全文获取类型
收费全文 | 8422篇 |
免费 | 983篇 |
国内免费 | 452篇 |
专业分类
电工技术 | 505篇 |
综合类 | 437篇 |
化学工业 | 1453篇 |
金属工艺 | 498篇 |
机械仪表 | 396篇 |
建筑科学 | 552篇 |
矿业工程 | 263篇 |
能源动力 | 271篇 |
轻工业 | 765篇 |
水利工程 | 181篇 |
石油天然气 | 292篇 |
武器工业 | 65篇 |
无线电 | 1322篇 |
一般工业技术 | 1228篇 |
冶金工业 | 428篇 |
原子能技术 | 81篇 |
自动化技术 | 1120篇 |
出版年
2024年 | 41篇 |
2023年 | 147篇 |
2022年 | 267篇 |
2021年 | 375篇 |
2020年 | 296篇 |
2019年 | 269篇 |
2018年 | 288篇 |
2017年 | 316篇 |
2016年 | 337篇 |
2015年 | 373篇 |
2014年 | 451篇 |
2013年 | 655篇 |
2012年 | 564篇 |
2011年 | 606篇 |
2010年 | 516篇 |
2009年 | 512篇 |
2008年 | 472篇 |
2007年 | 429篇 |
2006年 | 441篇 |
2005年 | 397篇 |
2004年 | 263篇 |
2003年 | 245篇 |
2002年 | 218篇 |
2001年 | 178篇 |
2000年 | 175篇 |
1999年 | 161篇 |
1998年 | 140篇 |
1997年 | 122篇 |
1996年 | 95篇 |
1995年 | 82篇 |
1994年 | 68篇 |
1993年 | 67篇 |
1992年 | 31篇 |
1991年 | 45篇 |
1990年 | 27篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1973年 | 6篇 |
1972年 | 5篇 |
排序方式: 共有9857条查询结果,搜索用时 31 毫秒
991.
Co contained MOR zeolite catalysts with high Co loadings were successfully synthesized by buffered ion exchange at pH 8, and were tested for N(2)O catalytic decomposition. The high exchange level of synthesized CoMOR(x)-BIE catalysts probably benefits from the maximizing hydroxycomplexes Co(OH)(+) ion in the buffered solution, which is more preferred for the ion exchange with the zeolites. It has been found that the novel CoMOR(x)-BIE catalysts exhibit excellent catalytic activities, which is attributed to the large population of isolated Co(2+) ions on ion exchange positions. The most active CoMOR(130)-BIE catalyst shows high resistance to the inhibition of oxygen, NO and water vapor. Furthermore, stability tests indicate that the CoMOR(130)-BIE catalyst has no obvious deactivation under simulated emission conditions after reaction for more than 100 h. This extraordinary durability could be related to its high Co(2+) content and low Br?nsted acidity sites in the catalyst, which facilitate the stability of active isolated Co(2+) on ion exchange positions. Thus, the CoMOR(130)-BIE catalyst shows a great potential as a cost-effective catalyst for N(2)O elimination in future applications. 相似文献
992.
Autophagy is critical to the process of development because mouse models have shown that lack of autophagy leads to developmental arrest during the pre-implantation stage of embryogenesis. The process of autophagy is regulated through signaling pathways, which respond to the cellular environment. Therefore, any alteration in the environment may lead to the dysregulation of the autophagic process potentially resulting in cell death. Using both in vitro and in vivo models to study autophagy in the pre-implantation murine embryo, we observed that the cells respond to environmental stressors (i.e. hyperglycemic environment) by increasing activation of autophagy in a differential pattern within the embryo. This upregulation is accompanied by an increase in apoptosis, which appears to plateau at high concentrations of glucose. The activation of the autophagic pathway was further confirmed by an increase in GAPDH activity in both in vivo and in vitro hyperglycemic models, which has been linked to autophagy through the activation of the Atg12 gene. Furthermore, this increase in autophagy in response to a hyperglycemic environment was observed as early as the oocyte stage. In conclusion, in this study, we provided evidence for a differential response of elevated activation of autophagy in embryos and oocytes exposed to a hyperglycemic environment. 相似文献
993.
