全文获取类型
收费全文 | 13330篇 |
免费 | 1357篇 |
国内免费 | 767篇 |
学科分类
工业技术 | 15454篇 |
出版年
2024年 | 47篇 |
2023年 | 213篇 |
2022年 | 469篇 |
2021年 | 626篇 |
2020年 | 479篇 |
2019年 | 384篇 |
2018年 | 428篇 |
2017年 | 485篇 |
2016年 | 466篇 |
2015年 | 605篇 |
2014年 | 717篇 |
2013年 | 776篇 |
2012年 | 945篇 |
2011年 | 905篇 |
2010年 | 845篇 |
2009年 | 828篇 |
2008年 | 757篇 |
2007年 | 750篇 |
2006年 | 672篇 |
2005年 | 542篇 |
2004年 | 475篇 |
2003年 | 428篇 |
2002年 | 529篇 |
2001年 | 442篇 |
2000年 | 335篇 |
1999年 | 295篇 |
1998年 | 170篇 |
1997年 | 146篇 |
1996年 | 164篇 |
1995年 | 115篇 |
1994年 | 113篇 |
1993年 | 74篇 |
1992年 | 45篇 |
1991年 | 35篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 22篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1976年 | 1篇 |
1975年 | 5篇 |
1973年 | 1篇 |
1969年 | 3篇 |
1959年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
Y Pei G Hercz C Greenwood G Segre A Manuel C Saiphoo S Fenton D Sherrard 《Canadian Metallurgical Quarterly》1993,44(1):159-164
To assess the effects of diabetes mellitus on renal osteodystrophy, we examined the database of 256 patients (45% on hemodialysis and 55% on peritoneal dialysis) who were prospectively studied in three Toronto dialysis centers between October of 1987 and 1989. All patients had serial documentation of their clinical, laboratory and risk parameters of bone disease, and completed a series of investigations that included the deferoxamine test, measurement of intact 1-84 PTH levels, and an iliac crest bone biopsy. Twenty-five percent of these patients were diabetic. When compared to non-diabetic patients, they were on dialysis for a shorter duration (2.4 +/- 0.3 vs. 4.7 +/- 0.3 years; P < 0.0002), used calcium carbonate as the only phosphate binder more frequently (40 vs. 25%; P < 0.007), and had lower parathyroid hormone levels (12 +/- 1.4 vs. 24 +/- 2.3 pmol/liter; P < 0.002). High-turnover bone disorders (that is, osteitis fibrosa and mixed disorder) were distinctly uncommon (8 vs. 33%; P < 0.01 by Fisher's exact test), while the mild (19 vs. 9%; P = NS) and the aplastic disorders (with mean stainable bone surface aluminum of 6.5 +/- 0.7%) (46 vs. 31%; P = NS) tended to be more common in diabetic patients. The prevalence of aluminum bone disease was the same in both groups (27%). Diabetic patients ingested a smaller cumulative dose of aluminum gels (3.7 +/- 0.6 vs. 9.3 +/- 1.1 kg; P < 0.005), yet had a higher rate of aluminium accumulation on bone surfaces than non-diabetic patients (1.5 +/- 0.19 vs. 0.96 +/- 0.10% per month on dialysis; P < 0.015).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
75.
本文提出了一种单模光纤偏振漂移补偿新算法,该算法不仅适用于简单的一维调制,也同样适用于复杂的二维调制。同时该算法不再局限于极化分割式的斯托克斯接收机。这对于充分发挥偏振调制的潜力和降低系统造价,提高系统性能有着重要意义。这一算法的计算机模拟结果也在本文中给出。一些和算法有关的问题在本文中作了必要的讨论。 相似文献
76.
77.
78.
79.
金刚石光电导探测器研制及在软X光测量中的初步应用 总被引:1,自引:0,他引:1
介绍了我们自己设计制造的天然Ⅱa型金刚石光导探测器的结构,原理,制造工艺,实验标定及其在ICF实验中软X光测量中的应用等。 相似文献
80.
Yufei Tao Xiaokui Xiao Jian Pei 《Knowledge and Data Engineering, IEEE Transactions on》2007,19(8):1072-1088
Skyline and top-k queries are two popular operations for preference retrieval. In practice, applications that require these operations usually provide numerous candidate attributes, whereas, depending on their interests, users may issue queries regarding different subsets of the dimensions. The existing algorithms are inadequate for subspace skyline/top-k search because they have at least one of the following defects: 1) they require scanning the entire database at least once, 2) they are optimized for one subspace but incur significant overhead for other subspaces, or 3) they demand expensive maintenance cost or space consumption. In this paper, we propose a technique SUBSKY, which settles both types of queries by using purely relational technologies. The core of SUBSKY is a transformation that converts multidimensional data to one-dimensional (1D) values. These values are indexed by a simple B-tree, which allows us to answer subspace queries by accessing a fraction of the database. SUBSKY entails low maintenance overhead, which equals the cost of updating a traditional B-tree. Extensive experiments with real data confirm that our technique outperforms alternative solutions significantly in both efficiency and scalability. 相似文献