全文获取类型
收费全文 | 87124篇 |
免费 | 7533篇 |
国内免费 | 3725篇 |
专业分类
电工技术 | 5150篇 |
技术理论 | 4篇 |
综合类 | 5656篇 |
化学工业 | 22309篇 |
金属工艺 | 10092篇 |
机械仪表 | 3089篇 |
建筑科学 | 10209篇 |
矿业工程 | 2159篇 |
能源动力 | 4949篇 |
轻工业 | 5878篇 |
水利工程 | 2287篇 |
石油天然气 | 3242篇 |
武器工业 | 866篇 |
无线电 | 4226篇 |
一般工业技术 | 9761篇 |
冶金工业 | 6123篇 |
原子能技术 | 960篇 |
自动化技术 | 1422篇 |
出版年
2024年 | 279篇 |
2023年 | 1211篇 |
2022年 | 2122篇 |
2021年 | 2837篇 |
2020年 | 2850篇 |
2019年 | 2345篇 |
2018年 | 2235篇 |
2017年 | 2791篇 |
2016年 | 2825篇 |
2015年 | 2990篇 |
2014年 | 4867篇 |
2013年 | 5154篇 |
2012年 | 5976篇 |
2011年 | 6280篇 |
2010年 | 5040篇 |
2009年 | 5283篇 |
2008年 | 4238篇 |
2007年 | 5683篇 |
2006年 | 5579篇 |
2005年 | 4550篇 |
2004年 | 3893篇 |
2003年 | 3398篇 |
2002年 | 2926篇 |
2001年 | 2399篇 |
2000年 | 1984篇 |
1999年 | 1542篇 |
1998年 | 1262篇 |
1997年 | 1082篇 |
1996年 | 850篇 |
1995年 | 722篇 |
1994年 | 529篇 |
1993年 | 429篇 |
1992年 | 413篇 |
1991年 | 359篇 |
1990年 | 264篇 |
1989年 | 262篇 |
1988年 | 178篇 |
1987年 | 126篇 |
1986年 | 104篇 |
1985年 | 108篇 |
1984年 | 101篇 |
1983年 | 78篇 |
1982年 | 63篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1966年 | 9篇 |
1964年 | 9篇 |
1959年 | 14篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
111.
An approach is presented to satisfy the demand for simple criteria, guidelines and models for the preliminary sizing of horizontal subsurface flow (SF) constructed wetland systems. This approach eliminates time-consuming calculations and iterations by providing graphical solutions for wetland system sizing. Therefore, it can be used for the preliminary assessment of new or performance evaluation of existing subsurface flow constructed wetland systems. The validity of this methodology is checked with data from existing systems and is found to be quite satisfactory. This methodology is combined with simple equations predicting the maximum wetland capacity in summer, so as to assist designers in sizing installations in tourist areas with increased summer populations. Furthermore, based on this methodology, a sensitivity analysis is performed of the area requirements for wastewaters of various strengths and various design conditions and performance criteria. The results provide a useful overview to engineers and further simplify the design methodology of new subsurface flow constructed wetland systems. 相似文献
112.
113.
水溶液全循环法尿素装置中压分解"三种工艺"的比较 总被引:1,自引:0,他引:1
以生产数据结合理论计算的方法系统地比较、分析了水溶液全循环法尿素装置中中压分解“三种工艺”的热能利用、甲铵分解率、总氨蒸出率、水平衡量、一分加热器生产能力等方面的情况,提出应用和配置预分离-预蒸馏工艺的方法,评论该工艺在水溶液全循环法中的地位和作用。 相似文献
114.
115.
I. Budić-Leto T. Lovrić J. Gajdoš Kljusurić I. Pezo U. Vrhovšek 《European Food Research and Technology》2006,222(3-4):397-402
Identification of anthocyanins in the wine made of the Croatian autochthonous grape variety of Babić (Vitis vinifera L.) was carried out and their profile was determined by means of high-performance liquid chromatography with diode array
and mass spectrometric detection. Dependence of anthocyanins content and profile on maceration treatment conditions was investigated.