Wong CC Barron D Orfila C Dionisi F Krajcsi P Williamson G 《Molecular nutrition & food research》2011,55(7):979-988
Scope: Hydroxycinnamic acids are abundant antioxidants in our diet. In humans, hydroxycinnamic acids are metabolized to form sulfates and glucuronides, with the majority recovered in urine. Methods and results: We assessed the potential roles of organic anion transporters (OATs) and ATP‐binding cassette (ABC) transporters in the renal uptake and efflux of hydroxycinnamic acid conjugates. Uptake studies using OAT1 (SLC22A6)‐, OAT2 (SLC22A7)‐, and OAT3 (SLC22A8)‐expressing 293H embryonic kidney cells showed that OAT1 and OAT3, but not OAT2, accepted hydroxycinnamic acid conjugates as substrates. OAT1 and OAT3 mediated the basolateral uptake of hydroxycinnamic acid sulfates and glucuronide conjugates, respectively. Hydroxycinnamic acid sulfates are substrates of OAT4 and were capable of trans‐stimulating 5‐carboxyfluorescein uptake mediated by OAT4. On the other hand, hydroxycinnamic acid conjugates are not substrates for the ABC transporters, multidrug resistance protein 2 (MRP2/ABCC2) or breast cancer resistance protein (BCRP/ABCG2), demonstrated by the inability to alter ATPase activity. Cis‐inhibition studies with OATs and MRPs revealed that hydroxycinnamic acid conjugates have limited impact on the transport of model substrates significantly at physiological concentrations. Conclusion: Concerted action of OAT1, OAT3, and OAT4 is involved in the elimination of hydroxycinnamic acid conjugates into urine, whereas MRP2 and breast cancer resistance protein are not involved in the disposition of these conjugates. 相似文献
994.
Abstract: This article presents an improved method to detect d ‐glucosamine hydrochloride in health foods. A simple precolumn derivatization procedure with 7‐flouro‐4‐nitrobenzo‐2‐oxa‐1,3‐diazole (NBD‐F) reagent was employed. The separation of the derivatized d ‐glucosamine hydrochloride (NBD‐d ‐glucosamine hydrochloride) was performed using a mobile phase consisting of acetonitrile, potassium dihydrogen phosphate (0.01 mol/L), and trifluoroacetic acid (350:649.74:0.26, volume ratio) at a flow rate of 1.0 mL/min with the column temperature 35 °C. Under the optimum chromatographic conditions, the peak area of NBD‐d ‐glucosamine hydrochloride compared with its absolute value of the peak area of NBD‐d ‐glucosamine hydrochloride in a standard solution concentration range from 1.0 to 500.0 mg/L showed a good linear calibration (R = 0.9999). Recoveries, at spiked concentrations of 10.0, 40.0, and 500.0 mg/L, varied between 97.2% and 102.6% with relative standard deviations ranging from 0.4% to 1.5%. The present method provides sufficient sensitivity as reflected by the values of limit of detection (LOD) and limit of quantification (LOQ). LOD was determined from the signal‐to‐noise ratios (S/N) of NBD‐d ‐glucosamine hydrochloride peak of at least 3 in the recovery test at 0.02 mg/L, and the estimated LOQ was 0.06 mg/L (S/N = 10). The proposed method was successfully applicable to detect d ‐glucosamine hydrochloride in health foods and drugs containing a variety of complex materials. 相似文献
995.
Miles D Jansson E Mai MC Azer M Day P Shadbolt C Stitt V Kiermeier A Szabo E 《Journal of food protection》2011,74(6):980-985
Cassava (Manihot esculenta Crantz) is a widely consumed food in the tropics that naturally contains cyanogenic glycosides (cyanogens, mainly composed of linamarin, acetone cyanohydrin, and hydrocyanic acid). If cassava is not adequately processed to reduce the level of cyanogens prior to consumption, these compounds can lead to the formation of hydrocyanic acid in the gut. Exposure to hydrocyanic acid can cause symptoms ranging from vomiting and abdominal pain to coma and death. In 2008, a survey of ready-to-eat (RTE) cassava-based snack foods was undertaken to determine levels of cyanogens measured as total hydrocyanic acid. This survey was undertaken in response to the New South Wales Food Authority being alerted to the detection of elevated levels of cyanogens in an RTE cassava-based snack food. This survey took 374 samples of RTE cassava chips available in the Australian marketplace. Significant variation in the levels of total hydrocyanic acid were observed in the 317 samples testing positive for cyanogens, with levels ranging from 13 to 165 mg of HCN equivalents per kg (mean value, 64.2 mg of HCN eq/kg for positive samples). The results from this survey serve as a timely warning for manufacturers of RTE cassava chips and other cassava-based snack foods to ensure there is tight control over the levels of cyanogens in the cassava ingredient. Evidence from this survey contributed to an amendment to the Australia New Zealand Food Standards Code, which now prescribes a maximum level for hydrocyanic acid in RTE cassava chips of 10 mg of HCN eq/kg, which aligns with the Codex Alimentarius Commission international standard for edible cassava flour. 相似文献
996.
