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91.
L. L. Hammond S. H. Chien A. H. Roy A. U. Mokwunye 《Nutrient Cycling in Agroecosystems》1989,19(2):93-98
Partially acidulated phosphate rock (PAPR) has been shown to be an effective source of P for plants grown on acid soils. Less information in available, however, regarding the effect of the phosphate rock (PR) source on the solubility and agronomic effectiveness of PAPR.The effect of Fe2O3 + Al2O3 content in PR on the quality of PAPR produced was investigated in this study. Nine sources of PR from Africa, Latin America, and the United States, representing a range of Fe2O3 + Al2O3 from 0.7% to 12.4%, were used. In a single-step process, the finely ground PRs were partially acidulated with H2SO4 at the 30% or 50% acidulation level and granulated (–3.35 + 1.18 mm or –6 + 14 mesh). It was found that the water-soluble P content in PAPR decreased with increasing Fe2O3 + Al2O content in the PR used. Apparently, the presence of Fe2O3 + Al2O3 resulted in a reversion of some of the water-soluble P to citrate-soluble P and sometimes even to citrate-insoluble P.A short-term (6 weeks) greenhouse study was conducted to evaluate crop response to PAPRs and single superphosphate (SSP); maize, the test crop, was grown on an acid soil (pH 4.5)—Hartsells silt loam (Typic Hapludults). The agronomic effectiveness of PAPRs with respect to SSP (in terms of dry-matter yield of maize) decreased with increasing Fe2O3 + Al2O3 content in PRs. Phosphorus uptake by maize from PAPRs was found to correlate well with water solubility but not with citrate solubility. The results obtained in this study show that the detrimental effect of Fe2O3 + Al2O3 content on the solubility and P availability of PAPR should be considered when selecting a PR for PAPR production. 相似文献
92.
提高肥料利用率化工部门能做些什么? 总被引:15,自引:0,他引:15
介绍了中国肥料利用率状况、所施肥料的去向及土壤中养分的积累与亏损。据估计,中国自1985~1996年,约有9900万吨N被淋失和逸散,6000万吨P2O5和1400万吨K2O固定于土壤中。如何提高肥料利用率是中国化学肥料工业紧迫的课题,针对不同类型化肥厂提出了生产控制释放肥料、腐植酸螯合尿素、稳定的碳酸氢铵、部分酸化磷矿复合肥料、完全水溶性复合肥料以及熔融钾镁肥的途径,以提高肥料利用率。 相似文献
93.
94.
为了研究早龄期混凝土材料时变性能,通过现场24组主梁同步养生试块力学试验结果,得到了早龄期混凝土弹性模量的时变规律.基于支持向量机(support vector machine,SVM)建立了施工期预应力混凝土(prestressed concrete,PC)刚构桥标高控制可靠度模型,结合蒙特卡洛法计算了PC刚构桥标高控制可靠指标.结果表明:主桥同样状态下,混凝土弹性模量与龄期之间的关系呈现幂函数关系,PC刚构桥中悬臂阶段与最大悬臂阶段应以不同的自由端挠度偏差容许值控制,中悬臂阶段自由端挠度偏差容许值最大不高于4 mm,最大悬臂阶段自由端挠度偏差容许值最大不高于20 mm. 相似文献
95.
Ram Chandra Reddy Jala Zheng Guo Thomas Bjerring Xuebing Xu 《European Journal of Lipid Science and Technology》2010,112(12):1375-1383
A multi‐stage temperature‐programmed fractionating crystallization process was carried out to examine the effects of the presence of stearic acid (SA), oleic acid (OA), and linoleic acid (LA) on the separation of elaidic acid (EA). The results showed that the efficiency of fractionating crystallization of EA depended largely on the crystallization temperature, initial concentration of EA and presence of SA. The content of SA plays very important role for the fractionating performance. It was a characteristic observation that only when SA <2%, substantial crystallization of EA (>50% in stepwise crystal fractions) were obtained regardless of the initial concentration of SA. In general, SA induced crystallization of EA in earlier stage but delayed further crystallization of EA in later stage; the crystallization of EA was independent from co‐existing OA and LA. After reduction of EA content in solution to certain extent (7–10%, at ?20°C), further reduction of EA content requires much lower crystallization temperatures (40°C, ~5%) with significant loss of OA, indicating the limitation of the method. Instead, SA content could be easily reduced down to low concentration (~0.5%, at ?20°C). Practical applications: Presently, development of methodologies for the removal of trans‐fatty acids (TFA) from partially hydrogenated soybean oil (PHSO) is of high commercial interest. One of the strategies is to selectively release TFAs as free fatty acids from PHSO enzymatically. However, all commercially available enzymes are far away from qualified to selectively release TFAs, where there are always substantial non‐trans FAs hydrolyzed simultaneously. Therefore, developing post‐processing technology is requisite in order to recover those non‐trans fatty acids. Thus, this model system was designed based on FA composition characteristic of PHSO, which aimed to acquire some basic data and experience that lack in available literatures, so as to serve designing efficient practical process for removing trans‐fatty acid moieties from PHSO. The results from this work may be of general value to achieve a better understanding of fractionating crystallization behaviors of different FAs, relationship with individual molecular feature and property, and their interference effects, which might contribute to the design of practically feasible protocol to remove TFAs from PHSO and recover non‐trans FAs at the same time. 相似文献
96.
97.
预应力锚索在岩土工程加固中应用广泛,其腐蚀耐久性对工程运行安全至关重要,而相关的腐蚀变化规律及机理还有待进一步明确。在总结当前预应力锚索腐蚀耐久性研究成果的基础上,对其腐蚀耐久性室内加速试验方案设计进行了探讨。分析了影响腐蚀的主要因素并拟定了各因素的不同影响水平;采用正交设计方法优化试验方案并通过有限元方法对试验模型尺寸和应力分布进行了计算模拟优化和验证;介绍了模型制作等工艺步骤。相关成果可供类似耐久性试验方案设计参考。
相似文献
98.
文中介绍了预应力钢筒混凝土管的概念、优越性,并结合山西省万家寨联接段引黄工程的实际施工,总结出了穿越各种地下管线的施工经验。 相似文献
99.
三峡水利枢纽右岸三期工程坝顶预应力门机大梁高度大、跨度长、钢筋密集、结构体型复杂、张拉吨位大、张拉要求高。针对门机大梁以上特点,对梁体模板设计、混凝土浇筑振捣、梁体张拉施工技术难点进行了深入研究。 相似文献
100.