Statistically significant differences of anthocyanins concentration in wines Babić produced by various maceration treatments
were confirmed by the use of multivariate analysis of variances. The investigation results indicated that the maceration temperature
exerts higher influence on anthocyanins concentration than the duration of maceration. In addition, on the basis of anthocyanin
composition and using different multivariate statistical analyses, differentiation of wines Babić according to maceration
treatments was procured. 相似文献
116.
牛头山水电站大坝为抛物线形混凝土双曲拱坝,最大坝高108.0 m,采用坝顶5孔开敞式溢洪道泄洪,挑流消能。为提前发挥水电站效益,在拱坝尚未完全封拱的情况下,通过计算分析,得出了水库可以下闸蓄水的结论。 相似文献
117.
氧对聚合物污水溶液黏度影响的实验研究 总被引:5,自引:2,他引:3
在45℃下对溶解氧对聚合物污水溶液表观黏度(170 s-1)的影响作了全面的实验研究。采油污水取自大庆采油二厂,矿化度4013、Fe3+、∑Fe、SO42-分别为0.2、1.09、.6 mg/L。厌氧实验操作和测试均在Bactron 1.5型厌氧室中进行。污水中SRB菌数随放置时间延长而增加,厌氧条件下增速远大于曝氧条件下的增速,放置7天时菌数相差6~600倍。用脱氧和含氧加盐蒸馏水配制的抗盐型和功能型聚合物溶液的黏度,均随放置时间延长(1~10天)而减小,脱氧溶液的黏度总是明显大于含氧溶液。0.5 g/L超高分聚合物溶液在厌氧和曝氧条件下放置时,黏度随放置时间延长而减小,分别由1天时的22.2和28.8 mPa.s减至60天时的2.7和3.4 mPa.s,曝氧条件下的黏度总是大于厌氧条件下的黏度;加入甲醛杀菌剂使溶液黏度的减小趋缓,60天时为8.9和9.6 mPa.s;在4~8mg/L范围改变含氧量,当含氧6 mg/L时放置2~40天时的黏度均最大,40天时为18.2 mPa.s。6 mg/L为污水的合理曝氧量。分析了聚合物降解、SRB菌作用、杀菌剂作用等机理。表6参10。 相似文献
118.
Saudino Kimberly J.; Wertz Annie E.; Gagne Jeffrey R.; Chawla Sonia 《Canadian Metallurgical Quarterly》2004,87(5):698
Twin studies suggest that parent ratings of temperament exaggerate differences between twins. The present study examined whether such contrast effects also operate for nontwin siblings. The activity level (AL) and shyness of 95 nontwin sibling pairs (ages 3 to 8 years) were assessed via parent ratings and objective measures (actigraph and observer ratings). Siblings showed no resemblance in either parent-rated AL or shyness; however, sibling resemblance for actigraph AL and observer-rated shyness was substantial. Thus, parents do contrast their nontwin siblings when rating these 2 temperament dimensions. Moreover, the importance of sibling differences in temperament to the sibling relationship and differential maternal treatment varied across the different measures of AL and shyness, suggesting that parent perceptions may play a role in these associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
119.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
120.
Thermodynamic and Transport Properties of Liquid HFC-227ea 总被引:1,自引:0,他引:1
The thermal conductivity and heat capacity of liquid 1,1,1,2,3,3,3-hepta-fluoropropane (HFC-227ea) have been studied by a high-frequency thermal-wave method over the temperature range of 294 to 345 K at pressures up to 2.8 MPa. The purity of the samples used throughout the measurements is 99.99 mol%. The experimental uncertainties of the thermal conductivity and heat capacity measurements were estimated to be within ±1.5 and ±2%, respectively. The thermal conductivity of HFC-227ea in the liquid phase decreases as temperature increases, while the pressure has an opposite effect. 相似文献