全文获取类型
收费全文 | 4181篇 |
免费 | 13篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 10篇 |
综合类 | 2篇 |
化学工业 | 86篇 |
金属工艺 | 25篇 |
机械仪表 | 15篇 |
建筑科学 | 54篇 |
能源动力 | 10篇 |
轻工业 | 41篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 42篇 |
一般工业技术 | 137篇 |
冶金工业 | 3685篇 |
原子能技术 | 5篇 |
自动化技术 | 83篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 33篇 |
2012年 | 17篇 |
2011年 | 25篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 28篇 |
2007年 | 25篇 |
2006年 | 24篇 |
2005年 | 21篇 |
2004年 | 35篇 |
2003年 | 29篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 21篇 |
1999年 | 127篇 |
1998年 | 1136篇 |
1997年 | 607篇 |
1996年 | 455篇 |
1995年 | 238篇 |
1994年 | 223篇 |
1993年 | 231篇 |
1992年 | 28篇 |
1991年 | 45篇 |
1990年 | 58篇 |
1989年 | 53篇 |
1988年 | 62篇 |
1987年 | 56篇 |
1986年 | 48篇 |
1985年 | 31篇 |
1984年 | 4篇 |
1983年 | 10篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 36篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 84篇 |
1976年 | 183篇 |
1975年 | 8篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1971年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有4200条查询结果,搜索用时 14 毫秒
1.
PA Grace 《Canadian Metallurgical Quarterly》1997,166(3):152-156
PURPOSE: To examine the management and possible causes of primary valve malfunction of the Krupin eye valve with disk. METHODS: The authors reviewed the results of 113 patients undergoing implantation of the Krupin eye valve with disk and identified eight patients with primary valve malfunction requiring surgical revision. RESULTS: Valve revision involved manipulation (n = 1 case), explantation of the malfunctioning valve and implantation of a new valve (n = 2), and amputation of the valve (n = 5). Six of eight patients had final intraocular pressures of < 21 mmHg on one or no medications at a mean interval of 15.9 months (range 5-36) after surgical revision. Transient postoperative hypotony was noted in three patients and chronic hypotony with loss of light perception in one patient. One explanted valve was examined and found to have partially fused leaflets. CONCLUSIONS: Surgical revision in cases of primary valve malfunction of the Krupin eye valve with disk may be accomplished relatively safely with an acceptable level of postoperative complications. The etiology of primary valve malfunction may be related to the sterilization process and prolonged storage before implantation. 相似文献
2.
3.
M. D. Beard M. J. S. Lowe 《International Journal of Rock Mechanics and Mining Sciences》2003,40(4):527-536
The research outlined in this paper is aimed at the development of a portable non-destructive testing instrument for evaluating the condition of rock bolts. In applications such as coal mine roof reinforcement, the opportunities for rock bolt inspection are currently limited to destructive techniques such as the pull-out test. It is proposed that guided ultrasonic waves can be used to solve this inspection problem, using a pulse-echo test carried out from the free end of the bolt. Suitable test frequencies have been identified through the use of modelling software, and successful laboratory and site trials have been undertaken. The research has shown that the proposed approach is capable of determining the bolt length, and of identifying major defects such as necking, deformation, and loss of resin encapsulation. 相似文献
4.
PJ Jenkins MA Satta M Simmgen WM Drake C Williamson DG Lowe K Britton SL Chew RV Thakker GM Besser 《Canadian Metallurgical Quarterly》1997,47(6):747-751
We report a patient with a metastatic parathyroid carcinoma and medullary carcinoma of the thyroid. This patient represents a variation of the multiple endocrine neoplasia syndrome (MEN) type 2A. There was no evidence of a phaeochromocytoma. The case illustrates the difficulties that may be encountered in localising the source of PTH secretion; the patient underwent four unsuccessful exploratory operations of the neck and mediastinum before further investigations revealed a single metastatic deposit of parathyroid carcinoma involving the first thoracic vertebra. PCR amplification and sequencing of the RET oncogene from the metastatic parathyroid carcinoma and genomic DNA revealed a heterozygous mutation (Cys634Tyr) in exon 11, as has previously been described to occur in MEN 2A. In addition, loss of tumour heterozygosity was demonstrated at loci from chromosomes 1, 2, 3p, 13q and 16p. This represents the first report of a parathyroid carcinoma in a MEN2A patient, in which the multiple allelic deletions are consistent with the generalised losses observed in aggressive tumours. 相似文献
5.
