | 4308篇 |
技术理论 | 6篇 |
综合类 | 9363篇 |
化学工业 | 12755篇 |
金属工艺 | 5724篇 |
机械仪表 | 3606篇 |
建筑科学 | 4723篇 |
矿业工程 | 1421篇 |
能源动力 | 2811篇 |
轻工业 | 6073篇 |
水利工程 | 2054篇 |
石油天然气 | 4200篇 |
武器工业 | 724篇 |
无线电 | 7588篇 |
一般工业技术 | 14511篇 |
冶金工业 | 2568篇 |
原子能技术 | 2204篇 |
自动化技术 | 20289篇 |
出版年
2024年 | 80篇 |
2023年 | 358篇 |
2022年 | 546篇 |
2021年 | 783篇 |
2020年 | 1249篇 |
2019年 | 1100篇 |
2018年 | 1230篇 |
2017年 | 1183篇 |
2016年 | 1734篇 |
2015年 | 2436篇 |
2014年 | 4332篇 |
2013年 | 5085篇 |
2012年 | 4418篇 |
2011年 | 5107篇 |
2010年 | 4311篇 |
2009年 | 5669篇 |
2008年 | 5726篇 |
2007年 | 6083篇 |
2006年 | 5530篇 |
2005年 | 4631篇 |
2004年 | 4003篇 |
2003年 | 3904篇 |
2002年 | 3881篇 |
2001年 | 2896篇 |
2000年 | 3287篇 |
1999年 | 3039篇 |
1998年 | 2564篇 |
1997年 | 2429篇 |
1996年 | 2601篇 |
1995年 | 2717篇 |
1994年 | 2460篇 |
1993年 | 1500篇 |
1992年 | 1530篇 |
1991年 | 1043篇 |
1990年 | 775篇 |
1989年 | 688篇 |
1988年 | 644篇 |
1987年 | 386篇 |
1986年 | 230篇 |
1985年 | 383篇 |
1984年 | 414篇 |
1983年 | 438篇 |
1982年 | 330篇 |
1981年 | 405篇 |
1980年 | 273篇 |
1979年 | 116篇 |
1978年 | 114篇 |
1977年 | 70篇 |
1976年 | 41篇 |
1975年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Xinzhi Li Anastasia Eu Shao-Quan Liu 《International Journal of Food Science & Technology》2021,56(12):6451-6462
In this study, the effect of co-fermentation and sequential fermentation with a typical halophilic soy sauce yeast Candida versatilis and a non-halophilic dairy bacterium Lactococcus lactis subsp. cremoris in pork hydrolysates was explored for the first time with regard to their viability, physicochemical changes and volatile compound production. It was observed that the growth of C. versatilis was suppressed (only 0.6 - 1.5 log CFU mL−1 increase), whilst L. lactis subsp. cremoris was stimulated (total cell counts exceeded 9.0 log CFU mL−1) in mixed-cultures relative to the respective monocultures. There were no significant differences between co-inoculation and sequential inoculation regarding glucose consumption, organic acid production and free amino acids utilisation. Some distinct volatile compounds such as methionol, 6-methyl-5-hepten-2-one and gamma-nonalactone were found in both co-inoculated and sequentially inoculated samples, with slightly different concentrations. These results suggest that the mixed-inoculation of C. versatilis and L. lactis have a positive impact on the volatile compounds formation in pork hydrolysates. 相似文献
92.
Ziauddin Sobia Asghar Ibrar Hussain Rahmat Ullah Muqaddar Abbas 《Journal of Modern Optics》2020,67(8):737-745
ABSTRACTWe present a theoretical model to realize the symmetric and asymmetric diffraction grating in a four-level atomic medium. The proposed atomic medium follows a double lambda configuration where four fields interact with it. We get control over symmetric and asymmetric behavior of the diffraction grating by manipulating the relative phase of the fields. Interestingly, the symmetric and asymmetric diffraction grating become prominent when the vortex beam is used instead of the plane wave. Enhanced first, second, and third-order diffraction gratings are achieved via the vortex beam. Further, we find control over asymmetric diffraction gratings by the relative phase of the fields. Coherent control of asymmetric diffraction grating in negative and positive diffracted angles is also achieved via the relative phase. 相似文献
93.
94.
J. Rodney Turner 《International Journal of Project Management》2018,36(1):231-240
In this paper I make a personal reflection on my research and writings in the field of Project Management over the past 30 years. My research has primarily been about the management of the project-based organization. Within that I have researched governance, organizational behaviour, contingency, marketing, success and shareholder value. 相似文献
95.
Govindan Suresh Kumar Gopalu Karunakaran Easwaradas Kreedapathy Girija Evgeny Kolesnikov Nguyen Van Minh Mikhail V. Gorshenkov Denis Kuznetsov 《Ceramics International》2018,44(10):11257-11264
We report the rapid microwave-assisted hydrothermal synthesis of mesoporous hydroxyapatite (HAp) nanocrystals with controlled size, morphology, and surface area using various organic modifiers as regulators. The products were analyzed for their crystalline nature, phase purity, morphology, particle size and pore size distribution. Results indicated that ascorbic acid, cetyltrimethyl ammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) play an important role to obtain needle like, rod like and fiber like mesoporous HAp nanocrystals with different specific surface area by controlling growth habit of HAp along c-axis. In addition, the prepared samples were B-type carbonated HAp similar to bone minerals. Therefore, the present approach can be a promising way to obtain precursor for making tissue engineering scaffolds, drug/protein delivery carriers and bone fillers with tunable characteristics. 相似文献
96.
