全文获取类型
收费全文 | 19833篇 |
免费 | 1796篇 |
国内免费 | 1241篇 |
专业分类
电工技术 | 1550篇 |
综合类 | 1744篇 |
化学工业 | 2330篇 |
金属工艺 | 869篇 |
机械仪表 | 1185篇 |
建筑科学 | 1115篇 |
矿业工程 | 516篇 |
能源动力 | 492篇 |
轻工业 | 1958篇 |
水利工程 | 407篇 |
石油天然气 | 396篇 |
武器工业 | 247篇 |
无线电 | 2049篇 |
一般工业技术 | 1736篇 |
冶金工业 | 3288篇 |
原子能技术 | 329篇 |
自动化技术 | 2659篇 |
出版年
2024年 | 86篇 |
2023年 | 262篇 |
2022年 | 562篇 |
2021年 | 732篇 |
2020年 | 531篇 |
2019年 | 386篇 |
2018年 | 407篇 |
2017年 | 468篇 |
2016年 | 411篇 |
2015年 | 679篇 |
2014年 | 847篇 |
2013年 | 1109篇 |
2012年 | 1333篇 |
2011年 | 1334篇 |
2010年 | 1316篇 |
2009年 | 1241篇 |
2008年 | 1284篇 |
2007年 | 1293篇 |
2006年 | 1065篇 |
2005年 | 961篇 |
2004年 | 692篇 |
2003年 | 497篇 |
2002年 | 464篇 |
2001年 | 420篇 |
2000年 | 377篇 |
1999年 | 223篇 |
1998年 | 828篇 |
1997年 | 453篇 |
1996年 | 352篇 |
1995年 | 232篇 |
1994年 | 215篇 |
1993年 | 223篇 |
1992年 | 102篇 |
1991年 | 75篇 |
1990年 | 93篇 |
1989年 | 84篇 |
1988年 | 81篇 |
1987年 | 67篇 |
1986年 | 61篇 |
1985年 | 79篇 |
1984年 | 62篇 |
1983年 | 75篇 |
1982年 | 62篇 |
1981年 | 55篇 |
1980年 | 67篇 |
1979年 | 49篇 |
1978年 | 47篇 |
1977年 | 98篇 |
1976年 | 175篇 |
1975年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The available surgical and non-surgical therapy options for treatment of gallstone disease are presented. Conventional cholecystectomy is regarded as standard therapy of symptomatic cholecystolithiasis. Other modes of therapy may be indicated under certain circumstances, depending on the results of imaging procedures. In this context conventional X-ray examination, oral and intravenous cholecystography, sonography, computed tomography, endoscopic retrograde cholangiography/cholecystography, and magnetic resonance imaging are discussed and their influence on therapeutic decisions is explained. 相似文献
42.
Stevenson D. Morow H. Blatecky A. Montgomery Davis P. Richardson P. Courter N.L.T. 《IEEE network》1994,8(6):32-38
The North Carolina Research and Education Network (NC-REN), formerly known as CONCERT, is an existing video and data network, owned and operated by MCNC. NC-REN's purpose has been to provide network-based support for collaboration in the research community within the state since 1985. The first major application planned for the North Carolina Information Highway (NCIH) is an interactive video distance learning system. A secondary application proposed is the use of Switched Multimegabit Data Service (SMDS) as a means of providing data communications services over NCIH. The user community currently supported by NC-REN has come to expect high levels of service, reliability, interoperability and performance for data and video communications. MCNC is committed to see that NC-REN users receive service that is equal to or better than what is currently provided by the existing network. The prospect of migrating NC-REN-provided services to NCIH-provided transport has raised challenging technical and unique service issues 相似文献
43.
攀钢转炉炼钢用碳化硅提温的试验研究 总被引:1,自引:1,他引:0
低品位碳化硅是转炉炼钢的有效提高温剂。工业性试验结果表明,碳化硅加入8.0kg/t钢水提温40.3-70.3℃(平均48.4℃);渣中TFe降低1.3%;加提温剂有利于转炉内造渣脱硫和碱少炉渣对耐火砖的侵蚀。文中还给出了攀钢转炉半钢冶炼铸用钢不水时加与不加碳化硅的tλ,[C]λ区域。 相似文献
44.
