全文获取类型
收费全文 | 1602篇 |
免费 | 174篇 |
国内免费 | 129篇 |
专业分类
电工技术 | 62篇 |
综合类 | 136篇 |
化学工业 | 50篇 |
金属工艺 | 25篇 |
机械仪表 | 79篇 |
建筑科学 | 66篇 |
矿业工程 | 21篇 |
能源动力 | 10篇 |
轻工业 | 29篇 |
水利工程 | 10篇 |
石油天然气 | 5篇 |
武器工业 | 718篇 |
无线电 | 81篇 |
一般工业技术 | 184篇 |
冶金工业 | 21篇 |
原子能技术 | 104篇 |
自动化技术 | 304篇 |
出版年
2024年 | 4篇 |
2023年 | 18篇 |
2022年 | 47篇 |
2021年 | 54篇 |
2020年 | 54篇 |
2019年 | 56篇 |
2018年 | 67篇 |
2017年 | 99篇 |
2016年 | 108篇 |
2015年 | 90篇 |
2014年 | 99篇 |
2013年 | 108篇 |
2012年 | 86篇 |
2011年 | 117篇 |
2010年 | 97篇 |
2009年 | 99篇 |
2008年 | 75篇 |
2007年 | 105篇 |
2006年 | 87篇 |
2005年 | 73篇 |
2004年 | 53篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 34篇 |
2000年 | 18篇 |
1999年 | 28篇 |
1998年 | 25篇 |
1997年 | 26篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1959年 | 3篇 |
排序方式: 共有1905条查询结果,搜索用时 15 毫秒
61.
《Journal of Nuclear Science and Technology》2013,50(1):5-10
Three versions of Japanese Evaluated Nuclear Data Library (JENDL) are briefly explained. The first version, JENDL-1, was made aiming mainly at application to fast reactors. The second version, JENDL-2, was built as a bigger general purpose evaluated nuclear data library. It stores nuclear data for 181 nuclides. It has, however, some drawbacks particularly for fusion neutronics calculation. To remove these drawbacks of JENDL-2 and further extend its applicability, the third version, JENDL-3, has now been made. JENDL-3 includes photon-production data for some nuclides, in addition to the data contained in JENDL-2. 相似文献
62.
63.
《Energy Policy》2016
Development of Mexican hydrocarbon reservoirs by foreign operators has become possible under Mexico's new Hydrocarbon Law, effective as per January 2015. Our study compares the economic returns of shallow water fields in the Gulf of Mexico applying the royalty and taxes due under the fiscal regimes of the U.S. and Mexico. The net present value (NPV) of the base case scenario is US$1.4 billion, assuming standard development and production cost (opex, capex), 10% discount rate accounting for the cost of capital and revenues computed using a reference oil price of $75/bbl. The impact on NPV of oil price volatility is accounted for in a sensitivity analysis. The split of the NPV of shallow water hydrocarbon assets between the two contractual parties, contractor and government, in Mexico and the U.S. is hugely different. Our base case shows that for similar field assets, Mexico's production sharing agreement allocates about $1,150 million to the government and $191 million to the contractor, while under U.S. license conditions the government take is about $700 million and contractor take is $553 million. The current production sharing agreement leaves some marginal shallow water fields in Mexico undeveloped for reasons detailed and quantified in our study. 相似文献
64.
Projectiles, such as turbine blades, can be released in an accident and impact structures. Airplanes and other flying objects can also become impact projectiles. These impacts occasionally cause fire when fire loads, such as oil, fuel, and other combustible materials, are present. This study examines the thermal insulation performance of concrete plates and the structural fire behavior of load-bearing reinforced concrete walls that are exposed to fire after a high-velocity impact by a hard projectile. Impact and fire tests were carried out using small-scale concrete plates and reinforced concrete walls. The results show the influence of local damage and the advantage of short-fiber reinforced concrete subjected to impact loads and fire. 相似文献
65.
为提高制导炮弹在大着角情况下导引头捕捉目标的速度,减小末制导起始点角度偏差,在传统制导炮弹方案弹道规划方法(trajectory programming method, TPM)的基础上考虑末制导段,提出一种考虑导引头多约束的弹道规划方法(trajectory programming method-constraints of seeker, TPM-CS)。根据导引头最大探测距离建立末制导起始点约束,根据弹目几何关系和导引头视场角建立攻击路径约束,并建立最小化前置角和控制变量幅值的目标函数。为实现制导炮弹初始弹道倾角、偏角、火箭点火时间、滑翔启控时间、导引头开启时间等参数的最佳匹配,建立了5阶段弹道规划模型,并采用多阶段Radau伪谱法将该弹道规划问题转化为非线性规划问题,最后调用非线性规划求解器SNOPT进行求解。选取不同性能参数的导引头进行仿真,分析了导引头最大探测距离和导引头视场角对方案弹道的影响。将文中提出的弹道规划方法与传统弹道规划方法进行对比仿真,结果表明,相比于传统方法,文中所提方法规划方案弹道的末制导初始角度偏差缩小71.590%,导引头对目标保持照射状态的时间延长6... 相似文献
66.
