全文获取类型
收费全文 | 87045篇 |
免费 | 8055篇 |
国内免费 | 4705篇 |
专业分类
电工技术 | 7235篇 |
综合类 | 6397篇 |
化学工业 | 14320篇 |
金属工艺 | 9319篇 |
机械仪表 | 6638篇 |
建筑科学 | 6509篇 |
矿业工程 | 1850篇 |
能源动力 | 4657篇 |
轻工业 | 5041篇 |
水利工程 | 1880篇 |
石油天然气 | 3746篇 |
武器工业 | 722篇 |
无线电 | 8915篇 |
一般工业技术 | 11406篇 |
冶金工业 | 5170篇 |
原子能技术 | 2010篇 |
自动化技术 | 3990篇 |
出版年
2024年 | 313篇 |
2023年 | 1239篇 |
2022年 | 2240篇 |
2021年 | 2707篇 |
2020年 | 2807篇 |
2019年 | 2378篇 |
2018年 | 2191篇 |
2017年 | 2950篇 |
2016年 | 3120篇 |
2015年 | 3176篇 |
2014年 | 4861篇 |
2013年 | 5233篇 |
2012年 | 6151篇 |
2011年 | 6856篇 |
2010年 | 4805篇 |
2009年 | 4986篇 |
2008年 | 4595篇 |
2007年 | 5683篇 |
2006年 | 5195篇 |
2005年 | 4292篇 |
2004年 | 3768篇 |
2003年 | 3236篇 |
2002年 | 2733篇 |
2001年 | 2313篇 |
2000年 | 1984篇 |
1999年 | 1628篇 |
1998年 | 1320篇 |
1997年 | 1214篇 |
1996年 | 1080篇 |
1995年 | 835篇 |
1994年 | 703篇 |
1993年 | 519篇 |
1992年 | 517篇 |
1991年 | 451篇 |
1990年 | 364篇 |
1989年 | 264篇 |
1988年 | 214篇 |
1987年 | 147篇 |
1986年 | 137篇 |
1985年 | 130篇 |
1984年 | 129篇 |
1983年 | 99篇 |
1982年 | 85篇 |
1981年 | 30篇 |
1980年 | 30篇 |
1979年 | 23篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1959年 | 16篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
设计并研制了一种用于压缩式致冷设备的电子式定温域多功能控制装置。它除具有控温范围宽、精度高、控温参数易调等优点外,还实现了低成本的温度显示、半自动除霜控制、加电延时保护、过欠压保护等功能。全部采用无触点控制方式,有良好的性能/价格比。 相似文献
102.
运放滞回比较电路在差动式温度控制中的应用研究 总被引:1,自引:0,他引:1
从差动式温度控制的角度研究了两种由集成运算放大器构成的滞回比较器(基型和交叉耦合型)的传输特性,发现它们均能用作闭环差动式控温单元,并都具有在温度设置点转换速度快、抗干扰能力强、控制单元设计简单等优点。分析和比较了这两种控温单元的控制参数的调节性能和参数的稳定性,获知后者的预置温度(Th或TL)和差动温度范围(△T)的设置值均能各自独立地调节,且系统的Th,TL,△T的实际值几乎仅决定于设置电路本身,因而显得更为优越。文中还讨论了应用中的有关问题,并给出了相关的应用实例。 相似文献
103.
Didier Lemoine 《Computer Physics Communications》1996,97(3):331-344
A quantum wave packet code for studying nonreactive scattering of closed-shell atoms or diatomic molecules from a rigid surface is described. The time evolution relies on the Chebychev propagator. Up to 5 collider degrees of freedom, 3 in translation and 2 in rotation, are treated in a pseudospectral way with the momentum or finite basis representation as the primary space. Potential matrix elements are efficiently evaluated by means of sequential 1D transformations between momentum and coordinate spaces. Fast Fourier transforms are performed for the translational and azimuthal coordinates whereas a Gauss-Legendre transform is used for the polar coordinate. This pseudospectral strategy minimizes memory requirements because no off-diagonal Hamiltonian matrix elements need to be stored. In addition, a wide variety of physical systems can be studied since no particular functional form is imposed for the interaction potential. 相似文献
104.
