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41.
本文对冰覆盖下的河道水流进行了区域划分,给出了区域分界面上的水流条件。应用水力学中的一些基本概念和基本原理,对冰覆盖下河道水流阻力、水流流速、切力、能坡及床面高程等问题进行了研究,给出了它们的物理概念和计算公式,并用实验观测资料进行了验证,结果令人满意。 相似文献
42.
几种吸附式致冷新工质对的性能预测 总被引:3,自引:1,他引:2
应用吸附平衡基本理论对几种可能的吸附式致冷新工质对的性能进行了预测。结果表明,烷烃系列的低混点工质与沸石的配对体系是不可取的,而沸石-氨、活性炭-丙酮、活性炭-氨及活性炭-乙醇则是沸石-水、活性炭-甲醇体系的适宜的替代物。 相似文献
43.
In the process of vitrifying aqueous suspensions for cryotransmission electron microscopy, water is solidified without crystallization. Vitrification can be achieved by rapidly plunging an aqueous thin film into a liquid cryogen. The preparation of aqueous thin films prior to vitrification must be performed in an environmental cabinet at controlled temperature and humidity in order to prevent evaporation and temperature-induced phase changes in the thin film. The device described here incorporates several important features which make the apparatus simpler and more convenient to use than similar devices described in the literature. One of these features includes the use of a totally enclosed environmental cabinet in which the grid, sample, micropipette and absorbent paper are equilibrated before thin-film preparation. Other features include a cryogen dewar on a swing arm for easy refilling, a guillotine shutter which is used to trigger the plunger electrically and a semiautomatic system which facilitates rapid transfer of the vitrified specimen from liquid propane to liquid nitrogen for storage and reduces handling of the specimen. To demonstrate the utility of the device, results showing the influence of temperature on the morphology of phospholipid vesicles are presented. A commercial cryotransfer apparatus (which is used for transportation of the vitrified specimen to the electron microscope cold-stage) has been modified to reduce the possibility of reversion of the vitreous phase to the crystalline ice phases. 相似文献
44.
Ice recrystallization rates in simple aqueous solutions comprising fructose and a hydrocolloid stabilizer were measured. The stabilizers were an enzyme-modified guar and a non-gelling high methoxy pectin. The stabilizer concentration dependence of the recrystallization rates for both materials was similar in that increasing the concentration resulted in decreasing rates until a point is reached where further addition had no additional effect. That recrystallization rates were reduced by both gelling and non-gelling stabilizers was strongly suggestive that gelation was not a requirement for recrystallization inhibition and another more specific mechanism applies, for example a weak interfacial effect such as adsorption or blocking. This behavior was also seen with locust bean gum and guar and provided further empirical evidence to support the hypothesis that stabilizers adsorb to ice crystal surfaces. 相似文献
45.
46.
事物未来的状态仅仅受事物现状的影响,而与过去的状态无关,也就是具有马尔可夫性。用马尔可夫链的理论与方法,对具有马尔可夫性产品的可靠性进行预测,既为产品的可靠性设计和产品售后服务的经济性分析提供了参考,也为马尔可夫模型的实际应用拓广了范围。通过实例说明在数学软件的帮助下这种预测方法的简单可行性。 相似文献
47.
48.
对我国石油可采资源量的预测研究 总被引:12,自引:6,他引:6
回顾了世界上现行的可采资源量预测方法,总结分析了在我国石油勘探开发过程中大型油气田的发现规律及储采比变化规律,探讨了累积发现可采储量、累积产量与可采资源量三者之间的内在关系及储采比的变化对它们的影响.在此基础上,利用累积发现的可采储量与累积产量建立了预测可采资源量的有效方法———全程历史拟合法和储采比递减阶段曲线拟合法.利用上述两种方法预测出中国石油的经济可采资源量为107.8×108t,次经济的可采储量约为(27~36)×108t,还对部分油区的可采资源量进行了预测.预测结果表明,两种方法对比使用,能获得较好的预测效果. 相似文献
49.
50.
Rajesh R. Shrestha Barrie R. Bonsal Ashish Kayastha Yonas B. Dibike Christopher Spence 《Journal of Great Lakes research》2021,47(3):677-689
This study assesses snow response in the Assiniboine-Red River basin, located in the Lake Winnipeg watershed, due to anthropogenic climate change. We use a process-based distributed snow model driven by an ensemble of eight statistically downscaled global climate models (GCMs) to project future changes under policy-relevant global mean temperature (GMT) increases of 1.0 °C to 3.0 °C above the pre-industrial period. Results indicate that basin scale seasonal warmings generally exceed the GMT increases, with greater warming in winter months. The majority of GCMs project wetter winters and springs, and drier summers, while autumn could become either drier or wetter. An analysis of snow water equivalent (SWE) responses under GMT changes reveal higher correlations of snow cover duration (SCD), snowmelt rate, maximum SWE (SWEmax) and timing of SWEmax with winter and spring temperatures compared to precipitation, implying that these variables are predominantly temperature controlled. Consequently, under the GMT increases from 1.0 °C to 3.0 °C, the basin will experience successively shorter SCD, slower snowmelt, smaller monthly SWE and SWEmax, earlier SWEmax, and a transition from snow-dominated to rain-snow hybrid regime. Further, while the winter precipitation increases for some GCMs compensate the temperature-driven changes in SWE, the increases for most GCMs occur as rainfall, thus limiting the positive contribution to snow storage. Overall, this study provides a detailed diagnosis of the snow regime changes under the policy-relevant GMT changes, and a basis for further investigations on water quantity and quality changes. 相似文献