Bufferless distributed circuit (BDC) broadcasting is proposed as a technique for broadcasting high-speed chip input signals to a series of on-chip destination cells as needed in crosspoint switch, parallel multiplier, distributed amplifier, etc., chip designs. In contrast with conventional techniques that use an on-chip buffer to assist broadcasting, BDC broadcasting offers the advantage of lower signal delay and power dissipation. In an experimental GaAs heterojunction bipolar transistor (HBT) 8×4 crosspoint switch assembly, BDC broadcasting was found to achieve a 40% power savings with little or no penalty in jitter or bit error rate performance at a 10-Gb/s data rate 相似文献
6.
KL Hopkins PK Dickson TI Ball RR Ricketts PA O'Shea CR Abramowsky 《Canadian Metallurgical Quarterly》1997,32(10):1476-1479
Fetus-in-fetu is an unusual condition in which a vertebrate fetus is enclosed within the abdomen of another fetus. These occurrences are usually benign. This report describes an instance of malignant recurrence after resection of a fetus-in-fetu. 相似文献
7.
The past year has seen significant advances in our understanding of the mechanism of RNA movement between the nucleus and the cytoplasm. The emerging view is that proteins bind to and escort RNAs to their proper subcellular location. The discovery of peptide signals that target nuclear export and the identification of novel protein mediators of RNA export are examples of significant recent discoveries. 相似文献
8.
JP Heiner SS Kohles PA Manley R Vanderby MD Markel 《Canadian Metallurgical Quarterly》1997,(341):233-240
In a canine model, the fixation stability of a prosthesis and proximal bone graft composite were measured relative to the distal femur. One group had the prosthesis graft composite cemented into the distal femur. The second group had the prosthesis graft composite press fit into the distal femur for biologic ingrowth. Displacements of the proximal femoral grafts relative to the host bone in each group were measured after ex vivo (acute with graft) implantation and 4 months after implantation. A third group with no osteotomy (acute intact) simulated perfect graft to host bone union. Relative displacements representing 6 degrees freedom (translation and rotation) were calculated from the displacement values measured by 9 eddy current transducers. Measurements of displacement were used to test the hypothesis that distal press fit fixation equals distal cement fixation at 4 months after implantation. In all cases the measured translations and rotations of the graft to implant construct were small and of a magnitude that should encourage bone ingrowth (< 0.05 mm and < 0.1 degree, respectively). The stability of the press fit group at 4 months was not significantly different from the cemented group in axial and transverse displacement during axial and transverse loading, respectively. There was no difference in stabilities at 4 months between distal press fit and cemented fixation in hip replacements requiring a proximal femoral graft. 相似文献
9.
BACKGROUND: To describe abortion utilization in the Canton of Vaud (Switzerland) and to identify desirable changes in the data collection system to improve the epidemiologic monitoring METHODS: Retrospective survey of the 5600 abortion requests to the Canton Health Authority for resident women between 1990 and 1993. RESULTS: Nine women out of 1000 residents requested an abortion, but the abortion rate was higher among women of foreign origin compared to Swiss women (17/1000 vs. 6/1000, p < 0.0001). The proportion of terminated recognized conceptions was 127/1000, and the ratio of IVG to livebirths was 0.18. The abortion rate was lower during adolescence (6/1000) or after 40 years of age (1.8/1000), whereas the proportion of terminated conceptions was highest at these ages (527/1000 and 312/1000). Abortion utilization in Canton of Vaud is among the lowest. CONCLUSIONS: Although these indicators do reflect a satisfactory accessibility and use of family planning services, improvements could be made. A better knowledge of the causes (motives, contraceptive method, reproductive history) and of the consequences of abortion (psycho-social implications, medical complications) would allow to design more focused prevention strategies and to fit health services to current needs. Updating the 1942 Swiss legislation is also desirable. 相似文献
10.