全文获取类型
收费全文 | 10639篇 |
免费 | 858篇 |
国内免费 | 37篇 |
专业分类
电工技术 | 135篇 |
综合类 | 13篇 |
化学工业 | 2140篇 |
金属工艺 | 237篇 |
机械仪表 | 388篇 |
建筑科学 | 231篇 |
矿业工程 | 4篇 |
能源动力 | 401篇 |
轻工业 | 744篇 |
水利工程 | 31篇 |
石油天然气 | 4篇 |
无线电 | 1754篇 |
一般工业技术 | 1976篇 |
冶金工业 | 2222篇 |
原子能技术 | 125篇 |
自动化技术 | 1129篇 |
出版年
2024年 | 13篇 |
2023年 | 91篇 |
2022年 | 152篇 |
2021年 | 226篇 |
2020年 | 187篇 |
2019年 | 233篇 |
2018年 | 312篇 |
2017年 | 249篇 |
2016年 | 364篇 |
2015年 | 307篇 |
2014年 | 411篇 |
2013年 | 667篇 |
2012年 | 499篇 |
2011年 | 652篇 |
2010年 | 512篇 |
2009年 | 525篇 |
2008年 | 509篇 |
2007年 | 409篇 |
2006年 | 378篇 |
2005年 | 317篇 |
2004年 | 305篇 |
2003年 | 266篇 |
2002年 | 245篇 |
2001年 | 221篇 |
2000年 | 194篇 |
1999年 | 238篇 |
1998年 | 691篇 |
1997年 | 482篇 |
1996年 | 332篇 |
1995年 | 217篇 |
1994年 | 193篇 |
1993年 | 155篇 |
1992年 | 71篇 |
1991年 | 93篇 |
1990年 | 88篇 |
1989年 | 84篇 |
1988年 | 72篇 |
1987年 | 80篇 |
1986年 | 67篇 |
1985年 | 50篇 |
1984年 | 26篇 |
1983年 | 30篇 |
1982年 | 15篇 |
1981年 | 27篇 |
1980年 | 35篇 |
1979年 | 11篇 |
1978年 | 17篇 |
1977年 | 59篇 |
1976年 | 115篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Chun Hong Park Yoon Jin Oh Joo Ho Hwang Deug Woo Lee 《Journal of Mechanical Science and Technology》2006,20(1):51-58
To compensate for the motion errors in hydrostatic tables, a method to actively control the clearance of a bearing corresponding
to the amount of error using actively controlled capillaries is introduced in this paper. The design method for an actively
controlled capillary that considers the output rate of a piezo actuator and the amount of error that must be corrected is
described. The basic characteristics of such a system were tested, such as the maximum controllable range of the error, micro-step
response, and available dynamic bandwidth when the capillary was installed in a hydrostatic table. The tests demonstrated
that the maximum controllable range was 2.4 /im, the resolution was 27 nm, and the frequency bandwidth was 5.5 Hz. Simultaneous
compensation of the linear and angular motion errors using two actively controlled capillaries was also performed for a hydrostatic
table driven by a ballscrew and a DC servomotor. An iterative compensation method was applied to improve the compensation
characteristics. Experimental results showed that the linear and angular motion errors were improved to 0.12 μm and 0.20 arcsec,
which were about 1/15th and l/6th of the initial motion errors, respectively. These results confirmed that the proposed compensation method improves the motion
accuracy of hydrostatic tables very effectively. 相似文献
992.
Three strong anion-exchange membranes (CIM QA, Q100 and HiTrap Q) were investigated for the separation of the major proteins,
which were contained in whey, such as α-Lactalbumin, BSA and β-Lactoglobulin. Experiments were performed to determine the
optimum mobile phase composition for separating the whey proteins using the standard chemicals of the proteins. The mobile
phase was buffer A (20 mM piperazine-HCl pH 6.4) and buffer B (buffer A+1 M NaCl) and the linear gradient elution changes
of salt concentration were applied. The standard chemicals of the proteins were used to investigate the optimal mobile phase
compositions with the three anion-exchange membranes. From the experimental results, it was found that HiTrap Q was the most
effective in separating whey proteins. 相似文献
993.
Sung Ho Moon Suwon Park Jae Kyun Kwon Sung D.K. 《Vehicular Technology, IEEE Transactions on》2006,55(2):510-527
Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E/sub b//I/sub 0/ values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E/sub b//I/sub 0/ value decrease. 相似文献
994.
Application of computational fluid dynamics analysis for improving performance of commercial scale selective catalytic reduction 总被引:1,自引:0,他引:1
Jin Man Cho Jeong-Woo Choi Sung Ho Hong Kwang Chu Kim Jung Hee Na Jun Yub Lee 《Korean Journal of Chemical Engineering》2006,23(1):43-56
The performance of commercial scale selective catalytic reduction (SCR) system is strongly dependant upon the degree of mixing
between NH3 and NOx or NH3 concentration distribution at the catalyst layer according to the reaction kinetics of SCR catalysts. Insufficient mixing
of the reduction agent and NOx mass flow necessitates an uneconomically large catalyst volume and high NH3 slip to meet the required NOx emission values. The effective methodology which can increase the performance of commercial
scale SCR through improving NH3 concentration distribution at the catalyst layer using computational fluid dynamics (CFD) analysis was suggested and applied
to the real operations. The operation results have shown that the performance of commercial SCR was improved from 54.4% to
74.8% as NH3 concentration deviation at the catalyst layer was reduced from 23.6% to 8.6%. It is established that the increase of NH3 concentration uniformity at the catalyst layer contributes to improvement of performance of commercial scale SCR. 相似文献
995.
