全文获取类型
收费全文 | 36029篇 |
免费 | 2526篇 |
国内免费 | 1375篇 |
专业分类
电工技术 | 1518篇 |
技术理论 | 11篇 |
综合类 | 4170篇 |
化学工业 | 3560篇 |
金属工艺 | 875篇 |
机械仪表 | 1688篇 |
建筑科学 | 8009篇 |
矿业工程 | 2137篇 |
能源动力 | 1300篇 |
轻工业 | 1504篇 |
水利工程 | 1898篇 |
石油天然气 | 1380篇 |
武器工业 | 296篇 |
无线电 | 1802篇 |
一般工业技术 | 2427篇 |
冶金工业 | 1804篇 |
原子能技术 | 276篇 |
自动化技术 | 5275篇 |
出版年
2025年 | 338篇 |
2024年 | 744篇 |
2023年 | 695篇 |
2022年 | 1073篇 |
2021年 | 1132篇 |
2020年 | 1173篇 |
2019年 | 909篇 |
2018年 | 724篇 |
2017年 | 913篇 |
2016年 | 1025篇 |
2015年 | 1175篇 |
2014年 | 2133篇 |
2013年 | 1877篇 |
2012年 | 2174篇 |
2011年 | 2464篇 |
2010年 | 2098篇 |
2009年 | 2117篇 |
2008年 | 1934篇 |
2007年 | 2398篇 |
2006年 | 2209篇 |
2005年 | 1818篇 |
2004年 | 1556篇 |
2003年 | 1387篇 |
2002年 | 1234篇 |
2001年 | 948篇 |
2000年 | 779篇 |
1999年 | 641篇 |
1998年 | 456篇 |
1997年 | 371篇 |
1996年 | 279篇 |
1995年 | 212篇 |
1994年 | 187篇 |
1993年 | 125篇 |
1992年 | 117篇 |
1991年 | 87篇 |
1990年 | 68篇 |
1989年 | 42篇 |
1988年 | 54篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 27篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1966年 | 9篇 |
1961年 | 10篇 |
1959年 | 13篇 |
1956年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The authors highlight several possible ways in which the construction industry could lower present emissions of the greenhouse gas, carbon dioxide. It is an excellent discussion document and is recommended reading. 相似文献
2.
Aboubakar Sako Kenneth G. MacLeod Catherine M. O’Reilly 《Journal of Great Lakes research》2007,33(4):806-815
In this study, we measured growth trends in oxygen and carbon isotopic ratios in whole sagittal otoliths from three adult centropomid fish (Lates stappersii) from each of three sub-basins of Lake Tanganyika, East Africa. Sampling density was 20 to 50 samples per otolith. Both δ18O and δ13C values increase with age. The δ18O data suggest that otoliths were precipitated near the expected equilibrium with the ambient environment (ca. +3.5‰) and support a migration pattern from surface waters during larval stages to deeper waters (40 to 80 m) for mature fish. Relatively high δ18O values in the southern sub-basin are consistent with cooler temperatures in the region during seasonal upwelling. The δ13C increase from otolith core to edge is large (up to 4‰) and is interpreted as due to ontogenetic changes in diet and contributions from a decrease in the proportion of respired CO2 incorporated into otolith carbonate as metabolic rates of the fish dropped with maturity. The data seem to successfully reveal life strategy and migration patterns of L. stappersii, document regional differences in lake conditions, and provide a record of temperature within the water column during which the fish lived. Higher resolution studies and analyses of historical samples could be used to constrain modern and past growth patterns, and to reconstruct past temperature gradients and productivity patterns in the lake. 相似文献
3.
