全文获取类型
收费全文 | 1121篇 |
免费 | 13篇 |
专业分类
电工技术 | 16篇 |
化学工业 | 124篇 |
金属工艺 | 35篇 |
机械仪表 | 22篇 |
建筑科学 | 24篇 |
矿业工程 | 9篇 |
能源动力 | 23篇 |
轻工业 | 46篇 |
水利工程 | 14篇 |
石油天然气 | 3篇 |
无线电 | 81篇 |
一般工业技术 | 120篇 |
冶金工业 | 520篇 |
原子能技术 | 17篇 |
自动化技术 | 80篇 |
出版年
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 32篇 |
2012年 | 21篇 |
2011年 | 24篇 |
2010年 | 23篇 |
2009年 | 24篇 |
2008年 | 25篇 |
2007年 | 28篇 |
2006年 | 18篇 |
2005年 | 32篇 |
2004年 | 17篇 |
2003年 | 11篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 19篇 |
1998年 | 101篇 |
1997年 | 68篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 32篇 |
1993年 | 32篇 |
1992年 | 24篇 |
1991年 | 11篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 24篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1976年 | 39篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 11篇 |
排序方式: 共有1134条查询结果,搜索用时 15 毫秒
91.
Kent D. Carlson Shouzhu Qu Christoph Beckermann 《Metallurgical and Materials Transactions B》2005,36(6):843-856
Feeding of the nickel-based alloys CZ-100, M-35-1, and CW-12MW, as well as of the austenitic stainless steel CN-7M, is investigated,
using a combination of casting experiments and simulation. Casting trials are performed at five foundries, to produce a total
of 55 plates of varying lengths and radiographic soundness levels. In order to develop the property databases necessary to
simulate the casting of these alloys, temperature data are recorded for each alloy during the casting trials. These measured
data are used in conjunction with material property simulation to develop the necessary property data for each alloy, including
the solidification path. These property data are used to simulate the casting trials. Good agreement between the simulation
results and the radiographic testing (RT) results for the castings is obtained. A quantitative relation between the measured
ASTM X-ray levels and the predicted minimum Niyama criterion value is established for all but the CZ-100 alloy, which does
not appear to suffer from shrinkage defects. A large number of additional simulations are used to develop general feeding
distance (FD) rules. The new rules are shown to provide accurate FDs for the casting trial plates. The FDs of the high-nickel
alloys (except CZ-100) are found to be at least 25 pct shorter than those for typical low-alloy steels. 相似文献
92.
Specimens of formalin-fixed, paraffin-embedded non-small-cell lung carcinomas (NSCLCs; n = 187) were analysed immunohistochemically for expression of cyclin A. The analysis was intended to determine whether cyclin A has additional prognostic value for predicting patients' survival and drug response. Of the 187 NSCLCs, 141 cases (75%) showed expression of cyclin A. Patients with cyclin A-positive carcinomas had significantly shorter median survival times than patients with cyclin A-negative carcinomas (79 vs 129 weeks, P = 0.045). Similar results were obtained with more homogeneous groups of patients: patients with only T3 tumours, patients with epidermoid carcinomas and patients with lymph node involvement. The clinical parameters (age, stage, histology, extent of tumour size, lymph node involvement) had no influence on expression of cyclin A. A direct correlation between cyclin A and the proportion of S-phase cells (P = 0.08) and an inverse relationship between cyclin A and the proportion of G0/G1-phase cells (P = 0.04) were found. Furthermore, a significant correlation between the expression of cyclin A and the response of NSCLC to doxorubicin in vitro was detected (P = 0.026). 相似文献
93.
Examines the content of school psychology books published between 1970 and 1985. The process of historical review reveals recent trends that have their genesis in both internal professional developments and external social, political, and legal pressures on the field. Perspectives on the current status and potential future of the profession of school psychology, as derived from the literature, are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
94.
C. Richard Carlson 《Information Systems Management》1990,7(4):36-41
In recent years, the use of remote or home computer terminals has made a significant impact on the IS department and its clients ( users). In response to IS and user needs, including a desire to decentralize the workplace (i.e., IS department) and a belief that home terminals would have a positive effect on productivity and employee morale, IBM decided to implement several such home terminals as a means of determining their effectiveness. This article describes an experiment that measured the effects of implementing a home terminal program. 相似文献
95.
Amantea R. Carlson N.W. Palfrey S.L. Evans G.A. Hammer J.M. Lurie M. 《Quantum Electronics, IEEE Journal of》1990,26(6):1023-1038
The modes and threshold gain characteristics of two-dimensional grating-surface-emitting diode laser arrays that are evanescently coupled in the lateral direction and mutually injection coupled in the longitudinal direction are analyzed. The ratio of the grating transmissivity to reflectivity is found to be a critical parameter in obtaining uniform power distribution inside the array. Good qualitative agreement between the theory and experimentally measured near-field patterns and threshold currents is obtained 相似文献
96.