996.
This article details permeation tests that were performed on sheet samples of elastomers, over a wide range of pressures and temperatures, to study their effects on gas diffusion and solubility. It also explains how ageing is affected by gas permeation, and how the permeation test results can be used as input data for finite element analysis to aid the design of elastomeric components. 相似文献
997.
998.
We conducted two feedlot trials and one metabolism trial to evaluate the effect of barley level, barley bulk density, and physical form of roughage on lamb growth performance and digesta kinetics. Level of whole barley (50, 70, 90%) and type of roughage (chopped or pelleted alfalfa) were evaluated in Trial 1 (50 d period). Trial 2 (50 d) evaluated barley bulk density (heavy = 671 and light = 607 kg/m3), form of roughage (pelleted or chopped alfalfa), and level of barley (80 or 40%). The influence of treatments used in Trial 2 on digesta kinetics was evaluated in Trial 3. Gain:feed increased and DMI decreased (P < .10) linearly with increasing level of barley, and ADG and DMI were greater (P < . 10) for lambs fed pelleted vs chopped alfalfa in Trial 1. The 70% barley diet produced the highest yield grade and kidney-pelvic fat and the lowest leg score among barley levels (P < .10). Lambs fed pelleted alfalfa had heavier carcasses and a thicker body wall than lambs fed chopped alfalfa (P < .02). In Trial 2, DMI was less and gain:feed greater (P < .01) for lambs fed the heavy barley than for lambs fed the light barley and for the 80% barley diet compared to the 40% barley diet. Lambs fed pelleted alfalfa had greater dressing percentages than lambs fed chopped alfalfa. Backfat and body wall thickness were greater (P < .10) for lambs fed the 80% barley diet than for those fed the 40% barley diet. In Trial 3, retention time of barley was greater (P < .10) for lambs fed light rather than heavy barley, and retention time of alfalfa was greater (P < .10) for lambs fed chopped compared with pelleted alfalfa. Acetate:propionate ratio was greater (P < .10) for lambs fed light vs heavy barley and lambs fed the 40 vs 80% barley diets. Ruminal pH was lower (P = .05) and in situ barley digestion greater (P = .03) over time in lambs fed the 80% barley diet than in lambs fed the 40% barley diet. Feedlot lamb ADG was not always greatest with high levels of barley; however, gain:feed improved at the higher barley levels. The higher barley levels seemed to result in fatter lambs. 相似文献
999.
JT Sandlund T Fonseca T Leimig L Verissimo R Ribeiro V Lira CW Berard J Sixbey WM Crist L Mao G Chen CH Pui M Heim F Pedrosa 《Canadian Metallurgical Quarterly》1997,11(5):743-746
The purpose of this paper was to define the histologic distribution, clinical features, and treatment response of childhood non-Hodgkin lymphoma (NHL) in northeastern Brazil. We reviewed medical records and histopathologic studies of 98 children treated for NHL from 1980 to 1987 at a major pediatric cancer center in Recife, Brazil. Treatment outcome was evaluated in relation to tumor burden (stage and serum LDH) and type of therapy (LSA2L2 vs other multiagent chemotherapy). There was a striking predominance of the small noncleaved cell (Burkitt) subtype, which occurred in 92 of the 98 children and adolescents diagnosed with NHL. Subsequent analyses focused on these patients. The majority (n = 84) had advanced (stage III/IV) disease at diagnosis. The abdomen was the most common site of disease (84 cases); jaw involvement was rare (three cases). Five-year event-free survival (excluding treatment refusals) was significantly better for patients with limited vs advanced stage disease (75 +/- 14% vs 42 +/- 6%; P < 0.04). Elevated serum LDH (>500 U/l) was associated with a poorer outcome (P = 0.008). The type of chemotherapy did not affect EFS (P = 0.95). Only 39% of patients are long-term survivors, reflecting the high rate of septic deaths (25% of patients) and parental refusal/abandonment of therapy (10%). Epstein-Barr virus (EBV) was detected in tumor cells from eight of the 11 cases studied. In clinical presentation, these cases resemble sporadic Burkitt lymphoma, yet in their apparent responsiveness to LSA2L2 therapy and association with EBV, they do not. Childhood NHL in northeastern Brazil is predominantly of the Burkitt subtype, and is associated with clinical features that appear to distinguish it from the endemic and sporadic forms of this tumor. These cases may represent a third or intermediate subtype of Burkitt lymphoma. 相似文献
1000.
D Finzi M Hermankova T Pierson LM Carruth C Buck RE Chaisson TC Quinn K Chadwick J Margolick R Brookmeyer J Gallant M Markowitz DD Ho DD Richman RF Siliciano 《Canadian Metallurgical Quarterly》1997,278(5341):1295-1300
The hypothesis that quiescent CD4+ T lymphocytes carrying proviral DNA provide a reservoir for human immunodeficiency virus-type 1 (HIV-1) in patients on highly active antiretroviral therapy (HAART) was examined. In a study of 22 patients successfully treated with HAART for up to 30 months, replication-competent virus was routinely recovered from resting CD4+ T lymphocytes. The frequency of resting CD4+ T cells harboring latent HIV-1 was low, 0.2 to 16.4 per 10(6) cells, and, in cross-sectional analysis, did not decrease with increasing time on therapy. The recovered viruses generally did not show mutations associated with resistance to the relevant antiretroviral drugs. This reservoir of nonevolving latent virus in resting CD4+ T cells should be considered in deciding whether to terminate treatment in patients who respond to HAART. 相似文献