全文获取类型
收费全文 | 264893篇 |
免费 | 3455篇 |
国内免费 | 831篇 |
专业分类
电工技术 | 5180篇 |
综合类 | 335篇 |
化学工业 | 38592篇 |
金属工艺 | 10328篇 |
机械仪表 | 8621篇 |
建筑科学 | 6325篇 |
矿业工程 | 1085篇 |
能源动力 | 6553篇 |
轻工业 | 23516篇 |
水利工程 | 2586篇 |
石油天然气 | 3927篇 |
武器工业 | 68篇 |
无线电 | 35039篇 |
一般工业技术 | 50854篇 |
冶金工业 | 46736篇 |
原子能技术 | 5468篇 |
自动化技术 | 23966篇 |
出版年
2021年 | 2283篇 |
2019年 | 2181篇 |
2018年 | 3644篇 |
2017年 | 3700篇 |
2016年 | 3942篇 |
2015年 | 2454篇 |
2014年 | 4247篇 |
2013年 | 11657篇 |
2012年 | 6883篇 |
2011年 | 9239篇 |
2010年 | 7238篇 |
2009年 | 8125篇 |
2008年 | 8930篇 |
2007年 | 8817篇 |
2006年 | 8009篇 |
2005年 | 7308篇 |
2004年 | 7011篇 |
2003年 | 6841篇 |
2002年 | 6460篇 |
2001年 | 6539篇 |
2000年 | 6240篇 |
1999年 | 6314篇 |
1998年 | 14306篇 |
1997年 | 10325篇 |
1996年 | 8161篇 |
1995年 | 6459篇 |
1994年 | 5738篇 |
1993年 | 5613篇 |
1992年 | 4565篇 |
1991年 | 4231篇 |
1990年 | 4065篇 |
1989年 | 3794篇 |
1988年 | 3636篇 |
1987年 | 3178篇 |
1986年 | 3074篇 |
1985年 | 3623篇 |
1984年 | 3393篇 |
1983年 | 3037篇 |
1982年 | 2868篇 |
1981年 | 2964篇 |
1980年 | 2766篇 |
1979年 | 2656篇 |
1978年 | 2507篇 |
1977年 | 2948篇 |
1976年 | 3559篇 |
1975年 | 2317篇 |
1974年 | 2314篇 |
1973年 | 2321篇 |
1972年 | 1849篇 |
1971年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
AG Shankar S Ashley M Radford A Barrett D Wright CR Pinkerton 《Canadian Metallurgical Quarterly》1997,15(7):2622-2630
PURPOSE: Histology has been identified as an important prognostic factor in Hodgkin's disease (HD) in adults. Information regarding the impact of histology on outcome in childhood HD is scarce. This study determines the effect of histology on the overall survival (OS) or progression-free survival (PFS) in a national series of children treated in a standardized manner. PATIENTS AND METHODS: The results of treatment of 331 assessable patients, treated between January 1, 1982 and June 30, 1992, in the United Kingdom Children's Cancer Study Group (UKCCSG) Hodgkin's study I were reviewed to evaluate OS, PFS, and deaths according to stage and histology. Treatment was either involved-field radiation alone (stage IA) or chlorambucil, vinblastine, procarbazine, and prednisolone (ChlVPP) chemotherapy with or without mediastinal radiation. All were clinically staged at diagnosis. RESULTS: Nodular sclerosing (NS) HD was the most common histologic subtype (155 of 331 patients [47%]) and was uniformly distributed through all stages. Lymphocyte-depletion (LD) HD was extremely uncommon (< 1%). Mixed-cellularity (MC) HD had the highest relapse rate, but this was only significant (P < .05) in stage I patients who received local irradiation alone. There was no other statistically significant difference in OS and PFS between the various histologic subtypes. Multivariate analysis for PFS and OS confirmed that stage was the most important prognostic factor and that histology did not have an effect after stratification by stage. CONCLUSION: This study demonstrates that with effective multiagent chemotherapy, histologic subtype does not influence outcome. The high relapse rates in stage I MC subtype indicates that MC HD is biologically aggressive and systemic treatment with or without local irradiation may be indicated. The high relapse rate in stage IV patients appeared to be independent of histology. 相似文献
992.
