全文获取类型
收费全文 | 21356篇 |
免费 | 1793篇 |
国内免费 | 898篇 |
专业分类
电工技术 | 1179篇 |
技术理论 | 2篇 |
综合类 | 1367篇 |
化学工业 | 3610篇 |
金属工艺 | 1169篇 |
机械仪表 | 1367篇 |
建筑科学 | 1938篇 |
矿业工程 | 747篇 |
能源动力 | 578篇 |
轻工业 | 1206篇 |
水利工程 | 365篇 |
石油天然气 | 1494篇 |
武器工业 | 121篇 |
无线电 | 2210篇 |
一般工业技术 | 2580篇 |
冶金工业 | 1051篇 |
原子能技术 | 232篇 |
自动化技术 | 2831篇 |
出版年
2024年 | 81篇 |
2023年 | 405篇 |
2022年 | 583篇 |
2021年 | 884篇 |
2020年 | 724篇 |
2019年 | 606篇 |
2018年 | 659篇 |
2017年 | 736篇 |
2016年 | 619篇 |
2015年 | 818篇 |
2014年 | 1113篇 |
2013年 | 1219篇 |
2012年 | 1403篇 |
2011年 | 1439篇 |
2010年 | 1308篇 |
2009年 | 1170篇 |
2008年 | 1164篇 |
2007年 | 1121篇 |
2006年 | 1175篇 |
2005年 | 1106篇 |
2004年 | 656篇 |
2003年 | 573篇 |
2002年 | 510篇 |
2001年 | 478篇 |
2000年 | 446篇 |
1999年 | 588篇 |
1998年 | 460篇 |
1997年 | 394篇 |
1996年 | 357篇 |
1995年 | 313篇 |
1994年 | 242篇 |
1993年 | 142篇 |
1992年 | 128篇 |
1991年 | 113篇 |
1990年 | 87篇 |
1989年 | 69篇 |
1988年 | 53篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
本文用大视场光学显微镜、电子探针观察和分析了掺钛蓝宝石激光晶体中夹杂物的形状、尺寸大小及元素组成,并提出消除和减少这些夹杂物的方法. 相似文献
53.
聚苯醚磺酸锂/共聚醚复合物的离子导电性研究 总被引:1,自引:0,他引:1
合成了3种不同磺化度的聚苯醚磺酸锂(SPPOLi)与P(MEO16-AM)/SPPOLi复合物。研究了复合物的离子导电性与磺化度,组成比及增塑剂含量的关系。含40%(mass)增塑剂的复合物具有单离子导电特征,锂离子迁移数高达0.97,室温电导率达2×10-5S/cm。 相似文献
54.
Role of macrophage overactivation in the development of acute pancreatic injury in rats 总被引:1,自引:0,他引:1
PURPOSE: To report quantitative changes in the anterior chamber configuration after small-incision cataract surgery with implantation of a posterior chamber intraocular lens by means of ultrasound biomicroscopy. METHODS: We examined the anterior chamber configuration of 20 eyes of 20 patients before and 3 months after small-incision cataract surgery (phacoemulsification and aspiration plus foldable intraocular lens implantation through a 3.0- to 4.0-mm self-sealing wound) by means of ultrasound biomicroscopy. The following variables were measured: the anterior chamber depth at the center of the cornea, the angle-opening distance 250 microns from the scleral spur (AOD250), the angle-opening distance 500 microns from the scleral spur (AOD500), and the trabecular-iris angle. RESULTS: The anterior chamber depth at the center of the cornea, AOD250, AOD500, and trabecular-iris angle increased significantly after surgery. The preoperative anterior chamber depth at the center of the cornea and trabecular-iris angle were negatively correlated with the differences between the postoperative and preoperative values (P < .01). The preoperative values of all variables examined were negatively correlated with the ratios of the postoperative value to the preoperative value (P < .002). CONCLUSIONS: The present results showed that small-incision cataract surgery significantly deepened the anterior chamber and widened its angle. The more shallow the preoperative anterior chamber was, the greater the postoperative change of the chamber was; and the more narrow the preoperative angle was, the greater the postoperative change of the angle was. 相似文献
55.
In a previous study we have demonstrated that endogenous neurotrophin 3 (NT3) is required for the survival of most sympathetic neurones in postnatal rats. However, the mechanisms underlying the action of NT3 on sympathetic neurones is not known. Neither is it understood whether NT3 is retrogradely transported from peripheral tissues or acts locally in an autocrine fashion. In the present study, NT3-mRNA was quantified in sympathetic effector tissues and NT3 protein was localized in intact and lesioned sympathetic nerves in rats. NT3-mRNA is expressed and developmentally regulated in many effector tissues including mesenteric arteries, salivary gland, heart and kidney but hardly detectable in the superior cervical ganglia of adult animals. The majority of sympathetic neurones express immunoreactivity for TrkA and TrkC in both neonatal and adult rats. Sympathetic somata are normally immunoreactive for NT3, but the immunoreactivity is abolished by systemic administration of NT3 antibodies or axotomy of postganglionic neurones, suggesting an accumulation of NT3 from extraneuronal sources. Furthermore, the detection of NT3-immunoreactivity in the internal carotid nerve as early as 3 h following a compression and only on the distal side indicates endogenous NT3 is retrogradely transported by sympathetic neurones. These studies provide evidence indicating that NT3, like nerve growth factor, is an effector tissue-derived neurotrophic factor for sympathetic neurones both during development and in the adult animal. Thus, we have provided a clear example that one type of neurone derives, through a retrograde transport mechanism, two neurotrophic factors simultaneously from its peripheral effector tissues. 相似文献
56.
PVDF中空纤维滤膜的形态结构 总被引:3,自引:0,他引:3
用L-S相转换法制备了聚偏氟乙烯(PVDF)中空纤维不对称滤膜。铸膜液由聚合物、溶剂和添加剂组成。用电子显微镜(SEM)考察了聚合物浓度、添加剂用量及种类对膜形态结构的影响。实验结果表明,聚合物浓度对膜形态结构有显著影响,当铸膜液中聚合物浓度较低时,无论用什么种类添加剂,都能形成大、且多的孔,但孔的形状随添加剂不同而异。当恒定聚合物浓度时,添加剂的用量对膜形态结构有很大的影响,但孔的大小及多少与添加剂含量的多少不成正比。 相似文献
57.
58.
59.
60.