全文获取类型
收费全文 | 241023篇 |
免费 | 28626篇 |
国内免费 | 9549篇 |
专业分类
电工技术 | 13212篇 |
技术理论 | 12篇 |
综合类 | 13815篇 |
化学工业 | 48492篇 |
金属工艺 | 11828篇 |
机械仪表 | 13779篇 |
建筑科学 | 18150篇 |
矿业工程 | 6303篇 |
能源动力 | 6390篇 |
轻工业 | 19481篇 |
水利工程 | 3943篇 |
石油天然气 | 11081篇 |
武器工业 | 1619篇 |
无线电 | 31058篇 |
一般工业技术 | 34216篇 |
冶金工业 | 10467篇 |
原子能技术 | 2436篇 |
自动化技术 | 32916篇 |
出版年
2024年 | 861篇 |
2023年 | 3075篇 |
2022年 | 5668篇 |
2021年 | 7937篇 |
2020年 | 7166篇 |
2019年 | 7613篇 |
2018年 | 8266篇 |
2017年 | 9370篇 |
2016年 | 9140篇 |
2015年 | 11528篇 |
2014年 | 13366篇 |
2013年 | 16599篇 |
2012年 | 15616篇 |
2011年 | 16397篇 |
2010年 | 15269篇 |
2009年 | 14985篇 |
2008年 | 14274篇 |
2007年 | 13610篇 |
2006年 | 13224篇 |
2005年 | 11493篇 |
2004年 | 8199篇 |
2003年 | 7132篇 |
2002年 | 6605篇 |
2001年 | 6055篇 |
2000年 | 5905篇 |
1999年 | 5678篇 |
1998年 | 4224篇 |
1997年 | 3724篇 |
1996年 | 3312篇 |
1995年 | 2735篇 |
1994年 | 2238篇 |
1993年 | 1710篇 |
1992年 | 1342篇 |
1991年 | 1058篇 |
1990年 | 845篇 |
1989年 | 707篇 |
1988年 | 548篇 |
1987年 | 395篇 |
1986年 | 306篇 |
1985年 | 221篇 |
1984年 | 152篇 |
1983年 | 106篇 |
1982年 | 116篇 |
1981年 | 79篇 |
1980年 | 71篇 |
1979年 | 42篇 |
1978年 | 36篇 |
1977年 | 31篇 |
1976年 | 49篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
本文提出了一种基于信息融合的物体三维特征的提取方法,该方法利用两幅互相配准的三维测距图像和灰度图像,来提取多面体的三维特征。首先,通过分析灰度图像中的灰度变化及测距图像中的测距值变化,分别求取各自图像中物体的特征点及特征边;然后,利用两配准图像之间的对应关系,求得所有特征点、面与多边形在三维测距图像中的三维表示;接着,通过分析三维测距图像中所测得的各候选平面上特定点与边处的曲率及法向,验证候选平面 相似文献
42.
43.
R Gollamudi Z Feng EO Dillingham SE Bond G Han S Salgia 《Canadian Metallurgical Quarterly》1993,69(4):361-367
This investigation retrospectively examined changes in marital satisfaction following stroke. The relationship between such changes and other pertinent factors were also examined, including severity of aphasia, knowledge of aphasia, number of months after stroke, and length of the marriage. The subjects were 40 spouses of patients with aphasia grouped according to severity of the aphasia (mild, moderate, severe). Spouses completed two different measures of marital satisfaction--the Marital Satisfaction Scale (MSS) and the Marital Comparison Level Index (MCLI). These measures were completed in both a prestroke (retrospective reporting) and a poststroke format to allow for change to be assessed. In addition, a Knowledge of Aphasia questionnaire was completed by the normal spouses to evaluate their understanding of the disorder of aphasia. There was a significant difference between prestroke and poststroke scores on both the MSS and the MCLI, indicating a lower level of satisfaction following the stroke. The amount of change between prestroke and poststroke MSS and MCLI scores was not related to either number of months poststroke or number of years married. Although there was no relationship between changes in prestroke and poststroke scores on the MCLI and Knowledge of Aphasia scores, there was a significant correlation between changes in these scores on the MSS and Knowledge of Aphasia scores. Hence, the more knowledge spouses had regarding aphasia, the less the negative impact the stroke had on marital satisfaction, as measured by the MSS. Results are discussed in terms of the interdisciplinary treatment needs of aphasic patients and the implications for future investigations. 相似文献
44.
通过探讨、分析无缝钢管壁厚偏差产生的原因,提出了改善钢管壁厚偏差的一些措施,并结合实际生产,得出了比较满意的结果。 相似文献
45.
46.
对菱镁矿在固体燃料燃烧过程中的固硫特性进行了理论研究,所得结论对进一步将菱镁矿作为固体燃料燃烧过程中的固硫剂具有非常重要的意义。 相似文献
47.