Kim J Hong AJ Kim SM Shin KS Song EB Hwang Y Xiu F Galatsis K Chui CO Candler RN Choi S Moon JT Wang KL 《Nanotechnology》2011,22(25):254006
We have demonstrated, for the first time, a novel three-dimensional (3D) memory chip architecture of stacked-memory-devices-on-logic (SMOL) achieving up to 95% of cell-area efficiency by directly building up memory devices on top of front-end CMOS devices. In order to realize the SMOL, a unique 3D Flash memory device and vertical integration structure have been successfully developed. The SMOL architecture has great potential to achieve tera-bit level memory density by stacking memory devices vertically and maximizing cell-area efficiency. Furthermore, various emerging devices could replace the 3D memory device to develop new 3D chip architectures. 相似文献
997.
998.
旋光性聚合物可以使通过它的偏振光发生偏转,在手性识别和对映体拆分、手性催化剂、液晶、生物医药、光学开关和非线性光学等领域展现出良好的应用前景。本文综述了几种利用旋光性单体缩聚合成具有光学活性高分子材料的方法,对所得聚合物的热稳定性、可溶性、旋光性等主要性能进行分析比较,得到一系列重要的结论,并对其影响机理进行讨论。在此... 相似文献
999.
Chi Zhang P.R. Shukla David G. Victor Thomas C. Heller Debashish Biswas Tirthankar Nag 《Energy Policy》2006
The study examines the dynamics of carbon emissions baselines of electricity generation in Indian states and Chinese provinces in the backdrop of ongoing electricity sector reforms in these countries. Two Indian states—Gujarat and Andhra Pradesh, and three Chinese provinces–Guangdong, Liaoning and Hubei have been chosen for detailed analysis to bring out regional variations that are not captured in aggregate country studies. The study finds that fuel mix is the main driver behind the trends exhibited by the carbon baselines in these five cases. The cases confirm that opportunities exist in the Indian and Chinese electricity sectors to lower carbon intensity mainly in the substitution of other fuels for coal and, to a lesser extent, adoption of more efficient and advanced coal-fired generation technology. Overall, the findings suggest that the electricity sectors in India and China are becoming friendlier to the global environment. Disaggregated analysis, detailed and careful industry analysis is essential to establishing a power sector carbon emissions baseline as a reference for CDM crediting. However, considering all the difficulties associated with the baseline issue, our case studies demonstrate that there is merit in examining alternate approaches that rely on more aggregated baselines. 相似文献
1000.
Jianming Li Ming Chong Liqing Yang Jiadong Xu Xiao-Feng Duan Min Gao Feng-Lian Wang Haitao Liu Li Bian Xun Chi Yonghui Zhai 《Solar Energy Materials & Solar Cells》2005,86(4):585-591
A new type of photovoltaic system with higher generation power density has been studied in detail. The feature of the system is a V-shaped module (VSM) with two tilted monocrystalline solar cells. Compared to solar cells in a flat orientation, the VSM enhances external quantum efficiency and leads to an increase of 31% in power conversion efficiency. Due to the VSM technique, short-circuit current density was raised from 24.94 to 33.7 mA/cm2, but both fill factor and open-circuit voltage were approximately unchanged. For the VSM similar results (about 30% increase) were obtained for solar cells fabricated by using mono-crystalline silicon wafers with only conventional background impurities. 相似文献