Biodegradation of monoaromatic hydrocarbons in aquifer columns amended with hydrogen peroxide and nitrate 总被引:1,自引:0,他引:1
The ability of indigenous microorganisms to degrade benzene, toluene, ethylbenzene and xylenes (BTEX) in laboratory scale flow-through aquifer columns was tested separately with hydrogen peroxide (110 mg/l) and nitrate (330 mg/l as NO3−) amendments to air-saturated influent nutrient solution. The continuous removal of individual components from all columns relative to the sterile controls provided evidence for biodegradation. In the presence of hydrogen peroxide, the indigeneous microorganisms degraded benzene and toluene (> 95%), meta- plus para-xylene (80%) and ortho-xylene (70%). Nitrate addition resulted in 90% removal of toluene and 25% removal of ortho-xylene. However, benzene, ethylbenzene, meta- and para-xylene concentrations were not significantly reduced after 42 days of operation. Following this experiment, low dissolved oxygen (< 1 mg/l) conditions were initiated with the nitrate-amended column influent in order to mimic contaminated groundwater conditions distal from a nutrient injection well. Toluene continued to be effectively degraded (> 90%), and more than 25% of the benzene, 40% of the ethylbenzene, 50% of the meta- plus para-xylenes and 60% of the ortho-xylene were removed after several months of operation. 相似文献
105.
106.
为了加热炉和锅炉的安全经济运行 ,分析了烟气余热回收中低温腐蚀的机理 ,提出了行之有效地解决和防止低温腐蚀的几种技术方法 相似文献
107.
108.
Critical-point drying and freeze drying were compared both quantitatively and qualitatively as preparative procedures for scanning electron microscopy. Isolated hepatocytes were used as model cells. Nomarski differential interference contrast microscopy was used for light microscopic measurements of the hepatocytes in the unfixed, the glutaraldehyde fixed, the glutaraldehyde + OsO4 fixed, the critical-point dried and the freeze dried states. Critical-point dried hepatocytes were found to shrink to 38% of glutaraldehyde + OsO4 fixed volume, whereas optimal freeze dried hepatocytes (frozen in water saturated with chloroform and freeze dried at 183 K for 84 h) were found to shrink to 51% of glutaraldehyde + OsO4 fixed volume. Transmission and scanning electron micrographs of the critical-point dried cells showed well-preserved ultrastructure and surface structure. Micrographs of the freeze dried cells showed ultrastructure destroyed by internal ice crystals and surface structure destroyed by external ice crystals. Double-fixed isolated hepatocytes were shown to swell during storage in buffer and to shrink during storage after critical-point drying. For low magnification scanning electron microscopy (up to about 3000 times) both critical-point drying and freeze drying can be used. However, for high magnification scanning electron microscopy, critical-point drying is superior to freeze drying. 相似文献
109.
通过对耐热耐蚀合金Incoloy 80 0H的性能分析 ,指出它与普通奥氏体不锈钢相比具有较优的抗氧化性能、耐蚀性和高温蠕变强度。针对催化裂化装置同轴式沉降再生器内部所用Incoloy 80 0H焊件易出现裂纹的问题进行分析 ,认为在施焊过程中由于合金凝固时有低熔点金属或化合物的液态膜残留在晶界区 ,该合金具有高的焊接热裂纹敏感性 ,若焊材选择不当 ,焊丝填充不充分、缺少保护气等将导致晶间裂纹产生。提出了该合金采用TIG焊接防止热裂纹产生的措施。 相似文献
110.
采用化学分析、金相检验及力学性能测定等方法,对锅炉对流管爆裂原因进行了分析。结果表明,长期超温运行而引起的蠕变是导致爆裂的主要原因。 相似文献