BACKGROUND: To determine the best cutoff values of aspartate aminotransferase (AST) and alanine amino-transferase (ALT) in detecting viral hepatitis C infection among patients of continuous ambulatory peritoneal dialysis (CAPD). METHODS: 90 (44 male and 46 female) CAPD patients and 526 adult controls (266 male, 260 female) were enrolled. Serum AST and ALT were measured by an auto-analyser monthly. Serum HBsAg was examined using a RIA method and anti-HCV by an second-generation EIA method. The best cutoff values of AST and ALT for detecting viral hepatitis were obtained from the ROC (receiver-operating characteristic) curve. RESULTS: The prevalence of anti-HCV(+) was significantly higher in CAPD patients (16.7%) than in normal controls (4.9%), while that of HBsAg(+) was similar in both groups. CAPD patients had significantly lower levels of serum aminotransferases compared to normal controls. Mean AST were 23.8 IU/l in normal control and 18.8 IU/l in the CAPD patients (P < 0.001). Mean ALT were 21.9 IU/l in normal controls and 15.3 IU/l in the CAPD patients (P < 0.001). CAPD patients with HCV infection had higher serum AST and ALT levels than those without. However, HBV infection did not cause significant serum aminotransferase elevation in patients. The conventional cutoff values of AST (40 IU/l) and ALT (40 IU/l) for detecting viral hepatitis yielded only a sensitivity of 27.3 and 18.2% respectively; on the contrary, our revised cutoff values of AST (24 IU/l) and ALT (17 IU/l) had better sensitivities (AST, 72.7%; ALT, 63.6%). For serial aminotransferase values, the sensitivity of AST and ALT for detecting HCV were 36.4 and 27.3% by conventional criteria, and were both 81.8%, by our newly revised criteria. CONCLUSIONS: Serum aminotransferase cutoff values should be modified for screening viral hepatitis in a CAPD population. Our new cutoff criteria had important clinical implications in providing benefits of earlier detection and possible prevention from chronic hepatic deteriorations. 相似文献
48.
BM Chen LY Chan SM Wang MF Wu JW Chern SR Roffler 《Canadian Metallurgical Quarterly》1997,73(3):392-402
We examined the in vivo efficacy of targeting beta-glucuronidase (betaG) to activate a glucuronide prodrug (BHAMG) of p-hydroxyaniline mustard (pHAM) at hepatoma ascites in Sprague-Dawley rats. Injection i.p. of 500 microg RH1-betaG, a conjugate formed between recombinant betaG and monoclonal antibody RH1 with specificity for an antigen expressed on AS-30D rat hepatoma cells, into rats bearing AS-30D ascites resulted in the accumulation of 54 microg conjugate per 10(9) tumor cells after 2 hr. Ascites fluid and serum contained 0.53 and 0 microg/ml, respectively, RH1-betaG 2 hr after injection of the conjugate. Conjugate binding to AS-30D cells was heterogeneous and non-saturated, as determined by flow cytometry. BHAMG was less toxic than pHAM to SD rats based on measures of animal mortality, weight loss and hematological toxicity. Treatment of rats bearing established hepatoma ascites with 500 microg RH1-betaG followed 2 hr later with a single i.p. injection of 30 mg/kg BHAMG or 3 i.p. injections of 10 mg/kg BHAMG 2, 3 and 4 hr later resulted in the cure of 6/8 and 8/8 animals, respectively. Treatment with BHAMG or pHAM alone did not produce cures, whereas treatment with a control antibody-betaG conjugate and BHAMG produced significantly greater hematological toxicity compared to treatment with RH1-betaG and BHAMG. All cured rats were completely protected from rechallenge with 2 x 10(7) AS-30D cells, indicating that successful treatment of animals induced protective immunity. 相似文献
49.
Control of peak sidelobe level in adaptive arrays 总被引:1,自引:0,他引:1
Renbiao Wu Zheng Bao Yuanliang Ma 《Antennas and Propagation, IEEE Transactions on》1996,44(10):1341-1347
Adaptive beamforming techniques are now widely used to reject interference (jammer/clutter) signals in radar, communication, and sonar applications. In adaptive arrays using the sample matrix inversion (SMI) algorithm, inadequate estimation of the covariance matrix results in adaptive antenna patterns with high sidelobes and distorted mainbeams. In this paper, a method is proposed to precisely control the peak (rather than average) sidelobe level of adaptive array patterns. The proposed method is also generalized to adaptive array antennas with moderate bandwidth and large random amplitude and phase errors. Theoretical analysis and simulation results are provided to illustrate the performance of the method proposed 相似文献
50.
This article deals with the kinetics of two-step anionic polymerization by way of a non-steady state method. Several molecular parameters can be evaluated using the formulae developed. A bimodal molecular weight distribution function for the resulting polymer is derived from the set of kinetic differential equations, which is in agreement with the experimental data reported. 相似文献