LD Rodger GP Carlson ME Moran TB Yarbrough JR Pascoe JA Reynolds 《Canadian Metallurgical Quarterly》1995,9(4):280-282
A 3-year-old Thoroughbred colt was presented for evaluation of azotemia and anorexia. Physical examination revealed a ureterolith in the left ureter, approximately 10 cm from the bladder, which was thought to obstruct urine flow by approximately 90% when viewed cystoscopically. Ultrasonographic examination of both kidneys revealed indistinct corticomedullary junctions, and the right kidney was more hyperechoic. A percutaneous biopsy of the right kidney revealed chronic interstitial nephritis with marked interstitial medullary fibrosis. Medical therapy consisting of IV fluids, sodium chloride PO, and ammonium chloride PO was initiated. Ureteroscopic electrohydraulic lithotripsy via a perineal urethrostomy was used to successfully remove the stone. Klebsiella oxytoca, which responded to oral enrofloxacin therapy, was cultured from the urine after surgery. Azotemia resolved and the horse resumed training. 相似文献
97.
Opt-out policies allow large customers to withdraw from participation in utility sector efficiency programs. Our analysis shows these policies impose high costs, including increased utility system investments due to higher demand, increased air pollution within the state and surrounding regions, higher health costs because of the increased air pollution, and lost bill savings opportunities for large customers, leading to lost economic growth. We examine the consequences using Ohio as an example. 相似文献
98.
99.
On the survivability and pyrosynthesis of PAH during combustion of pulverized coal and tire crumb 总被引:2,自引:0,他引:2
Ajay Atal Yiannis A. Levendis Joel Carlson Yuriy Dunayevskiy Paul Vouros 《Combustion and Flame》1997,110(4):462-478
Results are presented on the emissions of semivolatile polycyclic aromatic hydrocarbons (PAH) from the combustion of a pulverized bituminous coal and ground waste automobile tires. Streams of fuel particles were injected at steady-state steady-flow conditions, and burned inside an isothermal drop-tube furnace, in air, at a gas temperature and gas residence time of 1150°C and 0.75 s, respectively. Combustion occurred under either very fuel-lean conditions (bulk equivalence ratio, φ < 0.5) or substantially fuel-rich conditions (φ = 1.6–1.9). Emissions from fuel pyrolysis, in the absence of oxygen, were also examined. The survivability of the fuel-PAHs during combustion/pyrolysis was assessed by examining the reactants (fuels) and the products of their oxidation/pyrolysis. The PAH species in the effluent of combustion were: 1) qualitatively compared with indigenous PAH constituents of the input fuels, and 2) quantitatively contrasted with known amounts of deuterium-labeled PAH standards, which were absorbed on the input fuels. No PAHs were detected in the effluent of combustion of either fuel under sufficiently fuel-lean conditions, e.g., φ < 0.5. This indicated that the PAH constituents of the input fuels, either indigenous or adsorbed, as well as those formed by pyrosynthesis in either the diffusion volatile flames or during the heterogeneous oxidation of the chars were destroyed. Significant amounts of PAHs were detected in the effluent of the combustion of both fuels under sufficiently fuel-rich conditions, e.g., φ > 1.6 and, especially, under pyrolytic conditions in N2. These PAHs were mostly attributed to pyrosynthesis since none of the deuterated PAHs, adsorbed on the fuels, survived the combustion process. Small amounts of the labeled compounds, however, survived under purely pyrolytic conditions. These results were confirmed with separate experiments, where deuterium-labeled PAH standards were adsorbed on highly porous calcium/magnesium oxide or mullite particles. Again, small amounts of some PAHs survived in high-temperature pyrolytic conditions, but none in oxidative environments. These observations suggest that pyrosynthesis is the major contributing mechanism to the PAH emissions from the combustion of these fuels. Survivability of parent PAHs may be a minor mechanism at very high equivalence ratios.
Finally, both fuels were mixed with powders of calcium magnesium acetate (CMA), calcium carbonate (CaCO3), and calcium oxide (CaO), all of which are known sulfur reduction agents, at a molar Ca/S ratio of 1. Combustion of the fuels mixed with CMA or CaCO3 generated enhanced amounts of PAHs, while combustion with CaO had no effect on the PAH emissions. 相似文献
100.
Twenty pesticides and related analytes were measured in 28-day integrated precipitation samples from five U.S. sites in the Integrated Atmospheric Deposition Network (IADN) between 1997 and 2002. Consistent, significant decreases in concentration as a function of time were observed only for p,p'-DDE and p,p'-DDD, while increases in beta-HCH were observed at all sites. Significant annual variations were observed for most analytes at each site with higher concentrations in the summer for current-use pesticides (endosulfan and gamma-HCH) and peaks in the winter for most others. The increased concentrations in the winter are likely the result of the increased scavenging efficiency of snow compared to rain and, for some analytes, higher concentrations in the particulate phase during winter. These seasonal differences appear to account for a large portion of the observed variability in pesticide concentrations in precipitation samples. 相似文献