全文获取类型
收费全文 | 9787篇 |
免费 | 122篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 98篇 |
综合类 | 2篇 |
化学工业 | 1016篇 |
金属工艺 | 103篇 |
机械仪表 | 300篇 |
建筑科学 | 217篇 |
矿业工程 | 28篇 |
能源动力 | 129篇 |
轻工业 | 872篇 |
水利工程 | 107篇 |
石油天然气 | 15篇 |
无线电 | 863篇 |
一般工业技术 | 1022篇 |
冶金工业 | 4291篇 |
原子能技术 | 108篇 |
自动化技术 | 748篇 |
出版年
2021年 | 69篇 |
2020年 | 51篇 |
2019年 | 61篇 |
2018年 | 60篇 |
2017年 | 83篇 |
2016年 | 66篇 |
2015年 | 47篇 |
2014年 | 104篇 |
2013年 | 315篇 |
2012年 | 161篇 |
2011年 | 239篇 |
2010年 | 211篇 |
2009年 | 231篇 |
2008年 | 260篇 |
2007年 | 241篇 |
2006年 | 246篇 |
2005年 | 218篇 |
2004年 | 178篇 |
2003年 | 202篇 |
2002年 | 200篇 |
2001年 | 162篇 |
2000年 | 160篇 |
1999年 | 241篇 |
1998年 | 1089篇 |
1997年 | 679篇 |
1996年 | 555篇 |
1995年 | 355篇 |
1994年 | 309篇 |
1993年 | 322篇 |
1992年 | 125篇 |
1991年 | 144篇 |
1990年 | 158篇 |
1989年 | 154篇 |
1988年 | 156篇 |
1987年 | 154篇 |
1986年 | 126篇 |
1985年 | 135篇 |
1984年 | 94篇 |
1983年 | 103篇 |
1982年 | 72篇 |
1981年 | 92篇 |
1980年 | 79篇 |
1979年 | 79篇 |
1978年 | 72篇 |
1977年 | 142篇 |
1976年 | 264篇 |
1975年 | 77篇 |
1974年 | 71篇 |
1973年 | 64篇 |
1972年 | 54篇 |
排序方式: 共有9919条查询结果,搜索用时 46 毫秒
1.
The 2011 AASHTO Roadside Design Guide (RDG) contains perhaps the most widely used procedure for choosing an appropriate length of need (LON) for roadside barriers. However, this procedure has several limitations. The procedure uses a highly simplified model of vehicle departure, and the procedure does not allow designers to specify an explicit level of protection. A new procedure for choosing LON that addresses these limitations is presented in this paper. This new procedure is based on recent, real-world road departure trajectories and uses this departure data in a more realistic way. The new procedure also allows LON to be specified for a precisely known level of protection – a level which can be based on number of crashes, injury outcomes or even estimated crash cost – while still remaining straightforward and quick to use like the 2011 RDG procedure. 相似文献
2.
Dr. Hui Qiu Richard Caldwell Dr. Lesley Liu-Bujalski Dr. Andreas Goutopoulos Reinaldo Jones Justin Potnick Dr. Brian Sherer Dr. Andrew Bender Dr. Roland Grenningloh Dr. Daigen Xu Dr. Anna Gardberg Dr. Igor Mochalkin Dr. Theresa Johnson Dr. Ariele Viacava Follis Jared Head Dr. Federica Morandi 《ChemMedChem》2019,14(2):217-223
Bruton's tyrosine kinase (Btk) is an attractive target for the treatment of a wide array of B-cell malignancies and autoimmune diseases. Small-molecule covalent irreversible Btk inhibitors targeting Cys481 have been developed for the treatment of such diseases. In clinical trials, probe molecules are required in occupancy studies to measure the level of engagement of the protein by these covalent irreversible inhibitors. The result of this pharmacodynamic (PD) activity provides guidance for appropriate dosage selection to optimize inhibition of the drug target and correlation of target inhibition with disease treatment efficacy. This information is crucial for successful evaluation of drug candidates in clinical trials. Based on the pyridine carboxamide scaffold of a novel solvent-accessible pocket (SAP) series of covalent irreversible Btk inhibitors, we successfully developed a potent and selective affinity-based biotinylated probe 12 (2-[(4-{4-[5-(1-{5-[(3aS,4S,6aR)-2-oxo-hexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanamido}-3,6,9,12-tetraoxapentadecan-15-amido)pentanoyl]piperazine-1-carbonyl}phenyl)amino]-6-[1-(prop-2-enoyl)piperidin-4-yl]pyridine-3-carboxamide). Compound 12 has been used in Btk occupancy assays for preclinical studies to determine the therapeutic efficacy of Btk inhibition in two mouse lupus models driven by TLR7 activation and type I interferon. 相似文献
3.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
4.
