全文获取类型
收费全文 | 22067篇 |
免费 | 497篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 228篇 |
综合类 | 16篇 |
化学工业 | 2571篇 |
金属工艺 | 236篇 |
机械仪表 | 337篇 |
建筑科学 | 894篇 |
矿业工程 | 42篇 |
能源动力 | 452篇 |
轻工业 | 1946篇 |
水利工程 | 262篇 |
石油天然气 | 30篇 |
无线电 | 1706篇 |
一般工业技术 | 2387篇 |
冶金工业 | 8710篇 |
原子能技术 | 142篇 |
自动化技术 | 2628篇 |
出版年
2023年 | 65篇 |
2022年 | 116篇 |
2021年 | 265篇 |
2020年 | 135篇 |
2019年 | 199篇 |
2018年 | 268篇 |
2017年 | 247篇 |
2016年 | 271篇 |
2015年 | 253篇 |
2014年 | 388篇 |
2013年 | 660篇 |
2012年 | 677篇 |
2011年 | 923篇 |
2010年 | 637篇 |
2009年 | 666篇 |
2008年 | 699篇 |
2007年 | 675篇 |
2006年 | 566篇 |
2005年 | 558篇 |
2004年 | 508篇 |
2003年 | 476篇 |
2002年 | 430篇 |
2001年 | 344篇 |
2000年 | 321篇 |
1999年 | 535篇 |
1998年 | 2959篇 |
1997年 | 1724篇 |
1996年 | 1204篇 |
1995年 | 691篇 |
1994年 | 665篇 |
1993年 | 663篇 |
1992年 | 222篇 |
1991年 | 235篇 |
1990年 | 238篇 |
1989年 | 240篇 |
1988年 | 244篇 |
1987年 | 176篇 |
1986年 | 170篇 |
1985年 | 206篇 |
1984年 | 141篇 |
1983年 | 105篇 |
1982年 | 122篇 |
1981年 | 128篇 |
1980年 | 113篇 |
1979年 | 93篇 |
1978年 | 85篇 |
1977年 | 210篇 |
1976年 | 317篇 |
1975年 | 79篇 |
1974年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
61.
62.
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
63.
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
64.
A short-pulse 1.444-μm laser based on Nd:YAG technology has been demonstrated. The 1.444-μm is eye-safe. With the cavity-dump technique, a pulse of 50 m× and 14 ns was obtained. The beam quality was excellent with an M2 of 1.6 by the use of a telescopic resonator. Silicon-window polarizers were used to suppress the 1.06-μm radiation but showed 1.444-μm absorption as well 相似文献
65.
66.
67.
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
68.
The effect of caseinate and soy protein in the diet on the mutagenicity induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was assessed in-vivo and ex-vivo in the DNA-repair host-mediated assay and liquid suspension assay, respectively. Of the two proteins only casein showed a strong antimutagenic activity over the whole digestive tract, except in the stomach. It is suggested that the molecular structure of a protein determines its protective effect against mutagens: casein lacks secondary and tertiary structure so that amino acids are more readily available for interaction with the mutagen than with the amino acids in soy protein which is a globular protein. 相似文献
69.
70.
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