Today patients want to change their Christian names not so much for social support but in order to obtain sex change operations. For this reason among others we caution against casual and careless evaluations and plead for conscientiousness and thoroughness. The spectrum of 16 evaluation cases in the year 1995 is presented. Following this and looking for guiding principles, the most important aspects are discussed: the dilatable frame of the written law, the examiner's diagnostic process, the duty of being well informed, reconstruction of development as the first goal of examination, real-life self-testing and therapy, the obligation to report one's own findings, change of Christian name and indication of operation, evaluation for gender changing, problems of the judge-expert relationship and of future development. 相似文献
993.
The effect of sexual maturity on behavioral effects of stress was examined in male mice. Immature (4-week-old) or mature (8-week-old) animals were subjected to either social stress (exposure to an isolated adult male) or restraint stress for 5 days and examined for body weight, food intake, or plus-maze behavior. Social stress reduced food intake, body weight, and open-arm entries in 4-week-old but not 8-week-old mice. Restraint reduced body weight in 4-week-old but not 8-week-old mice. It is concluded that immature male mice show greater behavioral disturbances after stress than their mature counterparts. The findings are in agreement with much anecdotal evidence that children are more vulnerable to stress than adults. 相似文献
994.
A method of posterior mitral annulus remodeling is presented. The posterior annulus is divided into three segments, each segment encircled by a suture that is passed in a tourniquet. Coaptation of the leaflets can be achieved by tightening the tourniquets while the ventricle is being filled. This technique is simple and quick, avoids the use of foreign material, and requires less expertise and judgment than traditional annuloplasties. 相似文献
995.
Liu Y. Blostein S.D. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1992,38(1):177-182
Bayesian analysis is used to show that Wald's sequential probability ratio test with varying thresholds is optimal for the nonstationary situation, where the observed samples are independent but not identically distributed. Some important properties useful for the design of the test thresholds are discussed. Wald's lower bound, generalized to the nonstationary situation, is also presented. The results have important applications in situations where the observed signal is time-varying. such as in radar signal processing, image processing, and spread spectrum communications 相似文献
996.
The effect of DC flux on the core loss is examined for the practical range of power and frequency. Relevant core loss equations are derived and applied to an optimization algorithm to determine the minimum core loss at a given ratio of s (DC flux density to AC peak flux density). It has been found that the curves of hysteresis loss density versus the ratio of s exhibit a peak at a critical ratio. Below or above this critical ratio, the loss density decreases drastically. On the other hand, the curves of eddy-current loss density versus the ratio of s exhibits a minimum point at a critical ratio. Below or above this critical ratio, the loss density increases gradually 相似文献
997.
998.
999.
In large structures it is often necessary to estimate the reliability of the system by use of parallel systems. Optimality criteria-based algorithms for calculation of the joint design point in a parallel system are described and efficient active set strategies are developed. Three possible algorithms are tested in two examples against well-known general non-linear optimization algorithms. Especially one of the suggested algorithms seems to be stable and fast. 相似文献
1000.
G. D. Moss 《Computers & Education》1992,18(4)
The study reports on a survey into the use of content-free computer software by comprehensive school teachers in South Wales. The survey includes questions on computer resources, staff training, level of awareness and utilization by year group and by subject taught. The findings suggest that many more teachers are aware of the potential of content-free software than are actually using them in their lessons. A shortfall in training provision together with the inequitable distribution of computers between subjects are major factors limiting the use of such software. Modern Languages and Humanities are generally poorly provided for in terms of hardware resources. However, Science (which has ample hardware) seems to make relatively little use of content-free software while Business Studies and Design Technology use it extensively. Sixth form teaching seems generally to ignore the potentials of computer-aided learning by means of content-free software. 相似文献