全文获取类型
收费全文 | 33776篇 |
免费 | 4720篇 |
国内免费 | 2129篇 |
专业分类
电工技术 | 794篇 |
综合类 | 1661篇 |
化学工业 | 10214篇 |
金属工艺 | 1156篇 |
机械仪表 | 2779篇 |
建筑科学 | 1220篇 |
矿业工程 | 549篇 |
能源动力 | 1936篇 |
轻工业 | 8105篇 |
水利工程 | 115篇 |
石油天然气 | 985篇 |
武器工业 | 158篇 |
无线电 | 2389篇 |
一般工业技术 | 4604篇 |
冶金工业 | 2458篇 |
原子能技术 | 707篇 |
自动化技术 | 795篇 |
出版年
2024年 | 96篇 |
2023年 | 787篇 |
2022年 | 1232篇 |
2021年 | 1876篇 |
2020年 | 1589篇 |
2019年 | 1570篇 |
2018年 | 1417篇 |
2017年 | 1553篇 |
2016年 | 1563篇 |
2015年 | 1534篇 |
2014年 | 2188篇 |
2013年 | 2484篇 |
2012年 | 2464篇 |
2011年 | 2553篇 |
2010年 | 1737篇 |
2009年 | 1760篇 |
2008年 | 1446篇 |
2007年 | 1975篇 |
2006年 | 1779篇 |
2005年 | 1369篇 |
2004年 | 1213篇 |
2003年 | 1133篇 |
2002年 | 914篇 |
2001年 | 704篇 |
2000年 | 585篇 |
1999年 | 486篇 |
1998年 | 406篇 |
1997年 | 341篇 |
1996年 | 294篇 |
1995年 | 244篇 |
1994年 | 216篇 |
1993年 | 194篇 |
1992年 | 168篇 |
1991年 | 134篇 |
1990年 | 88篇 |
1989年 | 77篇 |
1988年 | 58篇 |
1987年 | 51篇 |
1986年 | 49篇 |
1985年 | 43篇 |
1984年 | 35篇 |
1983年 | 26篇 |
1982年 | 54篇 |
1981年 | 69篇 |
1980年 | 25篇 |
1979年 | 8篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
31.
32.
Shoji Nakamura Yuji Shibahara Atsushi Kimura Osamu Iwamoto Akihiro Uehara Toshiyuki Fujii 《Journal of Nuclear Science and Technology》2020,57(4):388-400
ABSTRACTThe thermal-neutron capture cross-section (σ0) and resonance integral (I0) were measured for the 135Cs(n,γ)136Cs reaction by an activation method and mass spectrometry. Because of difficulty in the preparation of pure 135Cs samples, we used 135Cs contained as an impurity in a normally available 137Cs standard solution. An isotope ratio of 135Cs and 137Cs in a standard 137Cs solution was measured by mass spectrometry to quantify 135Cs. Cesium-135 impurity along with the 137Cs standard solution was irradiated at the hydraulic conveyer of the research reactor in the Institute for Integral Radiation and Nuclear Science, Kyoto University. Wires of Co/Al and Au/Al alloys were used as neutron monitors to measure thermal-neutron fluxes and epi-thermal Westcott’s indices at an irradiation position. A gadolinium filter was used to measure the σ0, and a value of 0.133 eV was taken as the cut-off energy. Gamma-ray spectroscopy was used to measure induced activities of 137Cs, 136Cs and monitor wires. On the basis of Westcott’s convention, the σ0 and I0 values were derived as 8.57 ± 0.25 barn, and 45.3 ± 3.2 barn, respectively. The value of σ0 obtained in the present study agreed within the limits of uncertainties with the past-reported value of 8.3 ± 0.3 barn. 相似文献
33.
为研究铝合金三角形波纹夹芯板对平头弹体的抗冲击性能及损伤特性,利用有限元软件ABAQUS/Explicit建立弹体冲击靶板的数值模拟模型,并结合实验验证了模型及其参数的有效性。基于数值计算结果,分析了三角形波纹夹芯板几何结构对其防护性能、失效模式和能量吸收的影响规律及机理,并与等面密度单层板进行对比分析,研究结果表明,靶体几何结构对其抗冲击性能存在影响,三角形波纹夹芯板抗冲击性能低于单层板抗冲击性能。此外,增加芯体拓扑结构夹角能显著提高三角形波纹夹芯板的抗冲击性能,并且靶板几何形状会对其失效模式及耗能特性存在影响。 相似文献
34.
35.
Abiodun B. Ogbesejana Zhong Ningning Oluwadayo O. Sonibare 《Petroleum Science and Technology》2019,37(18):1969-1977
The occurrence and distributions of dibenzofurans (DBFs) and benzo[b]naphthofurans were investigated in crude oils from Niger Delta, Nigeria, by gas chromatography-mass spectrometry-mass spectrometry. The distribution of DBFs was characterized by the predominance of C2-dibenzofurans. 4-Methyldibenzofuran was the most abundant among the methyldibenzofurans isomers while dimethyldibenzofuran-2 (DMDBF-2), ethyldibenzofuran-1, DMDBF-3, and DMDBF-6 occurred in higher amounts when compared with other DMDBFs. Among the benzonaphthofurans, the abundance of benzo[b]naphtho[2,1-d]furan was higher than other isomers. The DBFs distributions in the oils were not affected by source facies and depositional environments. However, the DBFs concentrations increased with increasing maturity in oils from ADL and MJO oilfields. 相似文献
36.
