首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   28560篇
  免费   2159篇
  国内免费   1016篇
电工技术   1477篇
技术理论   3篇
综合类   1793篇
化学工业   5001篇
金属工艺   1657篇
机械仪表   1668篇
建筑科学   2088篇
矿业工程   842篇
能源动力   741篇
轻工业   1630篇
水利工程   422篇
石油天然气   2034篇
武器工业   189篇
无线电   3435篇
一般工业技术   3553篇
冶金工业   1268篇
原子能技术   384篇
自动化技术   3550篇
  2025年   2篇
  2024年   598篇
  2023年   549篇
  2022年   814篇
  2021年   1190篇
  2020年   968篇
  2019年   825篇
  2018年   871篇
  2017年   951篇
  2016年   815篇
  2015年   1035篇
  2014年   1357篇
  2013年   1637篇
  2012年   1672篇
  2011年   1844篇
  2010年   1593篇
  2009年   1462篇
  2008年   1401篇
  2007年   1285篇
  2006年   1403篇
  2005年   1312篇
  2004年   882篇
  2003年   727篇
  2002年   697篇
  2001年   605篇
  2000年   695篇
  1999年   806篇
  1998年   638篇
  1997年   577篇
  1996年   551篇
  1995年   439篇
  1994年   365篇
  1993年   286篇
  1992年   205篇
  1991年   151篇
  1990年   121篇
  1989年   106篇
  1988年   91篇
  1987年   57篇
  1986年   44篇
  1985年   20篇
  1984年   14篇
  1983年   15篇
  1982年   27篇
  1981年   12篇
  1980年   8篇
  1979年   2篇
  1977年   6篇
  1976年   2篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
制备了国内外文献未见报道的70%稻瘟灵可湿性粉剂(WP),对该剂型的配方组成、加工工艺、贮存稳定性进行了研究,并对其各项性能进行了测试,确定了优惠配方。实验结果表明,该产品的各项指标均符合可湿性粉剂标准的要求,悬浮率在90%以上,润湿时间在1min以内,在40±2℃下贮存60天后的分解率小于5%。  相似文献   
93.
Tomographic perfusion imaging is a significant imaging modality for stroke diagnosis.However,the low rotational speed of the C-arm(6-8 s per circle)is a chal-le...  相似文献   
94.
Gonadotropin-inhibitory hormone (GnIH) is a reproductive inhibitor and an endogenous orexigenic neuropeptide that may be involved in energy homeostasis and reproduction. However, whether GnIH is a molecular signal link of metabolism and the reproductive system, and thus, regulates reproductive activity as a function of the energy state, is still unknown. In the present study, we investigated the involvement of GnIH in glycolipid metabolism and reproduction in vivo, and in the coupling between these two processes in the testis level. Our results showed that chronic intraperitoneal injection of GnIH into male mice not only increased food intake and altered meal microstructure but also significantly elevated body mass due to the increased mass of liver and epididymal white adipose tissue (eWAT), despite the loss of testicular weight. Furthermore, chronic intraperitoneal administration of GnIH to male mice resulted in obesity-related glycolipid metabolic derangements, showing hyperlipidemia, hyperglycemia, glucose intolerance, and insulin resistance through changes in the expression of glucose and lipid metabolism-related genes in the pancreas and eWAT, respectively. Interestingly, the expression of GnIH and GPR147 was markedly increased in the testis of mice under conditions of energy imbalance, such as fasting, acute hypoglycemia, and hyperglycemia. In addition, chronic GnIH injection markedly inhibited glucose and lipid metabolism of mice testis while significantly decreasing testosterone synthesis and sperm quality, inducing hypogonadism. These observations indicated that orexigenic GnIH triggers hyperphagia-induced obesity-related metabolic derangements and hypogonadism in male mice, suggesting that GnIH is an emerging candidate for coupling metabolism and fertility by involvement in obesity and metabolic disorder-induced reproductive dysfunction of the testes.  相似文献   
95.
根据作者提出的血流动力学参数计算公式,研究了不同年令和不同血压下血流动力学参数的变化从中得出外周阻力的增高是高血压最主要的危险因素。并经理论分析和临床实测证实了这个结论。  相似文献   
96.
In order to reduce the computation of complex problems, a new surrogate-assisted estimation of distribution algorithm with Gaussian process was proposed. Coevolution was used in dual populations which evolved in parallel. The search space was projected into multiple subspaces and searched by sub-populations. Also, the whole space was exploited by the other population which exchanges information with the sub-populations. In order to make the evolutionary course efficient, multivariate Gaussian model and Gaussian mixture model were used in both populations separately to estimate the distribution of individuals and reproduce new generations. For the surrogate model, Gaussian process was combined with the algorithm which predicted variance of the predictions. The results on six benchmark functions show that the new algorithm performs better than other surrogate-model based algorithms and the computation complexity is only 10% of the original estimation of distribution algorithm.  相似文献   
97.
本工作测定了不同温度下硫酸高铈与对二甲苯反应的速率常数及表观活化能Ea= 111.5kJ·m ol- 1。在动力学测定的的基础上确定了此反应的速率方程为d[PTAL]/dt= k[PX][Ce(IV)]  相似文献   
98.
用姐妹染色单体交换(SCE)作为指标,研究了~(60)Coγ射线辐照及NADH-PMS(吩嗪硫酸甲酯)系统中产生的超氧阴离子自由基(0_2~(·-))对胎儿脐血淋巴细胞染色体的损伤作用,及活性氧清除剂SOD和甘露醇的保护作用。结果显示γ射线及0_2~(·-)都能诱发细胞SCE频率显著升高,且存在一定的剂量-效应关系。SOD及甘露醇对0_2~(·-)诱发的损伤有明显的保护作用。  相似文献   
99.
Nanocomposite Cr C/hydrogenated amorphous carbon(nc-CrC/a-C:H) coatings were deposited by a hybrid beams system comprised of a hollow cathode ion source and a cathodic arc ion-plating unit with varying H_2 flow rates. The influences of H_2 flow rates on the morphologies, microstructures, and properties of the coatings were systematically studied. The morphologies and microstructures of the coatings were characterized by SEM, AFM, XPS, Raman spectroscopy, GIXRD, and HRTEM. The mechanical and tribological properties were measured by a nano-indenter, scratch tester, and ball-ondisk tribometer. The wear tracks were evaluated using 3D profilometer, optical microscope, and EDS analysis. It has been found that a moderate H_2 flow rate can effectively smooth the surface, enlarge the fraction of a sp~3 bond, and improve the properties. The coating exhibits the highest hardness and elastic modulus at the H_2 flow rate of 40 sccm. A superior combination of adhesion strength,friction coefficient, and wear resistance can be achieved at the H_2 flow rate of 80 sccm.  相似文献   
100.
仿生眼的研究现状与发展趋势   总被引:10,自引:2,他引:10  
邹海荣  龚振邦  罗均 《机器人》2005,27(5):469-474
首先,在分析人眼眼球运动的特点和形式的基础上,详细介绍了国内外仿生眼研究对扫视性眼球运动、平滑性眼球运动、异向眼球运动、前庭动眼反射、视动反射等的模仿,最后总结了仿生眼研究的特点和发展趋势.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号