Pressurized fabric tubes, pressure-stabilized beams (known as air beams) and air-inflated structures are considered to be valuable technologies for lightweight, rapidly deployable structures. Design optimization of an inflated structure depends on a thorough understanding of woven fabric mechanics. In this paper the bending response of woven pressure-stabilized beams have been experimentally tested and analytically investigated. Additionally, the micromechanical effects of interacting tows have been studied through finite element models containing contact surfaces and nonlinear slip/stick conditions. Local unit cell models consisting of pairs of woven tows were created to characterize the effective constitutive relations. The material properties from the unit cell models were then used for the global continuum model subjected to 4-point flexure. An experimental set-up was designed and manufactured for testing of Vectran and PEN air beams. The air beam mid-span deflections were measured as functions of inflation pressure and bending load. Plots of the elastic and shear moduli with respect to the pressure and coefficient of friction have been generated. It was determined that the effective elastic and shear moduli were functions of inflation pressure, the material used and the geometry of the weave. It was shown that pneumatic or pressurized tube structures differ fundamentally from conventional metal structures. 相似文献
5.
Examination of the wreckage of a light aircraft revealed that approximately 20 cm was missing from one tip of the aluminum
alloy propeller. Fractographic and metallographic examination of the remaining portion of the propeller revealed extensive
grain-boundary separation in the vicinity of the fracture, and grain edges and corners rounded by corrosion on the fracture
surface. Energy dispersive X-ray analysis (EDXA) revealed fluorine on, and in the vicinity of, the fracture surface. In the
ensuing litigation, it was asserted that the crash occurred because the propeller fractured in flight as the result of intergranular
attack caused by the use of a fluorine-bearing cleaner. 相似文献
6.
Some specific characteristics of the aging of the Brazilian population in different areas, states and communities all over the country, have shown significant variations. Historical series of demographic and health indicators for the population in their sixties and over in Brazil, state of S. Paulo and in the municipal district of Araraquara are listed as follows: level of education and urban population growth rate, income distribution, mortality rates and main causes of death. In 1991 the aged constituted were 7.8% of the Brazilian population and 9.7% in Araraquara community. The elderly population (of 70 years of aged and above) as a proportion of the whole, has increased and already stands for 40%. The same trend holds good for both the proportion of aged within the urban population and their level of education which increased to 90% in 1991. The main causes of death are chronic degenerative diseases which have replaced the infectious illness: first, the diseases of the circulatory system (which account for more than 40% of all deaths) and the neoplasms (which let to 15% of the deaths). On the basis of these health and demographic data relating to people of 60 years of age and over, this study suggests some procedures for the improvement of the quality of the assistance given to the target population: a) the assistance give to the aged should be improved by providing gerontological training for general physicians and nurses, both of public and private clinics; b) the already existing educational activities for the aged, for health workers and for teachers of secondary education should be further developed; c) the number of day-hospitals should be increased for the purpose of avoiding unnecessary confinement so as maintain the low rate of institutionalization in homes for the elderly (0.7% in Araraquara). It is reported that at least 35% of the aged population in this area is entitled to private health assistance, which brings out the importance of including such services in the local health programs for this group. 相似文献
7.
Dyspnea may be easily appreciated during exercise with dyspneic scales, but methodological standardisation still needs to be specified. Authors review the basic physiological mechanism relating dyspnea to indices obtained during a stress test. They propose to use the dyspnea/VE relationship. With the concept of dyspneic threshold (close to the ventilatory threshold) and the ramp that both could be modified (for instance by rehabilitation programmes including exercise training). Interpretation of dyspnea during an exercise test obviously needs to be integrated with other parameters studied during exercise. 相似文献
8.
To meet the criteria of role accountability, nursing competence and ongoing staff development, an improved peer-evaluation system was designed to continuously monitor these new roles. This peer-evaluation process converts evaluation input into data, giving staff a visual picture of how their performance compares within their peer group. This peer-evaluation process was designed as a tool to assist in staff growth and development, not as a punitive system. 相似文献
9.
10.