目的建立高效液相色谱-质谱联用法(high performance liquid chromatography-masss pectrometer,HPLC-MS)测定薏苡仁中药饮片中黄曲霉毒素B_1、B_2、G_1、G_2的方法,并对比不同产地薏苡仁中黄曲霉毒素含量。方法样品经过免疫亲合柱处理后,采用HPLC-MS进行测定。分析柱为C18柱(50 mm×2.1 mm, 1.8μm),流动相为10 mmol/L醋酸铵溶液-甲醇溶液,梯度洗脱,流速为0.3 mL/min,柱温为25℃。结果黄曲霉毒素B_1在0.26~10.4ng/mL浓度范围内与峰面积值均呈现良好的线性关系(r~2=0.9995),平均加样回收率为75.4%~123.9%,黄曲霉毒素B2在0.0875~3.5 ng/mL浓度范围内与峰面积值均呈现良好的线性关系(r~2=0.9996),平均加样回收率为71.1%~124.2%,黄曲霉毒素G_1在0.295~11.89 ng/mL浓度范围内与峰面积值均呈现良好的线性关系(r~2=0.9995),平均加样回收率为78.9%~112.2%,黄曲霉毒素G2在0.1475~5.9 ng/mL浓度范围内与峰面积值均呈现良好的线性关系(r~2=0.9992),平均加样回收率为73.8%~123.9%。结论该方法准确、可靠、专属性强,通过精确化合物离子监测,可准确的测定薏苡仁中黄曲霉毒素含量。 相似文献
37.
S. Younessi Sinaki M. H. Panjeshahi F. Moattar 《Petroleum Science and Technology》2019,37(20):2122-2127
There is a wide range of resources for CO2 emissions. The net amount of CO2 emissions in the cement industry due to the consumption of fossil fuels and the chemical processes of cement production under heating raw materials is reported to be in the range of 15–25%; this industry, among all the industries and after the power plants and refineries, is the largest CO2 gas producer throughout the world. Using CO2 capture and storage (CCS), it can reduce greenhouse gas emissions in a short time. In this study, the technical feasibility study of recycling CO2 in Abyek Cement Company, with a cement production capacity of about 12,500 tons per day in two production lines, has been studied as one of the largest cement industries throughout the world. Fuel oil (Mazut) is used as the primary fuel for furnaces in this industry. Affected by combustion, the emissions emitted from the five-stage preheater contain 5/24% vol% of CO2, 7.6% H2O, 4.8% vol% of O2, and 63.1% N2. 相似文献
38.
Antonio Buonerba Francesco Della Monica Vito Speranza Carmine Capacchione Stefano Milione Alfonso Grassi 《Polymer International》2019,68(10):1681-1687
The thin‐film morphology of stereoregular syndiotactic poly(p‐methylstyrene)–(cis‐1,4‐polybutadiene) (sP(pMS–B)) multiblock copolymers has been investigated using tapping mode atomic force microscopy with variation of the polymer composition and monomer block lengths. The morphology of the thin films ranges from isolated circular domains of sP(pMS) embedded into a matrix of polybutadiene (PB) to isolated domains of PB embedded into a matrix of sP(pMS), passing through bicontinuous (jagged) lamellae when the pMS concentration is in the range 20–67 mol%. Multiple folding of the polymer segments, i.e. where reciprocal inclusions of polymer segments to each other phase are able to generate greater domain, has been postulated and validated by considerations on the polymer architecture and the thermal and crystalline behaviour. © 2019 Society of Chemical Industry 相似文献
39.
在进行能量色散X射线荧光光谱(EDXRF)解谱时,如果给定样品的元素构成,采用纯元素谱图剥离的方式会更加合理,但由于每个元素的谱线都不止一条,如果仅仅针对主线对齐做剥离,会导致结果的严重失真,同时剥离次序对解谱结果有较大影响。介绍了一种最优化算法与纯元素谱剥离相结合的EDXRF解谱方法,该方法以多个纯元素谱的强度大小和峰位漂移道数作为变量构建残差方程,并用最优化计算的方法去调整,直至残差达到极小。实验采用强度顺序剥离、能量顺序剥离和最优化算法拟合3种方法分别对谱线重叠较为严重的La-Ce-Pr-Nd混合液样品的L系谱线进行了解析,结果表明最优化计算方法拟合的谱图与原始谱的残差 (1415.0)比另两种方法(166094.0和3192.7)大幅度缩小,拟合谱与原始谱更为吻合,并且方法在实现时对初值不敏感,解谱精度也不依赖于剥离次序。 相似文献
40.
Flame spread over solid fuels in high‐pressure situations, such as nuclear containment shells during a pressurized period, has potential to result in catastrophic disaster, thus requiring further knowledge. This paper experimentally reveals the flame spread behaviors over fuel cylinders in high pressures. Polyethylene and polymethyl‐methacrylate cylinders with the diameter of 4.0 mm are used in this study. Ambient gas is air, and total pressures are varied from naturally normal pressure (100 kPa) to elevated pressure (500 kPa). Flame characteristics including flame appearance and flame size and burning rate and flame spread rate are investigated. Results show that in high pressure, the flame appearance is significantly affected. As the pressure increases, the blue flame disappeared, and the color of flame tip changes from luminous yellow to orange as well the orange part extends down towards the base of flame. The dimensionless flame height increases with pressure for pressure below 150 kPa and then decreases with pressure above that level. The burning rates show increasing trend with pressure and are proportional to P0.6 and P0.79 for polymethyl‐methacrylate and polyethylene, respectively. Besides, flame spread rates for polymethyl‐methacrylate and polyethylene both were found to be proportional to P0.5. 相似文献