R. James Maguire Richard J. Tkacz David L. Sartor 《Journal of Great Lakes research》1985,11(3):320-327
Water and sediment samples from 29 locations in the Detroit and St. Clair rivers were analyzed for the highly toxic tri-n-butyltin (Bu3Sn+) species and for the less toxic di-n-butyltin (Bu2Sn2+) and n-butyltin (BuSn3+) species and inorganic tin. In general, locations sampled in the St. Clair River were less contaminated with butyltin species than those in the Detroit River. Inorganic tin and BuSn3+ were detected in over 90% of all subsurface water samples, while Bu2Sn2+ and Bu3Sn+ were detected in 45 and 28% of the same samples, respectively. The highest concentration ofBu3Sn+ in subsurface water, 5.9 × 10?10 mol Sn/L, was at the mouth of the Ecorse River, a tributary of the Detroit River. The three butyltin species and inorganic tin were also detected in 23–46% of all sediment samples. The highest concentrations of Bu3Sn+ in sediment were found close to the mouths of the River Rouge, another tributary of the Detroit River, and the Ecorse River, and were 6.2 × I0–7 and 1.7 × I0–7 mol Sn/kg dry weight, respectively, for the top 2 cm of sediment. 相似文献
4.
5.
介绍了我国紫菜工业在工艺改进、资源开发、综合利用和深度加工等方面的情况,提出了提高产率、降低物耗、增进效益和增加品种的途径。 相似文献
6.
A combinatorial process has been developed for the high throughput production and evaluation of surface coatings. The workflow designed for the production of arrays of liquid coatings involves the robotic transfer of aliquots of solutions of raw materials to an array of glass vials and mixing of the coatings using an unconventional magnetic stirring process. An investigation of the capability of the workflow to accurately and repeatedly prepare coating arrays was conducted as a function of solution viscosity and aliquot size. In addition, mixing capability was evaluated as a function of solution viscosity, total solution volume, and mechanism of stirring. Overall, the results of the study indicated that adequate accuracy and repeatability of the coating preparation process can be achieved as long as raw material solutions are designed such that viscosity is below about 250 cP and aliquot sizes are above about 75 μl. With regard to mixing capability, total solution volume was found to have a profound affect as did the stirring mechanism. 相似文献
8.
Concrete structures in main coal cleaning plants have been rebuilt and reinforced in the coal mines of the Shanghai Da-tun Energy Sources Co. Ltd., the first colliery of the Pingdingshan Coal Co. Ltd. and the Sanhejian mine of the Xuzhou Mining Group Co. Ltd. In these projects, the operating environment and reliability of concrete structures in the main plants of the three companies were investigated and the safety of the structures inspected. Qualitative and quantitative analyses were made on the spe-cial natural, technological and mechanical environments around the structures. On the basis of these analyses, we discuss the long-term, combined actions of the harsh natural (corrosive gases, liquids and solids) and mechanical environments on concrete structures and further investigated the damage and deteriorating mechanisms and curing techniques of concrete structures in the main coal cleaning plants. Our study can provide a theoretical basis for ensuring the reliability of concrete structures in main coal cleaning plants. 相似文献
9.
物联网作为未来的发展趋势之一,将在各个方面决定未来世界和人类社会的发展方向。而自智慧地球、感知中国等战略提出以来,世界各国也纷纷开展物联网领域的规划布局,将物联网建设上升到国家战略。物联网在全世界范围内掀起了继计算机和互联网之后的第三次信息革命浪潮。在这空前火爆的物联网宏观背景下,微观企业也不可避免的受到物联网影响。在这一背景下,通过分析物联网环境对企业内部控制环境的影响。本文认为,物联网环境下企业内部控制环境将更加信息化、虚拟化、智能化。 相似文献
10.
通过产业集聚的EG指数对中国各省份信息服务业的空间集聚程度进行研究,得出集聚程度比较显著.在此基础上,找到这一服务业的两个相关指标,利用产业集中度CRn判断出信息服务业主要集中于北京、广东等六个地区,然后对两指标数据进行无量纲化处理,加权求和得到新的综合指标,最后对这一新指标进行了系统聚类分析,得知这一产业主要集中在北京和广东两个地区. 相似文献