《Journal of Nuclear Science and Technology》2013,50(3):242-249
A neutronics benchmark experiment on vanadium, which is a low activation fusion reactor material, was conducted by using the D-T neutron source facility of FNS/JAERI. Neutron spectra, dosimetry reaction rates, γ-ray spectra and γ-ray heating rates were measured in a vanadium experimental assembly. Benchmark tests for four evaluated nuclear data files were performed by analyzing the experiment. As a result, the following problems were pointed out in view of accuracy of fusion reactor designs. (1) JENDL-FF and JENDL-3.2: Total cross section should be reexamined especially at ~2keV. (2) ENDF/B-VI: Double differential cross sections for 14 MeV neutrons should be revised because of the isotropic angular distribution for continuum neutron emission. Gamma-ray production cross sections are too small and discrete γ-ray peaks are not represented clearly. (3) EFF-3: Gamma-ray production cross sections are too large. 相似文献
67.
数字化摊铺对限定作业时间的不停航施工而言,其作业速度快、精度高,测量人员能实时检测指导施工,在节约材料、节省劳动力、保障工程质量等方面有很强的优势,同时解决了传统人工基准架设速度慢这一难题,使不停航施工在退场清扫时间、摊铺厚度质量控制得到极大提升。 相似文献
68.
69.
Health risk concerns associated with household use of rooftop-harvested rainwater (HRW) constitute one of the main impediments to exploit the benefits of rainwater harvesting in the United States. However, the benchmark based on the U.S. EPA acceptable annual infection risk level of ≤1 case per 10,000 persons per year (≤10−4 pppy) developed to aid drinking water regulations may be unnecessarily stringent for sustainable water practice. In this study, we challenge the current risk benchmark by quantifying the potential microbial risk associated with consumption of HRW-irrigated home produce and comparing it against the current risk benchmark. Microbial pathogen data for HRW and exposure rates reported in literature are applied to assess the potential microbial risk posed to household consumers of their homegrown produce. A Quantitative Microbial Risk Assessment (QMRA) model based on worst-case scenario (e.g. overhead irrigation, no pathogen inactivation) is applied to three crops that are most popular among home gardeners (lettuce, cucumbers, and tomatoes) and commonly consumed raw. The infection risks of household consumers attributed to consumption of these home produce vary with the type of produce. The lettuce presents the highest risk, which is followed by tomato and cucumber, respectively. Results show that the 95th percentile values of infection risk per intake event of home produce are one to three orders of magnitude (10−7 to 10−5) lower than U.S. EPA risk benchmark (≤10−4 pppy). However, annual infection risks under the same scenario (multiple intake events in a year) are very likely to exceed the risk benchmark by one order of magnitude in some cases. Estimated 95th percentile values of the annual risk are in the 10−4 to 10−3 pppy range, which are still lower than the 10−3 to 10−1 pppy risk range of reclaimed water irrigated produce estimated in comparable studies. We further discuss the desirability of HRW for irrigating home produce based on the relative risk of HRW to reclaimed wastewater for irrigation of food crops. The appropriateness of the ≤10−4 pppy risk benchmark for assessing safety level of HRW-irrigated fresh produce is questioned by considering the assumptions made for the QMRA model. Consequently, the need of an updated approach to assess appropriateness of sustainable water practice for making guidelines and policies is proposed. 相似文献
70.
《Structure and Infrastructure Engineering》2013,9(11):1529-1547
AbstractAn iterative framework is introduced in this present study to detect seismic isolation precursors of the shortcut calculation method for the isolated benchmark high-speed railway RC bridge. The spatial finite element (FE) analysis model of a benchmark isolated high-speed railway reinforced concrete (RC) bridge system under high-speed railway vehicles is set up based on the equivalent linear method. The vehicle with two bogies is assumed to be represented by a 3?D discrete rigid multi-body system with 23 degrees of freedoms (DOFs). The present study compares the nonlinear seismic response of a high-speed railway bridge with and without isolation bearings. Numerical results demonstrate that the isolation system with the optimal parameters can simultaneously reduce the deck displacement and the internal force of the isolated railway bridge under near-fault (NF) ground motions with various peak accelerations and peak velocity ratios, to ensure the adequate isolation efficiency of isolated structures. Specifically, the study shows that the seismic response of the seismically isolated bridge (IB) and the running safety indexes of the train are primarily dominated by the contents around the fundamental frequency of the train-bridge system subjected to the earthquakes. 相似文献