全文获取类型
收费全文 | 266943篇 |
免费 | 3397篇 |
国内免费 | 838篇 |
专业分类
电工技术 | 5202篇 |
综合类 | 336篇 |
化学工业 | 38444篇 |
金属工艺 | 10336篇 |
机械仪表 | 8675篇 |
建筑科学 | 6364篇 |
矿业工程 | 1123篇 |
能源动力 | 6538篇 |
轻工业 | 23357篇 |
水利工程 | 2658篇 |
石油天然气 | 3924篇 |
武器工业 | 68篇 |
无线电 | 35145篇 |
一般工业技术 | 51148篇 |
冶金工业 | 48257篇 |
原子能技术 | 5466篇 |
自动化技术 | 24137篇 |
出版年
2021年 | 2143篇 |
2019年 | 2126篇 |
2018年 | 3599篇 |
2017年 | 3648篇 |
2016年 | 3851篇 |
2015年 | 2444篇 |
2014年 | 4234篇 |
2013年 | 11683篇 |
2012年 | 6892篇 |
2011年 | 9271篇 |
2010年 | 7267篇 |
2009年 | 8101篇 |
2008年 | 9022篇 |
2007年 | 8943篇 |
2006年 | 8097篇 |
2005年 | 7416篇 |
2004年 | 7123篇 |
2003年 | 6916篇 |
2002年 | 6581篇 |
2001年 | 6611篇 |
2000年 | 6288篇 |
1999年 | 6395篇 |
1998年 | 14434篇 |
1997年 | 10433篇 |
1996年 | 8261篇 |
1995年 | 6538篇 |
1994年 | 5839篇 |
1993年 | 5679篇 |
1992年 | 4653篇 |
1991年 | 4273篇 |
1990年 | 4153篇 |
1989年 | 3861篇 |
1988年 | 3703篇 |
1987年 | 3261篇 |
1986年 | 3128篇 |
1985年 | 3693篇 |
1984年 | 3440篇 |
1983年 | 3096篇 |
1982年 | 2905篇 |
1981年 | 2993篇 |
1980年 | 2801篇 |
1979年 | 2690篇 |
1978年 | 2536篇 |
1977年 | 2993篇 |
1976年 | 3590篇 |
1975年 | 2349篇 |
1974年 | 2333篇 |
1973年 | 2340篇 |
1972年 | 1865篇 |
1971年 | 1752篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Using time-of-flight technique between 100 K and 700 K a nearly constant IC modulation parameter is found. It depends only weakly on crystal composition. The intensity of the first-and second-order satellites decreases with temperature and at 700 K it is nearly disappeared. These facts are discussed with a view to the anti-phase domain model. 相似文献
994.
The concepts of categorical and dimensional assessment approaches and their specific advantages--and disadvantages are described. A combination of both concepts within the framework of Multiple Assessment of Psychiatric Disturbances is proposed. This includes the different levels of behavioural and emotional disturbances, different assessment methods, the situational specificity of behavioural and emotional disturbances and individually tailored and treatment related assessment procedures. Thereby two phases are distinguished. In the first phase basic procedures of the Multiple Assessment of Psychiatric Disturbances are accomplished, which cover a broad spectrum of behavioural and emotional problems. In the second phase a differentiated picture of the-specific disturbance is assessed by using symptom-specific instruments of the Multiple Assessment of Psychiatric Disturbances. In a case report the diagnostic procedure is explained. 相似文献
995.
D. S. Schnur Nicholas Zabaras 《International journal for numerical methods in engineering》1992,33(10):2039-2057
A numerical procedure which integrates optimization, finite element analysis and automatic finite element mesh generation is developed for solving a two-dimensional inverse/parameter estimation problem in solid mechanics. The problem consists of determining the location and size of a circular inclusion in a finite matrix and the elastic material properties of the inclusion and the matrix. Traction and displacement boundary conditions sufficient for solving a direct problem are applied to the boundary of the domain. In addition, displacements are measured at discrete points on the part of the boundary where the tractions are prescribed. The inverse problem is solved using a modified Levenberg-Marquardt method to match the measured displacements to a finite element model solution which depends on the unknown parameters. Numerical experiments are presented to show how different factors in the problem and the solution procedure influence the accuracy of the estimated parameters. 相似文献
996.
The paper describes the development of a software design aid for use at the conceptual stage of engineering design. It is intended for use in the design of mechatronic products but has wider potential uses. Early approaches were based on function structures and tables of options and the system that evolved allows the assembly of schemes linked by matching their input and output ports. A database of components is provided which can be accessed via different indexes and the designer can easily create and compare alternative schemes at the concept stage.A bond graph approach is used to define the interconnections between components. This allows correct port matching but also provides for future development such as constraint propagation through the design and links to simulation tools. 相似文献
997.
In crack detection and sizing by the alternating current field measurement technique, U-shaped wires or coils excited by a high-frequency AC current source can be used to induce the surface field in the workpiece. The authors present a modeling technique for the interaction of a fatigue crack in a ferromagnetic metal with the surface field resulting from an inducer with two U-shaped wires. This work is an extension of a previous modeling technique to have developed for infinitely long (one-dimensional) cracks. In the present technique, the boundary of the fatigue crack is approximated by a circular arc, leading to a formulation for an efficient computation of the field-flaw interaction. Various numerical and experimental results supporting the modeling and illustrating the behavior of the magnetic field and electric potential at the metal surface around circular-arc cracks are presented 相似文献
998.
999.
The hygienic adequacy of a commercial process for the collection and cooling of beef offals was assessed by a temperature function integration technique. The diverse operations for collection of offals were inspected. The rates of product movement through those operations, and the temperatures of products at the time of their being packed, were determined. From that information, four of the nine product types were selected for examination of their temperature histories during the assembly and cooling of the cartoned products. The products selected encompassed product at near-body and near-air-ambient temperatures at the time of packaging, product in the largest and smallest cartons used in the process, and product with relatively short and long residence times in an unchilled carton stack assembly area. Twenty-one temperature histories were collected for each of the products, and the possible proliferation of an indicator organism, Escherichia coli, calculated for each temperature history. The results were assessed against a temperature function integration criterion derived from studies of beef carcass and cartoned meat cooling processes. Products packaged at near-ambient temperature readily met with the criterion, but products packed at near-body temperatures did not comply. The latter non-compliance was extreme for product packaged in large cartons. However, the principal cause of non-compliance was identified as highly variable cooling conditions in the carton freezing facility. A brief survey of air speeds and temperatures within that facility indicated means by which product cooling could be better controlled. 相似文献
1000.
D. A. Kononov 《Automation and Remote Control》2002,63(9):1496-1505
Theoretical results of the development of the principles of scenario calculus are presented, which are obtained in the framework of the design of an emergency control system (ECS). Relying on the suggested system concept of the formation of a scenario system, consideration is given to the principles of the construction of operations in scenario spaces, which account for specific features of the scenario analysis and the process of the decision-making in the ECS. Principal problems of the development of scenario calculus on the basis of a system approach are treated, the classification of operations on scenarios is given, and a number of operations on elements of the basic metacollection are formalized. 相似文献