全文获取类型
收费全文 | 1529571篇 |
免费 | 27760篇 |
国内免费 | 8151篇 |
专业分类
电工技术 | 36102篇 |
技术理论 | 5篇 |
综合类 | 7767篇 |
化学工业 | 275725篇 |
金属工艺 | 66006篇 |
机械仪表 | 44577篇 |
建筑科学 | 47707篇 |
矿业工程 | 12191篇 |
能源动力 | 50655篇 |
轻工业 | 116208篇 |
水利工程 | 15513篇 |
石油天然气 | 39293篇 |
武器工业 | 433篇 |
无线电 | 199543篇 |
一般工业技术 | 287389篇 |
冶金工业 | 160307篇 |
原子能技术 | 34319篇 |
自动化技术 | 171742篇 |
出版年
2021年 | 16390篇 |
2020年 | 12377篇 |
2019年 | 15065篇 |
2018年 | 17153篇 |
2017年 | 16731篇 |
2016年 | 22223篇 |
2015年 | 18241篇 |
2014年 | 29641篇 |
2013年 | 89234篇 |
2012年 | 37335篇 |
2011年 | 50833篇 |
2010年 | 45009篇 |
2009年 | 53175篇 |
2008年 | 47070篇 |
2007年 | 44602篇 |
2006年 | 46203篇 |
2005年 | 41181篇 |
2004年 | 42214篇 |
2003年 | 41849篇 |
2002年 | 40900篇 |
2001年 | 37542篇 |
2000年 | 36026篇 |
1999年 | 34980篇 |
1998年 | 43513篇 |
1997年 | 38556篇 |
1996年 | 34779篇 |
1995年 | 30390篇 |
1994年 | 28499篇 |
1993年 | 28386篇 |
1992年 | 26240篇 |
1991年 | 23214篇 |
1990年 | 23571篇 |
1989年 | 22674篇 |
1988年 | 21211篇 |
1987年 | 19417篇 |
1986年 | 18799篇 |
1985年 | 22094篇 |
1984年 | 22376篇 |
1983年 | 20302篇 |
1982年 | 19261篇 |
1981年 | 19381篇 |
1980年 | 17960篇 |
1979年 | 18560篇 |
1978年 | 17772篇 |
1977年 | 17414篇 |
1976年 | 18446篇 |
1975年 | 16042篇 |
1974年 | 15577篇 |
1973年 | 15652篇 |
1972年 | 13119篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
901.
902.
Thin microtomed samples from hot-tool butt welds of polypropylene pipes are subjected to uniaxial tensile stress using a specially built instrumented microtesting machine. The deformation of the interface between the weld and the bulk polymer is measured by an optical method. An analysis of these measurements is carried out using the finite element method, and contours of the effective stress are obtained. There is a steep stress gradient at the junction of the weld flash and the bulk polymer, although the stress concentration factor is relatively low. The stress is essentially constant in the bulk polymer apart from the region near the weld zone. Tests on samples without the weld flash show that the maximum stress occurs within the weld zone. This is consistent with long-term tests on larger samples, where the fracture is found to initiate within the weld. The method of analysis enables the stress-strain response of the weld material to be determined. 相似文献
903.
904.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献
905.
906.
907.
Laparoscopic retroperitoneal lymph node dissection is a new surgical procedure used to enhance staging in men with clinical stage I nonseminomatous germ cell tumors of the testis. The procedure has been performed in a limited number of patients at several centers with extensive laparoscopic experience. Laparoscopic retroperitoneal lymphadenectomy is a technically demanding procedure which can be successfully completed in the majority of patients. However, the risk of complications is greater than in patients who undergo standard open retroperitoneal lymph node dissection. The primary advantage of a laparoscopic approach is shortened hospitalization and rapid return to normal activity. The role of laparoscopy in the management of patients with testis malignancy has not been defined. The use of this staging procedure may help minimize the need for surveillance studies following surgery and may be best utilized in men with a lower likelihood of nodal metastases. Ultimately, prospective study in large groups of patients will be necessary to determine the role of laparoscopic retroperitoneal lymph node dissection in patients with testis cancer. 相似文献
908.
Manku T. McGregor J.M. Nathan A. Roulston D.J. Noel J.-P. Houghton D.C. 《Electron Devices, IEEE Transactions on》1993,40(11):1990-1996
Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 1015-1019 cm-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×1019 cm-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon 相似文献
909.
Kringlebotn J.T. Morkel P.R. Reekie L. Archambault J.-L. Payne D.N. 《Photonics Technology Letters, IEEE》1993,5(10):1162-1164
We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er3+:Yb3+ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz 相似文献
910.
The present study has been divided into two sets. In the first set, the aim of the experiments was to investigate the dose-response effect of selective serotonin re-uptake inhibitor (SSRI) citalopram on rat exploratory behaviour in the elevated plus-maze. In the second set of experiments, the effect of cholecystokinin (CCK) CCKA and CCKB receptor antagonists, devazepide and L 365260, on citalopram-induced decrease of exploratory behaviour in the elevated plus-maze was studied. Citalopram (5 and 10 mg/kg) decreased the number of open and total arm entries, line crossings on open arms, and percentage of time spent exploring in open arm. Dose 15 mg/kg was without any effect on rat exploratory behaviour. Devazepide (0.01 and 1.0 mg/kg) failed to modify any of the citalopram-induced changes observed. L 365260 (1.0 mg/kg) reversed most of the effects of citalopram: the numbers of open and total arm entries, the number of line crossings, and the percentage of time spent exploring in open arms. L 365260 at dose level 0.01 mg/kg was ineffective. These results support the involvement of the CCKB receptor subtype in SSRI-induced anxiogenic-like effects in rodents. 相似文献