We report an unusual case of a 1 cm papillary renal cell carcinoma arising from the outer surface of the free wall of a radiographically simple renal cyst. Most malignancies arising from the wall of a renal cyst are present along the inner surface, usually adjacent to underlying renal parenchyma. While this is a rare occurrence, it does reinforce the need to explore even small solid renal masses. 相似文献
45.
SC Liang TR Schoeb JK Davis JW Simecka GH Cassell JR Lindsey 《Canadian Metallurgical Quarterly》1995,32(6):661-667
In several chronic diseases, lesions are more severe in LEW rats than in F344 rats. To determine whether or not acute viral diseases also are more severe in LEW rats than in F344 rats, we inoculated 6-7-week-old LEW and F344 rats with 10(7.2) cell culture infective units of sialodacryoadenitis virus or 10(4.7) infective units of Sendai virus. Twenty-four rats of each strain were given each virus. Lesions in nasal passages, tracheas, intrapulmonary airways, and pulmonary alveoli in 6 or 12 rats inoculated with each virus were assessed by scoring 5, 10, and 14 days after inoculation. Both viruses caused typical patchy necrotizing rhinitis, tracheitis, bronchitis, and bronchiolitis, with multifocal pneumonitis, in rats of both strains. Mean lesion indices for LEW rats given sialodacryoadenitis virus were significantly different from those for F344 rats for nasal passages on days 10 (0.999 vs. 0.680) and 14 (0.736 vs. 0.278), bronchi on day 5 (0.479 vs. 0.361), and alveoli on day 5 (0.677 vs. 0.275). Lesion indices for LEW rats given Sendai virus were significantly different from those for F344 rats for nasal passages on days 10 (1.000 vs. 0.611) and 14 (0.778 vs. 0.583); trachea on day 10 (0.625 vs. 0.028); bronchi on days 5 (0.476 vs. 0.331), 10 (0.123 vs. 0.013), and 14 (0.038 vs. 0); and alveoli on days 5 (0.413 vs. 0.114) and 10 (0.185 vs. 0.020). Thus, at the tested doses, both viruses caused more severe respiratory tract lesions in LEW rats than in F344 rats. 相似文献
46.
47.
地域通信网的干扰技术研究 总被引:1,自引:0,他引:1
本文在分析地域通信网结构及组成的基础上,研究了对地域通信网实施的节点破坏、末端信息封锁、局部阻塞瘫痪等对抗方法,并使用干扰地域通信网的程度、节点干扰率、末端节点封锁率和传递信息误差率等指标对干扰效果进行评估。 相似文献
48.
ECAP细化晶粒法的仿真与分析 总被引:7,自引:0,他引:7
ECAP(Equal Channel Angular Extrusion)方法,是实现材料纯剪切变形的有效方法。本文采用有限元(FEA)分析软件ANSYS对Al的挤压过程进行仿真与分析。分析结果表明:外切角Φ、圆角半径、试样与凹模之间的摩擦系数、凹模本身的特性(如弹性模量、泊松比等)等等,对材料的变形量都有不同程度的影响。 相似文献
49.
Davis R.F. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1991,79(5):702-712
Recent developments in III-V nitride thin-film materials for electronic and optoelectronic applications are reviewed. The problems that are limiting the development of these materials and devices made from them are discussed. The properties of cubic boron nitride, aluminum nitride, gallium nitride, AlN/GaN solid solutions and heterostructures, and indium nitride are discussed. It is pointed out that the lack of a suitable substrate, with the possible exception of SiC for AlN, is a problem of considerable magnitude. This is compounded by the presence of shallow donor bands in GaN and InN which are apparently caused by N vacancies. The question of whether these vacancies occur (if they do) as a result of intrinsic or extrinsic (as a result of deposition) nonstoichiometry has not been answered. However, the recent advances in the fabrication of p-type GaN and a p-n junction light emitting diode via the electron beam stimulation of the Mg dopant are very encouraging and may considerably advance the technology of this material. This would indicate that self-compensation effects, similar to those observed in ZnO and ZnSe, may not be present in the III-V nitrides, since cubic BN (cBN) AlN and now GaN have been reportedly doped both n- and p-type 相似文献
50.
A gait analysis system is described. It is designed for clinical use as well as research purposes. The system is simple to operate and can be used by non-computer specialist. The design philosophy is straightforward and allows for easy adaptation to other systems. Samples of the output are presented. 相似文献