全文获取类型
收费全文 | 678553篇 |
免费 | 31570篇 |
国内免费 | 17293篇 |
专业分类
电工技术 | 26897篇 |
技术理论 | 45篇 |
综合类 | 25654篇 |
化学工业 | 103249篇 |
金属工艺 | 33863篇 |
机械仪表 | 32144篇 |
建筑科学 | 35106篇 |
矿业工程 | 12693篇 |
能源动力 | 18935篇 |
轻工业 | 49444篇 |
水利工程 | 9412篇 |
石油天然气 | 27115篇 |
武器工业 | 2824篇 |
无线电 | 82902篇 |
一般工业技术 | 103478篇 |
冶金工业 | 83375篇 |
原子能技术 | 9592篇 |
自动化技术 | 70688篇 |
出版年
2023年 | 6298篇 |
2022年 | 11601篇 |
2021年 | 16479篇 |
2020年 | 12350篇 |
2019年 | 10917篇 |
2018年 | 13861篇 |
2017年 | 15106篇 |
2016年 | 14245篇 |
2015年 | 16691篇 |
2014年 | 22346篇 |
2013年 | 35640篇 |
2012年 | 30554篇 |
2011年 | 36290篇 |
2010年 | 31196篇 |
2009年 | 31388篇 |
2008年 | 31510篇 |
2007年 | 30642篇 |
2006年 | 29754篇 |
2005年 | 26347篇 |
2004年 | 20370篇 |
2003年 | 19155篇 |
2002年 | 17700篇 |
2001年 | 17213篇 |
2000年 | 16514篇 |
1999年 | 17746篇 |
1998年 | 29399篇 |
1997年 | 21390篇 |
1996年 | 17760篇 |
1995年 | 13437篇 |
1994年 | 11606篇 |
1993年 | 10269篇 |
1992年 | 7335篇 |
1991年 | 6726篇 |
1990年 | 6191篇 |
1989年 | 5614篇 |
1988年 | 5251篇 |
1987年 | 4183篇 |
1986年 | 4008篇 |
1985年 | 4151篇 |
1984年 | 3727篇 |
1983年 | 3514篇 |
1982年 | 3316篇 |
1981年 | 3118篇 |
1980年 | 2988篇 |
1979年 | 2721篇 |
1978年 | 2467篇 |
1977年 | 3022篇 |
1976年 | 4324篇 |
1975年 | 2019篇 |
1974年 | 1964篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The effects of anticancer drugs on cell growth have been investigated by MTT colorimetric assay using mouse and rat cultured cells transformed by various oncogenes and tumor viruses. Aclarubicin, mitomycin C and 1-hexylcarbamoyl-5-fluorouracil showed higher growth-inhibitory activities toward transformed cells than those toward the normal counterparts. Nimustine, bleomycin and 5-fluorouracil also showed selective growth-suppressive activities toward transformed cells except for a few cell lines. ras-oncogene-transformed cells were more sensitive toward 5-fluorouracil and 1-hexylcarbamoyl-5-fluorouracil than the normal parent cells and other transformed cells. These drugs would thus be effective in the chemotherapy of ras-induced cancer. 相似文献
992.
H Kuniyasu W Yasui F Shimamoto K Fujii M Nakahara T Asahara K Dohi E Tahara 《Canadian Metallurgical Quarterly》1996,46(12):1005-1010
A rare case of hepatoblastoma in a 61-year-old Japanese housewife is described. This liver tumor mainly consisted of two tissue components: embryonal hepatocytes and primitive mesenchymal tissue. Fetal hepatocytes with alpha-fetoprotein production, gland formation, cartilage and osteoid were also found in a small portion. Molecular analysis by slot blot method revealed increased copy numbers of c-met and K-sam proto-oncogenes and cyclin D1 genes. These findings suggest that alterations of these oncogenes might play a role in the development of adult hepatoblastoma. 相似文献
993.
Y Goto 《Canadian Metallurgical Quarterly》1996,91(12):753-757
AIM: The aim of the study is to analyse the benefits and risks of PEE in patients, cared for by a team with many years experience. PATIENTS AND METHODS: From 16. 2. 1988 until 31. 12. 1993 246 PEEs (229 gastrostomies, 6 duodenostomies, 7 jejunostomies, 4 attempts) were performed on 234 patients (56% male, 44% female, mean age 68.3 years). 117 patients had tumorous and 117 neurological diseases. We used the pull technique with the Fresenius Freka PEG-system. Analysis was performed using a standardised documentation sheet which was filled out until the end of tube feeding. In total, we registered 39,678 days of tube feeding, 4513 of which were in hospitalized patients. RESULTS: The mean intubation time was 192.6 days (maximum 1496). In 8 cases, the tube could be explanted before the patient was discharged; 68 patients were discharged to a nursing home and 71 patients were allowed to go home. The tube-independent hospital lethality was 36.64%. A PEE-specific lethality had not been registered. Complications arose in a total of 37 patients (15.04%), 4 of which were severe (1.63%) Fifty-nine patients (25.43%) reported short-term feelings of ill health (vomiting, diarrhoea, pain). CONCLUSION: PEE is an effective and low-risk method of long-term nutrition. The advantages are simple insertion, safe handling by patients and relatives/nursing staff and the low cost. 相似文献
994.
995.