97.
针对成庄煤矿四盘区层一次采全高煤壁失稳问题,对观测统计数据进行分析,发现片帮主要表现形式分五种:顶部、腰部、顶底部、底部以及斜切片帮,据此采用对顶板超前预爆破和煤壁超前预加固技术来控制大采高煤壁稳定性,不仅对煤壁失稳的控制取得了良好的效果,而且经济效益显著。可为相似条件下的厚煤层一次采全高煤壁失稳控制提供借鉴。 相似文献
98.
Isolation,purification, and antioxidant activities of polysaccharides from Ziziphus Jujuba cv. Muzao
In the present study, crude polysaccharides from Ziziphus Jujuba cv. Muzao were isolated and purified using DEAE cellulose-52 and Sephadex G-100 size-exclusion chromatography; four fractions were collected, namely GZMP-1, GZMP-2, GZMP-3, and GZMP-4. The molecular weights of these four fractions were measured to be 111.2, 95.1, 84.2, and 571.4 kDa, respectively, using high-performance gel permeation chromatography. Gas chromatography analysis of the monosaccharide composition confirmed that GZMP-1 was composed of rhamnose, arabinose, glucose, and galactose. Rhamnose, arabinose, and galactose were the main components present in GZMP-2 and GZMP-3, whereas GZMP-4 was composed of only rhamnose and arabinose. Scanning electron microscopy showed relatively smooth surfaces for GZMP-1 and GZMP-4, whereas GZMP-2 and GZMP-3 had more folds on their surfaces. Fourier transform infrared spectroscopy analyses indicated that GZMP-1 and ZMP mainly had α-type glycosidic linkages. The in vitro antioxidant activities of the polysaccharides revealed that jujube polysaccharides exhibit remarkable antioxidant activity, and can scavenge DPPH radical and OH radical in a concentration-dependent manner. The results of this work suggest that polysaccharides from Z. Jujuba cv. Muzao have potential to be used as functional food and in the development of natural antioxidant drug carriers. 相似文献
99.
Geophysical analysis was undertaken on the available suit of well logs, 3D seismic and checkshot data from the field in a view to carrying out reservoir characterization and volumetric estimation of Orok Field Niger Delta Province. Lithology delineation and Petrophysical evaluation including porosity, water saturation and net-to-gross were undertaken. Well to seismic tie, structural interpretation and horizon mapping were carried out. Time and depth maps were generated and volumetric estimation of the reservoirs were carried out. Four gas-bearing reservoir (A001, B001, C001 and D001) of variable thickness and depth from the subsurface were identified. Their effective porosity ranges from 19% for A001, 20% for B001, 20% for C002 and 18% for the basal D001 respectively. Water saturation estimated from the reservoir sands ranges from 23% for A001, B001 20%, C001 12% and 10% for D001. The hydrocarbon saturation of the reservoirs stood at 77%, 80%, 82%, 90% for A001, B001, C001 and D001 respectively. Only sand A001 and sand B001 had good seismic tie and were able to be mapped through the seismic. Three synthetic structural building listric faults were interpreted across the inlines intercepting the top of reservoir Sand A001 and B001. The volumetric estimation reveals that A001 and B001 have an area of 813.708 acres and 813.693 acres and volume of 151?billion cu.ft and 286?billion cu.ft of gas respectively. Three synthetic structural building listric faults (F1, F2 and F3) intercept the top of sandstones A001 and B001. The structural trapping mechanism in both sandstones resulted from synthetic fault assisting structures i.e rollover anticlines. The modeled faults trends approximately northwest to southeast direction and dip in the southwest direction. 相似文献
100.
《Intermetallics》2015
Electrical resistivity, Seebeck coefficient, specific heat and thermal conductivity measurements on the Ti50−xNi50+x (x = 0.0–1.6 at.%) shape memory alloys are performed to investigate their thermal and transport properties. In this study, anomalous features are observed in both cooling and heating cycles in all measured physical properties of the slightly Ni-rich TiNi alloys (x ≤ 1.0), corresponds to the transformation between the B19′ martensite and B2 austenite phases. Besides, the transition temperature is found to decrease gradually with increasing Ni content, and the driving force for the transition is also found to diminish slowly with the addition of excess Ni, as revealed by specific heat measurements. While the signature of martensitic transformation vanishes for the Ni-rich TiNi alloys with x ≥ 1.3, the characteristics of strain glass transition start to appear. The Seebeck coefficients of these TiNi alloys were found to be positive, suggesting the hole-type carriers dominate the thermoelectric transport. From the high-temperature Seebeck coefficients, the estimated value of Fermi energy ranges from ∼1.5 eV (Ti48.4Ni51.6) to ∼2.1 eV (Ti50Ni50), indicating the metallic nature of these alloys. In addition, the thermal conductivity of the slightly Ni-rich TiNi alloys with x ≤ 1.0 shows a distinct anomalous feature at the B19′ → B2 transition, likely due to the variation in lattice thermal conductivity. 相似文献