M Abe T Joh Y Hara K Hashida Y Koyama Y Kazatani 《Canadian Metallurgical Quarterly》1996,33(6):599-606
The purpose of this study is to determine whether left ventricular dysfunction following coronary artery spasm by 123I-BMIPP myocardial imaging. To reveal the clinical efficacy of 123I-BMIPP SPECT, 20 patients with vasospastic angina were studied using resting, 3-hour delayed image with 123I-BMIPP and exercise, 3-hour delayed image with 201Tl SPECT. 123I-BMIPP uptake was decreased compared to 201Tl (discordant) in 12 patients (60%) and in 49/100 myocardial segments (49%). The extent and severity score in resting image with 123I-BMIPP were significantly larger than that in delayed image with 201Tl (p < 0.01). In 123I-BMIPP SPECT, the severity score in the latest ischemia were significantly larger than that in others. The incidence of a complete agreement of decreased 123I-BMIPP uptake and coronary artery spasm was significantly higher (75%) than that in 201Tl (28%, p < 0.01). Furthermore, compared to 201Tl uptake, decreased 123I-BMIPP uptake much more corresponded to reduced wall motion in 9 of patients with mismatching. The severity of regional wall motion abnormality was significantly correlated with severity score of 123I-BMIPP. Late redistribution in delayed image with 123I-BMIPP was seen in 6 patients. The regional washout rate and the severity of regional wall motion abnormality in 6 patients was significantly lower than that in others (p < 0.05). Thus, metabolic abnormality assessed by 123I-BMIPP is well associated with left ventricular asynergy and spastic region in patients with vasospastic angina. In conclusion, 123I-BMIPP SPECT may sensitively delineate the impaired myocardium following coronary artery spasm, and it is very useful in diagnosing and estimating the severity of vasospastic angina. 相似文献
996.
997.
S Murakami H Yokomizo S Matsushita M Ogawa Y Nishimura 《Canadian Metallurgical Quarterly》1996,49(3):149-153
We investigated retrospectively 132 cases of open wedge high tibial osteotomy using an external fixation device, concentrating on the rate of neurological complications. One group of patients underwent surgery according to the conventional technique (n = 89). The rate of transient neurological complications was 15.7%; 7 months after surgery the rate of persistent deficits was 12.4%. For the second group (n = 43) a modified surgical technique was used that lowered the complication rate significantly (transient deficits 14%, persistent deficits 4.7%). In the modified technique the osteotomy is not performed in the conventional way using an oscillating saw but through consecutive drill holes of increasing diameter followed by osteoclasis. The lower complication rate in the second group is mainly due to the less extensive approach that leads to a smaller number of postoperative tibialis anterior syndromes (type B lesion). No differences were found with type C lesions (extension deficit of D1). No complete peroneal nerve palsy (type A) occurred in either group. We conclude that the reduction of neurological complications in group 2 is related to the less extensive approach of the proposed technique. 相似文献
998.
K. Tsuzuki T. Banno A. Kinbara Y. Nakagawa T. Tsukada 《Journal of Nuclear Materials》1993,200(3):291-295
The self-bias potential (Vdc) induced on an RF-powdered electrode (153 mm Ø) in a plasma is measured using electrical probes which are buried in, de-insulated from, and RF-connected to the electrode. The configuration of the probes allows to study the distribution of Vdc discretely on the electrode. The potential is homogeneous in the absence of external magnetic field. In the presence of a homogeneous magnetic field parallel to the electrode, it is reduced and a monotonous gradient takes place in its distribution due to the plasma shift induced by E × B drift. When the magnetic field is rotated along the axis of the RF-electrode at a frequency less than 50 Hz, the distribution, which is almost identical to the one in a static field, rotates with the magnetic field. On the coordinate system rotating with the magnetic field, the probes are regarded to be rotating. The potential distribution is obtained as a continuous function of the azimuthal angle. Thus the rotation of the field provides information for the experimental interpolation. 相似文献
999.
网络的性能与可靠性已分别得到广泛的研究,然而,怎样分析具有容错机制的环网的性能仍属有待开拓的研究领域,本文提出了一种分析具有自修复机制的多环网络系统的方法,并给出了报文传输时间分布的拉氏变换式,平均等待时间及平均队列长度公式,分析结果可用于评估故障与修复过程对实时令牌环网的实时响应特性的影响,对基于LAN的分布式实时系统设计具有指导意义。 相似文献
1000.
Winzker M. Gruger K. Gehrke W. Pirsch P. 《Solid-State Circuits, IEEE Journal of》1993,28(12):1354-1361
A chip set for 2D subband filtering of HDTV signals has been designed, fabricated and successfully tested. The two chips perform 10*14 quadrature mirror filtering for analysis filtering at the coder and synthesis filtering at the decoder. In order to achieve a very compact realization, the architectures utilize all a priori known properties of the filter algorithm. A 2D polyphase filter structure reduces the processing clock rate from the 72-MHz sampling rate to a moderate 18 MHz. The memory for vertical filtering is realized by on-chip parallel shift registers with multiphase clocking. A small silicon area for the filter arithmetic is achieved by application of carry save adder trees with fixed filter coefficients represented by canonical signed digits. A complete filterbank for luminance and chrominance signals consists of four identical chips, each with 450 000 transistors on 92 mm2 相似文献